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 8, Issue 2, 2010
To estimate and understand recent subsidence, we collected elevation and soils data on Bacon and Sherman islands in 2006 at locations of previous elevation measurements. Measured subsidence rates on Sherman Island from 1988 to 2006 averaged 1.23 cm/year (0.5 in/yr) and ranged from 0.7 to 1.7 cm/year (0.3 to 0.7 in/year). Subsidence rates on Bacon Island from 1978 to 2006 averaged 2.2 cm/year (0.9 in/yr) and ranged from 1.5 to 3.7 cm/year (0.6 to 1.5 in/yr). Changing land-management practices and decreasing soil organic matter content have resulted in decreasing subsidence rates. On Sherman Island, rates from 1988 to 2006 were about 35% of 1910 to 1988 rates. For Bacon Island, rates from 1978 to 2006 were about 40% less than the 1926-1958 rates. To help understand causes and estimate future subsidence, we developed a subsidence model, SUBCALC, that simulates oxidation and carbon losses, consolidation, wind erosion, and burning and changing soil organic matter content. SUBCALC results agreed well with measured land-surface elevation changes. We predicted elevation decreases from 2007 to 2050 will range from a few centimeters to over 1.3 m (4.3 ft). The largest elevation declines will occur in the central Sacramento-San Joaquin Delta. From 2007 to 2050, the most probable estimated increase in volume below sea level is 349,956,000 million cubic meters (281,300 acre-feet). Consequences of this continuing subsidence include increased drainage loads of water quality constituents of concern, seepage onto islands, and decreased arability.
- 2 supplemental PDFs
Salinity Inhabited by Age-0 Splittail (Pogonichthys macrolepidotus) as Determined by Direct Field Observation and Retrospective Analyses with Otolith Chemistry
Splittail (Pogonichthys macrolepidotus) is a fish species of special concern that is endemic to the San Francisco Estuary. It has been generally accepted that spawning and juvenile rearing occurs during spring in freshwater habitats upstream of the estuary. However, the recent discovery of a genetically distinct population of splittail in the relatively brackish Petaluma and Napa rivers has challenged this assumption. We used a combination of field observations and high resolution sampling of otolith 87Sr:86Sr ratios to identify the salinity inhabited by young age-0 splittail in the Sacramento, San Joaquin, Napa, and Petaluma rivers. Individual age-0 splittail, two to three months old, were observed in the Napa and Petaluma rivers in salinity as high as 8.5 ppt and 14.1 ppt, respectively, whereas salinity in the San Joaquin and Sacramento rivers was always <1.0 ppt. Otolith 87Sr:86Sr ratios corresponding to the first month of life suggested that individual splittail in all regions mostly inhabited freshwater, although several individuals from the Napa and Petaluma rivers inhabited brackish water up to about 10 ppt. In most instances, there was little intra-individual variability in 87Sr:86Sr signals, suggesting individuals remained within the natal salinity zone during the first month of life. The exceptions were two fish, one each from the Napa and Petaluma rivers, that appeared to move from freshwater natal to brackish rearing habitats. The apparent ability of age-0 splittail to rear in brackish water almost immediately after being born is one of the fundamental mechanisms supporting splittail production in the Napa and Petaluma rivers.
Policy and Program Analysis
California’s Sacramento-San Joaquin Delta has fragile levees subject to several trends that make them increasingly prone to failure. To assess the likely extent of Delta island flooding, this study presents an economic decision analysis approach for evaluating Delta levee upgrade and repair decisions for 34 major subsided agricultural islands that make up most of the Delta’s Primary Zone and include all subsided, non-urban islands. The decision analysis provides a quantitative framework to address several relevant questions about reasonable levee upgrade and repair investments. This initial analysis indicates that it is economically optimal not to upgrade levees on any of the 34 subsided Delta islands examined, mostly because levee upgrades are expensive and do not improve reliability much. If upgrades can improve reliability more, it becomes optimal to upgrade some levees. Our analysis also suggests that, accounting for land and asset values, it is not cost effective to repair between 18 and 23 of these islands when they fail. When property values for all islands were doubled, only four islands originally not repaired become cost effective to repair. The decision analysis provides a quantitative framework for addressing several relevant questions regarding reasonable levee upgrade and repair investments. These initial results may act as a springboard for discussion, and the decision analysis model as a working framework for islands of high priority. An inescapable conclusion of this analysis is that maintaining the current Delta landscape is unlikely to be economical from business and land use perspectives.