NEW FINDINGS ON SOURCES OF ORTHOPHOSPHATE IN UPPER MALIBU CREEK WATERSHED: A GEOLOGIC SOURCE PRIMARILY? (Abstract)

摘要

Recent studies have suggested dissolution of geologic strata by percolating groundwater is the most important source of orthophosphate during dry weather flow conditions (2 weeks after any rain event) in Upper Malibu Creek Watershed of Southern California. The earliest concepts on nutrient levels in the watershed, which were somewhat anecdotal, pointed to urban runoff as the principal source of orthophosphate in residential and commercially developed parts of the watershed. More recently, it has been established that baseflow is a principal source of dry weather stream flow in many parts of the watershed. The observation that creeks are fed to a significant extent by groundwater, and that orthophosphate is elevated in the creeks along the upper watershed corridor (where Monterey/Modelo . Miocene marine strata are the main source rocks feeding baseflow into the creeks and streams) led some investigators to conclude that the phospatic member of Monterey/Modelo strata is the source of elevated orthophosphate. Concentrations in surface water in Upper Malibu Creek Watershed are typically in the range of 0.4 to 1.0 mg/L dissolved orthophosphate.