Tropical wetlands

AG° = -17.7kJmor at pH 7. Consequently the microbes mediating the decomposition derive less energy and produce fewer cells per unit of carbon metabolized. The accnmnlation of organic matter in marshes and peat bogs illns-trates this point. (Bnt note the rarity of tropical wetland soils with large organic matter contents, discnssed in Section 3.7.)... 

Miyajima T., Wada E., Hanba Y. T., and Vijarnsorn P. (1997) Anaerobic mineralization of indigenous organic matters and methanogenesis in tropical wetland soils. Geochim. Cosmo-chim. Acta 61, 3739-3751. 

Cook, G. D., Setterfield, S. A., and Maddison, J. P. (1996). Shrub invasion of a tropical wetland implications for weed management. Ecol. Appl. 6, 531-537. 

Rejmankova, E. and Komarkova, J. (2000) A function of cyanobacterial mats in phosphorus-limited tropical wetlands. Hydrobiologia 431, 1 35-1 53. 

A highly significant, positive relationship has been shown between iron oxide reduction and organic nitrogen mineralization in tropical wetland soils (Sahrawat, 2004). The following empirical relationships were reported ... 

Corstanje, R., K. R. Reddy, J. P. Prenger, S. Newman, and A. V. Ogram. 2007. Soil microbial eco-physiologi-cal response to nutrient enrichment in a sub-tropical wetland. Ecol. Indicators 7 277-289. 

Mariot, M., Dudal, Y., Furian, S., Sakamoto, A., Valles, V., Fort, M., and Barbiero, L. (2007). Dissolved organic matter fluorescence as a water-flow tracer in the tropical wetland of Pantanal of Nhecolandia, Brazil. Sci. Total Environ., 388,184-193. 

Longer ice-core records show that methane concentrations have varied on a variety of time scales over the past 220 000 years (Fig. 18-15) Qouzel et al, 1993 Brook et al, 1996). Wetlands in tropical (30° S to 30° N) and boreal (50° N to 70° N) regions are the dominant natural methane source. As a result, ice-core records for preanthropogenic times have been interpreted as records of changes in methane emissions from wetlands. Studies of modem wetlands indicate that methane emissions are positively correlated with temperature, precipitation, and net ecosystem productivity (Schlesinger, 1996). 

Nahlik, A.M. and Mitsch, W. J., Tropical treatment wetlands dominated by free-floating macrophytes for water quality improvement in Costa Rica, Ecological Engineering, 28, 246-257, 2006. 

Air bubbles in the ice corroborated the increased wetness in other areas. The amount of methane in the bubbles indicates that this gas was entering the atmosphere 50 percent faster during the warming than it had earlier. The methane probably entered the atmosphere as wetlands flooded in the tropics and ice and snow thawed in the north. 

In data assembled by Greenland (1997), the mean level of organic carbon in the topsoils of wetland rice soils from across tropical Asia was 2%, and after excluding acid peaty soils the mean was 1 %. This compares with a range of 1.27-1.81 % for Oxisols and Ultisols of the Cerrado region of Brazil (Sanchez,... 

Despite the burning of crop residues in the productive, irrigated rice areas of tropical and subtropical Asia, and their removal for other purposes in the low-producing rainfed rice areas, soil carbon levels are largely constant (Bronson et al., 1998). In any case, the amount of carbon in the shallow puddled layer of ricefields amounts to only a few per cent of the amount in natural wetlands. 

FIGURE 3 Relationships between annual runoff and watershed export of DOC in streams and rivers reported in the literature. The respective lines extend only over the range of runoff values included in the dataset. The slopes of each line are approximately equivalent to the mean annual DOC concentration for that group (in parentheses). Sources for each relationship are as follows streams with wetlands, temperate (Mulholland, 1997) streams with wetlands, N. Carolina (Mulholland and Kuenzler, 1979) large rivers, global (Spitzy and Leenheer, 1991) large rivers, N. America (Mulholland and Watts, 1992) streams, tropical (McDowell and Asbury, 1994) streams, N. America (Mulholland, 1997). 

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.

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