Using Isotopes to Identify the Sources of Organic Carbon and Nitrogen in Surface Sediment in Shallow Lakes Alongside Poyang Lake

Water exchange in shallow lakes alongside Poyang Lake is weak because of sluggish water flow, and thus these lakes are susceptible to the effects of human activities and nutrient oversupply. Therefore, it is meaningful to study the sources of organic matter in these lakes, which is supposed to provide theoretical basis for the control of eutrophication of the lakes. The sources of organic matter in surface sediment in shallow lakes (Bang, Sha, Dahuchi, and Zhu lakes) alongside Poyang Lake and urban lakes (Qingshan and Xiang lakes) in Nanchang City were investigated by measuring the δ15N and δ13C values, total organic carbon and total organic nitrogen contents, and C/N ratios of sedimented organic matter (SOM). The δ15N, δ13C, and C/N ratios indicated that SOM in Sha and Dahuchi lakes mostly originated in phytoplankton, SOM in Bang and Zhu lakes was supplied by phytoplankton and soil organic matter, SOM in Qingshan Lake was strongly affected by sewage organic matter, and SOM in Xiang Lake mainly came from aquatic macrophytes. The results demonstrate that stable isotopes in SOM in lakes can be used to discriminate between different sources of organic material.