Xunxing Diao

Messaoud Kara

Jian-Jin Li

Kun-Mean Hou

Haiying Zhou

Aurelien Jacquot

Cooperative Inter-vehicle Communication Protocol with Low Cost Differential GPS

Keywords: ITS, IVC, MANET, WSN, auto-configuration, infrastructure support, hybrid routing protocol, contextaware, localization, differential GPS

This paper describes a cooperative MANET protocol dedicated to intelligent transport systems, named CIVIC (Communication Inter Véhicule Intelligente et Coopérative). The CIVIC protocol is an auto-configuration inter-vehicle communication protocol, which supports adhoc and infrastructure networks, contains reactive and proactive routing components, and adapts different wireless standards. It is a context-aware protocol reacting to vehicle status, road traffic, and geographic environment. It supports location-based communication. To improve the accuracy of GPS, it integrates a localization solution called LCD-GPS (Low Cost Differential GPS). It has been implemented and experimented on the LiveNode sensor developed by our lab. At the end of this paper, an application project MobiPlus is introduced.

I. INTRODUCTION

Each year in Europe, 1,300,000 vehicle accidents result in 1,700,000 personal injuries. The financial cost of vehicle accidents is evaluated at 160 billion euros (approximately the same cost in the USA [START_REF] Fitzgibbons | Simulation-Based Operations Planning For regional Transportation Systems[END_REF]). The ITS (Intelligent Transportation System) is considered as the key technology allowing 50% reduction of accident numbers by issuing hazard warnings [START_REF] Fiebig | European Traffic Accidents and Purposed Solutions[END_REF]. In addition to improve road traffic safety, the ITS contributes to optimize the traffic flow, offer a better driving experience, and increase the accessibility of public transports especially for disabled passengers.

An essential component of ITS is the IVC (Inter-Vehicle Communication). It ensures that the data from other ITS components, which includes sensing system and computing system, flows among vehicles and roadside infrastructures efficiently. In high mobility scenarios like IVC, non-cooperative client/server systems are not fully appropriate. A proposed solution is to introduce MANET (Mobile Ad-hoc NETwork) for its characteristic of cooperative communication and noncentral distributed control [START_REF] Singh | Wireless LAN Performance Under Varied Stress Conditions in Vehicular Traffic Scenarios[END_REF][4] [START_REF] Chlamtac | Mobile Ad Hoc Networking: Imperatives and Challenges[END_REF]. The economic impact of this solution is expected to be substantial, but there are still open issues in MANET such as the limitation of QoS, network interference, and incomplete cooperation methods [START_REF] Obreiter | Stimulating Cooperative Behavior of Autonomous Devices -An Analysis of Requirements and Existing Approaches[END_REF]. Until now, the practical MANET protocols and mathematic models are carried out within the scope of fixed and wired network, so the previous issues remain to be solved.

Moreover, comparing with general-purpose MANET communications, the IVC has its unique features that have not been fully explored [START_REF] Chlamtac | Mobile Ad Hoc Networking: Imperatives and Challenges[END_REF][7] [START_REF] Li | A Trust Model Based Routing Protocol for Secure Ad-hoc Networks[END_REF]. For example, the topology and density of vehicular network are much more variable, thus there is a requirement for a new routing protocol to minimize the administrative overhead [START_REF] Böhm | State of the Art on Network Layer Aspects for Inter-Vehicle Communication[END_REF]. The distribution of vehicular network is generally along roads. It provides the opportunity for IVC to deploy the roadside infrastructure for supporting network access and QoS, but as well, it raises the expectation for the adaptability to different wireless standards. Besides, the position and direction of network nodes could be obtained by GPS (Global Positioning System) on vehicles.

An accurate positioning system is one of the foundations for any IVC application. It is well known that the GPS is inaccurate in big cities, particularly in EU where the roads are narrow and crossroads are very close. To improve the accuracy of GPS, the DGPS (Differential GPS) [START_REF] Samama | Global Positioning, Technologies and Performance[END_REF] has been introduced. However, installing a reference station for DGPS is complex and very expensive (about 30,000 €). To solve this problem, we develop a localization solution called LCD-GPS (Low Cost Differential GPS). This solution improves the accuracy of GPS even in dense urban areas and it can be used for mobile tracking.

Based on the previous factors, this paper presents a new inter-vehicle communication protocol dedicated to ITS, named CIVIC (Communication Inter Véhicule Intelligente et Coopérative). The CIVIC protocol is a cooperative MANET protocol integrated the supports of roadside infrastructure. It has mechanisms to adapt to multiple wireless standards. The communications by CIVIC protocol are auto-configured and location-based. The CIVIC protocol provides the original position to LCD-GPS, and performs more efficiently based on the accurate position generated by LCD-GPS. The new experiments for both CIVIC protocol and LCD-GPS are presented in this paper. In these experiments, we use a specific sensor called LiveNode (LImos Versatile Embedded wireless sensor NODE) [START_REF] Hou | LiveNode: LIMOS versatile embedded wireless sensor node[END_REF].

The remainder of the paper is organized as follows. In the next section, an overview of related works will be summarized. Section 3 explains the details of CIVIC protocol. Section 4 is dedicated to the concept and experiments of LCD-GPS. Section 5 presents the experiments for the CIVIC protocol. Section 6 outlines the MobiPlus project, which consist of an application of CIVIC protocol and the LiveNode sensor. Finally, conclusion and ongoing work are presented.

II. RELATED WORKS

A. Research Projects

The ITS projects concerning IVC have been launched in Europe (FleetNet [START_REF]FleetNet Documents[END_REF][13], CarTALK2000 [START_REF] Morsink | CarTALK2000: Development of a Cooperative ADAS based on Vehicle-to-Vehicle Communication[END_REF] [START_REF] Cartalk | [END_REF]), Japan (cooperative driving [START_REF] Tsugawa | An Introduction to Demo 2000: The Cooperative Driving Scenario[END_REF]) and USA (VII [17][18]).

The IVC of FleetNet (2000FleetNet ( -2003) ) and CarTALK2000 (2001)(2002)(2003)(2004) [START_REF] Rudack | On Traffic Dynamical Aspects of Inter Vehicle Communication[END_REF]. The IVC based on the development of UMTS technology can minimize the cost of access medium, and guaranty the total compatibility with the 3G mobile phone.

In Japan, the cooperative driving project (1993-2000) is started by JSK (Association of Electronic Technology for Automobile Traffic and Driving). It utilizes 5.8 GHz DSRC (Dedicated Short-Range Communication) for transmitting data, and it employs DGPS for measuring vehicle location [START_REF] Tsugawa | An Introduction to Demo 2000: The Cooperative Driving Scenario[END_REF] [START_REF] Tsugawa | Issues and recent trends in vehicle safety communication systems[END_REF]. The DSRC is adapted to the applications of highway infrastructures management such as ETC (Electronic Toll Collection) and vehicle counting, but it may not be appropriate for general IVC applications such as security and Internet access. This project develops a short-range cooperative communication protocol named DOLPHIN (Dedicated Omni-purpose inter-vehicle communication Linkage Protocol for HIghway automatioN) [START_REF] Shiraki | Development of an Inter-Vehicle Communications System[END_REF].

In USA, the leading project is called VII (Vehicle Infrastructure Integration, 2004Integration, -2010)). This project is focused on improving safety and roadway management. Its communications involve vehicle-to-infrastructure and vehicle-to-vehicle by using 5.9 GHz DSRC [START_REF] Usdot | USDOT Outlines the New VII Initiative at the 2004 TRB Annual Meeting[END_REF] [START_REF]VII Architecture and Functional Requirements[END_REF]. In addition to VII project, there are researches at VTTI (Virginia Tech Transportation Institute, USA) trying to provide communication solution in high mobility scenarios by using the low-cost WLAN (Wireless Local Area Network) technologies such as IEEE802.11b [START_REF] Aziz | Implementation and analysis of Wireless Local Area Networks for high-Mobility Telematics[END_REF].

The previous projects provide cooperative IVC solutions either on the limited application domains, or with the fixed wireless techniques. Their research efforts are more focused on the general-purpose Internet access with lower real-time constraint, mobility and reliability. The CIVIC protocol gives emphasis to adaptability, and it puts more effort to design the robust auto-configured routing mechanisms.

B. MANET Routing Protocol

The MANET routing protocols can be divided into three classes: proactive, reactive, and hybrid.

The proactive routing protocols maintain up-to-date routing paths for partial or entire network. In order to keep correct routing paths, each node needs to generate sensing messages to explore network periodically. The network traffic therefore increases significantly. The main proactive protocols are OLSR (Optimized Link State Routing) [START_REF] Clausen | Optimized Link State Routing Protocol[END_REF], DSDV (Destination-Sequenced Distance-Vector) [START_REF] Perkins | Highly Dynamic Destination Sequence-Vector Routing (DSDV) for Mobile Computers[END_REF], and TBRPF (Topology Dissemination Based on Reverse-Path Forwarding) [START_REF] Ogier | Topology dissemination based on reverse-path forwarding (TBRPF)[END_REF].

The reactive routing protocols determine a routing path only when a demand is received. The main reactive protocols are DSR (Dynamic Source Routing) [START_REF] Johnson | DSR: The Dynamic Source Routing Protocol for Multi-Hop Wireless Ad-hoc Networks[END_REF], AODV (Ad-hoc On Demand Distance Vector) [START_REF] Kosch | Information Dissemination in Multihop Inter-Vehicle Networks -Adapting the Ad-hoc On-demand Distance Vector Routing Protocol (AODV)[END_REF], TORA (Temporally-Ordered Routing Algorithm) [START_REF] Park | A Highly Adaptive Distributed Routing Algorithm for Mobile Wireless Networks[END_REF], ABR (Associativity Based Routing) [START_REF] Toh | Long-lived Ad-Hoc Routing based on the concept of Associativity[END_REF], and SSR (Signal Stability Routing) [START_REF] Dube | Signal Stability based adaptive routing for Ad Hoc Mobile networks[END_REF].

The hybrid routing protocol combines the advantages of the proactive and reactive protocols. An example is ZRP (Zone Routing Protocol) [START_REF] Schaumann | Analysis of the Zone Routing Protocol[END_REF]. It includes two routing components: a proactive intra-zone routing component and a reactive inter-zone routing component.

In general, the reactive protocols are more efficient in terms of bandwidth utilisation and more adapted to networks with rapid changing topology, because their routing path explorations are performed only on demand. However, the proactive protocols are more interactive (the response time is shorter) because the message is sent immediately without performing route request. Hence, the proactive protocols are suitable for static network while the reactive protocols are more adapted to dynamic network.

