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Salt marshes can protect coastlines against flooding by attenuating wave energy and enhancing shoreline stabilization. However, salt-marsh functioning is threatened by human influences and sea level rise. Although it is known that protection services are mediated by vegetation, little is known about the role of vegetation structure in salt-marsh accretion. We investigated the role of vegetation presence, vegetation type and structural vegetation characteristics in sedimentation and sediment grain size. We established 56 plots on a salt marsh on the Dutch Wadden island of Texel. Plots were divided over four vegetation types contrasting in vegetation structure and varied in elevation and distance to creeks. Vegetation presence was controlled by clipping in subplots. Within each plot, we measured seven vegetation characteristics, sedimentation and the sediment grain size distribution. Furthermore, we explored the effect of the natural variation in vegetation structure on wave attenuation with a simple model approach. For this, we developed vegetation scenarios based on the field measurements of stem height, diameter and density. We found that vegetation presence increased sedimentation on average by 42%. Sedimentation was highest in Salicornia vegetation and increased with stem height and branching level. Grain size also seemed to increase with branching level. Modelled wave attenuation was 7.5 times higher with natural vegetation compared to topography only, was strongest for Spartina vegetation and most sensitive to the natural variance in stem density. Our results can be used to improve predictions of salt-marsh accretion and the implementation of salt marshes in nature-based flood defences.

The extensive loss of tidal marsh habitat surrounding the San Francisco Bay has led to numerous restoration projects to restore ecosystem function. Native cordgrass (Spartina foliosa) is important for sediment accumulation and nesting habitat for endangered California Ridgway’s Rail (Rallus obsoletus obsoletus), and because salt marshes are typically nitrogen-limited ecosystems, previous restoration studies in California have used nitrogen fertilizers to increase plant growth. This study compared the use of two low-nitrogen, high-carbon fertilizers (Macrosystis pyrifera (kelp) and sodium alginate) to stimulate N2-fixing bacteria inhabiting the S. foliosa rhizosphere in a historic and recently restored marsh in San Francisco Bay. Alginate increased N2-fixation, though there was no observed S. foliosa growth response. Kelp suppressed N2-fixation, and increased the foliar nitrogen content of Salicornia pacifica in mixed Spartina-Salicornia stands. The restored marsh had less than 0.5 μM phosphate in porewaters, suggesting phosphorus, not nitrogen, limits S. foliosa growth in this marsh. Alginate increased rates of N2-fixation and may promote plant growth in marshes exhibiting nitrogen limitation. Phosphate limitation was a surprise considering numerous previous studies indicate nitrogen as the primary limiting nutrient of tidal marsh plants. We recommend first assessing nutrient stoichiometry when considering manipulations to promote plant growth in restored marshes.

In tidal marshes, facilitative and competitive interactions between plant species can shift in response to variation in stress gradients (e.g., inundation and salinity) and resource gradients (e.g., nutrient availability). We measured plant competitive response using relative yield based on total biomass of salt marsh species Salicornia virginica and Triglochin concinna. We tested interactions between these species in two greenhouse experiments using an additive experimental design which included nitrogen supply, water level, and duration (4-months and 1-year) treatments. We repeated two N-supply treatments in a 1-year field experiment at two elevations. We found that competitive and facilitative processes were dependent on the type of stress, the species, and the experiment duration. We found a facilitation-competition shift along the N-availability gradient, but only for Salicornia in the 4-month experiment. We found no effect of N addition on competitive response in the 1-year experiment; relative yield values remained

Wind-tidal flats are the dominant coastal wetland type in southern Texas, USA. Succulent vascular plants are colonizing the flats in some locations, often where past dredge disposal along navigation channels and other activities have interrupted natural water communication between hypersaline bays and large areas of wind-tidal flats. The objective of this study was to test the feasibility of proposed removal of a causeway at Laguna Atascosa National Wildlife Refuge to restore the historic hydrologic regime and eradicate encroaching vascular plants, mostly Salicornia bigelovii, on the assumption that high sediment salt excluded these vascular plants under natural conditions. Assessment in spring 1998 of the density of Salicornia in relation to elevation and sediment salt of bare and vegetated zones on the vegetated flats on one side of the causeway and entirely barren flats with unimpaired connection to Laguna Madre on the other side of the causeway suggested that sediment salt > 0.1 g ml−1 excluded vascular plants. However, bimonthly sampling in 1999–2000 revealed that sediment salt concentrations were > 0.1 g ml−1 throughout the vegetated zone in July and more locally in the period of winter low water, with little impairment to established plants. This indicates that if control is desired, it must be exerted at germination and early establishment during and after fall high water. Continuous monitoring of water levels on either side of the causeway suggests that, even with removal of the causeway, flooding with hypersaline lagoon water will be too infrequent to counteract the freshening effect of a permanent hydraulic connection to the main agricultural drain of the lower Rio Grande Valley that has developed at the other end of the salt flat. Monitoring Salicornia distribution over six years documented huge variation between years but no trend toward increasing dominance of the flats. The results of this study illustrate that the most obvious alterations to a site may not be the most influential on function and that the scale of analysis may have to extend far beyond the site in space and time to evaluate a proposed restoration properly.

