Mitigated wetlands for the treatment of stormwater runoff: Monitoring and management.

摘要

The objective of the Clean Water Act (CWA) is to “restore and maintain the chemical, physical, and biological integrity of the Nation's waters.” While tremendous water quality improvements have been realized in the United States from increased control of point source discharges in the twenty-five years since the CWA was passed, non-point sources (NPS) of pollution still pose a significant threat to the integrity of our Nation's waters and bodies of water worldwide. Wetlands, as low points in the landscape and as transitional ecosystems between terrestrial and aquatic environments, are inexorably linked to NPS pollution. The research described in this dissertation leads to a number of conclusions concerning wetlands, particularly mitigated wetlands, as stormwater best management practices (BMP). Conclusions are drawn from analysis of monitoring data, examination of bench-scale experiment data, and examination of methods for incorporation of stormwater treatment wetlands (and other BMPs) into watershed modelling frameworks and watershed management analysis.; Monitoring of mitigated wetlands receiving highway runoff indicates that they may be as effective as conventional BMPs at improving the quality and controlling the quantity of highway runoff. Peak reductions in excess of 40% were observed, with attenuation of greater than 90% for a system combining a detention basin and a mitigated wetland in series. Average removal rates as high as 90% for TSS, 65% for COD, 70% for TP and OP, and 50% for Zn were monitored at study sites. Despite having stormwater runoff as a primary water source, sites monitored supported apparently healthy and diverse vegetation and a variety of wildlife. Differences in removal efficiencies for the sites monitored are likely attributable to differences in key design parameters including the configuration of inlets and outlets, the length to width ratio, and (consequently) residence time. Greatest removal is achieved for sites that maximize the length to width ratio and flow path through the system. Poor placement of inlets and outlets results in short-circuiting that decreases residence time of water in the wetland.; Hydrologic data from the monitoring of mitigated wetlands receiving stormwater runoff and TSS, TP, and COD data from the bench-scale experiment were examined using a first-order forward, zero-order reverse model. A single continuously stirred tank reactor (CSTR) was utilized for modelling of field-scale wetland hydrology and bench-scale TSS, TP, and COD data. A model using multiple CSTRs was applied for rudimentary examination of short circuiting, a phenomenon frequently observed in the course of monitoring. A method, known as e&barbelow;quivalent l&barbelow;and u&barbelow;se (ELU) analysis, was developed for examination of treatment wetlands and other BMPs in the context of a watershed. The ELU approach for incorporation of treatment wetlands and other BMPs with watershed modelling efforts is a highly versatile, easily applied method for assessment of spatially distributed wetlands/BMPs in a watershed. The ELU approach utilizes loading functions coupled with extended simulation to compare loading factors and annual loading for untreated runoff and BMP controlled runoff.