Typical scaled food web structure and total mercury enrichment characteristics in Xingkai Lake, China.

Abstract

Different from the widely used constant discrimination factor Δ15N = 3.4‰ between two adjacent trophic positions (TPs), a scaled Δ15N framework for evaluating the TP of species was developed in 2014, that is, the Δ15N between two adjacent TPs decreases as the TP increases which is considered to be in closer conformity to the trophic cascade in the natural food web. In this study, we compared the two TP calculation methods and then reconsidered the evaluation of the trophic magnification factors (TMFs). Our results show that the TPscaled value is higher and the TMFs value is lower under the scaled Δ15N framework, indicating that the TMFs value under the constant Δ15N framework is often overestimated. We further constructed a diet proportion food web model, which shows that species with lower TP has higher contribution rate as food sources. In Xingkai Lake, the enrichment process of mercury in the food web is not strictly consistent with the diet proportion of the food web. Based on the diet proportion food web model and the mercury enrichment model, it can be found that the White shrimp (Exopalaemon modestus) is not only an important food source, but also the main source of mercury transmission in the food web. Overall, our findings have quantified the food web construction and thus facilitated a better understanding of the interaction between the diet proportion and the bio-concentration in the food web.