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The future of coastal wetlands will depend on the combined effects of climate change and human impacts from urbanization and coastal management. Disentangling the effects of these factors is difficult, but satellite imagery archives provide a way to track biological and physical changes in wetlands over recent decades to reveal how coastal wetlands have been changing in response to climate and human drivers. In this study, we used Landsat to monitor the conditions of 32 coastal wetlands in southern California from 1984 to 2019 and identify environmental and human drivers of these trends. Wetland conditions were characterized by vegetation greenness, using the normalized difference vegetation index (NDVI), and by habitat composition, derived from areal estimates of wetland and subtidal habitats. Overall, wetlands displayed three types of long‐term response: greening and gaining wetland (10), greening and losing wetland (16), and browning and losing wetland (6). Regional environmental drivers with overall positive effects on wetland NDVI were sea level, wave height, and precipitation, whereas stream discharge, vapor pressure deficit, and air temperature had negative or nonlinear effects. Wetland area change was primarily correlated with sea level, but response was highly contextual among sites. Negative trends in wetland NDVI and area were more common in larger sites with low elevations and in sites with open inlets. Restoration had mixed effects, with only half of the restored sites showing positive changes in NDVI and wetland area post‐restoration. The important work of managing and restoring urban coastal wetlands is complicated by variability and context and requires us to account for the influence of humans and climate as we build a regional understanding of historic, present, and future wetland health. [ABSTRACT FROM AUTHOR]

Although the promotion of biodiversity has been recognized as an important conservation goal, salt marsh restoration typically focuses on reestablishing dominant foundation species. Salt marsh restoration projects that add or remove sediment to optimize marsh elevation often result in a bare landscape following construction. Restoration managers must decide whether to plant and, if so, which species. This decision can be difficult because few studies have examined the ecological functions of individual species, especially those that are less abundant. Within a major salt marsh restoration project in Elkhorn Slough, California, where 17,000 plants of five high marsh species were planted, we investigated how rarer species and the naturally recruiting dominant (Salicornia pacifica) differ in ecosystem function. We evaluated 31 different metrics related to blue carbon, plant productivity, environmental effects, and community interactions. No single species had the greatest ecological function across this suite of metrics, and measured effects were mainly independent, with only 16 of 435 pairwise comparisons revealing a strong correlation. We found significant differences among species for 18 metrics, revealing key contrasts in ecosystem function, with significant effects of marsh elevation and interaction between effects of species and elevation on some of these functions. S. pacifica scored highest for metrics such as recruitment and canopy height but other species outperformed Salicornia in other metrics. Frankenia salina had the greatest ecological function in the highest number of metrics, including cover and belowground biomass carbon content, but other species had higher rates of photosynthesis and harbored fewer individuals of invasive arthropods. We recommend planting a suite of less common species at restoration sites to provide more diverse functions across the landscape. F. salina in particular is recommended for its tolerance of hypersalinity and low moisture conditions. Our demonstration of the value of complementing restoration of the dominant foundation species with restoration of less common species is applicable to restoration of other ecosystems beyond salt marshes. The approach we implemented, evaluating a large suite of functions for multiple species across a restored landscape, can serve as a model for investigations of the importance of biodiversity for enhancing multifunctionality in other restored ecosystems. [ABSTRACT FROM AUTHOR]

The Stress Gradient Hypothesis predicts facilitation will become more important than competition where abiotic stress is high, and the framework successfully predicts positive interactions between species in many systems. Fewer studies have focused on intraspecific facilitation, and to our knowledge none examine intraspecific interactions in Pacific Coast salt marshes of North America. We used two species that tend to occur in large, monospecific patches to test for intraspecific facilitation in a restored California marsh, where tides and evaporation during summer create moisture and salinity gradients across elevation. We tested performance of Frankenia salina or Jaumea carnosa in restoration plots using two treatments: clustered plantings to promote facilitation, and widely spaced plantings to limit interaction between individuals. We characterized the soil water potential gradient and measured plant survival, cover, physiology, and susceptibility to herbivory across elevation and planting treatments. Soil water potential declined sharply with elevation, suggesting plant stress should be higher upslope. However, tissue water potential was unaffected by elevation, and survival was high—suggesting growing conditions remained benign. A seawater addition treatment did not alter the response of plants or plant interactions to the abiotic gradient. At 19 months, intraspecific competition prevailed across the entire elevation gradient for both species, with less transplant cover in clustered plantings. However, clustered Frankenia fared better during a transient period of heavy rabbit herbivory. Aside from this temporary benefit, clustering did not reduce stress and strongly suppressed growth—suggesting that restoration designs for the high marsh should minimize competition. [ABSTRACT FROM AUTHOR]

Sea level rise threatens coastal wetlands worldwide, and restoration projects are implementing strategies that decrease vulnerability to this threat. Vegetation monitoring at sites employing new restoration strategies and determination of appropriate monitoring techniques improve understanding of factors leading to restoration success. In Central California, soil addition raised a degraded marsh plain to a high elevation expected to be resilient to sea level rise over the next century. We monitored plant survival and recruitment using area searches, transect surveys, and unoccupied aircraft systems (UAS) imagery. We used random forest modeling to examine the influence of nine environmental variables on vegetation colonization and conducted targeted soil sampling to examine additional factors contributing to vegetation patterns. Limited pre-construction vegetation survived soil addition, likely due to the sediment thickness (mean = 69 cm) and placement method. After 1 year, about 10% of the initially bare area saw vegetation reestablishment. Elevation and inundation frequency were particularly critical to understanding restoration success, with greatest vegetation cover in high-elevation areas tidally inundated < 0.85% of the time. Soil analysis suggested greater salinity stress and ammonium levels in poorly-vegetated compared to well-vegetated areas at the same elevation. We found that both transect and UAS methods were suitable for monitoring vegetation colonization. Field transects may provide the best approach for tracking early vegetation colonization at moderate-sized sites under resource limitations, but UAS provide a complementary landscape perspective. Beyond elucidating patterns and drivers of marsh dynamics at a newly restored site, our investigation informs monitoring of marsh restoration projects globally. [ABSTRACT FROM AUTHOR]