The previous routing protocols have not considered the particularity of the ITS such as direction, location, road traffic, and road map. In addition, the requirements of MANET in IVC applications such as intelligent urban transportation system or agricultural vehicle system are different from the ones with general-purpose [START_REF]FleetNet Documents[END_REF] [START_REF] Aziz | Implementation and analysis of Wireless Local Area Networks for high-Mobility Telematics[END_REF]. Thus the existing MANET routing protocols are not adapted to IVC.

III. CIVIC PROTOCOL

The concepts and features of CIVIC protocol are listed as following:

A. Multiple Wireless Supports on Network Node

To adapt different roadside infrastructures and utilize more radio spectrum, the CIVIC protocol is designed to support multi-radio and multi-channel on network nodes. The radio and channel should be auto-configured to minimize interference.

The LiveNode sensor, to which the CIVIC protocol is implemented, can be equipped with three types of wireless access medium: Wi-Fi (IEEE802.11b), ZigBee (IEEE802.15.4), or GSM (GPRS). Several LiveNode sensors can be connected together to enable the multiple wireless supports by using extension connectors (SPI, I²C, and I/O connectors).

The Wi-Fi and ZigBee have been adopted by the CIVIC protocol. From inter-vehicle communication, smart home, to telemedicine, the Wi-Fi enables many applications to connect to the Internet. With an appropriate antenna, the radio range of Wi-Fi can reach 1 Km with the vehicle speed about 100 Km/h. A new trend of wireless standard is ZigBee, which requires lower cost and lower power. Its maximum outdoor radio range is up to 1.6 Km.

B. MMRS for Infrastructure

The topology and density of vehicular network change dramatically according to location and time. In some scenarios, for example at night and on bad weather, the density could get very low. Thus, only using mobile adhoc connections is not robust enough for IVC. The CIVIC protocol deploys the MMRS (Multi-support, Multi-service Routers and Servers) along the road to improve the network access and QoS.

The main functions of the MMRS are: i. Ensure the network connection to nodes in range; ii. Send the private message to a given node; iii. Send the alarm message to all nodes; iv. Forward message(s) to other MMRS.

The MMRS should be connected with wired networks, otherwise the network connectivity can not be assured. Each MMRS maintains at least two message queues. The first one stores alarm messages, and the second one holds private messages. When a mobile node reaches an MMRS, this node broadcasts a request message including its VID (Vehicle IDentifier). If an alarm and/or private messages exist, the MMRS sends these messages back to the mobile node. The private message for this mobile node will then be deleted from the private message queue. The Fig. 1 shows how a message is forwarded from one node to another by mixed networking of ad-hoc and infrastructure.

C. Context Based Communication

The CIVIC protocol considers the communication contexts in a vehicular network, which are quite different from the ones in general-purpose MANETs. The nodes in a vehicular network are generally distributed along roads with directional movements, but in the MANETs with general purposes, nodes are grouped around an access point with random movements.

A major context of IVC is the distribution. It can be used to estimate the bandwidth utilization and the capacity of a vehicular network. As previously mentioned, when a mobile node passes an MMRS, it sends a request message including its VID. The message may also contain its position, so the MMRS can estimate the distribution of vehicular network, and then a better knowledge concerning real-time traffic state will be obtained.

The direction of nodes is another major context of IVC. By introducing the direction, the PDR (Packet Delivery Ratio) and delay can be improved significantly [START_REF] Hao | The capacity and packets delivery of MANET On Road: MANETOR[END_REF].

Although the Euclidean direction is not appropriate for defining the direction of mobile node when roads are too winding, it may be applied for a short segment of a road. The CIVIC protocol assumes that all mobile nodes have an itinerary, and they move in a known environment. Thus, the direction of a mobile node is updated between two MMRS based on three factors: the itinerary and position of the mobile node, and the road map.

By considering the contexts of distribution and direction, the CIVIC protocol can determine how to transmit messages (ad-hoc or infrastructure, interval of sending messages, etc.). In addition, to obtain the correct position of a node, the LCD-GPS (described in section 4) implemented road maps will be used by mobile nodes and/or MMRS.

D. One-hop Link Stability

A common way to ensure QoS in network routing is to keep stable connections. In a high mobility scenario like vehicular network, the survival time of stable connections has great impact to QoS.

The CIVIC protocol assumes that the connection between one-hop neighbour nodes is stable. The stability of connection is maintained by the neighbour knowledge exploration. The exploration is proactive, it is implemented by the exchange of "Hello" messages, and it must be preformed only when the link stability is out of date. The dynamic interval of neighbour knowledge exploration is evaluated by

{ } r t Min t Δ = Δ
with equation set (

⎪ ⎪ ⎪ ⎪ ⎩ ⎪ ⎪ ⎪ ⎪ ⎨ ⎧ - - = Δ < < - - + = Δ > > - - + = Δ = ∞ = Δ r s s r r s r s r r s s r r s r s r s r r s r s r r v v x x t v v x x v v x x R t v v x x v v x x R t v v t
where R is the radio range in the worst case; x s is the location of source node, and v s is its average speed; x r max is the location of one of its neighbour nodes, and v r max is the speed of this neighbour node. Both x r max and v r max are adjusted by the worst case GPS error. The equation set [START_REF] Fitzgibbons | Simulation-Based Operations Planning For regional Transportation Systems[END_REF] means that the interval of sending "Hello" messages depends on the distances and the relative speeds between the source node and its neighbour nodes.

After neighbour knowledge explorations, each node stores its neighbour information for the further multi-hop routing algorithm.

E. Multi-hop DANKAB

Due to resource constraints of embedded sensor and negative effects from radio irregularity [START_REF] Zhou | Impact of Radio Irregularity on Wireless Sensor Networks[END_REF], broadcast may be a suitable transmitting scheme for IVC routing algorithm. However, broadcast in an MANET could cause serious redundancy, contention, and collision [START_REF] Tseng | Adaptive Approaches to Relieving Broadcast Storm in a Wireless Multihop mobile Ad-hoc Network[END_REF]. Therefore, it is important to determine a correct broadcasting technique for CIVIC protocol. Williams [START_REF] Williams | Comparison of broadcasting techniques for mobile Ad-hoc Networks[END_REF] classifies current broadcasting techniques of MANET to four categories: (1) node makes a decision on rebroadcast by its onehop or two-hop neighbour knowledge. The neighbour knowledge is achieved by the periodic "Hello" packets. Tseng [START_REF] Tseng | Adaptive Approaches to Relieving Broadcast Storm in a Wireless Multihop mobile Ad-hoc Network[END_REF] proved that the adaptive counter-based and location-based scheme could resolve the dilemma between reachability and broadcast storm. The interval of sending "Hello" packets is also important to achieve efficient broadcast. Moreover, the radio irregularity may seriously affect directional routing especially when a packet can only be sent to one direction. Zhou [START_REF] Zhou | Impact of Radio Irregularity on Wireless Sensor Networks[END_REF] proposes using the multi-round discovery technique to solve the problem.

The CIVIC protocol adopts DANKAB (Directional Area Neighbour Adaptive Broadcast) when transmitting message by multi-hop. To use DANKAB, every node stores the location knowledge from neighbour nodes, destination nodes, and next MMRS. In case of one-hop message sending, one-hop broadcast is used. In case of multi-hop message sending, if the location of destination node is unknown by the next MMRS, a request for the location of destination node will be performed by SF to all directions.

When the location of destination node is known, the next hop will be selected according to the locations of neighbour nodes. The Fig. 2 indicates this process. We define the direction area as an angle α with a default value of ±30°. In order to reduce the number of messages in the network, only the nodes within the direction area can broadcast the message. If there is no node within the direction area, the angle α will be gradually increased (e.g. 45°, 90° and 180°) until the next hop is found. An node can be a candidate in the next hop if -α

tg ≤ β tg ≤ α tg .
The β tg is calculated by the trigonometric equation ( 2):

( )( ) ( )( ) ( )( ) ( )( ) s d s r s d s r s d s r s d s r y y y y x x x x x x y y y y x x tg - - + - - - - - - - = β     
In equation ( 2), (x s , y s ), (x d , y d ) and (x r , y r ) are the locations of source node S, destination node D, and routing node R, respectively.

When there is more than one node in the direction area, two approaches can be adopted for selecting the next candidate node. The first one is energy aware competitive broadcast. The node with more remaining energy will rebroadcast more quickly. Thus, other nodes in the same direction area will discard the redundant message. The second one is to let the source node selecting the node for next hop. It requires the additional information of remaining energy when exchanging "Hello" messages, but it generates less routing data. We use the second approach for the experiments in this paper.

After defining the next hop of source node, the processes of DANKAB repeat hop-by-hop until the message reaches the destination node.

F. Summary

The CIVIC protocol stack is represented by the Fig. 3. In general, The CIVIC protocol has three mechanisms when transmitting data:

The first one is the neighbour knowledge exploration. At intervals, each node gets its one-hop neighbour information by exchanging "Hello" messages. This proactive mechanism will be performed only when neighbour information is out of date.

The second one is routing request. It can be proactive or reactive depending on the application requirements. The source node obtains the position of destination node by MMRS or by SF request. After that, the routing process performs only to the direction on demand by using DANKAB.

The last one is the sending of application data. After the routing path has been obtained, the data from application layer will be transmitted. If the data rate is low, DANKAB can also be integrated to the data sending, and the routing request can be ignored. For our experiments in this paper, the two mechanisms are separated. (2)

IV. LCD-GPS CONCEPT AND EXPERIMENTS

As previously mentioned, the CIVIC protocol is a location-based IVC protocol, and it requires accurate positions for transmitting data to the right direction. The Standard GPS Service (civil GPS) only provides accuracy around 13 m (95%) in the horizontal plane, and 22 m (95%) in the vertical plane [START_REF]Standard Positioning System Performance Specification[END_REF]. The measured performance in open areas is usually few meters (1-3 m) [START_REF] Samama | Global Positioning, Technologies and Performance[END_REF] [START_REF] Lamarca | Location Systems: An Introduction to the Technology Behind Location Awareness[END_REF], which is much better than specification [START_REF]Standard Positioning System Performance Specification[END_REF]. However, it is not the case for the urban scenarios where buildings may decrease accuracy. In urban scenarios, the accuracy of location-based services is estimated to be three meters. For the application like hazard warning, the minimum accuracy is one meter [START_REF] Sahinoglu | Ultra-wideband Positioning Systems: Theoretical Limits, Ranging Algorithms, and Protocols[END_REF].

