Constructed treatment wetlands for reducing nutrient loading in the lower Malibu Creek watershed (California)

Nutrient enrichment by point and non-point source discharges is a major concern in the Malibu Creek Watershed located in Los Angeles County California. The basis for this concern is the persistent and extensive "nuisance" algae growth that plague Malibu Creek and Lagoon in the late spring and summertime. These algae blooms interfere with the recreational enjoyment of these waters and have the potential to cause low-oxygen conditions in aquatic habitat. While nitrogen and phosphorus loading have been identified as major contributors to the problem, studies have indicated that other physical and environmental conditions, including flow velocity and light intensity, play a role in the occurrence of algae blooms.; Constructed wetlands are a low-cost, low technology means of improving water quality with the added benefit of habitat enhancement and/or creation. They are effective to varying degrees in the removal of pollutants such as nutrients, suspended solids pathogens and biochemical oxygen demand from source waters; and would be useful in addressing water quality problems on a watershed scale.; This dissertation provides a comprehensive overview of the algae problem in the Malibu Creek Watershed and efforts taken to curb it to date. A pilot-scale constructed wetland study is conducted to determine the extent of nitrogen reduction attainable when treating effluent from the single point source discharge in the watershed. This discharge is a tertiary-treated effluent that is high in nitrate and low in organic carbon. Results from this study indicate that significant nutrient reduction is achievable even with this type of influent. In the absence of readily available carbon sources, plant uptake was the primary removal mechanism of nitrate---as opposed to denitrification.; Malibu Creek and Lagoon will also benefit from the use of constructed wetlands to treat septic tank effluent and urban run-off in creek flows. However the lack of readily available land in the watershed limits opportunities for wetland creation. Thus, in the Malibu Creek Watershed, it is necessary to involve public agencies, with significant land holdings, in plans to create and operate constructed wetlands for the purpose of water quality enhancement.