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The impact of stream-groundwater exchange on seasonal nitrate loads in an urban stream
Hydrological Processes ( IF 2.8 ) Pub Date : 2021-07-26 , DOI: 10.1002/hyp.14324 Julio Beltran 1 , Laura K. Lautz 1, 2 , John R. Slosson 1
Hydrological Processes ( IF 2.8 ) Pub Date : 2021-07-26 , DOI: 10.1002/hyp.14324 Julio Beltran 1 , Laura K. Lautz 1, 2 , John R. Slosson 1
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Urbanization negatively impacts water quality in streams by reducing stream-groundwater interactions, which can reduce a stream's capacity to naturally attenuate nitrate. Meadowbrook Creek, a first order urban stream in Syracuse, New York, has an inverse urbanization gradient, with heavily urbanized headwaters that are disconnected from the floodplain and downstream reaches that have intact riparian floodplains and connection to riparian aquifers. This system allows assessment of how stream-groundwater interactions in urban streams impact the net sources and sinks of nitrate at the reach scale. We used continuous (15-min) streamflow measurements and weekly grab samples at three gauging stations positioned longitudinally along the creek to develop continuous nitrate load estimates at the inlet and outlet of two contrasting reaches. Nitrate load estimates were determined using a USGS linear regression model, RLOADEST, and differences between loads at the inlet and outlet of contrasting reaches were used to quantify nitrate sink and source behaviour year-round. We observed a nitrate load of 1.4 × 104 kg NO3− per water year, on average, at the outlet of the urbanized reach while the nitrate load at the outlet of the downstream, connected reach was 1.0 × 104 kg NO3− per water year, on average. We found the more heavily urbanized, hydrologically-disconnected reach was a net source of nitrate regardless of season. In contrast, stream-groundwater exchange caused the hydrologically connected reach to be both a source and sink for nitrate, depending on time of year. Both reaches alter nitrate source and sink behaviour at various spatiotemporal scales. Groundwater connection in the downstream, connected reach reduces annual nitrate loads and provides more opportunities for sources and sinks of nitrate year-round than the hydrologically disconnected stream reach. Mechanisms include groundwater discharge into the stream with variable nitrate concentrations, surface-water groundwater interactions that foster denitrification, and stream load loss to surrounding near-stream aquifers. This study emphasizes how loads are important in understanding how stream-groundwater interactions impact reach scale nitrate export in urban streams.
中文翻译：
河流-地下水交换对城市河流季节性硝酸盐负荷的影响
城市化通过减少河流与地下水的相互作用对河流的水质产生负面影响，这会降低河流自然衰减硝酸盐的能力。Meadowbrook Creek 是纽约州锡拉丘兹的一级城市河流，具有逆城市化梯度，高度城市化的源头与洪泛区断开，下游河段具有完整的河岸洪泛区并与河岸含水层相连。该系统可以评估城市河流中河流与地下水的相互作用如何影响河段范围内硝酸盐的净源和汇。我们在沿小河纵向定位的三个测量站使用连续（15 分钟）流量测量和每周抓取样本，以在两个对比河段的入口和出口处进行连续硝酸盐负荷估计。硝酸盐负荷估计是使用 USGS 线性回归模型 RLOADEST 确定的，对比河段入口和出口的负荷差异用于量化全年的硝酸盐汇和源行为。我们观察到硝酸盐负荷为 1.4 × 10城市化河段出口处平均每水年4 kg NO 3 −而下游连接河段出口处的硝酸盐负荷为 1.0 × 10 4 kg NO 3 −每水年，平均。我们发现，无论季节如何，城市化程度更高、水文断开的河段都是硝酸盐的净来源。相比之下，河流与地下水的交换导致与水文相连的河段既是硝酸盐的来源，又是硝酸盐的汇，这取决于一年中的时间。两者都在不同的时空尺度上改变硝酸盐的源和汇行为。下游的地下水连接，连接河段减少了年度硝酸盐负荷，并为全年硝酸盐源和汇提供了比水文断开的河流河段更多的机会。机制包括以可变的硝酸盐浓度排放到河流中的地下水、促进反硝化作用的地表水地下水相互作用以及河流负载损失到周围的近河流含水层。
更新日期：2021-08-10
中文翻译：
河流-地下水交换对城市河流季节性硝酸盐负荷的影响
城市化通过减少河流与地下水的相互作用对河流的水质产生负面影响，这会降低河流自然衰减硝酸盐的能力。Meadowbrook Creek 是纽约州锡拉丘兹的一级城市河流，具有逆城市化梯度，高度城市化的源头与洪泛区断开，下游河段具有完整的河岸洪泛区并与河岸含水层相连。该系统可以评估城市河流中河流与地下水的相互作用如何影响河段范围内硝酸盐的净源和汇。我们在沿小河纵向定位的三个测量站使用连续（15 分钟）流量测量和每周抓取样本，以在两个对比河段的入口和出口处进行连续硝酸盐负荷估计。硝酸盐负荷估计是使用 USGS 线性回归模型 RLOADEST 确定的，对比河段入口和出口的负荷差异用于量化全年的硝酸盐汇和源行为。我们观察到硝酸盐负荷为 1.4 × 10城市化河段出口处平均每水年4 kg NO 3 −而下游连接河段出口处的硝酸盐负荷为 1.0 × 10 4 kg NO 3 −每水年，平均。我们发现，无论季节如何，城市化程度更高、水文断开的河段都是硝酸盐的净来源。相比之下，河流与地下水的交换导致与水文相连的河段既是硝酸盐的来源，又是硝酸盐的汇，这取决于一年中的时间。两者都在不同的时空尺度上改变硝酸盐的源和汇行为。下游的地下水连接，连接河段减少了年度硝酸盐负荷，并为全年硝酸盐源和汇提供了比水文断开的河流河段更多的机会。机制包括以可变的硝酸盐浓度排放到河流中的地下水、促进反硝化作用的地表水地下水相互作用以及河流负载损失到周围的近河流含水层。
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