Delta Regional Monitoring Program Nutrients Synthesis: Modeling to Assist Identification of Temporal and Spatial Data Gaps for Nutrient Monitoring

Nutrient loads are an important water quality management issue in the Sacramento-San Joaquin Delta (Delta) and there is consensus that the current monitoring activities do not collect all the information needed to answer important management questions. The purpose of this report is to use hydrodynamic model outputs to refine recommendations for monitoring nutrients and related conditions in the Delta. Two types of modeling approaches were applied: 1) volumetric water source analysis to evaluate the mix of source waters within each subregion; and 2) particle tracking simulations.The analysis revealed that each Delta subregion has a unique “fingerprint” in terms of how much of its water comes from different sources. Three major recommendations for a future monitoring design were derived from this analysis:

Recommendation #1: The subregions proposed for status and trends monitoring in a previous report should be redrawn to better reflect the mixtures of source waters.

Recommendation #2: Long-term water quality stations are needed in the North Delta, Eastside, and South Delta subregions.

Recommendation #3: Areas with a long-residence time and where mixing of different water sources occurs are potential for nutrient transformation hotspots. High-frequency water quality mapping of these areas has the