State Key Laboratory of Geohazard Prevention and Geoenvironment Protection (Chengdu University of Technology), Chengdu 610059, China.
Molecular Eco-Geochemistry Laboratory, Department of Geological Sciences, University of Alabama, Tuscaloosa, AL 35487, USA.
Sci Total Environ. 2021 May 1;767:144372. doi: 10.1016/j.scitotenv.2020.144372. Epub 2020 Dec 26.
It has been well documented that agricultural activities lead to significant alterations in surface water dissolved organic matter (DOM), yet their impacts on groundwater DOM remain poorly constrained. The quantity, source, and composition of DOM play a pivotal role in a range of groundwater ecosystem services that are of important ecological and societal values. We assessed the impact of irrigation on the source and compositional characteristics of groundwater DOM in a large river basin supporting intensive agriculture in arid northwestern China. We sampled five water types along a river reach of approximately 40 km, including groundwater, river water, irrigation canal water, hyporheic water, and soil leachates. The excitation-emission matrix (EEM) measurements coupled with parallel factor analysis (PARAFAC) identified two terrestrial-derived, humic-like fluorescent components (C1 and C2) and one protein-like autochthonous component (C3). DOM composition and dissolved organic carbon (DOC) concentration varied as a function of water type, with subsurface waters showing relatively lower DOC and terrestrial humic fluorescence than surface waters. Combining nitrate, electrical conductivity, dissolved inorganic carbon (DIC), and δC-DIC, irrigation-influenced samples were identified, and the influence of irrigation on groundwater DOM appeared only in shallow aquifers (<50 m). Irrigation-influenced groundwater exhibited higher DOC and terrestrial fluorescence than unimpacted groundwater, suggesting that irrigation return flows accelerated the downward movement of terrestrial humic compounds and led to their accumulation in aquifers. This effect was propagated via surface water-groundwater interactions to upwelling hyporheic water, which also showed enrichment in terrestrial fluorescence. Our findings demonstrate that irrigation can accelerate the biogeochemical cycling of organic compounds via a subsurface pathway of from the soil to aquifer to hyporheic zone. The enrichment of soil-derived compounds in subsurface waters may have important ecological consequences, such as altering the transport of nutrients and pollutants and changing carbon and energy flows across the surface-subsurface boundary.
大量文献资料表明，农业活动会导致地表水溶解性有机质（DOM）发生显著变化，但其对地下水 DOM 的影响仍知之甚少。DOM 的数量、来源和组成在一系列地下水生态系统服务中起着关键作用，这些服务具有重要的生态和社会价值。本研究评估了灌溉对中国西北干旱地区一个大型支持集约化农业的河流流域地下水 DOM 的来源和组成特征的影响。我们沿约 40 公里的河流采样了五种水类型，包括地下水、河水、灌溉渠水、底潜流和土壤浸出液。激发-发射矩阵（EEM）测量结合平行因子分析（PARAFAC）确定了两种源自陆地的腐殖质样荧光组分（C1 和 C2）和一种源自陆地的蛋白样自生组分（C3）。DOM 组成和溶解有机碳（DOC）浓度随水类型而变化，地下水中的 DOC 和陆地腐殖质荧光相对低于地表水。结合硝酸盐、电导率、溶解无机碳（DIC）和δC-DIC，确定了受灌溉影响的样本，并发现灌溉对地下水 DOM 的影响仅出现在浅层含水层（<50 m）中。受灌溉影响的地下水的 DOC 和陆地荧光均高于未受影响的地下水，表明灌溉回流水加速了陆地腐殖质化合物的向下运移，并导致其在含水层中积累。这种效应通过地表水-地下水相互作用传播到上升的底潜流，底潜流也表现出陆地荧光的富集。我们的研究结果表明，灌溉可以通过从土壤到含水层到底潜流的地下途径加速有机化合物的生物地球化学循环。土壤衍生化合物在地下水中的富集可能会产生重要的生态后果，例如改变养分和污染物的运移，并改变地表水-地下水界面的碳和能量流动。
