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Taking Nitrogen By Storm: Spatial And Temporal Controls On Nitrogen Processing In A Small Reservoir, Eliza Balch

Master's Theses and Capstones

Nitrate inputs pose a threat to aquatic ecosystems, leading to eutrophication, algal blooms, and habitat loss in downstream coastal marine and estuarine habitats. Rivers and streams can attenuate nitrogen between inputs and coastal outputs, moderating ecosystem harm. While nitrogen dynamics in streams and rivers have been studied for decades, less is known about the wetlands through which they flow, namely small reservoirs. Storms can have a large influence on nitrogen processing in reservoirs through hydrologic changes and introduction of new solute sources, but are poorly understood. To understand the spatial and temporal variability of nitrogen processing in a small reservoir, …

Taking Nitrogen By Storm: Spatial And Temporal Controls On Nitrogen Processing In A Small Reservoir, Eliza Balch

Master's Theses and Capstones

Nitrate inputs pose a threat to aquatic ecosystems, leading to eutrophication, algal blooms, and habitat loss in downstream coastal marine and estuarine habitats. Rivers and streams can attenuate nitrogen between inputs and coastal outputs, moderating ecosystem harm. While nitrogen dynamics in streams and rivers have been studied for decades, less is known about the wetlands through which they flow, namely small reservoirs. Storms can have a large influence on nitrogen processing in reservoirs through hydrologic changes and introduction of new solute sources, but are poorly understood. To understand the spatial and temporal variability of nitrogen processing in a small reservoir, …

Rates And Drivers Of Nitrate Uptake In Fluvial Wetlands In Urbanizing, Coastal Watersheds, Christopher Thomas Whitney

Master's Theses and Capstones

Humans have had a substantial impact on the global nitrogen cycle, releasing large amounts of reactive nitrogen to the landscape. Watersheds have been found to remove substantial quantities of this anthropogenic nitrogen, with aquatic networks preventing much of it from reaching the coast. Within these aquatic networks, channelized streams have been studied extensively. However, in many coastal watersheds, fluvial wetlands are a large component of the aquatic network yet have not been studied as broadly as channelized reaches. As fluvial wetlands are also likely to have a sizeable impact on river network-scale nitrogen removal, a greater understanding of their effect …

Manganese Limitation As A Mechanism For Reduced Decomposition In Soils Under Long-Term Atmospheric Nitrogen Deposition, Emily D. Whalen

Master's Theses and Capstones

Long-term atmospheric nitrogen (N) deposition has been shown to reduce leaf litter and lignin decomposition in forest soils, leading to an accumulation of soil carbon. Reduced decomposition has been accompanied by altered structure and function of fungal communities, the primary decomposers in forest ecosystems; however, a mechanistic understanding of fungal responses to chronic N enrichment is lacking. A reduction in soil and litter manganese (Mn) concentrations under N enrichment (i.e., Mn limitation) may explain these observations, because Mn is a cofactor and regulator of lignin-decay enzymes produced by fungi. We conducted a 6-month incubation study to evaluate the effect of …

A Physiocratic Systems Framework For Open Source Agricultural Research And Development, Dorn Cox

Doctoral Dissertations

This dissertation presents a new participatory approach to agricultural research and development. It surveys the biological, sociological, economic, and technical landscape and proposes a framework for adaptive management based on the 18th century Physiocratic school of land-based economics. Industrial specialization and heavy emphasis on deductive approaches to science have contributed to the disconnection of large portions of the population from natural systems. Conventional agriculture and agricultural research methods following this pattern have created expensive social, environmental, and economic external costs, while adaptive management and resilient agricultural systems have been hindered by the cost and complexity of quantifying environmental services. However, …

Unraveling Depositional And Diagenetic Signals In Magnetic Susceptibility In Methane-Bearing Sediments Along The Indian, Cascadia, And Japanese Margins, Stephen C. Phillips

Doctoral Dissertations

Magnetic susceptibility is a bulk measure that reveals variation in ferromagnetic mineral content. High-resolution measurement of magnetic susceptibility in ocean drilling records reveals variability that can be attributed to primary depositional processes and/or secondary diagenetic processes that occur after deposition. Each chapter of my dissertation investigates magnetic susceptibility records along with geochemical, mineralogical, and rock magnetic techniques in methane-bearing marine sediments along the Indian, Cascadia, and Japanese margins. The overall goal of this work is to improve the understanding of the effects of detrital and biogeochemical processes on magnetic mineralogy, and thus magnetic susceptibility, in these continental margin marine environments. …

