Southern California Salt Marsh Research Articles

Evaluation of techniques for controlling non-native sea lavenders in California coastal salt marshes

AbstractTwo species of non-native sea lavender, Limonium ramosissimum (Poir.) Maire (Algerian sea lavender) and Limonium duriusculum (Girard) Fourr. (European sea lavender) are prolific invaders of California salt marshes. We examined the efficacy of three non-herbicide treatments [tarping, selective removal (hand pulling), and scraping], and one herbicide (Telar®) treatment, in eliminating L. ramosissimum and L. duriusulum, as well as treatment impacts to native vegetation within three southern California salt marshes. Our experiments demonstrated that the non-herbicide treatments initially suppressed cover of L. ramosissimum and L. duriusulum to near zero but varied over time in their suppression of L. ramosissimum and L. duriusulum, and their effects on native species. Depending on the tarping duration, tarping eradicates L. ramosissimum and L. duriusulum at least a year post treatment with little to no long-term negative impacts to native vegetation. Selective removal had minimal effect on native species but did not consistently suppress L. duriusulum over time. Scraping eradicates L. ramosissimum and L. duriusulum; however, its negative impacts on native species make it an undesirable treatment across large areas. The herbicide treatment was not as effective in suppressing L. ramosissimum, either initially or over time, and it negatively impacted native species. Our findings support the use of tarping as the primary management method to control or eradicate dense infestations of L. ramosissimum and L. duriusulum in salt marshes. We suggest that a combination of tarping and selective removal be used to control L. ramosissimum and L. duriusulum in areas of lower infestation.

Relationship of Sphaeroma quoianum to sediment characteristics and invertebrate community

Many important wetland functions are tied to sediment dynamics, which are influenced by infaunal invertebrate communities. These communities are sensitive to changes in sediment structure and to colonization by non-native species. In a southern California salt marsh, the non-native isopod Sphaeroma quoianum has created dense networks of burrows within the marsh banks. Since this isopod increases erosion in many areas and can change local invertebrate communities, its possible contribution to habitat loss in this already-scarce southern California ecosystem is an important issue. To determine the relationship of S. quoianum to invertebrate community and sediment characteristics, three burrowed transects and one unburrowed transect were surveyed and sampled for invertebrate and sediment cores. This study tested the association between burrows and grain size distribution, sediment carbon content, respiration rates, and invertebrate community composition. Sphaeroma quoianum burrows were correlated with altered invertebrate community composition, decreased carbon content, and steep marsh bluffs. These results highlight the potential susceptibility of salt marsh habitat with steep edges to invasion by non-native species. These results also suggest that S. quoianum invasion of salt marsh habitats can alter native communities and ecosystem functions; thus, incipient invasions should be of concern to managers and ecologists alike.

Aboveground competition influences density-dependent effects of cordgrass on sediment biogeochemistry.

Interspecific interactions between plants influence plant phenotype, distribution, abundance, and community structure. Each of these can, in turn, impact sediment biogeochemistry. Although the population and community level impacts of these interactions have been extensively studied, less is known about their effect on sediment biogeochemistry. This is surprising given that many plants are categorized as foundation species that exert strong control on community structure. In southern California salt marshes, we used clipping experiments to manipulate aboveground neighbor presence to study interactions between two dominant plants, Pacific cordgrass (Spartina foliosa) and perennial pickleweed (Sarcocornia pacifica). We also measured how changes in cordgrass stem density influenced sediment biogeochemistry. Pickleweed suppressed cordgrass stem density but had no effect on aboveground biomass. For every cordgrass stem lost per square meter, porewater ammonium increased 0.3–1.0 µM. Thus, aboveground competition with pickleweed weakened the effects of cordgrass on sediment biogeochemistry. Predictions about plant–soil feedbacks, especially under future climate scenarios, will be improved when plant–plant interactions are considered, particularly those containing dominant and foundation species.

Short-term impact of sediment addition on plants and invertebrates in a southern California salt marsh.

