Pietro Teatini
email: teatini@dmsa.unipd.it

Giuseppe Gambolati

Massimiliano Ferronato

Tony Settari

Dale Walters

Long Beach

Land uplift due to subsurface fluid injection

Keywords: land uplift, subsurface fluid injection, ground-and satellite-based measurements, hydro-geomechanical properties, case studies

The subsurface injection of fluid (water, gas, vapour) occurs worldwide for a variety of purposes, e.g. to enhance oil production (EOR), store gas in depleted gas/oil fields, recharge overdrafted aquifer systems (ASR), and mitigate anthropogenic land subsidence. Irrespective of the injection target, some areas have experienced an observed land uplift ranging from a few millimetres to tens of centimetres over a time period of a few months to several years depending on the quantity and spatial distribution of the fluid used, pore pressure increase, geological setting (depth, thickness, and area extent), and hydro-geomechanical properties of the injected formation. The present paper reviews the fundamental geomechanical processes that govern land upheaval due to fluid injection in the subsurface and presents a survey of some interesting examples of anthropogenic uplift measured in the past by the traditional levelling technique and in recent times with the aid of satellite technology.

INTRODUCTION

It is well known that subsurface fluid (groundwater, gas, oil, thermal water) removal induces a land settlement commonly called land subsidence. Magnitude, time of occurrence, and extent of the area involved depend on a large number of factors including the amount of the fluid withdrawn, the pore pressure decline, the depth, volume, and permeability of the pumped formation, and the geomechanical properties of the reservoir and the overburden. For a review of some famous anthropogenically subsiding sites worldwide see [START_REF] Gambolati | Anthropogenic land subsidence[END_REF]. The reverse, namely land uplift due to underground fluid injection, is a much less observed and recognized event although the practice of injecting fluids underground is more than a half century old.

Injection technology has been advancing continuously since it began to be widely used in the 1950s-1960s to re-inject formation water extracted along with the hydrocarbons, or to dispose of industrial wastes [START_REF] Donaldson | Mapping reservoir volume changes during cyclic steam stimulation using tiltmeterbased surface-deformation measurements[END_REF]. The number of injection wells has grown exponentially to the point that EPA (the U.S. Environmental Protection Agency) has identified about 400,000 injection boreholes in the USA alone (USEPA, 2002). The injection of water-based solutions, hydrocarbons, CO 2 or N 2 to enhance oil production (EOR) started in the 1940s and soon became an accepted technique to recover additional oil from reservoirs that were already depleted or waterflooded. Thermal recovery processes, used in reservoirs containing heavy (viscous) oil or bitumen, can also be classified as EOR. There are also examples of water pumped into an oil field to mitigate land subsidence caused by oil production, including, for example, the case of Long Beach, California, where the mitigation programme started in 1958 and was carefully controlled and monitored [START_REF] Rintoul | The case of the disappearing land[END_REF].

Land motion related to subsurface fluid injection went unnoticed for a long time in the vast majority of cases. There are a number of reasons for this. First, in most cases A c c e p t e d M a n u s c r i p t 4 the disposal of fluids occurred in deserted or sparsely inhabited areas where measuring surface displacements was not a priority, in part due to the large cost of levelling surveys. In other instances uplift was so small that no environmental hazards were created and that no monitoring programme was really needed, or the area involved was quite limited with no damages to the engineered structures and infrastructures reported or even expected. Only in recent times satellite technology has offered a relatively inexpensive, spatially distributed, and accurate methodology to detect ground movements practically worldwide and has revealed anthropogenic uplifts of some interest in terms of magnitude, size of the area involved and time of occurrence. The use of Interferometric Synthetic Aperture Radar (InSAR) techniques has grown rapidly over the last decade, thus facilitating immensely the detection and measurement of rising areas. This is particularly true for surface movements connected with natural fluctuations of the groundwater head and in areas of aquifer storage (ASR), which have been systematically monitored, e.g. [START_REF] Galloway | Detection of aquifer system compaction and land subsidence using interferometric synthetic aperture radar, Antelope Valley, Mojave Desert, California[END_REF], [START_REF] Amelung | Sensing the ups and downs of Las Vegas: InSAR reveals structural control of land subsidence and aquifer-system deformation[END_REF], [START_REF] Hoffmann | Seasonal subsidence and rebound in Las Vegas Valley, Nevada, observed by synthetic aperture radar interferometry[END_REF], [START_REF] Watson | Satellite interferometric observations of displacements associated with seasonal groundwater in the Los Angeles basin[END_REF], Hoffman and Zebker (2003), [START_REF] Schmidt | Time dependent land uplift and subsidence in the Santa Clara Valley, California, from a large InSAR data set[END_REF], [START_REF] Ferretti | InSAR Permanent Scatterer analysis reveals ups and downs in San Francisco Bay area[END_REF], [START_REF] Galloway | The application of satellite differential SAR interferometry-derived ground displacements in hydrogeology[END_REF], [START_REF] Bell | Permanent scatterer InSAR reveals seasonal and long-term aquifer system response to groundwater pumping and artificial recharge[END_REF]. Also surface and borehole tiltmeters have been widely used in recent years to monitor ground heave within relatively small areas.

This paper provides a survey of some interesting areas in the world where appreciable heave has been observed mostly as a "by-product" of fluid (water, gas, vapour) injection in geological formations. The mechanics of land rebound is first briefly addressed. The case studies are presented on the basis of the injection purpose, i.e. EOR, ASR, gas storage, land subsidence mitigation, and geomechanical characterization of the geologic formations. The focus is on the magnitude, spatial distribution, and extent of the anthropogenic uplift, with some effort also devoted to describing the geometry of the injected formation, fluid used, depth of disposal, A c c e p t e d M a n u s c r i p t 5 duration of the action, and increase of the fluid pore pressure, i.e., the factors controlling the observed displacement field. Finally, two projects on land subsidence mitigation by seawater injection in the Northern Adriatic are described and discussed.

MECHANICS OF LAND UPLIFT DUE TO FLUID INJECTION

Generally speaking, uplift is caused by the migration to the ground surface of the expansion of the geological formation where the fluid is injected. The deformation of the injected porous medium is mainly driven by the in situ pore pressure p and temperature T variations, with the amount of the total displacement mainly controlled by the rock compressibility and thermal expansion coefficient. Based on classical thermo-poro-elastic theory [START_REF] Coussy | Mechanics of Porous Continua[END_REF], the partial differential equations governing the rock deformation can be expressed as:

  b u u          T c p G G b s    div 2 (1)
where  and 2

 are the gradient and the Laplace operators, respectively, G and  are the Lamé coefficients generally dependent on the stress path, u is the displacement vector,  is the Biot coefficient,  s is the volumetric thermal expansion coefficient for the solid phase, c b is the volumetric bulk compressibility, and b is the vector of body forces. Well-known relationships link the mechanical coefficients in equation ( 1) to the soil uniaxial vertical compressibility c M . This is the fundamental geomechanical parameter which basically controls the amount of vertical soil deformation caused by p change and can be acquired from in-situ measurements and lab tests.

Different types of fluids can be pumped underground, most commonly water, e.g., to recharge an aquifer system, arrest or mitigate the anthropogenic land subsidence accompanying the development and depletion of aquifers and hydrocarbon fields; but also gas, e.g., steam for EOR, CO 2 for long-term sequestration, or natural gas (methane) contribution to a measurable rebound of the land surface [START_REF] Dusseault | Shear dilatancy and permeability enhancement in oil sands[END_REF][START_REF] Settari | Coupling of fluid flow and soil behavior to model injection into uncemented oil sands[END_REF][START_REF] Settari | Geotechnical aspects of recovery processes in oil sands[END_REF]. On summary, expansion of the injected formation is primarily caused by a vertical effective stress release due to the pore pressure increase, with the shear stress possibly contributing to deformation through dilation.

An additional source of deformation can be of thermal origin. If the temperature of the injected fluids are lower then in-situ temperature, poroelastic and thermal effects on stresses and deformations tend to counteract and may cancel each other. However, in thermal EOR, where the formations involved are usually shallow, both thermal and pressure effects cause expansion and are additive, resulting in appreciable surface heave. According to [START_REF] Wang | Surface heave due to fluid and steam injection[END_REF] in an analysis of Cyclic Steam Stimulation (CSS) operations conducted in an oil sand at Cold Lake, Alberta, Canada, the pressure effects can dominate because of high injection pressures reached in the CSS process.

Conversely, in the Stream Assisted Gravity Drainage (SAGD) process, which uses relatively lower steam injection pressure, experience in modelling [START_REF] Walters | Coupled geomechanical and reservoir simulation of the UTF Phase B pilot project[END_REF] shows that the thermal effects can account for 50% or more of the total heave, if the nonlinearity of the geomechanical properties is taken into account.

It must be kept in mind that rocks typically exhibit a hysteretic mechanical behaviour with stiffer properties in unloading conditions. For instance, the expansion induced by pore pressure rise in the Northern Adriatic basin is only a third of that of the compaction for a similar pressure decline [START_REF] Baù | Basin-scale compressibility of the Northern Adriatic by the radioactive marker technique[END_REF][START_REF] Ferronato | Unloading-reloading uniaxial compressibility of deep reservoirs by marker measurements[END_REF].

In the survey of uplifted sites that follows it will be shown that anthropogenic land heave can vary from a few millimetres to tens of centimetres depending on the mechanism of deformation (mechanical expansion, dilatancy, thermal deformation) and the several geological and geomechanical factors mentioned above.

A In CSS, the deformations from the pressure cycles (typically between 10 MPa to 2 MPa or less) and thermal expansion combine to produce an overall heave of 10-35 cm. [START_REF] Wang | Surface heave due to fluid and steam injection[END_REF] show the data and simulation results for an area of 3 well "pads"

(each consisting of 4 rows of 5 wells) for the period between January 6 and February 24, 1989. At the beginning of this period, injection and production was balanced, but due to previous injections, the maximum heave was already about 20 cm, as shown by the baseline on Figure 2a. During the period studied, most of the wells were injecting and this resulted in an additional 5-7 cm of uplift. This magnitude is typical and the heave generally increases with time as the area heats up and accumulates dilation strain. [START_REF] Wong | Surface heave induced by steam stimulation in oil sands reservoirs[END_REF] confirmed this magnitude by semi-analytical calculations using A c c e p t e d M a n u s c r i p t 9 the nucleus of strain concept. Satellite measurements of the Cold Lake project have been described by [START_REF] Stancliffe | The use of satellite-based radar interferometry to monitor production activity at the Cold Lake heavy oil field, Alberta, Canada[END_REF]. As shown in Figure 2b, large deformation changes can occur over small periods of time (2-3 months). They stated that their best data show that the total deformation can reach 36 cm during a single month.