Remote Sensing Of Foliar Nitrogen In Cultivated Grasslands Of Human Dominated Landscapes, Paul Adam Pellissier

Master's Theses and Capstones

Foliar nitrogen (N) concentration of plant canopies plays a central role in a number of important ecosystem processes and continues to be an active subject in the field of remote sensing. Previous efforts to estimate foliar N at the landscape scale have primarily focused on intact forests and grasslands using aircraft imaging spectrometry and various techniques of statistical calibration and modeling. The present study was designed to extend this work by examining the potential to estimate the foliar N concentration of residential, agricultural and other cultivated grassland areas within a suburbanizing watershed. In conjunction with ground-based vegetation sampling, we developed …

Parameterization Of Transient Storage And Nutrient Retention In Coastal New England Wetlands, Sophie Wilderotter

Master's Theses and Capstones

Wetlands may play an important role in the removal of nutrients from river networks. In order to better understand this process, field observations for eight wetland-dominated reaches in coastal Massachusetts and New Hampshire were parameterized for transient storage and nutrient uptake rate constants. Transient storage was observed in all study wetlands, but the amount of storage and how connected the storage areas were to the wetland channel were not easily related to wetland physical characteristics: including wetland length, wetland width, wetland area, sinuosity, and length-to-width ratios, depth of the off-channel area, width of the off-channel area, cross-sectional area of the …

Quantifying The Impact Of Urbanization On N And P Inputs, Transformations, Removal And Fluxes In Watersheds Draining To The Plum Island Estuary, Nathaniel Burr Morse

Doctoral Dissertations

A five-fold global urban population increase over the last century is driving global land use change and causing coastal eutrophication and dead zones. This dissertation was designed to better understand how suburbanization in the Ipswich and Parker River watersheds, the two major rivers draining to the Plum Island Estuary, affects nutrient loading the Plum Island Estuary. I used an almost 17-year long-term nutrient record to test whether ongoing watershed suburbanization has affected net fluxes of nutrients to the Plum Island Estuary over the study period. Additionally, I paired this long-term study with spatial sampling of headwater watersheds across a range …

Mechanisms Of Nutrient Limitation And Nutrient Acquisition In Managed And Unmanaged Forest Ecosystems, Matthew A. Vadeboncoeur

Doctoral Dissertations

Understanding the interactions between global change, human and natural disturbances, and other factors on biogeochemical processes in forests is necessary to ensure the sustainability of forest management. Here I report the results of several investigations into nutrient acquisition processes in the forests of New Hampshire. I begin with a meta-analysis of fertilization studies showing that phosphorus (P) and calcium (Ca) as well as nitrogen (N) may limit primary production in deciduous forests of the region. Because these limiting nutrients are all removed from the ecosystem when trees are harvested, I compared nutrient budgets under a range of harvesting scenarios with …

Modeling Long-Term Carbon Accumulation Of Tropical Peat Swamp Forest Ecosystems, Sofyan Kurnianto

Master's Theses and Capstones

Peatlands play an important role in the global climate system and carbon cycle; their large carbon stocks could be released to the atmosphere due to climate change or disturbance, resulting in increased climate forcing. I modified the Holocene Peat Model (HPM), a process-based model coupling water and carbon balance for simulating carbon dynamic over millennia, to be applicable for tropical peatlands.

HPMTrop outputs are generally consistent with the field observations from Indonesia. The simulated long-term carbon accumulation rate for coastal and inland peatlands were 0.63 and 0.26 Mg C ha-1 y -1, and the resulting peat carbon stocks at the …

Controls On Variability Of Dissolved Greenhouse Gas Concentration And Emissions From Small Streams In Southeastern New Hampshire, Jason Baillio

Master's Theses and Capstones

Small streams often present the first opportunity for dissolved greenhouse gases to exchange with the atmosphere and can be potential hot spots for evasion. In this study three streams in southeastern New Hampshire representing differing landuse were monitored for emissions of nitrous oxide, methane, and carbon dioxide. Average emission rates of N2O varied from -84 mug N m-2 day-1 to 2,561 mug N m-2 day-1 and correlated strongly with NO 3- concentration. One stream, Rum Brook, was found to be a net sink for N2O from the atmosphere. Methane emissions varied from 1.1 mg C m-2 day-1 to 21 mg …

Trace Metal Applications In Atmospheric And Watershed Dynamics: Case Studies Of Mercury Deposition In New England And Bedrock Groundwater-Surface Water Mixing, Melissa A. Lombard

Doctoral Dissertations

The studies presented in this dissertation focus on the environmental chemistry of two trace metals, mercury (Hg) and strontium (Sr). Both are naturally occurring and exist in the environment at trace levels.

