1. General context and origins of the exercise

   A first IBD intercalibration project has been foreseen in the frame of the activities of CEN/TC 230 WG2/TG3 " Macrophytes and Benthic Algae ". This project presents a big interest considering the setting in France in the year 2000 of an accreditation programme for hydrobiological laboratories by the Comité Français d’Accréditation (French Accreditation Committee = COFRAC). This procedure aims several biological indexes among which the Biological Diatom Index (IBD) which is subject to an authorised standard (AFNOR T 90-354) and a complete methodological guide conceived and edited by the Agences de l’Eau and the Cemagref. The IBD accreditation programme relies for a big part on the IBD standard, on specific requirements (procedures of internal control, traceability …) and on specific regulations (determination works, regular practice of the IBD by the personnels …). A participation to intercalibration exercises is recommended to accredited laboratories or candidate for accreditation. That’s why the Group of Scientific Interest (GIS = Groupement d’Intérêt Scientifique) " Diatoms of Continental Waters ", created in June 1999 (Prygiel and Ector, 2000), has proposed to carry on the big lines of the French-British initial project discussed in Lisbon in April 1998 and proposed in April 1999 in The Hague.

   A first intercalibration exercise was so organized during the 18° seminar of the Association des Diatomistes de Langue Française (ADLaF) which was held in Nice from 14 to 17 September 1999. This exercise was based on the data acquisition on the field, the preparation of observation slides, the realization of inventories, and the IBD calculation.

2. Researched objectives during this exercise

The principal objective of this intercalibration exercise is to estimate the variability of the Biological Diatom Index (IBD) at different stages of the methodology, since the sampling on field to the index calculation to try to answer to different questions :

1. Do several samplings, which are done in identical conditions on a same station, give the same results (inventories, relative abundances, index values) ?
2. Do several preparations done from a same sampling or from several samplings realized in identical conditions give the same results ?
3. Do inventories done on different slides issued from one or several samplings give a same qualitative and quantitative composition ?
4. Do calculated indexes from inventories realized from several samplings or from slides from a same sample give the same values ?
5. Which is the variability part due to the operator in the index calculation ?
6. Which is the " natural " IBD variability and which can be the consequence in term of biological classification by quality classes thresholds ?

    

7. Realization of the exercise

The intercalibration exercise has been organized and led by the Group of Scientific Interest (GIS) " Diatoms of Continental Waters " and co-ordinated by Jean Prygiel (Agence de l’Eau Artois-Picardie, France), Luc Ector (Centre de Recherche Public Gabriel Lippmann, Luxemburg) and Henri Vidal (Conseil Général des Alpes Maritimes, France). The sampling was realized on the river Loup on 15^th September 1999 at the place called " Le Colombier ", situated on the commune of Gourdon, at 1 km upstream of the gorges of the Loup.

1. Participants

   A total of about 30 searchers was present at the 18° seminar of the ADLaF in Nice, and interested in this problematic they agreed to contribute to the intercalibration. Have actively participated to this exercise diatomists from most of the regions of France and several neighbouring european countries (Belgium, Spain, Italy, Grand Duchy of Luxemburg, Portugal, Switzerland) : Salomé Almeida (Aveiro, Portugal), Nathalie Borel-Nouchet (Angers, France), Arlette Cazaubon (Marseille, France), Michel Coste (Bordeaux, France), Jean-Claude Druart (Thonon-les-Bains, France), Luc Ector (Luxembourg, Grand-Duché de Luxembourg), Claude Fauville (Namur, Belgique), Didier Guillard (Nantes, France), Marie-Ange Honoré (Lille, France), Robert Iserentant (Louvain-la-Neuve, Belgique), Louis Leclercq (Robertville, Belgique), Pieter Ledeganck (Anvers, Belgique), Christian Lalanne-Cassou (Cachan, France), Maria Leitao (Angers, France), Christophe Lesniak (Douai, France), Anna Maria Mannino (Palermo, Italie), Philippe Moncaut (La Bohalle, France), Maxence Nazart (Nantes, France), Valérie Peeters (Dijon, France), Florence Peres-Weerts (Boulogne-sur-Gesse, France), Jean Prygiel (Douai, France), Alain Rumeau (Ressons-sur-Matz, France), Sergi Sabater (Barcelone, Espagne), François Straub (La Chaux-de-Fonds, Suisse), Mariacristina Torrisi (Camerino, Italie), Rosa Trobajo Pujadas (Girona, Espagne), Loïc Tudesque (Luxembourg, Grand-Duché de Luxembourg), Bart Van de Vijver (Anvers, Belgique), Andy Van Kerckvoorde (Anvers, Belgique), Henri Vidal (Nice, France), Jessica Vizinet (La Varenne, France), Florence Zurstrassen (Robertville, Belgique).

