SFEWS Vol. 20, Issue 1 | March 2021
#CentralValley #ChinookSalmon #otolithchemistry #Steelhead #monitoring #surveys #catchability #detectionefficiency #DeltaSmelt #supplementation #Ich #pathogens #organiccarbon #stablecarbon #nitrogen #inputs #YubaRiver #watersheds
Variation in Juvenile Salmon Growth Opportunities Across a Shifting Habitat Mosaic
Coleman et al. found that juvenile Chinook Salmon grew faster in the Delta in some years (2016), but slower in the Delta during drought conditions (2014 to 2015). Habitat that featured faster growth rates varied within and among years, suggesting the importance of maintaining a habitat mosaic for juvenile salmonids, particularly in a dynamic environment such as the California Central Valley.
Counting the Parts to Understand the Whole: Rethinking Monitoring of Steelhead in California’s Central Valley
Eschenroeder et al. argue that a reallocation of monitoring resources to better understand the interaction between resident and anadromous Steelhead would provide better data to estimate the vital rates needed to evaluate the effects of recovery actions.
Relative Bias in Catch Among Long-Term Fish Monitoring Surveys Within the San Francisco Estuary
Huntsman et al. assessed relative catchability differences among four long-term fish monitoring surveys from the San Francisco Estuary. Their results demonstrate that catchability is a source of bias among monitoring efforts within the San Francisco Estuary, and assuming equal catchability among surveys, species, and size classes could result in significant bias when describing spatio-temporal patterns in catch if ignored.
Investigation of Molecular Pathogen Screening Assays for Use in Delta Smelt
Gille et al. conducted a pilot study that applied molecular assays originally developed in salmonids to assess the presence of a wide variety of pathogens in the gill tissue of cultured and wild Delta Smelt—as well as cultured fish—deployed in enclosures in the estuary. Although disease is not an overt cause of population decline of Delta Smelt in the San Francisco Estuary, comprehensive pathogen presence and prevalence data are lacking, and unintended transmission of pathogens can have devastating effects on populations already at-risk or on the natural ecosystem at large. Their results corroborate previous work that cultured Delta Smelt do not appear to present a high risk for pathogen transmission during population supplementation or reintroduction.
Multi-Biomarker Analysis for Identifying Organic Matter Sources in Small Mountainous River Watersheds: A Case Study of the Yuba River Watershed
Pondell and Canuel's study focused on identifying the composition of watershed-derived organic matter (OM). To better understand inputs to inland waters and improve distinguish between terrigenous and aquatic sources in downstream systems, such as estuaries and coasts, they surveyed OM sources from the Yuba River watershed in northern California to identify specific biomarkers that represent aquatic and terrigenous OM sources. Results demonstrate the utility of multi-biomarker studies for distinguishing between OM from different sources and land uses, offering new insights for biogeochemical studies in aquatic systems.
Volume 13, Issue 1, 2015
Policy and Program Analysis
Forecasting the Most Likely Status of Wild Salmon in the California Central Valley in 2100
Since the mid-1800s the Sacramento–San Joaquin river system in the California Central Valley has experienced a dramatic decline in the distribution and abundance of wild salmon, along with many extirpations. The causes of the decline are many, and have been well studied. Despite restoration efforts spanning decades and involving large expenditures, runs of wild salmon in the Central Valley continue to decline. Using the most probable policy and ecological scenarios (i.e., effects of continued harvest, continued stocking from hatcheries, changing climate, continued human population growth and associated demands for scarce water resources) and based on expert judgment, we assessed the most likely future of wild salmon runs in the Central Valley in 2100. We posed seven open-ended questions to senior salmon science and policy experts in federal and state agencies; local, regional, and national organizations; non-governmental organizations; and universities. With a promise of complete and permanent anonymity, these experts provided answers. Most experts concluded that by 2100 wild salmon in the Central Valley will be extirpated or minimally abundant if current trends continue.
Research Article
Three-Dimensional Modeling of Hydrodynamics and Salinity in the San Francisco Estuary: An Evaluation of Model Accuracy, X2, and the Low–Salinity Zone
The three-dimensional UnTRIM San Francisco Bay–Delta model was applied to simulate tidal hydrodynamics and salinity in the San Francisco Estuary (estuary) using an unstructured grid. We compared model predictions to observations of water level, tidal flow, current speed, and salinity collected at 137 locations throughout the estuary. A quantitative approach based on multiple model assessment metrics was used to evaluate the model's accuracy for each comparison. These comparisons demonstrate that the model accurately predicted water level, tidal flow, and salinity during a 3-year simulation period that spanned a large range of flow and salinity conditions. The model is therefore suitable for detailed investigation of circulation patterns and salinity distributions in the estuary.
The model was used to investigate the location, and spatial and temporal extent of the low-salinity zone (LSZ), defined by salinity between 0.5 and 6 psu. We calculated X2, the distance up the axis of the estuary to the daily-averaged 2-psu near-bed salinity, and the spatial extent of the LSZ for each day during the 3-year simulation. The location, area, volume, and average depth of the low-salinity zone varied with X2; however this variation was not monotonic and was largely controlled by the geometry of the estuary.
We used predicted daily X2 values and the corresponding daily Delta outflow for each day during the 3-year simulation to develop a new equation to relate X2 to Delta outflow. This equation provides a conceptual improvement over previous equations by allowing the time constant for daily changes in X2 to vary with flow conditions. This improvement resulted in a smaller average error in X2 prediction than previous equations. These analyses demonstrate that a well-calibrated three-dimensional (3-D) hydrodynamic model is a valuable tool for investigating the salinity distributions in the estuary, and their influence on the distribution and abundance of physical habitat.
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Modeling Tidal Freshwater Marsh Sustainability in the Sacramento–San Joaquin Delta Under a Broad Suite of Potential Future Scenarios
In this paper, we report on the adaptation and application of a one-dimensional marsh surface elevation model, the Wetland Accretion Rate Model of Ecosystem Resilience (WARMER), to explore the conditions that lead to sustainable tidal freshwater marshes in the Sacramento–San Joaquin Delta. We defined marsh accretion parameters to encapsulate the range of observed values over historic and modern time-scales based on measurements from four marshes in high and low energy fluvial environments as well as possible future trends in sediment supply and mean sea level. A sensitivity analysis of 450 simulations was conducted encompassing a range of porosity values, initial elevations, organic and inorganic matter accumulation rates, and sea-level rise rates. For the range of inputs considered, the magnitude of SLR over the next century was the primary driver of marsh surface elevation change. Sediment supply was the secondary control. More than 84% of the scenarios resulted in sustainable marshes with 88 cm of SLR by 2100, but only 32% and 11% of the scenarios resulted in surviving marshes when SLR was increased to 133 cm and 179 cm, respectively. Marshes situated in high-energy zones were marginally more resilient than those in low-energy zones because of their higher inorganic sediment supply. Overall, the results from this modeling exercise suggest that marshes at the upstream reaches of the Delta—where SLR may be attenuated—and high energy marshes along major channels with high inorganic sediment accumulation rates will be more resilient to global SLR in excess of 88 cm over the next century than their downstream and low-energy counterparts. However, considerable uncertainties exist in the projected rates of sea-level rise and sediment avail-ability. In addition, more research is needed to constrain future rates of aboveground and belowground plant productivity under increased CO2 concentrations and flooding.
- 2 supplemental PDFs
- 1 supplemental file