Population dynamics of three gammarid species (Crustacea, Amphipoda) in a French chalk stream. Part I. General aspects and environmental factors

This paper is the first of a series of four, it describes the general outline of a research project on the ecology of Gammarus pulex pulex (Linnaeus, 1758), G. fossarum Koch in Panzer, 1836, and Echinogammarus berilloni (Catta, 1878) in a small French chalk stream, the Slack. The entire study investigates the impact of (changes in) environmental factors on standing crop and migration of these three freshwater gammarids. An account is given of biological and physicochemical research methods used. Special methods to capture both drifting and upstream migrating gammarids were developed. In this first part, data on environmental factors are presented with an emphasis on the seasonal and microgeographic variation they show in this river. Detailed information about the diel variation of some environmental factors is given. After mathematical treatment of the data on environmental factors the Slack is classified in four zones: an unstable headwater, a large stable upper/middle region, a rather polluted lower region and an estuarine part.