Jill Bubier's Lab

(* indicates undergraduate coauthor ^ indicates graduate student or postdoctoral research associate)

Summer 2016

Julia Palorinne

Jani Antila

Jani Antila and Julia Palorinne - summer 2016

Jani is a second year undergraduate forest ecology and management student and Julia is a plant science student at University of Helsinki, Finland. Both are excited about having the opportunity to spend the summer at Mer Bleue bog in Ottawa. They are going to be working at the bog from May through August 2016, focusing on ecosystem CO2 fluxes and vegetation feedbacks at a nitrogen (N), phosphorus (P), and potassium (K) fertilization experiment, now in its 17th year. It has been three years since the last CO2 flux measurements at the site, so they will update the data with new measurements. They will also measure vegetation structure and species composition monthly to follow vegetation feedbacks to N with and without PK addition. In addition, they are going to help with the ongoing fertilization process, applying the nutrients dissolved in water to mimic atmospheric deposition.

Sini Arnkil

I am a forestry student in the University of Helsinki, Finland. In the summer of 2015 I had a chance to measure methane (CH4) emissions at Mer Bleue Bog, Ottawa, Ontario and collect data for my master’s thesis. The study was conducted in collaboration with Mount Holyoke College, McGill University, Carleton University and the University of Helsinki.

The purpose of this study was to investigate the effects of nutrient addition on CH4 fluxes and vegetation in an ombrotrophic bog after 11-16 years of fertilization with nitrogen, phosphorus and potassium or with nitrogen only. We measured methane flux in all of the 27 fertilized plots under nine of the treatments every week from the third week of May until the end of August. Environmental variables, such as water table level, peat temperature and volumetric soil water content were measured simultaneously with the CH4 flux measurements. Vegetation structure and species composition were measured five times during the summer using the point intercept method. The data from this experiment will be analyzed during the academic year 2015-16.

The Effects of Long-Term Nutrient Addition on Methane Fluxes and Vegetation in an Ombrotrophic Bog

Abstract of the Paper Presented to the Faculty of University of Helsinki in Partial Fulfillment of the Requirements for the Degree of MSc. Spring 2016

The atmospheric nitrogen (N) deposition has increased in industrialized and densely populated areas, which according to previous studies may cause changes in the vegetation, microtopography, and carbon (C) cycling of peatlands. Knowing the effects of nutrient deposition is important, because a significant amount of C is stored in boreal nutrient-limited ombrotrophic bogs, which are also a significant natural source of methane (CH4).
The aim of this study was to investigate how elevated N deposition affects the CH4 fluxes and vegetation in an ombrotrophic bog. This study was conducted at a long-term fertilization experiment at Mer Bleue, a Sphagnum moss and evergreen shrub dominated ombrotrophic bog in Ottawa, Southern Ontario. The experiment consisted of nine nutrient treatments, each with three replicate 3 x 3 m plots. In the summer of 2015, the plots had been fertilized for 11–16 years with 1.6, 3.2, and 6.4 g N m-2 with or without phosphorus (P) and potassium (K) and control plots received distilled water. Methane fluxes were measured weekly from the beginning of May to the end of August using closed chamber method. Peat temperature, water table level, and volumetric soil water content were also measured. The changes in vegetation abundance and species composition were monitored monthly using point-intercept method.
The results show that instantaneous CH4 fluxes at the bog are typically small (0–0.2 mmol m-2 h-1). The seasonal average CH4 emissions from N only treatments are equal to controls. However, the average CH4 emissions have increased after 15–16 years of fertilization from the highest NPK treatments compared to unfertilized control due to nutrient induced changes in vegetation, microtopography, and peat characteristics. The changes in vegetation include the loss of Sphagnum mosses and new deciduous species in the area. Due to the loss of moss cover, the peat has subsided and it has become wetter, which may explain the increased CH4 emissions. Direct effects of fertilization on the microbial communities may also be a factor.
The results of this study indicate that elevated atmospheric deposition of nutrients may increase loss of C as CH4 in peatlands through a complex suite of feedbacks and interactions among vegetation, microclimate, and microbial communities.

Kayla Smith '16

Throughout the summer of 2014, I worked as a research assistant to Tanja Zivkovic who is a PhD student in the Geography Department of McGill University in Montreal, Québec. Her work examines nitrogen (N2) fixation rates among Sphagnum mosses. I assisted in collecting data for two N2 fixation experiments. The first was looking at N2 fixation on a hydrological gradient within the Mer Bleue Bog in Ottawa, Ontario, which is where most of our field work took place. The second was looking at N2 fixation rates in samples along a latitudinal gradient ranging from southern to northern Québec and Ontario. Both experiments used acetylene reduction assay to determine the rates of N2 fixation.
I also worked with Veronica DeJesus, another Mount Holyoke student, to collect methane samples in the plots used for the fertilization experiment at Mer Bleue. This fertilization experiment has been attended to for fourteen years and the plots have been given different amounts of nitrogen, phosphorus, and potassium. The nutrient additions were originally to see if they had an effect on carbon cycling within the bog, so we started to collect samples to see if the nutrient additions have an effect on methane production and consumption.

