On the study of phytoplankton spatial structure of Eastern Siberia large rivers

The problem what factors determine the spatial structure of algal communities is widely discussed in the modern literature. We accumulated a significant amount of data on phytoplankton and physical and chemical structure of waters of the large rivers of Eastern Siberia. The aim of this study is to identify the basic regularities of spatial organization of planktonic algal communities of Arctic and subarctic oligotrophic rivers. We analyzed data on gathered plankton and hydrochemistry of 12 large rivers: Lena, Vilyui, Kolyma, Aldan, Olenek, Vitim, Indigirka, Amga, Olekma, Anabar, Yana and Chara. The analyzed data set includes parameters of phytoplankton (species composition, density, biomass and some taxonomic ratios) and the environment (climatic, hydrological and hydro- chemical parameters). Results of cluster and logit regressive analysis of the data testify that among phytoplankton indicators the greatest relationship with factors of environment shows the floristic structure (floristic proportions: species/families, subspecies/families, species/genera, subspecies/genera). Decrease in floristic proportions on gradient of strengthening of ecological conditions severity (from south to north) is established. Formation of spatial structure of phytoplankton of the rivers of the investigated region occurs mainly under the influence of climate conditions (water and air temperature, DHI) and hydrology (duration of ice-free period). The transparency of water does not show any relation with phytoplankton development, since this is unstable factor rapidly changing in the rivers of the region after heavy rainfall or at confluence of tributaries. Indicators of physical and chemical structure of water also do not show any significant relation with algal development, and accordingly have no regulating role in formation of spatial structure of phytoplankton. The reason is that there is no considerable environmental gradient on these parameters.