Potential influence of water level changes on energy flows in a lake food web

Yuyu Wang,Jun Xu,Yuwei Chen,Xiubo Yu,Wenhua Li,Na Fan

doi:10.1007/s11434-011-4649-y

Abstract

Large seasonal water-level fluctuations may influence isotopic signatures of primary producers and the types and amounts of these potential food sources accessible to aquatic fauna of Poyang Lake, the largest freshwater lake in China. In this study, the isotopic signatures of primary producers and consumers were determined, stable carbon and nitrogen isotope analysis and mixing models were combined to investigate the influence of water levels on the diet and isotopic composition of Poyang Lake fish and invertebrates. Five potential food sources (seston, benthic organic matter, aquatic macrophytes, attached algae, and terrestrial plants), 4 species of invertebrates, and 10 species of fish were collected from the lake area during dry and wet seasons between January 2009 and April 2010. The δ 13C values of invertebrates and most fish were within the range of δ 13C values of the potential food sources for both seasons. The δ 13C values of invertebrates and most fish were lower in the dry season than in the wet season, whereas the δ 15N values exhibited different patterns for different species. Mixing models indicated that the most important food sources for common lake fauna were seston in the dry season and aquatic macrophytes and terrestrial plants in the wet season. The fauna were more omnivorous in the wet season than in the dry season. The food web dynamics of Poyang Lake are strongly influenced by changes in the abundance and accessibility of different basal food sources that occur because of seasonal flood pulses. The trophic links within the aquatic communities of Poyang Lake are modified by water-level fluctuations.

Highlights

The mechanism by which energy and materials are transferred from the bottom to the top of food webs is important in ecosystem studies because it has a marked influence on trophic interactions, community structure and ecosystem processes [1,2] and modifies major ecosystem functions, such as nutrient cycling and primary productivity [3]
354 consumer and 338 basal-source samples collected during dry and wet seasons were analyzed for their carbon and nitrogen isotope ratios, respectively
Terrestrial plants were more 13C depleted compared with other potential food sources collected from Poyang Lake, whereas aquatic macrophytes were relatively enriched in 13C (−21.1‰ in the dry season vs. −21.4‰ in the wet season) (Figure 3)

Summary

Introduction

The mechanism by which energy and materials are transferred from the bottom to the top of food webs is important in ecosystem studies because it has a marked influence on trophic interactions, community structure and ecosystem processes [1,2] and modifies major ecosystem functions, such as nutrient cycling and primary productivity [3]. Determining the major basal food sources for lacustrine food webs is a major challenge because of the diversity in primary producers and the complex mobility of consumers. This problem has been greatly facilitated by measurement of stable carbon and nitrogen isotope ratios (δ 13C and δ 15N) to identify carbon sources and understand trophic relationships in aquatic food webs [11,12,13,14,15,16]. The aim of this study was to assess how water-level changes influence the food webs in Poyang Lake. The relative importance of the most significant basal production sources supporting fish and invertebrates were examined using a mixing model

Objectives

Methods

Results

Discussion

Conclusion