University of Alaska, Fairbanks, Institute of Arctic Biology, Fairbanks, AK, USA; University of California Davis, Department of Plant Sciences, Davis, CA, USA.
University of California Davis, Department of Plant Sciences, Davis, CA, USA.
J Environ Manage. 2020 May 15;262:110307. doi: 10.1016/j.jenvman.2020.110307. Epub 2020 Feb 29.
Stream and riparian zone networks embedded in agricultural landscapes provide a potential intervention point to ameliorate the negative effects of agricultural runoff by reducing transport of nitrate (NO) and suspended sediments (SS) downstream. However, our ability to support and promote NO and SS attenuation is limited by our understanding of vegetative and hydrogeomorphic controls in realistic management contexts. In addition, agricultural landscapes are heterogenous on multiple management scales, from farm field to regional water management scales, and the effect of these heterogeneities and how they interact across scales to affect vegetative and hydrogeomorphic controls is poorly explored in many settings. This is especially true in irrigated agricultural settings, where stream and riparian networks are entwined with and sensitive to water management systems. To fill these gaps, we related the vegetative and hydrogeomorphic features of 67 waterway reaches across two water management districts in the California Central Valley to reach-scale NO and turbidity attenuation and district-scale water quality patterns. We found that in-stream NO attenuation was rare, but, when it did occur, it was promoted by shallow and wide riparian banks, low flows, and high channel-edge denitrification potential. Nitrate concentrations were consistently higher in upstream reaches compared to water district outlets, suggesting that while exports from the district were low, agricultural runoff may impair within-district water resources. Turbidity attenuation was highly variable and unrelated to vegetative or hydrogeomorphic features, suggesting that onfield controls are crucial to managing suspended sediments. We conclude that waterway networks have the potential to mitigate the effects of agricultural NO runoff in this setting, but that more effective monitoring and adoption of NO attenuating features is needed. Using our findings, we make specific management and monitoring recommendations at both reach and water district scales.
嵌入在农业景观中的溪流和河岸带网络为改善农业径流的负面影响提供了一个潜在的干预点，通过减少硝酸盐（NO）和悬浮泥沙（SS）向下游的运输。然而，我们支持和促进 NO 和 SS 衰减的能力受到现实管理背景下植被和水文地貌控制的理解的限制。此外，农业景观在多个管理尺度上存在异质性，从农田到区域水资源管理尺度，这些异质性的影响以及它们如何在不同尺度上相互作用以影响植被和水文地貌控制在许多情况下还没有得到充分探索。在灌溉农业地区尤其如此，在这些地区，溪流和河岸带网络与水管理系统交织在一起，并对其敏感。为了填补这些空白，我们将加利福尼亚中央谷两个水管理区的 67 个水道的植被和水文地貌特征与水道尺度的 NO 和浊度衰减以及区域尺度的水质模式联系起来。我们发现，溪流中的 NO 衰减很少见，但当它确实发生时，它是由浅而宽的河岸、低流量和高渠道边缘的反硝化潜力促进的。与水区出口相比，上游的硝酸盐浓度始终较高，这表明尽管该地区的出口量较低，但农业径流可能会损害区内的水资源。浊度衰减高度可变，与植被或水文地貌特征无关，这表明田间控制对管理悬浮泥沙至关重要。我们的结论是，在这种情况下，水道网络有可能减轻农业 NO 径流的影响，但需要更有效地监测和采用 NO 衰减特征。根据我们的发现，我们在水道和水区尺度上提出了具体的管理和监测建议。
