Purr~rtzinrui

BcC:luse of intensification agriculture is now a significaot polluter affecting Wolrer quality wough nitrates. pathogens from animal wastes, and pesricides. To correct such dissarnenities water quality poliey relies upon legal insrruments and economic incentives.

The French «gularion. here presented, is based on speeific me:lSures dealing with agriculture. and the "Law of watet" (1964) which gives the general framework for warer management. Economie ineentives are not Yety developed. thus the discussion focuses on me: intcresr of nieragen taxation. In spire: of sorne view points chis instrument seems an efficient onc. The environrnc:ntal problems associarcd widl agriculture are rc:1arc:d ta intensifiC:ltion and specialisation in production. The priee support policies are generally seen as the main reason for this intensifiC:ltion. especially in the European Economie Community. But there is no direct relationship between the protection rates and the negative impacts on the environment. The increased output per worker and per hectare is rather due to change in factor COstS in parricular. the considerable rise of labour coses campated with C:lpital and agro-chemical COSts• Among the negative impacts of agriculture on the environment. water quality is a hot copie. To formulate a correct view of the problem in the firsr section we identify the main features of agricultural pollution. Then. in the second seaion wc analyu: them from a regulatoty view point. presenting the French situation where an extension of the Law of Woltet is still in progress. Lastly. we examine economic ineentives which cao he used to prevent environmental pollution.

Pierrt RAinel1i

.

'-THE MAIN FEATURES OF AGRICUlTURAL POLLUTION

Firstly. a general analysis of the agricultural sources of pollution as they affect water quality is pn:sentcd. This analysis focuses on nitrate and pesticide pollution. Secondly. a more complete presentation summarizes the relationship be!W<:en the pollutants, their effects and thoir consequences.

Cuv:rai analysis

There is actually a great concern for the effects of human health from pesticide and fertilizer residues. but also from heavy metals and other comaminants of water. Among these environmemal problerns special anention has becn paid to nitrate contamination and pesticide residues.

The spreading of liquid manures and minerai fertilizers. and pesticide applications give rise to the dispersion of pollution components into the envitonmem through infiltration or run-off. Beyond certain thresholds. which depend on how toxic the pollutams arc. and of the self-cleansing capability of the soils and waters concerned, environmental damage will occur.

The nitrogen coming from minerai and organic fertilizers. which is not taken up by plams. reaches groundwater aquifers. The nitrate losses depend on many variables such as the Nmin-balance in the root zone. soil type. agricultural practices. type of crop. The increased washout of nitrogen by leaching or nin-off contributes to higher nitrate concentration in drinking water. Consequently the EC Maximum Admissible Concentration (M.A.C.) of 50 mg NOil is often ""cceded. Depending on the degrcc of agricultural intensification. nitrate ptoblems may be more or less important. But the incidence of nitrate contamination also depends on the origin of drinking water. Thus. it is interesting tO compare France and the Federal Republic of Germany where the proportion of drinking water coming from gtoundwater sources is the same (about 70 %).

In the early 80's five per cent of drinking water was above MAC in the FRG. and thrce per cent in France. COM (88).708 p.9. In the FRG the nitrogen per ha offarmland (fertilizer consumption + manure production) is about 225 kg. In France the total is about 135 kg. However a direct relationship between agricultural intensification and nitrate ptoblems encountered in drinking water is nor evident because MAC is measured on distributed water. and water supplied can be mixed with cleaner water to dilute the nitrate concentration. In any case omer sources of contamination exist besides that of agricu! ture.

Within each country there is a tIemendous variation in the incidence of excessive nitrate levels. In France. geographical diversity and in particular vatying soil and climatic conditions involve very differcnt situations regarding nitrate levels in water.

The pollution from pesticides (herbicides. fungicides. insecticides and growth regulation products) is a more intricate problem. Ir results from the interaction of chemical persistence (Iengrh of Iife). water solubility. application rates, intensity of use in specific areas. the type of soils. and the number of rears over which chemicals have been used.

Environmmt Nonhan 5eaJ Confirmee Rtpon • Volum~6

ln devdoped countries the consumption levd varies according to the degree of agricultural incensification (table 1). Souret. ' OECD, 1991, L 'Erat tU l'tnvironnnntnt, p.197 Kg/km'

Rtlationship bttwttn pol/uranes, thûr tffiees and thtir eonstqutnCtS

Nitrate ingestion by human bcings may cause methaemoglobinemia. which is especi.Jly dangerous for babies. and perhaps stomachcancer. If the cause dfca rdationship for the first hcaIth problem is demonstrated. there is no proof that human metabolism tr.ulsforms nitr.ue inta carcinogenic N-nicroso compounds.

Nitrate ingestion is also dangerous for animais Illee pigs and poultry. bccausc it cao bc a possible cause ofJack of growth. abortions. or sreriliry... The pollution from pesticides is more alarming. An emerging issue is the cxposure of human populations to pesticide rcsidues. They arc undergoing research 10 discover their eareinogenic potencial. birrh defect potencial. and overaII lethalncss to humans.

The contamination of surface and groundwaccr sources also damages animal populations and natural ecosysrems. The control of aquatic wceds in irrigation canals is yct anothcr source of contamination. A5 a consequence, the numbc:r of thre2tcnc:d spccic:s incre3SCS. Graph 1. represencing the threatened species by percentage ofknown speeies in the late 1980•s. shows that in France marnmals. birds. and arnphibians reach the highest percentages. In the FRG. it is fish. reptiles and vascular plants which arrain the highest percentagcs. Graphie 1 : Thr~4re~d '1"0" in p=mt ofpto<s Imown (lare 1980's) (Source OECD, 1991) ~!y.~"-. .

As indicated in

If'"

o. u, r-r-r---r-.,....-,r-r-" '. The main consequence is a distuption of ecosystems in tesetvoirs. which affecrs fresh water supplies. and in coastal waters causes the proliferation of green algae (Ulva) and other algaes.

Spteading Iiquid manure increases rhe number of parhogenes in water-courses (faecal streptocci). This may be the panial cause of the baererial contamination of shells.

Various other problems cm arise such as ammonia emission which plays a role in rhe problem of acid tain. For example. chiny per cent of acid deposition in Nerherlands now cornes From animal manure.

-ASPECTS OF THE FRENCH REGULATION

Most agriculrural pollution is caused unintentionally. This demonsrrates a lack of awareness and knowledge. Education and persuasion have a role tO play in encounging pracrices which are friendlier towards the environmenr. Codes of good practiees are proposed to improve the efficiency of nitrogen uptake by plants and reduce the consumption of pesticides. A special acrion programme has been adopted in France promoting rational ferrilizing and a better use of manure.

But when protecring water qualiry requires severe reduetions in agro-chemicals or ferrilizers. regulatory measures are needed. The legal background to pollution problems associated wirh intensive farming contains both general and more specific regulations. Raindli.1991.

SI

Sp«ific r<gu/arions

These specific regulacions are considered through classified inscallacions and local health rcgulations.