Chapters II-IV of this dissertation focus on understanding the atmospheric chemistry of Hg and the wet and dry deposition of this toxic element. Chapter II presents results from Hg wet deposition measurements and ambient reactive gaseous Hg (RGM) measurements collected at Thompson Farm located in Durham, NH over a 3 year time period. The duration of this study allowed for seasonal and inter-annual comparisons. Seasonally, Hg wet deposition …

Effects Of Nitrogen-Fixing Symbiotic Cyanobacteria On The Microbial Ecology Of The Coral, Montastraea Cavernosa, Jessica K. Jarett

Doctoral Dissertations

Corals form the physical structure of coral reefs, one of the most ecologically and economically important ecosystems in the world. The abundant and broadly distributed Caribbean coral Montastraea cavernosa forms a symbiosis with intracellular nitrogen-fixing cyanobacteria in some, but not all colonies, which make up approximately 30% of the population and display a characteristic orange fluorescence. Diverse and functionally important microbial communities of dinoflagellates, bacteria, Archaea, viruses, fungi, and other organisms are also associated with corals and together with the host compose what is termed the coral holobiont. Whether the cyanobacteria are mutualists, commensals, or parasites, and their effects on …

Ecosystem Structure And Function In An Urban, Piped Stream, Amanda Hope

Master's Theses and Capstones

Piped streams, or streams that run underground, are common features in urban areas. However, there is little empirical evidence regarding their ecological structure and function. This study measured ecosystem metabolism, nutrient uptake, and related characteristics of Pettee Brook -- an urban stream that flows through several pipes under impervious surfaces near the UNH (Durham) campus.

Piped and open reaches of Pettee Brook had similar water quality, nutrient uptake, and ER. However, the absence of light in piped reaches led to their complete loss of GPP. Benthic AFDM and chlorophyll a biomass were also significantly reduced in piped reaches. For both …

Dissolved Organic Carbon Quantity And Quality In North American Rivers And Streams, Kevin Walker Hanley

Master's Theses and Capstones

The controls on the quantity and chemical composition of dissolved organic carbon (DOC) in freshwater systems are crucial to understanding and managing processes like carbon sequestration, heavy-metal transport, and municipal water sanitization. We analyzed DOC quantity and quality for 17 major North American rivers and the temporal variability of DOC quantity and quality in several thousand small basins. Among large basins, we found positive correlation between wetland-cover and both DOC concentration (R²=0.78; p<0.0001) and specific ultraviolet absorbance at 254nm (SUVA254; R²=0.91; p<0.0001). We found that the role of river networks in altering the annual DOC signal minimal except in systems with long residence times. Among small basins, we found characteristics like runoff, stormflow, and vegetation indices useful in predicting the temporal variability of DOC concentration. Further work should clarify where individual characteristics drive DOC variability and more rigorously define the role of processing in large rivers.

Investigation Of Chromophoric Dissolved Organic Matter As A Freshwater Tracer In The Kennebec River Estuary, Alison Barner

Master's Theses and Capstones

In an attempt to explore the feasibility of using chromophoric dissolved organic matter (CDOM) as a freshwater tracer in the Kennebec Estuary of Maine, potential causes of the variability of the CDOM absorption coefficient (ag412) in relation to salinity were investigated. A predictable relationship between CDOM variability and factors such as river discharge and season was sought to explain CDOM variability for use in remote sensing. To accomplish these objectives, ag412 was calibrated to continuous underway FDOM measurements using linear regressions from 14 cruises. USGS daily discharge rates were checked for possible relationships with ag412 values. Although no trends were …

Hydrogen Dynamics In Soil In Northern Boreal And Subarctic Sweden, Kaitlyn J. Steele

Master's Theses and Capstones

Molecular hydrogen (H2) is produced and consumed through syntrophic organic matter decomposition in soil. The purpose of this study was to determine if organic-rich soils can become a temporary source of H2 to the atmosphere under anoxic conditions and the release of labile carbon.