Veronica DeJesus'16

My work this summer centered on the relationship between methane emissions and fertilization addition at the Mer Bleue bog in Ontario, Canada. The fertilization site and research is now in its fourteenth year and is a collaboration between Mount Holyoke College, McGill University, and Carleton College. Kayla Smith and I took weekly methane measurements in the plots, under nine of the treatments. The methane emission process is two-part. Microbial methanogens produce methane in the water logged anoxic peat below the water table (Moore and Dalva 1997). The methane gas then filters up through the aerobic peat layer where microbial methane-oxidizers consume it. Under natural conditions the microbial activity and diffusion of the methane gas depends on temperature, relation to the water table, the vegetation, and perhaps the quality of the peat (Bubier et al. 1995, Bubier et al. 2005). The fertilized plots show changes in these variables as compared to the controlled plots including in microclimate, vegetation composition, and water table depth (Larmola et al. 2013, Chong et al. 2011). The loss of sphagnum moss and subsequent collapsing of the aerobic peat layer potentially leaves less habitable area for the methane-oxidizers. Additionally, by tipping the scale in favor ericaceous shrubs with fertilization the fertilized plots are shadier (Chong et al. 2011) To isolate the effect of fertilization on the microbial activity due to substrate quality, I did a lab incubation of peat samples taken from the anoxic area around the water table, where most of the methane production and consumption occurs, and from the aerobic zone where methane consumption occurs (Moore and Dalva 1997). The purpose of this experiment was to see if there was an increase in microbial production or consumption of methane with fertilization. The data from this experiment will be analyzed during the academic year.

Emma Singer '14

This summer I was given the opportunity to work at Mer Bleue Bog in Ontario, Canada. My research was part of a larger project through Professor Bubier’s lab examining the effect of nutrient addition on carbon cycling in northern peatlands. I, along with fellow student Sabrina Livne-Kennedy, worked primarily at McGill University in Montréal to examine the effect of fertilization on microbial communities within Mer Bleue. I am currently continuing this research through an independent study under the guidance of Professor Bubier. My work is looking at microbial CO2 production under different substrate additions. We added different plant substrates and bog-water substrates to peat samples from within the Mer Bleue fertilization experiment to determine CO2 production potential. Additionally, we looked at biodegradability of both bog waters and plant-substrates. I hypothesized that (1) microbial CO2 respiration would increase with in fertilized treatment, (2)substrate addition would increase microbial CO2 respiration across all treatments, (3) there would be an interaction between substrate and treatment, and that (4) rates of biodegradability amongst substrates would vary significantly. Results show that there is not a significant difference in rates of microbial CO2respiration between treatments, but respiration does increase significantly with the addition of substrate. Specifically, plant-based substrates induce significantly higher rates than bog-water substrates. Furthermore there was not a significant relationship between substrate and treatment. Rates of biodegradability did not differ significantly between substrates.

The Effect of Nutrient Limitation on Substrate Induced Microbial Respiration at Mer Bleue Bog

Abstract of the Paper Presented to the Faculty of Mount Holyoke College in Partial Fulfillment of the Requirements for the Degree of Bachelors of Arts with Honor (prepared under the direction of Professor Jill Bubier). May 2014

Peatlands act as an important global carbon (C) sink, storing approximately 30% of global soil organic C (Roulet et. al. 2007). Typically nutrient-limited, these ecosystems may be vulnerable to increasing atmospheric nitrogen (N) deposition from industrial pollution. In order to examine the effects of increasing atmospheric N deposition on C cycling in northern peatlands, a long-term fertilization experiment was established at Mer Bleue Bog, Ontario, Canada in 2000. The experiment adds N and N+PK at levels 5, 10, and 20 times higher than ambient atmospheric N levels. Significant changes in aboveground plant community dynamics have been found within the experiment; however previous work examining belowground microbial dynamics has been limited (Larmola et. al. 2013). In order to better understand the effect of nutrient addition on microbial communities, I added different plant and bog water substrates to surface peat samples within Mer Bleue bog and examined CO2 production potential with 24-hour incubations. Additionally, I examined substrate biodegradability characteristics through a series of 5-day incubations. I hypothesized that (1) microbial CO2 respiration would increase in fertilized treatments, (2) substrate addition would increase microbial CO2 respiration across all treatments, (3) there would be a significant interaction between substrate and treatment, and that (4) rates of biodegradability amongst substrates would vary significantly. After 13 years of fertilization, results show that there is not a significant difference in rates of microbial CO2 respiration from peat among treatments, but respiration does increase significantly with the addition of substrate. Specifically, plant-based substrates induced significantly higher rates of microbial respiration than bog-water substrates, with birch substrates inducing the highest rates of respiration. Within the four plant-based substrates, a strong trend indicated that birch substrates induced higher respiration than Sphagnum substrates, with leatherleaf and cottongrass producing similar intermediary rates. Furthermore, there was not a significant relationship between substrate and treatment, and rates of biodegradability did not differ significantly among substrates. These results suggest that substrate availability and quality play a significant role in microbial CO2 respiration. In addition, they suggest that plant functional type (PFT) is a major determinant of microbial CO2 production potential. An increase in microbial respiration rates in higher nutrient treatments with the addition of substrate suggests that microbial communities have changed in response to fertilization—either via increasing biomass or a change in functional group.

