The Sacramento Regional County Sanitation District (Regional San) is currently completing major upgrades to its wastewater treatment plant. In anticipation of these upgrades, USGS scientists are gathering data to establish baselines for current nutrient levels and dynamics in the Sacramento-San Joaquin Delta (Delta).
Scientists Collect Water Quality Data Prior to Wastewater Treatment Plant Upgrades
The plant is located two miles from the Sacramento River, near the city of Elk Grove. Known as the EchoWater Project, work on the upgrades broke ground in 2015. The project includes a Biological Nutrient Removal (BNR) upgrade which is due to be completed in late 2021. (The entire EchoWater project will reach completion in 2023.) The BNR upgrade includes enhanced water treatment processes such as the removal of the nutrients ammonium and nitrate.
While certain types and levels of nutrients are essential for animal and plant growth, excessive nutrients may have significant consequences to ecological communities. Of particular concern in the Delta is the formation of harmful algal blooms (HABs) due to increased nutrient loads. While some HABs are nontoxic, others contain cyanobacteria (also referred to as blue-green algae) which may produce dangerous toxins (cyanotoxins).
Treatment plant inprovements will reduce nutrient loads going into the River and Delta. This reduction of nutrient discharge is expected to alter the amount of nutrients distributed across the entire Delta and San Francisco Bay Estuary ecosystem. Data gathered from USGS research projects will later be used to measure post-upgrade changes in water quality and their effects on the Bay-Delta ecosystem.
USGS research projects will include the following:
Determining Relationship Between Nutrient Concentrations and Phytoplankton Abundance
USGS scientists will evaluate the current distribution and concentration of wastewater-derived nutrients (such as ammonium) across the Delta and relate that to the abundance and distribution of beneficial and harmful phytoplankton. Beneficial phytoplankton, like diatoms, serve as an indicator of a good aquatic habitat for threatened and endangered native fishes. Excess amounts of some nutrients, such as ammonium, can lead to production of types of phytoplankton that are less beneficial to the Delta’s aquatic food webs, and even result in growth of harmful phytoplankton, like cyanobacteria, which produce toxins. Understanding current levels, types, and distribution of nutrients is critical for evaluating expected environmental improvements following wastewater treatment plant upgrades.
Modeling Nitrogen Reduction Benefit to Invasive Aquatic Vegetation vs. Native Phytoplankton
Competing with phytoplankton for required nitrogen, invasive aquatic vegetation (IAV) has increased exponentially in recent years. Once established, IAV can negatively impact local ecosystems and infrastructure. In this project, scientists will model how reductions in Delta nitrogen levels due to the treatment plant upgrade may affect phytoplankton vs. IAV production. Scientists will also contribute to a SCHISM modeling effort to demonstrate how reductions in nitrogen loading are affecting vegetation throughout the Bay-Delta.
Assessing Sediment Nutrient Storage and Release
Sediments represent an important pool of nutrients in the Delta. The exchange of nutrients between the water column and the benthos (the bottom or floor of a water body) is an important determinant of water quality. In this study, USGS scientists will assess sediment nutrient inventories and fluxes in Delta. This information will be used to form a baseline prior to the reduction in nutrient inputs resulting from the treatment plant upgrade. Data from the research will also help scientists understand the role of the microbial community, including cyanobacteria, in benthic nutrient cycling.
Mapping Delta Cyanotoxin Concentrations
Cyanotoxins, which can sicken or kill people and animals, result from cyanobacteria found in harmful algal blooms (HABs). To help quantify cyanotoxin levels and the conditions that can lead to their production, scientists will collect and test water samples from the Delta using two approaches: fixed station monitoring and boat-based mapping.