Freshwater systems Wetlands

Figure 9. Attenuation of UV-B irradiance in saline prairie lakes, ponds, and wetlands of Canada (52°N) from Arts et al. [34]. Saline systems tend to have higher [DOC] than freshwater systems (probably because evaporation causes DOC to become more concentrated). For similar [DOC], greater penetration of UVR is observed in lakes (especially the large, deep ones) compared to small and shallow ponds and wetlands. The equation for all ponds and wetlands (triangle symbols) is K uy, = 6.1 DOC (r =0.41) for freshwater ponds and wetlands (open triangles) Rduv-B=2.5 DOC (r =0.56) for all lakes (squares), duv-B = 1A DOC (r = 0.50).

Table 2.9. P nuclear magnetic resonance spectroscopy studies of aquatic systems, including freshwater, estuary, wetland and ocean studies.

It is evident that oxygen-, nitrate-, sulfate-reducing and methanogenic conditions have a profound effect on various biogeochemical properties regulating organic matter decomposition in wetland soils (Table 5.14). A review on the comparison of microbial dynamics in marine and freshwater system as influenced by the availability of electron acceptors is presented by Capone and Kiene... 

The contribution of anaerobic ammonium oxidation reaction to overall nitrogen loss in wetlands and aquatic systems has been a subject to great speculation. The significance of this process has been demonstrated in marine systems, but to our knowledge there is no reported documentation in freshwater systems. Anaerobic ammonium oxidizers are obligate anaerobes and it is likely their activity can be promoted by other inorganic electron acceptors such as iron and manganese oxides and sulfates. However, there is no reported evidence that these reactions occur in wetland soils and aquatic sediments. 

Pezeshki SR, De Laune RD, Catallo WJ, Nyman JA, Milburn SA, Overstreet KB, Ochs CA, Melack JM, Mertes L, Hess L, Forsburg B (2003) Wetland Biogeochemistry. In Holland MM, Blood ER, Shaffer LR (eds) Achieving Sustainable Freshwater Systems A Web of Connections. Island Press, Washington, pp 125-156... 

In 1947, Patrick established a new department of limnology (the study of lakes, ponds, and streams) at the academy, a department that is now known as the Patrick Center for Environmental Research. The purpose of the department has been to study the structure and function of freshwater ecosystems, including rivers, lakes, and wetlands, along with the impact of human activities on these systems. Patrick served as curator of the center and chair of the Department of Limnology at the academy for more than decades. In 2003, at the age of 94, she still held the titles of Senior Scientist and Francis Boyer Chair of Limnology at the academy. 

In freshwater ecosystems, particularly streams and wetlands, biofilms account for a large portion of heterotrophic metabolism, as well as primary production (Edwards etal., 1990 see Chapter 12), acting as both sources and sinks for DOM. As the depth of the overlying water in the system increases, attached communities account for a declining share of system metabolism. 

Wetlands such as freshwater/salt marshes and mangroves have been shown to be major sources of primary production in estuarine systems (Kirby and Gooselink, 1976 Pomeroy and Wiegert, 1981). In fact, the outwelling hypothesis of Odum (1968) suggested that salt... 

Surface freshwater ecosystems consist of wetlands (e.g., bogs, fens, marshes, swamps, prairie potholes, etc.), streams, lakes (and artificial reservoirs), and rivers. Surface freshwater ecosystems receive most of their Nr from their associated watersheds, from atmospheric deposition, and from BNF within the system. There is hmited potential for Nr to accumulate within surface-water ecosystems, because the residence time of Nr within surface waters, like the water itself, is very brief. Residence times may be relatively longer in the sediments associated with wetlands and some larger lakes but are still short when compared to terrestrial ecosystems or the oceans. 

Sulfide methylation reactions couple dissimilatory sulfate reduction to DMS production and determine the rates of DMS emission in freshwater wetlands. This process involves acetogenic bacteria, some of which degrade aromatic acids to acetone. In soils, freshwater, and marine ecosystems a wide diversity of other anaerobic and aerobic bacteria can contribute to sulfur gas production. In addition, diverse aerobes (e.g. methylotrophs and sulfate oxidizers) and anaerobes (e.g. methanogenes) consume S gas, thereby regulating fluxes in the atmosphere-biosphere system. 

In all cases, the ratio of aerobic to anaerobic decomposition ranges from 3 to 6. Anaerobic decomposition in these systems represents a combined effect of alternate electron acceptors. Anaerobic conditions here represent a combined effect of several alternate electron acceptors (other than oxygen) present on organic matter decomposition. As mentioned previously, typically all wetlands are limited in electron acceptors, whereas electron donors are nonlimiting in most wetlands. Annual carbon loss due to decomposition processes varied between 0.7 and 3.7% of total carbon in the top 24 cm soil from four freshwater wetlands in the southeastern United States (Schipper and Reddy,... 

A wide range in nitrogen fixation rates is reported in wetlands and aquatic systems (Table 8.13 Buresh et al 1980 Howarth et al., 1988 Herbert, 1999). Rice paddies and coastal wetlands showed higher nitrogen fixation rates than freshwater wetlands, peat bogs, and lakes. 

In most freshwater wetlands and aquatic systems, sulfate concentrations are present at low concentrations to make them ineffective as electron acceptors to support organic matter decomposition. The suppression of methane production during Fe(HI) oxide reduction was demonstrated in laboratory experiments by Roden and Wetzel (1996) (Figure 10.34). In their study, methane was not produced until a major portion of the Fe(III) oxide was reduced, as evidenced by Fe(II) accumulation. Iron oxides are present in high concentrations in mineral wetland soils such as those... 

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