Food web structure of a shallow eutrophic lake (Lake Taihu, China) assessed by stable isotope analysis

Lake Taihu is a large, shallow, and eutrophic lake in China. It has provided local communities with valuable fisheries for centuries, but little is known of the trophodynamics, or of its faunal communities. Carbon and nitrogen isotopic composition was used to assess its trophic pathways and the food web structure [food sources and trophic levels (TL)]. Basal food sources were distinguishable based on their delta C-13 values, ranging from -27.2 to -15.2aEuro degrees. Consumers were also well separated in delta C-13 (-26.9 to -17.9aEuro degrees for invertebrates and -25.7 to -18.1aEuro degrees for fishes), which allowed for an effective discrimination of carbon sources between these fauna. An average trophic enrichment factor of 3.4aEuro degrees was used to calculate the TLs based on delta N-15 of zooplankton, with results indicating a food web having four TLs. Although delta N-15 values overlap and cover a large range within trophic compartments, the isotopic signatures of the species assessed revealed a general trend of N-15 enrichment with increasing TL. Stable isotope signatures were also used to establish a general food web scheme in which five main trophic pathways were analyzed.