H2 was generally consumed at the subarctic peatland, but the net H2 uptake decreased as site moisture increased from the dry palsa site to the wet Eriophorum site. The dissolved H 2 concentrations suggest that methanogenesis is the predominant decomposition pathway at depth and other decomposition processes or plant-mediated transport influence concentrations closer to the surface. …

Throughfall Chemistry In Deciduous And Coniferous Forest Stands At Thompson Farm, New Hampshire, Musa Dinc

Master's Theses and Capstones

In this study, I compare the chemical composition of throughfall in deciduous and coniferous forest stands to the chemistry of wet deposition. The study was conducted at Thompson Farm, Durham NH, which is owned and managed by the University of New Hampshire. Thompson Farm (43.11N, 70.95W) is at an altitude of 23 m and about 24 km from the Gulf of Maine. Throughfall samples were obtained from two forest stands using wet-dry Aerochem Metrics 301 collectors and rainfall samples were collected in a wet-only precipitation collector (N-CON Atmospheric Deposition Samples Model 00-120) from 14 April 2009 to 14 November 2009.The …

Interrelations Among Leaf And Canopy Nitrogen, Optical And Structural Traits, Franklin Brown Sullivan

Master's Theses and Capstones

A correlation between canopy nitrogen and albedo has been observed across a wide range of forest types. Determining the nature and mechanisms behind the relationship would help to understand the role of nitrogen in the climate system and better understand forest-climate interactions. The purpose of this study was to examine sources of variation in leaf and canopy optical traits with respect to variation in nitrogen concentrations at both scales.

We found that %N was significantly correlated with leaf and canopy albedo and that both %N and albedo were strongly correlated with forest composition. Many canopy structural traits were found to …

Saprotrophic Fungi As A Mechanism For Vertical Nitrogen Transport In A Chronically Fertilized Northern Hardwood Forest, Katharine M. Burnham

Master's Theses and Capstones

Decay studies often observe that plant litter increases in the amount of nitrogen within the first year of decomposition, yet sources are uncertain. The Harvard Forest Chronic Nitrogen Amendment Experiment, Petersham, MA, was utilized to quantify vertical N translocation from soil up into decomposing litter and determine if long-term, chronic N application has affected this process. Litter bags were designed to facilitate or restrict fungal hyphal connectivity between the soil-litter interface and placed in control, low N+S and high N plots. After five or 12 months, a 15N-(NH 4)2SO4 solution was horizontally injected into organic soil beneath bags. 15N enrichment …

Seasonal, Biogeochemical, And Microbial Response Of Soils To Simultaneous Warming And Nitrogen Additions, Alexandra R. Contosta

Doctoral Dissertations

Climate warming and nitrogen deposition are global environmental threats that could alter soil microbial communities and the biogeochemical processes they perform. Few studies have examined interactive effects of elevated temperatures and nitrogen inputs. Many studies have also not considered the role that season plays in mediating the response of soils to warming and nitrogen. Finally, most research has not linked changes in the soil microbial community with ecosystem-scale dynamics. One objective of this dissertation was to examine season-specific microbial and biogeochemical responses to simultaneous warming and nitrogen additions. Another aim was to investigate whether warming and nitrogen can restructure microbial …

Effect Of Carex Rostrata Removal On Methane Emissions From A Temperate Peatland, Genevieve L. Noyce

Master's Theses and Capstones

Peatlands are a large natural source of atmospheric methane (CH4). Carex rostrata, a sedge species, has a critical role in the production, oxidation, and emission of CH4 from these systems. This study examined the changes in CH4 emissions from a temperate peatland after removing all aboveground C. rostrata biomass. Methane flux, dissolved CH4 concentration at various depths, C. rostrata green leaf area, temperature, and water table depth were measured from June 2008 to November 2010.

There is a strong positive correlation between C. rostrata green area and CH4 flux and the mean summer CH4 flux from the control plots was …

A Feasibility Study: Forest Carbon Stocks And Stock Change Of The White Mountain National Forest, Erica Jane Cate

Master's Theses and Capstones

Interest has heightened for forest managers to account for the impacts of management activities on forest carbon sequestration. This study was designed to assess the feasibility of developing estimates of WMNF forest carbon based on the available information. The yield curves, inventory data and resulting carbon projections were dependent on a number of assumptions and subject to various sources of error and bias. Thus, they should not be relied on as definitive estimates and forecasts, or used as a basis for policy recommendations. Under the specific approaches used in this study, forest carbon stocks appear to be accumulating in the …

