Featured Projects — Modeling Modeling Nutrient Transformation and Losses in the Sacramento-San Joaquin Delta

In support of the Interagency Ecological Program (IEP), we are collaborating with Carol Kendall, isotopes project chief for the US Geological Services, and David Senn of San Francisco Estuary Institute to use isotope analyses in conjunction with numerical models to improve the accuracy of Delta nutrient models and better understand the role the Sacramento-San Joaquin Delta plays in transporting, transforming, assimilating, and removing various nutrient sources.

Working as co-primary investigators, Kendall, Senn and Marianne Guerin, RMA’s senior water resources analyst, are using the Delta Simulation Model (DSM2) and the RMA Bay-Delta model to develop a more complete picture of the nutrient processes found in the Sacramento-San Joaquin Delta.

Results and benefits

Isotopic analyses of nutrients can act as fingerprints to identify nutrient sources and processes, for example, by distinguishing between the nutrient sources in wastewater effluent versus agricultural return flows. Nutrient data and isotopic analyses can be used as information to refine nutrient transformation rates and to improve the DSM2-QUAL nutrient model calibration. Additionally, DSM2-QUAL and RMA volumetric source water (e.g., tributary inflow or wastewater) model calculations, along with hydrodynamic measurements, can be used to help interpret the information contained in the isotope measurements. The two-way analysis will be used to clarify the sources, sinks, and processes regulating the fate of nutrients in the Delta.

DSM2 and RMA historical simulations provide hydrodynamics and water-quality model output used in interpreting nutrient and isotope measurements, for example, by utilizing model capabilities to provide source water fingerprinting (the volumetric percentage of source water found at any point within the model domain).

Screenshot of model showing particle fate volume percentages ranging from 100% to 33%.

RMA Model of particle fate exiting insertion region into Cache Slough January 1 – 17, 2012


RMA models are also used to provide residence time calculations in selected regions and times of interest to investigate the relationship between primary productivity, nutrient supply, and hydrodynamic conditions, and to estimate the area of the low-salinity zone in the region downstream of the confluence of the Sacramento and San Joaquin Rivers. In addition, RMA particle-tracking model animations provide insight into the complex hydrodynamics of the region that includes Cache Slough and Liberty Island.

Relationships between Kendall’s isotopic analyses and RMA and DSM2 model results will provide the basis of the project findings and deliverables.