Eastern Michigan University DigitalCommons@EMU Senior Honors Theses Honors College 2018 Effects of Nutrient Addition and Two Invasive Plants on Wetland Methane Production Jaymes Dempsey Follow this and additional works at: https://commons.emich.edu/honors Part of the Biology Commons Recommended Citation Dempsey, Jaymes, "Effects of Nutrient Addition and Two Invasive Plants on Wetland Methane Production" (2018). Senior Honors Theses. 605. https://commons.emich.edu/honors/605 This Open Access Senior Honors Thesis is brought to you for free and open access by the Honors College at DigitalCommons@EMU. It has been accepted for inclusion in Senior Honors Theses by an authorized administrator of DigitalCommons@EMU. For more information, please contact lib- [email protected]. Effects of Nutrient Addition and Two Invasive Plants on Wetland Methane Production Abstract Wetlands provide a number of important ecosystem services, but their anoxic conditions also favor the production of several greenhouse gases. Wetlands are an ideal environment for methanogenesis, the process by which carbon dioxide is reduced to methane by wetland microbes (methanogens). As wetlands are the largest natural contributor to the atmospheric methane pool, it is important to understand variables that control wetland methane production. Nitrogen availability is one variable that likely affects methanogen communities. Nitrate drains from agricultural areas, where wetlands act as a nitrogen sink, preventing nitrate from contaminating aquatic systems. Another factor that may affect wetland methanogenesis is vegetation type. In recent years, invasives such as exotic cattail (Typha angustifolia and Typha x glauca} and Phragmites have spread through wetlands, negatively impacting ecosystem processes. To determine the influence of nitrate availability and vegetation type on wetland methanogenesis, we incubated sediment from Phragmites and exotic cattail dominated stands, added increasing concentrations of nitrate, and measured methane production. We hypothesized that if nitrate allows methanogens to be outcompeted by another group of wetland microbes, denitrifiers, then we would observe decreased methane production with high nitrate concentrations. Degree Type Open Access Senior Honors Thesis Department Biology First Advisor Kristin Judd Second Advisor Aaron Liepman Third Advisor Marianne Laporte Keywords Ecology, Wetlands, Methane, Emissions, Global Warming Subject Categories Biology This open access senior honors thesis is available at DigitalCommons@EMU: https://commons.emich.edu/honors/605 EFFECTS OF NUTRIENT ADDITION AND TWO INVASIVEPLANTS ON WETLAND METHANEPRODUCTION By Jayznes Dempsey A Senior Thesis Submitted to the EasternMichigan University Honors College In Partial Fulfillmentof the Requirements forGraduation With Honors in Biology SupervisingInstructor (Prin Name and Sign) Department Head (PrintName and Sign) 1 TABLEOF CONTENTS ABSTRACT........................................................................................... 3 INTRODUCTION.................................................................................... 4 MATERIALS& METHODS.................................................... ................... 16 RESULTS .............................................................................................20 DISCUSSION......... ................................................................................ 24 REFERENCES .......................................................................................29 2 ABSTRACT Wetlands provide a number of important ecosystem services, but their anoxic conditions also favorthe production of several greenhousegases. Wetlands are an ideal environment for methanogenesis, the process by which carbon dioxide is reduced to methane by wetland microbes (methanogens). As wetlands are the largest natural contributorto the atmospheric methane pool, it is important to understand variables that controlwetland methane production. Nitrogenavailability is one variable that likely affects methanogen communities. Nitratedrains fromagricultural areas, where wetlands act as a nitrogen sink, preventing nitrate from contaminating aquatic systems. Another factorthat may affectwetland methanogenesis is vegetation type. In recent years, invasives such as exotic cattail (Typha angustifoliaand Typha x glauca} and Phragmites have spread through wetlands, negatively impacting ecosystem processes. To determine the influence of nitrateavailability and vegetation type on wetland methanogenesis, we incubated sediment fromPhragmiles and exotic cattail dominated stands, added increasing concentrations of nitrate,and measured methane production. We hypothesized that if nitrateallows methanogens to be outcompeted by another