Sabrina Livne-Kennedy'14

During the summer of 2013, I was a research assistant with another Mount Holyoke student Emma Singer, collaborating with researchers and PhD students in the Geography Department at McGill University in Montreal, Quebec. We had the opportunity to work with Dr. Jill Bubier, Dr. Tuula Larmola, and PhD student Tanja Zivkovic. Emma and I mainly conducted laboratory experiments in a soil science lab at McGill University as well as periodic sampling at our field site, Mer Bleue Bog in Ottawa, Ontario. In addition to measuring microbial production of CO2 in peat extracted from a long-term fertilization experiment, I conducted independent research on a project focusing on nitrogen (N2) fixation. I continued my research as an independent study at Mount Holyoke the following fall semester summarized below.

Wetlands, and especially peatlands, are generally nitrogen limited. Biological N2 fixation can therefore play a major role in the nitrogen cycles of these ecosystems. The cyanobacteria and other bacterial groups living among Sphagnum mosses at the Mer Bleue bog in Ottawa, Ontario, Canada perform N2 fixation. I conducted two studies to understand N2 fixation rates among different dominant moss communities at Mer Bleue bog using acetylene reduction assay (ARA). The species versus environment study analyzed how the dominant moss species (S. magellanicum, S. capillifolium, Polytrichum strictum, and all three species mixed together) differed in N2 fixation rates based on their moisture content and their location (bog hummock vs. bog hollow). There was a significant trend of higher moisture content per dry weight correlated with higher ARA rates (nmol/g/day) in the first week of the species versus environment study, but not in the second week. Overall, this study showed a trend of higher ARA rates (nmol/g/day) in the hollow plot than in the hummock plot for all four different moss assemblages. The Sphagnum pigmentation study was similar to the previous study but focused on the different pigments (green vs. red) of S. capillifolium and how they affected N2 fixation rates. This study had some interesting trends but there were no significant differences in ARA rates among species and more specifically between the green and red pigmentation of S. capillifolium.

Vi N. T. Bui '13

Photosynthetic performance of Chamedaphne caclyculata after twelve years of Nutrient fertilization at Mer Bleue Bog, Ontario, Canada

Peatlands are important ecosystems in the global carbon cycle, as they store 30% of the world’s soil carbon. However, combustion of fossil fuels and fertilizer manufacture have increased reactive nitrogen in the form of nitrate and ammonium, which are limiting nutrients in many ecosystems including peatlands, and can cause cascading effects on these ecosystems. The fertilization experiment at Mer Bleue Bog in Ontario was set up in 2000 to investigate the impact of nutrient addition, including nitrogen (N), phosphorus (P) and potassium (K), on the carbon (C) sink function of this peatland.

This study examined the effect of nutrient addition on the dominant ericaceous shrub at the bog, leatherleaf (Chamaedaphne calyculata), after twelve years of exposure to five and twenty times the growing season ambient wet N deposition rates with and without P and K. Leaf-level CO2 gas exchange and chlorophyll fluorescence, an indicator of plant stress in terms of light harvesting capacity, of both current-year and previous-year leaves were measured using a leaf chamber and Licor 6400 infrared gas analyzer to investigate the photosynthetic performance of this shrub. Additionally, from each leaf, maximum electron transport rate (Jmax) and Rubisco carboxylation rate (Vcmax) were derived from the CO2 response curve, and chlorophyll content analyzed.