Shell Peace River, Canada

The Peace River oil sands deposits cover an area of about 47×10 7 m 2 west of the Cold Lake and Athabasca areas. The resource, containing bitumen of viscosity of 10,000 to 200,000 cp in a formation 30 m thick buried at a depth of 600 m, has been developed by Shell Canada, using modifications of the CSS technology. Injection takes place at pressures of above 13 MPa (the in-situ vertical stress), thereby producing formation fracturing. An extensive monitoring program, consisting of microseismic, surface time-lapse seismic, time-lapse 3D vertical seismic profiles, surface tiltmeters and InSAR, was implemented to better understand the production mechanisms, and determine the reservoir volume change. In particular, tiltmeter data were used extensively. The data interpretation indicated a similar magnitude of heave as that as Cold Lake, as shown in Figure 3 (Du et al., 2005). [START_REF] Mcgillivray | Making sense of the geomechanical impact on the heavy-oil extraction process at Peace River based on quantitalive analysis and modeling[END_REF] reported that during the first year (Oct. 2002-Oct. 2003), the reservoir volume increased by 400,000 m 3 .

Athabasca oil sands, Canada

The Underground Test Facility (UTF), located in the Athabasca area, was the first

Injection for ASR

Santa Clara Valley and Santa Ana Basin, California

The Santa Clara Valley is a structural trough running 110 km southeast of San

Francisco. The valley is bounded on the southwest by the Santa Cruz Mountains and the San Andreas fault, and on the northeast by the Diablo Range and the Hayward fault.

The fresh-water-bearing sediments forming the groundwater reservoir within the valley were mainly deposited during the Quaternary. They include semi-consolidated deposits of the Pliocene and Pleistocene epochs, and unconsolidated alluvial and bay deposits of the Pleistocene and Holocene epochs consisting of poorly sorted conglomerate, sandstone, siltstone, and clay as much as 600 m thick. Coarse-grained deposits predominate in the alluvial fans near the valley margins where the stream gradients are steeper. The proportion of clay and silt layers increases toward the San Francisco Bay (Poland, 1984).

From the early 1900s agriculture depended heavily on groundwater for irrigation. As farming was progressively replaced by urban and industrial development in the 1940s, the withdrawal continued to increase as the population grew. A decrease in rainfall during the first half of the twentieth century along with an increase in the pumping rate resulted in a significant drop of the artesian head, by as much as 80 m between 1912 and 1966. The well depth ranges from 90 to 360 m. Total annual groundwater withdrawal approached 250 Mm 3 by 1960 [START_REF] Ingebritsen | Santa Clara Valley, California[END_REF]. The piezometric head decline caused as much as 4 m of land subsidence (Poland, 1984). Using InSAR [START_REF] Schmidt | Time dependent land uplift and subsidence in the Santa Clara Valley, California, from a large InSAR data set[END_REF] showed the regional uplift of the ground surface in the Santa Clara Valley occurred from 1992 to 1999 (Figure 6a). A maximum upheaval of about 4 cm, reflecting the poroelastic response of the confined aquifer system, has been measured northward. In the south-eastern part of the valley a seasonal uplift signal is superimposed onto the long-term trend (Figure 6b). The long-term and seasonal displacements result from head changes in the aquifer system in the elastic range of stress. Observed water level fluctuations and borehole extensometer records provide evidence that the vertical compressibility of the confined aquifer system in the virgin stress range is from 20 to 100 larger than the average c M in the elastic range [START_REF] Poland | Land subsidence in the Santa Clara valley, California, as of 1982, mechanics of aquifer systems[END_REF].

InSAR investigations [START_REF] Bawden | Tectonic contraction across Los Angeles after removal of groundwater pumping effects[END_REF] show that the 2040 km Santa Ana Basin in the metropolitan area of Los Angeles displays a seasonal fluctuation with a 5 cm uplift during the late fall through mid-spring (Figure 7) and 6 cm subsidence during the late spring through mid-fall. Seasonal water table changes of the order of 30 m indicate a close relationship between aquifer management and land deformation as measured by InSAR. The aquifer is recharged all year round and is pumped during May -September to meet the summer water demand. Approximately 78% of the water pumped from the basin in 1996-1997 came from artificial recharge through surface spreading basins located in the proximity of the Santa Ana River and Santiago Creek.

The produced water-bearing units span the depth interval between 50 and 600 m below the ground surface (MWDSC, 2007).

A c c e p t e d M a n u s c r i p t 13

Las Vegas Valley, Nevada

The Las Vegas Valley is located in a structurally controlled alluvial basin containing up to 1500 m of unconsolidated sediments during the Pliocene through Holocene age.

Coarse-grained (sand and gravel) alluvial-fan deposits derived from the surrounding mountain ranges form broad piedmonts around the periphery of the valley, while Groundwater has greatly promoted the development of Las Vegas since the early 1900s when the first wells were drilled in the area. The Las Vegas metropolitan area increased in population from 0.8 million in 1990 to more than 1.5 million in 2000.

Although natural springs historically provided water to this arid valley (the average precipitation in a year is about 12-20 cm), groundwater pumping was drastically increased to help meet the rising demand. Total pumpage reached a peak of more than 100 Mm 3 /year in the late 1960s, remaining steadily above 70 Mm 3 /year until the 1990s.

Groundwater is mainly pumped from the upper 600 m of unconsolidated sediments. The long-term effects of pumping produced a regional decline of water levels of as much as 90 m by 1990 with more than 1.7 m of land subsidence measured by levelling surveys through 2000 [START_REF] Bell | Land subsidence in Las Vegas, Nevada, 1935-2000: New geodetic data show evolution, revised spatial patterns, and reduced rates[END_REF]. broad area of uplift with velocities as much as 1 cm/year adjacent to the easternmost margin of the main artificial recharge zone (Figure 8). Seasonal displacements of the order of 1 cm are superimposed on the larger uplift trend, indicating that there are both short-and long-term components in the elastic response of the system. The maximum seasonal uplift occurs during January through March each year during the peak period of artificial recharge [START_REF] Amelung | Sensing the ups and downs of Las Vegas: InSAR reveals structural control of land subsidence and aquifer-system deformation[END_REF][START_REF] Bell | Permanent scatterer InSAR reveals seasonal and long-term aquifer system response to groundwater pumping and artificial recharge[END_REF].

Based on the available subsidence/uplift measurements, the records of water level changes, and the thickness of the compacting/expanding geologic units, the ratio r between the inelastic (virgin loading) and elastic (unloading/reloading) compressibility of the aquifer system has been estimated to be in the interval of 3 to 20 [START_REF] Hoffmann | Seasonal subsidence and rebound in Las Vegas Valley, Nevada, observed by synthetic aperture radar interferometry[END_REF][START_REF] Bell | Permanent scatterer InSAR reveals seasonal and long-term aquifer system response to groundwater pumping and artificial recharge[END_REF].

Injection for gas storage

Krechba field, Algeria

The Krechba field is a gas reservoir located in the Algerian Sahara desert at a burial As part of a CO 2 sequestration research project, the PSInSAR technique [START_REF] Ferretti | Permanent scatterers in SAR interferometry[END_REF][START_REF] Colesanti | SAR monitoring of progressive and seasonal round deformation using the Permanent Scatterers technique[END_REF] has been used to monitor the injection effects on the ground surface [START_REF] Vasco | Satellite-based measurements of surface deformation reveal fluid flow associated with the geological storage of carbon dioxide[END_REF]. The study is based on satellite radar images

Lombardia field, Italy

To cope with the energy demand in the cold season, gas and oil companies dispose of methane in exhausted reservoirs during summer and extract it during winter. In Italy Apart from the general upheaval trend, that is most likely of tectonic origin, land motion appears to be elastic with an average difference between the peak values of about 1 cm.

A spatial kriging interpolation of the satellite images was used to map the areal distribution of the vertical displacements above the reservoir. As an example, Figure 11 shows the blocks. The sediments predominantly comprise rather loose and unconsolidated sands and siltstones, with intervening shale layers [START_REF] Mayuga | Subsidence in the Wilmington Oil Field, Long Beach, California, USA[END_REF].

Because of limited waterdrive activity, the pressure decline in the oil reservoir was relatively fast. By the mid-1960s about 9 MPa. of drawdown at 900 m depth, and nearly 9 m of land subsidence had occurred since the onset of production [START_REF] Allen | The mechanics of compaction and rebound, Wilmington oil field[END_REF]. The subsidence above the field was clearly recognized in 1941 when the U.S.

Coast and Geodetic Survey surveyed the levelling lines between San Pedro and Long

Beach, which had been previously monitored in 1933-1934. Subsequent measurements showed increasing subsidence up to the maximum 9 m value experienced in 1965 [START_REF] Colazas | Subsidence monitoring methods and beach mark elevation response to water injection, Wilmington oil field, Long Beach, California[END_REF]. Results from precision casing collar surveys, i.e. the periodic monitoring of the shortening (or lengthening) of well casing joints due to the A c c e p t e d M a n u s c r i p t 18 compaction (or expansion) of the oil-bearing formations [START_REF] Law | Interrelations between earth movements[END_REF], provided evidence that compaction occurred over the 650-1100 m depth interval.

In order to mitigate land settlement a massive water injection program was implemented in the late 1950s. Approximately 175,000 m 3 /day of water were injected into the field during the 1960s [START_REF] Mayuga | Subsidence in the Wilmington Oil Field, Long Beach, California, USA[END_REF], declining to 90,000 m 3 /day by the mid-1990s (Otott Jr and Clark, 1996). Both seawater withdrawn from shallow beds directly connected with the ocean and formation water produced along with the oil were used for injection. Subsidence stopped over a large portion of the field with the subsiding area reduced from 50 km 2 to 8 km 2 . The settlement rate at the historical centre of the subsidence bowl was reduced from a maximum of 71 cm/year in 1951 to zero in 1968, and in certain areas a surface rebound up to 33 cm was observed (Figure 12a). In the newest portions of the Wilmington field waterflooding and oil production began almost simultaneously. No significant subsidence occurred in those areas with overinjection generating a 20 cm increase of the original ground elevation (Figure 12b) [START_REF] Colazas | Subsidence monitoring methods and beach mark elevation response to water injection, Wilmington oil field, Long Beach, California[END_REF].

In-situ measurements by casing joints [START_REF] Allen | The mechanics of compaction and rebound, Wilmington oil field[END_REF], lab tests at high confining pressures [START_REF] Vesiĉ | Behaviour of granular soils under high stresses[END_REF]) and numerical modelling (Kosloff et al., 1980a(Kosloff et al., , 1980b) ) suggest that the Wilmington sandy formations under unloading/reloading are from 2 to 8 times stiffer than for virgin loading conditions.

Tokyo and Osaka, Japan

Over the 1950s-1960s a significant lowering of the groundwater level occurred in all the major cities of Japan because of an uncontrolled overdraft of the shallow multiaquifer systems. For example, the resulting land settlement in Tokyo was reported to be about 4.5 m relative to the ground elevation at the early 1920s [START_REF] Yamamoto | Recent trend of land subsidence in Japan[END_REF] with a number of serious related social problems. Full scale development of the aquifer system cm and a slightly irregular pattern. Similar results are found for the city of Osaka where several urban areas experienced uplift of about 3 cm in 5 years [START_REF] Sreng | Upheaval phenomenon in clay ground induced by rising groundwater level[END_REF].

