Freshwater requirements of a semi-arid supratidal and floodplain salt marsh

When rivers are impounded, the reduction in downstream flow can produce important and often adverse effects, especially in the estuarine environment. One or more dams have been proposed for the Olifants River system in the Western Cape, South Africa. This estuary has an extensive area of salt marsh that was examined to see whether it required occasional flooding with freshwater to wash out accumulated salts. The dominant salt marsh species,Sarcocornia pillansii, occurred in supratidal and floodplain areas where the water table was shallowest, the soil moisture highest, and the soil electrical conductivity lowest. Aerial photographs and simulated runoff data showed that no flood had covered the floodplain during the previous 80 years. The data indicate that salt marsh plants use saline groundwater during the dry months of the year in order to survive, but use the short season winter rainfall period with low salinity conditions to grow and reproduce. This study demonstrated that live roots ofS. pillansii reached the water table during the dry season. Tissue and soil water potentials, the relationship between vegetation cover, depth to the water table, and electrical conductivity of the groundwater support the conclusion that saline groundwater is the only source of water during the drier months of the year. Freshwater flooding of the river in winter may be important because it covers the supratidal area with less saline water and reduces the depth to the water table on the floodplain. This makes the groundwater more accessible to the halophytes growing on the floodplain.     

Interactive effects of animal disturbance and elevation on vegetation of a tidal freshwater marsh

We studied interactions between animal disturbance (geese, carp, and muskrat) and elevation in a field experiment in tidal freshwater marshes of the Patuxent River, Maryland, United States. Vegetation changes were recorded in fenced and unfenced plots in high and low marsh community types for 2 yr using measurements of areal cover and within-plot frequency (which were averaged to create a dominance index), Leaf Area Index (LAI), and aboveground biomass. We related light environment to differences in vegetation using below-canopy measurements of Photosynthetically Active Radiation (PAR). In the low marsh, total cover of all species, cover of annual species, biomass, and LAI were significantly higher in plots fenced to exclude animals (exclosures) than in unfenced plots (fenced/unfenced total cover=76/40%, annual cover=45/10%, biomass=936/352 g m^?2, LAI=3.3/1.4). PAR was significantly lower in fenced than unfenced plots (fenced/unfenced=115/442 μmol s-1 m^?2). Despite the strong effect of fencing on biomass, species richness per plot (i.e., the number of species per plot, or species density) was not affected significantly by fencing in the low marsh. Most of the observed differences in cover, biomass, LAI, and PAR were due to variation in the abundance of the herbaceous annual speciesBidens laevis (dominance index fenced/unfenced=45/10%) andZizania aquatica (30/12%). In the high marsh community, fencing had only minor effects on plant community composition and did not significantly affect species richness, cover, biomass, PAR, or LAI. Our results show that animals can dramatically affect low marsh vegetation, primarily via physical disturbance or herbivory of shallowly rooted seedlings of annual species.     

Effect of improved tidal flushing and competitive interactions at the boundary between salt marsh and pasture

Zonation of salt marsh plants has been widely recognized and studied, but the boundary between salt marsh and adjacent upland plants has seldom been considered. Three hypotheses about the boundary between salt marsh and adjacent upland pasture were tested on Kooragang Island, New South Wales, Australia. First, we hypothesized that increased tidal range resulting from removal of culverts that restricted tidal flow to areas of salt marsh would lead to landward spread of salt marsh into areas previously dominated by pasture. Monitoring results showed an increase in areal cover by salt marsh plants and a decrease in pasture plants along the boundary between salt marsh and pasture in areas affected by culvert removal, while no change could be detected at a reference site unaffected by culvert removal. Second, we hypothesized that the down-gradient distribution of the pasture species Stenotaphrum secundatum (buffalo grass) was restricted by physical conditions, while the up-gradient distribution of the salt marsh species Sarcocornia quinqueflora (samphire) was restricted by competition with pasture species. Results of a reciprocal transplant experiment were consistent with this hypothesis. Third, we hypothesized that the rate of salt marsh spread following culvert removal would be influenced by competition with pasture species. Results of an experiment in which pasture was removed adjacent to a salt marsh affected by culvert removal were consistent with this hypothesis. Results may help guide management of over 1,300 structures that restrict tidal flow to estuarine wetland habitat in New South Wales, Australia.     