Burrowing animals profoundly influence plant communities, and changes in the burrower and plant communities together with changing abiotic parameters can shift the influence of burrowers on plants. However, we lack an ability to predict when, where, and how burrowers will influence vegetation. To begin to understand how naturally, varying environmental conditions influence the impacts of burrowers, we need to examine how burrower impacts on marsh plants differ across sites differing in environmental conditions. We manipulated crab presence for multiple years and measured the responses of the dominant plants, Pacific cordgrass (Spartina foliosa) and perennial pickleweed (Sarcocornia pacifica), at three sites in northern California and two sites in southern California. Southern California (Point Conception, CA, to the U.S.–Mexico border) experiences higher air and water temperatures, lower precipitation, and higher porewater salinity levels. Combining data from these field studies with laboratory studies allowed us to generate predictions about burrowing crab effects in salt marshes. Our models included (1) an estimate of grazing pressure on marsh plants by the dominant burrowing crab (Pachygrapsus crassipes) and (2) several soil biogeochemical measurements. Crab effects varied from strongly positive to strongly negative and depended upon estimated crab grazing pressure and edaphic conditions (salinity, ammonium, and nitrate). Relative to crabs at other sites, crabs enhanced cordgrass at sites with intermediate levels of ammonium and extreme salinities. The dependence of crab effects on edaphic conditions suggests that projected interannual variability in temperature, precipitation, and nutrients could lead to more temporally variable impacts of crabs on cordgrass. Understanding the environmental controls on these interactions will help promote cordgrass productivity and stabilize salt marsh ecosystems. [ABSTRACT FROM AUTHOR]

Methanogenesis has recently been shown to fuel anaerobic oxidation of methane (AOM) within the sulfate-reducing zone of marine sediments, coining the term "cryptic methane cycle". Here we present research on the relationship between methanogenesis and AOM in a shallow hypersaline pool (∼130 PSU) within a southern California coastal wetland. Sediment (top 20 cm) was subjected to geochemical analyses, in-vitro slurry experiments, and radiotracer incubations using 35S-SO 4 2−, 14C-mono-methylamine, and 14C-CH 4 , to study sulfate reduction, methylotrophic methanogenesis, and AOM. An adapted radioisotope method was used to follow cryptic methane cycling in 14C-mono-methylamine labeling incubations with increasing incubation times (1 hour to three weeks). Results showed peaks in AOM (max 13 nmol cm−3 d−1) and sulfate reduction activity (max 728 nmol cm−3 d−1) within the top 6 cm. Below 6 cm, AOM activity continued (max 15 nmol cm−3 d−1), while sulfate reduction was absent despite 67 mM sulfate, suggesting AOM was coupled to the reduction of iron. Methane concentrations were low (<50 nM) throughout the sediment. Batch sediment slurry incubations with methylated substrates (mono-methylamine and methanol) stimulated methanogenesis, pointing to the presence of methylotrophic methanogens. Incubations with 14C-mono-methylamine revealed the simultaneous activity of methanogenesis and coupled AOM through the stepwise transfer of 14C from mono-methylamine to CO 2 via methane. Our results suggest that AOM is a crucial process in coastal wetland sediments to prevent the buildup of methane in the sulfate-reducing zone. We propose that cryptic methane cycling has been largely overlooked in coastal wetlands resulting in incomplete understanding of carbon cycling in this environment. [ABSTRACT FROM AUTHOR]

Burrowing animals can profoundly influence the structure of surrounding communities, as well as the performance of individual species. Changes in the community structure of burrowing animals or plants together with changing abiotic parameters could shift the influence of burrowers on surrounding habitats. For example, prior studies in salt marshes suggest that fiddler crabs stimulate cordgrass production, but leaf‐grazing crabs suppress cordgrass production. Unfortunately, testing this prediction and others are impeded because few studies have examined crab impacts on the plant community and across multiple sites, multiple years, or both. This challenges our ability to predict how burrowing animals will influence plant community structure, and when and where these impacts will occur. We manipulated the densities of the dominant burrowing crabs in plant assemblages dominated by Pacific cordgrass (Spartina foliosa) and perennial pickleweed (Sarcocornia pacifica) at three sites in southern California for three years (2016, 2017, 2018). Crab impacts on plant community structure differed among each of our three sites. In contrast to our predictions, (1) leaf‐grazing crabs (Pachygrapsus crassipes) had positive effects on cordgrass cover at one site and no effect on cordgrass production at a nearby site in the same marsh and (2) fiddler crabs (Uca crenulata) did not stimulate cordgrass production at another marsh. Because crabs affected traits of cordgrass, but not pickleweed, in the direction consistent with changes in cordgrass cover, we propose that marsh‐specific crab effects on community structure were largely mediated through changes in cordgrass, as opposed to pickleweed. Importantly, crabs facilitated cordgrass during marsh‐wide cordgrass loss, suggesting that crabs may mitigate environmental stress for this ecologically important plant. Because cordgrass abundance can be a critical measure of marsh functioning and is often a restoration target, we suggest that managing cordgrass populations would benefit from additional information about crab populations and their impacts among years, and among and within marshes. [ABSTRACT FROM AUTHOR]

