Earth and Environmental Sciences, University of Mary Washington, Fredericksburg, VA, USA.
Environ Sci Pollut Res Int. 2022 Feb;29(8):11481-11492. doi: 10.1007/s11356-021-16461-2. Epub 2021 Sep 18.
Human population growth and subsequent land use intensification are closely linked to contemporary increases in sediment and associated contaminants fluxes to fluvial systems, lakes, reservoirs, and coastal zones worldwide. In most urban areas, reservoirs that are the main source of fresh water supply, if not effectively managed, suffer from water quality decline and loss of capacity associated with accelerated siltation. This study analyzes watershed soil losses and sediment accumulation rates in two reservoirs in the Occoquan river basin, a sub-watershed of the Chesapeake Bay in the suburbs of the greater Washington, DC area. Lake Manassas is located in the upper reaches of the basin, characterized by mixed land use and cover of mostly forest, residential areas, and agriculture, whereas Occoquan Reservoir is located in the more urbanized lower reach of the basin in the heavily populated suburban zone south of Washington, DC. Five sediment cores from each lake were used in Pb-based sediment accumulation rates analysis, and GIS-based Revised Soil Loss Equation (RUSLE) model and a sediment delivery ratio (SDR) were used to evaluate basin soil losses and sediment fluxes to the fluvial systems. Pb sediment accumulation rate estimates in Occoquan Reservoir range from 0.26 g cm year in the upper reaches to 0.37 g cm year in the lower reaches. Lake Manassas also had comparable accumulation values ranging from 0.22 to 0.40 g cm year. RUSLE/SDR estimated watershed sediment fluxes were 0.26 Mg ha year (Mg-mega gram) in the upper watershed, which is significantly higher than 0.07 Mg ha year estimates for the lower reaches of the watershed. The variability in the reservoirs' sediment accumulation rates and basin soil losses reflects the variability of land use and cover, basin slopes, and erosion mitigation efforts within the watershed. The lower reaches, though more urbanized, have well-developed storm drain systems limiting run-off related soil losses. The well-managed riparian zones surrounding both reservoirs also limit sediment fluxes, hence the relatively low sediment accumulation rates. Although surficial sediment sources seem to be well managed, some of these efforts might be associated with the uptick in intrinsic sediment sources, leading to localized high sediment accumulation in the mouth of tributaries draining the high-intensity urban areas of the basin.
人口增长和随后的土地利用集约化与当代全球河流系统、湖泊、水库和沿海地区沉积物和相关污染物通量的增加密切相关。在大多数城市地区，如果水库得不到有效管理，作为主要淡水供应源的水库会出现水质下降和库容减少的问题，这是由于加速淤积所致。本研究分析了切萨皮克湾郊区大华盛顿地区奥科奎恩河流域两个水库流域的土壤流失和沉积物积累率。马纳萨斯湖位于流域上游，土地利用混合，主要覆盖森林、居民区和农业用地；而奥科奎恩水库位于流域下游更城市化的地区，位于华盛顿特区南部人口稠密的郊区，是一个人口众多的城市。每个湖泊采集了 5 个沉积物岩芯，用于基于 Pb 的沉积物积累率分析，利用 GIS 修正土壤流失方程（RUSLE）模型和泥沙输送比（SDR）评估流域土壤流失和泥沙向河流系统的通量。奥科奎恩水库的 Pb 沉积物积累率估计值从上游的 0.26 g cm 年到下游的 0.37 g cm 年不等。马纳萨斯湖的积累值也相当，范围在 0.22 到 0.40 g cm 年之间。RUSLE/SDR 估计流域泥沙通量为上游流域 0.26 Mg ha 年（Mg-百万克），明显高于流域下游 0.07 Mg ha 年的估计值。水库沉积物积累率和流域土壤流失的变化反映了土地利用和覆盖、流域坡度以及流域内侵蚀缓解措施的变化。尽管下游地区城市化程度较高，但发达的雨水排水系统限制了与径流相关的土壤流失。两个水库周围管理良好的河岸带也限制了泥沙通量，因此泥沙积累率相对较低。尽管表层沉积物源似乎得到了很好的管理，但这些措施中的一些可能与内在沉积物源的增加有关，导致流域内高强度城市地区的支流口局部高泥沙积累。