The acr of July 1976 on classified inscallacions for environmencal protecrion covers hazardous escablishmencs. including intensive livestock rearing acrivicies. Ir protecrs the incerescs of neighbourhood ameniry. hcalth. securiry. agriculture. nacural and environmental proccaion, and the conservation of sites and monuments.

An acriviry coming under chis acr has co be classified. i.e. listed wirhin a given nomenclature. Liyc:scock rearing installations of a certain sizc. for enumeraccd species arc: in chis nomenclature.

-the size depends both on che size of che flock or herd and the weighc of thc animais (for pigs only animais over 30 kg).

-th... species are those regarded as the most pollucant : veaI and beef fatstock. pigs and poultry. Dairy cows are excluded.

The cwo criteria are used co define the legal regulacions for any inscallation. the reporring requiremencs and the permission regulacions.

A reporring establishmenc must adhere co a certain number of rules. The installation must be locaced ac leasc 100 mecers away from dwellings. 35 meters away fiom wacercourses. 200 mecers away From bathing resons and beaches. and 500 mecers away fiom fishfarms. There are also tules for slurry spreading.

The permission regulacions are more demanding because permission is only granted

SmtÎtUIT on AgriC'Ulturt anJAqUIIOl/ruu afrer a public inquiry into the possible impacr of the projecr upon che inreresrs of the neighbourhood has been complered, afrer consultation of the local municipal councils concemed and upon the advice of che depanemental hcalch board. The keysrone of the permission regulations is the impacr study which the applicant has to provide giving details of the source, nature and magnitude of any disamenities liable to resulc From the installation in question. The applicanc has co stace: how he proposes to avoid such disamenities. Concerning healch regulation, the French legislation provides at che nationallevd a scrong control over che producrion of agrochemicals. As it is done in other countries, chis control concerns both the producrs performance and irs toxicological harmJessness. More specifically che French legislation provides sorne institurionaliu:d regulacions abouc the applicarion of pesticides and feniliu:rs. A noteworthy bture of rhis regulacion is its basis upon a local (depanmenr) scandard. This srandard is established by the Miniscry of Health, whose recommendarions are che leasc demanding. The local aurhoriry (depanmenr) may adapr them in a more rigourous way. Various modd documents have been formulared over rime and the resulr has been thar local regulations are somewhac disparace and variable.

Gaura/ "gufarions

The following enacrmenrs do nor apply ro agricu1rure as such bue affecr che ways in which any form of pollurion and dissaminiry associaced with inrensive farming has ro be dealt with. The rwo broad cacegories involve rown planning and water procecrion.

Environmental procecrion in the broad sense, inc1uding landscape and che incompatibiliry berween producrive acrivities and residential areas are a maner for land use and thus come under rown planning law. Buc the problem is nor simple in view of che principle of independence for rown-planning and environmenrallegislation.

The land use plan sets our general rules for land use wichin a commune, allowing IOr specialisarion of acriviries upon the local terrirory. Ir bases chese rules on che present and future desrinarions for che land, the main distincrion being berween urban and rural areas. In spire of sorne imperfecrions the land use plan is efficient to conuol che crearion and exrension of inrensive rearing facilities especially when wmers are associared with the formulation of this zoning sysrem. Bur sometimes the granting of permission IOr insrallations in protecred areas is given too easily.

Until now the warer prorecrion regularion is based on the 1964 Warer Acr, however an updating of chis law is currencly in progress. The aim is rhe exrension of powers in order ro obrain a bener management of surface warer and groundwater and che increase of penalries.

The acr of December 1964 refers ro the regularions and distribution of warer and to che conrrol of warer pollurion. Ir created a qualitarive and quantirative management system for the six major basins in France. The management is made chrough advisory basin comminees and execurive basin agencies which are financially independenr. Under chat act the agencies derermine and define qualiry targers for watercourses. Qualiry and flow problems are managed chrough a sysrem of charges, bue pollution discharges are also subjet ro a ser of srandards.

-ECONOMIC INCENTIVES

Enforcemcnc rnc:asures are nc:cessary whc:n there arc irrcversible dFecrs, but c:conomie approaches in a market economy are more efficient. The efficacy of the v-arious rncasures dc:pc:nds on c:conomic criteria, bue aIso on policica1 and administntivc: ones. This aspcct is cxarnined in the first point. Then the discussion focuses on fenilizcr taxation whichOis the most feasible mc:ans tO achicve better qualiry protection at the least social caSt.

ble [Q cause or increase water deterioration by modifying the physica!, chemica!, biolagica! or bacteriologica! characteristics of any watet including surface water, groundwater and littoral water wirhin the limits of territorial waters. Discharges are subject to rather strict regulations, and the govemment has cenain powe:rs in cases where safery or public health might be at risk. It can also regulate or prohibit cenain types of discharge.

In order tO protect drinking water qualiry from agricultural pollution the French legislation provides the determination of water catchment ar<:as. According•to the 1964 Water Act cvery nc:w water catchment made afrer 1967 must be surrounded by a prateaion arca in which mcre arc {wo zones wherc: prescriptions concerning fc:rtili:zcr and pesticide use are more or less strict. Howcver all cxisting installations belOre 1967 have not been submitted tO this regulation. So today only 20 pcr cent of the French drinking water installations are protected by such wnes, Sanorio. 1991, p.85. 53 Snninltr 0" A.grù:ulrurt and AquaculJur3

.1. AJusmunt of~conomicpollution control po/icùs

The: objective: in normative c:conomic analysis of the mcans of pollution conerol is the maximization of net benefits of pollution control [Q sociery. The aim is that the producer uses the environment as a production facror up to the limit at which its marginal production cost equals the cost [Q sociery of the marginal unit of pollurion. Classica!ly the Pollurer.Pays Principle is supposedly the best way to achicve the optimum.

Underlying the Pollurer-Pays-Principle (P.P.P.) is the notion of a social contract berwc:c:n the Fumees and the: rest of society. Farmc:rs who ca.used dcccrioracÎon of wacet qualiry would be obliged ro pay for the coses of water treatment. But there is also a posicive: contribution of agriculture to me e:nvironme:nt in ke:eping the: countryside attractive and thriving. Over the centuries agriculture has shaped a landscapc that is now highly valued. Maintening such recreational value can be vic:wccl as a production of positive cxre:rnalitie:s.

The social contraet supposes that if farmers are charged for the environmental deterioration, at the same time they have tO be compcnsatccl for the gencral wdfare they provide. Many problems arise when we try ro estimate: all the amenities produced by agriculture.

From another point of vic:w a tax on polluting F..rmers in accordance with thcir contribution tO pollution is difficult because liabiliry for pollution of water cannot be clc:ar-Iy attributed ta individual farmers. For the same type of farming f10w of pollutants depends on the nature and the state of the soil. According tO climatic conditions (rain, frost), the extent to which land is statured, the incline of the land, its location vis a vis wacercourse:s, warer pollution is more or lc:ss important. Non point pollutions arc inherently stochastic.