Damage to cordgrass by scale insects in a constructed salt marsh: Effects of nitrogen additions

Because tall cordgrass (Spartina foliosa) is needed for nesting by the endangered light-footed, clapper rail, managers of constructed salt marshes in southern California are proposing large-scale nitrogen fertilization to improve cordgrass growth. How this might affect an existing infestation of scale insects (Haliaspis spartina) and the degree of damage these insects cause to their cordgrass hosts was unknown. We explored the effects of timing and duration of fertilization onHaliaspis damage to cordgrass, as well as the timing ofHaliaspis dispersal, in a constructed marsh at Sweetwater Marsh National Wildlife Refuge in San Diego Bay, California. Fertilization did not result in increasedHaliaspis abundance. After a large dispersal pulse in late May,Haliaspis establishment in the long-term fertilized plots was greater than in the controls; however, this trend reversed in August, when many more stems in the control plots were infested with large numbers ofHaliaspis. Since adultHaliaspis cannot leave a feeding site, losses of individuals in the fertilized plots were apparently due to mortality, perhaps resulting from mechanical or chemical changes in the fertilized plants or increased predation. Late in the growing season, plots fertilized with 10 applications of urea over 20 wk had the lowest meanHaliaspis abundance. Plots fertilized only in March, April, June, or August did not differ from controls in meanHaliaspis abundance.Haliaspis was never abundant in the fertilized or control plots in the adjacent natural marsh. This study suggests that fertilization, of constructed salt marshes in San Diego Bay may proceed without concern that furtherHaliaspis outbreaks will be facilitated.     

Understanding the Impacts of Climate Change: an Analysis of Inundation,Marsh Elevation,and Plant Communities in a Tidal Freshwater Marsh

Tidal freshwater marshes around the world face an uncertain future with increasing water levels, salinity intrusion, and temperature and precipitation shifts associated with climate change. Due to the characteristic abundance of both annual and perennial species in these habitats, even small increases in early growing season water levels may reduce seed germination, seedling establishment, and late-season plant cover, decreasing overall species abundance and productivity. This study looks at the distribution of tidal freshwater marsh plant species at Jug Bay, Patuxent River (Chesapeake Bay, USA), with respect to intertidal elevation, and the relationship between inundation early in the growing season and peak plant cover to better understand the potential impacts and marsh responses to increased inundation. Results show that 62% of marsh plant species are distributed at elevations around mean high water and are characterized by narrow elevation ranges in contrast with species growing at lower elevations. In addition, the frequency and duration of inundation and water depth to which the marsh was exposed to, prior to the growing season (March 15–May 15), negatively affected peak plant cover (measured in end-June to mid-July) after a threshold value was reached. For example, 36 and 55% decreases in peak plant cover were observed after duration of inundation threshold values of 25 and 36% was reached for annual and perennial species, respectively. Overall, this study suggests that plant communities of tidal freshwater marshes are sensitive to even small systematic changes in inundation, which may affect species abundance and richness as well as overall wetland resiliency to climate change.     

The effects of thin layer sand renourishment on tidal marsh processes: Masonboro Island, North Carolina

The objective of this study was to determine if the placement of dredged material on sediment-starved back barrier marshes in southeastern North Carolina could offset submergence without negatively affecting function. Clean sediment was placed in thickness from 0 to 10 cm, on deteriorated and non-deteriorated marsh plots. Original stem densities were greater, in non-deteriorated plots (256 stems m⁻²) compared to deteriorated sites (149 stems m⁻²). By the second growing season (after sediment additions), stem densities in the deteriorated plots (308 stems m⁻²) approached levels in the non-deteriorated plots (336 stems m⁻²). Sediment additions to, both nos-deteriorated and deteriorated plots resulted in a higher redox potential with plots receiving the most sediment exhibiting the highest E_h values. In deteriorated plots, placement of dredged material had the greatest effect on plant density, but also affected soil oxidation-reduction potential and sediment deposition (or mobility). Following sediment placement, substrate texture and composition incrementally returned to prefill conditions due to a combination of bioturbation and sedimentation. Where infaunal differences occurred, they were generally less abundant in deteriorated plots, but responses to sediment addition were variable. Sediment addition had little effect on the non-deteriorated plots, suggesting that the disposal of certain types of dredged material in marshes may be useful to mitigate the effects of marsh degradation without adversely affecting non-deteriorating marsh.     