In this section, a solution called LCD-GPS (Low Cost Differential GPS) is presented. The LCD-GPS provides network nodes with the original positions and the accurate positions. It uses CIVIC protocol to collect original positions from network nodes, and then it maximizes the efficiency of CIVIC protocol by offering more accurate positions including differential GPS corrections.

A. Main Idea

The main idea of the LCD-GPS solution consists of a set of standard GPS integrated with communicating receivers (LiveNode sensor [START_REF] Hou | LiveNode: LIMOS versatile embedded wireless sensor node[END_REF] in our experiments). Unlike other Differential GPS solutions, which are very expensive and complicated to be installed, LCD-GPS uses only low cost standard GPS. Some fixed nodes are used as reference stations. The other nodes are mobile nodes. Reference stations and mobile node have the same hardware architecture. We assume all reference stations know their position coordinates with a good accuracy.

Reference stations analyze continuously the instantaneous GPS errors and cooperate to deduce a global error correction. This correction is sent by CIVIC protocol, and it has to be applied to get better accuracy for mobile node positions (or fixed nodes which are not part of reference stations) than the standard GPS one.

The LCD-GPS concept has been presented in details in papers [START_REF] Kara | Low Cost Differential GPS receivers (LCD-GPS): Urban vehicle tracking[END_REF][41] and [START_REF] Kara | Low Cost Differential GPS receivers (LCD-GPS): The differential correction function[END_REF]. This new contribution presents the state of development in multi-hop scenarios. New experiments and results prove the main ideas in our previous papers. With these new experiments, we want to validate especially some aspects of global difference.

Five processing methods have been evaluated: simple difference, filtering, intelligent difference, simple difference with filtering, and intelligent difference with filtering.

B. Experiment Description

Two experiments with respectively five and nine LiveNode sensors were undertaken. We explain only the experiment with five sensors, the only difference between the two experiments is the number of sensors, but the processing methods are the same.

Five LiveNode sensors (S1, S2 … S5) are placed on the tops of cars in the parking of our campus as shown on Fig. 4. GPS data from each node is broadcasted by CIVIC protocol. The data is recorded by a ZigBee base station connected to a laptop. The GPS data is processed offline using C++ and MATLAB. The experiment was conducted on November 25th 2008 between one and two PM (GMT). The experiment duration was about 50 minutes. More details about network deployment, hardware platform, and software platform are presented in the section 5.

The Table 1 summarizes the positioning information for the five sensors. Std Dev X, Std Dev Y and Std Dev Z represent respectively standard deviation of the errors in each direction (East, North and High) in meters (in all following tables measure unit is meter). The five sensors and their surroundings are presented on Fig. 4. The five sensors are represented with red, green, blue, magenta and cyan colours respectively. The sensor locations are presented with crosses (+) and their accuracy with ellipses depending on X and Y standard deviation errors. Fig. 5 presents the GPS instantaneous locations obtained for the five sensors.

From Fig. 6 which represents the accuracy in east and north direction for the five sensors, it is clear that the sensor 3 (blue ellipse) has the worst accuracy. It can be explained by the multi-path errors and limited visibility of the sky. The heights of buildings B1, B2, B3 are approximately 2, 5 and 10 m. The buildings affect the sensor S3 more than the other sensors.

For many applications of GPS, the altitude component is not used especially for vehicle navigation. This component is not discussed in the reminder of this paper.

The first left column in the following tables represents the sensor used as reference station. For each sensor (e.g. S1), X, Y represent East and North directions respectively.

C. Simple Difference Processing

The simple difference consists of subtracting errors measured on the reference sensors in each second. This experiment provides worst results than the original data (without correction) as shown in Table 2. This fact can be explained by two factors:

In our previous experiments [START_REF] Kara | Low Cost Differential GPS receivers (LCD-GPS): Urban vehicle tracking[END_REF][41] and [START_REF] Kara | Low Cost Differential GPS receivers (LCD-GPS): The differential correction function[END_REF], the nodes generally have a clear visibility of the sky without building obstructions. In the new experiment, depending on the five sensor locations, each node has its own error, and applying simple difference adds more errors to the locations of nodes, which then increases the standard deviation. Also, GPS data in the previous experiments is obtained once per second by one-hop direct communications. In the new experiment, with the negative effect of multi-hop, there is some missing data. Consequently, there is delay between the time of reference error and the time when this reference error is really used.

D. Filtering

The second step is applying filtering using EMA (Exponential Moving Average) with α=0.99. The standard deviation of filtered data is lower than the standard deviation of original data. Applying simple difference with filtered data gives better results than the first case, but it is still not sufficient. The number of improvements is less than the number of degradations. The Table 3 shows the results obtained by filtering and applying simple difference on filtered data.

E. Intelligent Difference Processing

The third step is to apply the intelligent difference, which consists of considering error correction as:

The minimum amount of errors of the two reference stations, if the two errors have the same direction (processing each component X and Y separately).

The sum of errors of the two reference stations, if the two errors have different directions (processing each component X and Y separately). The result presented in Table 4 shows that intelligent difference gives more interesting results than filtering. The sensor S5 (cyan) can correct the locations of the other sensors, but the sensor S3 (blue) gives always the worst results.

The forth step is to apply the intelligent difference with filtered data. The Table 5 lists the obtained results.

The Table 5 shows that intelligent difference method combined with filtered data gives the most interesting correction, which is more noticeable than filtering or intelligent difference alone. The sensor S3 always gives the worst results which means that a global view is needed to select which reference station(s) should be used or not. The drawback of intelligent different is that, it can not be applied to mobile nodes, because reference location for mobile nodes does not exist. To overcome this problem, the solution may be to get an average error based on two or more (or all) reference stations using filtered data, and then to use intelligent difference. We call this method as the "Global difference" and our works in this direction are in progress.

V. CIVIC IMPLEMENTATION AND EXPERIMENTS

The purpose of our experiments is to implement the CIVIC protocol on a sensor network, test its feasibility and make it reliable. At the same time, the experiments serve also to validate LCD-GPS.

A. Hardware Platform

The hardware platform used in experiments is the LiveNode sensor developed by our team [START_REF] Hou | LiveNode: LIMOS versatile embedded wireless sensor node[END_REF]. It is a versatile wireless sensor node, which enables to implement rapidly a prototype for different domains of applications such as telemedicine (wireless cardiac arrhythmias detection sensor for instance), communication, and environmental data collection.

The LiveNode sensor is a small board (70x55mm) and is powered by a 9V standard battery. It may be equipped with different types of components (GPS, Wi-Fi, ZigBee, GSM and different type of sensors) to meet the requirements of an application. The major components of LiveNode sensor used in our experiments of CIVIC protocol and LCD-GPS have three parts as shown in Fig. 7:

The Atmel AT91SAM7S256 [START_REF] Datasheet | AT91SAM7S Series Summary[END_REF][44] microcontroller is used for data processing. It is an ARM7TDMI based high-performance 32-bit RISC microcontroller with Thumb extensions with USB Device Interface, 32 I/O pins, one Advanced Interrupt Controller, one Periodic Interval Timer, two USARTs, 256 K bytes Flash and 64 K bytes SRAM.

The MaxStream XBee Pro [START_REF]XBee/XBee-Pro OEM RF Modules[END_REF] chip is to ensure the wireless communication of ZigBee (IEEE802.15.4). The module operates within the ISM 2.4 GHz frequency band. It is cheap ($32), it requires low power (60 mW), and it can reach a wide range (up to 1 mile). The ZigBee is chosen in our new experiments instead of Wi-Fi because ZigBee has an outdoor RF line-of-sight range up to 1.6 km and an indoor range of 100 m, which is equivalent to Wi-Fi indoor range one. Besides, the energy consumption for ZigBee module is less than the available Wi-Fi modules.

The GlobalSat ET-301 [START_REF]Product User Manual, Gps Engine Board[END_REF] GPS chip is for specific GPS signal processing. It is a 20-channel all-in-view tracking receiver. It communicates on the serial port with the micro-controller at the default baud rate of 4800 bps. The receiver automatically sends its complete message once every second. Then, the micro-controller detects and decodes the message.

B. Software Development

The software of our experiments is mainly written in C, except for hardware-related parts in assembly language. The monitoring software (in Java) is developed specially for our experiments (Fig. 8). The network screenshots and result analysis of this section are got from this monitoring software.

The CIVIC system is driven by three interrupt sources: one from PIT (Periodic Interval Timer) and the other two from USART (Universal Synchronous Asynchronous Receiver Transmitter).

The PIT is set to interrupt at a specified period depending on the task requiring minimum interval. Each task has a separate counter increased by every PIT interrupt. When a counter reaches its predefined limit, it goes back to zero and calls the related task. The major periodic tasks include data processing, neighbour searching, routing requesting, and application data sending.

The USART0 interrupt is occurred when data is received from GPS, and the USART1 interrupt is generated when data is received from ZigBee. The USART interrupt handlers then transfers the incoming data into their own FIFO buffers for data processing.

C. Network Deployment

The location of our CIVIC experiments is the same as previous LCD-GPS experiments: the parking (about 70x50 meters) of our campus as shown on Fig. 9. All LiveNode sensors are randomly distributed on the tops of cars. A sensor at the corner is set as the receiver of routing request and application data (original GPS data information in our experiments). The data is recorded by four ZigBee base stations, which are also randomly distributed. The Fig. 10 demonstrates a sample of network deployment when using nine sensors. A sample of network deployment for five sensors is shown in Fig. 4 of section 3.

Because the outdoor radio range ZigBee Pro is up to 1.6 km and the space available to our experiments is limited, we define a filter for each sensor to remove the packet sent from the distance longer than 40 meters. It forces some sensors to send data in multi-hops, so we can evaluate the efficiency of packet forwarding in CIVIC protocol. Because each sensor actually receives all packets from the network, if CIVIC protocol can work under this setting, it perform better in applications that are more practical.

D. Packet Deliver

As previously mentioned, there are three mechanisms when transmitting data in CIVIC protocol. Consequently, there are mainly three groups of packets as shown in Table 6: In addition, a packet type of PACK_MANAGEMENT is sent by the ZigBee station for controlling the previous mechanisms and running experiment sections.

Although the CIVIC is a location-based protocol, for practical reasons, it integrates SF technique as a part in the routing process. When there is no position obtained by GPS, the protocol can still perform the routing tasks. The PACK_ROUTE_REQ_SF is designed for this purpose.

Fig. 11 and Fig. 12 show the major dataflow in neighbour knowledge exploration and routing request in CIVIC protocol. In principal, if the source node has the position of destination node, it performs the CIVIC routing request; otherwise, it uses SF to send the position of source node, and asks the destination node reply in the CIVIC routing request.

