黄土高塬沟壑区氮素流失的时空变异特征

为了探讨黄土高塬沟壑区水体氮污染的时空变化情况,选取黑河流域(泾河支流)为研究区域,测定2013—2014年枯水期和汛期流域地表水和地下水中主要离子及NO_3~--N和NH+4-N的浓度并进行分析.结果表明,黑河流域枯水期水化学主要为Na+K-Cl-SO_4型,汛期主要为CaMg-HCO_3型.枯水期及汛期阳离子均主要为Na+,阴离子在枯水期主要为SO_4~(2-)而汛期则转变为HCO_3~-.汛期NO_3~--N浓度普遍大于枯水期,平均值分别为2.37和1.63 mg·L~(-1);且空间分布不均衡,地表水中的浓度为:上游(1.35 mg·L~(-1))中游(1.05 mg·L~(-1))下游(0.93 mg·L~(-1)),而地下水中的浓度为:下游(3.84 mg·L~(-1))中游(2.54 mg·L~(-1))上游(2.35 mg·L~(-1)).NH_4~+-N在时间分布上没有明显的规律,汛期及枯水期变化不大,空间分布特征与NO_3~--N类似,但其整体浓度较低,在0.11 mg·L~(-1)左右波动,较为稳定均且未超过IV类水标准.水体中NO_3~--N不仅来自于农田氮肥的施入等人类活动,还可能来自于酸性降雨.地表水的NO_3~--N污染程度存在空间差异,上游污染程度大于中、下游,而超过70%的地下水水质属于良好,对当地饮用水安全暂不造成威胁.

Spatio-temporal variations of nitrogen loss in the tableland-gully region of the Loess Plateau

To investigate the spatiotemporal variations of the nitrogen pollution in the tableland-gully region of the Loess Plateau, the surface water and groundwater in the Heihe watershed (tributary of the Jing River catchment) have been sampled in the dry and flood seasons for the period of 2013-2014 to determine the concentration of NO₃^--N and NH₄⁺-N. The major water type is Na+K-Cl-SO₄ during the dry seasons and Ca-Mg-HCO₃ during the flood seasons. Na⁺ is the major cation for both dry and flood season, while the major anions are SO₄^2- in the dry seasons and HCO₃^- in the flood seasons. The loss of nitrogen is mainly in the form of NO₃^--N, and the concentration of NO₃^--N in the flood seasons is higher than that in the dry seasons, which is respectively 2.37 and 1.63 mg·L^-1. Spatial variations exist in the concentration of NO₃^--N. For surface water, it is the highest in the upstream (1.35 mg·L^-1), intermediate in the midstream (1.05 mg·L^-1) and the lowest in the downstream (0.93 mg·L^-1); however, for groundwater, it is the lowest in the upstream (2.35 mg·L^-1), intermediate in the midstream (2.54 mg·L^-1), and the highest in the downstream (3.84 mg·L^-1). The pollution from NO₃^--N was further quantified by comparing the concentration with environmental standards. For surface water, the pollution in the upstream was greater than that in the midstream and downstream; for groundwater, more than 70% of the groundwater samples are good enough to be drinking water. The NO₃^--N is possibly from fertilizer application and acid precipitation. The concentration of NH₄⁺-N is spatiotemporally invariant and it fluctuates at around 0.11 mg·L^-1.