SFEWS: Volume 19, Issue 2
Welcome to the June issue of San Francisco Estuary and Watershed Science. At midyear in 2021, research surrounding the San Francisco Estuary looks forward. Here, six articles in four categories offer advances in science using new technologies and a re-examination of past efforts.
Photo: CA Dept. of Water Resources, public domain.
In Honor of Dr. Larry R. Brown
Herbold et al. remember Dr. Larry R. Brown, who died suddenly in February of 2021. This note captures how important his scientific work was in the San Francisco Estuary and why he will be intensely missed by many of his colleagues.
Photo: Canva stock image
Preparing Scientists, Policymakers, and Managers for a Fast-Forward Future
To accelerate forward-looking science, policy, and management in the Delta, Norgaard et al. propose that the State of California create a Delta Science Visioning Process to fully and openly assess the challenges of more rapid change to science, policy, and management and offer appropriate solutions, including legislation.
Photo: CA Dept. of Water Resources, public domain
Ecological Effects of Climate-Driven Salinity Variation in the San Francisco Estuary: Can We Anticipate and Manage the Coming Changes?
Ghalambor et al. review and summarize the presentations and discussions that arose during the symposium “Ecological and Physiological Impacts of Salinization of Aquatic Systems from Human Activities,” which brought together an interdisciplinary group of scientists, managers, and policy-makers to answer the central question: can we use existing knowledge and future projections to predict and manage anticipated ecological impacts?
Photo: Canva stock image
Effects of Tidally Varying River Flow on Entrainment of Juvenile Salmon into Sutter and Steamboat Slough
Previous studies suggest that fish generally “go with the flow”—however, complex tidal hydrodynamics at sub-daily time-scales may be decoupled from net flow. To further examine entrainment of acoustically tagged juvenile Chinook Salmon into Sutter and Steamboat sloughs, Romine et al. modeled routing of acoustic tagged juvenile salmon as a function of tidally varying hydrodynamic data. Results indicate that discharge, the proportion of flow that entered the slough, and the rate of change of flow were good predictors of the probability of an individual fish being entrained.
Photo: John Burau
Examining Retention-at-Length of Pelagic Fishes Caught in the Fall Midwater Trawl Survey
A study was conducted in 2014-2015 to investigate and quantify the efficiency of the Fall Midwater Trawl for catching the endangered fish species Delta Smelt (Hypomesus transpacificus). Mitchell and Baxter revisit the same gear efficiency study and further utilize the data set by fitting selectivity curves for three additional pelagic fish species: Threadfin Shad (Dorosoma petenense), American Shad (Alosa sapidissima), and Mississippi Silverside (Menidia beryllina), and by applying more statistically sensitive approaches.
Photo: Lara Mitchell
Use of the SmeltCam as an Efficient Fish Sampling Alternative Within the San Francisco Estuary
Resource managers often rely on long-term monitoring surveys to detect trends in biological data. However, no survey gear is 100% efficient, and many sources of bias can both detect or miss biological trends. Huntsman et al. evaulate the SmeltCam, an imaging apparatus developed as a sampling alternative to long-term trawling gear surveys within the San Francisco Estuary, with the potential to reduce handling stress on sensitive species like the Delta Smelt (Hypomesus transpacificus).
Photo: Ken Newman
Volume 11, Issue 2, 2013
Circulation in Clifton Court Forebay (CCF) was simulated using the three-dimensional (3–D) hydrodynamic model UnTRIM. These numerical simulations were performed to provide a better understanding of circulation patterns, flow pathways, and residence time in Clifton Court Forebay in support of ongoing studies of pre-screen loss and fish facility efficiency for delta smelt (Hypomesus transpacificus) at the California State Water Project (SWP) export facilities. The 3–D hydrodynamic model of CCF was validated through comparisons to observed water surface elevations inside CCF, and comparisons to observed drifter paths and velocity measurements collected by the U.S. Geological Survey as part of this study. Flow measurements collected near the radial gates for 2 days during relatively low inflows suggest that the Hills (1988) gate equations may over-estimate inflow by as much as 39% when the CCF radial gates are only partially opened. Several alternative approaches to improve the implementation of the radial gate flows in the UnTRIM model were evaluated. The resulting model accurately predicts water surface elevations and currents inside CCF over a range of wind and operating conditions. The validated model was used to predict residence time and other transport time scales for two 21-day simulation periods, one of very low daily SWP export pumping averaging 19.3 m3 s-1 and one for moderate daily SWP export pumping averaging 66.6 m3 s-1. The average transit time, indicating the time from entering CCF to reaching the fish facility, was estimated as 9.1 days for low export conditions and 4.3 days for moderate export conditions. These transport time scale estimates may be used to inform estimates of pre-screen losses inside CCF due to predation or other causes.