After at least one routing has been done, the original GPS data will be send to the destination node.

To keep CIVIC protocol adaptable to other MAC, we use only the "Broadcast Mode" provided by ZigBee chip. The IP addressing and data forwarding is done by CIVIC protocol. It is well known that the neighbourhood broadcasting easily causes collisions. Even if we apply CMSA/CA (with a slotted contention), which is commonly used by most MAC protocols, there will be a probability that two sensors would sense the same slot being free, and transmit data in the same slot [START_REF] Tourrilhes | Robust broadcast: improving the reliability of broadcast transmissions on csma/ca[END_REF]. Therefore, the CIVIC protocol must have the additional mechanism in the network layer to minimize the influence from collisions. The PACK_DATA_ACK and PACK_DATA_ACK_FWD are designed for this purpose. Depending on the application requirements, when the destination node receives the data, it can choose to send back an acknowledgement to the source node. If the source node does not receive this acknowledgement, it can thus choose further actions. It is not a standard approach of CIVIC protocol, and its efficiency will be evaluated in our experiments.

E. Three Experiment Scenarios

The first experiment is compare the DANKAB broadcast with the SF broadcast in the routing process of CIVIC protocol. There are reasons to choose SF in this experiment: SF is reliable in terms of coverage, and it has been practically used in low-density networks. Besides, to compare with two broadcasting methods, they must be implemented on the same hardware platform, and run under the same conditions. Resource constraints of embedded sensor limit the choice of broadcasting methods.

This experiment is done in a static network with nine sensors. The parameters used for evaluations are the overall packet number, the packet loss rate, and the average routing hop distance (the maximum hop is four). In both broadcasts, at five seconds intervals, eight sensors require routing to a single sensor at the corner as shown in Fig. 13 and Fig. 14. Both DANKAB and SF broadcast stop when 50 routings are found. The result of comparison is shown in Table 7. The DANKAB has better performance in all three parameters. Moreover, comparing to SF routing paths as shown in Fig. 13, all DANKAB routing paths are on the right direction to the destination node as shown in Fig. 14.

The second experiment is a comparison of the application packets sending with or without acknowledgement.

The network deployment and the target sensor is the same as in the first experiment. The experiments are run after all sensors obtain routing paths by DANKAB. At one-second intervals, sensors send their original GPS data to the target sensor. The GPS data are wrapped in the application packets. The experiments stop when 100 application packets are sent, thus ideal there should be 800 application packets received by the target sensor.

In the experiment without acknowledgement, all sensors just keep sending until finished. In the experiment with acknowledgement, if an acknowledgement has not been received, the sender assumes that the target sensor is busy, and waits three seconds before sending the data again.

This target sensor (S2) is connected to a laptop by its debug port. The main parameters for comparison are packet number received by debug port, and the overall packet number received by ZigBee stations. The result is shown in Table 8. For the LCD-GPS experiments, the packet receiving rate is satisfied when sending without acknowledgement. Therefore, in the next experiments we use the application packets without acknowledgement.

The third scenario is to evaluate the factor of mobile sensor. It is done in a network with nine sensors. This experiment compares a static network with nine sensors and a similar network with one mobile sensor (Fig. 15). The result in Table 9 shows that a part of the application data is lost because of the sensor movements, but overall the CIVIC protocol performs well in mobile network. The data analysis after experiments indicates that the packet loss is mainly caused by two reasons: i. Radio interference; ii. The interval for routing request is set to be too short, so the new routing path can not be updated in time.

VI. CIVIC APPLICATION: MOBIPLUS

The CIVIC protocol is used as a prototype to experiment three projects in different areas: inter-vehicle communication (MobiPlus project), environmental data collection (Net-ADDED European project) and telemedicine (LiveCare project). In this paper, we present only the MobiPlus project.

MobiPlus project is supported by the SMTC of Clermont-Ferrand city in France (Syndicat Mixte des Transports en Commun de l'agglomération clermontoise). It focuses on improving the public service on urban transportation system particularly to disabled passengers (Fig. 16).

The MobiPlus has two major components: LNB (LiveNode Bus) and LNS (LiveNode Station). The LNS contains an RFID (Radio-Frequency IDentification) reader, which detects the presence of the disabled passenger who has an RFID electronic ticket. The RFID electronic ticket contains the information about the specific needs of the passenger, and this information will be sent to the bus that he or she is waiting for. Thus, when LNB arrives at LNS, related services according to these specific needs will be provided. For example, if a wheelchair user is present, the wheelchair lift on LNB will be activated. If a sight-deprived passenger is present, the voice notice from LNS will be played.

The LiveNode sensors embedded at LNB and LNS communicate with CIVIC protocol, which adopts Wi-Fi and ZigBee. The GPS is used to localize the LNB and to estimate its arrival time.

VII. CONCLUSION AND ONGOING WORK

In this paper, a new inter-vehicle communication protocol named CIVIC has been described. The CIVIC protocol was implemented on LiveNode sensor, compared to the SF protocol, and tested on different scenarios. The obtained results meet the requirements of the IVC applications in term of performance, robustness and efficiency. This paper has also presented new results of LCD-GPS experiments cooperating with CIVIC protocol. The results confirm the results obtained in previous works especially the use of intelligent difference with filtered data [START_REF] Kara | Low Cost Differential GPS receivers (LCD-GPS): The differential correction function[END_REF].

The cooperating experiments present new challenges on developing CIVIC protocol and LCD-GPS. For the CIVIC protocol, we must continue to improve the efficiency of CIVIC protocol when the LCD-GPS requests higher data rate in communications. For adopting LCD-GPS in practical IVC applications, it is anticipated to have the negative effects of the multi-path, the limited visibility of the sky, and the packet loss in transmissions. The "Global difference" may be a better solution for the problems, but it would need to be proved by further works.

The LCD-GPS will enlarge the application domains of standard civil GPS (e.g. precision agriculture, precision mobile tracking in urban areas, etc.). With the improvement of GPS accuracy, the CIVIC protocol will be implemented on the infrastructure of the V2I (Véhicules et Infrastructures Innovants de la Fédération de Recherche TIMS) project: autonomous intelligent multi-modal electric cars and agricultural vehicles (tractor etc.). The CIVIC protocol will be also used in the Net-ADDED EU project to increase the wireless coverage range around an access medium in the rural area to improve the practice of precision agriculture. Moreover, in a bigger picture, although the CIVIC protocol is originally designed for IVC, its applications are not limited to inter-vehicle communication. With proper modifications, it can be adapted to other applications like smart home, telemedicine, and environment monitoring.

Figure 1 .

 1 Figure 1. Mixed ad-hoc and infrastructure networks.

Figure 2 .

 2 Figure 3. CIVIC protocol structure.

Figure 4 .

 4 Figure 4. The five GPS receivers layout.

Figure 5 .

 5 Figure 5. Instantaneous locations for five fixed nodes.

Figure 6 .

 6 Figure 6. Accuracy comparison for five fixed nodes.

Figure 7 .

 7 Figure 7. Hardware platform for experiments.

Figure 8 .

 8 Figure 8. An IDE for network deployment.

Figure 9 .

 9 Figure 9. Location of experiments.

Figure 10 .

 10 Figure 10. Network deployment for nine sensors.

Figure 11 .

 11 Figure 11. Dataflow driven by PIT interrupt.

Figure 12 .

 12 Figure 12. Dataflow driven by USART1 interrupt.

Figure 13 .Figure 14

 1314 Figure 13. Routings topology by SF

Figure 15 .Figure 16 .

 1516 Figure 15. Experiment with a mobile sensor

  are based on UTRA-TDD (UMTS Terrestrial Radio Access Time Division Duplex). The UTRA-TDD is a third generation mobile telephone technology. It has about 1 km radio range, and 384 Kbps to 2 Mbps bandwidth according to the vehicle speed. It operates in the free frequency band from 2.010 GHz to 2.020 GHz[START_REF]FleetNet Documents[END_REF][14][START_REF] Franz | Internet on the Road via Inter-Vehicle Communications[END_REF]

TABLE 1 .

 1

				FIVE RECEIVER POSITIONING SUMMARIZE
			Sensor	Sensor	Sensor	Sensor	Sensor
				1	2		3	4	5
	Std Dev X	0.698	0.430		0.855	0.433	0.427
	Std Dev Y	0.791	0.790		1.624	0.594	0.907
	Std Dev Z	4.564	1.928		5.872	2.381	2.300
		TABLE 2. SIMPLE DIFFERENCE APPLIED TO FIVE RECEIVERS
	Receiver	S1	S2		S3	S4	S5
	S1	X	-	0.673	1.007	0.820	0.702
		Y	-	0.662	2.009	1.148	0.673
	S2	X	0.663	-		0.923	0.597	0.540
		Y	0.651	-		1.921	1.013	0.659
	S3	X	0.845	0.863	-		0.673	1.033
		Y	1.893	1.926	-		1.319	1.881
	S4	X	0.802	0.554	0.868	-	0.592
		Y	0.972	0.915	1.699	-	1.037
	S5	X	0.856	0.547	0.913	0.655	-
		Y	0.769	0.811	2.031	1.020	-
		TABLE 3.	SIMPLE DIFFERENCE WITH FILTERED DATA
		Receiver	S1		S2	S3	S4	S5
	Filtered data X	0.550	0.305	0.555	0.221	0.292
			Y	0.546	0.719	1.354	0.410	0.725
	S1		X	-	0.496	0.606	0.495	0.554
			Y	-	0.619	1.719	0.786	0.345
	S2		X	0.505	-		0.540	0.439	0.385
			Y	0.550	-		1.581	0.839	0.434
	S3		X	0.505	0.347	-	0.587	0.519
			Y	1.603	1.065	-	1.581	1.669
	S4		X	0.518	0.345	0.472	-	0.355
			Y	0.693	0.814	1.414	-	0.865
	S5		X	0.641	0.363	0.539	0.392	-
			Y	0.379	0.550	1.645	0.795	-
	TABLE 4. INTELLIGENT DIFFERENCE APPLIED TO FIVE RECEIVERS
	Receiver	S1		S2		S3	S4	S5
	S1	X	-	0.542	0.805	0.452	0.445
		Y	-	0.464	1.306	0.668	0.487
	S2	X	0.520	-		0.741	0.426	0.352
		Y	0.424	-		1.372	0.622	0.586
	S3	X	0.694	0.726	-		0.521	0.772
		Y	1.282	1.415	-		1.060	1.225
	S4	X	1.965	2.022	1.729	-	2.294
		Y	0.767	0.683	1.078	-	0.725
	S5	X	0.558	0.350	0.669	0.377	-
		Y	0.520	0.579	1.227	0.591	-
		TABLE 5. INTELLIGENT DIFFERENCE WITH FILTERED DATA
	Receiver	S1		S2		S3	S4	S5
	S1	X	-	0.409	0.467	0.339	0.367
		Y	-	0.382	1.048	0.469	0.308
	S2	X	0.412	-		0.457	0.304	0.279
		Y	0.383	-		1.062	0.458	0.440
	S3	X	0.394	0.425	-		0.261	0.409
		Y	1.020	1.074	-		0.820	0.930
	S4	X	0.355	0.375	0.531	-	0.263
		Y	0.483	0.528	0.968	-	0.594
	S5	X	0.430	0.304	0.387	0.278	-
		Y	0.300	0.407	1.098	0.479	-

TABLE 6 .

