Dynamic Solutions

Delta Ecological Modeling

A part of a comprehensive modeling framework in support of the Sacramento Corps District’s Delta Islands Levee Feasibility study, Dynamic Solutions, LLC is developing an Comprehensive Aquatic Systems Model (CASM) of the entire Sacramento-San Joaquin Delta. A key component of this effort is the development of a detailed and informative food web model of the important lower trophic level (LTL) species in the Delta. The model provides a tool for understanding productivity and energy cycling in the LTL food web. Extensive field data and study on the Delta LTL food web exist, but no detailed models of the food web existed previously. The LTL food web model will be an important link between the several hydrodynamic and fish models that already exist or are in development for the system. The model has been be linked to hydrodynamic and water quality models to evaluate productivity and energy cycling in the LTL food web over seasons and among years due to changes in the physical-chemical conditions over time. Linking the model to hydrodynamic models, and potentially to fish models, allows for evaluation of bottom-up effects on the food web and fish populations.

The Comprehensive Aquatic Systems Model (CASM) was selected to simulate the dynamics of the LTL food web. The food web model was largely developed from the data and information available for the ecologically-important lower salinity zone (LSZ) of the system. The CASM food web is comprised of ten species/or functional groups and represents important LTL processes such as photosynthesis, respiration, and zooplankton grazing for the primary producers, and consumption, mortality, reproduction and growth of the consumer populations. The CASM food webs are set up in selected cell locations of the EFDC hydrodynamic model. Daily vertically-averaged conditions for each cell from the EFDC hydrodynamic model (e.g., temperature, salinity) and water quality model (e.g., nutrients, DOC) are used as direct concentration inputs in the CASM food web or else to differentially drive the exchange rates and processes of the component producer and consumer populations of the food web.

The predicted seasonal biomasses of the populations from the LTL food web CASM has been calibrated to the available biomass data from field stations for the long-term monitoring programs (i.e., IEP, USGS) in the Delta, and for the LSZ from the available food web studies. Biomass, production, and energy flow among key biota in the CASM food webs was compared in and around the LSZ within years, and compared for the different conditions among years.

Additional applications that could be addressed with the LTL food web CASM include: examining the bottom-up food web effects of turbidity and ammonium loading; examining the differential top-down food web effects of grazing by invasive clams; and determining the environmental conditions that promote zooplankton prey levels which could improve recruitment and potentially reduce population declines of important fish species (e.g., Delta smelt).

Sacramento Corps CASM Ecological Modeling: This was a CASM comprehensive modeling framework in support of the Sacramento District’s Feasibility study of the entire Sacramento-San Joaquin Delta.



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