Succulence, tissue chloride, bromide, and iodide levels were determined in the coastal salt marsh halophyte Salicornia virginica taken from three elevations over a 12-month period. Soil samples from each sampling area were also taken for the determination of halide concentrations. The average percent dry weight (% DWt) over the 12 months and three elevations ranged from 10.8 ± 0.4 to 16.1 ± 0.3 % (± sd), with a general increase in % DWt (decrease in succulence) in tissue from all elevations peaking in September, after the dry summer, followed by a decrease in % DWt (increase in succulence) during the rainy season. The mean halide levels in S. virginica tissues over the 12 months and three elevations ranged from 17.5 to 30.3 % Cl−, 0.27 to 0.76 % Br−, and from 3.00 to 1.21 × 104 ppm I−. Mean halide concentrations in plant water ranged from 0.66 to 1.6 M Cl−, 4.6 to 12 mM Br− and 3.3 μM to 16 mM I−. No environmental factors correlated with changes in tissue halide levels. Tissue Cl− levels tended to increase during the dry summer months and decrease during the wet winter months. Bromide levels were more stable. Large increases in tissue I− levels were found during the months of September and October when the plants were in flower, suggesting a developmental control of I− uptake. Soil concentrations of all three halides at the low elevation were consistently higher than those in the middle and high elevations. The high elevation soil Cl− was the most variable of the three halides. Higher I− soil levels in the low elevation during the spring/summer as compared to fall/winter probably reflect an increase in the biological and chemical reduction of IO3− to I−. Tissue halide levels at the three elevations did not correlate with their respective soil concentrations. Plant water halide molar ratios were lower than in seawater and soil, indicating the selective uptake of halides in the order I− > Br− > Cl−.

Extensive Salicornia beds along the Gulf of Kutchchh (northwest) and Tamilnadu (southeast) coasts were investigated with respect to vegetative structure and ambient environmental conditions. The width of the beds varied from approximately 5 m to 1000 m, depending upon the topography and tidal influence. The most extensive and healthy stands occurred in the regularly (20–50 tides month−1) inundated intertidal zones. The width of Salicornia beds in the Gulf of Kutchchh was greater than those along the Tamilnadu coast due to greater (0.83–7.2 m) tidal amplitude and flat topography. The sediments from beds of the Gulf of Kutchchh were rich (4.9–16.9% dry weight) in organic matter. The salt content in the sediments from Tamilnadu was relatively very low (0.08–0.1 % dry weight) compared to sediments from in the more frequently inundated regions were greater than in the poorly or less frequently inundated intertidal regions. The average total biomass varied from 0.2 to 4.5 kg (dry weight) m−2 and was mostly comprised of aboveground components. Peak biomass values of Salicornia were observed during September to February in the Gulf of Kutchchh, while along the southeast coast, they were observed during December to March. The growth of the S. brachiata seemed to be influenced primarily by the frequency of inundation, duration of atmospheric exposure at ebb tide, rainfall, and salinity and salt content of the ambient water and sediments, respectively. Average carbon and nitrogen content in the plants were estimated to be 21.7±1.9% and 0.8 ±0.17% (dry weight), respectively. The carbon content increased with increasing age of the plant, while protein content decreased. Constantly increasing anthropogenic pressures on coastal wetlands warrant immediate protection of S. brachiata and other obligate halophytes, which are either threatened/vulnerable or endangered.

Salicornia virginica (common pickleweed) is the dominant vascular plant of many saline marshes of the US west coast, yet little is known about seasonal patterns or abiotic factors controlling it. In a southern California salt marsh, quarterly sampling revealed strong seasonal trends, with 2x greater S. virginica biomass in summer than in winter. Tissue nitrogen (N) and phosphorus (P) concentrations were highest in winter and lower in spring and summer, suggesting a dilution of nutrients as plants accumulated biomass during the growing season. Despite high sediment nutrient levels in this marsh, an experiment examining N and P effects still found strong S. virginica responses to N applied biweekly for > 1 year. Increases in succulent tissue biomass after N addition were first seen in April 1998 (after fertilization for 11 months); two-fold increases in biomass and the number of branches resulted by the end of the experiment in August 1998. Addition of N increased N concentration in the woody tissues when sampled in August. The N:P ratio increased with N addition beginning in winter (7 months after fertilization began) and continuing through the remainder of the experiment. Effects of P addition were less marked, as adding P did not result in biomass responses; however, it did influence tissue nutrient levels. These amendments increased P concentrations in the woody tissue in August 1998. In contrast to N amendments, which did not affect root nutrient concentrations, P addition led to increases in P content of root tissues in the latter portion of the growing season. These data suggest that increases in nutrients (especially N, but also P) can lead to large changes in S. virginica characteristics even in estuaries with high sediment nutrient levels.

Yearly above-ground production estimates in natural, ditched, and impounded high salt marshes along the Indian River Lagoon in east central Florida ranged from 834.9 g/m2 in the impounded marsh to 2.316.5 g/m2 in the natural one. Mosquito control activities in the impounded marsh prior to the start of this study resulted in larger stocks of dead and litter biomass there during the first year than at the other two marshes. High soil temperature and salinity during the summer may have caused a decrease in production during that season. Annual tumover rales varied from 5.8 at the impounded marsh during the first year to 1.1 at the impounded marsh and at a nearby ditched marsh during the second year. Prduction was inversely correlated with flooding frequency. No significant differences were found in the rates of litter loss from any of the sites, but litter from the impounded marsh had greater organic content than litter from the open and the ditched marshes. The data suggest that flooding for mosquito control during the summer can curtail production, but the effects upon yearly production are minor, as production during the summer is naturally low.

Nitrogen effects were examined by experimentally enriching plots of pureSpartina foliosa and mixedSpartina-Salicorniavirginica at Tijuana Estuary, California. Even with large inputs of organic nitrogen from sewage spills in 1983, plants responded to experimental urea enrichment. In pure plots, the addition of nitrogen increasedSpartina growth (as measured by total stem length and August biomass) and foliar nitrogen (TKN) concentration. In mixed plots, enrichment had no apparent effect onSpartina but increased the growth ofSalicornia. The experimental removal ofSalicornia from mixed stands increasedSpartina production, but removal ofSpartina did not affectSalicornia. Salicornia is a superior competitor for nitrogen and checks the growth ofSpartina in enriched and unenriched conditions.