- 1 supplemental PDF
Salmon Lifecycle Considerations to Guide Stream Management: Examples from California’s Central Valley
A primary goal of the Central Valley Project Improvement Act is to at least double natural production of Chinook salmon (Oncorhynchus tshawytscha), in California Central Valley (CV) streams on a sustainable basis. Achievement relies on restoration actions that involve both discharge (e.g., dam releases) and non-discharge (e.g., gravel augmentation, screening) components. Annual adult and juvenile abundance estimates for individual watersheds must be tracked to assess effectiveness of individual actions. However, to date, no substantial efforts have been taken to demonstrate success or deficiencies of their implementations. A major challenge in interpreting time series of counts at any one life stage is that they reflect the cumulative effects of both freshwater and marine factors over the full life cycle. To address this issue, we developed a conceptual framework based on ratios of the abundance of consecutive CV fall-run Chinook salmon life stages and how variation in these ratios tracks key independent variables during the freshwater portion of the life cycle. Model validation with several case studies shows that estimates of previous stage class production correlate well with estimated individuals produced in the next class, indicating that transition rates tend to vary within a constrained range, and that monitoring programs generate abundance estimates whose errors are small enough not to swamp out the underlying signal. When selected environmental parameters were added to demonstration models, abundance estimates were more closely modeled and several tested relationships between environmental drivers and life-stage transition rates proved consistent across watersheds where data were available. Results from this generalized life-stage conceptual model suggest a potential framework for tracking the success of actions meant to improve survival for a given life stage within an individual stream and for determining how successive stages respond to these changes. Though examples are provided for CV Chinook salmon, these concepts can be applied wherever migratory salmonid populations and associated environmental data are being adequately monitored.
Erratum dated 2014 June 25
Pharmaceuticals and personal care products (PPCPs) are found in surface waters worldwide. Wastewater treatment plant effluent is a major source of these contaminants. The Sacramento–San Joaquin Delta (Delta) is a unique aquatic ecosystem, a source of drinking water for over 25 million Californians, and a primary source of water for Central Valley agriculture. The sharp decline of four pelagic fish species in the Delta in the last decade is just one of several indicators that the ecosystem is severely impaired. Several wastewater treatment plants (WWTPs) discharge into the Delta, directly or through tributaries. The presence of PPCPs in the Delta has received very little attention relative to the immense effort underway to rehabilitate the ecosystem. This study determined concentrations of PPCPs in the Sacramento River in the vicinity of the Sacramento Regional Wastewater Treatment Plant using passive sampler monitoring. These data were used to estimate loads of three of the detected pharmaceuticals (carbamazepine, fluoxetine, and trimethoprim) from nine other WWTPs that discharge to the Delta. The 2-D, finite element, Resource Management Associates (RMA) Delta Model was then applied to determine the distribution that might result from these discharges. The model was run for the 2006, 2007, and 2009 water years. Results indicate that it is feasible that WWTP discharges could result in chronic presence of these pharmaceuticals at low ng L-1 levels at all 45 model output locations and, therefore, aquatic organisms within the Delta may be continually exposed to these contaminants.
- 1 supplemental PDF
We used a combination of published literature and field survey data to synthesize the available information about habitat use by delta smelt Hypomesus transpacificus, a declining native species in the San Francisco Estuary. Delta smelt habitat ranges from San Pablo and Suisun bays to their freshwater tributaries, including the Sacramento and San Joaquin rivers. In recent years, substantial numbers of delta smelt have colonized habitat in Liberty Island, a north Delta area that flooded in 1997. The species has a more upstream distribution during spawning as opposed to juvenile rearing periods. Post-larvae and juveniles tend to have a more downstream distribution during wetter years. Delta smelt are most common in low-salinity habitat (<6 psu) with high turbidities (>12 NTU) and moderate temperatures (7 °C to 25 °C). They do not appear to have strong substrate preferences, but sandy shoals are important for spawning in other osmerids. The evidence to date suggests that they generally require at least some tidal flow in their habitats. Delta smelt also occur in a wide range of channel sizes, although they seem to be rarer in small channels (<15 m wide). Nonetheless, there is some evidence that open water adjacent to habitats with long water-residence times (e.g. tidal marsh, shoal, low-order channels) may be favorable. Other desirable features of delta smelt habitat include high calanoid copepod densities and low levels of submerged aquatic vegetation (SAV) and the toxic algae Microcystis. Although enough is known to plan for large-scale pilot habitat projects, these efforts are vulnerable to several factors, most notably climate change, which will change salinity regimes and increase the occurrence of lethal temperatures. We recommend restoration of multiple geographical regions and habitats coupled with extensive monitoring and adaptive management. An overall emphasis on ecosystem processes rather than specific habitat features is also likely to be most effective for recovery of the species.