groupof wetland microbes, denitrifiers,then we would observe decreased methane production with high nitrate concentrations. Increased nitratelowered methane production (p=0.03) and heightened denitrificationpotential (p<0.005). Exotic cattail increased methane production (p<0.0 1 ). Our fmdings suggest that nitrate bolsters denitrifiers, causing methanogens to be outcompeted. Our fmdings also suggest that exotic cattail facilitates methane production. Nitrate availability and vegetation type likely influence sediment methane production. It is importantto integratethese conclusions into our understanding of invasive vegetation, water contaminants, and methane production, to consider the best possible methods of mitigation and prevention. 3 INTRODUCTION Wetlands provide myriad ecosystem services. They supply habitat fororganisms and offerrecreational value (Silvius 2000, Millenium Ecosystem Assessment 2005). As a primary contributorto flood mitigation, millions of people depend upon wetlands {Silvius 2000, Millenium Ecosystem Assessment 2005). Additionally, their unique biogeochemical processes situate wetlands at the center of several significantenvironmental issues. Wetlands are nitrogen sinks, decreasing agriculturalrun-off from contaminating downstreamwaterways {Huang and Pant 2009). However, wetlands also contributeto global warming {Segers 1998). Wetlands emit methane, a potent greenhousegas, which is produced by sediment microbes (methanogens) (Segers 1998, Huang and Pant 2009). Methanogen communities are affected by soil properties such as nitrate availability (Kim et al. 2015), and by direct interactions with vegetation (Wolfe and Klironomos 2005). Different plant species offerroot exudates, leachates, and leaf litter that shapes soil microbial communities (Wolfe and Klironomos 2005, Weidenhamer and Callaway 2010). The invasion of exotic cattail to wetlands in the Great Lakes region, followedby the more recent invasion of Phragmitesgenotypes, has resulted in a need to understand the effectsthese plants have on wetland ecosystems. Wetlands and Methane Wetlands negatively impact the environment by releasing methane and other greenhouse gases into the atmosphere. Wetlands are the single largest natural methane source, contributing approximately 78% of methane produced in natural systems (Figure l; Bosquet et al. 2006). Wetlands also account for32-47% of total methane emissions (Denman et al. 2007). 4 Natural Sources of Methane Emissions ■ Wetlands ■ Termites ■ Oceans Figure 1 Wetlands are the largest natural contributorsto the global methane pool, followedby termites and oceans (based on figure fromBosquet et al. 2006). This is due to the anaerobic conditions in water-logged wetland sediments, which are ideal for methane-producing microbial processes called methanogenesis (Huang and Pant 2009). As methane is a potent greenhouse gas (28 times stronger than CO2) (Segers 1998), the release of methane fromecosystems can substantially increase global warming and alter natural systems. Wetland methanogenesis is part of the natural decomposition process. During methanogenesis, the breakdown of organic matter under anaerobic conditions results in accumulation of carbon dioxide, before it is reduced by microbes to methane (Figure 2). These carbon dioxidereducing microbes are members of the domain Archaea, known as methanogens (Segers 1998, Denman et al. 2007). While the atmospheric methane pool has been rising fordecades, in recent years it has experienced significant unexplained growth (Kirschke et al. 2013). Possible explanations include increased anthropogenic combustion of fossil fuels, and increased wetland methanogenesis (Kirschke et al. 2013; Figure 3). s Methane oxidation: Methanogenesls· CH4 + 2 OJ ➔ COJ + 2 HiO co,+ 4 H1 ➔ 2 H,o + cH,. CH1 COOH ➔ CO2 + CH,. Figure 2 Methanogens talce up CO2, and convert it to CH.. This methane may then be released into the atmosphere directly fromthe sediment; alternatively,it may escape through the leaves of wetland plants (Diagram modifiedfrom Brevik 2012). 6 20 - NOAA l.800 - AGAGE -uc1 15 CSIRO 1.750 "' 10 > !;. .r, 0 ..s-C. ., 1,700 .. � �· 5 ,, n l # e ?/ 3 0 ·; // .z: 0- iil C. /I 1,650 a. / r E e I .,.... ,. "0 :r. ., "0 u -5 ,, e I I 1,600 -10 -15 1,550 I 1980 1985 1990 1995 2000 2005 2010 Year Figure 3 Atmosphericmethane levels since 1980 (Modifiedfrom Kirschke et al. 2013). Methane concentrationsleveled offfrom 2000-2005, then began increasing in 2006. Dotted lines correspond to methane mole fractions,and solid lines correspond to growth rate. 7 Nutrient Enrichment and Methane Nutrient enrichment (eutrophication) negatively impacts ecosystems (Smith et al. 1999). Excess nitrogen and phosphorus in aquatic systems cause increased algae growth, decreased biodiversity, and