Impacts of forest conversion and agriculture practices on water pathways in Southern Brazil
Impacts of forest conversion and agriculture practices on water pathways in Southern Brazil
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DOI：
10.1002/hyp.13155
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发表时间：
2018-06
影响因子：
3.2
通讯作者：
J. Robinet;J. Minella;C. A. P. de Barros;A. Schlesner;A. Lücke;Y. Ameijeiras-Mariño;S. Opfergelt;J. Vanderborght;Gerard Govers
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文献类型：
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作者：
J. Robinet;J. Minella;C. A. P. de Barros;A. Schlesner;A. Lücke;Y. Ameijeiras-Mariño;S. Opfergelt;J. Vanderborght;Gerard Govers
土地利用/覆盖变化（LUCC），特别是森林砍伐和多年代际农业，是山坡或流域尺度上水通量的各种控制因素之一。研究了巴西南部亚热带地区土地利用/土地覆盖变化对水通道和河流暴雨生成过程的影响。通过对河流水、孔隙水、地下水和雨水的溶解硅浓度（DSi）和18O/16O （δ18O）特征的监测、采样和分析，确定了森林和农业下河流流的贡献来源。在流量和浅层地下水位方面，森林和农业集水区对降雨事件的响应都很高。DSi与δ18O的散点图表明，对于两种土地利用类型，两种径流组分对河流流量有贡献。密集的大孔隙网络的存在，加上紧凑和阻碍的B -层的存在，导致了森林流域快速的地下水流。在农业流域，对降雨的快速响应主要是由于地表径流。2组分同位素水线分离表明，降雨事件中农业集水区的雨水径流贡献较大。我们将这一较高的贡献归因于与农业实践相关的表土水力导电性的降低。森林集水区老水成分的化学特征与浅层地下水和孔隙土壤水的化学特征非常相似，因此浅层地下水可能是老水的主要来源。但在农业集水区，旧水组分的DSi浓度远高于浅层地下水和土壤孔隙水。由于农业集水区较大，这在某种程度上可能只是一种规模效应。然而，在农业条件下较高的水量和在旧农业条件下观察到的高DSi浓度表明，深层地下水对农业条件下的流域径流有重要贡献，这表明土地覆盖变化可能对风化速率和模式有显著影响。
Land‐use/cover change (LUCC), and more specifically deforestation and multidecadal agriculture, is one of the various controlling factors of water fluxes at the hillslope or catchment scale. We investigated the impact of LUCC on water pathways and stream stormflow generation processes in a subtropical region in southern Brazil. We monitored, sampled and analysed stream water, pore water, subsurface water, and rainwater for dissolved silicon concentration (DSi) and 18O/16O (δ18O) signature to identify contributing sources to the streamflow under forest and under agriculture. Both forested and agricultural catchments were highly responsive to rainfall events in terms of discharge and shallow groundwater level. DSi versus δ18O scatter plots indicated that for both land‐use types, two run‐off components contributed to the stream discharge. The presence of a dense macropore network, combined with the presence of a compact and impeding B‐horizon, led to rapid subsurface flow in the forested catchment. In the agricultural catchment, the rapid response to rainfall was mostly due to surface run‐off. A 2‐component isotopic hydrograph separation indicated a larger contribution of rainfall water to run‐off during rainfall event in the agricultural catchments. We attributed this higher contribution to a decrease in topsoil hydraulic conductivity associated with agricultural practices. The chemical signature of the old water component in the forested catchment was very similar to that of the shallow groundwater and the pore soil water: It is therefore likely that the shallow groundwater was the main source of old water. This is not the case in the agricultural catchments where the old water component had a much higher DSi concentration than the shallow groundwater and the soil pore water. As the agricultural catchments were larger, this may to some extent simply be a scale effect. However, the higher water yields under agriculture and the high DSi concentration observed in the old water under agriculture suggest a significant contribution of deep groundwater to catchment run‐off under agriculture, suggesting that LUCC may have significant effects on weathering rates and patterns.