Department of Civil & Environmental Engineering, Campus Delivery 1372, Colorado State University, Fort Collins, CO 80523, USA; College of Engineering, Athens, Georgia, USA.
College of Engineering, Athens, Georgia, USA.
J Environ Manage. 2019 Mar 15;234:104-114. doi: 10.1016/j.jenvman.2018.12.074. Epub 2019 Jan 4.
Phosphorus and fine sediment pollution are primary causes of water quality degradation. Streambank erosion is a potentially significant source of fine sediment and particulate phosphorus to watersheds, but it remains difficult to quantify the magnitude of this loading. A new, easily applied, watershed scale model was used to simulate the potential for future phosphorus and sediment loading from channel erosion in two watersheds: Big Dry Creek, Colorado and Lick Creek, North Carolina. The projected magnitude of loading for phosphorus is about an order of magnitude higher in Big Dry Creek compared to Lick Creek (∼280 kg/yr and ∼50 kg/yr, respectively), while sediment loading results are similar (∼950 ton/yr). In both watersheds, model results suggest that channel erosion will not contribute a significant amount of phosphorus to the watershed (∼1-4% of historic watershed total from all pollutant sources) but will contribute a large amount of sediment (30-100% of historic watershed total). Uncertainty in these estimates is high, but quantifying confidence in model projections is important for understanding and using model results. Importantly, modeling shows no decrease in loading over the 40-year model time frame in either watershed, suggesting that the channels are not adjusting to a new stable state and erosion will continue to be a pollutant source. Lick Creek model results are sensitive to upstream sediment supply while Big Dry Creek's are not, reinforcing the importance of considering alterations to both the hydrologic and sediment regimes when analyzing potential channel changes - at least in vertically active channels. This new modeling approach is useful for estimating historic and future phosphorus and sediment loading from channel erosion, an important first step in effective management to improve water quality.
磷和细沉积物污染是水质恶化的主要原因。河岸侵蚀是流域细沉积物和颗粒态磷的一个潜在重要来源，但要量化这种负荷的大小仍然很困难。一种新的、易于应用的流域尺度模型被用于模拟两个流域：科罗拉多州的大干溪和北卡罗来纳州的利克溪的未来河道侵蚀潜在的磷和泥沙负荷。与利克溪相比，大干溪的磷负荷预测值要高一个数量级（分别约为 280kg/yr 和 50kg/yr），而泥沙负荷结果相似（分别约为 950 吨/yr）。在这两个流域，模型结果表明，河道侵蚀不会向流域输送大量的磷（约占所有污染源历史总磷的 1-4%），但会输送大量的泥沙（占历史流域总泥沙的 30-100%）。这些估计值的不确定性很高，但量化模型预测的置信度对于理解和使用模型结果非常重要。重要的是，模型显示在两个流域的 40 年模型时间内，负荷没有减少，这表明河道没有调整到新的稳定状态，侵蚀将继续成为污染源。利克溪模型的结果对上游泥沙供应很敏感，而大干溪的则不敏感，这强调了在分析潜在的河道变化时，考虑水文和泥沙条件变化的重要性——至少在垂直活跃的河道中是这样。这种新的建模方法可用于估算河道侵蚀的历史和未来磷和泥沙负荷，这是改善水质的有效管理的重要第一步。
