Abstract
This study aimed to understand the spatiotemporal variation of nutrient concentrations in stream water, using analyses of total nitrogen (TN), NO3−-N, NH4+-N and total phosphorus (TP) concentrations from April to October in 2016 in the upper Shule River basin in the northeastern margin of the Qinghai-Tibetan Plateau. Dissolved inorganic nitrogen (DIN; NO3−-N + NH4+-N) concentrations in both groundwater and stream water were the predominant form of TN, accounting for about 88%. Median concentrations in stream water were 815 μg L−1 for TN, 459 μg L−1 for NO3−-N, 253 μg L−1 for NH4+-N, and 25 μg L−1 for TP. Great spatiotemporal variations of nitrogen and phosphorus concentrations in stream water were observed, which likely resulted from varying recharge sources (snow and groundwater) and biogeochemical processes. Monthly variations in nutrient concentrations in stream water had a reciprocal pattern between nitrogen and phosphorus concentrations. Our results demonstrated that the quality of steam water in the upper reach of Shule River basin was basically good for drinking purposes according to the environmental quality standards for surface water, China. The results also improved our understanding of how nutrient concentrations varied in stream water and provided baseline information for future studies on nutrients in the Qinghai-Tibetan Plateau.
Highlights
Nitrogen (N) and phosphorus (P) are essential elements in freshwater, marine and terrestrial environments for a variety of life forms [1,2]
Shule total nitrogen (STN) and NH4 + -N tend to increase with altitude, whereas STP and STC trend to decrease with altitude (Figure 2; Table 2)
Our findings showed that the increase of NO3 − -N and NH4 + -N in mid- and late-July collected at the rainy seasons may be explained by more intense agricultural activities in the lower regions and increased atmospheric mixing during this time associated with low-elevation rain events frequency [36]
Summary
Nitrogen (N) and phosphorus (P) are essential elements in freshwater, marine and terrestrial environments for a variety of life forms [1,2]. Headwater streams are important sources of nutrients, nitrogen and phosphorous, to rivers and lakes [3,4], and have affected the aquatic ecosystem productivity, water quality and utilization of water resources in the downstream reaches [3,5,6,7]. Concentrations of nitrogen and phosphorous in rivers have been influenced by a variety of natural and anthropogenic factors, the relative influences of which vary spatially and temporally [8]. An increasing number of studies have shown that eutrophication has intensified in coastal waters and downstream estuarine [9,10]. The problem has usually been characterized by increased supplies of nutrients, nitrogen and phosphorous, to aquatic systems when exceeding the assimilation capacity of receiving water [11].
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