 6 PACKET GROUP FOR CIVIC

	Group	Packet Name	Maximum
			Size (Byte)
	Hello	PACK_HELLO_REQ_CIVIC	38
		PACK_HELLO_RPY_CIVIC	45
	Routing	PACK_ROUTE_REQ_CIVIC	45
		PACK_ROUTE_REQ_SF	24
		PACK_ROUTE_RPY_CIVIC	64
		PACK_ROUTE_RPY_BY_PATH.	44
	Application PACK_DATA_SEND	63
		PACK_DATA_FWD	63
		PACK_DATA_ACK	25
		PACK_DATA_ACK_FWD	25

TABLE 7 .

 7 COMPARING SF AND DANKAB

		Packet	Packet Loss	Average Routing
		Number	Rate	Hop
	SF	3453	9.13%	2.10
	DANKAB	1144	2.97%	1.39

TABLE 8 .

 8 COMPARING THE EFFICIENCY OF ACKNOWLEDGEMENT

		Packet Number	Packet	Overall Packet
		(by debug port)	Receiving Rate	Number
	No Ack	773	97%	1043
	With Ack 851	100%	2260

TABLE 9 .

 9 COMPARING THE FACTOR OF MOBILE SENSOR

		Packet Number	Packet Receiving Rate
		(debug port)
	Static Network	773	97%
	Mobile Network	652	82%

Journal of netwoks, 2009, 4(6), 445-457 -© Academy Publisher

ACKNOWLEDGEMENTS

We would like to thank the EU (NeT-ADDED FP6 EU project), the "Conseil Régional d'Auvergne", and the French and Chinese governments through PHC PFCC 2009 (20974WG) project for their supports to CIVIC project.

BIOGRAPHIES

Xunxing DIAO


Georg Wolfram
email: georg.wolfram@dws-hydro-oekologie.at

Christine Argillier

Julien De Bortoli

G Buzzi

Martin T Dokulil

Eberhard Hoehn

Aldo Marchetto

Pierre-Jean J Martinez

Giuseppe Morabito

Markus Reichmann

Fabio Buzzi

Antonio Dalmiglio

Špela Remec-Rekar

Ursula Riedmüller

Christelle Rioury

Jochen Schaumburg

Liselotte Schulz

Gorazd Urbanič

Reference conditions and WFD compliant class boundaries for phytoplankton

Keywords: Alpine lakes, phytoplankton biomass, chlorophyll-a, reference conditions, Water Framework Directive, intercalibration

published or not. The documents may come   L'archive ouverte pluridisciplinaire

Introduction

Lake assessment using phytoplankton has a long tradition in the Alpine region. It has tasked and shaped limnology from its very beginning in the late 19 th century until today (Forel, 1892(Forel, -1902;;[START_REF] Vollenweider | The loading concept as a basis for controlling eutrophication philosophy and preliminary results of the OECD programme on eutrophication[END_REF][START_REF] Solheim | Ecological threshold responses in European lakes and their applicability for the Water Framework Directive (WFD) implementation: synthesis of lakes results from the REBECCA project[END_REF]. During the 20 th century, our knowledge about the limnology of Alpine lakes steadily increased. For some lakes, there exists a continuous series of limnological data covering several decades.

Predominantly, in the second half of the 20 th century, many Alpine lakes were suffering from eutrophication as an attendant symptom of increased tourism in the Alps and the growing economic prosperity. The problems arising for lakes and rivers stimulated and intensified the effort of limnological research on the functioning of aquatic ecosystems and the role of nutrients for lake productivity.

The International Biological Programme (IBP; Worthington, 1975) and the OECD research programme on eutrophication (Fricker, 1980;OECD, 1982) were two milestones for limnological research in Alpine lakes. These two programs provided a deep knowledge of the driving processes in lakes, but worked also as a platform for broad international co-operation in theoretical and applied limnology. The experience and the databases that arose from IBP and OECD programs provide the fundamental basis for this paper.

After substantial efforts to remediate Alpine lakes by various measures, such as improving the sewage treatment in the catchment area or building ring channels, the limnological monitoring during the last few decades has provided information on the re-oligotrophication process in many lakes and the response of the algal community. Data on the quantity and composition of phytoplankton is now available for Alpine lakes representative of all trophic states.

The introduction of the EU Water Framework Directive (WFD; [START_REF] Directive | Directive 2000/60/EC of the European Parliament and of the council of 23 October 2000 establishing a framework for community action in the field of water policy[END_REF] marks a new phase of lake assessment, both from a scientific point of view [START_REF] Dokulil | Bewertung der Phytoplanktonstruktur stehender Gewässer gemäß der EU-Wasserrahmenrichtlinie: Der modifizierte Brettum-Index[END_REF] and as regards the need for intensifying international co-operation and data exchange. Lake classification under the WFD is based on the degree of deviation of the present state from type-specific reference conditions.

Phytoplankton is one of the biological quality elements which are to be used for lake classification. Section 1.1.2 of Annex V of the WFD names the following criteria for lake assessment using phytoplankton: composition, abundance and biomass. This paper deals with the quantitative aspect of phytoplankton assessment in Alpine lakes larger than 0.5 km 2 and located between 50 and 800 m above sea level (a.s.l.). The objectives are to describe typespecific reference conditions and the process of class boundary setting for phytoplankton biomass and chlorophyll-a. The paper is the outcome of an ongoing intercalibration (IC) exercise, which is carried out in order to ensure comparability of the ecological classification scales and to obtain a common understanding of the good ecological status of surface waters throughout the EU (CIS, 2003a).

Material and methods

Lake typology

The Alpine Geographical Intercalibration Group (GIG), which comprises Austria, France, Germany, Italy and Slovenia, defined two common IC lake types. They are characterized by few and broad criteria including altitude, mean lake depth, lake surface area and alkalinity (Table 1). The values given for these descriptors are not strict boundaries, but have to be regarded as estimates, which may help assign Alpine lakes to two groups of lakes with comparable abiotic and biological reference conditions.

Sampling sites and dates

A database of 161 sites (sampling stations) in 144 Alpine lakes was compiled, which included abiotic parameters as well as data on total phosphorus, total biovolume and chlorophyll-a.

Most of the lakes belonged to the IC common types L-AL3 and L-AL4 (Table 2). In order to broaden the data base some smaller lakes, which did not significantly differ from L-AL4 lakes in terms of hydro-morphology except for the lake area, were included in the regression analyses. The IC criteria were, however, more strictly applied to the site selection for the calculation of ranges of reference values. Very large and deep lakes (mean depth >100 m) were treated separately in the regression analyses, but not defined as separate lake type for the definition of reference values.

The number of years with data on total phytoplankton biomass ranged from 1 to 57 per site, total number of site-years with biomass data was 783 in 116 lakes, with some time series starting as early as the 1930s and ending in 2005. Total phosphorus data were available for 764 site-years in 134 lakes, chlorophyll-a data for 463 site-years in 126 lakes. For 275 siteyears, a complete data set with TP, total biovolume and chlorophyll-a was available.

In most cases only one sampling site was sampled in each lake. Lake basins of some highly structured lakes are regarded as separate sites in most monitoring programs. The data from these sites were treated separately in the analyses and were not used to calculate means for the whole lake.

In most cases only years with at least four sampling dates per year were considered for the data analysis. From some sites with low interannual trophic variability, where phytoplankton data from subsequent years were available, also site-years with less than 4 sampling dates were included in the analyses.

Eight lakes with historical phytoplankton biomass data given in [START_REF] Ruttner | Ökotypen mit verschiedener Vertikalverteilung im Plankton der Alpenseen[END_REF] were not treated as separate sites. The data were, however, averaged and treated as one data set in the analyses, in order to minimize errors due to methodological uncertainties (e.g. a lower sampling frequency). For facilitating the readability, this data set is termed and referred to as 'site' in the subsequent text.

Sampling of phytoplankton and chlorophyll-a usually occurred during whole year, including the spring peak of diatoms. All data stemmed from integrated or mixed samples from the epilimnion or the euphotic zone. No data from single depth samples were included in the database.

Chlorophyll-a and biomass analysis

Chlorophyll-a data were available commencing from 1972. Chl-a concentrations were analysed with spectrophotometry according to the procedure described in [START_REF] Iso | Bestimmung des Chlorophyll-a-Gehaltes von Oberflächenwasser[END_REF]. Ethanol or acetone was used as extraction solvent. All chlorophyll-a data are turbidity corrected following [START_REF] Lorenzen | Determination of chlorophyll and phaeopigments: spectrophotometric equations[END_REF].

Total phytoplankton biomass (including picoplankton) was calculated as total biovolume following [START_REF] Utermöhl | Zur Vervollkommnung der quantitativen Phytoplankton-Methodik[END_REF]. Abundance counts and biomass calculations were performed following the principles as outlined in [START_REF] En | Water quality -Guidance standard on the enumeration of phytoplankton using inverted microscopy (Utermöhl technique)[END_REF][START_REF] Cen | Phytoplankton biovolume determination using inverted microscopy (Utermöhl technique)[END_REF].