The implementation and monitoring of management strategies is integral to protect coastal marshes from increased inundation and submergence under sea-level rise. Sediment addition is one such strategy in which sediment is added to marshes to raise relative elevations, decrease tidal inundation, and enhance ecosystem processes. This study looked at the plant and invertebrate community responses over 12 months following a sediment addition project on a salt marsh located in an urbanized estuary in southern California, USA. This salt marsh is experiencing local subsidence, is sediment-limited from landscape modifications, has resident protected species, and is at-risk of submergence from sea-level rise. Abiotic measurements, invertebrate cores, and plant parameters were analyzed before and after sediment application in a before-after-control-impact (BACI) design. Immediately following the sediment application, plant cover and invertebrate abundance decreased significantly, with smothering of existing vegetation communities without regrowth, presumably creating resulting harsh abiotic conditions. At six months after the sediment application treatment, Salicornia bigelovii minimally colonized the sediment application area, and Spartina foliosa spread vegetatively from the edges of the marsh; however, at 12 months following sediment application overall plant recovery was still minimal. Community composition of infaunal invertebrates shifted from a dominance of marsh-associated groups like oligochaetes and polychaetes to more terrestrial and more mobile dispersers like insect larvae. In contrast to other studies, such as those with high organic deposition, that showed vegetation and invertebrate community recovery within one year of sediment application, our results indicated a much slower recovery following a sediment addition of 32 cm which resulted in a supratidal elevation with an average of 1.62 m (NAVD88) at our sampling locations. Our results indicate that the site did not recover after one year and that recovery may take longer which illustrates the importance of long-term monitoring to fully understand restoration trajectories and inform adaptive management. Testing and monitoring sea-level rise adaptation strategies like sediment addition for salt marshes is important to prevent the loss of important coastal ecosystems.

Short-term impact of sediment addition on plants and invertebrates in a southern California salt marsh

Short-term impact of sediment addition on plants and invertebrates in a southern California salt marsh

Effects of Salt and Drought Stress on Germination of Non-native Plants in the Salt Marsh to Upland Transition Zone

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.

Optical Characterization of Chromophoric Dissolved Organic Matter (CDOM) and Fe(II) Concentrations in Soil Porewaters Along a Channel-Bank Transect in a Salt Marsh

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.

Coastal flooding and the 1861-2 California storm season

A series of large storms attributed to Atmospheric River conditions struck the California coast in the winter of 1861-2. Although historical accounts document inland flooding, little is known about how the 1861-2 storms impacted the now heavily-developed California coast. Here we show that the 1861-2 storms emplaced a deposit of beach sand up to 50 cm thick over 450 m inland within a southern California salt marsh. This deposit is unprecedented in the post-European sediments of the marsh and more extensive than that derived from any other historical event. It is comparable in scale to hurricane and tsunami washover fans in back-barrier environments along other coastlines. The presence of overwash deposits in Carpinteria suggests that the 1861-2 storm season was erosive enough to remove coastal barriers, allowing for inundation of parts of the coastline currently developed. Efforts to prepare for a recurrence of an 1861-2-like storm season should address potential coastal impacts; likewise, interpretations of past washover deposits should consider these unusually prolonged stormy periods in addition to hurricane and tsunami inundation.

Optical properties of chromophoric dissolved organic matter (CDOM) in surface and pore waters adjacent to an oil well in a southern California salt marsh

Chromophoric dissolved organic matter (CDOM) optical properties were measured in surface and pore waters as a function of depth and distance from an oil well in a southern California salt marsh. Higher fluorescence and absorbances in pore vs. surface waters suggest soil pore water is a reservoir of CDOM in the marsh. Protein-like fluorophores in pore waters at distinct depths corresponded to variations in sulfate depletion and Fe(II) concentrations from anaerobic microbial activity. These variations were supported by fluorescence indexes and are consistent with differences in optical molecular weight and aromaticity indicators. Fluorescence indices were consistent with autochthonous material of aquatic origin in surface waters, with more terrestrial, humified allochthonous material in deeper pore waters. CDOM optical properties were consistent with significantly enhanced microbial activity in regions closest to the oil well, along with a three-dimensional excitation/emission matrix fluorescence spectrum peak attributable to oil, suggesting anaerobic microbial degradation of oil.

