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Spatial and temporal patterns of dissolved organic matter quantity and quality in the Mississippi River Basin, 1997-2013

机译：1997-2013年密西西比河流域溶解性有机质数量和质量的时空格局

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Recent studies have found insignificant or decreasing trends in time-series dissolved organic carbon (DOC) datasets, questioning the assumption that long-term DOC concentrations in surface waters are increasing in response to anthropogenic forcing, including climate change, land use, and atmospheric acid deposition. We used the weighted regressions on time, discharge, and season (WRTDS) model to estimate annual flow-normalized concentrations and fluxes to determine if changes in DOC quantity and quality signal anthropogenic forcing at 10 locations in the Mississippi River Basin. Despite increases in agriculture and urban development throughout the basin, net increases in DOC concentration and flux were significant at only 3 of 10 sites from 1997 to 2013 and ranged between -3.5% to +18% and -0.1 to 19%, respectively. Positive shifts in DOC quality, characterized by increasing specific ultraviolet absorbance at 254 nm, ranged between +8% and +45%, but only occurred at one of the sites with significant DOC quantity increases. Basinwide reductions in atmospheric sulfate deposition did not result in large increases in DOC either, likely because of the high buffering capacity of the soil. Hydroclimatic factors including annual discharge, precipitation, and temperature did not significantly change during the 17-year timespan of this study, which contrasts with results from previous studies showing significant increases in precipitation and discharge over a century time scale. Our study also contrasts with those from smaller catchments, which have shown stronger DOC responses to climate, land use, and acidic deposition. This temporal and spatial analysis indicated that there was a potential change in DOC sources in the Mississippi River Basin between 1997 and 2013. However, the overall magnitude of DOC trends was not large, and the pattern in quantity and quality increases for the 10 study sites was not consistent throughout the basin.
机译：最近的研究发现时间序列溶解有机碳（DOC）数据集的趋势微不足道或呈下降趋势，这质疑以下假设：地表水中长期DOC浓度响应于人为强迫而增加，包括气候变化，土地利用和大气酸沉积。我们使用时间，流量和季节的加权回归（WRTDS）模型来估算年度流量归一化浓度和通量，以确定DOC数量和质量的变化是否表示密西西比河流域10个地点的人为强迫。尽管整个流域的农业和城市发展都有所增加，但从1997年到2013年，DOC浓度和通量的净增加仅在10个站点中的3个站点中显着，分别在-3.5％至+ 18％和-0.1至19％之间。 DOC质量的正向变化（以在254 nm处的特定紫外线吸收率增加为特征）介于+ 8％至+ 45％之间，但仅在DOC数量显着增加的位置之一发生。整个盆地中大气硫酸盐沉积的减少也不会导致DOC的大幅增加，这可能是由于土壤的高缓冲能力所致。在本研究的17年时间跨度中，包括年排放量，降水量和温度在内的水文气候因素没有显着变化，这与以前的研究结果相反，该研究表明降水量和排放量在一个世纪的时间范围内显着增加。我们的研究还与小流域的研究形成对比，后者显示了DOC对气候，土地利用和酸性沉积的更强响应。这项时空分析表明，密西西比河流域的DOC来源在1997年至2013年之间存在潜在的变化。但是，DOC趋势的总体幅度并不大，并且这10个研究地点的数量和质量都有所增加在整个盆地上都不一致。

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