Geology topics

David Bosworth

Publications and source records attributed to David Bosworth.

3 recordsLinked to original sources

USGS2025

Effects of flow on pesticides in water and zooplankton in the northern Sacramento-San Joaquin Delta

Zooplankton are a key food source for juvenile fishes in estuaries worldwide, including California’s Sacramento–San Joaquin Delta (hereafter Delta); both zooplankton quality and quantity are critical to ecosystem health. Zooplankton may be affected by pesticides in water and the food web, and the Delta is known to contain complex pesticide mixtures. In this study, we evaluated pesticide concentrations in water and zooplankton in the northern Delta during (1) the summer–fall of 2017, 2018, and 2019, which included periods of augmented pulse flows from agriculture tailwater, and (2) across a full seasonal cycle from May 2019 to March 2020. We quantified changes in pesticide concentration in response to environmental factors. We found that zooplankton showed more frequent detections of hydrophobic pesticides compared to more frequent detections of hydrophilic compounds in water. Pesticide concentrations were influenced by flow, pesticide application, and season, but the effects of these environmental factors differed by habitat (Sacramento River or Yolo Bypass Toe Drain). Pesticides in water responded similarly to environmental factors in the Sacramento River and Yolo Bypass, whereas pesticides in zooplankton responded differently. In water, we found more detections and higher concentrations at higher flows in the Yolo Bypass and Sacramento River, but responses to pesticide application varied by habitat. Alternatively, pesticide concentrations in zooplankton increased in the Yolo Bypass with increasing flow (correlated with flow pulses) and changed seasonally; whereas, pesticide concentrations in zooplankton in the Sacramento River decreased at higher flows, and decreased with or did not respond to higher pesticide application in the watershed. Our study suggests that augmented flows—particularly those using agricultural tailwater—may have unintended negative ecological effects that could partially offset benefits to the food web and fishes in the northern Delta, underscoring the complex interplay among factors that drive increased pesticide exposure.

California↗

USGS2024

The anatomy of a drought in the upper San Francisco Estuary: Water quality and lower-trophic responses to multi-year droughts

Multi-year droughts are important and impactful features of California’s Mediterranean climate and can fundamentally affect the water quality and the ecosystem response of the San Francisco Estuary (Estuary) and the Sacramento-San Joaquin Delta (Delta). This study assesses data collected by long-term monitoring programs over the past 46 years (1975-2021) to evaluate how water quality in the Estuary changes during multi-year droughts. We found that multi-year droughts alter multiple physical and chemical parameters in the Estuary, increasing water temperature, salinity, water clarity, and nutrient levels. This trend was consistent across regions and seasons, with few exceptions. Increases in these parameters during droughts are likely caused by reduced Delta inflows that intensified in each successive dry year because of reduced precipitation and reservoir releases. Droughts did not substantially effect on tidal velocities within the Estuary, which remained mostly consistent across wet and dry periods. Trends in chlorophyll concentrations during droughts were more nuanced with higher concentrations occurring in the South-Central Delta region and during the winter and spring. Together, these results paint a picture of drought in the Estuary as warm, clear, high in nutrients, with patchy phytoplankton blooms (as indexed by chlorophyll), all of which have implications for higher trophic levels. Considering that droughts are expected to increase in frequency and intensity in California with climate change, it is imperative to understand the effects of multi-year droughts on the water quality conditions of the Estuary when making water management decisions.

California↗

USGS2024

Delta blue(green)s: The effect of drought and drought-management actions on microcystis in the Sacramento–San Joaquin Delta

Cyanobacterial phytoplankton blooms are more prevalent in the freshwater Sacramento-San Joaquin Delta (Delta) since the late 1990s, including blooms driven by overgrowths of potentially toxigenic organisms of the genus Microcystis . Data from 2014 to 2021 were used to show how flow dynamics, water temperature, and water clarity drive occurrence of Microcystis . We used a Microcystis bloom in the central Delta from 2021 as a case study for how novel monitoring tools can track blooms in real-time and be used post hoc to evaluate the effects of management actions. Microcystis was detected throughout the Delta in all but the highest-flow years, and bloom incidence and severity increased during drier years. In the South Delta, Franks Tract, lower San Joaquin River, and Old River regions, where blooms are most prevalent, higher water temperatures and clarities combined with lower exports from state and federal water projects were the best explanatory factors for the occurrence of Microcystis blooms. Nutrient concentrations were lower in summer than in winter, but only became limiting at high phytoplankton concentrations. We used satellite data and in situ continuous monitoring of flow, phytoplankton communities, and water quality to track hydro-biogeochemical conditions during the 2021 case study Microcystis bloom in the Central Delta. We did not find evidence that changes to Delta outflow regulatory standards contributed to this bloom, but changes in flow caused by a salinity barrier placed in west False River may have exacerbated the bloom. The frequency and severity of droughts are expected to increase in the future as a result of climate change, and our study demonstrates how continued monitoring of cyanotoxins, water quality, and phytoplankton communities could help improve management of cyanobacterial blooms in the Delta and other estuaries.

California↗