Gaseous Nitrogen Losses from Gulf Coast Marshes

The low evolution of N2O and NH3 from unamended brackish and salt marsh soils suggests a conservative internal nitrogen cycle exists in Louisiana\u27s coastal marshes. The gaseous evolution of NH3 and N2O increased following the addition of (NH4) 2SO4. The maximum rates of NH3 volatilization from the salt and brackish marshes were 5.7 and 3.2 mg N m_2 d_1, respectively. The corresponding total NH3 volatilization was 34 and 15 mg N m_2 for the salt and brackish marshes. Volatilization from unamended cores amounted to 6.0 and 0.9 mg NH3-N m_2 from the salt and brackish marshes. Approximately 29 and 15 mg N2O-N m_2 was evolved from the brackish and salt marsh sediment amended with 1243 and 1469 mg NH4+ -N m_2. The N2O evolution from the unamended cores was 0.4 and 2.2 mg N m_2 from the brackish and salt sediment

Plant Functions in Wetland and Aquatic Systems: Influence of Intensity and Capacity of Soil Reduction

Wetland or hydric soils, in addition to excess water and limited air-filled porosity, are characterized by anaerobic or reducing conditions. Wetland plants have developed physiological and morphological adaptations for growing under these conditions. Various methods exist for measuring plant responses to reducing conditions in wetland and aquatic environments, including assessment of radial oxygen transport, cellular enzymatic transformations, changes in root structure, and nutrient uptake. However, a gap exists in quantifying the chemical properties and reducing nature of soil environment in which plant roots are grown. The variation in reducing conditions, oxygen demand, and other associated processes that occur in wetland soils makes it difficult to truly compare the plant responses reported in the literature. This review emphasizes soil-plant interactions in wetlands, drawing attention to the importance of quantifying the intensity and capacity of reduction and/or oxygen demand in wetland soils to allow proper evaluation of wetland plant responses to such conditions

Processes of formation and degradation of marshes along the Louisiana Gulf Coast

Processes governing the stability of Louisiana's rapidly deteriorating Gulf coast marsh were investigated. Vertical marsh accretion determined from 137 Cs dating were compared to water level increase obtained from tide gauge data. In subsiding coastal environments the continued existence of marsh habitat is dependent on the ability of marsh to maintain elevation through vertical marsh accretion (mineral sediment and organic matter accumulation). Coast-wide average vertical accretion was 0.60 to 0.80 as compared to water level increase of over 1 cm year. Rapid water level increase, attributed primarily to subsidence, was 3 to 5 times greater than eustatic sea level changes reported to be 0.23 cm yr-1The measured accretionary deficits (difference between water level increase and vertical marsh accretion) parallels reported marsh disappearance of over 100 km2 yr -1Organic matter accumulation was identified as an important component of marsh aggradation in response to changes in water level. A appreciable amount of organic production of marsh macrophytes remains on the marsh as peat or is decomposed to carbon dioxide or methane. Organic matter on a dry weight basis constituted an increasing fraction of soil solids as its marine influence diminishes inland from the coast. Organic matter is of greatest structural significance in low density, fresh, and brackish marsh environments. However, on a unit volume basis, the organic matter occupies the same volumes in fresh, brackish, and salt marshes.Louisiana Gulf coast marsh will likely continue disappearing at a rapid rate unless means are implemented for distributing Mississippi River sediment to the marshes. The combined effect of rapid subsidence, eustatic sea level rise and accompanying salt water intrusion will likely destroy much of these marshes. Results presented may represent future conditions for many coastal regions of the world, which may experience a rapid rise in water level as a result of the predicted "greenhouse" warming and resultant accelerated worldwide sea level rise.</p

Accretion rates in salt marshes in the Eastern Scheldt, Southwest Netherlands

Vertical accretion and sediment accumulation rates were determined from the distribution of 137Cs in sediment cores, from historic documents, and from artificial white-coloured tracer layers in salt marshes in the Eastern Scheldt. Salt marsh accretion is related to the steady rise of the mean high tide in the Eastern Scheldt during the last few decades. Mean accretion rates vary from 0?4-0?9 cm year−1 in the St Annaland marsh to 1?0–1?5 cm year−1 in the Rattekaai marsh. Sediment accumulation in accreting marshes exceed the loss of sediment, by retreat of the marsh cliffs, by a factor of 10–20. Short-term spatial and temporal variations in accretion rates are large. Spatial variations are associated with levee and backmarsh sites and the density of marsh vegetation. Temporal variations are mainly related to fluctuations in hydrodynamic conditions. The net vertical accretion rate of organic carbon is 0?4±0?1 kg m−2 year−1; approximately half this rate is associated with the current deposit, and the other half with net additions from the belowground root biomass. A simple model for the root biomass distribution of Spartina anglica with depth and the depth-dependent fossilization of root biomass in sediments of the Rattekaai marsh is presented

Distribution of organic and reduced sulfur forms in marsh soils of coastal Louisiana

Soil samples from a Louisiana Barataria Basin brackish marshes were fractionated into acid-volatile sulfides (AVS), HCl-soluble sulfur, elemental sulfur, pyrite sulfur, ester-sulfate sulfur, and carbon-bonded sulfur. Inorganic sulfur composed 13% of total sulfur in brackish marsh soil with HCl-soluble sulfur representing 63–92% of the inorganic sulfur fraction. AVS represented less than 1% of the total sulfur pool. Pyrite sulfur and elemental sulfur together accounted for 8–33% of the inorganic sulfur pool. Organic sulfur, in the forms of ester-sulfate sulfur and carbon-bonded sulfur, was the most dominant pool representing the majority of total sulfur in brackish marsh. Results were compared to values reported for fresh and salt marshes. Reported inorganic sulfur fractions were greater in adjacent marshes, constituting 24% of total sulfur in salt marsh, and 22% in freshwater marshes. Along a salinity gradient, HCl-soluble sulfur represented 78–86% of the inorganic sulfur fraction in fresh, brackish, and salt marsh. Organic sulfur in the forms of ester-sulfate sulfur and carbon-bonded sulfur was the major constituent (76–87%) of total sulfur in all marshes. Reduced sulfur species, except elemental sulfur, increased seaward along the salinity gradient. Accumulation of reduced sulfur forms through sedimentation processes was significant in marsh energy flow in fresh, brackish and salt marshes