Management of nutrients and trace metals in urban runoff in a southern California coastal watershed

The goals of this research were to assess the relative importance of the pollutant loading in urban dry weather runoff (DWF) and wet weather runoff (WWF) in a western watershed and to develop a wetland restoration planning tool for waterbodies that are adversely impacted by DWF. WWF and DWF watershed loading models were developed and a receiving water quality model was calibrated for the Ballona Creek Watershed (BCW), a highly urbanized coastal watershed in Los Angeles, California. WWF and DWF pollutant loading from this watershed was estimated using the EPA's Storm Water Management Model and an empiric model generated using historic water quantity and water quality data. The EPA's Water Analysis Simulation Program was used to simulate the receiving water response to the DWF pollutant loading. The receiving water quality model was parameterized for copper and nickel in the system and was used to develop an approach for assessing wetland culvert placement options in a wetland restoration in terms of water quality.; This study indicates DWF is an important source of trace metals and some nutrients. Trace metals in DWF are found primarily in the dissolved phase and therefore may increase aquatic toxicity following discharge to coastal waters. Although DWF is an important source, WWF is the predominant non-point pollutant source of most trace metals and nutrients on an annual basis. WWF pollutant loads are large acute loads that may be impacting pelagic species during the storm event and benthic species in the area receiving the contaminated suspended sediment load. During the dry season, DWF is the predominant source, and the concentrations of pollutants in the receiving water exceed water quality criteria. The poor water quality in the dry season may adversely affect threatened ecosystems such as the Ballona Wetlands. This research shows DWF may be an important pollutant source in other arid and semi-arid cities. The techniques used in this research will be useful in conducting comparisons of DWF and WWF pollutant loading of the contaminants studied in this research as well as other contaminants, such as trace organics, in other cities with distinct wet and dry seasons.