Seasonality of stable carbon and nitrogen isotopes within the pelagic food web of Taihu Lake

Abstract

Particulate organic matter (POM), dissolved organic matter (DOM), bacteria and cladoceran were sampled seasonally at Zhihugang Estuary and Lake Center in Taihu Lake. The δ 13 C of the four organic matter fractions showed consistent temporal variation, with heaviest values in summer and lower at other times of the year. The cladoceran δ 13 C showed a significant correlation with that of POM, reflecting a heavy dietary dependence on POM during the study period. The bacteria became enriched in 13 C compared with that of DOM throughout the sampling dates, although no significant relationship was found between the two fractions. δ 13 C values of POM, cladoceran and bacteria were all negative significantly correlated with oxidation and reduction potential (ORP), and specific conductivity (SpCond). As for δ 15 N, the seasonal pattern of food web components was variable. The POM δ 15 N signature exhibited the most enriched isotope ratios during the summer months when dissolved inorganic nitrogen (DIN) nutrients were at their lowest concentrations. The consumption of DIN in summer can explain in part the progressive accumulation of heavy nitrogen isotopes during this period. Spatially, δ 13 C and δ 15 N of the food web components were all slightly depleted at Estuary than that at Lake Center during the study period, possibly due to large allochthonous inputs at Zhihugang Estuary. Relatively wide ranges of stable isotopic values from both sites suggest that seasonality should be considered when attempting to establish food web structures in a eutrophic lake.

Latitudinal gradients in biotic niche breadth vary across ecosystem types

“…Further, both temperate streams and lakes tend to experience seasonal strong pulses of allochthonous inputs (e.g. fallen leaves, terrestrial invertebrates [46][47][48]). These trends combined mean that, relative to estuarine and marine communities, freshwater food webs may experience high turnover in both community composition and productivity [49][50][51].…”

Depth‐specific and spatiotemporal variation of δ13C and δ15N in Charophytes of Lake Constance: implications for food web studies

“…[6] Food-web studies in lakes often focus on the pelagic habitat. These studies have demonstrated that the stable isotope ratios at the base of food webs often vary seasonally [7][8][9] and spatially within and between lakes. [10] For example, studies on algae demonstrated large changes in δ…”

Patterns and controls of nitrogen stable isotopes of particulate organic matter in subtropical lakes

“…In addition, the 15 N enrichment in eutrophic lakes may also be due to the contributions of urban wastes from surface runoff which is an important source of nitrogen to lakes (Carpenter et al, 1998) and is typically enriched with 15 N. For example, Lake Taihu in central China is a large urban lake influenced by high human population in the watershed. Anthropogenic disturbances to this lake can be illustrated by high d 15 N of DIN and POM (Xie et al, 2007;Zeng et al, 2008). Savage (2005) Figure 4 may be due to the presence of microzooplankton and/or inputs from human wastes.…”