Another complicatio!, f.octor is the temporal discontinuities.Conceming erosion the time between soil detachment and sediment damage can vary from hours, tO yeats. Concerning nitrate leaching the nitrogen can reaches the aquifers alter yeats, or even decades. This taises the problem as to how liabiliry can he shared hetween eurrent and past polluters.

For all of these reasons the Pareto optimal allocation of resourees in presence of diffuse pollution is not achievable and only second best optima are possible. In consequence the aim of polieies implemenred becomes pollution control at the minimal social cost.

According to De Haen, 1990, four categories of economic ineenrives can be applied: -lowering product priees -subsidies for cenain f.orming practiees -allocation of tradable fertilizer rights -taxation of feniliz.er use For each of these categories the efficacy is appreciated through eeonomie criteria, but also through political and administrative ones.

Conccrning economic criteria, the cc:ntral issue in normative economic analysis of the means of pollution control is their relative capaeiry to maximize the net henefirs tO sociery. As remarked by Shonle and Abler, 1991, measures that are equally effective in reducing pollution will have equal benefilS. The rdative capaciry of the alternatives tha! are potentially equally effective 10 maximize social net benefilS depends on their rd.tive eOSl-effectiveness. At the wm levd the four categories of ineentives are quite similar with higb effieiency.

Coneerning political criteri., the first is the wiUingness of the producers ro a=pt the measures. lt is clear that any means Ime • priee eut or a fenilizer tax, whose effect is • wm income loss, will he poorly or very poorly .ccepted by the farmers. Conversely, subsidies are very weil .=pted. The situation of a=ptahiliry for tradable permilS depends on how the rigblS to permilS are allocated. If the permilS are given to the producers, they will agree. But if they are considered as a common properry, the effect for the wmers is the same as taxes.

The second political criterion is rd.ted to the group of environmenta1isrs. For this group ail the measures leading to a decrease of pollution is good. The diseussed ineentive policies.re a=prable acept for the tradable rigbts category if permits are given to the produeers.

T.ble 3. Eva/U4tions ofri" <eonomie incmtiws The last erirerion which has ro be c:xarnined is adminisrrative COsts. Lawering praducc priees and rhe raxation of ferriliu:r use have rhe advanrage of costing lcss. Giving subsidies and controling rheîr use imply imporranr adminisrrarive coses. Tradable righes suppose coses of moniroring and enforcement as weil.

Table 3 summariu:s rhis discussion:

3.2. Th. in"'""t oftitX on ftrti/i.un

Table 3 indicares rhar no policy dominares rhe orhers wirh respecc ro all of rhe crireria. Bur we can see rhar curring ourpur priees and raxing ferriliu:rs arrain rhe besr scores. For cach of rhose policies rhe cosr of moniroring and enforcemenr are low.

However rhe relative cosr elfeccivencss of rhose policies is nor equal becausc rhe raxarion policy is cheaper in rerros of agriculrura! profirabiliry. AlI orher chings being equal. a rax on ferriliu:rs in French cercal indusrry would have an impacc on income rwice as small as lowering ourpur priees. Bonnieux and Rainelli. 1990. This is obvious because expendirure on ferriliu:rs is a small mare of rhe value of rhe cereal ourpur. abour 10%.

Bur for many aurhors a rax on ferriliu:rs. mainly on nirrogen. is inelfeccive. sec De Haen. 1982 ;England. 1986Dubgaard. 1987. Theîr opinion is based on empirical resules. The own-priee dasriciry indicates a range of -0.08 te -0.40. For exarnple. Dubgaard. 1989 using empirical resules from Denmark, esrimares rhar, achieving a 30 per ecnt reduaion in nietagen use requires a tax rate cquai to 150 pet cent.

Aeeording te Dubgaard such a rax would have a perver.;e effecc encouraging rhe profirabiliry of nirrogen fixing crops (peas. beans) to rhe derrimenr of rhe ieasr polluring crops (winter whear, oilseed mpe).

Given rhe large impaer on margins (a 100% rax rate induees a 30% gross margin reduerion), sorne system of rax refund to ptoducer.; would be necessary. In consequence administrative cases would rise. The general conclusion is mat a tax on njetagen fertiliu:r.; is an inappropriare mechanism for resrriering nirrogen use, TEAGASC, 1989.

The argumenr is based on rhe very low own-price elasriciry of rhe nirrogen demand. but figures are derived from linear programming models. As Burrel, 1989 points our programming esrimates of own-prices dasriciry are biaised downwards due te restrierions on crop substitution. Econometrie approaches give higher figures. Wirh a dualirybased impur-ourpur sysrem of equations, Burrell shows rhar rhe UK ferriliu:r.; demand te own-price change is grearer ranging from -0.4 ro -0.6 depending on restricrions imposed (versus -0.08, -0.13 or -0.24 in England 1986).

Linear programming models rely on rhe assumprion rhar individuals apply nirrogen ar whar would be optimal rares under conditions of cerrainry. The slope of rhe crop response funcrion in rhe region of rhe oprimum is quire flar involving a price-inelasrie nitrogen demand.

Many empirical srudies show, despite a huge surplus of animal wasres, rhar an significanr utilizarion of inorganie ferriliu:r.; exisrs. Such behaviour reveals rechnical and allacarive inefficiencies, because a eost minimiu:r would have boughr lcss minera! ferriliu:r. If we compare the own-price elasriciry of minerai nirrogen demand for efficienr farms and for inefficienr ones wc have a dramarie diffecence : -0.36 for rhe former and -0.68 for rhe larrer, Vermesch an al.. 1991. Lastly. rhe above resulrs are derived under farnily labour and land fixily. If impur 55 Snnintlr Dn AgrinJtun ilnJAqUJUUlturr fixity is re:laxed a new equilibrium involving the utilization ofless labour and more land would emerge. On the one hand. the long run own-price elasticity of nitrogen demand will he greater than the short run elasticity. On the other hand. there will be a substitution hetween land and fertilizers implying a stronger response to the tax. The combination of these two effects is not negligible. In French cereal industty [START_REF] Vermersch | L'allocation du uavail dans les exploitations céréaliéres. Une modélisation Tobit d'une demande de facteur semi-fixe[END_REF] shows that a 10% tax would induce a 16.6% decrc:ase of the amount of inorganic fenilizer per ha.

Environmtnt Northtm

S~a; Confirma R~ort• Volume' 6

CONCLUSION

In a second best world a tax on purchased inorganic fenilizers is the most efficient economic incenrive because :

-in the short run the own-price elasticity demand of nitrogen is greater than supposed.

-in the long run there is a substitution between land and fenilizers allowing for cxtensification.

-it would increase the opportunity COSt of organic fenilizer and would push farmers towards more efficient pracrices.

ir is administrativdy easiest control option with the least cost to producers.

-it is consistent with a strategy for environrnentaJ co-operation requiring the dcvelopmenr of codes of good farming practices.

