Scaling Methane Emissions Using Vegetation Cover Type at Sallie’s Fen
Scaling Methane Emissions Using Vegetation Cover Type at Sallie’s Fen
During the summer of 2018, I had an amazing opportunity to study methane emissions in a unique ecosystem just down the road from the University of New Hampshire (UNH). As an environmental science major with a minor in wildlife and conservation biology, I had always loved to learn about the natural world while surrounded by it. When Dr. Ruth Varner, who became my mentor, introduced this research opportunity to me, I figured it would be a perfect fit, and I was awarded a Summer Undergraduate Research Fellowship (SURF) from the Hamel Center to support the work.
The author consults with her research mentor, Dr. Ruth Varner, on-site in Sallie’s Fen, Barrington, New Hampshire. (Photo by Jeremy Gasowski.)
I chose to focus my research project on methane emissions because of the strong connection between methane and the extensive negative effects of climate change, and the need for more knowledge on this topic. One process by which methane can be emitted into the atmosphere is through plant-mediated transport. My research took place in a wetland site; wetlands are important ecosystems in which to study methane emissions because globally, they are the largest natural source of methane to the atmosphere. The objective of my research was to determine how methane emissions vary depending on the plant species composition at Sallie’s Fen, a long-term research site in Barrington, New Hampshire. I conducted some of my fieldwork in collaboration with Michael Zampini, an environmental science major at UNH who also had a SURF project that involved working on the construction of a vegetation map of Sallie’s Fen.
One of the major aims of this project was to continue the data collection of the methane emission from Sallie’s Fen for the thirtieth consecutive year. Sallie’s Fen has the longest record of methane emissions data for wetlands worldwide. Multi-decadal-scale data sets are important for understanding how methane emissions are changing over time with changing climate and vegetation. The data collected from Sallie’s Fen has benefited many scientists and research projects for the past thirty years. Overall, my objective focused on expanding our understanding of the complex wetland ecosystems and their relation to methane, a greenhouse gas.
Wetlands and Methane
Methane is a greenhouse gas that has a global warming potential greater than thirty-two times that of carbon dioxide (Holmes, Prather, Søvde, & Myhre, 2013). Freshwater wetlands are the largest natural source of atmospheric methane (Hein, Crutzen, & Heimann, 1997). Methane emissions from wetlands contributed to one-third of the global greenhouse methane emissions, according to estimates from 2000 to 2009 (IPCC, 2013). Three processes that control how much methane is released from wetlands are the rate of production by microbes, the amount of methane consumed by oxidation (by different microbes), and the physical transport of methane out of the wetland (Smith, Ball, Conen, Dobbie, Massheder, & Rey, 2003). Once methane is produced, there are three modes of transport of methane out of wetland ecosystems: diffusion (movement through the soil/water column), ebullition (bubbling), or plant-mediated transport (Bubier & Moore, 1994). The focus of my research is plant-mediated transport, in which methane is transported directly from the soil to the atmosphere through vegetation.
The magnitude of methane emissions in wetlands varies with factors such as temperature, precipitation, and vegetation (Noyce, Varner, & Bubier, 2014). Many studies suggest a positive correlation between high methane emissions and vascular plant vegetation presence, particularly sedges (Bellisario, Bubier, Moore, & Chanton, 1999; Noyce et al., 2014; Shannon & White, 1994; Ström, Mastepanov, & Christensen, 2005). Vascular plants have tissues that distribute resources throughout the plant. Sedges are vascular plants that vent methane to the atmosphere through aerenchyma, hollow, soft tissue in their stems that act like straws for methane to move from the soils to the atmosphere (Bellisario et al., 1999).
It is not fully understood what the driving factor is that influences methane emissions in wetlands. It’s possible that there is a relationship between vegetation characterization based on plant functional traits (such as the presence of aerenchyma) and methane emissions that may be helpful in predicting methane emissions across large spatial areas (Bhullar, Edwards, & Venterink, 2013). To be able to predict methane emissions, it is critical that more vegetative species be investigated (Koelbener, Ström, Edwards, & Venterink, 2010).
My main research question was, “What are the differences in methane emission at sites with different vegetation species composition?” And, secondarily, “Can I scale methane emissions according to vegetation species composition across a larger landscape?” Scaling methane emissions means that we take information collected on a small scale and apply it to the larger extent. Scaling methane emissions across the larger landscape is important for understanding how whole ecosystems play a role in the increase in methane in the atmosphere.
Out in the Fen
The author takes a static chamber flux sample at Sallie’s Fen. (Photo by Jeremy Gasowski.)
Each week during the summer months of 2018, I collected methane emission samples at Sallie’s Fen from six sites. I used the static flux chamber method to collect the samples. This involved using a rectangular plastic chamber (60 x 60 x 90cm) to trap gas emissions from the soil surface and from the vegetation, and collecting air samples from the headspace of the chamber at regular time intervals to calculate the rate of emission. Because the chamber sites were already in place at Sallie’s Fen, I did not have to spend my time setting up the chambers.