Background and Aims Sea level rise (SLR) associated with climate change is intensifying permanent submersion and salinity in salt marshes. In this scenario, hybridization between native and invasive species may result in hybrids having greater tolerance of abiotic stress factors than their parents. Thus, understanding the responses of native and invasive halophytes and their hybrids to interacting physiological stresses imposed by SLR is key to native species conservation. We analysed how salinity, inundation depth and their interaction impact the functional traits of native and invasive cordgrass species and their hybrid (genus Spartina ; Poaceae). Methods In a mesocosm experiment, we evaluated interactive stress effects of three inundation depths (4.5, 35.5 and 55 cm) and four aqueous salinities (0.5, 10, 20 and 40 ppt) on 27 functional traits of native Spartina foliosa , invasive S. densiflora and their hybrid S. densiflora × S. foliosa from San Francisco Estuary. Key Results The combined effect of salinity and inundation led to synergistic effects on leaf biochemical stress indicators. Spartina foliosa behaved as a stress-tolerant species, with high leaf sodium exudation rate and glycine betaine concentrations that also increased with stress. Spartina foliosa was less sensitive to salinity than S. densiflora and the hybrid but was highly growth-limited in response to increased inundation and salinity. Spartina densiflora was fast-growing in low-stress conditions and tolerated moderate interactive stresses. The hybrid produced more biomass, rhizome reserves and tillers than its parents, even under the most stressful conditions. Transgressivity improved the hybrid's capacity to deal with flooding stress more so than its response to increasing salinity. Conclusions Based on our observations, we predict that established populations of both native and invasive cordgrasses will experience reduced vegetative and sexual fitness in response to SLR. In particular, the combined effects of high salinity and deep inundation may decrease floret production in S. densiflora , a key trait for the spread of its invasive populations. In contrast, the hybrid likely will be able to sustain its invasiveness under SLR based on its ability to maintain growth and biomass production under stressful conditions. [ABSTRACT FROM AUTHOR]

Non-native plants are often found in the transition between the high salt marsh and upland zones of southern California salt marshes. Although plants in these transition zones experience high levels of abiotic stress associated with high salinity and seasonally variable moisture levels, non-native plants are often able to germinate during brief periods of lowered soil salinity that occur after winter rain. In this study, the germination response of four non-native plants (Glebionis coronaria, Mesembryanthemum crystallinum, Atriplex semibaccata, and Bassia hyssopifolia) was tested in a growth chamber at a range of soil salinity and moisture conditions found within this zone. Glebionis coronaria and Mesembryanthemum crystallinum were restricted to a narrow range of less stressful soil conditions, with successfully germination generally only at soil salinity values of 10 ppt or lower, and germination greatly diminished by low moisture levels. Atriplex semibaccata and Bassia hyssopifolia had successful germination at a wider range of soil conditions. The pattern of lower germination with low moisture levels was less pronounced for these species, and successful germination occurred at soil salinity levels of 20 ppt and 30 ppt, respectively. This indicates that non-native plants in the salt marsh vary in the extent to which germination is constrained by seasonal change in soil conditions. These results suggest that the potential management technique of controlling non-native plants through salt addition might not be effective for all non-native species. Species with a greater tolerance for high soil salinity and low moisture conditions might become more successful in the future, as rising sea levels and increase in drought conditions associated with global climate change create conditions that favor these species. [ABSTRACT FROM AUTHOR]

Chromophoric dissolved organic matter (CDOM) optical properties were measured in surface and porewaters as a function of depth and distance from the channel in a transect up the bank in a southern California salt marsh. Higher absorbance coefficients and fluorescence intensities in porewaters at depth vs. surface waters and shallower porewaters suggest soil porewater is a reservoir of CDOM in the marsh. Higher values were observed at the marsh sites compared to the channel site, suggesting increased production and storage in the marsh sites, and reduced leaching into overlying surface waters, is occurring. Spectral slope ratios decreased with depth, consistent with more aromatic, higher molecular weight material in the deeper porewaters, possibly due to different bacterial processing in the anaerobic vs. aerobic zones. Fe(II) concentrations, indicative of anaerobic bacterial processing, increased significantly at depth to values > 1000 μM, consistent with active anaerobic microbial processing occurring at depth. The transitions to higher reduced iron concentrations correlated with increased absorbance and fluorescence, suggesting processing by anaerobic iron-reducing bacteria in these deeper zones may not mineralize as much carbon as in the shallower aerobic zones. Alternatively, this may be due to reduction of solid iron oxides coated with organic matter releasing both DOM and Fe(II). The ratio of humic-like fluorescence to the absorption coefficient decreased with increasing iron concentration, possibly due to optical interference by iron species. Taken together, the data indicate that marsh sites in the salt marsh act as a reservoir for higher molecular weight, more aromatic organic matter. [ABSTRACT FROM AUTHOR]

Contrary to many estuaries where the increase in inputs of nitrogenous nutrients results in a macro-algal or phytoplanktonic bloom, no proliferation of this kind has ever been observed in the waters of Mont-Saint-Michel bay (north-western France) owing to a very high turbidity which greatly limits light penetration. On the other hand, it is well known that the factor that usually limits the growth of vascular plants in salt marshes is not the light resource but nitrogen availability; these plant species are therefore able to benefit fully from the enrichment of water by nitrogenous compounds. This seems to be the case of the sea couch grass Elymus athericus that has spread very rapidly on the salt marshes of this site since the mid-1980s. Firstly, the present study (i) accurately documents, from a compilation of data from administrative archives, the changes in agricultural land use in the major watersheds during the period 1970-2010, together with related changes in the nitrate contents of the rivers flowing into the bay; (ii) quantifies the spatial spread of sea couch grass between 1984 and 2013 from the five maps made during this period. In the second part, using in-depth analysis based on the findings of previous studies, it shows that the expansion of this native grass corresponds to a biological invasion phenomenon, for which nitrogen enrichment of the bay seems to be the only plausible explanation. [ABSTRACT FROM AUTHOR]

