Nonpoint source water pollution management : Monitoring, assessment and wetland treatment

Sammanfattning: The management of nonpoint (diffuse) sources of-water pollution has received increased attention during the past decade. New techniques that aid in the identification and assessment of these diffuse sources can increase the chances for success of nonpoint source control efforts. This dissertation presents several new strategies for the monitoring, assessment and control of non point sources. The results are based on research in Sweden and Washington State.A framework for definition of monitoring program objectives is presented. It was concluded that it is better to define specific rather than general objectives. This reduces monitoring program costs and can provide more relevant information for decision makers. Stratified and event sampling, and the careful choice of sampling locations arc demonstrated as important components of a nonpoint source monitoring program.Nonpoint source loading estimates can vary significantly depending on the applied estimation technique and the type of data collected from a monitoring program. Analyses showed that a representative cross-section of samples, collected during different flow conditions, is necessary to reduce the possibility of under- or overestimating true loadings. Event sampling is recommended if cost constraints limit the frequency of sample collection. Comparisons between a monitoring- program, designed to address non point sources, and an ongoing routine program showed significant differences between the information obtained, as measured by its validity and reliability.A Geographic Information System (GIS) was developed to perform spatial analyses on land use, soils, topographic and hydrologic in formation for purposes of nonpoint source assessment. The GIS identifies critical areas for sediment-related water quality problems and land resource protection. Comparisons with a concurrent water quality study of non point loadings showed a strong correlation between identified critical areas and the annualloadings of total phosphorus and total suspended solids.The potential for wetlands to reduce sediment and nutrient toadings associated with nonpoint-source runoff was examined in a study of two wetlands. The loading and net removal of sediment and nutrients were found to vary by season, flow conditions and residence time. Removal of total phosphorus occurred during storm conditions, but the overall annual removal was negligible. For nitrate-nitrogen, removal rates were 146 and 262 kg ha-1 yr-1 based on the effective area of the two wetlands.In summary, this dissertation synthesizes several issues important to non point source water pollution management. Specifically, recommendations are made for: (1) directed nonpoint source monitoringefforts, (2) appropriate usage o'f loading estimation techniques, (3) evaluation of the validity and reliability of monitoring program information, (4) application of GlS technology in nonpoint source assessment, and (5) consideration of wctland treatment options for nonpoint sources.