To take air samples from each chamber, I used a polypropylene syringe to pull air from inside the chamber. I then took the air samples back to the trace gas biogeochemistry lab in Morse Hall at UNH. I injected the air samples from the syringe into a gas chromatograph equipped with a flame ionization detector to be analyzed. A flame ionization detector separates the components of a sample, analyzes the components, and draws a chromatograph (chart) that has peaks representing the relative concentration of methane for that sample.
For my vegetation sampling, I collected data by using an approach similar to that used in the creation of a vegetation map of Sallie’s Fen in 2007. First, Michael Zampini and I marked five parallel transects, or straight lines, across the fen using PVC pipes to mark points on the transect. To ensure they were straight transects, we used a compass. One of us would stand at the post we had just set up, holding the compass and directing the other person which way to walk to keep the transects along the same coordinate.
The quadrat used for vegetation sampling at Sallie’s Fen.
We used a method called quadrat sampling to record vegetation species composition at the designated points on each transect. We also did vegetation quadrat sampling at each of the six static flux chamber sites. The quadrat we used was a 0.5m x 0.5m frame made from PVC pipes, with strings dividing the quadrat into thirty-six smaller and equal sections. Visually, we estimated and recorded the percent coverage of each species in the quadrat.
With the data from the static flux chambers and the quadrat sampling, we could scale the methane emissions and vegetation species across the whole fen. We constructed a map using aerial photography collected by Dr. Michael Palace. He used an unmanned aerial system, commonly known as a drone, to collect images that were then processed through a geographic information system (ArcGIS). We overlaid the methane data and vegetation data onto the aerial photos using QGIS mapping software.
I encountered many challenges throughout my research experience, but I was able to address them and progress with the project. One of my first challenges involved determining the number of locations where I would collect methane emissions. I originally wanted to collect samples from the ten static flux chamber sites already located throughout the fen. The chamber sites are accessed and connected by a boardwalk. Unfortunately, I was not able to collect data from four of the ten sites because the boardwalk had to be taken down when it was found that some of the boards were rotting at those locations. Having a boardwalk next to the chamber sites is important to reduce the impact of humans on the collection of flux samples. When the wetland surface is pressed or stepped on, the pressure causes methane to bubble out of the landscape. If I had to walk to sites that were not along a boardwalk, there would be significant error in measuring the natural methane flux.
The toughest challenges revolved around the quadrat vegetation sampling. Fortunately, Michael Zampini and I were able to work together, as well as with our mentor, to solve the obstacles that arose while vegetation sampling.
The author carrying research equipment through Sallie’s Fen, Barrington, New Hampshire. (Photo by Jeremy Gasowski.)
The last vegetation map of Sallie’s Fen was created during a study in 2007. We wanted our transects to match those that were used to create the 2007 vegetation map. The 2007 study used five transects, with four to eleven posts spread along each, depending on the length of the transect. We assumed that a few posts from 2007 would still exist out in the fen. We planned to find them and replace them with new PVC pipes that would be more durable and easier to find in the fen. We had GPS points for the locations of the posts from the 2007 study, but we had difficulty finding the old post locations because the 2007 GPS points were collected with a device that had a lower precision than the one we were using.
Michael and I trudged around in the fen for a day looking for rotting wooden boards that had once marked the transects clearly in 2007. Many times we would get our hopes up, thinking we had found a post, only to be disappointed when, with further inspection, we realized we had found only a dead tree stump.
After an unsuccessful day in the field, we talked to our mentor, Ruth Varner, about the difficulties we were having finding the old posts. She then found a map showing the locations of the 2007 posts. This helped us orient approximately where the transects and old posts should be. We were able to find a few of the old posts that had not rotted, fallen over, or sunk into the fen, which guided us in aligning our transects to match those used in the creation of the 2007 vegetation map. The process was difficult and at times frustrating, but collaboration with Michael Zampini and Ruth Varner helped in overcoming this obstacle.
Vegetation composition of Sallie's Fen was broken down into four classifications based on a K-means cluster analysis: blueberry, leatherleaf, alder, and sedge. I constructed a map of methane emissions relative to vegetation at Sallie’s Fen to visibly portray these patterns (Figure 1). I found that the blueberry category had the highest methane emissions, at an average of 1,198.92 milligrams per square meter per day (mg m-2 d-1), and I found that the alder category had the lowest methane emissions, at an average of 50.46 mg m-2 d-1. Both the sedge and the leatherleaf classifications had similar methane emissions (sedge average: 226.50 mg m-2 d-1; leatherleaf average: 267.40 mg m-2 d-1).
Figure 1. Methane emissions scaled to vegetation in Sallie’s Fen, Barrington, New Hampshire, 2018.
I expected that the sedge classification, which had aerenchyma, would show greater plant-mediated transport of methane, but I did not observe this in my data. Overall, the leatherleaf classification dominated the vegetation across Sallie’s Fen, so even though the average emissions from blueberry-dominated sites were higher, the overall fen emissions are dominated by the leatherleaf cover type (Figure 2). This suggests that currently overall Sallie’s Fen has methane emissions of approximately 7,171.64 g d-1.
