Elkhorn Slough National Estuarine Research Reserve

Elkhorn, CA, United States

Elkhorn Slough National Estuarine Research Reserve

Elkhorn, CA, United States
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Anderson B.,University of California at Davis | Phillips B.,University of California at Davis | Hunt J.,University of California at Davis | Largay B.,Elkhorn Slough National Estuarine Research Reserve | And 2 more authors.
Environmental Toxicology and Chemistry | Year: 2011

The California, USA, central coast is one of the most productive agricultural areas in the world, and numerous stakeholders are working there to implement conservation practices to reduce contaminated runoff. Practices include vegetated treatment systems (VTS) designed to promote contaminant reduction and breakdown. The current study evaluated the effectiveness of a vegetated drainage ditch incorporating a sedimentation basin, a vegetated section, and a Landguard organophosphate-A (OP-A) enzyme dosing system. The VTS was constructed on a working farm and was designed to remove organophosphate and pyrethroid pesticides, the primary pesticides causing toxicity in Salinas Valley watersheds. The present study was conducted during five separate irrigation events on tailwater runoff containing mixtures of pesticides and suspended sediments. Water samples were collected at four stations within the system, and these were subjected to chemical analyses and tested for toxicity to Ceriodaphnia dubia. All inflow samples were highly toxic to C. dubia, and this was largely because of diazinon. Treatment of diazinon-contaminated runoff was only partially effective using aquatic vegetation. All diazinon remaining after vegetated treatment was effectively removed after treatment with the Landguard OP-A enzyme. Chemical analysis of the VTS water samples showed that pyrethroid and organochlorine pesticide concentrations in water were greatly reduced in the sedimentation section of the ditch, and these pesticides were further reduced in the vegetated section of the ditch. The overall conclusion from these analyses is that the VTS was effective at reducing the more hydrophobic organochlorine and pyrethroid pesticides from water. The water-soluble pesticide diazinon was not sufficiently removed during the VTS residence times observed in this study; however, residual diazinon was effectively removed using Landguard OP-A. © 2011 SETAC.

Zabin C.J.,Smithsonian Environmental Research Center | Zabin C.J.,University of California at Davis | Wasson K.,Elkhorn Slough National Estuarine Research Reserve | Wasson K.,University of California at Santa Cruz | Fork S.,Elkhorn Slough National Estuarine Research Reserve
Biological Conservation | Year: 2016

Restoration of native species may be hampered by competition with non-native species. The outcomes of competition are often context-dependent, with one species dominating under some conditions but not others. Where non-natives differ from natives in their ability to tolerate stressful environmental conditions, restoration practitioners may be able to manipulate conditions or strategically locate restoration projects along naturally occurring stress gradients to favor native species. We tested the responses of native oysters and a suite of non-native sessile invertebrate species (mostly soft-bodied organisms) to varying tidal elevations, shoreline types, and distances from source populations. Cover of non-natives was lower at higher tidal elevation and far from adult populations. Native oyster recruitment was also reduced at the high tidal elevation. At this elevation oyster dominance was increased, but abundance was reduced. To test an adaptive management approach, we moved substrates from the low to high tidal elevations. Cover of non-natives had decreased dramatically one year later, while oyster metrics were unaffected or improved compared to those on substrates remaining at the low elevation. Our study indicates that reduction of non-native species abundance, often an explicit goal of restoration, may be achieved by strategic location of restoration units, although abundance of target species may also be reduced, at least over the short term. However, restoration practitioners may be able to increase abundance of target species and reduce non-natives by applying stress differentially over time, with benign conditions during sensitive early life stages, and increasing stress after target organisms become more tolerant. © 2016

Cheng B.S.,University of California at Davis | Bible J.M.,University of California at Davis | Chang A.L.,San Francisco Bay National Estuarine Research Reserve | Ferner M.C.,San Francisco Bay National Estuarine Research Reserve | And 6 more authors.
Global Change Biology | Year: 2015

