Urbanization and aquatic ecosystem health in Malibu Creek, California: Impacts on periphyton, benthic macroinvertebrates, and environmental policy

In this study we conducted biological assessments in Malibu Creek, California and an analysis of implementation of water quality regulations in the watershed, by local and federal government regulators. The biological assessments were designed to determine the effects of increased urbanization on periphyton cover and benthic macroinvertebrate communities in Malibu Creek. Other studies have shown that increased urbanization generally leads to increased urban runoff containing pollutants such as nutrients and sediments. Urbanization is also associated with degraded habitat quality, due to increased erosion and sedimentation and loss of riparian vegetation. Multiple regressions of periphyton cover with nutrients, canopy cover and substrate size indicated nutrient concentrations were most often related to periphyton cover, with canopy the next most important factor after nutrients. Nutrient concentrations in the water and percent cover of periphyton were lower at reference sites than at impacted sites. The diversity and sensitivity of the benthic macroinvertebrate (BMI) community were lower at sites impacted by urban runoff. Multiple regressions of BMI community metrics with habitat variables indicated that embeddedness of the substrate, percent canopy cover, and conductivity in the water were the most important environmental factors influencing the BMI community. These environmental factors are affected by urbanization in the watershed, which thus impacts the BMI community. I discuss the ecological and management implications of these results.; The implementation of section 303(d) of the federal Clean Water Act has raised numerous regulatory and policy issues in the Malibu Creek watershed and throughout the state. One response of the state of California has been to increase the stringency of data requirements for obtaining a s. 303(d) listing for an impaired waterbody, thereby reducing the number of listed waterbodies. The results of these changes in California may be fewer TMDLs and potentially decreased ability of regulators and citizens to protect water quality. I analyzed the new state and federal guidelines and policies for implementing s. 303(d) of the Clean Water Act, and present a case study of how citizen monitoring data provided crucial information for a new 303(d) listing and future TMDL development in Malibu Creek, California.