USDA-ARS, Southeast Watershed Research Laboratory, 2316 Rainwater Road, Tifton, GA 31793, USA.
USDA-ARS, Southeast Watershed Research Laboratory, 2316 Rainwater Road, Tifton, GA 31793, USA.
Sci Total Environ. 2020 May 15;717:137165. doi: 10.1016/j.scitotenv.2020.137165. Epub 2020 Feb 6.
Dissolved organic matter (DOM) represents an essential component of the carbon cycle and controls biogeochemical and ecological processes in aquatic systems. The composition and reactivity of DOM are determined by the spatial distribution of its sources and its residence time in a watershed. While the effects of agricultural land cover on DOM quality have been reported across spatial and temporal scales, the influence of riparian land cover on stream DOM composition has received little attention. Furthermore, the combined effects of riparian land cover and streamflow rates on DOM composition require investigation. To this end, a multi-year (2016-2018) DOM characterization study was conducted using bi-weekly water samples collected from seven sub-watersheds nested within the Little River Experimental Watershed (LREW) near Tifton, Georgia, USA. DOM optical properties were determined to assess compositional variations using UV-Vis and excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor (PARAFAC) analysis. PARAFAC analysis indicated that DOM in the LREW was dominated by three humic-like fluorescing components of terrestrial, microbial, and anthropogenic origin and a protein-like component. DOM composition was influenced by riparian land cover and hydrology, and shifted towards recently produced, low molecular weight DOM with low aromaticity as the percentage of agricultural land within riparian wetlands increased. During periods of high discharge and high baseflow, the DOM pool was dominated by recalcitrant and terrestrial-derived material but shifted towards protein-like and microbial-derived with increasing cropland in the riparian area. The results of this two-year study indicate that the replacement of forested riparian buffers with agricultural land can result in altered DOM composition which may affect carbon cycling and downstream water quality in agricultural watersheds.
溶解有机物质（DOM）是碳循环的重要组成部分，控制着水生系统中的生物地球化学和生态过程。DOM 的组成和反应性取决于其来源的空间分布及其在流域中的停留时间。虽然已经报道了农业土地覆被对 DOM 质量的影响在空间和时间尺度上，但对河岸带土地覆被对溪流 DOM 组成的影响关注较少。此外，河岸带土地覆被和径流量对 DOM 组成的综合影响需要研究。为此，在美国乔治亚州蒂夫顿附近的小河实验流域（LREW）内嵌套的七个子流域中，进行了一项为期多年（2016-2018 年）的 DOM 特征研究，每两周采集一次水样。使用紫外-可见分光光度法和激发-发射矩阵（EEM）荧光光谱法结合平行因子（PARAFAC）分析来测定 DOM 的光学性质，以评估组成变化。PARAFAC 分析表明，LREW 中的 DOM 主要由三种腐殖质样荧光成分（陆地、微生物和人为来源）和一种蛋白质样成分组成。DOM 组成受河岸带土地覆被和水文学的影响，随着河岸带湿地中农业用地的比例增加，DOM 向新产生的、低分子量、低芳香度的 DOM 转移。在高流量和高基流期间，DOM 库主要由抗降解和陆地来源的物质组成，但随着河岸带区域的耕地增加，DOM 库向蛋白质样和微生物来源的物质转移。这项为期两年的研究结果表明，用农业用地替代森林河岸带缓冲区会导致 DOM 组成发生变化，这可能会影响农业流域的碳循环和下游水质。