Humboldt Bay has the highest rate of sea level rise (SLR) in California (47.2 cm/century). Due to compaction and tectonic subsidence, former tidelands and pastures behind dikes surrounding Humboldt Bay are lower in elevation than bay waters at high tide. Adaptation to future climate change and SLR requires that resource managers understand vulnerability and risk to each wildlife area at a local level, because adaptation to SLR is a risk-based management strategy against an uncertain future requiring site-specific solutions. We conducted a vulnerability assessment of the shoreline of three State wildlife areas surrounding Humboldt Bay: Elk River (ERWA), Fay Slough (FSWA), and Mad River Slough (MRSWA). Breaching of shorelines that border each refuge has the potential to flood a diversity of wetland communities, wildlife habitats, and critical infrastructure within the historic tidal inundation footprint. The total length of diked 1-m shoreline segments potentially impacted by SLR was 6.2 km. The relationship between vulnerability and elevation of diked shoreline segments was significantly correlated for all wildlife areas. Vulnerability of diked shoreline was significantly affected by the type of surface covering. MRSWA had the highest percentage of shoreline fortified with concrete and rock (62.2% [2,876 m]), followed by ERWA (0.3% [2,815 m]). ERWA and FSWA had the greatest percentage of shoreline anchored by vegetation (99.3% [2,834 m] and 91.5% [3,385 m], respectively); FSWA had the highest percentage of unvegetated (i.e., exposed) shoreline (7.4% [252 m]); and ERWA had the highest percentage (86.6% [436 m]) of diked shoreline followed by FSWA (69.2% [633 m]) and MRSWA (33.0% [276 m]). The highest overall ratings of shoreline vulnerability were at ERWA (91.7%), followed by FSSWA (72,4%), and MRSWA (34.4%). Issues related to retention of unique characteristics of each wildlife area, natural resources and species at risk, and adaptive planning for future SLR are discussed. [ABSTRACT FROM AUTHOR]

Tidal marshes are dynamic ecosystems that are influenced by oceanic and freshwater processes and daily changes in sea level. Projected sea-level rise and changes in storm frequency and intensity will affect tidal marshes by altering suspended sediment supply, plant and wildlife communities, and the inundation duration and depth of the marsh platform. The objective of this research was to evaluate how regional weather conditions resulting in low-pressure storms changed tidal conditions locally within three tidal marshes. We hypothesized that regional storms will increase sea level heights locally, resulting in increased inundation of the tidal marsh platform and plant communities. Using site-level measurements of elevation, plant communities, and water levels, we present results from two storm events in 2010 and 2011 from the San Francisco Bay Estuary (SFBE), California, USA. The January 2010 storm had the lowest recorded sea level pressure in the last 30 years for this region. During the storm episodes, the duration of tidal marsh inundation was 1.8 and 3.1 times greater than average for that time of year in 2010 and 2011, respectively. At peak storm surges, over 65% in 2010 and 93% in 2011 of the plant community was under water. We also discuss the implications of these types of storms and projected sea-level rise on the structure and function of tidal marshes and how that may affect the hydrogeomorphic processes and marsh biotic communities. This type of information is useful to managers for incorporating local climate change into developing their monitoring, management, and adaptation strategies. [ABSTRACT FROM AUTHOR]

Tidal wetlands play an important role with respect to climate change because of both their sensitivity to sea-level rise and their ability to sequester carbon dioxide from the atmosphere. Policy-based interest in carbon sequestration has increased recently, and wetland restoration projects have potential for carbon credits through soil carbon sequestration. We measured sediment accretion, mineral and organic matter accumulation, and carbon sequestration rates using Cs and Pb downcore distributions at six natural tidal wetlands in the San Francisco Bay Estuary. The accretion rates were, in general, 0.2-0.5 cm year, indicating that local wetlands are keeping pace with recent rates of sea-level rise. Mineral accumulation rates were higher in salt marshes and at low-marsh stations within individual sites. The average carbon sequestration rate based on Pb dating was 79 g C m year, with slightly higher rates based on Cs dating. There was little difference in the sequestration rates among sites or across stations within sites, indicating that a single carbon sequestration rate could be used for crediting tidal wetland restoration projects within the Estuary. [ABSTRACT FROM AUTHOR]

Abstract: Tidal marsh restoration projects that cover large areas are critical for maintaining target species, yet few large sites have been studied and their restoration trajectories remain uncertain. A tidal marsh restoration project in the northern San Francisco Bay consisting of three breached salt ponds (≥300ha each; 1175ha total) is one of the largest on the west coast of North America. These diked sites were subsided and required extensive sedimentation for vegetation colonization, yet it was unclear whether they would accrete sediment and vegetate within a reasonable timeframe. We conducted bathymetric surveys to map substrate elevations using digital elevation models and surveyed colonizing Pacific cordgrass (Spartina foliosa). The average elevation of Pond 3 was 0.96±0.19m (mean±SD; meters NAVD88) in 2005. In 2008–2009, average pond elevations were 1.05±0.25m in Pond 3, 0.81±0.26m in Pond 4, and 0.84±0.24m in Pond 5 (means±SD; meters NAVD88). The largest site (Pond 3; 508ha) accreted 9.5±0.2cm (mean±SD) over 4 years, but accretion varied spatially and ranged from sediment loss in borrow ditches and adjacent to an unplanned, early breach to sediment gains up to 33cm in more sheltered regions. The mean elevation of colonizing S. foliosa varied by pond (F =71.20, df =84, P <0.0001) and was significantly lower in Ponds 4 and 5 compared with Pond 3 which corresponded with greater tidal muting in those ponds. We estimated 16% of Pond 3, 13% of Pond 4, and 24% of Pond 5 were greater than or equal to the median elevation of S. foliosa. Our results suggest that sedimentation to elevations that enable vegetation colonization is feasible in large sites with sufficient sediment loads although may occur more slowly compared with smaller sites. [Copyright &y& Elsevier]