Taipei, Northern Taiwan

Taipei City is the political and economical centre of Taiwan with a dense population (Wu, 1977). In order to mitigate the subsidence and prevent any possible Taipei Basin, except for its westernmost margin, experienced a rather homogeneous uplift of 7 to 10 cm with a maximum of 17 cm (Figure 14a). The largest rate, more than 1 cm/year, was measured between 1989 and 1994 (Figure 14b). The observed elastic rebound was used to quantify a ratio of about 10 between the aquifer-system compressibility under virgin loading and unloading/reloading conditions [START_REF] Chen | Thirty-year land elevation change from subsidence to uplift following the termination of groundwater pumping and its geological implications in the Metropolitan Taipei Basin, Northern Taiwan[END_REF]. Ea is much weaker. More detailed information about the geology and the properties of Chioggia Mare are provided in [START_REF] Teatini | Water-gas dynamics and coastal land subsidence over Chioggia Mare field, Northern Adriatic sea[END_REF].

Injection of seawater is planned to take place in pool C lateral aquifer at a rate of 5,000 m 3 /day for 25 years after the inception of gas production. The injected water will be properly filtered to remove particles larger than 5-10 μm that could cause a reduction of the aquifer permeability. It will be also chemically treated for compatibility with the in situ water to avoid the activation of corrosion of the well intakes. shown in Figures 15c and15d. In the present case, water injection helps mitigate the expected land subsidence and does not necessarily induce an appreciable anthropogenic heave. Figure 16 shows the simulated vertical ground displacement in Chioggia without and with the injection wells for the various plausible combinations of hydro-geomechanical parameters investigated by [START_REF] Gambolati | Convenzione tra il Ministero dell'Ambiente e l'Università degli Studi di Padova per la realizzazione di un modello matematico previsivo degli eventuali effetti di subsidenza connessi alla coltivazione di giacimenti di idrocarburi in Alto Adriatico[END_REF] in their report to the Ministry. As an example, in the most favourable scenario using geomechanical properties derived from lab tests, the predicted land uplift occurs 13 years after the cessation of gas withdrawal and is on the order of 6 mm.

Ravenna, Adriatic coastline, Italy

The Ravenna Adriatic coastline is underlain by a major gas field, named Angela-Angelina (Figure 17a), that extends down to 2900-4000 m depth and consists of a very large number of gas pools (about 300) separated by intervening clayey layers and crossed by a number of geological faults. Initially, the gas reserve was estimated to be 22,000 MSm 3 of which about 12,000 were produced as of January 2002 and 10,000 more are planned to be pumped out over the following 25-30 years. In a few depleted pools the maximum fluid pore pressure drawdown has amounted to as much as 35 MPa.

The land subsidence caused by gas production in the vicinity of Angela-Angelina has received the attention of a number of studies [START_REF] Teatini | CENAS, Coastline Evolution of the Upper Adriatic Sea due to Sea Level Rise and Natural and Anthropogenic Land Subsidence[END_REF][START_REF] Gambolati | Coastline regression of the Romagna Region, Italy, due to natural and anthropogenic land subsidence and sea level rise[END_REF][START_REF] Schroot | Subsidence induced by gas production: an integrated approach[END_REF] and is a matter of concern regarding the stability of the Ravenna coastland. To mitigate it, ENI-E&P has implemented an experimental project called "Angela Pressure Maintenance" with the final objective to oppose the anticipated coastland settlement through the injection of water in the aquifer connected to the 1-re-injection of the formation water, i.e. the water extracted along with the gas from Angela-Angelina and the nearby offshore fields Amelia, Antares and Porto Corsini Mare. At the beginning of the operation in 2003, the injection rate was 150 m 3 /day and soon increased to 300 m 3 /day with the addition of the seawater obtained with the aid of the Beach Management System (BMS) [START_REF] Ciavola | The new Beach Management System at Lido Adriano, Ravenna, Italy[END_REF][START_REF] Piccini | Modeling groundwater response to beach dewatering at Ravenna shoreline[END_REF] and chemically treated for compatibility with the situ water;

2-increase of the injection rate using additional wells from the cluster Angela;

3-further increase of the injection rate using the dismissed production wells from the Angela-Angelina platform.

The cumulative water injected from March 2003 to April 2007 is shown in Figure 17c ( [START_REF] Eni | Progetto sperimentale Angelina Pressure Maintenace -Rapporto trimestrale alla Provincia di Ravenna[END_REF]. Despite the very modest quantity of water injected underground some benefits in terms of a delayed propagation of the depressurization below the coastline have been observed. No evidence is so far available of any significant mitigation of land subsidence. However, the ENI-E&P pressure maintenance experiment is of great practical interest, and especially so in view of the planned progressively increased rate of injection. Future modelling predictions and field measurements will help reveal the hopefully effective impact of the above programme.

By the use of recent geophysical logs and marker measurements from deep offshore boreholes drilled in the vicinity of Angela-Angelina, [START_REF] Baù | Basin-scale compressibility of the Northern Adriatic by the radioactive marker technique[END_REF] estimate a ratio r between loading and unloading-reloading c M ranging from 3 to 2 over the depth interval 3000-4000 m. However, because of the large injection depth, the medium compressibility in expansion is expected to be about one order of magnitude smaller than that of the shallower Chioggia Mare field. Kontinentale Tiefbohrung der Bundesrepublik Deutschland (KTB) [START_REF] Jahr | Fluid injection and surface deformation at the KTB location: modelling of expected tilt effects[END_REF][START_REF] Jahr | Monitoring fluid induced deformation of the earth's crust: a large scale experiment at the KTB location, Germany[END_REF]. The pore pressure increase exceeded 10 MPa at KTB over the injection time and induced a land deformation that was detected by the tiltmeter array. The measured tilts were reproduced with the aid of a finite element model. The results [START_REF] Jahr | Deformation, seismicity, and fluids: results of the 2004/2005 water injection experiment at the KTB, Germany[END_REF] reveal a maximum anthropogenic uplift of approximately 3 mm above the injection point which dissipates quickly as one moves far from it (Figure 18a). Figure 18b shows the modelling reconstruction of the tiltmeter measurements around KTB.

DISCUSSION AND CONCLUSIONS

A survey of sites worldwide where underground fluid (water, gas, steam) injection has caused a measurable land uplift (or heave) has been performed. Fluid is injected for a variety of purposes, from enhancing oil production to storing gas in depleted gas/oil fields, recharging pumped aquifers, disposing of industrial liquid wastes and mitigating anthropogenic land subsidence. Vertical land displacement is measured using traditional levelling, tiltmeters, or, most recently and relatively inexpensively, with the aid of the satellite interferometry. Land may rise as a consequence of the migration to ground The uniformity of uplift at the ground surface is basically related to the location, arrangement, and strength of the injection sources and the depth of the injection that, in turn, depend on the purpose of the disposal. If the injected formation is deep enough, the uplift may be expected to be rather uniform for a regular distribution of the injection wells. Conversely, if the injection is irregularly distributed and the injected formation is shallow, the anthropogenic uplift may result in irregular patterns.

The case studies described above provide a clear affirmative answer to the question: is it physically possible to appreciably raise the ground surface by injecting fluids underground? This concern has been advanced by a few geotechnical and hydrological experts (see [START_REF] Ferronato | A pilot project using seawater to uplift Venice anthropogenically[END_REF], in relation to a possible anthropogenic land uplift as an innovative defence from periodical flooding that affect high-value coastal areas that are experiencing land settlement and/or seal level rise due to climate changes. Recent modeling studies [START_REF] Comerlati | Can CO 2 help save Venice from the sea?[END_REF][START_REF] Comerlati | Saving Venice by seawater[END_REF] suggest that injecting seawater into a investigation. This is why, concerning the project mentioned above of anthropogenic Venice raising, a pilot ad hoc injection experiment has been recently advanced [START_REF] Castelletto | Can Venice be raised by pumping water underground? A pilot project to help decide[END_REF].

Acknowledgments

  Figure 1 moves rightward, i.e. farther from the failure line bounding the envelope of the allowable stress states. By contrast, when fluid is injected p rises and possibly exceeds p 0 . In this case the effective stress decreases under the original in situ value with Mohr's circle moving leftward, i.e. toward the failure line. Two failure mechanisms can be experienced: (a) if Mohr's circle touches the envelope line a shear failure may occur; (b)

  field scale project designed to test the SAGD recovery method for oil sands. UTF operates at a depth of about 140 m. During the first phase, started in 1984, 3 pairs of short horizontal wells were drilled from an underground tunnel accessed by a vertical shaft. The second phase followed with 3 pairs of long (500 m) horizontal wells from A c c e p t e d M a n u s c r i p t 10 which commercial quantities of bitumen were produced (seeO'Rourke et al., 1999, for review). Flue gas was also injected at a later stage[START_REF] Yee | Flue gas injection into a mature SAGD steam chamber at the Dover Project (Formerly UTF)[END_REF]) and the project is now in a commercial stage. Separate vertical wells were drilled to monitor temperature and deformations. About 5 cm of heave was recorded in the centre of the deforming area from September 1993 to in April 1994, as shown in Figure4. As the project matured, the heave increased up to 30 cm in 2001.Following the success of the UTF project, several commercial projects using SAGD technology started, and are now producing in the Athabasca area. A complete set of heave surveys is available for the MacKay River project of PetroCanada(Petro-Canada, 2008) and the Firebag project of Suncor[START_REF] Suncor | ERCB Annual Review Suncor Firebag. Suncor Report to ERCB[END_REF]. The MacKay River SAGD produces from the McMurry sand at a depth of about 100 m, at an operating pressure of 1.7 MPa and steam temperature of 205 °C. Deformations were measured by repeated monitoring of 97 monuments (leveling) and supplemented by an array of tiltmeters and microseismic monitoring. In December 2007, an additional 67 monuments were installed. The heave contours between the baseline surveys of December 2002 and December 2007 are shown in Figure 5a. The overall heave pattern follows the orientation of the injection/production well pairs running NE to SW. The heave exceeds 30 cm in several areas and reaches a maximum of 37 cm over the field. Heave along a profile oriented perpendicular to the well pairs is shown for three different times in Figure 5b. The Firebag project of Suncor also produces from the McMurry formation but it is in an earlier stage of development. Heave surveys have been conducted yearly from 2004 to 2008 and the cumulative heave during this period has reached 15.3 cm, with the incremental heave over the last year having a maximum of 4.9 cm. Coupled geomechanical and thermal flow studies carried out by the authors on various Athabasca sites confirm the range of uplift observed at the sites discussed above (i.e., 20-35 cm).

  contributing to heave include thermal expansion, decrease of the effective stress, nonlinear decrease of stiffness associated with decrease of effective stress and change in Poisson's ratio.