After twelve years of fertilization, nutrients were still being invested in chlorophyll and Rubisco, which are the main sinks of nutrients, especially N. Chlorophyll content also reflected differences between old and new leaves due to nutrient transport and light availability. Chlorophyll fluorescence ratios of all measured leaves were within the range of healthy leaves (0.75 to 0.83); therefore, there is no sign of plant stress in terms of maximum light harvesting capacity. New leaves had a significantly lower light harvesting capacity than old leaves due to physiological immaturity. Investment of nutrients both in light and dark reactions of photosynthesis did not translate into higher maximum gross photosynthetic rate (Pmax); in fact, net assimilation rates (Amax) were lowest in the highest nutrient treatments. The decreasing trend in Amax with increased nutrients was due to increased dark respiration along the treatment gradient, and this trend mirrored the response pattern of net ecosystem CO2 exchange, ecosystem respiration and gross ecosystem photosynthesis to nutrient addition. Thus, the shrub, in response to fertilization, contributes to a weaker C sink in the bog through increased respiration and unchanged photosynthesis.

Maria Paula Mugnani '13

Ecosystem-vegetation dynamics in Sub-Arctic Stordalen Mire, Sweden

Increased global temperatures have contributed to the thaw of permafrost and a subsequent atmospheric production and release of methane (CH4) from subarctic ecosystems. Other climate change-related developments, including seasonal abnormalities, might alter vegetation diversity and abundance. I measured vegetation composition and percent cover-based abundance in five distinct ecosystems two hundred kilometers north of the Arctic Circle in Stordalen Mire (68° 21’ N, 19° 03’ E), a subarctic peatland near Abisko, Sweden. These five ecosystems included palsa, Eriophorum-dominated fen, Sphagnum-dominated peatland, lakeshore edge and lakeside heath. The mire is an area of discontinuous permafrost populated by micro-ecosystems that vary in plant species and soil nutrients that provide beneficial services to support a range of life forms including rodents, birds, insects and reindeer.
In the vegetation data analysis, lakeside heath had the highest mean species quantity, evenness and diversity based on the Shannon Diversity Index. It had a mean of nine species and a 1.80 diversity value, followed by lakeshore edge, palsa, Sphagnum peatland and Eriophorum fen. High lakeside heath diversity can be associated with its high ammonium concentrations and medium water table depth, which created a variety of niches for high growth form diversity. In both species diversity and mean species quantity, the other sites were significantly different from each other except between palsa and lakeshore edge and Eriophorum Fen and Sphagnum peatland (p<0.05).
In soils results, the mean total carbon decreased along the moisture gradient, with Eriophorum fen the lowest and dry palsa the highest. The high carbon in the palsas can be attributed to the presence of permafrost, which maintains accumulated organic matter frozen with minimal decomposition. Sites did not differ in C:N ratio except for Sphagnum peatland, which had the highest ratio at 68:1. This large quantity of carbon could due to waterlogged conditions or slow rates of nitrogen mineralization due to slow decomposition.

Vegetation composition varied between ecosystems, especially in the palsas that supported mostly low-lying dry-tolerant species, not found in the wetter, anaerobic ecosystems. The wet, less diverse ecosystems contained several highly dominant species observed to be moving into drier sites. The results, combined with recent studies indicating permafrost thaw, suggest changing mire dynamics to wetter and more homogenous in vegetation, likely reducing total carbon and the lakeside heath niches and anaerobic-intolerant species. Thawing permafrost would promote higher CH4 emissions owing to wetter conditions and dominance of sedges that facilitate CH4 emission through vascular plant transport. In the future, vegetation shifts and soil characteristics within subarctic peatlands like Stordalen Mire can be used as indicators of changing ecosystem dynamics in thawing permafrost and methane emissions with possible climate impacts.

Cori Magnusson '13

Effects of nutrient addition on C. calyculata growth rate, leaf longevity, and leaf production

The purpose of this study is to investigate the phenology of Chamaedaphe calyculata on a bog in southern Canada in order to determine if the growth rate of the plant, leaf longevity and leaf production was influenced by fertilization. Hypotheses relating to the research questions are as follows: 1. Average plant growth would be faster in the fertilized plots (20NPK and 20N) than the unfertilized plots due to higher nutrient availability; 2. Plants in unfertilized plots would hold onto their old leaves longer into the growing season due to having less nutrient availability;3. Plants in fertilized plots would grow more new leaves due to higher nutrient availability. Results from this study show average plant growth was significant, leaf longevity was significant, and leaf production was not significant.