Understanding wetland food webs is critical for effective habitat management, restoration and conservation. Microalgae are recognized as key food sources for marsh invertebrates but the importance of different groups under various conditions is rarely examined. We tested the hypothesis that faunal utilization of microalgae, and cyanobacteria in particular, is significant in Southern California created and natural salt marshes but varies with habitat type (creek bank versus marsh interior) and season (spring versus autumn). We used stable isotope analysis and mixing models (IsoSource) to compare food webs in adjacent young (created) and mature (natural) salt marshes. Isotopic values of some primary producers, macrofauna, epifauna, and fish demonstrated significant differences between the adjacent salt marshes. δ13C and δ34S values of the benthic microalgal community varied with taxonomic composition (diatoms versus cyanobacteria) and to a lesser extent with season. Depleted δ15N values of benthic diatoms and macroalgae indicated that N2 fixed within algal mats was recycled within the benthic algal community. Marsh fauna, including most major macrofauna taxal, Cerithidea, and Fundulus, also exhibited seasonal differences in isotopic composition, and Cerithidea and selected macrofauna (oligochaetes, polychaetes) from the marsh interior were more enriched in 13C and depleted in 15N than those from the creek bank. In the young marsh, the cyanobacteria contributed a minimum of 17-100% of the primary production in food webs supporting macrofauna, and cyanobacteria contributed at least 40% of the primary production included in Ce rithidea and Fundulus food webs. A wider range of primary producers contributed to food webs in the mature marsh. Cyanobacteria were a greater source of trophic support for macrofauna from the marsh interior than the creek bank, whereas Spartina was a more important food source for creek bank macrofauna in both marshes. Insect larvae largely consumed cyanobacteria, whereas polychaetes exhibited greater utilization of Spartina. Phytoplankton was the primary food resource for mussels in both marshes. Although the spatial and temporal complexity of food webs has traditionally been collapsed into the study of relatively simplified food webs, isotope signatures reveal fine-scale patterns in food web structure that may be used to make more accurate assessments of ecosystem state. Accurate interpretation of marsh trophic structure using natural abundance stable isotopes requires fine-scale resolution in space and time, a large number of samples, and a high level of taxonomic resolution. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the responses of wetland to sedimentation and nitrogen loading through nitrogen-fixing microbes (diazotrophs) inhibition and diversification at Tijuana Estuary, California. It notes that the diazotroph responses demonstrate conformance to a more general ecological pattern of high function among low diversity assemblages. It points out that nitrogen fixation establishes a mechanism for rapid transfer of fixed nitrogen to sulphur.

Abstract: Trophic support functions for fishes are a key goal of salt marsh restoration. Food availability in restored sites may be enhanced by creation of shallow pools, which are important sources of prey items in tidal wetlands. Young restored salt marshes are typically sparsely vegetated and are subject to rapidly changing geomorphology. Scouring and sedimentation create and fill shallow depressions, producing a shifting mosaic of tidal pools. In a large (8-ha) southern California experimental restoration site, we created shallow pools and assessed their development of foods for fishes. Created pools quickly developed abundant invertebrate prey, with densities exceeding those found in older, naturally formed pools (P <0.0001). Opportunistic mobile and disturbance-associated taxa (calanoid copepods, nematodes, Polydora complex, and Trichocorixa reticulata) accounted for higher invertebrate densities in created pools. We repeated experiments in spring, summer, and fall and found seasonal variability in trophic development. We also applied bottom-up (nitrogen addition) and top-down (fish exclusion) treatments to pools. Some measures of algal biomass were increased by nitrogen fertilization (P =0.001–0.06), but there were no upward-cascading effects on invertebrate composition or abundance. Fish abundance in the site varied seasonally, but there were no compelling effects of fish exclusion treatments on algal or invertebrate abundance. Incorporating shallow depressions into salt marsh restoration projects is a potential tool to jumpstart fish-support functions. [Copyright &y& Elsevier]

Chloroform (CHCl3), carbon tetrachloride (CCl4), and methyl chloroform (CH3CCl3) are important carriers of chlorine to the stratosphere and account for an estimated 15% of the total organic chlorine in the troposphere, roughly equivalent to chlorine load due to methyl chloride (CH3Cl). The tropospheric burden of chlorine has declined since 1994, largely due to the restriction of CH3CCl3 and CCl4 use as specified by the Montreal Protocol. However, few field studies have been conducted on the terrestrial-atmosphere exchange of these chlorinated hydrocarbons, leading to uncertainties about the natural cycling of these trace gases. This work shows the results of 75 flux measurements conducted in a variety of southern California ecosystems, including coast sagebrush, chamise chaparral, creosote bush scrub, shoreline, and coastal salt marsh. We find no evidence of a significant soil sink in these ecosystems but rather a small net source of CHCl3 and possibly CCl4. [Copyright &y& Elsevier]