Balanced Sediment Fluxes in Southern California’s Mediterranean-Climate Zone Salt Marshes

Salt marsh elevation and geomorphic stability depends on mineral sedimentation. Many Mediterranean-climate salt marshes along southern California, USA coast import sediment during El Nino storm events, but sediment fluxes and mechanisms during dry weather are potentially important for marsh stability. We calculated tidal creek sediment fluxes within a highly modified, sediment-starved, 1.5-km2 salt marsh (Seal Beach) and a less modified 1-km2 marsh (Mugu) with fluvial sediment supply. We measured salt marsh plain suspended sediment concentration and vertical accretion using single stage samplers and marker horizons. At Seal Beach, a 2014 storm yielded 39 and 28 g/s mean sediment fluxes and imported 12,000 and 8800 kg in a western and eastern channel. Western channel storm imports offset 8700 kg exported during 2 months of dry weather, while eastern channel storm imports augmented 9200 kg imported during dry weather. During the storm at Mugu, suspended sediment concentrations on the marsh plain increased by a factor of four; accretion was 1–2 mm near creek levees. An exceptionally high tide sequence yielded 4.4 g/s mean sediment flux, importing 1700 kg: 20 % of Mugu’s dry weather fluxes. Overall, low sediment fluxes were observed, suggesting that these salt marshes are geomorphically stable during dry weather conditions. Results suggest storms and high lunar tides may play large roles, importing sediment and maintaining dry weather sediment flux balances for southern California salt marshes. However, under future climate change and sea level rise scenarios, results suggest that balanced sediment fluxes lead to marsh elevational instability based on estimated mineral sediment deficits.

Soil Organic Carbon and Nitrogen Storage in Two Southern California Salt Marshes: The Role of Pre-Restoration Vegetation

Abstract Soil organic carbon and nitrogen storage represent important ecosystem services provided by salt marshes. To test the importance of vegetation on soil properties, we measured organic carbon, total nitrogen, and belowground biomass in two southern California salt marshes. In both marshes, cores were collected from areas which differed in dominant vegetation cover prior to the restoration of tidal influence. There were no differences in organic carbon or total nitrogen density between vegetation classes at either site; however, a relationship between belowground biomass and soil organic carbon suggests that vegetation may influence soil properties.

Lignocellulose-responsive bacteria in a southern California salt marsh identified by stable isotope probing.

Carbon cycling by microbes has been recognized as the main mechanism of organic matter decomposition and export in coastal wetlands, yet very little is known about the functional diversity of specific groups of decomposers (e.g., bacteria) in salt marsh benthic trophic structure. Indeed, salt marsh sediment bacteria remain largely in a black box in terms of their diversity and functional roles within salt marsh benthic food web pathways. We used DNA stable isotope probing (SIP) utilizing 13C-labeled lignocellulose as a proxy to evaluate the fate of macrophyte-derived carbon in benthic salt marsh bacterial communities. Overall, 146 bacterial species were detected using SIP, of which only 12 lineages were shared between enriched and non-enriched communities. Abundant groups from the 13C-labeled community included Desulfosarcina, Spirochaeta, and Kangiella. This study is the first to use heavy-labeled lignocellulose to identify bacteria responsible for macrophyte carbon utilization in salt marsh sediments and will allow future studies to target specific lineages to elucidate their role in salt marsh carbon cycling and ultimately aid our understanding of the potential of salt marshes to store carbon.

Evaluating Monoculture Versus Polyculture Planting Regimes in a Newly-Restored Southern California Salt Marsh