Nitrogen and phosphorus distribution and utilization bySpartina alterniflora in a Louisiana gulf coast marsh

Nitrogen and phosphorus content ofSpartina alterniflora Loisel and soil nitrogen were measured along a transect perpendicular to a stream in a Louisiana salt marsh in order to provide information on differences between the so-called streamside and inland regions. Total plant nitrogen and phosphorus levels in June and September tended to be greater at streamside than inland sites. Total soil nitrogen on a dry soil weight basis increased with distance inland from a natural stream toward an interdistributary basin in the marsh. Soil extractable ammonium-nitrogen levels measured in June were very low in vegetated streamside and inland areas, but they were much higher in inland areas devoid of plants. Nitrogen and phosphorus utilization byS. alterniflora was also investigated at an inland location in the salt marsh. Labelled ammonium-nitrogen and phosphate-phosphorus were added in May at a rate of 200 kg/ha to the soil of replicated plots. Added nitrogen significantly increased total above-ground plant biomass and plant height by 28 and 25%, respectively, 4 months after application. The ratio of belowground macro-organic matter to total aboveground biomass was decreased from 5.7 to 4.7 by the additional nitrogen. Added phosphorus did not significantly affect plant height and biomass. The use of¹⁵N-depleted nitrogen tracers showed that about half of the nitrogen in the aboveground portion ofS. alterniflora from 1 to 4 months after the nitrogen addition was derived from the added ammonium-nitrogen. After 4 months, 28 and 29% of the added labelled nitrogen was recovered in the aboverground and belowground biomass ofS. alterniflora, respectively. Recovery of added nitrogen was overestimated with a non-tracer method based on the difference in total nitrogen uptake between nitrogen-amended plots and untreated plots. Soil organic nitrogen comprised the majority of the nitrogen in the salt marsh. Nitrogen in the standing crop biomass ofS. alterniflora represented only about 2% of the total nitrogen in the plantsoil system of an inland marsh to a 20 cm soil depth.     

Seasonal and spatial distribution of the Carolina marsh clamPolymesoda caroliniana (Bosc) in a Mississippi tidal marsh

The abundance of the marsh clamPolymesoda caroliniana at four stations on a Mississippi tidal marsh was followed from February 1977 through April 1978. The stations varied with respect to inundation time and vegetative cover. The largest population was found in an area flooded 12% of the year (136 individuals per m²) and in an area flooded 3.2% of the year (126 individuals per m²). However, the latter area contained no large clams (>25.5 mm). Smaller populations were found in the upper reaches of a tidal creek draining the marsh (68 individuals per m²) and in an area flooded 5.8% of the year (73 individuals per m²). The average abundance of the clams on the marsh was 100 per m². At least three recruitment periods were apparent. In laboratory studies, clams larger than 15 mm survived longer than 30 days without water. Clams smaller than 12 mm survived less than 6 days without water. Several decapods (Callinectes sapidus, Uca longisignalis, andSesarma reticulatum) consumed clams smaller than 10 mm but were unable to eat larger clams under laboratory conditions.Polymesoda caroliniana may be important to the functioning of the marsh by removing large quantities of particulate matter from flooding water.     

Growth dynamics of cordgrass,Spartina alterniflora loisel., on control and sewage sludge fertilized plots in a Georgia salt marsh

Seasonal plant growth dynamics were followed for a year in undisturbed plots of tall and short formSpartina alterniflora Loisel. and in plots of short formS. alterniflora which were enriched with sewage sludge at a rate of 100 g dry sludge m^?2wk^?1, corresponding to a nitrogen enrichment of 2 g N m^?2wk^?1. Monthly determinations of aboveground live and dead biomass, density of live stems, the ratio of number of young shoots to total number of shoots, and belowground mass of macro-organic matter to a depth of 30 cm were made for each area. Sludge fertilization increased the live biomass of the short formS. alterniflora by up to 150% of the control live biomass, but had little effect on the dead biomass, stem density, or proportion of young shoots. There was a trend of increased amount of belowground macro-organic matter in fertilized compared to control plots during the last 6 months of the study. In all areas, there was a marked decrease in the proportion of young shoots from winter to early summer, followed by a rapid increase in the percent of young shoots from late summer to fall. Sampling of plots 7 and 20 months after termination of sludge enrichment showed higher plant biomass and % N content in surface soils, but no difference in N content of live plant tissue, in fertilized compared to unfertilized marsh. After 20 months, about half of the sludge nitrogen remaining in the soils of the fertilized plots had disappeared.     