But this solution cannot solve ail the environmental problems due to agriculture:. therefore regulatoty measures will always be necessary ., 1986

  wcamer and the denitrification capaciry of the soil. Surface waters, watercourscs, and rcservoirs arc contaminated by run~of[

BIBLIOGRAPHY

  BONNIEUX F. and RAINELLI P.• 1988. Agricultural policy and environment in developped countries. European Review ofAgricultural Economies, 15 -263-286. BURREL A.. 1989, The demand for Fenilizer in the United Kingdom. Journal of Agricultural Economies. 40. 1-20. Commission des Communautè Europèennes COM(88) 708 Proposition de directive du Conseil concernant la protection des eaux douces. cltiares et marines contre la pollution par les nitrates à partir de sources diffuses. 53 p. de HAEN H .. 1984. Interdependance of Prices. Production Intensity and Environmental Damage from Agricultural Production, Paper presented at the 4 th European CongressofAgricultural Economists, Kiel. J uly 1984. de HAEN H .• 1990. Economie aspects of controlling the nitrate contamination of drinking watet. Strategies, costs, financing in Nitrates-Agriculrure:-Eau. International Symposium organized by INA-PG Paris-La DÇfense Nov. 1990. Calvet (ed.) -INRA. 23-40. DUBGAARD A

Table 1 :

 1 Consumption ofp<JtiâtUs in somt tUvtloptd eounrrûs (kg ofactivt ingrtdima ptT lm? ofUtilistd Agricu/ruralArta)

	Canada	us	Fr	FRG	UK	Jap
	90	180	440	420	580	1770

on AgrinJtur~/Inti AqUlUUilun '

  Table 1 the consumption bd of pesticides is higher in Europe (average: 450 kg/km') than in North America (average: 160 kgIkm'). But in ]apan the consumption is rour times that of Europe. Since 1975 the volume of pesticides used has incrcascd by 69 per cenc in Denmark and 30 per cent in the Federal R.cpublic of Germany. In addition. the frcquency of pesticide application incrcascd 115 per cent bcrween 1981 and 1984 in Denmark, OECD. 1989. p.34. W-."_.

	1 ;1 " , '\ "h ; , ' Il , , 1 ,1 !I SnnÙJAT PierTt RJzJnt/Ji l ,	.

Table 2 :

 2 Summary ofrtlatWruhips bttwttn thtpoUutlln~in tffietJ and inCOTlJt'1utnttJ

	1	1
	,	J
	1 /. , JI l ' 1 , " 1: 11 !Ii	~!:=n~=====:::1 ~r'-,--r-......,.-.r-"1I. ...
	Il /1 l,Il		Type of pollutanù nitrogen infiltration	Effect nitrate and nitrite production	Consequence drinking grWldwater
			nitrogen run-off	nitrate and nitrite production	drinking surface water
			organic matter (trom ~uny)	oxygen absorption in water courses	disruption of ecosystems
			nitrogen trom liquid manure	volatilisation of ammonia	aàd rain
			phosphorus and nitrogen run-off eutrophication of reservoirs	• fresh water supplies
	1			eutrophication of standing waters	• disruption of ecosystems
	' 1 ,			eutrophication of coastal waters	• 'green tides' (Ulva)
			pathogens (~uny spreading)	bacterial contam. of marine shellfish Human health huard
			pesticides	contamination of surface and	• Human health huard
				groundwater sources	• damage to fish
					and ecosystems
			nitrogen trom Iiquid manure	volatilisation of ammonia	acid rain
			50

1 ......................................•.......•••............ GOVERMENTAL REGUlA TlONS AND ECONOMIC INCENTIVES Run-off watets involving phosphoric acid give tise. as soluble orthosphosphates. in association wim niccogen, co cucrophicacion.

  ................................................................. GOVERMENTAL REGUU110NSAND ECONOMIC INCENTIVES

	The 1964 Water Acr provides che basis for «gularions concerning ail rypes of dis-
	charge, direcr and indirecr of any kind of marerial. In genetal it concerns all rhings lia-
	52

Environmmt North(rn S(/IJ

Confirma R(jJort • Voumu 6 ..

.

  . Reconciliation of Agricultural Policy and Environmenral Interests in Denmark. Paper presented to the European Seminar on Multipurpose Agticulture and Forestty. Venetian Region May 1986. DUBGAARD A., 1989. Input levies as a means of controlling the intensities of nitrogenous fenilizer and pesticides. In A. Dubgaard and A. Nielsen (eds), Economie Aspects of Environmental Regulations in Agriculture. Kiel: Wissenschaftsverlag Vaulk. ENGLAND R.A.. 1986. Reducing the Nitrogen Input on Arable Farms. Journal of Agricultutal Economies. 37. 13-24. O.E.C.D.• 1989. Agricultural and environmental policies. Opponunities for integration O.E.C.D.• 1991. L'état de l'environnement. 317 p


Ph N S A R Le Goffe

-Eçonomie

TNC BENEFITS OF IMPROVEMENTS IN COASTAL WATER QUALITY : TNE COruTINGENT APPROACH AS APPLIED TO BNCST NATURAL HARBOUR

Brest natural harbour was chosen by the European Community as a pilot site in respect to improvements in coastal water quality

1. INTRODUCTION ln a synthesis on water pollution control policies, [START_REF] Freeman | Water pottution poticy[END_REF] insisted on the interest society has in making àn economic choice for depollution objectives. The first point, and this is true whatever the eventual goals may be, is to select the means to be implemented with the idea of minimising depollution costs e.g. use of economic instruments such as taxes, negotiable permits. Secondly, objectives should be fixed with the aim of making the benefits from depollution superior to the corresponding costs. An examination of the arising costs and benefits is therefore an integral part of the construction of a pollution control policy and ensures an efficient allocation of resources. ln this same study, Freeman tried to evaluate the nationwide benefits in 1985 accruing from the application of the Federal Water Pollution Act Amendments 1972 . The benefits from the rise in water quality can be classified into four categories according to the different functions of water: drinking water, production, recreation and ecology [START_REF] Amigues | Bénéfices potentiels d'une amélioration de Ia qualité des eaux continentales[END_REF]. For Freeman, the benefits associated with the recreational and ecological functions of water i.e. recreational use + passive use represent over 60% of total benefits. lt is precisely these non-market benefits which are examined in this Paper.

The litterature concerning the non-market benefits of improvements in water quality mainly deals with continental waters. Most papers measure the on site recreational use values of water to the exclusion of any measurement of the passive use values of water (synthesis from Walsh et al 1992, [START_REF] Navrud | Pricing the european environmenf[END_REF] These daily values for recreational use represent the total surplus per day of leisure resulting from the enjoyment of a ressource of a given quality. With the background of a policy of pollution control, more rare studies have estimated the variation in consumers'surplus induced by a variation in surface water quality (Mitchell and[START_REF] Mitchell R | An experiment in determining willingness to pay for nationalwater quatity improvemenfs[END_REF][START_REF] Hanemann | Welfare evaluation in contingent valuation experiments with discrete responses[END_REF] ; [START_REF] Smith | Measuring Water Quality Benefits[END_REF]. When measured ex ante by the contingent valuation method (CVM), these non-market benefits represent the total economic value, including values for active and passive uses. Studies on marine water falling into this second category are very limited. Bockstael et al (1989) and Magnussen (1992) studied the benefits associated with a reduction in nutrients in coastal waters :Chesapeake Bay and the North Sea respectively, using two different approaches.