  Valley was the first area in the United States where organized remedial actions were undertaken against groundwater overdraft with land subsidence substantially halted by about 1969. Importation of surface water reduced the subsurface pumping and allowed for an effective program of aquifer recharge leading to a recovery of groundwater levels. Such a program began in the 1960s and continues presently.

  predominantly fine-grained (silt and clay) compressible materials underlie the central part of the valley. Intervening sequences of both coarse-and fine-textured sediments give rise to a well-developed multi-aquifer system cut by several Quaternary faults extending from the underlying bedrock to the ground surface. Most of the groundwater in the aquifer system originates from the precipitation in the Spring Mountains to the west.

  Since 1988 the Las Vegas Valley Water District (LVVWD) has maintained a groundwater recharge program in to augment the local water supply during periods of high demand. Water is recharged primarily in the coolest months using treated surface water imported from the nearby Lake Mead on the Colorado River. Since the beginning A c c e p t e d M a n u s c r i p t 14 of the artificial recharge program, water levels have stabilized and recovered by as much 30 m from 1990 to 2005 (LVVWD, 2005). Persistent Scatterer InSAR for the periods 1995-2000 and 2003-2005 show a general reduction of the subsidence rate and a

  depth of about 2000 m. The 20-m thick producing layer lies on a north-northwest trending anticline and mainly consists of quartzose fine-grained sandstone of Early Carboniferous period. The overburden comprises of a sequence of alternating mudstones and sandstones. The horizontal stress field in the basin is highly anisotropic with faults on the flanks of the anticline trending north-northwest. The gas produced from the Krechba field contains a high mole fraction of CO 2 which must be separated and disposed of for both economic and environmental reasons. The CO 2 is re-injected into the reservoir through three nearby wells located at about 8 km northeast of the A c c e p t e d M a n u s c r i p t 15 cluster of the production wells. At the reservoir pressure the CO 2 behaves as a supercritical fluid with a density of about 0.85 kg/dm 3 . The well-head injection pressure varies during the operations with an average value of 15 MPa and peak values achieving 18 MPa.

  obtained fromJuly 12, 2003 to March 19, 2007. With this approach, stable scatterers are identified using a statistically based analysis of the phase and amplitude characteristics of the energy reflected by the earth surface. A subset of such scatterers is denoted as permanent and used to estimate the atmospheric and orbital errors. In the Krechba field case the quality of the data is particularly good because the rock outcrops in the desert area are stable reflectors. The mean vertical ground velocity for the investigated 2003-2007 time interval as provided by the PSInSAR data analysis is shown in Figure9. The areas shown in blue are increasing in elevation by more than 5 mm/year and are clearly correlated with the location of the three injection wells. The cumulative upheaval measured above the Krechba field amounts to about 2 cm with a rather uniform areal distribution.

  Stogit S.p.A. manages a number of depleted gas fields for storage purposes. The Lombardia field, located in the Po river plain, Northern Italy, is one such reservoir, consisting of three mineralized layers (named A, B and C) made of turbiditic sediments deposited during the late Pliocene epoch with about 30-m thick shale caprocks. Layer C, m thick and 1200-m deep, is the main pool containing about 93% of the overall gas originally in place. About 2,700 MSm 3 were produced from pool C between 1981 and 1986, and since 1986 pool C has been used for storage purposes. The largest pore pressure drawdown achieved in 1986 was about 3 MPa. In the following years water ingression from the surrounding aquifer led to a partial recovery of about 2 MPa.Currently, the average operative pore pressure is about 1 MPa below the original value, with a difference of 2.5 MPa between the maximum at the end of the storage phase and the minimum at the end of withdrawal. The maximum pore pressure in the reservoir exceeds the original in situ value by about 3%(IGU, 2003). An integrated monitoring system has been implemented above the Lombardia field to monitor the land movements induced by the cyclic injection-extraction activity operated in the reservoir. From 2003 to 2007 traditional high-precision levelling surveys were carried out yearly along with a much more frequent PSInSAR analysis. The levelling surveys reveal that the region above the field exhibits a slight upheaval trend with a positive vertical ground velocity of about 1 mm/year. The PSInSAR data do show cyclic ups and downs phased with the pressure variation within the reservoir. An example of the vertical displacements vs. time for a few pixels from the PSInSAR analysis located above the field is given in Figure10, with the magnitude of the occurrence gradually dissipating on the observation points farther from the reservoir.

  maps over the periods November 2005 -April 2006 (a) and April 2006 -November 2006 (b). In the former time interval gas is withdrawn and land subsides, and in the latter gas is injected and the land rises by about the same magnitude. Moving

  reservoir boundary the vertical displacements quickly vanish and appear to be un-influenced by gas storage.A modeling study by[START_REF] Castelletto | 3D geomechanics in UGS projects. A comprehensive study in northern Italy[END_REF] and[START_REF] Teatini | Monitoring and modelling 3D ground movements induced by seasonal gas storage in deep reservoirs[END_REF] shows that the PS records are successfully matched with a finite element model using a loading unloading-reloading compressibility ratio of 4.3.4. Injection for land subsidence mitigation3.4.1. Wilmington, Long Beach, CaliforniaThe Wilmington oil field is a broad asymmetrical anticline extending lengthwise approximately 18 km in a SE-NW direction and about 5 km in the SW-NE direction below Long Beach, in the southwestern part of the Los Angeles basin, California. The reservoir is made of seven overlying oil-bearing formations of the Pliocene and Miocene epoch spanning the depth range 600-2000 m below m.s.l. The pools are divided into six structural blocks by five major faults that restrict the fluid flow between

  Figure 13 shows the piezometric increase and the associated vertical uplift for the city of Tokyo. Inspection of Figure 13a reveals the close relationship between aquifer recovery occurring after the implementation of the 1970 regulations and land upheaval, which amounts to about 20 cm. The areal distribution of the Tokyo uplift from 1991 to 2005 is shown in Figure 13b, with several zones experiencing an uplift of more than 5

of about 3

 3 million inhabitants plus several million people in the surrounding suburban areas. Like many other big cities in the world, early development of the city was enhanced by the development of the groundwater resources. The city centre lies on 300m thick late-Quaternary fluvial deposits laid down over deformed Miocene bedrock starting from about 400,000 years ago.

  occurred from 1955 to 1970 from a confined aquifer lying between 50 and 140 m depth below the ground surface. Piezometric head has decreased by more than 40 m with the lowest value reached in 1975. The massive pumping was accompanied by large land settlements amounting to as much as 2.2 m in the city centre

  associated damages, the government stopped the use of groundwater in the Taipei Basin during the early 1970s. The settlement rate has significantly decreased as the hydraulic head gradually recovered and stabilized after approximately the late 1990s. The establishment of a fine network of levelling benchmarks has allowed for accurate monitoring and control of the ground movements during the recovery. The behaviour of the post-pumping ground elevation is characterized by a relatively long period of declining subsidence followed by a period of uplift from 1989 to 2003. Most surface rebound was observed in the central to eastern portion of the basin, roughly corresponding to the area of maximum subsidence. From 1989 to 2003 most of the

3. 4

 4 .4. Chioggia Mare, Northern Adriatic, Italy ENI-E&P, the Italian national oil company, has recently advanced a plan for the development of a number of gas fields (about 15) located in the Northern Adriatic. The largest field, named Chioggia Mare, is the closest to the coastline (the westernmost margin of the field is 12 km from the city of Chioggia, south of Venice). Gas production A c c e p t e d M a n u s c r i p t 21 from Chioggia Mare raises some concerns about the risk of contributing to anthropogenic settlement of Chioggia and the surrounding lagoon, including Venice. To offset this environmental hazard ENI-E&P designed a project of land subsidence mitigation using two deep seawater injection wells located halfway between the field and the coastline. The Italian Ministry of Environment gave the University of Padova, Department of Mathematical Models and Methods for the Scientific Applications (DMMMSA), the task of checking the environmental sustainability of the ENI-E&P mitigation programme, with the aid of ad hoc numerical models able to reliably predict the expected land subsidence in the presence of the injection wells. The Chioggia Mare gas field is seated at a 1100-1400 m depth and consists of four pools. The upper pools (C and C2) are formed by a structural trap and the lower ones (E and Ea) pinch out against a thick clayey formation (called Santerno), which represents a natural hydraulic barrier. The estimated total gas withdrawn from Chioggia Mare over its 12-year production life will be about 5,000 MSm 3 . Pools C and C2 are surrounded by a strong lateral and bottom waterdrive. The lateral aquifer partially encompassing pools E and

  Figures 15a and 15b show the simulated fluid pore pressure variation in pool C and the associated waterdrive predicted at the end of the field production life without and with the injection of water. It can be noted that the depressurization caused by gas pumping does not propagate coastward because of the barrier effect exerted by the injection wells. Note

  experienced by the waterdrive in the vicinity of the injection boreholes. The simulated influence of injection on vertical ground displacement is

  depth interval 3100-3700 m. The ENI-E&P injection project was designed in 2001 and consists of three phases (Figure17b):

  experiment intended to study deformation of the upper crust, improve knowledge of coupled hydro-geomechanical processes and characterize the affected subsurface porous medium was performed from June 2004 to April 2005 in the Upper Palatinate, Eastern Bavaria, Germany[START_REF] Kumpel | Two massive hydraulic tests completed in deep KTB borehole[END_REF]. Water was injected at a rate of about 290 m 3 /day to a total of 84,000 m 3 through an open hole that was 3850-4000 m deep. Land deformation was monitored by high-resolution borehole tiltmeters installed at 5 locations (Berg, Eiglasdrof, Stockau, Mittelberg and Pullersreuth) at a variable 1.5-3.3 km distance from the injection well denoted as

  injected formation expansion. This is due primarily to the release of the effective intergranular stress and secondarily to the shear dilation (or dilatancy) on condition that the induced fluid pore overpressure is large enough so as the yield surface (or friction line) is intersected by the Mohr-Coulomb circles. Thermal expansion may also contribute significantly to the observed heave. Careful inspection of each single occurrence reveals that: 1-the observed land uplift may vary from a few millimetres to tens of centimetres over a time interval of some months to several years according to the specific location; 2-the largest uplift depends on a number of factors, including the fluid pore pressure increase, the depth, thickness and areal extent of the pressurized and heated geological formation, and the hydro-geo-thermo-mechanical properties of the porous medium involved in the process.

  800-meter-deep brackish aquifer underlying Venice, Italy, might induce an upheaval of this much loved city by 25-30 cm over 10 years. Such an uplift would be enough to offset the most likely scenario of relative sea level rise expected in 2100[START_REF] Carbognin | Global change and relative sea level rise at Venice: what impact in term of flooding[END_REF].A second point enlightened by the present survey regards the ratio r of virgin to second cycle elastic compressibility c M . The available data are summarized in Figure19 and show that, almost irrespectively of the site, r tends to increase for shallower depth. If at very large depths the virgin c M is only from two to three times the elastic c M , in shallow aquifer systems (~50-300 m) the former can be one order of magnitude larger than the latter. The actual prediction of the expected medium expansion due to fluid injection, and thus the related ground uplift, requires the knowledge of c M in the unloadingreloading cycle. On first approximation, it might be obtained from the more frequently and easily known c M in virgin loading and a r estimate based on the depth of the injected formation. For sure, a more accurate evaluation requires a site-specific

.Figure 1 .

