Upland marshes

The first global CH4 budgets were compiled by Ehhalt (1974) and Ehhalt and Schmidt (1978), who used available published information to estimate emissions of CH4 to the atmosphere. They considered paddy fields, freshwater sources (lakes, swamps, and marshes), upland fields and forests, tundra, the ocean, and enteric fermentation by animals as biogenic sources. Anthropogenic sources included industrial natural gas losses and emission from coal mining, and were considered to be free. Observations of CH4 placed an upper limit on anthropogenic sources. Oxidation by the OH radical, as well as loss to the stratosphere by eddy diffusion and Hadley circulation, were presumed to be methane sinks. In spite of lack of data, this work correctly identified the major atmospheric sources and did... 

There is tremendous geographic variability in the spatial orientation and connections of salt marshes within estuaries and of estuaries with adjacent uplands and the ocean (Fig. 22.1). This paper focuses on the salt marsh ecosystem and associated tidal creeks and not the larger estuarine ecosystem, which may include deeper and extensive bays and sounds. However, it should be recognized that some marshes, especially those that do not have freshwater inputs from rivers, have no true open estuarine area and directly exchange with the ocean. Salt marshes are linked to adjacent terrestrial environments through water and material inputs from rivers, groundwater and precipitation. In cases where the majority of these inputs first pass though the open... 

Inputs, outputs and exchanges of N with systems adjacent to salt marshes are generally much smaller in magnitude than internal fluxes (Table 22.7). The source and relative importance of various external inputs of N to salt marshes varies from system to system. While the input of N from rivers is potentially large, most of this N is probably not taken up by salt marshes but is processed in aquatic portions of estuaries or routed to the open ocean. On average, the largest input is from N fixation (2-15 g N m year ), followed by atmospheric deposition (0.5-2.2 g N year ). Groundwater inputs are a major source of N in some smaller salt marshes with developed uplands such as found in the northeastern United States. 

Harvey, H. W., and Odum, W. E. (1990). The influence of tidal marshes on upland groundwater discharge to estuaries. Biogeochemistry 10, 217—236. 

Figure 1 Summary of the steps used in the isolation of DOC from the two upland samples (Deciduous and Coniferous), a wetland (sedge marsh) and an aquatic site (Blackman Stream).

Figure 2 Observed fluorescence, Fobs, and corrected fluorescence, Fcor, versus ppm DOC for the aquatic site sample (Blackman stream — Black), the two upland samples (Coniferous Con, and Deciduous Dec), and the wetland sample (Sedge marsh -Sedge).

There is no rigorous way to compare the DOC concentrations between an aquatic or marsh environment and an upland environment. However one rough method of conparison is to use the concentration of DOC leached from the soil columns. With this as a basis, the Deciduous sample contains 26 times as much DOC as the Blackman Stream sample. Furthermore, the upland samples have the highest Kb values. These fects suggest that the upland environments will bind greater percentages of pyrene. 

Such independent estimates are available from direct measurements of Pb in total precipitation and from the standing crops present in undisturbed soils. Previous measurements of the atmospheric flux have been made in New Haven by Benninger (1976) using open-bucket collectors sampled at monthly intervals. Soil-standing crops have been measured at various sites in the eastern U.S., including a forested upland site within the Farm River salt marsh, and are compared in Table X. It is evident that the Pb flux derived from salt-marsh core FRl IB is indistinguishable from the current rate of deposition of Pb from the atmosphere in nearby New Haven. 

An upland-soil source is also consistent with the metal concentrations found at lower levels in the salt-marsh cores. The iron content is generally proportional to the mass of inorganic sediment and is found in concentrations (almost 4%) considered reasonable for soil (Bowen, 1966). In an analogous plot for Cu, Fig. 16, the concentrations in deep peat and many of the lower clay-band samples are also typical of soil. 

Indeed, salt marshes like the Farm River marsh, which lie adjacent to well-stratified tidal rivers, seem biased to receive soil from upland... 

The standing crop of excess Pb activity beneath the salt marsh is equivalent to a constant deposition rate of 1.07 0.03 dpm cm yr". This long-term average flux is the same as the total atmospheric deposition of excess Pb measured recently in nearby New Haven and is within 20% of the standing crop of excess Pb found in local upland soil. 

Although this definition primarily focuses on uplands, in a broader sense, it does include soils that undergo periodic or continuous flooding. Depending on scientific disciplines and ecosystems, soils saturated with water are often called flooded soils, wetland soils, waterlogged soils, and marsh soils. Soil scientists have used terms such as flooded soils, waterlogged soils, and paddy soils. Ecologists refer to these systems as wetland soils. Now, wetland soils have been defined as hydric soils. 

Upland marshes are ombrotrophic (nutrients from atmosphere and ground water) and acidic, whereas lowland marshes are rheotrophic (nutrients from surface and ground water) and have pH 5-6. 

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