Optimizing sampling methods for monitoring pollutant trends in San Francisco Bay urban stormwater

San Francisco Estuary Institute (SFEI) | July 1st, 2016

The Small Tributaries Loading Strategy (STLS) focuses on urban stormwater loadings from small tributaries. To date, STLS monitoring has been geared towards dete

The Small Tributaries Loading Strategy (STLS) focuses on urban stormwater loadings from small tributaries. To date, STLS monitoring has been geared towards determining concentrations and annual loads of PCBs and Hg; the sampling approach has yet to be fully optimized for detecting trends over time. Here, we evaluate the variability and statistical power for detecting future trends in PCBs based on baseline STLS data in the Guadalupe River watershed. The objective was to improve our understanding of the influence of climatic and seasonal factors on baseline stormwater pollutant conditions, and inform refinements to the STLS monitoring design for detecting trends.

Ordinary High Flows and the Stage–Discharge Relationship in the Arid West Region

U.S. Army Corps of Engineers (USACE) | July 14th, 2011

The Ordinary High Water Mark (OHWM) defines the lateral extent of non-wetland waters and is regulated as “Waters of the United States” under Sec. 404 of the Clean Wat

The Ordinary High Water Mark (OHWM) defines the lateral extent of non-wetland waters and is regulated as “Waters of the United States” under Sec. 404 of the Clean Water Act. Previous research has developed a reliable and repeatable methodology for identifying the OHWM on ephemeral and intermittent streams in the Arid West using the physical features of the channel (Lichvar and McColley 2008, Curtis and Lichvar 2010). This study expands upon the previous reports by providing an analysis of how gage data may be utilized in OHW determinations. We clarify the methodology for using gage data, review the potential errors encountered in developing a stage–discharge relationship, compare the position of the gage-predicted OHWM to the field OHW signature, and determine the recurrence interval and flow duration of OHW events. The field OHW signature often is not associated with a 2-year flood event like many assume, but ranges from <1- to 15.5-year flood event. This large variation in recurrence intervals for the field OHWMs makes it impossible to define the frequency of the ordinary high flow from gage data because the OHW event is unique to each channel.

Patterns and magnitude of flow alteration in California, USA

Freshwater Biology (Wiley) | December 27th, 2017

The importance of the natural flow regime to stream and river health has received growing attention over the last two decades. Quantifying natural river flows has become

The importance of the natural flow regime to stream and river health has received growing attention over the last two decades. Quantifying natural river flows has become an essential component of water resource planning, including assessments of water supplies (Vicuna,Maurer, Joyce, Dracup, & Purkey, 2007; Wurbs, 2005), reservoir operations (Hejazi, Cai, & Ruddell, 2008) and drought risk (Meko,Therrell, Baisan, & Hughes, 2001). Understanding the natural flow regime is also crucial for managing stream ecosystems.

Per and Polyfluoroalkyl Substances (PFASs) in San Francisco Bay: Synthesis and Strategy

San Francisco Estuary Institute (SFEI) | June 1st, 2018

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are a broad class of fluorine-rich specialty chemicals. Some types of PFASs, and in particular the perfluoroalkyl f

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are a broad class of fluorine-rich specialty chemicals. Some types of PFASs, and in particular the perfluoroalkyl forms, possess thermal stability, non-reactivity, and surfactant properties, making them useful for many different types of applications. More than 4,700 PFASs are used in consumer, commercial and industrial applications, including food packaging materials, waterproof textiles, stain-resistant carpets and furniture, fire-suppression foams, processing aids for the production of fluoropolymers like Teflon, mist suppressants in metal-plating, and hydraulic aviation fluids.

Per- and polyfluoroalkyl substances (PFASs) in San Francisco Bay wildlife: Temporal trends, exposure pathways, and notable presence of precursor compounds

Chemosphere (Elsevier) | April 21st, 2017

Concentrations of perfluorooctane sulfonate (PFOS) in San Francisco Bay (SF Bay) wildlife have historically been among the highest reported globally. To track continuing

Concentrations of perfluorooctane sulfonate (PFOS) in San Francisco Bay (SF Bay) wildlife have historically been among the highest reported globally. To track continuing exposures to PFASs and assess the impact of the 2002 phase-out of production of PFOS and related chemicals in the US, nine perfluoroalkyl carboxylic acids (PFCAs; C4-C12), three perfluoroalkyl sulfonic acids (PFSAs; C4, C6, C8) and perfluorooctane sulfonamide (PFOSA, a PFOS precursor) were measured in SF Bay cormorant eggs in 2012 and harbor seal serum sampled between 2009 and 2014. PFOS remained the dominant perfluoroalkyl acid (PFAA) in both cormorant eggs (36.1–466 ng/g) and seals (12.6–796 ng/g) from 2012 and 2014, respectively. Concentrations in seal and bird eggs from the South Bay have declined approximately 70% in both matrices. To elucidate potential pathways of exposure, prey fish, sediments and wastewater effluent were analyzed for PFASs, and in the case of sediment and effluent, a suite of PFAA precursors. PFOS was the dominant PFAA in prey fish and sediment. In effluent, different mixtures of PFAAs were measured, with PFOS, PFHxA, and PFOA detected in the highest concentrations. Polyfluoroalkyl phosphate diesters (PFCA-precursors) were observed at concentrations over an order of magnitude higher than PFCAs in sediment, highlighting their importance as a potential, on-going source of PFCAs to SF Bay wildlife. These findings suggest that the PFOS phase-out has resulted in reduced burdens to wildlife in SF Bay, but that exposure to diverse and incompletely characterized PFASs continues.

