Schwartz Daniel, Sample David J, Grizzard Thomas J
Occoquan Watershed Monitoring Laboratory, Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, 9408 Prince William St, Manassas, VA, 20110-5666, USA.
Department of Biological Systems Engineering, Virginia Polytechnic Institute and State University, Hampton Roads Agricultural Research and Extension Center, 1444 Diamond Springs Rd., Virginia Beach, VA, 23455, USA.
Environ Monit Assess. 2017 Jun;189(6):256. doi: 10.1007/s10661-017-5930-6. Epub 2017 May 6.
This paper describes the performance of a retrofitted stormwater retention pond (Ashby Pond) in Northern Virginia, USA. Retrofitting is a common practice which involves modifying existing structures and/or urban landscapes to improve water quality treatment, often compromising standards to meet budgetary and site constraints. Ashby Pond is located in a highly developed headwater watershed of the Potomac River and the Chesapeake Bay. A total maximum daily load (TMDL) was imposed on the Bay watershed by the US Environmental Protection Agency in 2010 due to excessive sediment and nutrient loadings leading to eutrophication of the estuary. As a result of the TMDL, reducing nutrient and sediment discharged loads has become the key objective of many stormwater programs in the Bay watershed. The Ashby Pond retrofit project included dredging of accumulated sediment to increase storage, construction of an outlet structure to control flows, and repairs to the dam. Due to space limitations, pond volume was less than ideal. Despite this shortcoming, Ashby Pond provided statistically significant reductions of phosphorus, nitrogen, and suspended sediments. Compared to the treatment credited to retention ponds built to current state standards, the retrofitted pond provided less phosphorus but more nitrogen reduction. Retrofitting the existing stock of ponds in a watershed to at least partially meet current design standards could be a straightforward way for communities to attain downstream water quality goals, as these improvements represent reductions in baseline loads, whereas new ponds in new urban developments simply limit future load increases or maintain the status quo.
本文描述了美国弗吉尼亚州北部一个经过改造的雨水滞留池（阿什比池塘）的性能。改造是一种常见做法，涉及修改现有结构和/或城市景观以改善水质处理，通常要在标准上做出妥协以满足预算和场地限制。阿什比池塘位于波托马克河和切萨皮克湾一个高度发达的源头流域。由于过多的沉积物和养分负荷导致河口富营养化，2010年美国环境保护局对该海湾流域实施了总最大日负荷（TMDL）规定。由于TMDL规定，减少养分和沉积物排放负荷已成为海湾流域许多雨水项目的关键目标。阿什比池塘改造项目包括疏浚堆积的沉积物以增加蓄水量、建造一个出口结构以控制水流以及修复大坝。由于空间限制，池塘容积不太理想。尽管有这个缺点，阿什比池塘在磷、氮和悬浮沉积物的减少方面有统计学上的显著效果。与按照当前国家标准建造的滞留池的处理效果相比，改造后的池塘减少的磷较少，但减少的氮较多。对流域内现有的池塘进行改造，使其至少部分符合当前设计标准，可能是社区实现下游水质目标的一种直接方式，因为这些改进意味着基线负荷的减少，而新城市开发区新建的池塘只是限制未来负荷的增加或维持现状。