Response of estuarine marsh vegetation to interannual variations in precipitation

The response of deltaic emergent marsh vegetation to increases in precipitation was examined over a 14-mo period at three sites in the lower Nueces Estuary in south Texas. At all three sites, significant changes in plant biomass, percent cover, and allocation of aboveground and belowground tissues were associated with more than double the rainfall in late winter and early spring 1992 compared to the previous year and the 50-yr average for this region. Water column salinities, which ranged from 10‰ to 35‰ at all three sites in 1991, remained below 10‰ through August 1992. Significant changes in marsh vegetative structure included decreases in bare space, increases in the percent cover and aboveground biomass of a relatively less salt tolerant halophytes (Borrichia frutescens), and significant increases in root:shoot ratios inB. frutescens, Batis maritima andSuaeda linearis (inSalicornia virginica root:shoot ratios decreased significantly). Higher precipitation generally led to an overall increase in the biomass of most marsh perennials, but these increases were not statistically significant. For one species,Lycium carolinianum, additional rainfall extended its growing season through August 1992, 2 mo longer than in the previous year. The expansion (+58%) ofB. frutescens at one site was also coincident with the significant loss ofB. maritima, whose cover decreased nearly 20%. In an ecological context, these responses suggest that precipitation events in arid environments may be considered a major physical disturbance that can result in large changes in the composition and relative abundance of emergent vascular plants over a relatively short period. The long-term significance of these changes is unknown and demonstrates the value of ecological studies that are conducted over several years for a more complete understanding of the dynamic processes that regulate marsh productivity.     

Effects of nitrogen addition and salt grass (Distichlis spicata) upon high salt marsh vegetation in Northern California, USA

In the salt marshes of Tomales Bay, California, where grazing by cattle increases the input of nitrogen to the marsh (either directly or indirectly as runoff from within the salt marsh watershed), high salt marsh vegetation is dominated byDistichlis spicata and is less diverse than marshes without excess nutrients. Using a field experiment, I investigated the role of soil fertility on the plant community of the high salt marsh. I hypothesized that when soil fertility is increased by nitrogen addition plant productivity will increase, as indicated by height, biomass, and cover, and competitive exclusion, byD. spicata, will lead to a reduction in species richness and evenness, especially where the initial density ofDistichlis is high (from transplanting). After two growing seasons, biweekly nitrogen addition to the high salt marsh led to increased plant biomass and cover. Diversity was not reduced, and space preemption byDistichlis-transplants did not confer a competitive advantage. Although the dominant species thrived (e.g.,Salicornia virginica, D. spicata, Triglochin concinna) they did not displace subdominant species and decrease diversity. The vegetation response in this high salt marsh system does not support the hypothesis that as biomass and cover (indicators of productivity) increase in response to increased nitrogen, competitive exclusion will occur and diversity will decrease.     

Accretion and canal impacts in a rapidly subsiding wetland II. Feldspar marker horizon technique

Recent (6–12 month) marsh sediment accretion and accumulation rates were measured with feldspar marker horizons in the vicinity of natural waterways and man-made canals with spoil banks in the rapidly subsiding environment of coastal Louisiana. Annual accretion rates in aSpartina alterniflora salt marsh in the Mississippi deltaic plain averaged 6 mm in marsh adjacent to canals compared to 10 mm in marsh adjacent to natural waterways. The rates, however, were not statistically significantly different. The average rate of sediment accretion in the same salt marsh region for a transect perpendicular to a canal (13 mm yr^?1) was significantly greater than the rate measured for a transect perpendicular to a natural waterway (7 mm yr^?1). Measurements of soil bulk density and organic matter content from the two transects were also different. This spatial variability in accretion rates is probably related to (1) spoil bank influences on local hydrology; and (2) a locally high rate of sediment input from lateral erosion associated with pond enlargement. In a brackishSpartina patens marsh on Louisiana’s Chenier plain, vertical accretion rates were the same along natural and canal waterways (3–4 mm yr^?1) in a hydrologically restricted marsh region. However, the accretion rates for both waterways were significantly lower than the rates along a nonhydrologically restricted natural waterway nearby (11 mm yr^?1). The vertical accretion of matter displayed semi-annual differences in the brackish marsh environment.     