Eutrophication resulting from the over enrichment of water in nitrate and phosphate is one of the major problems of pollution in Brest natural harbour. Brest natural harbour is situated at the point of Brittany in western France. The nitrate concentration in the harbour's estuaries has doubled over the past fifteen years. ln Brittany the principal sources of nutrients are, in decreasing order of importance : animal faeces, fertilisers and domestic and industrial waste water. High concentrations of nutrients in coastal waters can provoke THE BENEF|TS oF tMpRovEMENTs tN CoASTAL WATER euALtw : THE coNTtNcENT APPRoACH As APPLIED To BREST NATURAL HARBoUR Ph. Le Goffe blooming in seaweed or phytoplancton (coloured waters). The ultimate result of this is the asphyxiation of deep water letding to the disappearance of fish and other forms.of marine life. Until now, the harbour was protected from eutrophication by the strong currents which are to be found there but the estuaries and the internal bays are potentially threatened.

Another important problem is microbe contamination from domestic sewage which effectively by-passes the water treatment plants which serve the coastal communities. The harbour water is mostly of medium quality or momentaneously bad quality for bathing. lt is not advised to eat wild shellfish fished on shore due to possible health hazards such as gastro enteritis or viral hepatitis. Lastly, other contaminating agents whose effects are not fully known are equally present. These contaminants range from pesticides to heavy metals and tributyl tin i.e. TBT, an antifouling agent. 1992 saw the signing of a bay contract for Brest harbour, linking the European Community, the French Government and all the local and regional governments, as well as the main economic actors of the region. The bay contract, whose head of works is the City of Brest, aims to improve water quality and to safeguard and restore marine life in the bay area. The urban pollution control measures plan, amongst other things, to restructure the existing purification networks and to construct new water treatment plants. ln order to reduce agricultural pollution, current methods of crop cultivation and animal rearing will have to be modified. One means of reducing polluting inputs i.e. pesticides and fertilisers would be to tax these inputs [START_REF] Vermersch | Can we expect abatement of agricultural pollution using economic incentives ? The case of intensive livestock farming in France[END_REF]. Another solution which could be applied to the case of Brest would be to negotiate with the farmers themselves and eventually subsidise agricultural techniques respectful of the environment. ln this paper, we have tried to evaluate the non-market value which is accorded by residents to an improved water quality and to the preservation of the marine ecosystem in Brest natural harbour. On the scientific front this study is aimed at increasing the knowledge of the value of such natural assets (there are only two such studies available for France : Bonnieux et al, 1992) and the determinants of their demand. On the practical side, the study aims to evaluate to what point the non-market services provided by the harbour area generate benefits which would socially justify the costs of depolluting the harbour area. We were also concerned with making our results transferable for other comparable situations which are numerous in France. To determine the residents' demand function for good water quality in the bay area, the CVM was chosen [START_REF] Mitchell R | IJsing surueys to value public goods: the contingent valuation method[END_REF]Cummings et al, 1986 ). Although this study was not centered on the methodology of non-market benefit measurement, it does allow for the drawing of some lessons on the conditions surrounding the use of the CVM.

THE BENEFITS oF IMPRoVEMENTS IN coASTAL wATER oUALITY : THE coNTINGENT APPROACH AS APPLIED TO BREST NATURAL HARBOUR Ph. Le Goffe

SURVEY METHODOLOGY AND CONTINGENT VALUATION Onsite surueys

The contingent valuations were gathered from direct interviews onsite on the banks of the harbour bay, principally in Brest, between June and September 1993.607 interviews were conducted on five different locations with approximately 120 interviews conducted per site. Four locations were chosen to cover the different recreational activities which are practised along the bay area: beach , sandbank at low tide in periods of spring tide, sailing harbour, coastalwalk. The fifth recreational site : Brest Botanical Gardens, was purposefully chosen outside of the immediate area in order to include some non users. The goods under focus are of a local nature. Some problems of bias may come into play with foreign consumers : part-whole bias since the good may be mentally included in a wider context, strategic bias because they do not pay local taxes. Therefore only local inhabitants were interviewed. This is quite logical since this area is more of a local attraction due to its morphology and the lack of beaches. Out of the 607 people interviewed, 7oo/o live in Brest itself and 95% live less than 15 km from the bay area. The interviews were conducted by 12 people, students in Geography at the university in Brest. They had all received one day's preliminary training during the course of which the objectives, the content and the underlying scientific basis were presented to them. For practical reasons, it was not possible to prevent certain interviewers from intervening more than others at certain sites and at certain times.

On average two people had to be approached in order to obtain one interview (50% participation). The average time for an interview was twenty minutes.

Contingent markets

The interview questionnaire underwent a preliminary test. lt was centred on the measurement of the non-market beneflts from an improvement in the water quality in Brest natural harbour. Two contingent markets were proposed successively to the interviewees.

The corresponding goods were constructed from the two major pollution problems, short and long term, facing the bay area : pollution from microbes and nutrients. Care was taken to select problems which were scientifically recognised and familiar to users (origins, consequences on the environment and the various means of combatting the problems ), as well as being ecologically important. That is why potentially worrying problems such as pesticide contamination or TBT pollution have not been treated. The first scenario evokes the microbian quality of the harbour waters in 1992. lt presents the risks to man from bathing and the consumption of wild shellfish in such unhealthy waters. The second scenario THE BENEFITS oF IMPRoVEMENTS IN CoASTAL WATER QUALITY : THE CONTINGENT APPROACH AS APPLIED TO BREST NATURAL HARBOUR Ph. Le Goffe evokes the high concentrations of nutrients in the waters and their consequences on the marine ecosystem. This is done using photographs : especially of coloured waters. ln each case, the nature of the pollutùn and the solutions proposed to reduce or to remedy the problem are made explicit. The plausability of the scenarios was reinforced by two unexpected events which took place during the course of the survey. Firstly, the fishing of wild shellfish in the harbour bay area was the subject of a government ban during two months beginning the end of may 1993 because of health concerns. Secondly, august witnessed a sudden development of coloured waters in one estuary and in the northern sector of the bay area. This was important enough to provoke fears about the possible asphyxiation of the shellfish reared in the sector.

