Effects of eutrophication and fish yield on the diatom community in Lake Fuxian, a deep oligotrophic lake in southwest China

This study investigated the effects of eutrophication and fish yield on the diatom community of Lake Fuxian by examining changes in species composition and abundance in sediment cores dating back 172 years. In the 1950s, four Chinese carp species were introduced into Lake Fuxian (an oligotrophic plateau lake) to enhance fish production, followed by a further introduction in the 1980s of the planktivorous fish, Neosalanx taihuensis, which then became dominant. The total fish yield increased about threefold. Although the lake remains oligotrophic, it has received an increased nutrient loading from the increase in human activities in the drainage basin. Our results show that the absolute abundance of total diatoms increased substantially after the late 1950s when there was also a change in the community composition with the appearance of Cyclotella ocellata, Fragilaria crotonensis, Stephanodiscus hantzschii, Aulacoseira granulata, Stephanodiscus minutulus and Cyclostephanos dubius at the same time as a decline in the absolute abundance of the previously dominant species before 1950, Cyclotella rhomboideo-elliptica. Our study indicated that eutrophication was the most important factor affecting diatom community composition and abundance but that fish introductions have also been an additional factor.