Water quality improvement and methane emissions from tropical and temperate wetlands

The objective of this dissertation is to investigate the biogeochemistry, specifically water quality improvement and CH4 emissions, of natural and created wetlands in tropical and temperate climates.;Five tropical treatment wetlands dominated by floating aquatic plants and constructed to deal with a variety of wastewaters were compared for their effectiveness in treating organic matter and nutrients in the Parismina River Basin in eastern Costa Rica. Wastewaters were from a dairy farm, a dairy processing plant, a banana paper plant, and a landfill. Four of the five wetland systems were effective in reducing nutrient levels of effluents before water was discharged into rivers. Ammonia nitrogen (N) levels in water entering most wetlands were considerably higher than ambient (i.e., riverine) levels; concentrations were reduced by as much as 92% in the wetlands, which retained, at a maximum, more than 166 g NH4-N m-2 y-1. Nitrate N removal occurred in low concentrations in the inflows (less than 1 mg-N L-1). Phosphate phosphorus (P) was effectively reduced through the wetlands (92 and 45% reductions through dairy farm wetlands, 83% reduction through banana paper wetlands, and 80% reduction through dairy processing wetlands). Retention of phosphate ranged from 0.1 to 10.7 g-P m-2 year-1 in the treatment wetlands. Dissolved oxygen in the wetland outflows were ≤2 mg L-1 in three of the sampled wetlands, most likely a result of the abundant free-floating macrophytes that sheltered the water from diffusion and shaded aquatic productivity.;The objective this research was to compare wetland CH4 emissions from three natural tropical wetlands located in different climatic and ecological areas of Costa Rica. There were three distinct tropical wetland ecosystems: (1) a humid flow-through wetland slough with high mean annual temperatures (25.9°C) and precipitation (3700 mm yr-1); (2) a stagnant rainforest wetland with high mean annual temperatures (24.9°C) and precipitation (4400 mm yr-1); and (3) a seasonally wet riverine wetland with very high mean annual temperatures (28.2°C) and lower mean annual precipitation (1800 mm yr-1). CH4 emission rates measured from sequential gas samples using non-steady state plastic chambers during 6 sampling periods over a 29-month period from 2006-2009 were higher than most rates previously reported for tropical wetlands. Means (medians) were 356 (116), 906 (145), and 1004 (371) mg CH4-C m-2 d-1 for the three sites, with highest rates (p = 0.000) occurring at the seasonally flooded wetland site compared to the humid sites. Highest CH4 emissions occurred when water levels were between 30 and 50 cm. We estimate that Costa Rican wetlands produce about 1.3 Tg yr -1 of CH4, or approximately 1 percent of global tropical wetland emissions. Elevated CH4 emissions at the seasonally wet/warmer wetland site suggests that some humid tropical wetlands of Central America may emit more CH4 if temperatures increase and precipitation decreases with climate change.;There have been few studies of CH4 emissions in created and restored wetlands. We measured seasonal and spatial patterns of CH4 emissions over a two-year period (2006-08) from two 12 to 14-year-old created wetlands in central Ohio, one initially planted and the other allowed to self-colonize, to determine how season, hydrology, and the original wetland creation approach influence those emissions. Mean CH4 emissions from the two created wetlands were 21 and 83% of the CH4 emission of 82 g CH4-C m-2 y-1 measured in a natural wetland in Ohio with similar hydrologic patterns. Annual CH4 emissions increased at a higher rate in the planted wetland than in the self-colonized wetland over a four-year period with increases of 4 and 16 g CH4-C m -2y-1 in the planted and self-colonized wetland, respectively. CH4 emissions from created wetlands in their early decades may depend as much or more on the methods used to create the wetlands (e.g. planting vs. natural colonization) as on the hydrogeomorphic conditions of the wetlands. (Abstract shortened by UMI.)...