Definition of natural trophic state

The Alpine GIG mainly followed the spatial approach using monitoring sites in defining reference conditions (cf CIS, 2003b). In addition, historical data (temporally based reference conditions), modelling of anthropogenic nutrient load or natural trophic state, and expert judgement were also used: i) Historical data: Earliest information on trophic state can be derived from data on transparency (e.g. [START_REF] Halbfaß | Grundzüge einer vergleichenden Seenkunde[END_REF]. Historical quantitative data on phytoplankton in Alpine lakes are available from the 1930s for Carinthian lakes [START_REF] Findenegg | Limnologische Untersuchungen im Kärntner Seengebiet[END_REF][START_REF] Findenegg | Versuch einer soziologischen Gliederung der Kärntner Seen nach ihrem Phytoplankton[END_REF] and for several lakes in the Northern Calcareous Alps [START_REF] Ruttner | Ökotypen mit verschiedener Vertikalverteilung im Plankton der Alpenseen[END_REF]. Since these lakes were not affected by major anthropogenic pressure from industrialisation, intensive urbanisation or agriculture, the 1930s reflect reference conditions with insignificant anthropogenic impact.

In only a few Alpine lakes intensive urbanisation had led to an increased discharge of nutrients into lakes and subsequent eutrophication already in the 19 th century (e.g. Amann 1918). This is confirmed by paleolimnological data that indicates that some Alpine lakes have suffered from anthropogenic eutrophication more than 100 years ago due to major urbanisation (e.g. [START_REF] Feuillade | Trophic status evolution of Lake Nantua as revealed by biological records in sediment[END_REF][START_REF] Guilizzoni | Historical records of changes in the chemistry and biology of Italian lakes[END_REF]. The time before the Second World War can thus be accepted as a "reference period" only if impacts from anthropogenic land use and urbanisation were negligible.

ii) Paleolimnology: Paleolimnological data have been checked for many lakes and indicated that oligotrophic nature of many Alpine lakes (e.g. [START_REF] Löffler | The paleolimnology of some Carinthian lakes with special reference to Wörthersee[END_REF][START_REF] Guilizzoni | Basic trophic status and recent development of some Italian lakes as revealed by plant pigments and other chemical components in sediment cores[END_REF][START_REF] Klee | Eutrophication of Mondsee (Upper Austria) as indicated by the diatom stratigraphy of a sediment core[END_REF][START_REF] Schmidt | Diatomeenstratigraphische Untersuchungen zur Trophieänderung und Industrieschlammakkumulation im Traunsee/Österreich[END_REF][START_REF] Schaumburg | Seen in Bayern -Limnologische Entwicklung von 1980 bis 1994[END_REF][START_REF] Klee | Alleröd diatom assemblages in prealpine hardwater lakes of Bavaria and Austria as preserved by the Laacher See eruption event[END_REF][START_REF] Marchetto | Reconstruction of the phosphorus history of two deep, subalpine Italian lakes from sedimentary diatoms, compared with long-term chemical measurements[END_REF][START_REF] Alefs | Die jährliche Änderung der Diatomeenvergesellschaftung seit 1958 in einem warvendatierten Sedimentkern aus dem Ammersee (Oberbayern)[END_REF][START_REF] Loizeau | Evolution of the trophic state of Lake Annecy (eastern France) since the last glaciation as indicated by iron, manganese, and phosphorus speciation[END_REF][START_REF] Marchetto | Comparison between sedimentary and living diatoms in Lago Maggiore (N. Italy): implications of using transfer functions[END_REF].

However, paleolimnology has also proved that some Alpine lakes clearly were oligomesotrophic or even slightly eutrophic before any significant anthropogenic impact (e.g. [START_REF] Frey | Längsee: A history of meromixis[END_REF][START_REF] Löffler | The paleolimnology of some Carinthian lakes with special reference to Wörthersee[END_REF], Danielopol et al. 1985, Higgit et al. 1991[START_REF] Lotter | The palaeolimnology of Soppensee (Central Switzerland), as evidenced by diatom, pollen and fossil-pigment analysis[END_REF][START_REF] Schmidt | Impact of late glacial climate variations on stratification and trophic state of the meromictic lake Längsee (Austria): validation of a conceptual model by multi proxy studies[END_REF][START_REF] Hofmann | Seesedimente in Bayern: Waginger-Tachinger See, Diatomeenflora in Sedimentkernen August 2002[END_REF]. This was the case especially for some small, shallow and meromictic lakes, which naturally had reached higher levels of productivity.

iii) Modelling data: Theoretical considerations using the Vollenweider phosphorus loading model [START_REF] Vollenweider | Advances in defining critical loading levels for phosphorus in lake eutrophication[END_REF]OECD, 1982) were used to check the natural trophic state of Alpine lakes. This was done by converting the critical total phosphorus load after [START_REF] Vollenweider | Advances in defining critical loading levels for phosphorus in lake eutrophication[END_REF] at the boundary oligo-/mesotrophy ) 1 ( 10

s m s c q z q L + = (Eq. 1) Where L c = critical TP load [mg m -2 ]; q s = Q/A = z m /τ w = hydraulic load [m a -1 ]; Q = annual discharge [m 3 a -1 ]; A = lake surface area [km 2 ] and Z m = mean depth [m] to a critical export rate, ER c : 100 E A L ER c c = (Eq. 2)
For some shallow to moderately deep Alpine lakes, the potential natural TP export rate turned out to be significantly lower than the critical export rate, if the catchment is assumed to be entirely covered by forest (Fig. 1).

Definition of reference conditions using monitoring data

Two sets of criteria were used by the Alpine GIG to select reference lakes from monitoring data: i) general reference criteria, which focus on the level of anthropogenic pressure exerted on reference lakes, and ii) specific reference criteria, which focus on ecological changes caused by the anthropogenic pressure.

The criteria are based on the general requirements for the selection of reference sites following the 'Refcond Guidance' (CIS, 2003b). They describe the level of anthropogenic pressure in terms of catchment use, direct nutrient input, hydrological and morphological changes, recreation pressure etc (Table 3). These descriptors were not used as strict exclusion/inclusion criteria, especially those of minor relevance for trophic state and phytoplankton such as connectivity to tributaries or presence of non-indigenous species.

In a second step, specific reference criteria, which focussed particularly on eutrophication, were defined (Table 4). Since phosphorus is the limiting factor for primary productivity in almost all Alpine lakes and data on the TP concentration (volume weighted annual mean or during spring overturn) were available in most cases, a threshold value of the TP concentration was used for a pre-selection of reference sites. Examples from the literature show that a significant increase of phytoplankton biomass may occur already below a TP concentration of 10 µg L -1 , but also the taxonomic composition of planktonic algae may change along a TP gradient of 5 to 10 µg L -1 (e.g. Fricker, 1980;[START_REF] Bmgu | Ergebnisse des österreichischen Eutrophieprogrammes 1978-1982[END_REF]IGKB 2004a, b). Hence, a TP threshold value of ≤8 µg L -1 was defined to select reference sites among L-AL3 lakes. The slightly higher natural trophic state of shallow and moderately deep lakes was taken into account, when a threshold value of TP ≤12 µg L -1 was set for selecting reference sites among (pre-)Alpine lakes of IC type L-AL4.

The TP threshold values were not used for selecting reference sites in two cases: 1) Sites with slightly higher TP concentrations were also accepted as reference sites if nutrient load calculations had proved that the anthropogenic contribution to the total nutrient load was insignificant. 2) Sites that underwent a re-oligotrophication process were not considered as reference sites even if they met the TP criterion, as long as TP and chlorophyll-a concentrations were still declining. A delay in re-oligotrophication and especially in the response in one or more biological quality elements has been shown by [START_REF] Anneville | Recovery of Lake Geneva from eutrophication: quantitative response of phytoplankton[END_REF] and Kaiblinger et al. (submitted).

Setting of reference and class boundary values

For each lake, the arithmetic mean of total biomass was calculated by using data from all years available. The median of biomass values from the population of reference lakes was defined as the reference value and the 95 th percentile as the high/good (H/G) boundary. The reference value and the H/G class boundary for chlorophyll-a were derived from a regression with phytoplankton total biomass.

The boundaries between good and moderate status were set, in a first step, by adopting boundary values suggested by [START_REF] Nixdorf | Bewertung von Seen anhand des Phytoplanktons[END_REF] for deep Alpine lakes (L-AL3). In a second step, a 2-to 3-fold increase of phytoplankton biomass was proposed as tolerable within the good status. This is considered as being compliant with 'slight changes in the abundance' as defined in Annex V of the WFD. The values derived as such were validated by the 'undesirable conditions and secondary effects' (Annex V of the WFD) as well as by the decline of sensitive taxa, such as some Cyclotella species, which commonly dominate under oligotrophic conditions in Alpine lakes (e.g. [START_REF] Wunsam | Cyclotella-taxa (Bacillariophyceae) in lakes of the Alpine region and their relationship to environmental variables[END_REF][START_REF] Schaumburg | Ökologische Typisierung des Phytoplanktons[END_REF].

Finally, the good/moderate (G/M) boundary for phytoplankton total biomass was fixed by defining equal class widths on a logarithmic scale. The same class widths -applied to different H/G boundaries as starting points -were used for IC lake type L-AL3 and L-AL4.

Like for the reference value and H/G boundary, the G/M boundary of the chlorophyll-a concentration was derived from a regression with phytoplankton total biomass.

For all class boundaries, ecological quality ratios (EQR) were calculated by dividing the class boundary values by the corresponding reference value.

Ranges for reference values and class boundaries of biomass and chlorophyll-a

Following an initial first test phase of lake classifications in the Alpine GIG, ranges of reference and class boundary values rather than fixed values were defined. This was in order to cover geographical or other typological differences within the Alpine region and to facilitate transposing the values of the common IC types to more detailed national typologies.

The range for the reference value of L-AL3 lakes was set using the uncertainty in the regression equation (95% confidence interval) between trophic pressure (TP concentration)

and phytoplankton response (total biomass). The ranges for the class boundaries of L-AL3 lakes were derived by applying the same EQR as given for the fixed values. All values were finally rounded to one digit.

The range for the reference value of L-AL4 lakes was derived by combining two approaches: 1) by re-calculating the reference value and boundaries with new data (from 2006), but applying the same boundary setting protocol, 2) by varying the set of lakes used in the calculations (i.e. by excluding two pre-selected reference sites with a surface area <0.2 ha). The ranges for the class boundaries of L-AL4 lakes were subsequently set in the same way as for L-AL3, viz. by applying the same EQR as given for L-AL4.

Results

The range of TP concentration in the lakes used for this paper was 2 to 407 µg L -1 . Total biovolume data ranged from 0.1 to 10.2 mg L -1 , chlorophyll-a concentration between 0.3 and 75.8 µg L -1 (all values as annual means).

A regression between TP and total biovolume was calculated separately for three groups of lakes: L-AL3, very large and deep lakes (mean depth >100 m) and L-AL4 (including some lakes <50 ha) (Fig. 2). Despite the high variability (with r 2 ranging between 0.33 and 0.40), the regression coefficients and intercepts were significantly different between large lakes of L-AL3 and the other two groups (p<0.01), but not between L-AL3 and L-AL4 (p=0.33).

