ANALYSIS OF ELEVATED CONCENTRATIONS IN TRACE ELEMENTS AND NUTRIENTS IN URBAN CREEK

摘要

Dry weather runoff (imported and recycled water) contributes to perennial flows in the Malibu Creek Watershed located in southern California. Our study investigates an urban creek for selenium, nutrients, and stable water isotopes to further understand inputs and sources. We have found concentrations of 9.9 to 32 ug/L Se and 0.37 to 6.6 mg/L NO_3~-N from groundwater seeps that flow within a storm drain. From the input of a storm drain where dry weather runoff provides perennial flow, concentrations range from 4.1 to 11 ug/L Se and 1.5 to 4.9 mg/L NO_3~-N. Concentrations decrease from 4.1 to 0.74 ug/L Se and 0.12 to 0.59 mg/L NO_3~-N downstream. Moderately high concentrations of nitrate-nitrogen correlating with elevated concentrations of selenium suggest that enriched selenium is oxidized by elevated concentrations of nitrate found in local shallow groundwater and urban runoff. Our results coupled with seasonal analysis of hydrogen and oxygen isotopes further suggest perennial input and mixing of local groundwater throughout the riverine system.