Sacramento River Nutrient Change Study 2019

Regional San staff and collaborators are studying the potential environmental effects of a change in nutrient loading to the Sacramento River in September 2019, which resulted from a wastewater hold at the Sacramento River Wastewater Treatment Plant (SRWTP). This hold, which was planned as part of the EchoWater Project construction process, prevented treated wastewater from entering the Sacramento River for 48 hours. Given the relatively high river flows in 2019, the hold created a zone of wastewater-free river water over 20 miles long in the lower Sacramento River. The wastewater-free zone also stretched into nearby channels with differing water flows and turbidity, including Georgiana Slough, the North Fork Mokelumne River, and the South Fork Mokelumne River. Scientists used a small fleet of four research boats to collect water samples in all these river regions before and during the wastewater hold.

Sampling included:

• Hydrodynamic (Water Flow) Modeling (Resource Management Associates)
• High Frequency Water Quality Boat Mapping (US Geological Survey)
• Water Quality Sampling and Laboratory Analysis (Regional San)
• Plankton Enumerations (BSA Environmental Services, Inc.)
• Phytoplankton Carbon Uptake (to determine growth rates) (Applied Marine Sciences, Inc.)
• Zooplankton Growth (San Francisco State University)
• Clam Collection and Analysis (Regional San and Applied Marine Sciences, Inc.)

Data and hydrodynamic modeling will be used to evaluate how phytoplankton (small aquatic plants) and zooplankton (tiny aquatic animals) responded to changes in physical and biological factors during the study. These factors include differences in nutrient loads and forms, water residence times, light levels, turbidity, and grazing by zooplankton and clams. It is important to understand the conditions regulating phytoplankton and zooplankton growth in the watershed because these organisms are a primary food source to the Delta’s ecosystem.

This study is jointly funded by the Delta Regional Monitoring Program, State Water Contractors, and US Bureau of Reclamation, with in-kind contributions from Regional San and the US Geological Survey.