Emily J. Eshleman '13

The effects of land use an dnovel stream pollutants on extracellurlar enzyme activity in Baltimore County, Maryland urban streams

Urban streams are characterized by their impervious surface cover, lack of riparian vegetation,and pollutant loading. Studies have shown that urban streams uniquely cycle nutrients and pollutants leading to degradation of water quality throughout the watershed. The goal of my study was to understand the differences in aquatic ecosystem health and resilience between rural and urban streams in order to develop more effective ecological restoration practices.
Previous studies within Baltimore County, Maryland, have found pollutants such as the antimicrobial triclocarban and the poly-aromatic hydrocarbons (PAH) phenanthrene, fluoranthene, and benzo(a)pyrene in the urban streams. Microbes assimilate dissolved organic matter (DOM) using extracellular enzymes, which have been studied as an indicator of microbial function. I measured extracellular enzyme activity (EEA) in the water of two rural and two urban streams focusing on the EEA of three enzymes, phosphatase (PHOS), beta-glucosidase (BG), and leucine amino peptidase (LAP) to account for phosphorus, carbon and nitrogen substrates, respectively, in the DOM. For each site I measured EEA under ambient conditions and with four pollutant treatments at low and high doses.
Overall, the EEA for the untreated water did not show consistent similarities or differences between the rural and urban sites, which were categorized by amount of impervious surface cover in the watershed. This suggests that additional site characteristics, such as hydrologic base flow, temperature or density of septic systems, might be important for determining land use effects on water quality and microbial function.

With the addition of pollutant treatments, I hypothesized that urban sites would have higher EEA than rural sites because the microbial communities would have adapted to the degraded conditions; but that all sites would decrease in enzyme activity as dose of the treatment increased. However, the results showed the rural sites generally had higher activity than the urban sites, and that neither the urban nor the rural sites consistently declined in EEA with an increase in treatment dose. This suggests that greater microbial biodiversity and competition in the rural sites may be as important as the assimilation period of the microbial community in the more degraded sites. In contrast to the PHOS and BG enzyme activity, LAP activity was not significantly affected by any of the treatments or doses, suggesting that the nitrogen sources in these sites may primarily be found in the soil and sediment rather than dissolved as gases in water. These results demonstrate that EEA is an important, but complex tool for understanding microbial function in an ecosystem.

Bethany Nagid '12

I was given the opportunity to work with Dr. Tuula Larmola and fellow student Vi Bui at Mer Bleue Bog in Ontario, Canada. While my work as a part of professor Bubier's lab has only spanned one summer, I began independent research to better understand species composition changes as correlated with chemical fertilization of bog plots. Understanding these shifts in species composition may, in time, help us better understand growth patterns during times of varying nutrient types and levels, as well as the area's function with regards to carbon sequestration.

Bianca Young '11

The Role of Sphagnum Mosses in Methane Oxidation in a Temperate Fen

Peatlands are a global source of atmospheric methane (CH4); however oxidation of CH4 by methanotrophic microbes residing in the moss layer provides the potential for mitigation of CH4 emissions (Bubier and Moore, 1994). Determining the controls on CH4 oxidation in Sphagnum mosses will increase our understanding of CH4 dynamics in wetlands, and will allow a better understanding of the influence of climate change on these ecosystems. Studies have shown that the primary controls of oxidation are environmental, i.e. water table and temperature; however little is known about the role of moss species in controlling CH4 oxidation (Basiliko et al., 2004; Larmola et al., 2010).
A Sphagnum transplantation experiment was conducted at Sallie’s Fen, a temperate peatland in Barrington, New Hampshire, to observe the effect of environmental conditions on CH4 oxidation rates in Sphagnum fallax and Sphagnum magellanicum and to investigate the relative importance of species versus environment in controlling CH4 oxidation. The mosses were sampled four times over a 28 day period. Triplicate control and transplanted samples were incubated in the lab at two concentrations of CH4, 1000 parts per million (ppm; limiting to low affinity methanotrophs) and 10,000 ppm (non-limiting). Averages of the potential CH4 oxidation of all four sampling days show that when CH4 is limiting there is an interaction between Sphagnum species and the environment. The effect of environment on the microbes of S. magellanicum was evident when host rates of potential CH4 oxidation (0.4 mmol g dw-1 d-1 s.e. 0.10) in the hummock increased significantly (p < 0.05) upon transplantation to the hollow (1.8 mmol g dw-1 d-1 s.e. 0.38). The Sphagnum species effect is supported by the response of S. fallax, which, after transplantation, exhibited potential CH4 oxidation rates that were not significantly different (p > 0.05) from the host rates (1.5 mmol g dw-1 d-1 s.e. 0.20) in the hollow. There was no difference between the sites or species when CH4 was not limiting (p > 0.05). These results indicate that there is a joint control of the environment and Sphagnum species on CH4 oxidation; however the particularly dry summer may have confounded the results.