Outbreaks of infectious agents in natural ecosystems are on the rise. Understanding host-pathogen interactions and their impact on community composition may be central to the conservation of biological diversity. Infectious agents can convey both exploitive and facilitative effects that regulate host populations and community structure. Parasitic angiosperms are highly conspicuous in many plant communities, and they provide a tractable model for understanding parasite effects in multispecies communities. I examined host identity and variation in host infectivity of a holoparasitic vine (Cuscuta sauna) within a California salt marsh. In a two-year parasite removal experiment, I measured the effect of C. sauna on its most frequent host, a rare hemiparasite, and the plant community. C. sauna clearly suppressed the dominant host, but rare plant fitness and plant species diversity were enhanced through indirect effects. Priority effects played a role in the strength of the outcome due to the timing of life history characteristics. The differential influence of parasites on the fecundity of multiple hosts can change population dynamics, benefit rare species, and alter community structure. The continuum of negative to positive consequences of parasitic interactions deserves more attention if we are to understand community dynamics and successfully restore tidal wetlands. [ABSTRACT FROM AUTHOR]

The article explores how ecological theory predicts habitat heterogeneity into restoration sites. It also examines how topographic heterogeneity affects higher trophic levels. In this context, the author mentioned that the southern California restoration experiment tested effects of tidal creek networks and pools on trophic structure of salt marsh habitat and high-tide use by two regionally dominant fish species. These include California killifish or Fundulus parvipinnis and longjaw mudsucker or Gillichthys mirabilis. Tidal creeks are expected to function as conduits that would enhance connectivity between subtidal and intertidal habitat and pools to serve as microhabitat oases for fishes.

Knowing that diverse plantings enhanced biomass and nitrogen (N) accumulation in a restored California salt marsh, we asked if the ‘biodiversity effect‘ was due to species selection or complementarity. In a two-year greenhouse experiment, we found positive biodiversity effects on total, root, and shoot biomass, total and root N crop, and on biomass and N allocation; negative effects on root and shoot N concentration; and no effect on shoot N crop. Overyielding among trios and sextets was supported by significant deviations in observed yield from that expected relative to solo yields (DT). However, both trios and sextets strongly underyielded relative to the highest yielding solo in the assemblage (Dmax) in all attributes, and to the dominant species in the assemblage (Ddom) in most attributes. When we decomposed biodiversity effects on shoot characteristics, selection effects primarily drove over- and underyielding. The only complementarity effect was underyielding of sextet shoot biomass. These analyses were possible because we replicated assemblages and evaluated 11 response variables. One species (Salicornia virginica) dominated functioning when present; when absent, another dominated (e.g., Frankenia sauna). Effects varied with the response tested, however. For both shoot biomass and N crop, S. virginica was the dominant overyielding species (based on Dij and comparisons of trios ± target species). For shoot N concentration, however, the dominant was Triglochin concinna, a species that had low biomass but was capable of reducing assemblage performance, presumably by concentrating N. Evidence for strong species selection effects led us to predict that three species would eventually dominate our parallel field experiment that tested the same assemblages. Exactly that happened in nine years, but (we predict) without losing function, because the site retained the three highest-performing species. Biodiversity loss was nonrandom in the field, and because trios with two top performers sustained critical functions in the greenhouse, we predict that many functions will not decline, even if the salt marsh becomes dominated by a single species, e.g., S. virginica. Unmeasured functions (e.g., resilience) might not persist, however. Knowing how assemblages perform made biodiversity-ecosystem function theory both explanatory and predictive. [ABSTRACT FROM AUTHOR]

Fluoroquinolones, a widely used class of antibiotics, are frequently detected in sediments and surface waters. Given their antimicrobial properties, the presence of these compounds may alter the composition of microbial communities and promote antibiotic resistance in the environment. The purpose of this study was to measure sorption, and effects of ciprofloxacin on microbial community composition, in sediment samples from three California salt marshes. Sediments were exposed to a ciprofloxacin concentration gradient (0–200 μg ml−1 ciprofloxacin) and microbial community composition characterized using phospholipid fatty acid (PLFA) analysis. Sorption coefficients, expressed as log Kd, were calculated from fits using the Freundlich isotherm model. Ciprofloxacin strongly sorbed to all sediments and had log Kd values, ranging from 2.9 to 4.3. Clay content was positively (r2=0.98) and pH negatively (r2=0.99) correlated to Kd values. Biomass, PLFA richness, sulfate reducer and Gram-negative bacteria markers increased with ciprofloxacin concentrations, while the 17 cy/precursor and saturated/unsaturated biomarker ratios, indicators of starvation stress, decreased. The magnitude of the effect of ciprofloxacin on microbial communities was inversely correlated to the degree of sorption to the sediments. Despite the fact that ciprofloxacin is a wide-spectrum antibiotic, its impact on sediment microbial communities was selective and appeared to favor sulfate-reducing bacteria and Gram-negative bacteria.The ISME Journal (2007) 1, 585–595; doi:10.1038/ismej.2007.71; published online 6 September 2007 [ABSTRACT FROM AUTHOR]

We evaluated interspecific habitat use within a salt marsh small mammal assemblage on Mare Island, Solano County, California, USA, from 1989 to 1992, with emphasis on the endangered salt marsh harvest mice (Reithrodontomys raviventris). We livetrapped small mammals during 125 trap sessions at 20 different areas throughout Mare Island for a total of 55,189 trap-nights. We captured the salt marsh harvest mouse 4,147 times; the house mouse (Mus musculus), 1,936 times; the California vole (Microtus californicus), 372 times; and the shrew (Sorex spp.), 117 times, among 12,927 captures. We captured fewer than 10 rats (Rattus spp.), and we did not capture any western harvest mice (Reithrodontomys megalotis) or deer mice (Peromyscus maniculatus). We sampled vegetation characteristics at each trap location during 79 of 125 trap sessions for a total of 5,523 trap locations. During the summer, breeding, and fall seasons, habitats characterized by increased cover of forbs, particularly fat hen (Atriplex patula), were used to a greater extent by male than female salt marsh harvest mice. Both sexes of salt marsh harvest mice used areas with less cover of forbs, particularly fat hen and pickleweed (Salicornia virginica), during the winter, spring, postbreeding, and prebreeding seasons. House mice used habitats that were more patchily distributed or fragmented than salt marsh harvest mice. Habitat characteristics that were positively associated with salt marsh harvest mice tended to be negatively associated with house mice. Voles used habitats characterized by positive associations with shrub, pickleweed, litter, and woody debris cover, foliage height densities (0 to >40 cm), and mean vegetation height. Vole habitat use was negatively associated with water cover and depth. We suggest that reducing habitat patchiness throughout tidal marshes may reduce salt marsh harvest mouse competition with house mice, and restoring tidal action may reduce habitat competition with voles. [ABSTRACT FROM AUTHOR]

