Research Areas > Nutrients > Identification of Nutrient Sources > Estimating Terrestrial Sources > Nutrient Mass Balance of the Southern California Bight

Project: Nutrient Mass Balance of the Southern California Bight

Background and Objectives

SCCWRP routinely quantifies anthropogenic contributions of contaminants to the coastal ocean based largely on collated data from the many discharge monitoring programs that are required by NPDES permits. These programs typically focus on quantifying contributions of metals and organics to the coastal ocean. Nutrients present a greater challenge, though, because many nutrient species are not measured in routine monitoring programs. In addition, while natural sources are of less concern for other contaminants, anthropogenic contributions of nutrients need to be separated from natural nutrient sources such as ocean upwelling.

This project, which is one aspect of the Bight Offshore Water Quality component, will determine the relative contributions of four major sources of nutrients to the Southern California Bight (SCB), including wastewater effluent discharge, terrestrial runoff, atmospheric deposition and upwelling.

Status

This project was initiated in 2008 with anticipated completion in 2012.

Methods

The magnitude of wastewater effluent discharge loads to the SCB will be calculated through analyses of monthly effluent samples and measured discharge rates from the four largest (plus several smaller) POTWs in southern California. Upwelling will be estimated by combining ship-based discrete samples with the Regional Ocean Model System (ROMS) physical circulation model. A combination of measured and modeled wet weather and dry weather loads from all coastal watersheds that drain to the SCB will be used to estimate the nutrient loading rates from terrestrial runoff. Watershed wet and dry weather models will be calibrated using existing data on nutrient concentrations and loads collected by Storm Water Monitoring Coalition agencies from 38 mass emission stations. Atmospheric deposition will be determined from both wet and dry deposition samples collected from several sites in the SCB.

 

Partners

This project is being conducted in cooperation with the more than 30 organizations participating in the Bight ’08 Water Quality component.