Quantifying Longitudinal Variation in Morphology, Metals, and Nutrients of Los Peñasquitos Creek, CA

Authors: Suzanne Walther*, University of San Diego, Ravleen Khalsa-Basra, University of San Diego, Michael Bennett, University of San Diego
Topics: Geomorphology, Environmental Science, Water Resources and Hydrology
Keywords: urbanization, geomorphology, total metals, fluvial, watershed management
Session Type: Virtual Paper
Day: 4/8/2021
Start / End Time: 4:40 PM / 5:55 PM
Room: Virtual 3
Presentation File: No File Uploaded

In highly urbanized coastal regions, such as Southern California, rare open spaces are vital for providing ecosystem services. Rivers in semi-arid climates are directly influenced by local geographic and hydrologic conditions and impacted by modifications to hydrology via urbanization. Los Peñasquitos Creek, one of few perennial freshwater streams in San Diego County, flows through a small coastal watershed that has increased urbanization ~10% in the past 10 years, and discharges into an estuary. To plan for future urban and climate change impacts, it is important to understand the current conditions of the watershed. This study combines work conducted over several years using GIS analysis, field surveying and sampling, and laboratory methods to quantify urbanization, river characteristics, sediment distribution, and total metal concentration and organic carbon (%OC) in the sediment. The morphological data highlight three distinct river reaches (upper, middle, lower). Longitudinally, D50 grain size decreases, metal concentrations vary, and %OC correlates with fines and specific metals. Copper and Mercury exceed SQuirT screening concentrations. Highest %OC were positively correlated with fine-grained samples and with high Zinc and Lead concentrations. Variations from some expected patterns reflect the influence of local geomorphology and vegetation cover. These data form the foundation of flood modeling in the watershed and can be used to aid in monitoring and management of the watershed by both the City of San Diego and California State Parks.

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