Chrissy Kobyljanec '11

Microbial respiration and substrate utilization across a nutrient gradient at Mer Bleue Bog

Atmospheric nitrogen (N) deposition is increasing in North America and Europe owing to fossil fuel burning and agricultural practices. This study was part of a long-term investigation at Mer Bleue Bog, Ontario, Canada, to test whether peatlands, which are typically N-limited, will become stronger or weaker carbon (C) sinks. I measured the CO2 production potential from microbial communities under different substrate additions in peat samples harvested from an ombrotrophic bog that has been fertilized for the past 9 years. Fertilization treatments include control, 5 N+PK, 10 N+PK, and 20 N+PK, where the constants represent how many times higher the added N is from ambient N flux (0.8 g N m-2 yr-1), and PK is added at a constant rate across treatments (6.3 g P m-2 yr-1 and 5.0 g K m-2 yr-1). Substrates included both synthetic (p-coumaric acid, lignin, glucose, cellulose, and amino acids) and plant-derived (Chamaedaphne, Ledum, Vaccinium, Sphagnum, Eriophorum, and a Chamaedaphne/ Vaccinium leachate) carbon compounds. The CO2 production did not increase across the 4 fertilization treatments under control conditions (i.e. no substrates added). However, the addition of substrates increased respiration rates 3, 17, 30, and 23 times over the controls across fertilization treatments. Synthetic C substrates induced lower respiration rates than substrates made from the dominant plant species at the site. Significant preferential utilization of substrates was restricted to amino acids, which was higher in the fertilized plots compared to control, and p-coumaric acid, which was lower in the control than the fertilized plots. These results indicate that when labile C substrates are available, CO2 production potential will increase along a nutrient gradient, potentially increasing CO2 emissions to the atmosphere. Microbial communities appear to respond similarly to substrate additions regardless of fertilization levels, which suggests that they will adapt well to vegetation changes that may take place due to increased nutrient deposition.

Published paper:

Larmola^, T., J.L. Bubier, C. Kobyljanec*, N. Basiliko, S. Juutinen^, E. Humphreys, M. Preston^, T.R. Moore. 2013. Vegetation feedbacks of nutrient deposition lead to a weaker carbon sink in an ombrotrophic bog, Global Change Biology, doi: 10.1111/gcb.12328. [Full text]

Genevieve Noyce '09

THE ROLE OF SEDGES IN METHANE EMISSIONS FROM A TEMPERATE FEN

Peatlands are the largest single natural source of methane (CH4) to the atmosphere, which has the next largest radiative forcing potential of any greenhouse gas after CO2. Sedges (e.g. Carex spp.) play a critical role in the production, oxidation, and emission of CH4 from these systems. This study examined the effect of Carex rostrata on belowground methane storage and net methane flux from a temperate fen through a vegetation removal experiment. We also studied the effect of sedge removal on responses to environmental variables. During the summer of 2008 we established an experiment in Sallie's Fen, Barrington, NH where we removed sedges and sealed the stems in three replicate experimental plots, while three control plots were kept intact. Methane fluxes, pore water CH4 concentrations, and C. rostrata biomass, along with temperature and water table depth, were measured throughout the growing season.
We observed a strong positive correlation between seasonal averages of C. rostrata biomass and CH4 fluxes. Methane emissions increased by 30% throughout the summer in the control plots, but decreased by 22% in the experimental plots. In addition, the average 18 cm (C. rostrata rooting depth) pore water CH4 concentrations in the clipped plots were significantly higher than in the unclipped plots, suggesting increased methanogenesis, decreased methane transport or oxidation, or a combination of any of the above. The 60 cm pore water CH4, which is well below the rooting zone, was not affected by clipping. This suggests that Carex are very influential in methane dynamics.

Published paper:

Noyce^, G., R.K.Varner, and J.L. Bubier. 2014. Effect of Carex rostrata on seasonal and interannual variability in peatland CH4 emissions. J. Geophys Res. Biogeosciences, 119, 1-11, doi:10.1002/2013JG002474 [Full text]

Rose Smith '09

Effects of Nitrogen, Phosphorous, and Potassium (N and NPK) Fertilization on Leaf Morphology and Photosynthesis for Evergreen and Deciduous Shrubs in a Boreal Peatland
Rose M Smith 1, Sari Juutinen 1, Jill L. Bubier 1, Tim R. Moore 2
1 Environmental Studies Program Mount Holyoke College, South Hadley, MA, 01075
2 Department of Geography, McGill University, Montreal, Quebec H3A 2K6

