Freshwater ecosystems wetlands

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. 

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. 

The iron is especially important. In freshwater ecosystems, fluxes of hydrogen sulfide are also relatively small owing to the lack of sufficient sulfate as a substrate for dissimilatory reduction and to the relatively greater incorporation of the available sulfur into biomass. However, the release of hydrogen sulfide is significant from wetlands. In addition, H2S emission from plant canopy occurs when S plant uptake is in excess of biosynthetic demands. The latter process may account for as much as 40% of total natural S emission. 

Zillioux EJ, Porcella DB, Benoit JM. 1993. Mercury cycling and effects in freshwater wetland ecosystems. Environ Toxicol Chem 12 2245-2264. 

Meng, F., Arp, P., Sangster, A., Brun, G.I., Rencz, A., Hall, G., Holmes, J., Lean, D., Clair, T. 2005. Modeling dissolved organic carbon, total and methyl mercury in Kejimkujik freshwaters. In Mercury Cycling in a Wetland Dominated Ecosystem A Multidisciplinary Study. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 267-284. 

Figure 6.1. Ecosystem area and soil carbon content to 3-m depth. Lower Panel Global areal extent of major ecosystems, transformed by land use in yellow, untransformed in purple. Data from Hassan et al. (2005) except for Mediterranean-climate ecosystems transformation impact is from Myers et al. (2000) and ocean surface area is from Hassan et al. (2005). Upper Panel Total C stores in plant biomass, soil, yedoma/permafrost. D, deserts G S(tr), tropical grasslands and savannas G(te), temperate grasslands ME, Mediterranean ecosystems F(tr), tropical forests F(te), temperate forests F(b), boreal forests T, tundra FW, freshwater lakes and wetlands C, croplands O, oceans. Data are from Sabine et al. (2004), except C content of yedoma permafrost and permafrost (hght blue columns, left and right, respectively Zimov et al., 2006), and ocean organic C content (dissolved plus particulate organic Denman et al., 2007). This figure considers soil C to 3-m depth (Jobbagy and Jackson, 2000). Approximate carbon content of the atmosphere is indicated by the dotted lines for last glacial maximum (LGM), pre-industrial (P-IND) and current (about 2000). Reprinted from Fischlin et al. (2007) in IPCC (2007). See color insert.

Ahmad, I., M. Pacheco, and M.A. Santos. 2006. Anguilla anguilla L. oxidative stress biomarkers An in situ study of freshwater wetland ecosystem (Pateira de Fermentelos, Portugal). Chemosphere 65 952-962. 

Gosselink, J.G, and Turner, R.E. (1978) The role of hydrology in freshwater wetland ecosystems. In Freshwater Wetlands Ecological Processes and Management Potential (Good, R.E., Whigham, D.F., and Simpson, R.L., eds.), pp. 63-78, Academic Press, New York. 

Hopkinson, C. S. (1992). A comparison of ecosystem dynamics in freshwater wetlands. Estuaries 15, 549-562. 

Spatial variation in the abundance of electron donors and acceptors explains large-scale and small-scale patterns of anaerobic metabolism. Sulfate reduction dominates anaerobic carbon metabohsm on about two-thirds of the planet because of the high abundance of SO4 in seawater (Capone and Kiene, 1988). Fe(III) reduction is important in aU anaerobic ecosystems with mineral-dominated soils or sediments, regardless of whether they are marine or freshwater (Thamdrup, 2000). Methanogenesis is important in freshwater environments generally, and it dominates the anaerobic carbon metabolism of bogs, fens, and other wetlands that exist on organic (i.e., peat) soils. 

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. 

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