Salt marsh plants are a key source of primary productivity, ameliorate harsh abiotic conditions, and provide habitat structure to many organisms. As a consequence, rapid re-establishment of plant cover following restoration can speed the recovery of degraded ecosystems. Despite demonstrated positive relationships between plant biodiversity and ecosystem functions, many salt marsh restoration plans still incorporate single-species plantings under the belief that this approach will lead to faster increases in plant cover (a typical management goal). In this study, we evaluated post-restoration recovery of a non-vegetated high marsh berm in Brookhurst Marsh, Huntington Beach, CA, with two active planting strategies: monoculture plots of the competitive dominant Sarcocornia pacifica (pickleweed) versus polyculture plots of pickleweed and eight other common salt marsh plant species. Although monocultures did increase in total percent plant cover faster than polycultures, both treatments had reached 80-100% cover after one year, easily exceeding the permit-mandated goal of 20–40% cover in that time. The effects of increasing plant cover on abiotic parameters (e.g., % light reaching the ground, soil temperature, and soil salinity) were comparable between the two treatments and provided physical conditions sufficient to support similar macroinvertebrate communities. In contrast, plant species richness and canopy complexity were significantly higher in polyculture versus monoculture plots by the end of the experiment. Mean plant height was lower in polyculture plots, but maximum plant height (which can influence habitat use by perching birds) did not differ by treatment. Our data suggest that polyculture plots performed as well as, or better than, S. pacifica alone with respect to multiple indicators of ecosystem function. Active planting of high-diversity plots should therefore be seriously considered as a restoration tool to achieve common management goals in southern California salt marshes.

Abiotic Limitation of Non-native Plants in the High Salt Marsh Transition Zone

Native plants in the upland to high-marsh transition zone of southern California salt marshes are mostly perennials and therefore experience the abiotic stress of low soil moisture and high soil salinity throughout much of the year. However, many annual non-native plants reproduce during the brief period of reduced salinity and increased moisture during winter rainfall. We investigated the seasonal and spatial variation in vegetation and soil properties of the transition zone using an observational study. Next, we explored the potential for managing non-native plants using a field experiment with varying timing, quantity, and frequency of salt addition treatments. The observational study showed that the distribution of non-native plants is related to changes in soil salinity and soil moisture that accompany changes in elevation, although there are variations among species. In the field experiment, salt was effective at reducing non-native plant cover, but the timing of treatment was important. Although additional work is needed to refine the salt treatments, this work supports the idea that altering abiotic conditions can effectively reduce the presence of non-native species in the upland to high-marsh transition zone.

Soil Organic Carbon Storage in Restored Salt Marshes in Huntington Beach, California

There is a growing interest in managing wetland restoration and conservation projects to maximize carbon sequestration. We measured soil organic carbon storage and methane flux from two southern California salt marshes which had been restored for 2 and 22 years. We hypothesized that organic carbon would accumulate following restoration and that methane flux would be negligible in both sites. While methane flux was minimal, soil organic carbon content was generally higher in the more recently restored site. Although there is a potential for carbon sequestration in salt marshes, tracking this process through time may be complicated by initial site conditions.

The Effect of Nitrogen Enrichment on C1-Cycling Microorganisms and Methane Flux in Salt Marsh Sediments

Methane (CH4) flux from ecosystems is driven by C1-cycling microorganisms – the methanogens and the methylotrophs. Little is understood about what regulates these communities, complicating predictions about how global change drivers such as nitrogen enrichment will affect methane cycling. Using a nitrogen addition gradient experiment in three Southern California salt marshes, we show that sediment CH4 flux increased linearly with increasing nitrogen addition (1.23 μg CH4 m−2 day−1 for each g N m−2 year−1 applied) after 7 months of fertilization. To test the reason behind this increased CH4 flux, we conducted a microcosm experiment altering both nitrogen and carbon availability under aerobic and anaerobic conditions. Methanogenesis appeared to be both nitrogen and carbon (acetate) limited. N and C each increased methanogenesis by 18%, and together by 44%. In contrast, methanotrophy was stimulated by carbon (methane) addition (830%), but was unchanged by nitrogen addition. Sequence analysis of the sediment methylotroph community with the methanol dehydrogenase gene (mxaF) revealed three distinct clades that fall outside of known lineages. However, in agreement with the microcosm results, methylotroph abundance (assayed by qPCR) and composition (assayed by terminal restriction fragment length polymorphism analysis) did not vary across the experimental nitrogen gradient in the field. Together, these results suggest that nitrogen enrichment to salt marsh sediments increases methane flux by stimulating the methanogen community.

