Ecological Effects of Climate-Driven Salinity Variation in the San Francisco Estuary: Can We Anticipate and Manage the Coming Changes?

Abstract

Climate change-driven sea level rise and altered precipitation regimes are predicted to alter patterns of salt intrusion within the San Francisco Estuary. A central question is: Can we use existing knowledge and future projections to predict and manage the anticipated ecological impacts? This was the subject of a 2018 symposium entitled “Ecological and Physiological Impacts of Salinization of Aquatic Systems from Human Activities.” The symposium brought together an inter-disciplinary group of scientists and researchers, resource managers, and policy-makers. Here, we summarize and review the presentations and discussions that arose during the symposium. From a historical perspective, salt intrusion has changed substantially over the past 10,000 years as a result of changing climate patterns, with additional shifts from recent anthropogenic effects. Current salinity patterns in the San Francisco Estuary are driven by a suite of hydrodynamic processes within the given contexts of water management and geography. Based on climate projections for the coming century, significant changes are expected in the processes that determine the spatial and temporal patterns of salinity. Given that native species—including fishes such as the Delta Smelt and Sacramento Splittail—track favorable habitats, exhibit physiological acclimation, and can adaptively evolve, we present a framework for assessing their vulnerability to altered salinity in the San Francisco Estuary. We then present a range of regulatory and structural management tools that are available to control patterns of salinity within the San Francisco Estuary. Finally, we identify major research priorities that can help fill critical gaps in our knowledge about future salinity patterns and the consequences of climate change and sea level rise. These research projects will be most effective with strong linkages and communication between scientists and researchers, resource managers, and policy-makers.

Climate Change Impacts on San Francisco Estuary Aquatic Ecosystems: A Review

“…This work builds on an extensive literature review of climate effects on the estuary by the Interagency Ecological Program (IEP) Climate Change Team (CC MAST 2022). We also build on recent climate-related discussions about effects and adaptation (Ghalambor et al 2021;Norgaard et al 2021). Our goal is to identify priority topics for research and monitoring that can facilitate sound management of the estuary under climate change.…”

“…Future droughts are likely to be longer, warmer, and drier than the recent extreme drought of 2012-2016 (Meko et al 2014;Dettinger et al 2016). Extreme drought will further influence ecosystems in the estuary through the effect of salinity intrusion (Ghalambor et al 2021). Sea level rose 20 cm over the 20th century, and conservative estimates indicate it will rise by another 20 to 170 cm by 2100 (Flick et al 2003;NRC 2012).…”

“…Tidal marsh ecosystems face multiple interacting stressors from climate change (Colombano, Litvin, Ziegler et al 2021), including rising sea level (Stralberg et al 2011;Schile et al 2014), shifting sediment dynamics (Barnard et al 2013), and elevated temperature and salinity (Ghalambor et al 2021;Bashevkin et al 2022).…”

Long-term trends in seasonality and abundance of three key zooplankters in the upper San Francisco Estuary

“…Since A. sinensis is predatory it could be following the abundance shifts of other species, resulting in changes to the location and timing of reproduction, thus impacting both adult and juvenile abundances. Alternatively, this shifted phenology could be caused by changes to the salinity field in recent years which have resulted in higher salinity intrusions further into the estuary due to increased and persisting droughts (Ghalambor et al 2021).…”

Warming in the upper San Francisco Estuary: Patterns of water temperature change from five decades of data

“…The upper estuary is formed by the confluence of five major rivers that drain 40% of the land in California (Delta Stewardship Council 2013), which has been dramatically transformed in the past 200 yr. The upper estuary was originally a vast swath of marsh with meandering channels and a highly variable salinity field (Whipple et al 2012; Ghalambor et al 2021). Since the early 1800s, 97% of wetlands have been lost as they were drained for agriculture, and meandering channels were converted to straightened, diked channels protecting those agricultural lands (Whipple et al 2012).…”