Plant Cover,Herbivory, and Resiliency in a Cape Cod Salt Marsh: Multi-year Responses and Recovery Following Manipulation of Nutrients and Competition

To assess responses and recovery of salt marsh grass species, we manipulated external nutrient supply and removed shoots of Spartina alterniflora or Spartina patens from fertilized and control plots in a Massachusetts marsh. The pulse-and-recovery experiment included treatments for 5 years, and recovery for an additional 7 years. Responses of these potential competitors sensitively depended on local contingencies of elevation and nutrient dose, and, moreover, the differences in outcomes were emphasized at longer time scales. Local contingencies became manifest as differences in responsiveness and resiliency of the different grass species, with differing time courses and longer-term outcomes as to what species were present. These features might explain the diverse results obtained in shorter-term salt marsh experiments, and provide a view of the complex suite of species-specific and external environmental variables that may control competitive interactions in general.     

Primary production and seasonal aspects of emergent plants in a tidal freshwater marsh

Seasonal changes in aboveground plant biomass, cover, and frequency were monitored in Sweet Hall Marsh, a tidal freshwater marsh located on the Pamunkey River, Virginia, during the 1974 growing season.Peltandra virginica accumulated the most biomass, 423.40 g per m², followed byLeersia oryzoides at 67.75 g per m². Annual net community production was estimated to be 775.74 g per m² by using a multiple-harvest technique. Comparisons with other studies revealed that production was somewhat low for tidal freshwater marshes but mostly higher than production in Virginia brackish and saline wetlands. Measurements revealed an annual succession of plant species from spring to fall. The pattern observed was early dominance byPeltandra followed by a rise in importance ofPolygonum spp.,Impatients capensis andLeersia.     

Measurement of cordgrass,Spartina alterniflora,production in a macrotidal estuary,Bay of Fundy

A one-year field study was conducted of the growth, mortality, and loss dynamics of aSpartina alterniflora low marsh in the Minas Basin, a macrotidal estuary at the head of the Bay of Fundy. Data were used to examine the suitability of four methods for estimating annual net aerial primary production (NAPP) of a marsh subject to energetic tidal flooding. Shoots start to grow in April and reach maximum height (about 0.5 m) and weight in October. Maximum shoot density (900–1,600 m^?2) occurs around June and drops thereafter due to the export of entire shoots. The average shoot produces about seven leaves and at least 2–3 are lost during the growing season. All remaining vegetation dies before the end of November. Methods based on harvesting vegetation underestimated NAPP, especially at lower elevations where export is greater due to more frequent and prolonged tidal flooding. The highest NAPP values, on the order of 500–600 g m^?2 y^?1, were obtained using methods based on the population dynamics of individual shoots. These methods are recommended for energetic tidal environments because they include the production of vegetation exported during the growing season.     

A comparison of early juvenile red drum densities among various habitat types in Galveston Bay, Texas

Seagrass meadows are often cited as important nursery areas for newly settled red drum even though many estuaries, such as Galveston Bay, Texas, support large numbers of red drum and have limited seagrass cover, suggesting the use of alternate nursery areas. We examined patterns of habitat use for newly settled red drum at six sampling areas in Galveston Bay; two areas had seagrass beds and four areas had no seagrass. We measured densities in different habitat types using epibenthic sleds and enclosure samplers. Peak recruitment of young red drum to the estuary occurred during September through December. Highest densities of new settlers were found in seagrass meadows (primarilyHalodule wrightii), but when seagrass was absent, the highest densities of red drum occurred along theSpartina alterniflora marsh edge interface. Densities were relatively low on nonvegetated bottom away from the marsh edge. We also examined density patterns in other habitat types at selected sampling areas and found no red drum within marsh vegetation away from the marsh edge interface (5 and 10 m into the marsh interior). Oyster reefCrassostrea virginica was sampled using lift nets, and we found no red drum using this habitat, although adjacent seagrass and marsh interface habitats were used. Even though red drum densities in marsh edge were low relative to seagrass, the large areal extent of marshes in the bay complex probably makes marsh edge the most important nursery habitat for red drum in Galveston Bay.     

