Abstract
As one of the most widespread elements, nitrogen has been broadly concerned in water bodies. Understanding variations in nitrogen is of paramount importance to ecosystem stability and human health. The spatiotemporal variations in total nitrogen (TN) and ammonia in the Middle Route of the South-to-North Water Diversion Project (MRP) during the period from 2015 to 2019 were evaluated. The correlation between anthropogenic activities based on quantitative land use cover and nitrogen concentration was addressed. The results indicated that TN increased by 0.072 mg/L from south to north over the period (p < 0.05), but ammonia decreased by 0.018 mg/L (p < 0.05), notably, in five years. In addition, Chl a had the highest concentration in autumn, showing seasonal variation. The linear regression showed that ammonia concentration was significantly negatively correlated with Chl a (p < 0.1). Furthermore, as human activities’ intensity increased by 6‰ from 2015 to 2019, TN increased and ammonia decreased. The rhythm of meteorological conditions could also result in the variation in nitrogen, which affected N concentration in the MRP. The increase in construction land and agricultural land led to TN increase, and algae absorption was one of the reasons leading to the decrease in ammonia. It could be concluded that climatic changes and anthropogenic activities were the driving forces of nitrogen changes in the MRP. Thus, land use changes around the MRP should be the focus of attention to reduce the nitrogen concentration. This study is the first report on the nitrogen distribution pattern in the MRP. It could be useful to authorities for the control and management of nitrogen pollution and better protection of water quality.
Highlights
Nitrogen is an important component of ecosystems [1,2]
The results revealed that total nitrogen (TN) concentration was positively correlated with human activity intensity of land surface (HAILS)
TN and ammonia levels were higher in spring and summer than in other seasons
Summary
Nitrogen is an important component of ecosystems [1,2]. Excessive nitrogen can cause adverse effects on the environment, including soil acidification [5], loss of oxygen, and subsequent fish death [6]. A high concentration of nitrogen is the main element responsible for eutrophication in the aquatic environment [7,8], which leads to a reduction in biodiversity and deterioration of water quality [9]. High contents of nitrogen exist in drinking water, posing a threat to human health [10]. Excessive nitrite in drinking water could lead to a condition known as “methemoglobinemia” or “blue baby syndrome”, and has been associated with an increased risk of certain cancers through the formation of carcinogenic
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