Exchange between Soil and Water Column

Wetland plants growing in flooded soil possess well-developed aerenchyma (airspace tissue) systems that act as conduits for the diffusion of oxygen from the atmosphere through the plant leaves and stems to the roots. The root rhizosphere contains an oxidized area where reduced sulfide can be oxidized to snlfafe or elemenfal snlfnr (Fignre 11.20). Sulfide can be oxidized either chemically or microbiologically to elemental snlfnr. Beggiatoa organisms that oxidize H2S to elemental sulfur are abundant in the root zone. 

FIGURE 11.21 Schematic showing sulfur oxidation-reduction at the sediment-water interface. 

Rates of S Accumulation in the Louisiana Barataria Basin Marsh Soils (Mean SE, A/ = 15) 

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These are typical characteristics of wetlands with overlying floodwater and lake and marine sediments. The exchange rates between soil and water column determine whether wetland soils or sediments are functioning as a sink or source for nutrients. The rate of exchange of dissolved species depends on ... 

FIGURE 14.1 Schematic showing major exchange processes between soil and water column. 

List the important biogeochemical process regulating the exchange of dissolved substances between soil and water columns, and water column and atmosphere. 

Exchange of dissolved nitrogen species between the soil and water column support several nitrogen reactions. For example, nitrification in aerobic soil layer is supported by ammonium flux from the anaerobic soil layer. Similarly, denitrification in anaerobic soil layer is supported by nitrate flux from the aerobic soil layer and water column (see Chapter 14 for discussion on transport processes). 

PHOSPHORUS EXCHANGE BETWEEN SOIL AND OVERLYING WATER COLUMN... 

Transport-related non-equilibrium behavior (e. g., physical non-equilibrium) is excluded, which plays an important role in non-ideal solute transport in the field and in some experimental column systems. Physical non-equilibrium is due to slow exchange of solute between mobile and less mobile water, such as may exist between particles or between zones of different hydraulic conductivities in the subsurface soil column, and occurs for sorbing and non-sorbing molecules alike. 

Briefly discuss the exchange of dissolved N, O2, Fe, Mn, S, and C species between wetland soil and the overlying water column. 

Ammonia loss through volatilization to the atmosphere is a complex process mediated by a combination of physical, chemical, and biological factors. The exchange of ammonia between water column, soils, and the atmosphere plays an important role in wetland nitrogen cycle. However, the significance of this process is not well established. 

FIGURE 9.67 A schematic showing exchange processes between water column and soil of a wetland. 

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