Abstract

Atmospheric nitrogen deposition may have serious implications for the species composition, primary production, and carbon dioxide exchange in northern peatlands. Our previous results after five years of fertilization at the Mer Bleue Bog indicated that high N (+PK) supply may reduce net ecosystem carbon uptake as a result of reductions in ecosystem gross photosynthesis (Pg). The present study examines possible mechanisms for this photosynthetic draw down by measuring leaf photosynthesis rates and morphology of the three dominant dwarf ericaceous shrubs including the deciduous Vaccinium myrtilloides, and evergreen Chamadaphane calyculata and Ledum groenlandicum. Treatments included low (1.6g N y-1) and high (6.4g N y-1) N with and without PK. We measured leaf photosynthesis for individual leaves and calculated Vcmax in order to estimate the effects of fertilization on Rubisco enzyme activity. Morphometric measurements included length, width, thickness, area, mass and specific leaf area (SLA, cm2/g).
Species responded differently to fertilization in Vcmax as well as morphology. Ledum groenlandicum had significantly higher Vcmax in low N and low NPK but not high N or high NPK treatments. V. myrtilloides had significantly lower Vcmax in low N plots, but no response in the other treatments. C. calyculata did not respond significantly to treatment. Of the three species, V. myrtilloides had the lowest Vcmax values in all treatments. Differences between Vcmax values for these species were smaller in high-N and high NPK plots than in controls. Morphology of L. groenlandicum and V. myrtilloides leaves showed significant responses to treatments. V. myrtilloides increased in leaf area in low-NPK treatments and L. groenlandicum increased in SLA in low NPK treatments. Treatments did not affect C. calyculata leaf morphology. The differences in species responses may be explained by leaf nitrogen concentrations. None of the species measured showed significant increases in Vcmax in the high N or NPK treatments, but moderate N addition might increase photosynthetic capacity of L. groenlandicum. Preliminary results indicate that species at Mer Bleue may be nitrogen-saturated with high-N and NPK treatments.

Published paper:

Bubier, J. R. Smith*, S. Juutinen^, T. Moore, R. Minocha, S. Long, S. Minocha. 2011. Effects of nutrient addition on leaf chemistry, morphology, and photosynthetic capacity of three bog shrubs. Oecologia, 167:355–368, DOI 10.1007/s00442-011-1998-9.[Full text]

Paliza Shrestha '10

Paliza had been working with Professor Jill Bubier during summer of 2008 on her research at Mer Blue bog, Ottawa, Canada. She measured net CO2 exchange to investigate the effects of nutrient addition on photosynthesis and ecosystem respiration in the long-term fertilization plots, and quantified the above ground biomass among the control and nutrient treatment plot and measured the net CO2 exchange and litter decomposition.

Elizabeth Szarkowski '08

Elizabeth had been working with Professor Jill Bubier doing independent research at Mount Holyoke College since spring of 2007. Over the summer of 2007 she worked with Dr. Ruth Varner at the University of New Hampshire in Sallie’s Fen, a poor fen near UNH. There she took CO2 and CH4 gas exchange measurements, phenology measurements, and percent coverage data to form a vegetation map of the Fen. In the fall of 2007, Libby used the percent coverage data to create a vegetation map of Sallie’s Fen and compared it to a similar map created in 1995. Her future projects will include multivariate analysis of the vegetation data.

Lisa Brunie'06

Plant Response to Fertilization at a Cool Temperate Peatland
Abstract of the Paper Presented to the Faculty of Mount Holyoke College in Partial Fulfillment of the Requirements for the Degree of Bachelors of Arts with Honor (prepared under the direction of Professor Jill Bubier), May 2006.

   Peatlands are nutrient-limited ecosystems. Human activities are causing an increase in nitrogen (N) deposition, which may lead to fertilization of bogs and alter vascular plant densities and biomass. N deposition affects ecosystem function, and potentially alters the system’s ability to sequester carbon. In the summer of 2005 we measured this effect in an ombrotrophic bog, Mer Bleue, near Ottawa, Canada with a fertilization experiment established in 2000.
   We measured leaf-level CO2 exchange with a LI-6400 portable photosynthesis system. We used these data to calculate the maximum rate of photosynthetic capacity (Vmax) between the high fertilization (20NPK, 20 times the ambient summer N deposition, or 6.4 g N m-2 as NH4NO3, and 6.3 g P m-2, 5.0 g K m-2 as KH2PO4) treatment plots and control plots. We quantified above ground vascular plant biomass through non-destructive measurements of stem height and stem number within the 0.6 x 0.6m quadrat where we measured net ecosystem CO2 exchange. We destructively measured shrub biomass, number of leaves, leaf size, number of stems, C: N ratio of the leaves, and stem length for clipped plant samples collected from outside the CO2 measurement quadrats. We also measured leaf area index, the mass of litter and litter cover with in the 0.6x 0.6m quadrats.
   After five years of nutrient addition, above ground biomass of shrubs significantly increased between the control and high fertilization plots (20NPK). This pattern is perhaps explained by the increase in both stem length and leaf area with the fertilizer addition. A decrease in C: N ratio suggests that plants in the fertilizer treatments are taking up the added nutrients. However, an important difference was found in the leaf level photosynthesis data, which showed a significant decrease in Vmax between the control and the high fertilization treatment. These results have important implications for the ecosystem response to environmental changes. The increase in biomass and litter production of vascular plants will have effects on carbon storage as a result of the decomposability of this matter. The increase in biomass may be offset by decreases in leaf-level photosynthesis, potentially altering the carbon uptake within the system.