 1 FIGURE CAPTIONS Figure 1. Mohr-Coulomb circles. When the pore pressure p increases because of fluid injection, the circles move leftward and may achieve the limiting yield surface or

Figure 2 .

 2 Figure 2. (a) Differential heave in 3 pads of the Cold Lake CSS during one steam injection period (modifed from Wong and Kry, 1997). The upper figure is the total heave at the beginning of the period, and the lower figure is the incremental heave between the beginning and the end of the one month period. (b) Deformations over a time period of 86 days (August 5, 1996 -November 1, 1996) measured by InSAR in Cold Lake CSS project (adapted from Stancliffe and van der Kooij, 2001). Uplift is positive.

Figure 3 .

 3 Figure 3. Heave (a) over a one-year period and (b) from April 26, 2005 to June 5, 2005 calculated by tiltmeter data in the Shell Canada Peace River CSS project (modified from Du et al., 2005).

Figure 4 .

 4 Figure 4. Distribution of heave with depth from September 1993 to April 1994 at the UTF BE2 extensometer site (adapted from Collins, 2007).

Figure 5 .

 5 Figure 5. Heave (a) in the MacKay River SAGD project from December 2002 to December 2007. The leveling monuments used to map the ground displacements are shown. (b) Heave development in time along the cross section AB traced in (a) (modified from Petro-Canada, 2008).

Figure 6 .

 6 Figure 6. Vertical land displacement recorded by Differential InSAR in the Santa Clara Valley, California. (a) Cumulative uplift measured from September 1992 to October 1999; (b) seasonal upheaval measured from August 1998 to March 1999. The bottom

Figure 7 .

 7 Figure 7. (a) Ground displacement in the Santa Ana Basin, California, detected by Differential InSAR from July 1998 to January 1999. (b) Uplift behaviour along the A-A' cross-section traced in (a) (modified after[START_REF] Bawden | Tectonic contraction across Los Angeles after removal of groundwater pumping effects[END_REF].

Figure 8 .

 8 Figure 8. Velocity map for the northwest portion of Las Vegas Valley, Nevada, obtained by Persistent Scatterer InSAR from ENVISAT data between April 2003 and May 2005. The contour lines of the water-level change (m) recorded in the same interval are shown. The inset on the right shows the time series of the vertical displacement for the persistent scatterer indicated on the map (modified after Bell et al., 2008).

Figure 9 .

 9 Figure 9. Mean land vertical velocity above the Krechba field, Algeria, as detected by the analysis of PSInSAR data in the period 2003-2007 (modified after Vasco et al., 2010).

Figure 10 .

 10 Figure 10. Vertical displacements (mm) vs. time for a few pixels monitored by InSAR located above the Lombardia field, northern Italy.

Figure 11 .

 11 Figure 11. Land vertical displacements above the Lombardia field between: (a) November 2005 and April 2006; (b) April 2006 and November 2006. The maps are obtained with a kriging interpolation of InSAR data. The reservoir outline is also shown.

Figure 12 .

 12 Figure 12. (a) Land uplift (inches) at Long Beach, California, from 1958 to1975 as a result of elastic unloading caused by repressurization of the producing field blocks (modified afterKosloff et al., 1980b). (b) Increase in elevation (feet) measured at a leveling benchmark above a eastern block of the Wilmington field (modified after[START_REF] Colazas | Subsidence monitoring methods and beach mark elevation response to water injection, Wilmington oil field, Long Beach, California[END_REF].

Figure 13 .

 13 Figure 13. Ground upheaval in Tokyo: (a) groundwater level and vertical displacement over period 1962-2005; (b) cumulative upheaval distribution in the urban area over the period 1991-2005 (modified after Sreng et al., 2009).

Figure 14 .

 14 Figure 14. (a) Map of land uplift in the Taipei basin from 1989 and 2003 as obtained by interpolation of the leveling records. (b) Land upheaval rate over the period[START_REF] Settari | Coupling of fluid flow and soil behavior to model injection into uncemented oil sands[END_REF] -1994 (modified after Chen et al., 2007)).

Figure 15 .

 15 Figure 15. Fluid pore pressure change (10 -1 MPa, above) and anthropogenic land subsidence (cm, below) at the end of the Chioggia Mare gas field production life as predicted with the aid of numerical models: (a) and (c) without, (b) and (d) with the seawater injection wells. Negative values denote pressure decline, positive values pressure increase. The outline of the Chioggia Mare reservoir is also shown (modified after[START_REF] Teatini | Water-gas dynamics and coastal land subsidence over Chioggia Mare field, Northern Adriatic sea[END_REF].

Figure 16 .

 16 Figure 16. Anthropogenic land subsidence and land heave in Chioggia as predicted with the aid of numerical models without (solid lines) and with (dashed lines) seawater injection wells for the various hydro-geo-mechanical scenarios addressed by Gambolati et al. (1998).

Figure 17 .

 17 Figure 17. (a) Location of the Angela-Angelina gas field along the Northern Adriatic coastline, Italy. The trace of the reservoir is highlighted in red. (b) Representation of the three-phase ENI-E&P injection programme "Angela Pressure Maintenance". (c) Cumulative volume of water injected from March 2003 to April 2007 in the ENI-E&P injection programme "Angela Pressure Maintenance".

Figure 18 .

 18 Figure 18. Results from the finite element interpretation and reconstruction of the tiltmeter measurements: (a) land uplift; (b) tilts at the land surface (modified after Jahr et al., 2008).

Figure 19 .

 19 Figure 19. Ratio r between virgin and second cycle elastic compressibility versus depth as derived from the case studies addressed in the present paper (1: Santa Clara Valley,

  Figure 1

  Figure 2

  Figure 3

  Figure 4

  Figure 6

  Figure 8

  Figure 9

  Figure 10

  Figure 12

  Figure 14

  Figure 15

  Figure 16

Figure 19

 19 Figure 19

CASE STUDIES 3.1. Injection for EOR

	3.
	3.1.1. Cold Lake, Alberta, Canada
	Cold Lake is the oldest of the four developed oil sand production areas of northern Alberta, Canada. It is producing from the 15-30 m thick Clearwater sand lying at a depth of about 450 m. The sand is primarily quartz and in the best quality area is quite homogeneous and densely packed; it exhibits dilation when sheared. Above the Clearwater is the Grand Rapids formation consisting of interbedded shale/sand sequences (often containing small gas reservoirs), and the Colorado shale group. A fresh water sandy aquifer at a depth of 100-150 m overlies the Colorado shale. The a n u s c r i p t bitumen viscosity in the Clearwater varies between 50,000 and 100,000 cp at an in-situ M temperature close to 13 °C. The area was developed initially by Imperial Oil Ltd. using
	CSS consisting of cycles of steam injection (30-40 days) at fracturing pressure followed by a production period of several months. Currently, the SAGD process is favoured for c c e p t e d new projects.
	8

A c c e p t e d M a n u s c r i p t


Mariana Boadella
email: mariana.boadella@gmail.com

Christian Gortazar

Pelayo Acevedo

Tania Carta

María Paz

José Fuente

Joaquín Vicente

José De La Fuente

A Aguirre

M P Martín-Hernando

Six recommendations for improving monitoring of diseases shared with wildlife

Keywords: Disease monitoring, Paratuberculosis, Time trends, Tuberculosis, Wildlife diseases, Zoonoses

Introduction

The history of wildlife disease surveillance in Europe possibly started with the first passive surveillance schemes set up in Scandinavian countries in the 1930s [START_REF] Mörner | Surveillance and monitoring of wildlife diseases[END_REF]. Surveillance of rabies [START_REF] King | Historical perspective of rabies in Europe and the Mediterranean Basin[END_REF]) and trichinellosis [START_REF] Blancou | History of trichinellosis surveillance[END_REF]) started afterwards. However, the first scientific meetings did not occur until the early 1990s (Symposium on the health and management of freeranging mammals held in Nancy, France, in 1991; First conference of the European section of the Wildlife Disease Association EWDA, in Paris, France, in 1994). These meetings prompted a more widespread interest in wildlife disease surveillance. In the last decades, classical swine fever in Eurasian wild boar (Sus scrofa; [START_REF] Rossi | Long-term monitoring of Classical swine fever in wild boar (Sus scrofa sp.) using serological data[END_REF] and highly pathogenic avian influenza [START_REF] Chen | Avian flu: H5N1 virus outbreak in migratory waterfowl[END_REF] further contributed to a growing interest on diseases shared with wildlife such as zoonotic diseases and diseases that have potential risk for domestic species [START_REF] Gortazar | Diseases shared between wildlife and livestock: a European perspective[END_REF]. Detection of these relevant diseases in wildlife was identified as a determinant of the structure and function of European surveillance schemes [START_REF] Leighton | Surveillance of wild animal diseases in Europe[END_REF]. At a worldwide scale, the World Organization for Animal Health or OIE working group on wildlife diseases was also established in 1994. It is now recognized that those countries which conduct disease surveillance of their wild animal populations are more likely to detect the presence of infectious and zoonotic diseases and to swiftly adopt counter measures [START_REF] Mörner | Surveillance and monitoring of wildlife diseases[END_REF].

In Spain, the interest in wildlife diseases started in the 1980s and was boosted in 1989 with the emergence of rabbit hemorrhagic disease in European wild rabbits (Oryctolagus cuniculus; [START_REF] Villafuerte | First epizootic of rabbit hemorrhagic disease in free-living populations of Oryctolagus cuniculus at Doñana National Park, Spain[END_REF]). In the last decade, however, resources for studying wildlife diseases increased after the identification of wildlife species as actors in the epidemiology of important livestock diseases, such as Aujeszky's disease [START_REF] Müller | Pseudorabies in the European wild boar from Eastern Germany[END_REF], bluetongue [START_REF] Ruiz-Fons | Spatial and temporal evolution of bluetongue virus in wild ruminants, Spain[END_REF]) and bovine tuberculosis (bTB; [START_REF] Naranjo | Evidence of the role of European wild boar as a reservoir of Mycobacterium tuberculosis complex[END_REF], and more recently after realizing the importance of diseases in Iberian lynx (Lynx pardinus) conservation [START_REF] Millán | Disease threats to the endangered Iberian lynx (Lynx pardinus)[END_REF]. Risk factors for the appearance of wildlife reservoirs are commonly the spillover from domestic livestock in combination with anthropogenic activities such as translocation of wildlife, supplemental feeding of wildlife and wildlife populations reaching densities beyond normal habitat carrying capacities [START_REF] Gortazar | Disease risks and overabundance of game species[END_REF][START_REF] Palmer | Tuberculosis: A reemerging disease at the interface of domestic animals and wildlife[END_REF]. This, along with the size of the Spanish livestock industry and the significant proportion of free range breeding systems, prompted specific calls for wildlife disease research in the national grant scheme in 2006 and 2008 (INIA-FAU, http://sp.inia. es/ucc/contenidos/memo1.pdf).

