Three-year Survey of Nitrogen Dynamics in a Stratified Reservoir of the North China Plain

Abstract

Freshwater ecosystem health and water supply safety are under severe threat due to the recent increase in anthropogenic nitrogen. Therefore, this study investigated the seasonal variation and vertical distribution of nitrogen and other environmental factors from April 2012 to April 2015 in the Zhoucun Reservoir. The results show that nitrate was the primary nitrogen species in the entire water column except the hypolimnion, where ammonium dominated. Total nitrogen fluctuations were larger in near-surface water, with a range of 0.38–3.11 mg/L. Nitrate concentrations were homogeneous throughout the water column and experienced a clear decline in spring. In contrast, ammonium was in stratification from May to October. Surface ammonium reached a maximum in the high flow period during summer, while bottom ammonium remained high throughout stratification. Our results suggest that aerobic denitrification and nitrogen load from inflow rivers were the main processes that affected surface nitrogen content, while bottom nitrogen content was primarily affected by anaerobic denitrification and nutrient release from sediment. Of the measured environmental factors, water temperature, water residence time, dissolved oxygen, rainfall, and total phosphorus were the most critical in affecting nitrogen content. Our field surveys show the effects of complex process and environmental factors on the dynamics of nitrogen in the lacustrine zone of the reservoir, helping people understand and predict nitrogen dynamics in temperate, stratified lentic waters. Based on our results, the water resource managers can select suitable measures to control the eutrophication.