The role of cyanobacteria in Southern California salt marsh food webs

AbstractUnderstanding 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 Cerithidea 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.

Patterns in Estuarine Vegetation Communities in Two Regions of California: Insights from a Probabilistic Survey

Monitoring wetlands at the ecoregion level provides information beyond the site scale and can inform regional prioritization of management and restoration projects. Our study was a component of the United States Environmental Protection Agency’s 2002 Environmental Monitoring and Assessment Program Western Pilot and is the first quantitative comparison of regional condition of California estuarine wetland plant communities. We measured indicators of estuarine emergent wetland condition in southern California and San Francisco Bay at probabilistically selected sites. In southern California, we also assessed potential anthropogenic stressors (presence of modified tidal hydrology, intensity of surrounding land use, and population density). Southern California salt marsh exhibited higher species diversity and greater percent cover of invasives. Seven of eight common plant species showed less variation in their distributions (zonation) across the marsh in southern California than in San Francisco Bay. Modified tidal hydrology was associated with absence, in our data, of certain native species, and higher relative percent cover of invasives across the marsh; however, our measures of landscape-level anthropogenic stress did not correlate with cover of invasives. We discuss lessons learned regarding the use of probabilistic site selection combined with our spatially complex data-collection arrays, and comment on utility of our protocol and indicators.

Southern California Salt Marsh Dominance Relates to Plant Traits and Plasticity

The three most abundant tidal marsh species at Tijuana Estuary rank Salicornia virginica > Jaumea carnosa > Frankenia salina in occurrences and cover, despite being equally productive in a greenhouse study. The same abundance ranking (Sv>Jc>Fs) developed within 10 years in a restoration site that was planted with near-equal numbers per species. In this paper, we show that resistance to invasion and invasiveness also ranked Sv>Jc>Fs, helping to explain how the restored community lost diversity over time. To explain differential dominance, we assessed 20 traits (including trait ratios), expecting several traits to rank Sv>Jc>Fs, but that was not so. Nor were field abundance ranks explained by the number of superior traits, since Salicornia ranked first in only four traits; Jaumea ranked first in seven, Frankenia in three, and six traits involved ties. Instead, we found explanatory power in two traits (height and runner length) and plasticity (ability to shift trait ratios with changing conditions). We propose that Salicornia becomes dominant by growing tall (height ranked Sv>Jc = Fs) and capturing light first, and that Jaumea co-dominates by extending its runners throughout the understory. Both dominants are more plastic than the subordinate Frankenia, which allocates the greatest proportion of dry weight to roots. Our multi-trait approach explained abundance ranks where focusing on a single trait (potential productivity) could not.

Characterizing patterns of plant distribution in a southern California salt marsh using remotely sensed topographic and hyperspectral data and local tidal fluctuations

We used LiDAR topographic data, AVIRIS hyperspectral data, and locally measured tidal fluctuations to characterize patterns of plant distribution within a southern California salt marsh (Carpinteria Salt Marsh (CSM)). LiDAR data required ground truthing and correction before they were suitable for use. Twenty to forty percent of the uncertainty associated with LiDAR was due to variance in the elevation of the target surface, the balance was attributed to error inherent in the LiDAR system. The incidence of LiDAR penetration of plant canopy cover (i.e., registration of ground elevation) was only three percent. The depth of LiDAR penetration into the plant canopy varied according to plant species composition; plant species-specific corrections significantly improved LiDAR accuracy (58% reduction in overall uncertainty) and with the use of ground-based surveys, reduced overall RMSE to an average of 6.3 cm in vegetated areas. A supervised classification of AVIRIS data was used to generate a vegetation map with six classification types; overall classification accuracy averaged 59% with a kappa coefficient of 0.40. The vegetation classification map was overlaid with a LiDAR-based digital elevation model (DEM) to compute elevation distributions and frequencies of tidal inundation. The average elevations of the dominant plant classifications found in CSM (e.g., Salicornia virginica, Jaumea carnosa, and salt-grass mix, a mixture of multiple marsh plant species) occurred within a 17 cm range, a vertical change that resulted in a 7% difference in the period of tidal inundation.