Vascular plants strongly control belowground environments in most ecosystems. Invasion by vascular plants in coastal wetlands, and by cordgrasses (Spartina spp.) in particular, are increasing in incidence globally, with dramatic ecosystem-level consequences. We examined the trophic consequences of invasion by a Spartina hybrid (S. alterniflora ⊗ S. foliosa) in San Francisco Bay (USA) by documenting differences in biomass and trophic structure of benthic communities between sediments invaded by Spartina and uninvaded sediments. We found the invaded system shifted from an algae-based to a detritus-based food web. We then tested for a relationship between diet and tolerance to invasion, hypothesizing that species that consume Spartina detritus are more likely to inhabit invaded sediments than those that consume surface algae. Infaunal diets were initially examined with natural abundance stable isotope analyses and application of mixing models, but these yielded an ambiguous picture of food sources. Therefore, we conducted isotopic enrichment experiments by providing 15N-labeled Spartina detritus both on and below the sediment surface in areas that either contained Spartina or were unvegetated. Capitellid and nereid polychaetes, and oligochaetes, groups shown to persist following Spartina invasion of San Francisco Bay tidal flats, took up JSN from labeled native and invasive Spartina detritus. In contrast, we found that amphipods, bivalves, and other taxa less tolerant to invasion consumed primarily surficial algae, based on 13C enrichment experiments. Habitat (Spartina vs. unvegetated patches) and location of detritus (on or within sediments) did not affect 15N uptake from detritus. Our investigations support a ‘trophic shift’ model for ecosystem response to wetland plant invasion and preview loss of key trophic support for fishes and migratory birds by shifting dominance to species not widely consumed by species at higher trophic levels. [ABSTRACT FROM AUTHOR]

Inter-tidal marshes are dynamic diverse ecosystems at the transition zone between terrestrial and ocean environments. Geomorphologically, inter-tidal salt marshes are vegetated landforms at elevations slightly greater than mean tidal levels that have distributed channels formed under ebb (drainage) tidal flows that widen and deepen in the seaward direction. The drainage channels enable tidal flows to circulate sediments and nutrients through the marsh system during normal tidal events, while depositing sediments during storm or seismic events. This dynamic system encourages considerable bio diversity while simultaneously providing water quality enhancement features that service marsh terrestrial life and marine life in the estuary. Reservoir creation limiting sediment transport, anticipated large increases in sea levels as well as agricultural and urban development have resulted in significant loss of inter-tidal marshes and subsequent adverse impacts on waterfowl, infauna and fisheries. The complex and continuously changing marsh channel hydraulics and sedimentary processes have severely constrained quantitative modeling of these marsh systems such that restoration/creation efforts remain something of an empirical science and further assessments are needed. The purpose of this paper is to outline current understanding of salt marsh hydrodynamics, sediment accretion processes and subsequent response of marsh vegetation to set the stage for assessment of a marsh restoration effort along San Pablo Bay near San Francisco, California. Several kilometers of drainage channels were constructed in a 624 ha disturbed salt marsh to restore tidal circulation and vegetation so as to enhance habitat for threatened species (e.g. clapper rail, harvest mouse, delta smelt and potentially anadromous fish species). Two distinct drainage channel systems (`east' and `west') were installed having similar channel dimensions common to salt marshes in the region, but having design bankfull tidal prism volumes differing by a factor of two. Following channel excavation, main channel tidal flows and sediment loads as well as marsh sediment accretion rates were monitored to assess the relative success of the excavation in restoring tidal circulation and vegetation (Salicornia spp.) to the marsh. Annual aerial surveys corroborated with ground-truthing indicated that marsh vegetation rapidly expanded, from 40 to 85% coverage several years following excavation. The `east' channel intake was nearly completely silted in within three years. However, channel surveys and flow measurements indicated that the `east' channel system tidal prism was only about 1200 m³, more than an order of magnitude less than that of the stable `west' channel system. Marsh sediment accretion rates were on the order of 7-8 mm yr-1, a rate common to the Pacific coast region that exceeds estimated sea level rise rates of ∼2 mm yr-1. East channel network siltation resulted in storm and spring tidal flood ponding such that marsh vegetation coverage decreased to 51% of the marsh area and related habitat expansion decreased. These results are considered in terms of the primary inter-tidal marsh factors affecting possible restoration/creation strategies. [ABSTRACT FROM AUTHOR]

