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 8, Issue 1, 2010
An increase in the rate of sea level rise is one of the primary impacts of projected global climate change. To assess potential inundation associated with a continued acceleration of sea level rise, the highest resolution elevation data available were assembled from various sources and mosaicked to cover the land surfaces of the San Francisco Bay region. Next, to quantify extreme water levels throughout the bay, a hydrodynamic model of the San Francisco Estuary was driven by a projection of hourly water levels at the Presidio. This projection was based on a combination of climate model outputs, an empirical model, and observations, and incorporates astronomical, storm surge, El Niño, and long-term sea level rise influences.
Based on the resulting data, maps of areas vulnerable to inundation were produced, corresponding to specific amounts of sea level rise and recurrence intervals, including tidal datums. These maps portray areas where inundation will likely be an increasing concern. In the North Bay, wetlands and some developed fill areas are at risk. In Central and South bays, a key feature is the landward periphery of developed areas that would be newly vulnerable to inundation. Nearly all municipalities adjacent to South Bay face this risk to some degree. For the bay as a whole, as early as mid-century under this scenario, the one-year peak event nearly equals the 100-year peak event in 2000. Maps of vulnerable areas are presented and some implications discussed. Results are available for interactive viewing and download at http://cascade.wr.usgs.gov/data/Task2b-SFBay.
We used multivariate methods to explore changes in benthic assemblage structure over 27 years (1977–2003) at four monitoring stations located along a salinity gradient in the upper San Francisco Estuary. Changes in benthic assemblage composition were assessed relative to hydrologic variability and to the presence of the high-impact invader Corbula amurensis in the estuary. We also explored the composition of benthic assemblages during a recent collapse of several pelagic populations in the upper estuary. Our results show that the Corbula invasion had both direct and indirect effects on the benthos in the estuary, causing significant changes in assemblage structure. We found no unprecedented patterns of benthic assemblage composition during the period of the Pelagic Organism Decline (2000–2003) in the upper estuary. Hydrologic variability was associated with significant changes in benthic assemblage composition at all locations. Benthic assemblage composition was more sensitive to mean annual salinity than other local physical conditions. That is, benthic assemblages were not geographically static, but shifted with salinity, moving down-estuary in years with high delta outflow, and up-estuary during years with low delta outflow, without strong fidelity to physical habitat attributes such as substrate composition or location in embayment vs. channel habitat. Organism abundance and species richness showed a bi-modal distribution along the salinity gradient, with lowest abundance and richness in the 5 to 8 psu range. We conclude that the continuity of benthic assemblages and community metrics along the salinity gradient is a powerful and necessary context for understanding historical variability in assemblage composition at geographically static monitoring stations.
- 4 supplemental PDFs
The hydraulic gold-mining process used during the California Gold Rush and in many developing countries today contributes enormous amounts of sediment to rivers and streams. Commonly, accompanying this sediment are contaminants such as elemental mercury and cyanide used in the gold extraction process. We show that some of the mercury-contaminated sediment created by hydraulic gold mining in the Sierra Nevada, between 1852 and 1884, ended up over 250 kilometers (km) away in San Francisco Bay; an example of the far-reaching extent of contamination from such activities. A combination of radionuclide dating, bathymetric reconstruction, and geochemical tracers were used to distinguish the hydraulic mining sediment from sediment deposited in the bay before hydraulic mining started (pre-Gold Rush sediment) and sediment deposited after hydraulic mining stopped (modern sediment). Three San Francisco Bay cores were studied as well as source material from the abandoned hydraulic gold mines and river sediment between the mines and bay. Isotopic and geochemical compositions of the core sediments show a geochemical shift in sediment deposited during the time of hydraulic mining. The geochemical shift is characterized by a decrease in εNd, total organic carbon (TOC), Sr and Ca concentrations, Ca/Sr, and Ni/Zr; and, an increase in 87Sr/86Sr, Al/Ca, Hg concentrations, and quartz/plagioclase. This shift is in the direction of the geochemical signature of sediments from rivers and gold mines in hydraulic mining areas. Mixing calculations using Nd isotopes and concentrations estimate that the hydraulic mining debris comprises up to 56% of the sediment in core sediments deposited during the time of hydraulic mining. The surface sediment of cores taken in 1990 were found to contain up to 43% hydraulic mining debris, reflecting a continuing remobilization and redistribution of the debris within the bay and transport from the watershed. Mercury concentrations in pre-Gold Rush sediment range between 0.03 and 0.08 μg g-1. In core sediments that have characteristics of the gold deposits and were deposited during the time of hydraulic mining, mercury concentrations can be up to 0.45 μg/g. Modern sediment (post-1952 deposition) contains mercury concentrations up to 0.79 μg/g and is likely a mix of hydraulic mining mercury and mercury introduced from other sources.