Research Studies & Collaborations

Research Studies & Collaborations


A primary focus of the Regional San science team is working in partnership with other agencies and organizations to study the importance of a wide range of stressors on the Delta ecosystem (and on the Delta’s beneficial uses) so that the best possible science can be brought to bear on critical policy and management issues in the Delta and watershed.

Potential stressors include hydrologic modification, fish entrainment, invasive species, predation, contaminants, habitat loss or alteration, climate change, and our treatment plant’s discharge.

Recent Efforts

Our science section has recently supported four large-scale scientific studies on the Sacramento River conducted by the USGS, university researchers, and our own staff. Our aim is to better understand the role of Sacramento Regional Wastewater Treatment Plant (SRWTP) discharge in the Sacramento River and the Bay-Delta ecosystem, with an emphasis on phytoplankton growth, abundance, and species presence in association with nutrients and other environmental factors.

Results suggest that (1) a factor other than the presence of wastewater is leading to the decline in phytoplankton biomass along the river near SRWTP, (2) high stress and low production of phytoplankton in Suisun Bay is related to some factor(s) other than ammonia, and (3) non-native clams are widely present in the Sacramento River between Sacramento and Isleton, potentially reducing phytoplankton abundance.

Photo Gallery

Delta Cross Channel Study 2020

In the spring of 2020, Regional San staff studied how environmental conditions can affect phytoplankton living in Delta river channels. Many factors can influence the amount of phytoplankton occurring in Sacramento–San Joaquin River Delta, including nutrient concentrations, water clarity, water flow rates, and grazing by clams and zooplankton. One method to investigate the relative importance of these factors is by measuring how phytoplankton respond to a dramatic change in environmental conditions, such as nutrient concentrations, water clarity, or flow rate.

Photo Gallery
Map of the stations and transects sampled for the Sacramento River Nutrient Change Study

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.


Sacramento River Phytoplankton Studies 2016

Some previous research on the Sacramento River found declining phytoplankton concentrations at downstream locations. The cause for the observed phytoplankton decline is not easily discernible, because the loss does not appear to be driven by effluent-derived nutrient concentrations, and while phytoplankton-consuming organisms, such as clams and zooplankton, are present in the river, they are not abundant enough to fully explain the decline.


Sacramento River Phytoplankton Lagrangian Study

We supported a large-scale research study by USGS and university scientists to investigate the effects of SRWTP discharge of treated wastewater on phytoplankton health in the Sacramento River, using a presence and absence study.

This study addressed concerns about reduced phytoplankton abundance and potential changes in relative phytoplankton species abundance reported in the Lower Sacramento River.


“Bad Suisun” Phytoplankton Study

The nutrient ammonia in the Sacramento River is derived from multiple sources, including effluent from the SRWTP. Ammonia may be used by phytoplankton for growth, but some studies have suggested that excessive concentrations of it may inhibit phytoplankton growth.


Sacramento River Clam Survey

We investigated the presence, distribution, and abundance of invasive clams in the Sacramento River between Sacramento and Isleton in 2013 and 2014.

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