The phenomonon of eutrophisation and its ultimate result i.e. the asphyxiation of the marine depths demand special treatment, due to the uncertainty surrounding them. lt is in practice difficult to fortell the growth rate in nutrients. Research is however being carried out in an attempt to determine thresholds for nutrient concentrations which would be succeptible to trigger acute eutrophication in the harbour bay area. [START_REF] Edwards | Option Prices for Groundwater Protection[END_REF], in a paper on nitrate contamination of underground waters, introduced uncertainty on supply (contamination risk) and on demand : the probability of being present at the moment of any eventual contamination. Here we limited ourselves to supply uncertainty. Three versions of the questionnaire were distributed equally amongst the twelve inquirers and the five sites. They differed only in respect to the risks of coloured water developing and the risks of asphyxiation of the water in the harbour bay : weak, noteworthy or very high.

After a reading of the two scenarios, valuation questions were asked. The interviewees were asked to allocate between the two pollution problems, the value accorded by them for a clean harbour bay . This precaution was destined to avoid any part-whole bias arising from the separation of the two goods. This separation was necessary in order to account for the characteristics and the mode of acquisition specific to each good. The interviewees were first asked about their willingness to pay (WTP) to be able , without risk, to bathe and to consume wild shellfish in the harbour bay area. This defines the good "salubrity". Next it was asked what would be the annual WTP to prevent the asphyxiation of the harbour waters due to high concentrations of nutrients. This defines the good "ecosystem". The method of payment used for the first good was the water bill. Here it was necessary to take into account the fact that the inhabitants of Brest had just seen a recent increase in their water billsan increase designed to provide this very good (construction of a new water treatment plant, restructuring of the purification network). We needed to guard THE BENEFITS oF IMPRoVEMENTS IN coAsTAL WATER QUALITY : THE CoNTINGENT APPROACH AS APPLIED TO BREST NATURAL HARBOUR Ph. Le Goffe against the bias of budgetary constraint. The payment vehicle for the second good was modified immediately after the return of the first interviews because of a proportion of nul responses which was too high.Ïhe local housing tax which was initially chosen is a local tax serving to finance the municipal budget. lt is judged to be too high by most inhabitants of Brest. The high level of the tax seems to be due to overequipment in the public sector. The tax was replaced by participation in a special fund exclusively consecrated to the preservation of the harbour bay area. For both goods the open valuation question was asked using the same payment card comporting amounts from FF 0 to FF 2000.

Descriptive resulfs

All of the 607 people interviewed accepted to reply to valuation questions. This being said however, the proportion of positive WTP's was more important for the good "salubrity" than for the good "ecosystem" '.75o/o against 49% respectively (table 1). Amongst the nul responses we tried to distinguish between real zero values and protest bids by asking the interviewees the reason for their nul response. Real zero responses corresponded to reasons such as "haven't got the means to pay" or "indifferent to the problem" (no variation in the utility function). The reasons given which permitted us to recognise protest bids are : refusal to pay, refusal of the payment vehicle, a fear of paying for others, insufficient information or non-replies. These reasons represent 8, 3, 4, 3 and 1o/o of interviewees respectively for the good "salubrity" and 11, 10,5, 2 and 15o/o of interviewees for the good "ecosystem". ln all the good "salubrity" generated less protest bids than the good "ecosystem" : 20Vo against 45o/o. 4.4o/o of interviewees valued "salubrity" at more than FF 500, two of whom valued it at FF 2000. These categories represented respectively 1.6% of interviewees and one person for the good "ecosystem ". The arithmetic mean of the WTP was FF 218for "salubrity" and FF 173for "ecosystem". Table 1. Descriptive statistics of willingness to pay (n=607) (1) 1 r household per year (2) Protest bids excluded.

The questionnaire also allowed the interviewees to be categorised in order to explain variations in the WTP. Only those variables retained for the construction of models are post primary school, revenue (1Qo/o of interviewees refused to reply) and profession turned out to be quite useful. The inte?viewees were asked to indicate their income group out of a possible seventeen ; the data in table 2 were calculated using the central point of these brackets. Our sample contained 6.10/o executives and higher level intellectual professions, 12.7o/o intermediate professions (teachers, technichians) and 5.6% blue collar workers. The importance attached to the preservation of the harbour bay area for leisure activities is one of the criteria used in the survey to measure environmental sensitivity. As far as quality is concerned, those individuals who have already observed the appearance of coloured waters in the bay area (23% of interviewees), are probably more conscient than the others of the problem of water pollution. The practice of recreational activity and the frequenting of the bay area (on average 58 times per year) give an objective view of the use of the good in a global context. 73o/o of those interviewed frequent one or more seaside substitutes. Finally, the risks of asphyxiation of the depths and the payment vehicle (modified during the course of the survey) were incorporated into those models relating to the good "ecosystem". The determination of a functional relationship between the WTP and individual characteristics may be useful in enabling the results to be widened to the whole population benefitting from the goods to be valued. lt is desirable to obtain the demand functions from the utility maximisation. ln the case of a closed question with a yes-no type answer, Hanemann (1984) showed that the probability of accepting a payment was a function of the differences in the utility values (Logit model). This modelisation allows the Logit coefficients to be interpreted using the specification chosen for the utility function. ln the case of an open question with payment card, [START_REF] Bonnieux | Bénéfices et coÛts de la protection de I'eau : application de I'approche contingente à la pêche sportive[END_REF] developped a dual approach version of the preceeding model by formalising the WTP by a difference in restrained expenditure functions; the WTP is then explained by a Tobit model. This proceedure seemed to be applicable to the goods "salubrity" and "ecosystem".

We note however that for the good "salubrity", the WTP corresponds to a compensatory variation in well-being i.e. the reduction in revenue agreed to in order to benefit from an increase in the "salubrity" of the water without any modification in utility. On the other hand, the WTP for the good "ecosystem" measures an equivalent variation in welfare i.e. the payment accepted in order to avoid the deterioration in the ecosystem. This would lead to the same reduction in utility as that provoked by the deterioration in the ecosystem with constant earnings. The measurement of these hicksian surplusses necessitates the distinction to be made between those individuals who refuse to place a monetary value on the goods (protest bids), and those who accept to participate in the exercise of contingent valuation. The latter can equally be divided into two separate categories according to whether they wish or do not wish to see that part of their budget consecrated to the depollution of the harbour bay area rise.

Let Z be the individual expenditure necessary for the provision of water of a given quality z,z1is the initial level and z2the final level after improvement. We can see that for the first category of individuals there is a positive WTP which expresses an increase in the demand for better water quality (tZ = Z2-Zp0). For the others, the observed WTP is nul.

This corresponds probably to a desire to see that part of their budget consecrated to the depollution of the harbour bay area reduce '. (-0,e) 0,007 (0,9) 0,030 (0,9) -0,031 (-0,8) -0,030 (-0,1) -0,002 (-1,0) -0,275

(-1 ,1 )
-0,141 (-0,8) 0,021

(3,1) 0,055 (2,1) -0,014 (-0,5) 0,1 95 (0,8) -0,001 (-0,6) 0,229

(1,1) -0,372 (-1,9) -0,312 (1) Using 17 brackets

Tobit models

Amongst those variables explaining the WTP for the good "salubrity" (table 4), the most significant and the most robust when you pass from one model to another are : environmental sensitivity, revenue, the sight of coloured waters and sex. lndividuals for whom the preservation of the harbor bay area is very important accept paying FF 92 to FF 100 more than the others to be able to benefit from the good "salubrity". ln accordance with micro-economic theory, the WTP rises along with revenue : FF 7 to FF 9 per bracket. Having already seen coloured water noticeably increases the WTP "salubrity" : FF 60 to FF 67.