Despite the abundance of literature on organismal responses to multiple environmental stressors, most studies have not matched the timing of experimental manipulations with the temporal pattern of stressors in nature. We test the interactive effects of diel-cycling hypoxia with both warming and decreased salinities using ecologically realistic exposures. Surprisingly, we found no evidence of negative synergistic effects on Olympia oyster growth; rather, we found only additive and opposing effects of hypoxia (detrimental) and warming (beneficial). We suspect that diel-cycling provided a temporal refuge that allowed physiological compensation. We also tested for latent effects of warming and hypoxia to low-salinity tolerance using a seasonal delay between stressor events. However, we did not find a latent effect, rather a threshold survival response to low salinity that was independent of early life-history exposure to warming or hypoxia. The absence of synergism is likely the result of stressor treatments that mirror the natural timing of environmental stressors. We provide environmental context for laboratory experimental data by examining field time series environmental data from four North American west coast estuaries and find heterogeneous environmental signals that characterize each estuary, suggesting that the potential stressor exposure to oysters will drastically differ over moderate spatial scales. This heterogeneity implies that efforts to conserve and restore oysters will require an adaptive approach that incorporates knowledge of local conditions. We conclude that studies of multiple environmental stressors can be greatly improved by integrating ecologically realistic exposure and timing of stressors found in nature with organismal life-history traits. © 2015 John Wiley & Sons Ltd.

Hughes B.B.,University of California at Santa Cruz | Eby R.,Elkhorn Slough National Estuarine Research Reserve | Van Dyke E.,Elkhorn Slough National Estuarine Research Reserve | Tinker M.T.,University of California at Santa Cruz | And 5 more authors.
Proceedings of the National Academy of Sciences of the United States of America | Year: 2013

A fundamental goal of the study of ecology is to determine the drivers of habitat-forming vegetation, with much emphasis given to the relative importance to vegetation of "bottom-up" forces such as the role of nutrients and "top-down" forces such as the influence of herbivores and their predators. For coastal vegetation (e.g., kelp, seagrass, marsh, and mangroves) it has been well demonstrated that alterations to bottom-up forcing can cause major disturbances leading to loss of dominant vegetation. One such process is anthropogenic nutrient loading, which can lead to major changes in the abundance and species composition of primary producers, ultimately affecting important ecosystem services. In contrast, much less is known about the relative importance of apex predators on coastal vegetated ecosystems because most top predator populations have been depleted or lost completely. Here we provide evidence that an unusual four-level trophic cascade applies in one such system, whereby a top predator mitigates the bottom-up influences of nutrient loading. In a study of seagrass beds in an estuarine ecosystem exposed to extreme nutrient loading, we use a combination of a 50-y time series analysis, spatial comparisons, and mesocosm and field experiments to demonstrate that sea otters (Enhydra lutris) promote the growth and expansion of eelgrass (Zostera marina) through a trophic cascade, counteracting the negative effects of agriculturally induced nutrient loading. Our results add to a small but growing body of literature illustrating that significant interactions between bottom-up and top-down forces occur, in this case with consequences for the conservation of valued ecosystem services provided by seagrass.

Hughes B.B.,Elkhorn Slough National Estuarine Research Reserve | Hughes B.B.,University of California at Santa Cruz | Haskins J.C.,Elkhorn Slough National Estuarine Research Reserve | Wasson K.,Elkhorn Slough National Estuarine Research Reserve | And 3 more authors.
Marine Ecology Progress Series | Year: 2011

