Eutrophic Status and Functional Genes Responsible for Nitrogen Cycling in the Sediment of the Sheyang Lake

To evaluate the environmental quality of the Sheyang Lake National Aquatic Germplasm Reserve, the seasonal changes in water quality at the sampling stations from May 2018 to February 2019 were monitored. Eleven sampling stations were distributed in the periphery (S1-S6) and core area (S7-S11) of the reserve. Several representative stations were selected to monitor the carbon, nitrogen and sulfur contents and the abundance of nitrogen cycling functional genes in the sediment. Comprehensive trophic level index (TLI) method was used to assess water eutrophication status. The interpolation method was used to simulate the spatial-temporal variation of nitrogen and phosphorus concentrations. The relationship between nitrogen cycling functional genes and essential environmental parameters was examined. The results indicate that the Sheyang Lake was slightly eutrophia; the concentration of total nitrogen reached the maximum in winter(1.64 ±0.29) mg·L^-1, whereas the concentration of total phosphorus was the maximum in summer(0.21±0.13) mg·L^-1. They were the critical factors determining the grade of environmental quality. The abundance of denitrifying functional genes (e. g., narG and nirS) was relatively higher during the investigation. The abundance of nirS gene in summer was significantly higher than that in spring and in autumn (P < 0.05). These findings suggest that the sewage discharge and agricultural pollution might be responsible for the eutrophication problem in the Sheyang Lake. Thus, it is essential to initiate the control of rural environmental pollution sources as well as to encourage the development of eco-agriculture, so as the water quality can be improved and aquatic germplasm resources can be conserved.