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Research

Overview:

My research group and I investigate the biogeochemistry of both aquatic and terrestrial ecosystems. Biogeochemistry is the study of the biological processes that impact the geochemistry of the environment. Specifically, we are interested in how different aspects of environmental change, such as nutrient pollution, climate warming, vegetation community alteration and elevated CO2, impact the cycling of organic matter and nutrients in ecosystems ranging from mangrove estuaries to subArctic forests. Much of our work involves the use of stable isotopes to track elements as they cycle through the environment. Our work has relevance to understanding water resources as well as the impact of environmental change on global elemental cycles which in turn impact our climate.

Current Research Projects

Investigating the source, composition and cycling of dissolved organic matter in a large boreal watershed

Boreal surface waters are typically high in dissolved organic matter due to large contribution of organic matter from forest soils and peatlands. Recently there has been growing evidence for increases in dissolved organic carbon export from large rivers in high latitude or boreal regions. Hypotheses for these trends include soil processes and responses to environment change including changes in climate, atmospheric deposition, and land use.

To get a better handle on the factors regulating dissolved organic matter (DOM) export from the landscape we are investigating how the composition of this reservoir is related to its watershed source and microbial and photochemical processing. We have focused our research efforts on the 9500 km2 Humber River watershed located in western Newfoundland. This region offers an excellent array of watersheds differing in landcover, isolated from atmospheric deposition, allowing us to (1) assess the relationship between catchment composition and DOM composition and (2) determine how DOM cycling and fate varies across the landscape. This array of catchments provides us with a range of sites to assess how change in landcover due to climate change, such as deforestation due to insect infestation, reduction in peatlands or shifts in forest composition, may impact the transport and cycling of DOM and nutrients in this boreal watershed. The landscape patterns within this watershed were investigated in collaboration with Dr. Yolanda Weirsma, a landscape ecology in the Department of Biological Sciences at MUN. Alexandra Roulliard, an NSERC USRA student conducted an extensive analysis of the forestry, soils, geologic, and hydrologic database for this watershed enabling investigation at the small subcatchment scale. Her efforts have provided us with a unique set of stream sites representing end-member headwater streams in terms of the vegetation composition (organic matter sources) of their watersheds.

Within the context of the variation in watershed landcover and type we are investigating the role of microbial and photochemical processing in the cycling and fate of DOM, how nutrient limitation impacts microbial activity, function and use of substrates in these headwater boreal streams. Investigations will include identification of DOM sources using stable isotopes, in situ mesocosm experiments to track carbon and nutrient cycling through biofilm communities using isotopic labeling approaches, and bioassay experiments to investigate biofilm utilization of DOM. Earth Sciences graduate student Doreen Franke is currently investigating variations in microbial and photochemical lability of DOM in this watershed. Jennifer Bonnell, Environmental Sciences graduate student, is currently investigating the chemical composition of DOM and how it relates to watershed composition and stream microbial processes in these headwater streams. Jennifer’s more detailed study of the chemical composition of DOM is being conducted in collaboration with Dr. Christina Bottaro in the Department of Chemistry at MUN.

The impact of climate change on boreal forest soil organic matter: Exploiting the Newfoundland and Labrador Boreal Ecosystem Latitudinal Transect (NL-BELT)

This is a large collaborative research program involving international collaborators Drs. Sharon Billings, Jianwei Li (University of Kansas), Dr. Martin Moroni (Tasmania Forestry), Dr. Ronald Benner (University of South Carolina), Drs. Marilyn Fogel and Roxane Bowden (Carnegie Institute of Washington), Dr. Chad Lane (MUN), and Dr. Kate Edwards (Canadian Forest Service) and researchers and staff of the Newfoundland and Labrador Forest Service. This program aims to combine our ongoing research efforts on dissolved and soil organic matter cycling in boreal watersheds in Newfoundland and Labrador in an effort to determine how soil organic matter reservoirs are likely to change with climate in this region. Specific aims of this research include:

1. Determine the variation in the temperature sensitivity of microbial processing and soil organic matter destabilization along the NL-BELT. Laboratory warming experiments and in situ reciprocal exchange experiments have been completed and established, respectively. These are being used to specifically investigate the impact of warming on soil respiration, enzyme activities, and changes in the composition of active microbial groups in these boreal soils. Current results indicate cooler sites are more sensitive to soil organic carbon losses to CO2 via microbial respiration and that these increased losses follow shifts toward increased oxidative enzyme fungal activity.

2. Assess the extent of soil organic matter processing along NL-BELT by employing a combination of isotopic and geochemical biomarkers. The variation in soil organic matter composition will provide insight into relative differences in soil organic matter processing with mean annual temperature along this transect. These results will be compared with our laboratory experiments enabling us to determine the extent microbial processing and C loss from the soil profile via CO2, dissolved organic carbon, and organo-mineral interaction.

