How to Respond? An Introduction to Current Bay–Delta Natural Resources Management Options

Sommer, Ted

doi:10.15447//sfews.2020v18iss3art1

Cited by 13 publications

(17 citation statements)

References 43 publications

(54 reference statements)

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“…Novel Flow Action to Improve Habitat Freshwater inflow has previously been a major focus of resource management in estuaries, including the San Francisco Estuary, based on the understanding that it supports a broad suite of ecological processes (Jassby et al 1995;Kimmerer 2002). For example, management of the position of the salinity field (as indexed by the daily-averaged, near-bottom, 2-psu isohaline [X2]) using outflow from the Sacramento-San Joaquin Delta is a major seasonal regulatory criterion in the upper San Francisco Estuary (Sommer 2020;SWRCB 1995)-it is designed as a relatively longterm and geographically broad water quality standard to maintain suitable habitat for a suite of estuarine species. That regulatory framework is not, however, designed to target specific regions, trophic levels, or habitats (e.g., off-channel areas).…”

Section: Discussionmentioning

confidence: 99%

Use of a Managed Flow Pulse as Food Web Support for Estuarine Habitat

Frantzich¹,

Davis²,

MacWilliams³

et al. 2021

SFEWS

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While freshwater inflow has been a major focus of resource management in estuaries, including the upper San Francisco Estuary, there is a growing interest in using focused flow actions to maximize benefits for specific regions, habitats, and species. As a test of this concept, in summer 2016, we used a managed flow pulse to target an ecologically important region: a freshwater tidal slough complex (Cache Slough Complex–CSC). Our goal was to improve estuarine habitat by increasing net flows through CSC to enhance downstream transport of lower trophic-level resources, an important driver for fishes such as the endangered Delta Smelt Hypomesus transpacificus. We used regional water infrastructure to direct 18.5 million m³ of Sacramento River flow into its adjacent Yolo Bypass floodplain, where the pulse continued through CSC. Simulations using a 3-D hydrodynamic model (UnTRIM) indicated that the managed flow pulse had a large effect on the net flow of water through Yolo Bypass, and between CSC and further downstream. Multiple water quality constituents (specific conductivity, dissolved oxygen, nutrients [NO₃ + NO₂, NH₄, PO₄]) varied across the study region, and showed a strong response to the flow pulse. In addition, the lower Sacramento River had increased phytoplankton biomass and improved food quality indices (estimated from long-chain essential fatty acids) after the flow pulse. The managed flow pulse resulted in increased densities of zooplankton (copepods, cladocerans) demonstrating potential advection from upper floodplain channels into the target CSC and Sacramento River regions. This study was conducted during a single year, which may have had unique characteristics; however, we believe that our study is an instructive example of how a relatively modest change in net flows can generate measurable changes in ecologically relevant metrics, and how an adaptive management action can help inform resource management.

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Section: Discussionmentioning

confidence: 99%

Use of a Managed Flow Pulse as Food Web Support for Estuarine Habitat

Frantzich¹,

Davis²,

MacWilliams³

et al. 2021

SFEWS

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“…This volume represented approximately 9.6% of the total net Delta outflow during the SMSCG operation period. The additional outflow was allocated to ensure that this action influenced the widest possible area and time period without substantively altering salinity intrusion into the Bay–Delta, which is controlled by water quality regulations (Sommer 2020). Implementation of this action was a major undertaking that required coordination among a broad suite of state and federal government, academic, and nongovernment entities.…”

Section: Methodsmentioning

confidence: 99%

“…The SMSCGs are located on Montezuma Slough on the eastern edge of Suisun Marsh (Figure 1) and have been typically operated between October and May to lower salinity in the Suisun Marsh region (Sommer 2020). The SMSCGs alter salinity by closing during flood tides to restrict the flow of high‐salinity water from Grizzly Bay into Montezuma Slough and opening during ebb tides to allow flow of lower‐salinity water from the Sacramento River.…”

Section: Methodsmentioning

confidence: 99%

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Large‐Scale Flow Management Action Drives Estuarine Ecological Response

Beakes

Graham

Conrad³

et al. 2021

N American J Fish Manag

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Resource managers rely on large‐scale flow and habitat enhancement actions to support sensitive species in the San Francisco Bay–Delta. The effects of these actions on target species and ecosystems are largely unknown. In 2018, we implemented an ecosystem‐scale experiment to reduce salinity and improve access to high‐quality habitat in Suisun Marsh, California, for Endangered Species Act‐listed Delta Smelt Hypomesus transpacificus. The action included a release of approximately 46 million m3 of additional flow in conjunction with the operation of a novel water management facility, the Suisun Marsh Salinity Control Gates. This experimental action resulted in more low‐salinity habitat in Suisun Marsh than would have been present as compared to similar historical low‐flow summer conditions. We evaluated the effect of decreasing salinity on the species assemblage in Suisun Marsh using a combination of ordination analyses and circular statistics. We focused this analysis on long‐term monitoring data collected within Suisun Marsh during July and August and found that the aquatic community changed significantly in small sloughs but not large‐slough habitat in response to the Suisun Marsh action. The assemblage shift from July to August 2018 differed from historical trends in both slough sizes, albeit not significantly in large‐slough habitat. Specifically, we observed (1) a shift in California bay shrimp Crangon franciscorum and Striped Bass Morone saxatilis abundance like that occurring in low‐salinity, wet water year types; and (2) an uncharacteristic seasonal decline in Black Sea jellyfish Maeotias marginata. We posit that the observed community changes were driven by a combination of behavioral responses to lower‐salinity conditions and physical displacement by directional flow resulting from the flow management action.

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“…However, there is a disconnect between the information gathered from zooplankton data and management decisions. This is part of a broader issue about how science informs management, and how managers use field data; disconnects between scientists and managers are common throughout estuary resource management (Sommer 2020).…”

mentioning

confidence: 99%