School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
Sci Total Environ. 2016 Mar 1;545-546:184-99. doi: 10.1016/j.scitotenv.2015.12.025. Epub 2015 Dec 31.
This paper examines relationships between rainfall-runoff, catchment connectivity, antecedent moisture conditions and fertiliser application with nitrate-N and total phosphorus (TP) fluxes in an arable headwater catchment over three hydrological years (2012-2014). Annual precipitation totals did not vary substantially between years, yet the timing of rainfall strongly influenced runoff generation and subsequent nitrate-N and TP fluxes. The greatest nitrate-N (>250 kg N day(-1)) and TP (>10 kg TP day(-1)) fluxes only occurred when shallow groundwater was within 0.6m of the ground surface and runoff coefficients were greater than 0.1. These thresholds were reached less frequently in 2012 due to drought recovery resulting in lower annual nitrate-N (7.4 kg N ha(-1)) and TP (0.12 kg P ha(-1)) fluxes in comparison with 2013 (15.1 kg N ha(-1); 0.21 kg P ha(-1)). The wet winter of 2013 with elevated shallow groundwater levels led to more frequent activation of sub-surface pathways and tile drain flow. Throughout the period, dry antecedent conditions had a temporary effect in elevating TP loads. Evidence of TP source exhaustion after consecutive storm events can be attributed to the repeated depletion of temporarily connected critical source areas to the river network via impermeable road surfaces. Fertiliser application varied considerably across three years due to differences in crop rotation between farms, with annual N and P fertiliser inputs varying by up to 21% and 41%, respectively. Proportional reductions in annual riverine nitrate-N and TP loadings were not observed at the sub-catchment outlet as loadings were largely influenced by annual runoff. Nitrate loadings were slightly higher during fertiliser application, but there was little relationship between P fertiliser application and riverine TP load. These data indicate that this intensive arable catchment may be in a state of biogeochemical stationarity, whereby legacy stores of nutrients buffer against changes in contemporary nutrient inputs.
本研究考察了降雨-径流、集水区连通性、前期湿度条件和施肥与硝酸盐-N 和总磷（TP）通量在 3 个水文年内（2012-2014 年）在一个旱地集水区之间的关系。年降水量在各年均无明显差异，但降雨时间强烈影响径流产出及随后的硝酸盐-N 和 TP 通量。只有当浅层地下水距地面 0.6m 以内且径流量系数大于 0.1 时，才会出现最大的硝酸盐-N（>250kgNday-1）和 TP（>10kgTPday-1）通量。2012 年由于干旱恢复导致年硝酸盐-N（7.4kgNha-1）和 TP（0.12kgPha-1）通量较低，这些阈值的出现频率较低，而 2013 年则分别为 15.1kgNha-1和 0.21kgPha-1。2013 年冬季湿润，浅层地下水位升高，导致地下途径和排水渠流量更频繁地激活。在整个研究期间，干旱的前期条件对提高 TP 负荷具有暂时的影响。在连续的风暴事件后 TP 源枯竭的证据可以归因于通过不透水的道路表面，暂时连通的关键源区反复耗尽对河网的影响。由于农场之间的轮作差异，三年间肥料的施用量变化很大，每年的 N 和 P 肥料输入分别变化了高达 21%和 41%。由于径流量主要受年度径流量影响，因此在子流域出口处并未观察到硝酸盐-N 和 TP 年排放量的比例减少。在施肥期间硝酸盐负荷略高，但 P 肥料施肥与河流 TP 负荷之间几乎没有关系。这些数据表明，这个集约化的旱地集水区可能处于生物地球化学稳定状态，即养分的遗留储存缓冲了当前养分输入的变化。