3. Develop watershed scale indicators for the impact of climate change on soil organic matter. This objective will be met through a chemical and isotopic study of soil-derived dissolved organic matter and headwater stream dissolved organic matter. Combining amino acid, carbohydrate, lignin, and sterol analyses with spectrophotometric and spectrfluorometric analyses will enable us to study changes in composition at both frequent and seasonal time scales. Results from the upper reaches of the headwater streams associated with our forest sites where soil investigations are being carried out will enable us to determine if stream DOM provides an indication of the variation in soil organic matter processing along this climate transect.

 

Tracing dissolved organic matter sources contributing to organohalide formation in rural Newfoundland water supplies.

The use of chlorine as a disinfectant in water supplies is common and cost effective, however, it also results in the formation of chlorinated organic compounds which are known carcinogens. This is a critical issue across Canada. In rural Newfoundland and Labrador where water supplies are primarily from surface waters, and which are typically high in dissolved organic matter content, formation of organochlorides can be an enormous problem. Tap water measurements of the two most common classes of these chlorination disinfection byproducts (DBPs), namely trihalomethanes and haloacetic acids, have revealed a significant problem in Newfoundland and Labrador. Further, investigations by the provincial government indicate that concentrations of these contaminants in tap water is not significantly correlated to dissolved organic matter (DOM) concentration. At present little is understood regarding the relationship between DOM source and composition and the formation of these contaminants. Initial efforts by Sheldon Huelin in our laboratory indicated that DBP yields may be related to drinking water supply catchment composition (vegetation cover). Graduate student Susan Hannan has been following upon this lead by specifically testing DOM derived from common watershed sources of organic matter (different forest floor litters, organic horizon soils, and peat) for its trihalomethane and haloacetic acid formation potential. Susan is currently working as a MITACS intern in conjunction with the provincial government’s Water Resources Management Division (WRMD) carrying out experiments designed to assess the role of potential watershed DOM sources in controlling DBP concentrations. Her research efforts coincide with the NL Department of Environment and Conservation’s ongoing DBP-related research and development, a component of the Multi-Barrier Strategic Action Plan used by the NL government to fulfill its commitment to providing the public with safe and clean drinking water. Results of this research will be used to expand on current corrective measures for addressing DBP issues particularly in regard to specific water treatment options, water supply location and future sampling.

 

Determining the utility of hydrogen isotopes for tracking terrestrial dissolved organic matter in the marine environment.

Terrestrial DOM is a key source of energy and nutrients for estuarine ecosystems, as it comprises approximately 60% of riverine organic matter input to marine environments. This is especially important where concentrations of riverine DOM are high, such as at boreal and arctic latitudes. The role of terrestrial DOM in regulating estuarine ecosystem processes is poorly understood in part because of difficulties in tracking terrestrial DOM in marine environments. Because of the large differences that exist between terrestrial and marine organic hydrogen isotopic signatures, graduate student Nicole DeBond is testing how well hydrogen isotopes may be used to track terrestrial DOM.

This research entails laboratory experiments on boreal terrestrial organic matter, a survey of DOM hydrogen isotope composition along salinity gradients in the Salmonier Arm and Lake Melville estuary in Newfoundland and Labrador, Canada, and the development and construction of an equilibration device that will improve the determination of hydrogen isotope values. This work is being conducted in collaboration with Dr. Penny Morrill here at MUN and Drs. Marilyn Fogel and Roxane Bowden at the Geophysical Laboratory.

Understanding the affects of changes in the quantity and quality of terrestrial DOM are of particular importance to Canada, since the vast majority of Canada’s coastline occurs in boreal and arctic biomes. Recent changes in DOM concentrations and loadings in large high-latitude rivers globally over the past two decades signify potential alteration in the terrestrial landscape due to climate change. It will be important to capture these changes in the boreal and arctic coastal regions of Canada.

Availability of boreal watershed dissolved organic matter to estuarine bacterioplankton. This work aims to further our understanding of what factors might alter the fate of riverine-derived DOM in the estuarine environment. Environmental change including climate, hydroelectric development, and nutrient enrichment has the potential to not only alter the delivery of riverine DOM but also its chemical composition, the physical and chemical environment in which it enters the estuary (availability of nutrients and light), and ultimately its fate. We need basic knowledge regarding what factors influence the fate of riverine-derived DOM (i.e. CO2 or microbial biomass) to be able to assess how estuarine productivity and coastal C-cycling will be impacted by key components of environmental change. As part of a larger project aimed at understanding the impacts of hydroelectric development on estuarine trophodynamics were are involved in research to determine the extent and factors regulating the use of riverine dissolve organic matter (DOM) in the Lake Melville estuary, Labrador. This work is being conducted in collaboration with Drs. Robin Anderson of DFO and Richard Rivkin at the Ocean Sciences Centre, MUN and Environmental Science graduate student Claire Moore-Gibbons (see photo). Both field sampling and experimentation have been conducted to directly assess: (1) the consequence of varied riverine vs. marine/estuarine derived DOM on the bacterial carbon flux (DOCàbacterioplankton), (2) how the availability of labile sources of C, N, or P limits the bacterial carbon flux, and (3) how the availability of C, N, or P impact the use riverine vs. marine/estuarine derived DOM.

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