Multi-Year USGS and State Collaboration
Advances Understanding of Pesticides in the Delta
A new publication from the U.S. Geological Survey and the California Department of Water Resources summarizes multiple years of collaborative work between the two agencies in the northern Sacramento–San Joaquin Delta.
The Sacramento and San Joaquin rivers converge in the Delta after flowing through agricultural and urban regions across much of California. As the rivers flow from their headwaters to their confluence in the Delta, chemicals, such as pesticides, enter the system. The specific pesticide compounds and their concentrations shift over the course of the year, reflecting differences in land use, pesticide application timing, and river flow. Tracking how these substances move through water and into the food web requires coordinated sampling, long-term monitoring, and sustained collaboration among agencies.
The study assessed how pesticide concentrations in water and zooplankton respond to pesticide application, season, river flow, and augmented flow pulses in summer–fall. The work brought together hydrologists, chemists, and biologists to connect changing flow conditions with chemical measurements and biological sampling.
Working Across Agencies and Disciplines
The publication reflects several years of coordinated field sampling, laboratory analysis, and shared data evaluation. Scientists aligned sampling with shifts in river flow, seasonal pesticide use, and managed summer–fall flow pulses. Field crews collected water and zooplankton samples, laboratory scientists analyzed pesticide concentrations, and researchers integrated the results with hydrologic data.
By examining both water and zooplankton, the team evaluated how pesticide concentrations in the water column were reflected in organisms at the base of the food web.
According to USGS scientist Michelle Hladik, “This publication was the summary of multiple years of work with the USGS and DWR in the Delta. While this project is done, we hope to continue this type of work in the future, allowing us to highlight the USGS’ unique capabilities.”
Those capabilities include long-term monitoring infrastructure, specialized laboratory capacity, and the ability to integrate hydrology, water chemistry, and biology within a single study framework.
Connecting Flow to the Food Web
Zooplankton are a primary food source for many fish species in the Delta. Measuring pesticides in both water and zooplankton provides insight into how contaminants move from runoff into the aquatic food web under varying flow conditions.