Productivity,detritus flux,and nutrient cycling in a Carex lyngbyei tidal marsh

Net annual primary production of a sedge Carex lyngbyei dominated tidal marsh in the Fraser River estuary, British Columbia, Canada was 634 g ash-free dry weight (AFDW) per m² per yr (687 g dry weight per m² per yr). Mean maximum shoot elongation during the short (May to August) growing season was 1.88 cm per day from overwintering shoots. The maximum aboveground standing crop of 690 g AFDW per m² represented only 25% of the total below-ground biomass, which appears to be controlling most of the critical life history processes of the sedge marsh. An estimate of 14 percent of the aboveground standing crop was lost through leaching of dissolved organic carbon from the growting plant. Aboveground tissue losses, which were negligible during the growing season, occurred primarily via translocation in autumn and tidal export during the winter. In situ measurements showed that of the original maximum standing crop, approximately 38%, 37%, and 25% were lost by downward translocation, tidal export, and sediment burial, respectively. Based on changes in above and belowground nutrient pools, rapid spring (May to late June) uptake rates of 109 mg N per m² per day and 23.0 mg P per m² per day by shoots were followed by downward translocation rates of 44.8 mg N per m² per day and 12.2 mg P per m² per day during late June to the end of August. Aboveground leaching rates were estimated as 23.9 mg N per m² per day and 7.8 mg P m² per day and belowground uptake rates as 100 mg N per m² per day and 26 mg P per m² per day; root uptake occurred primarily after late June. Nutrient levels in decomposing litter more than doubled over the winter period showing a pattern of nutrient enrichment characteristic of marsh ecosystems. *** DIRECT SUPPORT *** A01BY023 00004     

Halophyte recruitment in a salt marsh restoration site

In restored salt marshes, seedling recruitment can be limited where large areas of soil are exposed and physical conditions are harsh. On a 0.7-ha excavated marsh plain, we studied recruitment as a function of abiotic (elevation) and biotic factors in 2 × 2 m plots planted with 0, 1, 3, or 6 species from the pool of 8 native halophytes. The random draws of 3-species and 6-species assemblages produced approximately equal numbers of plants per species for the experiment as a whole, yet only three species recruited> 10 seedlings per plot.Salicornia virginica andSalicornia bigelovii each produced> 15,000 seedlings in 1998, andSuaeda esteroa produced> 2,500 seedlings in 1999. For these 3 species, seedling recruitment increased with elevation in 1998, but this trend weakened in 1999, when species richness affected recruitment (fewer seedlings in more species-rich plots). Abiotic effects preceded biotic interactions in determining seedling recruitment patterns early in the development of the salt marsh. Effects of species richness appeared to be scale-dependent in that having all species present in the site likely enhanced overall recruitment (all species had 2 or more seedlings), while plantings of 6 species in a 2 × 2 m plot reduced seedling density.S. virginica was the only species that increased its presence and relative cover in the experimental site over the 4-yr study. Protocols for planting southern California salt marsh restoration sites could omit this species, but all others probably need to be introduced to restore diverse vegetation.     

Climatic controls of the middle marsh zone in the Bay of Fundy

The ecological importance of Plantago maritima within a salt marsh on the Bay of Fundy is documented through measurements of cover, density, and biomass. During late August 1993, peak standing crops of Plantago were as high as 532 g m^?2, and composed as much as 96% of the biomass of a stand of vegetation. Plantago is a dominant component of the marsh vegetation at an elevation just above the Spartina alterniflora-dominated low marsh, and is found as a dominant when growing in association with a number of plant species characteristic of the high marsh. We hypothesize that the existence of this community is dependent upon regular ice-shearing of Spartina patens, which would otherwise competitively exclude Plantago. This hypothesis is supported by the elevational limits of Plantago dominance and the geographical limitation of Plantago communities to portions of the northwestern Atlantic subjected to winter temperatures which average below 0°C.     

Restoration of an impounded salt marsh in New England

The restoration of a 20 ha tidal marsh, impounded for 32, yr, in Stonington, Connecticut was studied to document vegetation change 10 yr after the reintroduction of tidal flushing. These data were then compared to a 1976 survey of the same marsh when it was in its freshest state and dominanted byTypha angustifolia. Currently,T. angustifolia remains vigorous only along the upland borders and in the upper reaches of the valley marsh. Live coverage ofT. angustifolia has declined from 74% to 16% and surviving stands are mostly stunted and depauperate. Other brackish species have also been adversely effected, except forPhragmites australis which has increased. In contrast, the salt marsh speciesSpartina alterniflora has dramatically expanded, from <1% to 45% cover over the last decade. Locally, high marsh species have also become established, covering another 20% of the marsh.