Phd Dissertation

WATER QUALITY IMPROVEMENT AND METHANE EMISSIONS FROM TROPICAL AND TEMPERATE WETLANDS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Amanda M. Nahlik, B.A., M.S. Environmental Science Graduate Program The Ohio State University 2009 Dissertation Committee: Dr. William J. Mitsch, Advisor Dr. Nicholas T. Basta Dr. Richard P. Dick Dr. Jay F. Martin Copyright by Amanda M. Nahlik 2009 ABSTRACT Wetlands are important ecosystems in our landscape because of the broad array of ecosystem services they provide to humans and the environment. Wetlands have unique biotic and abiotic chemical interactions among soil, water, and vegetation that, combined with long retention times that are characteristic of wetlands, allow for nutrients, metals, and organic pollutants to be removed from the water column, resulting in cleaner water. The same characteristics that make wetlands so efficient at improving water quality also provide anaerobic conditions and organic substrate that is optimal for methanogenesis, the microbial production of the greenhouse gas (GHG) methane (CH4). 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; ii concentrations were reduced by as much as 92% in the wetlands, which retained, at a −2 −1 maximum, more than 166 g NH4-N m y . 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 efficacy of these created wetlands to treat effluents from different sources varied, and modified wetland designs or active management may be necessary to further improve water quality. Recommendations on tropical wetland design and management are presented, as are suggestions for implementing an ecological engineering approach with farmers in Central America. Wetlands are one of the largest natural sources of the greenhouse gas CH4 released to the atmosphere. Despite the fact that a large percentage of wetlands occur in tropical latitudes, CH4 emissions from natural tropical wetlands are not well understood. 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 ºC) and precipitation (3700 mm yr-1); 2) a stagnant rainforest wetland with high mean annual temperatures (24.9 ºC) and precipitation (4400 mm yr-1); and 3) a seasonally wet riverine wetland with very high iii mean annual temperatures (28.2 ºC) 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 -2 -1 (116), 906 (145), and 1004 (371) mg CH4-C m d 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 -1 estimate that Costa Rican wetlands produce about 1.3 Tg yr 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. Median (mean) spring/summer CH4 emissions for the planted and self-colonized wetlands were 56 (84) -2 -1 and 111 (287) mg CH4-C m d for Wetland 1 and Wetland 2 respectively, while autumn -2 -1 and winter emissions were considerably lower (11 (28) and 24 (66) CH4-C m d , respectively). Overall, the two created wetlands were different with respect to CH4 emissions, with the plant self-colonized wetland emitting higher annual CH4 emissions -2 -1 (median and mean emissions of 19 and 68 g CH4-C m y , respectively) than the planted iv -2 -1 wetland (median and mean emissions were 6 and 17 g CH4-C m y , respectively). Since hydrology and soil/water temperature were identical for the two wetlands, we hypothesize that differences in carbon accumulation due to higher net primary productivity in the self-colonized wetland may be causing higher CH4 emissions in that wetland. Net primary productivity in the self-colonized wetland was higher 7 out of 11 years prior to the study. Mean CH4 emissions from the two created wetlands were 21 and -2 -1 83 % of the CH4 emission of 82 g CH4-C m y 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 -2 -1 of 4 and 16 g CH4-C m y 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. v DEDICATION To my parents, without whom I would never have had so many opportunities to get this far, Siobhan Fennessy, who opened the great door of Wetland Ecology to me, and Eric Emerson, who has been by my side from the start of my Ph.D., even through cold and rainy field work and amidst tears of frustration, cheering me on all the way to the end. vi ACKNOWLEDGMENTS The research conducted for this dissertation would not have been possible without the help of my mentors, colleagues, friends, and family. The generosity of the community around me to lend a hand in the field, read over a manuscript, or help in the lab was constant throughout my graduate tenure at The Ohio State University. First and foremost, I would like to acknowledge my advisor, Dr. William Mitsch, for all his insight and help during my Ph.D. I am honored to have received two degrees under Bill, and have enjoyed getting to know Bill during my time at OSU. Never have I seen the contagious enthusiasm that Bill has when it comes to wetlands. I fondly remember following Bill, machetes in hand, into the wild Reserva wetland at EARTH University when we first learned of its existence. After the unpleasant tick-extraction that resulted from that tropical exploration, I have been more careful about my curious tendencies, but Bill, I would still follow you into [almost] any wetland! Thanks so much for all the knowledge and experience you have imparted upon me. It has been a pleasure working with you and I look forward to collaborating in the future! My dissertation committee, Dr. Nick Basta, Dr. Richard Dick, and Dr. Jay Martin have also been helpful in providing comments on my dissertation and manuscripts and input into the initial projects. I truly enjoyed the challenges I received in both their classes and in my oral exams for my candidacy and defense. vii Blanca Bernal has become one of my closest friends and most trusted field-mate since starting my dissertation. Blanca may have given as much blood to my project as I have, and she has been nothing less than amazing in the wetlands swarming with crocodiles, ant-infested cabins, and jungles teeming with pit vipers and spiders. Even in Ohio, Blanca has been by my side more than anyone else in the field. Blancs, thanks for all your help, company, and friendship. Dr. Anne Altor, friend and colleague, has been especially helpful and taught me much of what I needed to know to run the gas chromatograph and sample for methane. Her wisdom and encouragement continued even after she finished her doctorate, and it has been greatly appreciated. Like a good friend, Anne was almost always able to convince me to step away and take a break, for a caipirinha or a climb, which is probably why I still have my sanity! Eric Emerson often helped me in the field on those early mornings when I could not convince others to get out of bed and on the cold winter days on Lake Erie.

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