Figure 2. Vegetation cover map of Sallie’s Fen, Barrington, New Hampshire, 2018.
Specifically, my data collection helps to further understand the relationship between vegetation and methane emissions in wetlands. The vegetation map I constructed will be helpful to others who plan to study vegetation systems at Sallie’s Fen and for assessing changes in vegetation cover over time. The vegetation map enables scaling of methane emissions across Sallie’s Fen and improves predictions of overall methane flux from the site. This project has the potential to assist in wetland management plans that regulate methane as a greenhouse gas. Management on wetland sites is critical, considering the large role they play in methane emissions.
Beyond Research in Sallie’s Fen
My work on Sallie’s Fen taught me about what doing research truly means. From learning to write a grant proposal to learning skills in the field, I was able to gain much from the experience. I learned about the different struggles of doing fieldwork and that some days require a lot of patience with the natural world. This includes patience with the weather and with the ecosystem you are working in. For example, I spent weeks itching from poison ivy, sweating from trudging through the fen in the heat, and stepping in areas that were not stable, resulting in sinking into the fen water. One day I managed to take a step where I thought I wouldn’t sink in but ended up waist-deep in the fen, with my phone in my pants pocket! I also experienced difficulties with lab supplies, such as materials breaking or running out of supplies while out in the field. A few times Michael Zampini and I found ourselves short on filters or vials and unable to collect all the samples we wanted to that day. These experiences may have been challenging to deal with, but they were beneficial to endure as I learn more about patience and problem solving in the researching world.
I also had many positive experiences while completing my research. I got to know graduate students who informed me about paths to graduate school, which I hope to attend in my future. Some graduate students told me that they worked for a while before entering a graduate program, whereas a few decided to go straight from undergraduate to graduate school. I found it most helpful to listen to the graduate students who had not been confident in what they wanted to do in graduate school but with a year of working were able to gain a lot from their experiences to prepare them for graduate school.
I learned about and became involved with some of the research others are doing in the lab I worked in as well. I had the opportunity to help with data collection at Caribou Bog in Orono, Maine for a modeling project my mentor is working on. On this trip we took air samples using a chamber method similar to the method I used in Sallie’s Fen. I was able to apply what I learned for my research project to a separate, larger project. During the school year following my summer of research, I began working for Dr. Alix Contosta on her research involving trace gas emissions and soil analysis.
I had opportunities to strengthen my skills in collaboration, communication, problem solving, and much more throughout this project. These are valuable skills that cannot be taught well in a classroom setting. I believe these skills were most developed while dealing with the obstacles and difficulties I came across during my summer research. Although conducting research in the field was not always easy, the struggles made it a much more beneficial experience for me.
My plans from this point on are to prepare for the Undergraduate Research Conference in the spring of 2019, which will help me develop my scientific writing skills and public speaking skills. After graduation, I plan to gain more experience working in the field and then pursue graduate school in an area within environmental science and conservation. Overall, I am very grateful for the opportunities this project has given me to grow in multiple ways as an individual.
This project would not have been possible without such a supportive network. First, I’d like to thank my mentor, Dr. Ruth Varner, who supported and encouraged me throughout my entire project. Special thanks to Clarice Perryman (Earlham College, BA, May 2016; UNH, MS, December 2017) and Dr. Michael Palace for their mentorship and willingness to assist me with my project. I’d also like to thank Michael Zampini for his hard work in and out of the field to collaboratively construct a vegetation map. Lastly, I want to thank the Hamel Center for Undergraduate Research and my donors, Mr. Dana Hamel and the J. Raymond Hepler Endowed Fund. I am very appreciative of all who played a role in making this project possible and rewarding.
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Author and Mentor Bios
Madeline Juffras, from Hopkinton, Massachusetts, will graduate from the University of New Hampshire in May 2019 with a bachelor of science degree in environmental science and a minor in wildlife and conservation biology. Her research was inspired by a class she took with her research mentor, Dr. Ruth Varner. Madeline became interested in wetland science, and through her Summer Undergraduate Research Fellowship she was able to focus full-time on learning more about it, including fieldwork in a wetland. Madeline points out that the challenges during the project ultimately helped her become a better scientist. She decided to publish in Inquiry to gain unique experience in writing and publishing about her own research work. Madeline plans to attend graduate school in environmental science and feels her research experience will give her a head start in knowing what a long-term research project entails.
Ruth K. Varner has mentored more than forty undergraduate researchers over the years, including some past Inquiry authors. She is a professor in the Department of Earth Sciences and the director of both the Earth System Research Center and the Joan and James Leitzel Center for Mathematics, Science, and Engineering Education. She began working at the University of New Hampshire as a research faculty member in 2003. For the past nineteen years, she has maintained the research site at Sallie’s Fen in Barrington, New Hampshire, where Madeline conducted her research. Dr. Varner recruited Madeline for this project from the field course she teaches. She says that she always enjoys working with undergraduates, and Madeline was no exception. She commends Madeline for always rising to meet the challenges of her research, gaining valuable experience in overcoming obstacles, and maintaining enthusiasm for her research project throughout the year.
Copyright 2019, Madeline Juffras