Using mycobacterial diseases as an example, we discuss herein the pros and cons of the current Spanish Wildlife Disease Surveillance Scheme (http://rasve.mapa.es/Publica/ Programas/NORMATIVA%20Y%20PROGRAMAS% 5C PROGR AMAS%5C FA UNA%2 0SILVESTR E% 5CPLAN%20NACIONAL%20DE%20VIGILANCIA% 20SANITARIA%20EN%20FAUNA%20SILVESTRE_2011. PDF), providing suggestions for wildlife disease monitoring in other regions facing similar challenges.

Mycobacterial diseases in European wildlife

TB in Eurasian badgers (Meles meles) was first diagnosed in Switzerland [START_REF] Bouvier | Transmission possible de la Tuberculose et de la Brucellose du gibier a l'home et aux animaux domestiques et sauvages[END_REF], a country where no further reports on wildlife TB exist in the scientific literature [START_REF] Wyss | Farm and slaughter survey of bovine tuberculosis in captive deer in Switzerland[END_REF]. Later, Mycobacterium bovis was isolated from badgers in southwest England in 1971 and Ireland in 1973. Since then, the infection in badgers has been found throughout dense badger populations of southwestern England and parts of Wales [START_REF] Krebs | Bovine tuberculosis in cattle and badgers[END_REF] and throughout Ireland [START_REF] Dolan | Badgers and bovine tuberculosis in Ireland: A review[END_REF]. By contrast, there was no published TB case in badgers from the continent since the first description in Switzerland in the 1960s, until a recent case report from Spain [START_REF] Sobrino | Bovine tuberculosis in a badger (Meles meles) in Spain[END_REF]. This is surprising, since many countries in continental Europe have both TB and badgers. Lower badger densities as compared to Britain and Ireland may partly explain this absence. However, a lack of targeted surveillance could also contribute [START_REF] Artois | Development and validation of an enzyme-linked immunosorbent assay for antibodies against Mycobacterium bovis in European wild boar[END_REF].

More recently, a growing body of evidence suggests that other wildlife hosts do also act as M. bovis reservoirs in different parts of Europe (Gortazar et al. accepted for publication), including the Eurasian wild boar in Spain [START_REF] Naranjo | Evidence of the role of European wild boar as a reservoir of Mycobacterium tuberculosis complex[END_REF] and Portugal [START_REF] Santos | Epidemiology of Mycobacterium bovis infection in wild boar (Sus scrofa) from Portugal[END_REF]) and several cervids in different countries (e.g., [START_REF] Gortazar | bovine tuberculosis in Doñana biosphere reserve: the role of wild ungulates as disease reservoirs in the last Iberian lynx strongholds[END_REF]. As many countries attempt to eradicate bTB from domestic livestock, success is impeded by spillback from wildlife reservoirs. It will not be possible to eradicate M. bovis from livestock until transmission between wildlife and domestic animals is halted. Such an endeavor will require a collaborative effort between agricultural, wildlife, environmental and political interests [START_REF] Palmer | Tuberculosis: A reemerging disease at the interface of domestic animals and wildlife[END_REF]). Nowadays, TB is among the wildlife diseases receiving more attention by scientists and government agencies.

Paratuberculosis in wildlife, by contrast, is receiving far less attention in wildlife than TB. This disease, caused by Mycobacterium avium paratuberculosis (MAP), has been considered as a major disease of ruminants for more than a century and has significant economic and welfare effects on livestock in all continents. Recently, this bacterium has received an increasing interest because of scientific evidence that suggest that human infection with this microorganism may be causing some, and possibly all, cases of Crohn's disease [START_REF] Naser | Culture of Mycobacterium avium subspecies paratuberculosis from the blood of patients with Crohn's disease[END_REF][START_REF] Uzoigwe | Epidemiological evidence for Mycobacterium avium subspecies paratuberculosis as a cause of Crohn's disease[END_REF]). The incidence of paratuberculosis is high in animals kept intensively under environmental and husbandry conditions which are conducive to the spread of the infection [START_REF] Chiodini | Paratuberculosis (Johne's disease): The current status and future prospects[END_REF]. Cervids and other wild ruminants have frequently been identified as MAP hosts, and high prevalence along with clinical disease was reported in some cases [START_REF] Balseiro | Histopathological classification of lesions observed in natural cases of paratuberculosis in free-ranging fallow deer (Dama dama)[END_REF], but not in others (Carta et al. in press). In Scotland, wild rabbits have been identified as true wildlife MAP reservoirs too [START_REF] Beard | Natural paratuberculosis infection in rabbits in Scotland[END_REF], and a similar status may locally apply in Spain (Maio et al. in press).

However, regular surveillance, other than the annual reporting of TB cases and far more sporadic reporting of wildlife paratuberculosis to the OIE, is not done at the (European) country level, or at least not recorded in the scientific literature.

Wildlife disease monitoring

Wildlife disease monitoring can be defined as the systematic recording of epidemiological data, with the specific purpose of detecting spatial and temporal trends as well as the presence/absence of the disease. Data and samples gathered can be used for detecting emerging diseases [START_REF] Rhyan | Emergence of diseases from wildlife reservoirs[END_REF] and in retrospective studies [START_REF] Oleaga | Sarcoptic mange in red deer from Spain: Improved surveillance or disease emergence?[END_REF][START_REF] Ruiz-Fons | Spatial and temporal evolution of bluetongue virus in wild ruminants, Spain[END_REF]. Ideally, monitoring information should integrate data on the risk factors determining the pathogen epidemiology, such as host abundance and distribution, as they can inform us on potential disease spread in a given spatial or temporal frame. The concept is similar to surveillance, which is done in order to meet the objectives of controlling the disease [START_REF] Artois | Development and validation of an enzyme-linked immunosorbent assay for antibodies against Mycobacterium bovis in European wild boar[END_REF]. In contrast to disease surveillance, which may be passive based on clinical cases or active based on random sampling, monitoring is more often active.

Disease control at the human-livestock-wildlife interface should be based on a thorough knowledge of the "natural history" (ecology) of the disease agent and its human, domestic and wild hosts [START_REF] Woodford | Veterinary aspects of ecological monitoring: The natural history of emerging infectious diseases of humans, domestic animals and wildlife[END_REF]. Disease and population monitoring is a fundamental part of disease ecology. Figure 1 presents a diagram of how new diseases usually lead first to descriptive epidemiology and eventually to risk factor analyses and control actions. If humans or domestic animals are affected, disease monitoring will start early in time. The decision to monitor this disease in wildlife will depend on the relevance of wildlife hosts as disease reservoirs for humans or domestic animals or on the effects of the disease on wildlife population dynamics. Only if at least one of these options is suspected will monitoring of the disease among wildlife hosts be considered. As a consequence, wildlife disease monitoring usually starts much later in time. However, while this is the case for most regions in developed countries, in areas where wildlife species provide greater economic returns than livestock, the opposite might be the case. This has driven wildlife research and monitoring schemes in less developed countries where livestock and human health care are poor or nonexistent [START_REF] Kock | Wildlife and pastoral society -Shifting paradigms in disease control. Domestic Animal/Wildlife Interface: Issue for Disease Control[END_REF].

Disease monitoring in wildlife is promoted in order to obtain information to compare with the distribution and prevalence trends in livestock, as a basis for decision making regarding wildlife disease control, and as a means for assessing the effects of any disease management action. Monitoring, by definition, has no limited time frame. Monitoring wildlife disease trends requires adequate diagnostic methods and differential diagnoses; a large-scale and long-term sampling network; the logistics linked to the preparation, distribution and conservation of valuable wildlife samples; and expertise for data management and analysis. In addition, a vital need exists to gather data from the ecology and wildlife management field in order to combine them with disease information regarding both wildlife and livestock [START_REF] Delahay | The science of wildlife disease management[END_REF]. Wildlife disease monitoring will mainly occur if wildlife species are identified as significant reservoirs for humans or domestic animals, or if the disease has a significant impact on wildlife populations. This will probably happen later in time than monitoring in humans or domestics

Recommendations for monitoring diseases in wildlife

To properly monitor a wildlife disease, several points must be considered. This includes: (1) making sure the disease, if shared, is properly monitored in the relevant domestic animals or even in humans; (2) also making sure that background information on wildlife population ecology is available to maximize the benefits of the monitoring effort;

(3) selecting the appropriate wildlife hosts for monitoring, while being flexible enough to incorporate new ones if research suggests their participation; (4) selecting the appropriate methods for diagnosis and for time/space trend analysis; (5) deciding which parameters to target for monitoring: one or more disease agents, or lesions or contact as revealed by serum antibodies; and finally (6) establishing a reasonable sampling effort and a suitable sampling stratification that can be prolonged over time.

First, if the disease is shared with humans or domestic animals, do appropriate monitoring programs that allow, for instance, trend comparisons between these and wildlife exist? Regarding bTB, good information on the prevalence and incidence in bovine livestock will be available in most European situations. But, at the same time, information may be lacking for other relevantor potentially relevantdomestic species such as goats and free-range pigs.

Second, wildlife disease monitoring will only make sense if population monitoring is carried out at the same time, allowing to link changes in abundance or management with changes in disease indicators [START_REF] Acevedo | Estimation of European wild boar relative abundance and aggregation: a novel method in epidemiological risk assessment[END_REF]). This should include not only the target wildlife hosts but also other relevant competitor or prey species [START_REF] Sobrino | Carnivore population trends in Spanish agrosystems after the reduction in food availability due to rabbit decline by rabbit haemorrhagic disease and improved waste management[END_REF].