Extensive restoration efforts in southern California coastal wetlands highlight several challenges for urban salt marsh restoration, including: habitat isolation and fragmentation, impacts from exotic species, the loss of transitional upland habitats, and other alterations to hydrologic and sediment dynamics. Habitat isolation impairs colonization by dispersal-limited plants, so planting becomes essential to achieve diverse salt marshes. Low species richness slows the development of salt marsh functions (e.g., biomass and nitrogen accumulation) in southern California. A variety of exotic species have invaded the upper reaches of salt marshes in southern California, most commonly in marshes with hydrological modifications. The replacement of gradual slopes between wetlands and uplands by sharp transitions abutting urban development limits our ability to restore rare plant and animal populations. Where hydrologic connections are impaired by roads and other structures, the natural migration of channels is constrained, and sediment dynamics often lead to lagoon mouth closure. A case study from Tijuana River National Estuarine Research Reserve (hereafter, Tijuana Estuary) further illustrates a specific lesson for urban salt marsh restoration concerning watershed issues and sediment dynamics. In the south arm of Tijuana Estuary, watershed urbanization, along with local climate, topography, and soils, has resulted in extreme rates of sediment accumulation. Sedimentation rates in a salt marsh in the south arm of the estuary ranged from 10 to 30 cm over a single winter (1994-95), substantially greater than historic sedimentation rates in the estuary or rates from other coastal wetlands with storm sedimentation. Sediment buried salt marsh vegetation in place and is converting intertidal salt marsh to uplands. These impacts illustrate the need to consider watershed issues and sediment control in managing and restoring urban salt marshes. [ABSTRACT FROM AUTHOR]

Abstract Since 1972 over 940 ha (2,300 ac) of leveed former salt marsh sites around San Francisco Bay have been restored to tidal action, purposely or through natural processes. The evolution of these sites can inform predictions of rates of marshplain evolution and establishment of tidal channel systems. A review of the history of 15 re-flooded sites ranging in size from 18 to 220 ha (45 to 550 ac) and in age from 2 to 29 years indicates that marshplain vegetation with more than 50% cover was established at nine of the sites within 4 to 20 years. The remaining six sites aged 2 to approximately 20 years continue to be less than 50% vegetated. The evolution of these sites is consistent with the following simple conceptual model of the physical evolution of restored tidal marshes in subsided breached sites. Initially, deposition of estuarine sediment builds up mudflats that allow vegetation establishment once elevations are high enough for vegetation to survive. Sites that are initially lower in the tidal frame take longer to vegetate than those that are initially higher. Three factors appear to retard the time frame for vegetation establishment: limited estuarine suspended sediment supply, erosion of deposited estuarine muds by internally generated wind waves, and restricted tidal exchange. These factors affect evolution more significantly in larger sites. The comparatively short time frame for vegetation colonization and marshplain evolution experienced in earlier, smaller, and/or less subsided breached levee restorations may not necessarily be replicable by simple levee breaching on larger subsided restoration sites now being planned. Our review of the 15 sites also indicates that the formation of tidal channels within the marshes is greatly dependent on whether and how high the site was filled before breaching. Filled sites at high intertidal elevations (above approximately 0.3 m below mean higher high water) can vegetate quickly but after several decades may... [ABSTRACT FROM AUTHOR]

All-terrain vehicles (ATVs) are widely used in a variety of wetland management activities, but their ecological effects on vegetation are poorly known. Two types of ATVs – the ArgoTM, and LightfootTM – were tested in Petaluma Marsh, Sonoma Co., California, to determine their effects on pickleweed ( Salicornia virginica) in terms of: (1) stem-height reductions and stem breakage (as biomass), by simulating light (a path traversed twice) and heavy vehicle use (20 times), and by evaluating damage immediately after manipulation and one year later; and, (2) biomass and growth by using a BACI (before-after-control-impact) design, with two sets of replicated samples collected before a light-use treatment, two sets after treatment (during the same growing season), and one set the following year. Stem height was significantly reduced by both vehicles immediately following use, and was similar for both light and heavy use; biomass of broken stems was significantly higher for the LightfootTM than for the ArgoTM, and with heavy use by both vehicles. One year later, biomass of broken stems was not significantly different in light use treatments with either vehicle, but lower stem height was still visually evident from LightfootTM in heavy use treatments. Post-treatment biomass-growth measurements were significantly lower for both vehicles during the same growing season, but no significant differences were found between either vehicle treatment and controls one year later. However, the LightfootTM treatment had lower productivity. Results indicated that even limited ATV use can cause immediate impact to pickleweed but that limited use with soft-tread vehicles, like the Argo, can recover within a year. Management of pickleweed wetlands should involve vehicles with non-damaging tracks or tire tread and, when possible, walking is preferable to reduce immediate habitat damage. [ABSTRACT FROM AUTHOR]

Despite long-term monitoring of water quality in the coastal lagoonsof California, USA, the fate of organochlorines discharged from agricultural and urban sources to salt marsh habitats has received littleattention. We measured organochlorine concentrations in Upper Newport Bay marsh and channel sediments and salt marsh plants. Sediment grain-size analyses show that organochlorines are fractionated and concentrated in the organic material traveling with the clay fraction of the washload discharged into the bay from San Diego Creek. Hydrophobiccompounds such as DDT are not associated with the sand and silt fractions. The most frequently detected analyte was p,p'- I,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (DDE), occurring in 100% of the sediment samples and 87% of the plant root samples. Maximum concentrations in sediment were 122 ng/g (dry wt) for DDE and 162 ng/g DDT plus metabolites (Sigma DDT) in salt marsh deposited since 1980. Ratios of DDT to its metabolites suggest that anaerobic degradation of DDT occurs in the cordgrass (Spartina fnliosa Trin.) sediments. Cordgrass and pickleweed (Saticornia virginica L.) partition organochlorine residues to the root epidermis, attaining values of 50,000 ng/g lipid for SigmaDDT and 80,000 ng/g lipid for heptachlorepoxide (1,4,5,6,7,8,8-heptachloro-2.3-epoxy-3Alpha,4,7,7a lpha-tetrahydro-4,7-methanoindan). [ABSTRACT FROM AUTHOR]