Pesticide Concentrations Associated with Augmented Flow Pulses in the Yolo Bypass and Cache Slough Complex, California

U.S. Geological Survey (USGS) | July 23rd, 2020

Surface-water and suspended-sediment samples were collected and analyzed by the U.S. Geological Survey for multiple current-use pesticides and pesticide degradates approx

Surface-water and suspended-sediment samples were collected and analyzed by the U.S. Geological Survey for multiple current-use pesticides and pesticide degradates approximately every 2 weeks at up to five sites in the Yolo Bypass and Cache Slough Complex before, during, and after augmented flow pulses in summer and fall 2016 and 2018 as well as during ambient flow conditions in summer and fall 2017 (no flow pulse). In 2016, augmented flows occurred during the summer (July) and required the pumping of Sacramento River water by local Reclamation Districts into the Colusa Basin Drain and Yolo Bypass Toe Drain. In contrast, augmented flows in 2018 occurred in the fall (August–September) and used agricultural tailwater (primarily rice field discharge water) to create the flow pulse. Water samples were analyzed by the U.S. Geological Survey for a suite of 175 current-use pesticides and pesticide degradates using gas chromatography with mass spectrometry and liquid chromatography with tandem mass spectrometry laboratory methods. Suspended sediments filtered from the water samples were analyzed for 143 pesticides and degradates by gas chromatography with mass spectrometry. During the study, 53 pesticides were detected, and all the samples contained mixtures of multiple pesticides at concentrations ranging from below method detection limits to 8,780 nanograms per liter. Pesticides used in growing rice were the dominant pesticides present at four of the five sites sampled and urban-use pesticides dominated at the remaining site. Overall, total pesticide concentrations tended to be higher at sites in the northern part of the Yolo Bypass and lower at southern sites, except for the farthest downstream site which received additional pesticide inputs from the Sacramento River. Flow-pulse water source influenced total pesticide concentrations in the Yolo Bypass and Cache Slough Complex, and the highest total pesticide concentrations at each site were detected either immediately before or during the flow pulse generated with agricultural tailwater in 2018. Data gathered during this study will aid the California Department of Water Resources and other agencies working in the region in adaptively managing pulse flows in the Yolo Bypass and Cache Slough Complex, as one of several California Natural Resources Agency’s Delta Smelt Resiliency strategies.

Pesticide contamination detected across five wildlife refuges in the Sacramento Valley of California

Science of the Total Environment (Elsevier) | March 1st, 2025

An important goal for the applied ecological sciences is to understand the extent to which the biodiversity on conserved or managed lands is exposed to anthropogenic stre

An important goal for the applied ecological sciences is to understand the extent to which the biodiversity on conserved or managed lands is exposed to anthropogenic stressors. Among the various categories of conserved lands in the United States, the National Wildlife Refuge System is focused on the protection and management of native wildlife and plant populations. Refuge lands can be associated with wetlands and, especially in California, tend to be near areas of intense human use, including agriculture. The proximity of refuges to cultivated lands results in potential exposure to pesticide drift, which increases the possibility of non-target effects on plants and wildlife. We used a passive sampler approach to quantify aerial pesticide deposition during 28 days in spring of 2023, across five refuges in the Sacramento Valley of California. Pesticides were detected across all refuges and plots within the study area, with 36 individual compounds identified, including insecticides, herbicides, and fungicides, from 176 silicone bands from 49 plots. Distance to agriculture was not an important predictor in our models for most indices of contamination. However, our models revealed that the nearest crop type was an important mediator of the importance of distance to agriculture, as fungicide contamination decreased with distance to agriculture only when orchards were the nearest crop type. The overall lack of distance effects suggests that the interior of refuges in the study area do not necessarily provide more protection from pesticides than refuge edges, although larger refuges could offer more protection. We currently lack information on how the level of contamination found herein is biologically relevant to wildlife, and ongoing monitoring efforts have found productive communities of insects in the study area. The results of this study provide a foundation for future investigations on refuges to analyze impacts of specific pesticide compounds on plants and wildlife.

Pesticide Mixtures in the Sacramento–San Joaquin Delta, 2016–17: Results from Year 2 of the Delta Regional Monitoring Program

U.S. Geological Survey (USGS) | December 6th, 2019

PFAS in San Francisco Bay Water

San Francisco Estuary Institute (SFEI) | November 14th, 2022

Per- and polyfluoroalkyl substances (PFAS), a family of thousands of synthetic, fluorine-rich compounds commonly referred to as “forever chemicals,” are known for the

Per- and polyfluoroalkyl substances (PFAS), a family of thousands of synthetic, fluorine-rich compounds commonly referred to as “forever chemicals,” are known for their thermal stability, non-reactivity, and surfactant properties. These unique compounds have widespread uses across consumer, commercial, and industrial products, resulting in widespread occurrence in the environment and wildlife across the globe. This study analyzed ambient surface water in San Francisco Bay for 40 PFAS to discern the occurrence, fate, and potential risks to ecological and human health.

Pilot Study Examining Spatial Differences in Water Quality Between Shoal and Channel Habitats

San Francisco Estuary Institute (SFEI) | August 1st, 2019

Under the umbrella of the Nutrient Management Strategy (NMS; www.sfbaynutrients.sfei.org), we are investigating relationships between the SFB’s elevated nutrient levels

Under the umbrella of the Nutrient Management Strategy (NMS; www.sfbaynutrients.sfei.org), we are investigating relationships between the SFB’s elevated nutrient levels and phytoplankton production, with the goal of identifying protective nutrient loads and effective nutrient management options. To address these goals, NMS work includes continued ship-based monitoring (in collaboration with USGS); augmenting that monitoring with high-frequency sensor data and intensive field studies; and developing coupled hydrodynamic-biogeochemical models -- calibrated using field observations -- to simulate water quality under a range of forcings.