2. Site characteristics

   The river Loup is a coastal river of a length of 48 km which takes its source at an altitude of 1240 m in the commune of Andon at the foot of the Massif of Audibergue and which flows on a well developed karstic set and constituted by Jurassic limestones. The surface of the hydrographic basin is of 283 km_. The river Loup flows through 11 communes before joining the Mediterranean at Villeneuve-Loubet. Until Pont de Loup, situated just downstream of the sampling site, the river Loup is a torrent presenting an average fall of 3,4 ‰ and going through deeply embanked gorges. In its downstream course, its average fall is only of 0,9 ‰.

   In 1994, this mediterranean river has been the subject of a detailed hydrobiological study, from the source to the mouth, dealing with chemical parameters and samplings on fauna and flora (Conseil Général des Alpes Maritimes, 1995). For the studied area, the average annual flow is of 2,1 m³/s, while the smallest average flow calculated on 30 consecutive days is close to 1 m³/s. Water of the river Loup is alkaline (pH between 7,8 to 8,6), rather fresh (14 to 20° C), distinctly mineralized (350 to 780 µS/cm near the mouth) and well oxygenated. The nitrogen and phosphorus concentrations are weak. In the study area, the river Loup records a chemical quality class 1A according to the water quality grid used by the Agence de l’Eau Rhône-Méditerranée-Corse (excellent water quality), confirmed by the Specific Polluosensitivity Index IPS (updated version of Omnidia v3) close to 17/20.

3. Terms and conditions of the exercise

The intercalibration has carried on following aspects : sampling, counting, determination and IBD calculation. A project of the IBD standard (NF T 90-354) and the final project of the determination keys illustrating the 209 taxa taken into account in the IBD calculation (extract of the methodological guide for the implementation of the Biological Diatom Index (Agences de l’Eau-Cemagref, 2000) have been transmitted to all participants. The IBD calculation programme can be loaded freely by everyone at the following internet address : http://perso.club-internet.fr/clci/decharge.htm

The intercalibration exercise has included 2 phases :

1. Each participant has realized 3 samplings. For each sample, 3 slides were prepared and for each slide 3 inventories counting 400 individuals were requested. According to the participants (scientifics, managers, research offices), identifications have been pushed to the species, at the identification level required for the IBD calculation or at an intermediate identification level. Each one has thus realized 27 diatomic inventories (3 samples x 3 slides x 3 inventories).
2. Each participant has also received a " witness " slide realized from a unique sample collected by Loïc Tudesque (CRP Gabriel Lippmann, Luxemburg). This second phase should allow seeing if significant differences do exist in the floristic lists and in the IBD calculation for inventories realized by different operators from slides issued from the same sample.
3. Results exploitation

The results (inventories and IBD values at Omnidia format, Excel or paper format), the samples and slides have been centralized in a confidential way by the Agence de l’Eau Artois-Picardie for data analysis.

The deadline for reception of the inventories has been fixed to 31^st March 2000 for a first restitution during the Symposium " Use of Algae for Monitoring Rivers IV " which will be held in Durham in July 2000. And a discussion in the form of a communication and/or a round-table conference with the majority of the 30 participants of this first intercalibration exercise will be held during the 19° seminar of the ADLaF in Robertville (Mont-Rigi) in Belgium, in September 2000.