Third, wildlife disease monitoring should select for the most appropriate wildlife hosts, considering not only distribution, abundance, degree of protection, prevalence and disease susceptibility but also ease of sample collection and diagnostic sensitivity and specificity. For instance, in Spain, TB has mainly been recorded in wild boar, red deer (Cervus elaphus) and fallow deer (Dama dama; e.g., [START_REF] Gortazar | bovine tuberculosis in Doñana biosphere reserve: the role of wild ungulates as disease reservoirs in the last Iberian lynx strongholds[END_REF], and as previously stated, sporadically in badgers [START_REF] Sobrino | Bovine tuberculosis in a badger (Meles meles) in Spain[END_REF]). TB has also occasionally been described in red fox (Vulpes vulpes; Martín-Atance et al. 2005) and Iberian lynx (L. pardinus; [START_REF] Peña | Histopathological and immunohistochemical findings in lymphoid tissues of the endangered Iberian lynx (Lynx pardinus)[END_REF]). However, wild boar are considered the best TB surveillance target because of their wider distribution, higher abundance and high availability as a game species and because of their lesion distribution [START_REF] Martín-Hernando | Lesions associated with Mycobacterium tuberculosis complex infection in the European wild boar[END_REF]). The recent design of a specific and sensitive enough enzymelinked immunosorbert assay (ELISA) test [START_REF] Sobrino | Bovine tuberculosis in a badger (Meles meles) in Spain[END_REF][START_REF] Boadella | Serological tests for detecting antibodies against Mycobacterium bovis and Mycobacterium avium subspecies paratuberculosis in Eurasian wild boar[END_REF]) makes sample harvesting and laboratory analyses relatively easy even if only head lymph nodes and blood samples are available. By contrast, the detection of TB-compatible lesions in cervids requires the inspection of the head and neck, thorax and abdomen [START_REF] Vicente | Wild boar and red deer display high prevalences of tuberculosis-like lesions in Spain[END_REF][START_REF] Martín-Hernando | Distribution of lesions in red and fallow deer naturally infected with Mycobacterium bovis[END_REF]). Moreover, wild ruminants are often infected with other mycobacteria, such as MAP, further compromising diagnostic specificity of some tests, particularly those based on serum antibodies [START_REF] Reyes-García | Large-scale ELISA testing of Spanish red deer for paratuberculosis[END_REF]Carta et al. in press). In turn, badgers have a more limited distribution in Spain and are protected by law, making sampling difficult. However, monitoring schemes should be flexible enough to allow incorporating new species if research suggests their participation in disease epidemiology [START_REF] Delahay | Wildlife disease reservoirs: the epidemiology of Mycobacterium bovis infection in the European badger (Meles meles) and other British mammals[END_REF].

Fourth, the diagnostic and statistic methods should be defined in a way that assures repeatability and data quality. Diagnostic methods selected for wildlife disease monitoring will depend on factors such as the selected host species and expected sample size, the cost of each test, and its specificity and sensitivity. Tests suitable for their use in wildlife are not always available, and the difficulties imposed by field sampling contribute to reduce test sensitivity [START_REF] Donnelly | Is there an association between levels of bovine tuberculosis in cattle herds and badgers? Stat Comm Infect Dis 2:3 European Food Safety Authority (EFSA)[END_REF]. Statistical methods will depend on factors such as the expected prevalence, the geographic scale, the length of the time series and the degree of change in time of the measured variable, being it prevalence or lesion intensity [START_REF] Joly | Surveillance to detect chronic wasting disease in white-tailed deer in Wisconsin[END_REF]. It is often of use to study the age-specific prevalence rates, particularly using juvenile prevalence as a proxy for incidence [START_REF] Wobeser | Investigation and management of disease in wild animals[END_REF]. Epidemiological data are peculiar from a statistical perspective. Data with aggregated distributions are usual in the epidemiological databases, so parametric statistics, which are requiring normal distribution of the data, cannot be generally used (e.g., Jewell 2009). So in risk factor and disease trend assessment, generalized modelswith Poisson, negative binomial, zero-inflated or binomial distributionsare needed. Information is often generated at different spatial scalesfrom individual to population or even to regionand so it is required to use mixed models in which, by means of random variables, pseudoreplication can be avoided [START_REF] Zuur | Mixed effects models and extensions in ecology with R[END_REF]. Another essential peculiarity is that the epidemiological data of different host species is rarely available at the same spatial resolution and at a high enough resolution to allow meaningful inferences to be made. In general terms, data analyzed should be referred to the same territorial units (municipalities or provinces, for example), and the lowest resolution will determine the spatial resolution of the analysis (see [START_REF] Pfeiffer | Spatial analysis in epidemiology[END_REF].

Fifth, once the host species are defined, it must be decided what to target for monitoring. This means defining the agent or agents: M. bovis only, or members of the M. tuberculosis complex (MTBC), or MTBC and MAP, for instance; and also defining what data will be needed, be it the antigen by culture or PCR, specific antibodies or even characteristic lesions [START_REF] Vicente | Wild boar and red deer display high prevalences of tuberculosis-like lesions in Spain[END_REF][START_REF] Sobrino | Bovine tuberculosis in a badger (Meles meles) in Spain[END_REF][START_REF] Santos | Diagnosis of Tuberculosis in the Wild Boar (Sus scrofa): A Comparison of Methods Applicable to Hunter-Harvested Animals[END_REF]. It is important to choose parameters for which detection tools of known effectiveness are available [START_REF] Wobeser | Investigation and management of disease in wild animals[END_REF]. In addition, it is important to consider testing expenses and budget limitations. Thus, if funding is limited, it can be wise to combine more expensive techniques, such as culture, applied for confirmation to a subsample, with cheaper techniques such as gross pathology (e.g., [START_REF] Vicente | Wild boar and red deer display high prevalences of tuberculosis-like lesions in Spain[END_REF]. In most cases of mycobacterial disease monitoring, the target will be MTBC, but under certain circumstances, monitoring may need to include MAP because of the relevance of crossreactivity to the tests used or because of the importance of MAP for the regional livestock industry (e.g., [START_REF] Balseiro | Histopathological classification of lesions observed in natural cases of paratuberculosis in free-ranging fallow deer (Dama dama)[END_REF]. Moreover, prevalence rates have a limited value for monitoring chronic diseases with a very protracted course [START_REF] Wobeser | Investigation and management of disease in wild animals[END_REF]) such as mycobacterial infections.

Finally, it is of paramount importance to define an adequate and reasonable sample size as well as number and distribution of sampling localities according to statistical recommendations (Table 1). We must keep in mind the budget and the current and future logistic constraints such as the laboratory analysis throughput per day, the space available for short-and long-term sample storage and the design of proper databases and sample banking registers. Moreover, sampling must be adequately stratified by age and sex [START_REF] Vicente | Wild boar and red deer display high prevalences of tuberculosis-like lesions in Spain[END_REF], management [START_REF] Vicente | Risk factors associated with the prevalence of tuberculosis-like lesions in fenced wild boar and red deer in south central Spain[END_REF]) and study zone [START_REF] Muñoz | Spatial distribution and risk factors of Brucellosis in Iberian wild ungulates[END_REF]. Epidemiology software can help identify suitable sample sizes and can detect time trends when a known initial prevalence and an expected prevalence change are given (e.g., Win Episcope, http://www.clive.ed.ac.uk/cliveCatalogueItem.asp? id=B6BC9009-C10F-4393-A22D-48F436516AC4; European Food Safety Authority 2010). For instance, sampling requirements will depend on the expected initial prevalence or the expected degree of change in these prevalences from time 1 to time 2 (Table 1). In order to spare costs, it may be advisable to pool samples for analysis (e.g., [START_REF] Tayce | Minimum sampling effort for reliable non-invasive estimations of excretion abundance of Elaphostrongylus cervi L1 in red deer (Cervus elaphus) populations[END_REF] or to accumulate samples gathered during several years until the required sample size is achieved (see Table 2).

Monitoring mycobacterial diseases in Spanish wildlife

Spain is a 504,782 km 2 country in southwestern Europe that includes two archipelagos, the Canary Islands off the West African coast, the Balearic Islands in the Mediterranean, and the autonomous towns of Ceuta and Melilla in the north of Africa. Based on habitat and climate features and wildlife population characteristics, Spain can roughly be divided into six bioregions [START_REF] Muñoz | Spatial distribution and risk factors of Brucellosis in Iberian wild ungulates[END_REF]; Fig. 2). The compulsory control of bTB in Spanish cattle has been successful, so that current individual cattle incidence is below 0.5%. However, the distribution of positive cattle herds is not uniform, with higher prevalence in Mediterranean habitats of the south and west of the Spanish mainland. Islands with no potential wildlife reservoirs are almost bTB-free (http://rasve.mapa.es/Publica/Programas/ NORMATIVA%20Y%20PROGRAMAS/PROGRAMAS/ 2010/TUBERCULOSIS/PROGRAMA%20NACIONAL% 20DE%20ERRADICACION%20DE%20TUBERCULOSIS %20BOVINA.%20A%C3%91O%202010.PDF). Of the susceptible domestic hosts, bTB is only monitored in cattle and in goats living in close contact to cattle. Some regions have also implemented compulsory or voluntary bTB control programs in goats. In Spain, paratuberculosis has been diagnosed for over 20 years in all three (cattle, sheep and goat) domestic ruminant species [START_REF] Aller | Paratuberculosis ovina[END_REF][START_REF] Garrido | Diagnóstico de paratuberculosis caprina en Andalucía[END_REF], but is not monitored.

The current situation regarding tuberculosis in Spanish wildlife was recently reviewed (Gortazar et al. in press). Paratuberculosis, in turn, has been recorded in farmed red deer [START_REF] Fernández-De-Mera | Factors affecting red deer skin test responsiveness to bovine and avian tuberculin and to phytohaemagglutinin[END_REF]), but preliminary data from nationwide surveys suggest that wildlife is only locally relevant in MAP epidemiology (Carta et al. in press). This is the case of fallow deer in an intensively grazed mountain area in northern Spain [START_REF] Balseiro | Histopathological classification of lesions observed in natural cases of paratuberculosis in free-ranging fallow deer (Dama dama)[END_REF]) and possibly of European wild rabbits sharing pastures with infected domestic ruminants in southern Spain (Maio et al. in press). Sporadic records of MAP are also available for wild boar (Álvarez et al. 2005).

Therefore, wildlife TB prevalence is two orders of magnitude higher than in cattle, and it is most likely that certain wildlife reservoirs might locally interfere with the cattle bTB eradication efforts [START_REF] Gortazar | bovine tuberculosis in Doñana biosphere reserve: the role of wild ungulates as disease reservoirs in the last Iberian lynx strongholds[END_REF]). In addition, TB has killed several endangered Iberian lynxes causing conservation concerns [START_REF] Peña | Histopathological and immunohistochemical findings in lymphoid tissues of the endangered Iberian lynx (Lynx pardinus)[END_REF]). These are clear reasons for targeting wild ungulates for TB monitoring and for taking into account the possible interference of MAP in certain diagnostic tools and host species [START_REF] Boadella | Serological tests for detecting antibodies against Mycobacterium bovis and Mycobacterium avium subspecies paratuberculosis in Eurasian wild boar[END_REF]Carta et al. in press). Table 3 presents an overview of the application of the six abovementioned recommendations to the current Spanish circumstances.

Table 1 Sample effort needed for the detection of disease according to the expected prevalence (assuming a population size of >10,000) and for the detection of prevalence variations over 50% according to the initial prevalence (with a power of 90% and confidence level of 95%, Win Episcope 2.0)

Discussion

As our knowledge on wildlife diseases grows, disease control becomes more often an option. However, monitoring is needed to identify changes in disease occurrence and to measure the impact of interventions [START_REF] Mcdonald | Perturbing implications of wildlife ecology for disease control[END_REF]. Despite this fact, wildlife disease monitoring is largely in its infancy [START_REF] Artois | Development and validation of an enzyme-linked immunosorbent assay for antibodies against Mycobacterium bovis in European wild boar[END_REF], and setting up stable, comprehensive and accurate schemes at different spatial scales (local, national and global) should become a priority for health authorities and wildlife managers.

