摘要：Variations of δ 13 C and δ 15 N in dissolved organic matter and size-fractionated plankton, ranging from 0.7 to 200 μm, were studied in Taihu Lake on two occasions during a cyanobacterial bloom. Paired-sample t-tests indicated that stable isotope ratios of samples collected did not significantly differ from each other on the two sampling dates. The overall correlation between δ 13 C and δ 15 of forty taxa of the plankton community was weak (r 2 =0.227, N=40), indicating a non-trophic enrichment effect in δ 13 C. The δ 15 N values increased along with plankton size. We used δ 15 as an index of the trophic level and demonstrated that logarithmic organism size was positively and significantly related to trophic level, indicating that a size-dependent approach is preferable in the analysis of trophic isotope enrichment in microplankton food webs.
