diatom database

1- Diatom sampling and analysesDiatoms were sampled as part of the national biomonitoringprogram for rivers. The sampling procedure followed the French standard (Afnor, 2007). Diatoms were collected once per year, during the low-flow period. Benthic diatoms were collected from at least five stones from the lotic parts of the sampling sites. The upper surfaces of the stones were scrubbed with a toothbrush to collect the biofilms in which diatoms live. Then the sample was fixed in 4% formaldehyde. In laboratory, the diatom valves were cleanedusing 40% H2O2 and HCl. Clean valves were mounted in a resin (Naphrax©). At least 400 valves from each sample were counted and identified using a light microscope (1000× magnification) according to European (European Committee for Standardization, 2004) and French (Afnor, 2007) standards. The abundances of all observed taxa were expressed as relative counts. Identifications were carried out using Krammer and Lange-Bertalot (1986–1991) to species and sub-species level.<br>2- Physical and chemical sample analysesPhysical and chemical analyses were carried-out at the same sampling sites every month. Dissolved oxygen and conductivity were measured in the field. For NO3−, NH4 +, Kjeldahl nitrogen (TKN), PO43−, Na+, Ca2+, Cl−, K+, Mg2+, SO42−, Biological-Oxygen-Demand (BOD), Chemical-Oxygen-Demand (COD), water samples were collected and analysed in the laboratory according to standard procedures (APHA, 1995).