In many countries including New Zealand, the United States and several ones in the European Union, wildlife vaccination as a means to contribute to bTB control in livestock is being seriously considered (e.g., [START_REF] Tompkins | Oral vaccination reduces the incidence of tuberculosis in free-living brushtail possums[END_REF][START_REF] Carta | in press) Wild red deer are not a Mycobacterium avium paratuberculosis reservoir in the Iberian Peninsula[END_REF][START_REF] Corner | Tuberculosis in European badgers (Meles meles) and the control of infection with Bacille Calmette-Guérin vaccination[END_REF][START_REF] Ballesteros | First data on Eurasian wild boar response to oral immunization with BCG and challenge with a Mycobacterium bovis field strain[END_REF]. In this context, the implementation of wildlife TB-monitoring schemes is a real need.

One point to consider is who takes charge of the monitoring costs. Wildlife disease monitoring produces knowledge that benefits at least three different agencies, namely, animal health, public health and conservation. It Probability of detection: Annual samples by taxon and bioregion (BR 1-6). Shadings indicate that sampling is sufficient for the detection of prevalences of 10% (light grey), 5% (medium grey), and 1% (dark grey), with a power of 90% and confidence level of 95%; Win Episcope 2.0.

White boxes represent situations where these levels are not achieved in only 1 year of sampling would be wise to combine efforts and resources from all three compartments and to take advantage of the expertise of government agencies and academic institutions. Government attitudes toward wildlife disease research have changed during the last decades for reasons already listed in the "Introduction." Now it is needed to convince other stakeholders too, such as the livestock industry, the hunting lobby or the conservationists, and even medics of the need to monitor wildlife diseases if we are thinking about their future control. Successful examples of collaboration between conservationists and vets [e.g., the detection and management of feline leukemia in the endangered Iberian lynx [START_REF] López | Management measures to control a feline leukemia virus outbreak in the endangered Iberian lynx[END_REF]], between Improve information exchange with medics.

Human cases not always differentiated from M. tuberculosis.

(2) Background information on wildlife population ecology is available to maximize the benefits of the monitoring effort.

Tools for estimating relative abundance and spatial aggregation are available for wild boar [START_REF] Acevedo | Estimation of European wild boar relative abundance and aggregation: a novel method in epidemiological risk assessment[END_REF]. No easy density estimation methods are available for wild boar.

Decide a tool (dung counts and/or hunting yields) and apply to all selected sampling sites.

In deer, population density can be estimated [START_REF] Acevedo | Estimating red deer abundance in a wide range of management situations in Mediterranean habitats[END_REF][START_REF] Acevedo | Estimating roe deer abundance from pellet group counts in Spain: An assessment of methods suitable for Mediterranean woodlands[END_REF].

Characterize other risk factors and monitor their changes through time. Management-related risk factors (feeding, waterholes, fencing) have been identified [START_REF] Vicente | Risk factors associated with the prevalence of tuberculosis-like lesions in fenced wild boar and red deer in south central Spain[END_REF] Use ELISA for calculating serum antibody prevalence, pathology for additional lesion scoring, and culture a subsample, for confirmation and molecular epidemiology.

Cross-reactions and low sensitivity limit the use of ELISA in deer, and TB monitoring in deer requires inspecting whole carcass and using expensive and time-demanding pathology and culture [START_REF] Martín-Hernando | Distribution of lesions in red and fallow deer naturally infected with Mycobacterium bovis[END_REF].

Expertise required for data management and statistical analysis.

(5) Decide which parameters to target for monitoring: one or more disease agents, or lesions, or contact as revealed by serum antibodies?

Serum antibodies and TB-compatible lesions are time-and cost-effective in wild boar [START_REF] Vicente | Wild boar and red deer display high prevalences of tuberculosis-like lesions in Spain[END_REF][START_REF] Sobrino | Bovine tuberculosis in a badger (Meles meles) in Spain[END_REF][START_REF] Santos | Diagnosis of Tuberculosis in the Wild Boar (Sus scrofa): A Comparison of Methods Applicable to Hunter-Harvested Animals[END_REF][START_REF] Boadella | Serological tests for detecting antibodies against Mycobacterium bovis and Mycobacterium avium subspecies paratuberculosis in Eurasian wild boar[END_REF].

Use wild boar serum antibody prevalence as main parameter, lesion scoring as additional tool.

Pay attention to prevalence in juvenile age classes. Some proportion of culture confirmation is advisable for strain characterization and epidemiology. (6) Establish a reasonable sampling effort and distribution.

Wildlife sampling bioregions have been defined [START_REF] Muñoz | Spatial distribution and risk factors of Brucellosis in Iberian wild ungulates[END_REF]) and cattle bTB prevalence and distribution is well described.

Stratify sampling by bioregion and cattle bTB prevalence. Better sample from permanent sampling sites, which can be monitored for host abundance and management. Sampling effort depends on regional wild boar abundance and the collaboration of hunters and local authorities.

vets and medics regarding many zoonoses such as trichinellosis (e.g., [START_REF] Wacker | Epidemiological analysis of Trichinella spiralis infections of foxes in Brandenburg, Germany[END_REF]; and between conservationists, medics and vets [e.g., in zoonoses where wildlife are both reservoirs and victims, such as TB [START_REF] Gortazar | Molecular characterization of Mycobacterium tuberculosis complex isolates from wild ungulates in southcentral Spain[END_REF][START_REF] Gortazar | bovine tuberculosis in Doñana biosphere reserve: the role of wild ungulates as disease reservoirs in the last Iberian lynx strongholds[END_REF]] should serve as a trigger for future collaborations. The six steps for surveillance of relevant shared diseases can be adapted to many other geographical settings and different disease situations. Regarding mycobacterial diseases, these are worldwide distributed and do frequently affect multihost systems at the domestic animal-wildlife interface as described for Spain. In any such situation, similar requisites to those outlined in Table 2 do apply. The same requisites are also valid for other disease systems, if they affect domestic animals or humans. instance, deer might be better indicators of bluetongue virus circulation than vaccinated domestic sheep or cattle [START_REF] Rodríguez-Sánchez | Bluetongue virus serotypes 1 and 4 in red deer, Spain[END_REF].

Wildlife disease-monitoring programs that are integrated within national animal health surveillance infrastructures should have the capacity to respond promptly to the detection of unusual wildlife mortality and to institute epizootiological researches into new and emerging wildlife diseases [START_REF] Mörner | Surveillance and monitoring of wildlife diseases[END_REF]. Increased training and preparedness of human and animal health staff and government agencies, improved communication and continued research will enhance wildlife-monitoring efforts [START_REF] Belant | Importance of wildlife disease surveillance[END_REF]. Resources are always a limiting factor, but the developments toward the monitoring of TB in Spanish wildlife show that combined efforts of local and national government agencies, along with the commitment of trans-disciplinary research, can allow setting up acceptable schemes with a low enough cost to be sustainable in time. Improvements, such as extending animal TB surveillance to goats and pigs and establishing improved links and data exchange with the human health system, are still needed. There exist opportunities for similar approaches elsewhere regarding other diseases, hosts, and geographic circumstances.

Fig. 1

 1 Fig. 1 Schematic representation of disease management in humans and domestic animals (upper part) and wildlife (lower part). Dotted boxes indicate decisions and the arrow at the bottom suggests time. Wildlife disease monitoring will mainly occur if wildlife species are

Fig. 2

 2 Fig. 2 Map of Spain, with a division into six large bioregions for sampling and wildlife disease monitoring, according to the Spanish Wildlife Disease Surveillance Scheme

Table 2

 2 Example regarding the Spanish Wildlife Disease Surveillance Scheme

		Birds	Carnivores Hares	Rodents	Wild boar	Red deer	Roe deer	Wild bovids
	BR 1	200	60	0	100	400	70	50	20
	BR 2	100	60	120	200	570	190	60	40
	BR 3	100	60	90	100	510	250	35	30
	BR 4	100	60	60	100	245	120	40	60
	BR 5	200	60	65	0	345	50	20	75
	BR 6	100			0
	TOTAL	800	300	335	500	2070	680	205	225

Table 3

 3 Main requisites, current circumstances, and recommendations for TB monitoring in Spanish wildlife

	Requisite	Current circumstances	Recommendations
	(1) Disease is properly monitored in the	Excellent monitoring in cattle.	Include most goat herds in monitoring.
	relevant domestic animals or even in humans.	No nationwide compulsory monitoring in other domestic animals.

Eur J Wildl Res (2011) 57:697-706

Acknowledgments This is a contribution to MCINN Plan Nacional I+D+i research grant AGL2008-03875 and FEDER and to TB-STEP EU grant 212414. Studies on diseases shared between domestic animals and wildlife are also supported by Grupo Santander -Fundación Marcelino Botín. Tania Carta acknowledges a grant from Regione Sardegna, and Pelayo Acevedo and Maria Paz Martín-Hernando acknowledge a Juan de la Cierva (Fondo Social Europeo) and an ISCIII postdoctoral contract from MCINN, respectively. Jose Luis Sáez made valuable comments to the first draft.


Caroline Godard

Joachim Boissy

Benoit Gabrielle

Life-cycle assessment of

come

System boundaries

Figure 2 :Figure 3 :

 23 Figure 2 : Mobilization hypothesis of biomasses

Figure 6 :

 6 Figure 6 : Contribution analysis of the fertilization (fertilizer production + fertilizer field emissions).

Figure 7 :Figure 9 :

 79 Figure 7 : Net energy yield of biomasses.

loading: Loader Storage on boiler site Mean distance= 20 km Tractor+platfrom trailer Handling with farmer material Collective storage Unloading/loading: Loader Mean distance= 35 km

  Boundaries of the studied system.

		Transport
	Machines, buildings		Energy losses
		Mean distance= 12 km	Straws, miscanthus and triticale
		Tractor+platform trailer
	By-products (grains) Cropping operations (e.g. cultivation, harvesting) field: Loader Figure 1 : Loading on Energy (fuel, electricity) Inputs (fertilizers, pesticides, seeds)	Any biomass +loader	By-products (fibres, seeds) Factory process (flax) Unloading/Collective transportation by Flax Flax shives Intermediate Stock Farm storage lorries(empty return)	Heat 10000 Mwh Boiler combustion

Mean distance= 15 km Tracteur+ platform trailer Loading on field: Loader Crop production 50% 50% Loading on field: Loader Mean distance= 12 km Tractor+platform trailer +loader Farm storage Unloading/loading: Loader Storage on boiler site Flax production Mean distance= 20 km

	<50 km	Tractor+platform trailer
	>50 km	Mean distance= 35 km Collective transportation by lorries (empty
		return)
		Intermediate storage