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.
Our science section is currently supporting three 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.
Preliminary 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.
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.
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.
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.
We investigated the presence, distribution, and abundance of invasive clams in the Sacramento River between Sacramento and Isleton in 2013 and 2014.
Invasive clams graze on phytoplankton and compete for food with native Delta organisms. It was known that phytoplankton abundance is limited by grazing in the Low Salinity Zone (LSZ) of the Bay-Delta system (near Suisun Bay, between Martinez and Pittsburg). In the LSZ, clams and microzooplankton can consume phytoplankton faster than it is produced, and clams can filter all of the water in the Sacramento River in 1.25 days.
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