Abstract
In order to protect the water quality of Dongting Lake, it is significant to find out its nitrogen pollution characteristics. Using long-term monthly to seasonally data (1997–2014), we investigated the spatial and temporal variations in nitrogen in Dongting Lake, the second largest freshwater lake in China. The average concentrations of total nitrogen (TN) in the eastern, southern, and western parts of the lake were 1.77, 1.56, and 1.35 mg/L, respectively, in 2014. TN pollution was generally worse in the southern area than in the western area. Concentrations showed temporal variation, and were significantly higher during the dry season than during the wet season. Based on the concentration and growth rate of TN, three different stages were identified in the long term lake data, from 1997 to 2002, from 2003 to 2008, and from 2009 to 2014, during which the concentrations and the growth rate ranged from 1.09–1.51 mg/L and 22.09%-40.03%, 1.05–1.57 mg/L and -9.05%-7.74%, and 1.68–2.02 mg/L and 57.99%-60.41%, respectively. The main controls on the lake water TN concentrations were the quality and quantity of the lake inflows, spatial and temporal variations in hydrodynamic conditions within the lake (flow velocity, flow direction), and point and nonpoint inputs from human activities. Diffuse nutrient losses from agricultural land are a significant contributor. As a priority, the local government should aim to control the pollutant inputs from upstream and non-point nutrient losses from land.
Highlights
Significant disturbances from anthropogenic activities over the past decades have accelerated the process of eutrophication and threatened the health of aquatic ecosystems [1, 2]
The spatial distribution of total nitrogen (TN) was more uniform in East Dongting (ED), while there were obvious concentration gradients in South Dongting (SD) and West Dongting (WD)
The TN concentrations decreased from the river inflows to the central area of the lake
Summary
Significant disturbances from anthropogenic activities over the past decades have accelerated the process of eutrophication and threatened the health of aquatic ecosystems [1, 2]. Excessive nutrient inputs are the main reason for lake eutrophication [3], and surplus nitrogen (N) is one of the main driving factors [4]. More than 80% of eutrophic waters in China suffer from serious N pollution [5, 6]. N concentrations distributions are related to the hydrodynamic conditions and anthropogenic input intensity in a river basin [7]. Most studies have identified that different industrial and agricultural activities under.
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