However, this information was gathered during the scenario presented to define the good "ecosystem". Women, who as we have seen tend to more strongly express their preferences, have a WTP which is inferior to that of men by FF 50 to FF 60.

Age and education are two variables which are negatively linked in our study. They have an opposed but unsignificant effect on the WTP "salubrity". Contrary to what one might have expected, those interviewees who frequent a substitute for the Brest harbour bay are willing to pay FF 56 to FF 68 more than the others. Here we are dealing with a population which is on average younger, better educated and richer, to such a point that we may ask if these variables were sufficiently taken into account by the model. lt is also possible that the relations between the harbour bay area and coastal sites should be analysed more in terms (FF 0.16 to FF O.22per day) and is higherforthose who dive or sail : approximately FF 70 more per day than those practising other recreational activities. Lastly it must be said that there is a large calendar effect independant from the others : the WTP is reduced by FF 130 between June and September. This factor has not been taken into account since it is difficult to interprete : is it due to the interviewer, the site, or a real calendar effect linked for example to the events which took place at the time of the survey? When comparing the WTP models for the goods "salubrity" and "ecosystem" similar tendencies can be seen especially in relation to the signs of the coefficients of the explanatory variables. This being said, the WTP "ecosystem" is above all influenced by revenue (+FF 10 to FF 13 per bracket) and education (+f,p 11 per school year), with coeff1cients higher than those observed for "salubrity" (table 5). The difference between (FF) these two goods is particularly great on education. These revenue and education effects are to be found at least partially_ at the professional level. ln relation to other categories, executives and intermediate professions agree to a suppliment of FF 100 and FF 58 respectively whilst blue collar workers have a WTP FF 144 less.

In comparison with the WTP "salubrity", the WTP "ecosystem" depends less significantly and with a weaker coefficient, on sex (FF 40 to FF 50), feeling about preservation of the bay area (FF 38 to FF 61), the sight of coloured waters (FF 32 to FF 36) and on the frequenting of a substitute (FF 28 to FF 38). lt is now independant of the frequentation of the bay area. On the other hand the effects linked to sailing and diving remain. The risk of asphyxiation which reduced the probability of recording a protest bid, has litge or no influence on the WTP. Finally the differences between the payment vehicle (not given in table 5) disappear when the effect of the date is taken into account.

Table 5. WTP for ecosystem preservation against eutrophication : Tobit models (l) french public. lt therefore seemed more sure to begin by gathering data directly from the recreational sites themselves. This choice will make it more difficult to agregate the benefits to the entire population. Nevertheless redressment procedures may be used, especially from previous data surrounding the practice of recreational activities in Brest according to socioprofessional brackets. ln all, individuals accepted paying quite substiantial amounts to see better water quality in the bay. The average reconstructed WTP was FF 215 and FF 160 respectively for the goods "salubrity" and "ecosystem". The WTP "salubrity" represents 10o/o of the annual water bill. These amounts are less than those obtained by Bockstael et al (1989) for Chesapeake bay (here the WTP for swimmable water corresponded to FF 350 in 1987) and especially than those obtained by [START_REF] Magnussen | Valuing reduced water pollution using the contingent valuation method -Testing for amenity misspecification[END_REF] for a national good (FF 1000 in 1991 for a 50% reduction in nutrients). But our flgures are two to three times higher than the WTP's estimated by Desaigues and Lesgards (1992) for goods which are admittedly different, but within the French context. We may ask ourselves if our values haven't been circumstantially increased by the events which took place just before the start of our survey.

ln a context of benefit aggregation it might be reasonable to reduce their importance so as to smooth this accidentaleffect.

  Seaside substitute (1=yes; 0=no) Risk of asphyxiation (1=very high ; O=noteworthy or slight) Special fund/housing tax (1 = SF, 0 = HT) SCOPE OF THE DEMAND ANALYSIS

  LZ<O. A simple Tobit model then allows us to include this particular category : WTPi= 62' if ÂZ;>0 0 otherwise and LZi= x; b + ui THE BENEFITS oF IMPRoVEMENTS IN CoASTAL WATER QUALITY : THE CoNTINGENT APPROACH AS APPLIED TO BREST NATURAL HARBOUR Ph. Le Goffe

  THE BENEFITS oF IMPRoVEMENTS IN CoASTAL WATER QUALIW : THE CoNTINGENT APPROACH AS APPLIED TO BREST NATURAL HARBOUR Ph. Le Goffe of the type of recreational use qrade of the bay area. The WTP rises with regular frequenting

( 1 )

 1 Per household per year - -(3) Whole ng reconstituted values THE BENEFITS oF IMPRoVEMÊNTS IN CoASTAL WATER QUALIw : THE CONTINGENT APPROACH AS APPLIED TO BREST NATURAL

table 2 .

 2 Classic socio-economic characteristics such as sex, age, education i.e.

		Amount (2) -(FF)
			Standard
	Mean	Maximum	deviation

THE BENEF|TS oF tMpRovEMENTs tN CoASTAL WATER euALrw : THE CoNTTNGENT AppRoAcH AS APPLTED To BREsr NATUML HARBoUR Ph. Le Goffe

Table 2 .

 2 Descriptive statistics of individual characteristics used in demand models

	Variable	Mean	Minimum	Maximum	Standard deviation
	Sex (1=women ; O=men)
	Age (years)
	lncome (FF) (1)
	Education (years)
	Higher professions (1=yes ; O=no)
	lntermediate professions(1 =yes ; O=no)
	Blue collarWorkers (1=yes; O=no)
	Brest natural harbour preservation (1=very important;
	O=somewhat, not very, or not at all important)
	Observation of coloured waters (1=yes ; O=no)
	Brest natural harbour frequenting (times a year)
	Sailers (1=yes ; O=no)
	Divers (1=yes ; O=no)

(1) Using midpoints of brackets THE BENEFITS oF rMpRovEMENTs rN CoASTAL WATER ouALtw : THE CoNTTNGENT AppRoAcH As AppLrED To BREsr NATUML HARBoUR Ph. Le Goffe

Table 3 .

 3 Probability to give protest bids for water quality improvement or preservation : Logit models

	Good

Table 4 .

 4 wTP for water salubrity improvement : Tobit models(1)

	(1) Per	per year -(2) Using 17 brackets -	population	ng reconstituted values.

. The depollution program will be financed by the Community, the French Government and the regional authorities.

where xi is the vector of characteristics and ui a random variable.