Coastal eutrophication models have proposed that various environmental conditions can serve as filters mediating the effects of nutrient loading on coastal ecosystems. Variation in such filters due to natural or anthropogenic causes can potentially lead to varied responses in overall eutrophication expression as well as in individual eutrophication indicators. In this study, we sought to identify factors that affect eutrophication expression at contrasting sites within one nutrient-loaded estuary in central California. We developed and applied a eutrophication expression index to 18 sites in the Elkhorn Slough estuary and then used principal components analysis of environmental drivers (nutrients) and filters to determine how they relate to overall eutrophication expression as well as to individual eutrophication indicators. We also examined the relationship between one key filter, tidal range, and eutrophication indicators. Elkhorn Slough was determined to be a moderately eutrophic estuary, with individual sites varying from being low to hypereutrophic. Eutrophication expression was explained mostly by tidal range, depth, temperature, salinity, distance to estuary mouth, and turbidity, but not by nutrient concentrations. Tidal range in particular correlated strongly with most eutrophication indicators. Sites with artificially dampened tidal range through water control structures were more eutrophic than sites with full tidal exchange. Results from this study emphasize the importance of filters in mediating the negative ecological effects of eutrophication. Coastal managers can decrease eutrophication expression at a local scale by managing for filters (e.g. increasing tidal exchange to managed wetlands), complementing efforts to reduce eutrophication at a regional scale by decreasing nutrient loading. © Inter-Research 2011.

Caffrey J.M.,University of West Florida | Hollibaugh J.T.,University of Georgia | Bano N.,University of Georgia | Haskins J.,Elkhorn Slough National Estuarine Research Reserve
Aquatic Microbial Ecology | Year: 2010

We examined short-term variability in sediment microbial processes and biogeochemistry in response to decreased irradiance accompanying an upwelling event. Potential nitrification, extractable nutrients, solid phase iron and pore water sulfide concentrations were measured several times at 3 locations in Elkhorn Slough, California, USA. Benthic fluxes of nitrate+nitrite, ammonium, phosphate, sediment oxygen consumption and denitrification from N 2/Ar flux were also measured. Fog that was associated with upwelling in Monterey Bay reduced photosynthetically active radiation in Elkhorn Slough, which led to increased duration of water column hypoxia. Solid phase Fe 3+ concentrations and potential nitrification rates declined while pore water sulfide increased over this period. While potential nitrification rates from this study are lower than rates from estuaries that do not experience hypoxia or anoxia, nitrifiers in Elkhorn Slough appear to be capable of adjusting to changing environmental conditions, specifically of tolerating low levels of sulfide. The nitrifying assemblage was similar to the community of ammonia-oxidizing bacteria and ammonia-oxidizing archaea that was previously reported from this system. Eutrophic shallow estuaries like Elkhorn Slough are delicately poised such that their sediment biogeochemistry responds quickly to relatively small changes in the light environment. © Inter-Research 2010.

Wasson K.,Elkhorn Slough National Estuarine Research Reserve | Wasson K.,University of California at Santa Cruz | Woolfolk A.,Elkhorn Slough National Estuarine Research Reserve | Fresquez C.,Elkhorn Slough National Estuarine Research Reserve | Fresquez C.,University of California at Santa Cruz
Estuaries and Coasts | Year: 2013

Ecotones, the narrow transition zones between extensive ecological systems, may serve as sensitive indicators of climate change because they harbor species that are often near the limit of their physical and competitive tolerances. We investigated the ecotone between salt marsh and adjacent upland at Elkhorn Slough, an estuary in California, USA. Over a period of 10 years, we monitored movement of the ecotone-upland boundary, plant community structure, and physical factors likely to drive ecotone response. At three undiked sites, the ecotone boundary migrated about 1 m landward, representing a substantial shift for a transition zone that is only a few meters wide. Analysis of potential correlates of this upward migration suggests that it was driven by increased tidal inundation. Mean sea level did not increase during our study, but inundation at high elevations did. While the ecotone boundary responded dynamically to interannual changes in inundation at these undiked sites, the plant community structure of the ecotone remained stable. At two diked sites, we observed contrasting patterns. At one site, the ecotone boundary migrated seaward, while at the other, it showed no consistent trend. Diking appears to eliminate natural sensitivity of the ecotone boundary to interannual variation in oceanic and atmospheric drivers, with local factors (management of water control structures) outweighing regional ones. Our study shows that the marsh-upland ecotone migrated rapidly in response to environmental change while maintaining stable plant community structure. Such resilience, stability, and rapid response time suggest that the marsh-upland ecotone can serve as a sensitive indicator of climate change. © 2013 Coastal and Estuarine Research Federation.

