INRAE, BEF, F-54000, Nancy, France.
Luxembourg Institute of Science and Technology (LIST), Environmental Research and Innovation Department (ERIN), Catchment and Eco-Hydrology Research Group (CAT), L-4422, Belvaux, Luxembourg.
Environ Pollut. 2023 Nov 1;336:122477. doi: 10.1016/j.envpol.2023.122477. Epub 2023 Aug 29.
In rural areas, nitrate concentrations in surface waters most often originate from the leaching of excess N fertilizer in agricultural lands, whereas forested catchments often have good water quality. However, Douglas-fir plantations may induce nitrogen cycle unbalances which may lead to an excess of nitrate production in the soil. We hypothesize that the excess of production of nitrate in the soil and nitrate leaching to streamwater is greater in catchments planted with Douglas fir. We used paired catchments in both France and Luxembourg with different land covers (Douglas-fir, Spruce, Deciduous, Grassland and clearcut) which were monitored over a 3-5 year period in order to assess the effect of Douglas-fir plantations on the chemical composition of surface water. Nitrate concentration in the soil and groundwater were also monitored. The results show that nitrate concentrations in streams draining Douglas-fir catchments were two to ten times higher than in streams draining other land covers, but were similar to the clearcut catchment. Nitrate concentrations under Douglas-fir in groundwater (up to 50 mg L) and in the soil were also higher than under all other land covers. Soil nitrate concentration was related to stream nitrate concentration. This suggests that soil processes, through excessive nitrate production under Douglas-fir, are driving the nitrate concentration in the stream water and our hypothesis of a transfer of a fairly large proportion of this excessive production from the soil to the stream is supported. This study also shows that nitrate concentrations in surface and ground waters in rural areas could also originate from Douglas fir forested catchments. The impact of Douglas-fir is nevertheless reduced downstream through a dilution effect: mixing tree species at the catchment scale could thus be a solution to mitigate the effect of Douglas-fir on nitrate concentration in surface waters.
在农村地区，地表水中的硝酸盐浓度通常源自农业用地中过量 N 肥料的淋溶，而森林流域通常水质良好。然而，花旗松种植园可能会导致氮循环失衡，从而导致土壤中硝酸盐的过度产生。我们假设，土壤中硝酸盐的过度产生和硝酸盐向溪流的淋溶在种植花旗松的流域中更为严重。我们使用了法国和卢森堡的配对流域，这些流域具有不同的土地覆盖（花旗松、云杉、落叶林、草地和皆伐），并在 3-5 年的时间内进行了监测，以评估花旗松种植园对地表水化学组成的影响。还监测了土壤和地下水中的硝酸盐浓度。结果表明，从花旗松流域流出的溪流中的硝酸盐浓度是从其他土地覆盖流域流出的溪流的两到十倍，但与皆伐流域相似。花旗松下的地下水（高达 50mg/L）和土壤中的硝酸盐浓度也高于所有其他土地覆盖物。土壤中的硝酸盐浓度与溪流中的硝酸盐浓度有关。这表明土壤过程通过花旗松下的过度硝酸盐产生，正在推动溪流中硝酸盐浓度的升高，我们关于相当大比例的这种过度产生从土壤转移到溪流的假设得到了支持。本研究还表明，农村地区地表水和地下水中的硝酸盐浓度也可能源自花旗松森林流域。然而，通过稀释效应，花旗松的影响在下游会降低：因此，在集水区范围内混合树种可能是减轻花旗松对地表水硝酸盐浓度影响的一种解决方案。