No significant difference between the lake types was found in the regressions of total biomass against chlorophyll-a (L-AL3 vs L-AL4: p>0.36, L-AL3 vs 'L-AL3 large': p=0.08, L-AL4 vs 'L-AL3 large': p=0.38). The regression equation given in Fig. 3 was thus calculated for the whole data set.

Based on the criteria given in Table 3 and 4, reference sites were selected. The historical data from the 1930s included five L-AL3 and two L-AL4 data sets (Table 5), 14 L-AL3 and 12 L-AL4 data sets came from monitoring programs after 1978 (Table 6). Since Faaker See and Weißensee, which were represented both in the historical and in the monitoring data, were treated only once, the total sum of reference sites belonging to IC lake type L-AL3 was 18, whereas 13 reference sites belonged to IC lake type L-AL4.

Biomass values of deep (L-AL3) and shallow (L-AL4) reference sites were significantly different (Mann-Whitney test, p=0.002). The median of the phytoplankton total biomass in the L-AL3 reference sites was 0.3 mg L -1 , the median value for 13 L-AL4 lakes was 0.7 mg L -1 . These values were defined as reference values for total biomass in the two lake types. The boundary between high and good ecological status, which was set at the 95% percentile, is 0.5 mg L -1 for L-AL3 and 1.1 mg L -1 for L-AL4 (Table 7).

The reference values for chlorophyll-a, which were calculated using the regression given in Fig. 2, are 1.9 µg L -1 in L-AL3 lakes and 3.3 µg L -1 in L-AL4 lakes. Table 8 summarizes the reference values and class boundaries for total biomass as well as for chlorophyll-a, which were derived according to the boundary setting protocol described above. It also gives the ecological quality ratios, which lie between 0.60 and 0.75 for the H/G boundary and between 0.25 and 0.41 for the G/M boundary.

The ranges of the reference values, which were calculated following the boundary setting protocol, are 0.2-0.3 mg L -1 (L-AL3) and 0.5-0.7 mg L -1 (L-AL4) for biomass and 1.5-1.9 µg L -1 (L-AL3) and 2.7-3.3 µg L -1 (L-AL4) for chlorophyll-a. The EQR values given in Table 8 were used to set the ranges of the class boundaries. Hence, only the absolute values are different within each lake type, whereas the EQR values are fixed. The final values for classifying lakes using phytoplankton biomass or chlorophyll-a are summarized in Table 9.

Discussion

The definition of type-specific reference conditions is a major prerequisite for the WFD compliant assessment of the ecological status of aquatic ecosystems. Reference conditions for phytoplankton require a clear description of the trophic state, which should have as little variability as possible within each type.

Trophic state

The trophic state as defined in this paper for deep lakes (L-AL3, mean depth >15 m) complies well with the general understanding of oligotrophy as a reference trophic state in most Alpine lakes [START_REF] Lawa | Gewässerbewertung -stehende Gewässer. Vorläufige Richtlinie für eine Erstbewertung von natürlich entstandenen Seen nach trophischen Kriterien[END_REF][START_REF] Premazzi | Lake management in Italy: the implications of the Water Framework Directive[END_REF][START_REF] Buraschi | Characterization of the Italian lake-types and identification of their reference sites using anthropogenic pressure factors[END_REF]. The situation is less clear for moderately deep lakes belonging to GIG type L-AL4. Whereas some lakes are currently or previously oligotrophic [START_REF] Hofmann | Seesedimente in Bayern: Waginger-Tachinger See, Diatomeenflora in Sedimentkernen August 2002[END_REF][START_REF] Kis | Kärntner Seenbericht[END_REF], historical and paleolimnological data provide evidence that others have been oligo-mesotrophic or mesotrophic prior to significant anthropogenic impact [START_REF] Frey | Längsee: A history of meromixis[END_REF].

A WFD compliant lake classification requires, however, an assessment base, which is more precise than a general description of the trophic state. (2007) appear, however, too high (L-AL3: 16 µg L -1 , L-AL4: 10.9 µg L -1 , other lake types not specified: 34.5 µg L -1 ). These discrepancies are probably owing to the different criteria for selecting reference sites, which were less strict in [START_REF] Cardoso | Phosphorus reference concentrations in European lakes[END_REF] than in the GIG work.

Validating the class boundaries

The class boundary between good and moderate status is doubtless the most critical one for the river basin management plans, since exceeding the G/M boundary forces the member states to set actions for improving the ecological status. A validation of the values was done using the TP -biomass response curves for several phytoplankton taxa, with sensitive Cyclotella species as the most important taxon. Cyclotella often dominates in nutrient poor Alpine lakes [START_REF] Wunsam | Cyclotella-taxa (Bacillariophyceae) in lakes of the Alpine region and their relationship to environmental variables[END_REF][START_REF] Schaumburg | Ökologische Typisierung des Phytoplanktons[END_REF] and may reach a relative proportion of annual mean total biomass of up to 95% in single years and about 2/3 for lake annual means. A decline of the relative proportion of Cyclotella to ≤20% corresponds to a total biomass of about 1 to 2 mg L -1 . The boundary set for L-AL3 lakes lies well within this range.

Another approach for validating the boundary setting is the detection of significant undesirable disturbances in the condition of other biological quality elements and the physicochemical quality of the water or sediment. There are numerous examples from Alpine lakes in the literature, such as the decline of macrophytes, especially of charophytes and reeds (e.g. [START_REF] Deufel | Veränderungen der Schilf-und Wasserpflanzenbestände im Bodensee während der Eutrophierung und ihre Auswirkungen auf die Fische[END_REF][START_REF] Lachavanne | Les macrophytes du lac de Morat[END_REF][START_REF] Schroeder | Decline of reed swamps in Lake Constance[END_REF][START_REF] Melzer | Seelitorale in Bayern, Chiemsee. Makrophyten-Kartierungen 1985 und[END_REF], and of white fish, Coregonus spp., and arctic charr, Salvelinus umbla (L.), with increasing eutrophication [START_REF] Brutschy | Gutachten über den Rückgang des Fischbestandes im Hallwilersee[END_REF][START_REF] Stadelmann | Die Zustandsentwicklung des Baldeggersees (1900 bis 1980) und die Auswirkung von seeinternen Maßnahmen[END_REF][START_REF] Hartmann | Fecundity of whitefish (Coregonus lavaretus) during the eutrophication and oligotrophication of Lake Constance[END_REF][START_REF] Gassner | Die Fischartengemeinschaften der großen österreichischen Seen[END_REF]. In some lakes touristic use was heavily affected by Planktothrix blooms in the 1970s [START_REF] Schulz | Der Millstätter Seelimnologische Langzeitentwicklung 1970-2002[END_REF]. Nevertheless, these examples of 'undesirable conditions' can only be used for validating, but not for definitively setting the class boundaries, since the responses remain more or less descriptive in most papers and reports. The interactions between phytoplankton and other biological quality elements can vary a lot and in many cases, they are not well understood and/or quantified. Besides, they are often different in phases of eutrophication and re-oligotrophication (Dokulil et al., 2001;[START_REF] Anneville | Recovery of Lake Geneva from eutrophication: quantitative response of phytoplankton[END_REF].

Weak correlations were found also for other tools for selecting reference values and setting class boundaries. Pressure criteria such as land use (using Corine land cover data) and population density equivalents were poorly correlated with trophic state, maybe because none of them include information about sewage treatment for point sources in the catchment area.

A simple site-specific predictive model based on the morpho-edaphic index MEI [START_REF] Vighi | A simple method to estimate lake phosphorus concentrations resulting from natural background loading[END_REF] was used by [START_REF] Cardoso | Phosphorus reference concentrations in European lakes[END_REF] for defining total phosphorus concentrations under reference conditions of European lakes. According to the authors, the MEI compared favourably to more sophisticated predictive models. In the data set used for this paper, it turned out to be of limited use. Since the MEI regression of [START_REF] Vighi | A simple method to estimate lake phosphorus concentrations resulting from natural background loading[END_REF] estimated significantly higher TP concentrations for several (ultra-)oligotrophic lakes than are currently present, the MEI approach to defining reference status and setting boundaries was therefore considered as being not precautionary enough and was thus not pursued further.

Reference values

The reference values proposed in this paper are of the same magnitude as those published for comparable lakes in Europe by [START_REF] Carvalho | Chlorophyll reference conditions for European lake types used for intercalibration of ecological status[END_REF] as an outcome of the REBECCA project. The chlorophyll-a reference value of deep Alpine lakes was 2.8 µg L -1 in the analysis of [START_REF] Carvalho | Chlorophyll reference conditions for European lake types used for intercalibration of ecological status[END_REF] and thus slightly higher than those proposed for L-AL3 lakes in this paper (Table 8). This discrepancy comes mainly from the different and much smaller data set used by [START_REF] Carvalho | Chlorophyll reference conditions for European lake types used for intercalibration of ecological status[END_REF]. It included only lakes from Germany and focussed on the mean of the vegetation season, whereas the annual mean is used in this paper. In the GIG data set, the mean phytoplankton biomass in the period from March to November was 5.3%

(± 1.3%, 95%C.L.) higher than the annual mean, the mean for the period April to October differed even by 9.3% (± 2.2%).

In other GIGs, reference values similar to those proposed for Alpine lakes have been found in oligotrophic northern European lakes, in contrast to the significantly higher values in moderately deep and shallow lakes in the Central-Baltic region (EU Commission, 2008). In comparable lakes in the United States, chlorophyll-a reference values of 1.9 µg L -1 (ecoregion II, Western forested mountains), 2.4 µg L -1 (ecoregion VIII, Nutrient poor largely glaciated upper Midwest and Northeast) and 2.8 µg L -1 (ecoregion XI, Central and Eastern forested uplands) were defined (U.S. EPA, 2000a,b,c). These values are broadly similar to those proposed for L-AL-3 and L-AL4, although the setting of the reference values was done in a different way (viz. at the 25% percentile of all values occurring in the data set).

Methodological constraints and future prospects

Apart from the boundary setting protocol, which is described in this paper, there are two aspects which strongly influence the confidence of the values: lake types, and sampling and analytical methods. Differences between sites within each of the two lake types of the Alpine GIG are probably well covered by the ranges of reference values and class boundaries as defined for L-AL3 and L-AL4.

An unknown proportion of variability, however, is owing to methodological differences in sampling (e.g., frequency, sampling depth) and analytics (e.g., counting method). The fact that there are differences in methods is not surprising facing the long period the data come from. It was tried to minimize uncertainties due to these methodological differences in the selection of the sites, which were included in the analyses.