For each good, this model was estimated on the population not including those individuals having given protest bids. The implicit values of these non-replies are then reconstituted by the model and a mean WTP for the entire population can then be calculated. After unfruitful attempts to carry out a logarithmic transformation or box-cox, we chose the brut WTP as the dependent variable and used a linear equation. ln the case of revenue, the use of a variable equal to the rank of the wage group gave better results than the use of the midpoints of the brackets in FF, or its logarithm, Amongst the independent variables, age, education, profession and the recreational activity show relationships. ln order to avoid any problems of multicolinearity, these variables are separated into three distinct models. We limited ourselves to retaining only the most significant modalities of profession and recreational activity.

At first it seemed useful to characterise briefly those respondants not having placed a value on the goods. This was done in an attempt to analyse the interviewees' perception of the contingent valuation scenario. The probability of giving a protest bid was estimated by a Logit model. ln this case the dependent variable is dichotomic. [START_REF] Bonnieux | Bénéfices et coÛts de la protection de I'eau : application de I'approche contingente à la pêche sportive[END_REF] point out that a generalized Tobit model [START_REF] Gourieroux | Econométrie des variables qualitatives[END_REF]) might allow the simultaneous treatment of protest bids, real nulWTP's and positive WTP's.

ESTIMATION RESULTS

Logit models

The prediction of replys and the significance of the coefficients of the Logit model values are on the whole better for the good "ecosystem" (table 3). The probability of making a protest bid increases with age and revenue, but more rapidly for the good "ecosystem" than for the good "salubrity". Whatever the good, the probability of a false zero value is weaker amongst women and seems to diminish with education and the frequentation of the area. Unfortunately the statistical significance of these variables is weak. Environmental sensitivity and substitutes have no significant role and have an opposed sign according to the good considered. Finally the probability of giving a protest bid for the good "ecosystem" is less strong when the risk of asphyxiation is very high and where the payment vehicle used is the special fund rather than the local governmenl lax (42o/o against 51% false zeros respectively).

THE BENEFITS oF IMPRoVEMENTS IN CoASTAL WATER QUALITY : THE CoNTINGENT APPROACH AS APPLIED TO BREST NATURAL HARBOUR Ph. Le Goffe 5. DTSCUSSION -CONCLUSION Brest natural harbour is an integral part of the resident's environment. They are quite well informed on the problems bf pollution. This explains the relatively good acception of this contingent valuation exercise from the bay area dwellers. We can nevertheless ask ourselves why there exists such a difference in behaviour towards the goods "salubrity" and "ecosystem". Amongst possible reasons we have to distinguish those treating the measurement methodology, and those which express differences in the utility functions.

The good "ecosystem" provoked more protest bids, especially amongst the elderly.

The corresponding WTP depends essentially on two factors : revenue and education These results might suggest that there were difficulties surrounding the comprehension of the scenarios and a good insufficiently familiar to interviewees. Over the past ten years however, the local media have been informing the population about the overenrichment of freshwater in nutrients and occasional accidents with anoxia and deaths of fish. The extension of these phenomonon to saltwaters was quite evident, especially since accidents have already taken place at other points of the Brittany coastline. On the other hand the initial payment vehicle clearly had a negative effect on the revelation of preferences, and we experienced difficulties in redefining a payment vehicle as natural as the water bill for the first good. We note however that the WTP was unaffected by this change. Another methodological problem arises from the fact that here we have chosen to study two goods simultaneously even though the traditional CVM approach treated goods individually. The part-whole bias which is under question here was studied for goods whose level of agregation was decreasing [START_REF] Magnussen | Valuing reduced water pollution using the contingent valuation method -Testing for amenity misspecification[END_REF]. lt has been studied little for goods of the same level of aggregation as in our study. Did not the fact that the good "ecosystem" came second after the good "salubrity" perturb the very valuation of the good "ecosystem"? ln a study on the alternative strategies for the management of a dam on the river Seine, Desaigues and Lesgards (1992) had already sought to disassociate the recreational and the ecological functions of water by estimating two categories of benefits : 1) the benefits drawn from an improvement in the attributes of the ecosystem, 2) the benefits to be drawn from an improvement in possible recreational uses. Moreover, these authors had assimilated the ecological benefits to an existence value and the recreational benefits to a use value. Without going as far as that, is is probable that our good "ecosystem" is proportionally more valued for motives of existence than the good "salubrity". lt is worth noting that the WTP "ecosystem" is independant of the frequentation of the bay area . THE BENEFTTS oF tMpRovEMENTs tN coAsrAL WATER euALrw : THE CoNTTNGENT AppRoAcH AS APPLTED To BREsr NATURAL HARBoUR Ph. Le Goffe Everything happens as if the good "ecosystem" were a luxury which only those disposing of sufficient means and a good level of education could offer themselves. Finally, the uncertain character of the supply of ùe good "ecosystem" has weighed on the revelation of preferences which improve whilst the risk of the harbour waters asphyxiating rises. On the other hand and contrary to Edwards (1989), the option price does not depend on the risk of asphyxiation.

Other approaches or methods have been used to evaluate the non-market damage resulting from the eutrophication of coastal waters. [START_REF] Magnussen | Valuing reduced water pollution using the contingent valuation method -Testing for amenity misspecification[END_REF] also used the CVM model to estimate the value of a 50% reduction in the output of nutrients : nitrogen and phosphor into the north sea. To do this, she distributed cards to interviewees showing the evolution of overall water quality and the corresponding uses, before and after reductions in outputs of these nutrients. ln addition to metric bias which is always possible, the risk here is of using figures for water quality which are too global and do not take into account the specifïcity of the eutrophication phenonomon e.g. threshold effects. Bockstael et al (1989) used the travel cost method indexing the demand to the total production of nitrogen and of phosphor. They then calculated the variation in surplus corresponding to a 20o/o drop in nutrient production. This approach does not take into account threshold effects. Moreover it gives an equal importance to nitrogen and phosphor, although it would seem that marine eutrophication is more dependant on nitrogen. This approach could not be used in the case of Brest, notably because of the abscence of spacial or temporal time series data indicating a sufficient variation in transport costs, visits and water quality. This is why we retained a scenario of eutrophication sufficiently extreme so as to seriously affect the services provided by the bay area whilst still remaining within the realms of the probable. When compared to previous studies, one of the inconveniences of our approach is that the scientific knowledge concerning the bay area is to this day insufficient to establish any relationship between the outputs of nutrients and the acute phenonomons of eutrophication, and therefore between the polluting outputs and the damage. One of the scientific programmes planned under the bay contract aims to establish this physical relationship.

The onsite enquiry technique used in this study lead to the selection of a population of recreational space users. This population is not necessarily representative of the total population susceptible to benefit from the goods to be valued. Contingent valuations made by telephone surveys, postal surveys or house to house surveys where the sample is drawn at random would allow us to reduce this sample bias. However, due to the only recent beginnings of contingent valuation in France, there are no data on their acceptance by the