Gareth Crosby'05

Gareth had been working with advisor Jill Bubier for the two summers on climate change research at Mere Bleue Bog in Ottawa Canada. With data taken from the past two summers she is working on a thesis on peatland vegetation patterns in response to water table gradient changes and the implications of climatic change on methane emissions. It has been found that some species actually aid in methane release from bogs. Since methane is an important greenhouse gas, a loss of a certain type of vegetation could have an important impact on methane accumulation in the atmosphere.

Published paper:

Bubier, J., T. Moore, and G. Crosby*. 2006. Fine-scale vegetation distribution in a cool temperate peatland. Can. J. Bot., 84, 910-923. [Full text]

Claire Treat'05

Claire with Dr. Jill Bubier (MHC) and Dr. Ruth Varner (University of New Hampshire) presented "Variations in Methane Emissions and Net Ecosystem Exchange in a Temperate Peatland, 2000-2004" in Washington, DC in 2004 meeting, for the Research and Discover Program, at NASA-Goddard Space Flight
Center.
Abstract: Global climate change has the potential to greatly affect carbon storage in peatlands, which store about 30% of the pool of global soil carbon. Increasing temperature may cause peatlands to function either as a sink or a source of C to the atmosphere. Whether the ecosystem will store or lose carbon is uncertain: climate change may lead to increased plant productivity and C storage, while it could also lead to increased respiration and C loss as both CO2 and methane. This ecosystem dynamic can be measured by net ecosystem CO2 exchange (NEE), which is the sum of two components: photosynthesis and respiration. This study examined the seasonal and interannual variations in NEE and methane emissions and possible links between the two processes in an attempt to determine the environmental controls responsible for the variations. This past summer, we collected and used NEE, methane fluxes, water table level, and meteorological data from the summer (1 May-31 August) for 2000-04, we were able to determine seasonal and interannual patterns for NEE, photosynthesis, respiration, and methane emissions. We observed that photosynthesis and respiration values become larger as the summer progressed. Methane fluxes also became greater in magnitude and variability due to higher peat temperatures and episodic events as the season progressed. Additionally, methane emissions had a positive relationship with photosynthesis and respiration, suggesting that plants exert control over methane emissions and that similar environmental factors control both respiration and methane production.

Recently published paper:

Treat*, C., J. Bubier, R. Varner and P. Crill. 2007. Time scale dependence of environmental and plant-mediated controls on CH4 flux in a temperate fen. Journal of Geophysical Research-Biogeosciences,112, G01014,1-9, doi:10.1029/2006JG000210. [Full text]

Kathryn McKain'05

Kathryn had been working with thesis advisor: Dr. Steve Wofsy (Harvard University), MHC advisor: Dr. Jill Bubier, Mount Holyoke College and project mentor: Elizabeth Hammond-Pyle (Harvard University) on "Carbon Accumulation at the Harvard Forest: A Comparison of Measurement Methods and an Investigation of Spatial and Temporal Trends".
Although an abundance of data about local forest carbon cycling dynamics exists from the Prospect Hill tract, the relevance of this data depends on our ability to scale individual sites to the larger forested region. From 2000-2002, the Big Foot Project monitored an array of ecological measurement plots centered on the EMS tower over a 25 km2 area with the purpose of linking the ground-based measurements to Landsat ETM+ data and validating MODLand science products. The continued monitoring of the Big Foot plots by the Wofsy research group will provide a valuable opportunity to increase the scale of the Wofsy group’s area of study. However, an initial comparison of the Big Foot and Wofsy plots revealed that while the Wofsy plots yielded an average of 108 ± 33 MgC/ha as of 2002, the Big Foot plots yielded an average of 73± 26 MgC/ha. This discrepancy could have resulted from the different measurement methods employed by the two groups, or may reflect true spatial differences in forest composition. Whereas the Wofsy group uses fixed-radius plots, the Big Foot project used a prism method and variable-radius plots. A resurvey of the Big Foot plots using both fixed and variable radius plots has allowed for an additional comparison of the two methods. Preliminary results reveal that both methods yield equivalent biomass figures, numbers which also correspond with that calculated from the Prospect Hill tract, but not with that of the original Big Foot survey. Further investigation of the 2004 Big Foot data, including the incorporation of mortality and recruitment, will allow for the better use of existing data and thus for regional extrapolation.