Variation In Foliar Nitrogen And Albedo In Response To Nitrogen Fertilization And Elevated Carbon Dioxide, Haley F. Wicklein

Master's Theses and Capstones

It has recently been demonstrated that foliar nitrogen is positively correlated with surface albedo over a broad range of plant functional types. However, the mechanism(s) driving the nitrogen-albedo relationship remain elusive. This study investigated leaf spectral properties from three deciduous species subjected to either nitrogen or CO2 fertilization and compared results to measured chemical and structural properties. We measured reflectance and transmittance, foliar nitrogen, leaf mass per unit area, water content, and d13C values for stacks of 1, 2, 4, and 8 leaves. Nitrogen was the best predictor of leaf-level albedo of the traits that we measured. There were no …

Effects Of Physical And Chemical Disturbance On Stream Ecosystem Structure And Function, Elena M. Traister

Doctoral Dissertations

A variety of natural and anthropogenic disturbances influence the structure and function of stream ecosystems. While past investigations have focused on the response of community indicators to stream disturbances, functional indicators may also be helpful for assessing stream ecosystem health. To date, few studies have compared the response of structural and functional indicators to ecosystem-level disturbances. I separately measured the effects of long-term acidification, a large-scale avulsion, and the individual and combined effects of physical streambed disturbance and altered refugia availability on stream structural and functional metrics.

I found that acidification was associated with changes in macroinvertebrate communities including reduced …

Hydrologic And Nutrient Dynamics In An Agriculturally Influenced New England Floodplain, Michelle Galvin

Master's Theses and Capstones

Non point-source pollution from agricultural activity is a major cause of water quality degradation. In particular, nutrient loading can lead to eutrophication and related anoxia in rivers, streams and lakes. Floodplains adjacent to these water bodies are sites of active nutrient cycling that can mediate the flux of nutrients to and from these water bodies. This study examines the hydrologic and nutrient dynamics of an agriculturally-influenced creek and floodplain in Lee, New Hampshire. Chemical mixing models were used to assess cycling of nutrients in response to flooding. The floodplain acted primarily as a sink for phosphate (PO43-), ammonium (NH4+) and …

Identifying Temporal Patterns And Controlling Factors In Methane Ebullition At Sallie's Fen, A Temperate Peatland Site, Using Automated Chambers, Jordan Goodrich

Master's Theses and Capstones

Despite leading to a potentially significant positive climate feedback, the processes controlling wetland methane fluxes remain relatively poorly understood. Automated chambers were employed in a temperate peatland site to quantify the timing and magnitude of methane ebullition (bubbling), one of the three pathways for wetland methane flux. The resulting datasets offer high temporal coverage of both components of this flux pathway, allowing for the first analysis of ebullition variability on seasonal, synoptic and diel timescales. The seasonal peak in ebullition occurred in August, likely due to high methane production rates and low methane solubility, both driven by temperature. Synoptic scale …

Modeling Permafrost Stability In Peatlands With Climate Change And Disturbance, Claire Treat

Master's Theses and Capstones

Boreal and arctic regions are predicted to warm faster and more severely than temperate latitudes. They contain large stocks of below- ground soil carbon in peatlands and frozen soil, and the flux of the soil C to the atmosphere may be a strong feedback to climate change.

Increases in air temperature due to climate change will increase surface soil temperatures, soil temperatures at depth, active layer depths, and growing season length, but not degrade permafrost by 2100 at this site. Both wildfire and climate change increase active layer depths by 25 cm, but effects of wildfire diminish following vegetation recovery.

Mycorrhizal Colonization And Nutrient Supply Rate Influence Elemental And Isotopic Tracers Of Calcium Cycling In Plant-Substrate Systems, Claire J. Hoff

Master's Theses and Capstones

Intraplant (root-foliage) fractionation of Ca isotopes and Ca/Sr were determined in Pinus sylvestris seedlings grown at different nutrient supply rates with or without ectomycorrhizal colonization. Foliar 44Ca/40Ca and Ca/Sr are uniformly higher than those of roots in individual seedlings, and these ratios in both foliage and roots differed significantly from those of nutrient sources. The measured offsets indicate that isotopic and trace element ratios can identify relative contributions from distinct calcium pools in terrestrial ecosystems. Furthermore, the results clearly show that fractionation of calcium isotopes and calcium from strontium in plants must be assessed in ecosystem-scale budgets and large watershed …