Tidal wetland sediments

Catallo WJ (1999) Homly and daily variation of sediment redox potential in tidal wetland sediments. USGS Biological Resources Division, Biological Science Report, USGS/BRD/BSR-01-1999. US Dept of Interior, US Geological Survey, National Wetlands Research Center, Lafayette, LA... 

The balance in tidal wetlands is complicated by the tidal inflow and outflow of water across the submerged sediments and the greater influence of subsurface leaching under the large tidal head of water. 

Chanton, J.P., Martens, C.S., and Kelley, C.A. (1989a) Gas transport from methane-saturated, tidal freshwater and wetland sediments. Lirnnol. Oceanogr. 34, 807-819. 

Much of the coastal sedimentation accretion work has been conducted in the Mississippi River deltaic plain, where vertical accretion rates are large, and where there are also very high rates of subsidence and coastal land loss. In other coastal areas of the United States and Europe, a wide range of results have been found, with sedimentation rates varying from 0 to 1.5 cm year". Many coastal marshes are not accreting at a rate sufficient to compensate for the present rates of sea level rise. Many factors affect accretion rates in wetlands. These include plant community, density of vegetation, tidal elevation, sediment input from riverine, estuarine and marine sources, proximity to sediment sources, total organic matter input from primary productivity of wetland, and relative sea level rise. 

In the Delaware and Chesapeake estuaries (USA), uranium shows distinctly nonconservative behavior at salinities <5 (Sarin and Church 1994 Church et al. 1996). This was suggested to be due to sedimentary redox processes in the extensive salt marshes in the Delaware and Chesapeake bays. From mass balance calculations it was concluded that almost two-thirds of the uranium in the tidal waters were retained in the sediments. It was also suggested that, extrapolated globally, uranium removal in salt marshes and marine wetlands, including mangroves, are important sinks for U that may responsible for up to 50% of the total marine removal (Church et al. 1996). Removal of U is also observed within the Baltic Sea, related to the association of U with colloids (see Section 2.5). 

The partitioning of trace metals between the dissolved and particulate fractions in estuaries can be affected by variability in river flow, tidal and wind energy, storms, coagulation, and flocculation in the estuarine turbidity maximum (ETM), resuspension events (of sediments and porewaters), and inputs from wetland and mudflat processes. 

Although the data on N burial is somewhat sparse, Chmura et al. (2003) compiled an extensive data set on rates of C sequestration in tidal sahne wetlands, which included more than 110 salt marsh sites. They concluded that on average salt marshes store 210 g C m year. Sediment C/N data for salt marshes has been compiled by VaHela (1983) and Craft et al, 1991 and while this data also comprises a wide range of values the majority of the sites have C/N values that fall between 14 and 30. Combining estimates of C accretion and C/N ratios, yields an overall... 

As a result of bacterial sulfate reduction and decomposition of organic material, large amounts of reduced sulfur gases are emitted into the atmosphere annually from wetland systems, especially tidally influenced marine sediments and salt marshes (Adams et al., 1979,1981). 

Heavy metals in wetlands have both natnral and anthropogenic sources and can be delivered by either eolian, fluvial, or tidal sources. Once within a wetland or aquatic environment, the ability of a metal to be transported depends on its chemical properties. The chemical properties of metal pollutants also influence toxicity. The species of metal or metal speciation determine the behavior in aquatic and wetland enviromnents. Valence, the formation of oxyanions, sorption to the particulate or sediments, complexation with organic matter, precipitation, and interaction with microorganisms are processes governing the availability or toxicity of heavy metals in wetlands. 

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