Nitrate contamination in rivers has raised widespread concern in the world, particularly in arid/semi-arid river basins lacking qualified water. Understanding the nitrate pollution levels and sources is critical to control the nitrogen input and promote a more sustainable water management in those basins. Water samples were collected from a typical semi-arid river basin, the Weihe River watershed, China, in October 2014. Hydrochemical assessment and nitrogen isotopic measurement were used to determine the level of nitrogen compounds and identify the sources of nitrate contamination. Approximately 32.4% of the water samples exceeded the World Health Organization (WHO) drinking water standard for NO 3´-N. Nitrate pollution in the main stream of the Weihe River was obviously much more serious than in the tributaries. The δ 15 N-NO 3´o f water samples ranged from +8.3 to +27.0. No significant effect of denitrification on the shift in nitrogen isotopic values in surface water was observed by high dissolved oxygen (DO) values and linear relationship diagram between NO 3´-N and δ 15 N-NO 3´, except in the Weihe River in Huayin County and Shitou River. Analyses of hydrochemistry and isotopic compositions indicate that domestic sewage and agricultural activities are the main sources of nitrate in the river.
As a crucial agricultural and economic development zone since the Qin Dynasty (221 to 206 BC), the Guanzhong section of the Weihe River basin is facing serious water resource shortages due to population growth and regional development. Its water resource amount per capita is only 361 m3, about 1/6 of the average in China and less than 1/20 of the average in the world. Surface water and groundwater (SW‐GW) interaction, having a significant influence on the spatiotemporal distribution of water resources, was qualitatively and quantitatively investigated during a wet year based on stable isotopes and hydrochemistry. The results show that the recharge pattern in the north part varies with season, that is, 40% of the surface water recharge comes from groundwater in the dry season, but 93% of the groundwater recharge comes from surface water in the rainy season. In the south part, groundwater is always recharged by surface water, with contributions of 47% and 61% in the rainy and dry seasons, respectively. For the main stream, the recharge pattern is complicated and varies with season and site. This study will provide useful information about SW‐GW interaction at basin scale. Integrated management of groundwater and surface water could improve the efficiency of regional water resources utilization and promote accurate and sustainable water management in the semi‐arid basin.
The impacts of climate change and human activity, combined with streamflow reduction in the Yellow River Basin, have presented significant challenges to water resource management strategies. Here, the trends and change points of streamflow were determined for the period 1956–2017 via five statistical methods. A runoff-sensitive coefficients method (the Budyko hypothesis) and a conceptual rainfall–runoff model (the TUW model) were applied to assess the streamflow variation. The following conclusions were ascertained: (1) 1989, 1986, and 1990 were the change points for streamflow in the upstream Tang-Nai-Hai and Lan-Zhou stations and the downstream Hua-Yuan-Kou hydrological station; (2) the streamflow showed statistically significant decreasing trends with spatiotemporal variations in the Yellow River Basin; (3) the relationship between runoff and precipitation showed a downward trend over time; (4) comparisons of the Budyko and TUW models show that human activity is responsible for more than 65% of streamflow reduction, while climate change contributes to less than 35% of the reduction. Therefore, human activity is the main reason for streamflow reduction in the Yellow River Basin. This finding is of critical importance for water resources management under changing environment.
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