Freshwater marsh soils

There is little information on the presence of anaerobic FeOB in the rhizosphere. A preliminary survey of a Maryland tidal freshwater marsh soil indicated that nitrate-reducing anaerobic FeOB were present, albeit in low numbers ( 10 to 10 cells niL i Emerson, unpublished data). In freshwater sediments, Straub and Buchholz-Cleven (1998) found greater numbers of anaerobic nitrate-reducing FeOB (1 X 10 to 5 X 10 cells g ) than anaerobic phototrophic FeOB (0.1 to 3.9 X 10 cells g ). 

There are two types of marsh soils freshwater marsh soils and saltwater marsh soils. These soils are generally permanently waterlogged. Freshwater marshes occur in the areas adjacent to lakes and streams, whereas saltwater marshes occur in estuaries. Typical characteristics of these soils are... 

Floodwater Flooded soils Freshwater sediments Ocean sediments Marsh soils... 

Results, University of Florida), (b) Relationship between methane concentration in soils and methane emissions from freshwater marsh (Ding et ah, 2005). 

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). 

In Louisiana coastal marsh soils, inorganic sulfur constitutes 13-30% of the total sulfur pool, with HCl-soluble sulfur representing 78-86% of the inorganic sulfur fraction in freshwater, brackish, and salt marsh (Pezeshki et al., 1991 Krairapanond et al., 1992). AVS accounted for <1% of the total sulfur pool. Pyrite sulfur and elemental sulfur together accounts for 8-33% of the inorganic sulfur pool (Krairapanond et al., 1992). 

Approximately 90% of the methane transport from soils to the atmosphere in rice paddies and freshwater marshes is through aerenchyma portion of roots and stems of the plants. Gases are transported according to their concentration gradient, not only for CH4 but also for N2O (Yu et al.,... 

The bulk density of the marsh soil prohles showed a signihcant increase (p < 0.05) in sediment in the surface (0-9 cm) at the sites nearest to the freshwater input. The bulk density in the surface (0-9 cm) averaged over 0.30 g cm at sites nearest to the diversion. The higher bulk density represented a sediment spike or bulk density increase in the surface prohle as compared to the lower bulk density observed with depth in the marsh prohle (DeLaune et al., 2003). 

This case study demonstrated that freshwater diversion projects such as Caernarvon serve an important role in the reintroduction of freshwater and limited amount of mineral sediment necessary for promoting growth of marsh vegetation (the source of organic matter in marsh soil) in subsiding delta environments. In addition to sediment input, an important influence of the diversion on enhancing marsh stability is associated with the lowering of salinity, which reduces the sediment requirement for marsh maintenance (freshwater marshes have lower mineral sediment requirement than saline marshes). 

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. 

Prenger, 1. P. and K. R. Reddy. 2004. Microbial enzyme activities in a freshwater marsh after cessation on nutrient loading. Soil Sci. Soc. Am. J. 68 1796-1804. 

Surface water can be defined as any river, lake, stream, pond, marsh, or wetland as ice and snow and as transitional, coastal, and marine water naturally open to the atmosphere. Major matrix properties, distinguishing water types from each other, are hard and soft water, and saline and freshwater. Groundwater is typically defined as water that can be found in the saturated zone of the soil. Groundwater slowly moves from places with high elevation and pressure to places with low elevation and pressure, such as rivers and lakes. Partitioning interactions of the groundwater with the solid soil matrix is an important factor influencing the fate of toxicants. Physicochemical properties of water that may affect toxicity of chemicals in all water types are listed in Table 2.2. 

There have been remarkably few attempts to determine the contribution of Fe(III) reduction to anaerobic carbon metabolism in freshwater ecosystems where it may be the dominant pathway. The most extensive such study examined 16 rice paddy soils collected from China, Italy, and the Philippines (Yao et al., 1999). Fe(III) reduction was 58-79% of carbon metabohsm during the reduction phase (Section 8.08.8.1), with most of the remainder attributed to methanogenesis. Fe(III) reduction contributed —70% of the anaerobic metabolism in a Juncus effusus marsh (Roden and Wetzel, 1996). 

Wetlands of humid climatic zones often emit H2S, as is evident from the rotten-egg odor of marshes and swamps. As long as the dominant exchangeable base cations are Ca " and Mg ", which is the case in most freshwater wetlands, H2S formation should not cause the soils to become strongly alkaline. In these nonsodic soils, alkalinity generated by reduction forms precipitates of Ca (and Mg) carbonates. The low solubility of these carbonates prevents the pH from rising much above 8. In sodic soils, however, reaction 7.64 causes alkalinity to build up in the form of soluble Na carbonates (see Chapter 8, Section 8.1). 

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