Wasson K.,Elkhorn Slough National Estuarine Research Reserve | Wasson K.,University of California at Santa Cruz | Woolfolk A.,Elkhorn Slough National Estuarine Research Reserve
Wetlands | Year: 2011

Ecotones, zones of abrupt biological transition typically reflecting strong physical gradients, may be particularly sensitive to changes in environmental conditions. Our characterization of the ecotone between salt marshes and uplands in the Elkhorn Slough watershed in central California revealed that extent of appropriate habitat for native high marsh species endemic to this zone is extremely limited. The ecotone is highly invaded, with nonnative upland weeds accounting for a significant proportion of cover. We investigated responses to two anthropogenic landscape management strategies, restriction of tidal exchange through water control structures and cattle grazing. Moderate tidal restriction resulting in muted tidal exchange dramatically decreased ecotone width, native marsh plant richness, and cover by native ecotone specialists. Even stronger tidal restriction resulting in very low tidal exchange led to a seaward shift of the ecotone into the area formerly occupied by mid-marsh vegetation; upland plants now occupy the former ecotone zone so net loss of wetland habitat has occurred. Cattle grazing led to a very substantial increase in bare ground, a significant decrease in native marsh plant richness and a significant increase in non-native plant cover. Thus, both of these management regimes can have significant negative impacts on rare salt marsh ecotone extent and biodiversity. © Society of Wetland Scientists 2011.

Wasson K.,Elkhorn Slough National Estuarine Research Reserve
Wetlands | Year: 2010

The goal of this investigation was to inform restoration strategies by determining which factors are most important in limiting Olympia oyster (Ostrea lurida) distribution and abundance at a Pacific coast estuary, Elkhorn Slough in central California, where Olympia oysters are currently extremely rare but were formerly abundant. An array of mensurative experiments and correlative analyses were used to examine the role of potential limiting factors. Absence of oysters was associated with symptoms of eutrophication, including elevated nutrient concentrations and turbidity. Oysters were also absent from all sites where water control structures resulted in minimal tidal exchange. Predation and competition did not appear to play a major role in surveyed oyster populations above Mean Lower Low Water but at lower elevations oysters were heavily fouled by non-native species. In most sites oysters were found only on large artificial substrates; survival on small natural hard substrates was apparently precluded by burial by fine sediments. Restoring more natural ecosystem processes by reducing nutrient and sediment inputs, increasing tidal exchange to areas behind water control structures, and preventing establishment of new non-native species would benefit Olympia oysters as well as support broader ecosystem-based management goals. © 2010 Society of Wetland Scientists.

Fork S.K.,Elkhorn Slough National Estuarine Research Reserve
Environmental Entomology | Year: 2010

Biological invasions by nonnative plant species are a widespread phenomenon. Many studies have shown strong ecological impacts of plant invasions on native plant communities and ecosystem processes. Far fewer studies have examined effects on associated animal communities. From the perspective of a reserve's land management, I addressed the question of whether arthropod assemblages on two nonnative plant species of concern were impoverished compared with those assemblages associated with two predominant native plant species of that reserve. If the nonnative plant species, Conium maculatum L., and Phalaris aquatica L., supported highly depauperate arthropod assemblages compared with the native plant species, Baccharis pilularis De Candolle and Leymus triticoides (Buckley) Pilger, this finding would provide additional support for prioritizing removal of nonnatives and restoration of natives. I assessed invertebrate assemblages at the taxonomic levels of arthropod orders, Coleoptera families, and Formicidae species, using univariate analyses to examine community attributes (richness and abundance) and multivariate techniques to assess arthropod assemblage community composition differences among plant species. Arthropod richness estimates by taxonomic level between native and nonnative vegetation showed varying results. Overall, arthropod richness of the selected nonnative plants, examined at higher taxonomic resolution, was not necessarily less diverse than two of common native plants found on the reserve, although differences were found among plant species. Impacts of certain nonnative plant species on arthropod assemblages may be more difficult to elucidate than those impacts shown on native plants and ecosystem processes. © 2010 Entomological Society of America.

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