Mechanisms of Nitrate Transfer from Soil to Stream in an Agricultural Watershed of French Brittany
Mechanisms of Nitrate Transfer from Soil to Stream in an Agricultural Watershed of French Brittany
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DOI：
10.1023/a:1012903626192
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
J. Molénat;P. Durand;C. Gascuel-Odoux;P. Davy;G. Gruau
中科院分区：
文献类型：
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作者：
J. Molénat;P. Durand;C. Gascuel-Odoux;P. Davy;G. Gruau
在法属布列塔尼，由于集约化农业造成的硝酸盐水污染已成为主要的环境问题之一。本文通过对某一级农业流域地下水和河流中硝酸盐、硫酸盐和氯化物浓度的分析，推断了硝酸盐在流域内分布和转移的机制。含水层由薄土层、风化页岩和裂隙页岩三层组成。风化的页岩地下水似乎是该流域硝酸盐的一个大水库。事实上，硝酸盐的量估计约为450千克N / ha，是河流中硝酸盐年总通量的5至9倍。上坡区NO3-L-1的硝酸盐浓度较高（138.4±10.5 mg），沿流向河流的方向下降（77.1±13.8 mg）。与硝酸盐不同，硫酸盐浓度从上坡到下坡呈上升趋势（从6.1±0.8 mg SO42-L-1到12.5±5.4 mg SO42-L-1），氯化物浓度变化不大。这些模式被认为是由裂缝页岩地下水向上流动的结果，其中黄铁矿氧化的反硝化作用以硫酸盐为最终产物。提出了一种由上坡风化地下水、深层地下水和洼地最上层土壤层水这三种末端组分混合而产生径流排放的硝态氮转移方案。基流中硝酸盐浓度的时间变化反映了各端元相对贡献的变化。
In French Brittany, water pollution with nitrate due tointensive agriculture has become one of the major environmentalconcerns. In this article, the nitrate, sulfate and chlorideconcentrations from the groundwater and the stream of a first-order agricultural watershed, are analyzed to infer the mechanisms responsible for the distribution and transfer of nitrate within the watershed. The aquifer is constituted by three layers: the thin soil cover, the weathered shale and thefissured shale. The weathered shale groundwater appears to bea large reservoir of nitrate in the watershed. Indeed the amount of nitrate is estimated at about 450 kg N ha-1, 5 to 9 times the total annual nitrate flux in the stream. In the upslope zones, this groundwater exhibited high nitrate concentrations (up to 138.4±10.5 mg NO3-L-1), which decreased along the flow paths towards the stream (77.1±13.8 mg NO3-L-1). Unlike nitrate, sulfate concentrations showed an increase from uphillto downhill (from 6.1±0.8 to 12.5±5.4 mg SO42-L-1) with little change in chloride concentrations. These patterns are presumed to result from upward flows from fissured shale groundwater where denitrification by oxidation of pyrite occurs with sulfate as end product. A scheme of nitrate transfer is proposed where stream discharge would result from the mixing of three end members which are: uphill weathered groundwater, deep groundwater and water in the uppermost soil horizons ofthe bottomlands. Temporal variability of nitrate concentrationsin base flow reflects changes in the relative contribution of each end member.