Brackish marsh

Marine/estuarine phytoplankton C—4 salt marsh plants Benthic microalgae C-3 Freshwater/brackish marsh plants... 

Figure 9.49 Syringyl-to-vanillyl (S/V) and cinnamyl-to-vanillyl (C/V) ratios in soils and sediment samples collected from a forest-brackish marsh-salt gradient in a southeastern U.S. estuary (North Inlet, USA). (Modified from Gorii and Thomas, 2000.)...

Meyerson, L.A., Saltonstall, K., Windham, L., Kiviat, E., and Findlay, S.E.G. (2000) A comparison of Phragmites australis in freshwater and brackish marsh environments in North America. Wetlands Ecol. Manag. 8, 89-103. 

DeLaune, R. D., and Patrick, W. H., r. (1990). Nitrogen cycling in Louisiana Gulf Coast brackish marshes. Hydrobiologia 199, 73—79. 

Jordan, T., CorreU, D., and Whigham, D. (1983). Nutrient flux in the Rhode River Tidal exchange of nutrients by brackish marshes. Estuar. Coastal Shelf Sci. 17, 651—667. 

Brackish marsh soil 7-70 N assay Tobias et al. (2001a)... 

Salt or brackish marshes are important ecosystems because they are the habitat of many birds and fish that feed on a wide variety of invertebrates including crabs, snails, and worms. Some of these organisms burrow into the sediments providing a path for oil to penetrate if a spill occurs. These marshes are also the nurseries for many land and sea birds and animals. Salt marshes are especially vulnerable to oil spills because they are flooded at high tide and their complex surface traps large quantities of oil. It is also difficult to get into a marsh to assess the damage and clean up the oil. 

In controlled laboratory mesocosms, Spartina patens, a dominant brackish marsh species found along the U.S. Gulf coast, and rice (0. sativd) showed a decrease in net photosynthesis in response to reduced soil redox potentials. Net photosynthesis decreased when soil redox potential or Eh was below -100 mV (Kludze and DeLaune, 1995b). A similar reduction in photosynthetic rates was observed in 0. sativa with increase in intensity of reduction (Figure 7.31). However, wetland plants... 

In intertidal marsh soils, total inorganic phosphorus accounted for 14-40% of total phosphorus in freshwater marsh and 33-85% of total phosphorus in salt marshes. Inorganic phosphorus associated with Fe was most abundant in snrface sediments of both freshwater and brackish marshes, whereas Ca-bonnd P dominated inorganic phosphorus in salt marshes (Paludan and Morris, 1999). 

Sulfate reduction rates are also controlled by the availability of sulfate and carbon as an energy source. Salt and brackish marsh generally have more sulfate present as compared to the fresh marsh or swamp forest soils due to saline water containing sulfate. Significant sulfate reduction can occur when adequate organic or label carbon is available to support intense reduction or low sediment... 

Fresh, brackish, and saline marshes have different mineral matter requirements for maintaining accretion. It is estimated that to vertically accrete at 1 cm year" fresh marsh required 424 g m year", brackish marsh required 1,052 g m year", and saline marsh required 1,789 g m" year" (Nyman et al., 1990). Marsh loss may occur if low mineral and organic matter accumulation result in inadeqnate rates of vertical accretion to keep pace with submergence or if the composition in the soil substrate is insufficient to snpport growth of marsh vegetation in individual marsh types. 

Increase in salinity (salt stress to fresh and brackish marsh plant species)... 

Saltwater intrnsion is a dominant edaphic factor that inflnences the survival, growth, and species composition in coastal wetlands along the Louisiana Gnlf Coast. The net effect of sublethal salt stress is the redaction in growth especially in marsh soils with low bulk density or mineral content in the soil profile. For most species growing in salt and brackish marshes, elevated salinity does not create a favorable environment for growth and productivity (Figure 18.14). In fact, numerous... 

DeLaune et al. (1983b) triplicate determination in fresh and salt marshes duplicate in brackish marsh 13 sampling dates during 1980-1981. 

Studies indicate that under natural conditions the gaseous N losses from salt and brackish marshes of the Louisiana Gulf Coast are minimal (Smith and DeLaune, 1983 Smith et al., 1983a) (Table 18.7). A 2-year study of N2O emission from Barataria Basin salt marshes indicated the annual emission of 31 N m year" (Smith et al., 1983a). 

Salt marsh Brackish marsh Fresh marsh... 

The amounts and profile distribution of various sulfur forms in Louisiana coastal marshes are important in understanding sulfur cycling as related to the origin and type of tidal wetland marshes. Sulfur forms and distribution were determined in P. hemitomon freshwater marsh, a S. patens brackish marsh, and a S. alterniflora salt marsh along a salinity gradient in Barataria Basin, Louisiana. Soil samples were fractionated into acid volatile sulfur (AVS), elemental sulfur, HCl-soluble sulfur, pyrite sulfur, ester sulfate sulfur, carbon-bonded sulfur, and total sulfur (see Chapter 11 for details). 

Potential sulfate reduction rates for three Louisiana marsh soils of varying salinities (salt, brackish, and freshwater) have been determined (DeLanne et al., 2002a). The three Louisiana marshes represent different physiochemical environments. The fresh and brackish marsh soils are composed predominantly of organic matter, whereas the salt marsh soils are higher in mineral matter. Sulfate content is higher in the salt marsh. 

The brackish and fresh marshes contain similar sulfate contents, although means were higher in the brackish marsh. Average potential sulfate reduction rates over three sampling periods (Angnst, December, and April) were 45.9, 40, and 33.4 mol S m year respectively, for fresh, brackish, and salt marsh (Table 18.12). Turnover times are consistently longer in the salt marsh (approximately 40 days, Fignre 18.23) than in either the fresh or the brackish marshes (3-8 days). 

Seasonal field sulfur emission measurements (DeLaune et al., 2002b) were determined in a Spar-tina alterniflora salt marsh (10-12 ppt salinity), a Spartina patens brackish marsh (5-8 ppt), and a Sagittaria lancifolia freshwater marsh (0 ppt salinity), along a salinity gradient extending inland from the coast in the Mississippi River deltaic plain region of the coastal Lonisiana. Results... 

Hydrogen sulfide was the predominant sulfur gas emitted from the brackish marsh an average emission was 21.22 pg S m h (Table 18.13b). HjS emission ranged from 5.29 to 79.20 pg S... 

TABLE 18.13b Spartina patens Louisiana Brackish Marsh ... 

Measured emission of total reduced sulfur was considerably less in the freshwater marsh as compared to emissions from the salt and brackish marsh sites (Table 18.13c). Carbonyl sulfide emitted at a rate of 1.09 pg S m h was the dominant form evolved from the freshwater marsh site. Emissions of H2S, DMS, MeSH, and CS2 to the atmosphere were less and averaged 0.30, 0.27, 0.46, and... 

Kearney, M. S. and L. G. Ward. 1986. Accretion rates in brackish marshes of a Chesapeake Bay estuarine tributary. Geo Marine Lett. 6(l) 41-49. 

The wetlands at this site are classified as brackish marshes, based on the presence of indicator plants (Penfound and Hathaway, 1938 O Neil, 1949 Wicker, 1980 Gosselink, 1984) and are mostly dominated by Spartina patens, with subordinate amounts of Eleocharis spp., Vigna lutea, Baopa monneiri. Aster tenufolius, and Scirpus olneyi (Guntenspergen et al, 1995). 

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