The monitoring programs carried out in each of the Alpine countries will improve the data base by providing not only more data, but data that will bear less methodological uncertainties since they will increasingly follow international standards in sampling and analytics. Within a few years it will be possible to re-calculate reference values and class boundaries with higher confidence.

Conclusion

The protocol to define reference conditions and set boundaries as proposed by the Alpine GIG within the IC exercise and described in this paper proved to be useful and applicable. It Tables Table 1. IC lake types in the Alpine GIG. L-AL4 0.5-0.7 0.8-1.1 1.9-2.7 5.0-6.9 12.5-17.4

Type

L-AL3 1.5-1.9 2.1-2.7 3.8-4.7 6.8-8.7 12.5-15.8 Chlorophyll-a 2.7-3.3 3.6-4.4 6.6-8.0 11.7-14.6 22.5-26.7

[µg L -1 ] L-AL4

  One of the key criteria used to set reference values and class boundaries for phytoplankton biomass and chlorophyll-a are the TP threshold values. These values are based on an extensive literature review on the relationship between nutrients and phytoplankton in Alpine lakes and supported by the modelling approach shown in Fig. 1. They are thus consistent with the normative definitions of the WFD.The median TP values and the TP range given in[START_REF] Cardoso | Phosphorus reference concentrations in European lakes[END_REF] for Alpine lakes also support these threshold values. They were derived independently from the Alpine GIG work using a different data set of 19 reference L-AL3 and 5 L-AL4 sites. Different to the median values, the maximum TP values for Alpine reference lakes given in Cardoso et al.

  followed a broad approach including historical, paleolimnological and monitoring data, but included also expert judgement and the experience of several decades of limnological research in Alpine lakes. The response of sensitive taxa to increased nutrient levels as well as 'undesirable conditions and secondary effects' (as described in Annex V in the WFD) was used to validate the boundaries.The values proposed here are partly implemented in national law (e.g.[START_REF] Dokulil | Leitfaden zur Erhebung der Biologischen Qualitätselemente, Seen. Teil B2-01d -Phytoplankton[END_REF] and form the basis for decisions within the national river basin management plans as required by the WFD. The intercalibration between the five Alpine EU member states was thus an important step towards a harmonization of the common understanding of 'Good Ecological Status'. A second step has been made by starting the intercalibration on the taxonomic composition of phytoplankton. The final intercalibration outcome -with both biomass/chlorophyll-a and taxonomic composition based trophic indices included -is expected in 2010.

Table 2 .

 2 Database of Alpine lakes used for the calculations. For lake types see Table1.

			L-AL3			L-AL4		<0.5 km 2			Total
		Lakes Sites Site-years	Lakes Sites Site-years	Lakes/Sites Site-years	Lakes Sites Site-years
	FR	12	14	41	5	5	5			17	19	46
	IT	11	19	64	12	13	26			23	32	90
	GE	16	18	138	23	23	70			39	41	208
	AT	22	25	320	22	22	223	15	53	59	62	596
	SI	2	2	19						2	2	19
	CH	4	5	6						4	5	6
	Total 67	83	588	62	63	324	15	53	144 161	965

Table 4 .

 4 Specific criteria for selecting reference sites. The total phosphorus (TP) concentration is calculated as volume weighted annual mean or as volume weighted spring overturn concentration. Both the annual mean and the spring concentration have to remain below the suggested threshold value over at least three subsequent years.

	Criteria	Requirement
	Historical data Prior to major industrialisation, urbanisation and intensification of
		agriculture
	Anthropogenic	Insignificant contribution to total nutrient load
	nutrient load
	Trophic state	No deviation of the actual from the natural trophic state
		Natural trophic state of L-AL3: oligotrophic (threshold value for the pre-
		selection of reference sites: TP ≤8 µg L -1 )
		Natural trophic state of L-AL4: oligo-mesotrophic (threshold value for the
		pre-selection of reference sites: TP ≤12 µg L -1 )

Table 5 .

 5 Reference sites from Alpine lakes belonging to IC lake type L-AL3 and L-AL4, based on historical data. MS = member state of the Alpine GIG (AT = Austria). BM = total phytoplankton biomass, N = number of years available for each site. Due to methodological uncertainties, the data from[START_REF] Ruttner | Ökotypen mit verschiedener Vertikalverteilung im Plankton der Alpenseen[END_REF] are treated as one data set (site) in the analyses.

	MS Lake	IC	Mean	Year(s)	BM	N lake
		type	depth [m]		[mg L -1 ]	years
	AT Millstätter See	L-AL3	89	1932-1938	0.32	7
	AT Ossiacher See	L-AL3	20	1932-1938	0.29	7
	AT Weißensee/AT	L-AL3	37	1932-1934	0.15	21
	AT Wörthersee	L-AL3	42	1931-1938	0.29	8
	AT data from Ruttner (1937)	L-AL3	20-65	1931-1932	0.26	8
	AT Faaker See	L-AL4	16	1931-2004	0.32	5
	AT Längsee	L-AL4	13	1934-1935	0.86	2

Table 6 .

 6 Reference sites from Alpine lakes belonging to IC lake type L-AL3 and L-AL4, based on the criteria in Table3 and 4. MS = member state of the Alpine GIG (AT = Austria, FR = France, GE = Germany, IT = Italy, SI = Slovenia), TP = total phosphorus concentration [µg L -1 ] (volume weighted annual mean or concentration during spring overturn). The last two columns give the number of lake years, where biovolume data were available, as well as the mean phytoplankton total biomass BM for these years. n.a. = no data available or site not regarded for other reasons (e.g., too few sampling dates per year).

	MS Lake	IC	Mean	TP	Year(s)	BM	N lake
		type	depth [m]	[µg L -1 ]		[mg L -1 ]	years
	GE Alpsee bei Füssen	L-AL3	28	5	2001	0.36	1
	AT Altausseer See	L-AL3	35	4	1983-2003	0.19	2
	AT Attersee	L-AL3	84	3	1989-2003	0.20	4
	SI Bohinjsko jezero	L-AL3	28	<5	1997-2005	0.15	1
	AT Fuschlsee	L-AL3	37	6	1997-2000	0.60	4
	AT Grundlsee	L-AL3	41	3-4	1981-2003	0.11	2
	AT Hallstätter See	L-AL3	65	9	2002-2003	0.06	2
	GE Königssee	L-AL3	98	5	2000	0.44	1
	AT Lunzer See	L-AL3	20	4-7	1979-1981	0.29	3
	GE Obersee/Berchtesgaden	L-AL3	30	6	2000	0.51	1
	GE Tegernsee	L-AL3	36	7	1991-1992	0.48	2
	GE Walchensee	L-AL3	81	4	1995-2003	0.31	2
	AT Weißensee/AT	L-AL3	37	5	1987-2004	0.34	18
	AT Zeller See	L-AL3	38	6	1999-2000	0.49	2
	GE Bannwaldsee	L-AL4	6	10	1997-2001	0.70	4
	AT Faaker See	L-AL4	16	6	1987-2004	0.37	18
	AT Feldsee	L-AL4	15	9	2000-2004	0.77	5
	AT Irrsee	L-AL4	15	8	2002-2003	0.59	2
	AT Keutschacher See	L-AL4	10	9	2000-2003	0.85	4
	GE Lustsee	L-AL4	6	6	1996-2000	0.35	5
	AT Magdalenensee	L-AL4	3	8	2000-2004	1.14	3
	AT Mattsee	L-AL4	17	10	1997-2000	0.29	4
	AT Pressegger See	L-AL4	3	5	2001-2004	0.22	4
	AT Rauschelesee	L-AL4	6	11	2000-2004	0.84	5
	AT Turnersee	L-AL4	8	10	2000-2003	1.03	3
	GE Wörthsee	L-AL4	15	8	1993-2002	0.43	3

Table 7 .

 7 Statistics (minimum, median, arithmetic mean, percentiles) of the annual mean phytoplankton biomass [mg L -1 ] for Alpine lakes, calculated from pre-selected reference sites (Table5 & 6). Ref = reference value, H/G = high / good class boundary.

	IC lake type min median	mean	75%	90%	95%	max	N
			Ref		perc.	perc.	perc
							H/G
	L-AL3	0.06	0.30	0.31	0.42	0.49	0.52	0.60	18
	L-AL4	0.22	0.70	0.65	0.85	0.99	1.07	1.14	13

Table 8 .

 8 Reference values, class boundaries and EQR (ecological quality ratio, in italics) for the annual mean total biomass [mg L -1 ] and the annual mean chlorophyll-a concentration [µg L -1 ] in Alpine lakes. H/G = class boundary high/good status, G/M = good/moderate, M/P = moderate/poor, P/B = poor/bad.

	Parameter	IC lake type	Ref	H/G	G/M	M/P	P/B
	Total biomass	L-AL3	0.3	0.5	1.2	3.1	7.8
	[mg L -1 ]	EQR	1.00	0.60	0.25	0.10	0.04
		L-AL4	0.7	1.1	2.7	6.9	17.4
		EQR	1.00	0.64	0.26	0.10	0.04
	Chlorophyll-a	L-AL3	1.9	2.7	4.7	8.7	15.8
	[µg L -1 ]	EQR	1.00	0.70	0.40	0.22	0.12
		L-AL4	3.3	4.4	8.0	14.6	26.7
		EQR	1.00	0.75	0.41	0.23	0.12

Table 9 .

 9 Ranges for reference values and class boundaries for the annual mean total biomass [mg L -1 ] and the annual mean chlorophyll-a concentration [µg L -1 ] in Alpine lakes. The EQR values given in Table8are fixed and apply to all reference values and class boundaries.

	Parameter	IC lake type	Ref	H/G	G/M	M/P	P/B
	Total biomass	L-AL3	0.2-0.3	0.3-0.5	0.8-1.2 2.1-3.1	5.3-7.8
	[mg L -1 ]

Acknowledgements

The authors thank the data owners and providers of chemical and biological data (Gisela Ofenböck and Veronika Koller-Kreimel/BMLFUW, Peter Schaber/Amt der Salzburger Landesregierung, Ute Mischke/IGB, Hubert Gassner/BAW Scharfling, IGKB) for their cooperation in the establishment of the Alpine GIG phytoplankton intercalibration data set.

Thanks to the JRC, especially to Sandra Poikane, for accompanying the Alpine GIG during the whole IC exercise, and to numerous experts from other GIGs for fruitful discussions and constructive criticism.