Nicholas School of the Environment

Permanent URI for this collectionhttps://hdl.handle.net/10161/52

Master's projects by Nicholas School of the Environment students, including the Duke Marine Laboratory.

The masters project is done in partial fulfillment of the degree requirements for the professional Master of Environmental Management or the Master of Forestry degree. While the MP may include original laboratory or field research, it may also take the form of management plans, handbooks, educational curricula, or other such products. Each student is advised by a faculty member who reviews and approves the project prior to completion.

A masters projects that is original research should not be as large as a masters thesis although it should be of publishable quality but not necessarily comprehensive enough to stand alone as a publication. A masters projects that does not follow the usual format for scientific research should follow a framework that is considered good practice in an appropriate field.

Duke migrated to an electronic-only system for masters projects between 2006 and 2010. As such, projects completed between 2006 and 2010 may not be part of this system, and those created before 2006 are not hosted here except for a small number that have been digitized.

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Now showing 1 - 9 of 9

Open Access
A Comparison of Remote Sensing Methods for Estimating Above-Ground Carbon Biomass at a Wetland Restoration Area in the Southeastern Coastal Plain
(2012-04-19) Riegel, Ben
Developing accurate but inexpensive methods for estimating above-ground carbon biomass is an important technical challenge that must be overcome before a carbon offset market can be successfully implemented. Previous studies have shown that full-waveform LiDAR (light detection and ranging) is well suited for modeling above-ground biomass in mature forests; however, there has been little previous research on the ability of discrete-return LiDAR to model above-ground biomass in areas with relatively sparse vegetation. This study compared the abilities of discrete-return LiDAR and high-resolution optical imagery to model above-ground carbon biomass at a wetland restoration area in eastern North Carolina. The optical imagery model explained more of the overall variation in biomass at the study site than the LiDAR model did (R2 values of 0.36 and 0.19 respectively). Moreover, the optical imagery model was better able to detect high and low biomass areas than the LiDAR model. These results suggest that the ability of discrete-return LiDAR to model above-ground biomass is rather limited in areas with relatively small trees and that high spatial resolution optical imagery may be the better tool in such areas.
Open Access
A ridge-to-reef framework to protect Guam's water quality and coral reef ecosystem
(2023-04-25) Castro, Frances
Watershed pollution and fisheries exploitation are the priority, chronic stressors that impact Guam’s coral reefs. Yet, quantifying the relative contribution of individual stressors to any particular reef is difficult due to natural variations in biological assemblages across island scales and uncertain site-specific disturbance histories. A study of 26 sites in southern Guam watersheds shows the effects of pollution on coral reef and fish assemblages. Community, government, and legislative action need to take place to improve Guam’s water quality standards.
Open Access
Aquatic Macroinvertebrates and Metal Contamination in Forested and Urban Streams
(2024-04-26) Good, Elizabeth
Subsidies are the transfer of materials between habitats, including the movement of critical nutrients but also the movement of unwanted pollutants. In riparian ecosystems, aquatic insects can act as important vectors for moving subsidies into terrestrial ecosystems. In this study, stonefly larvae collected from Stone Mountain State Park, NC were fed leaves from Durham, NC forested and urban stream sites to assess impacts on growth and development. Larvae and leaves were then analyzed for metals to assess contamination loads across sites and the potential for larvae to export metals into terrestrial ecosystems. Some metals bioconcentrated (Zn, Cu, Ag) while some biodiluted (Pb, Ni, Co, Cr, As) in stoneflies, and leaves from urban streams generally showed higher metal concentrations than forested streams. These results indicate the potential for stoneflies to act as vectors for metal pollutants to terrestrial environments in different riparian ecosystems.
Open Access
Changes in stream ecosystem structure as a function of urbanization: Potential recovery through stream restoration
(2007-05) Cada, Peter
I documented reach scale changes in the physical structure of 12 stream channels in the summer months of 2006, comparing four small streams draining forested catchments with eight streams from developed watersheds of similar catchment size. Study sites in four of the urban streams are within recently implemented natural channel design restoration projects. To assess whether restoration projects increase stream habitat and flow heterogeneity and increase water exchange with floodplain and hyporheic sediments I compared reach-scale geomorphic (e.g. slope, cross section, degree of incision, variation in water depth) and hydrologic (e.g. transient storage volume (TS), surface-water groundwater exchange, fine scale variation in velocity) features of each stream. I used ArcGIS to compile watershed maps and to produce detailed maps of reach habitat for each stream, and the hydrologic model OTIS-P to estimate transient storage from field rhodamine releases. Minimally impacted reaches were found to have shallower average depths with a greater variation in depth than urban or restored stream reaches. Streams restored to provide habitat had the lowest flow habitat heterogeneity of the three stream classes. Channel incision was the only physical channel feature for which the urban restored streams were more similar to the forested streams than the urban degraded condition. Surprisingly, I was unable to detect significant differences in transient storage volume or hyporheic exchange between our three stream classes. My results suggest that restoration designs are placing inadequate attention on recreating the physical template seen in less degraded streams.
Open Access
Linking upstream mining to downstream water quality: Mountaintop mining in West Virginia
(2010-04-30T16:33:20Z) Carter, Catherine
Mountaintop mining valley fill (MTM/VF) coal mining is currently the dominant form of land use change in the central Appalachians. MTM/VF activities level mountains, remove forests and forest soils, bury headwater streams and generate substantial amounts of acid and alkaline mine drainage. Numerous case studies have documented elevated concentrations of sulfate and trace metal and metalloids with known toxicity in surface waters downstream from MTM/VF activity, yet no comprehensive effort has been made to link landscape scale mining activity and water quality. Here, I used newly obtained remote sensing data of surface mining activity delineated from 1976 to 2005 to estimate the extent of MTM/VF impact on downstream surface water quality in the Coal and Guyandotte river basins of WV. Hydrologic connectivity between mining and water quality was estimated using an inverse distance weighting technique in GIS (ESRI, Inc.). The findings show significant biogeochemical alterations, including streamwater conductivity and sulfate concentrations, even when small amounts of surface mining (<5%) are observed. Results provide the first comprehensive analysis of the cumulative impact of mining activity in these watersheds on water quality and demonstrate the need for further investigation involving strategic water quality sampling with the ultimate goal of developing an empirical basis on which to form regulations governing MTM/VF throughout the central Appalachians.
Open Access
Mountaintop Mining’s Impact on Watershed and Regional Scale Nitrogen Export
(2017-04-28) Brooks, Alexander C
Mountaintop removal coal mining with valley fills (MTM) is the largest contributor to land use change in the Central Appalachia Region. MTM uses explosives and draglines to uncover shallow seems of coal from mountaintops and ridgelines. The coal residues and overburden are disposed of into adjacent valleys forming valley fills. The large quantities of unconsolidated rock increase watershed storage potential and vastly increase rates of rock weathering via sulfuric acid generated by coal residues. This leads to high concentrations of coal and rock derived ions in receiving surface waters and causes a number of associated water quality impairments. Alongside known these known impairments, recent studies have also reported high dissolved nitrogen (N) concentrations in samples from affected streams. This project quantifies, for the first time, the magnitudes and persistence of this elevate nitrogen export from MTM affected catchments and investigates how MTM increases N inputs and alters catchment N cycling. Using two years of hydrologic measurements and regular baseflow and storm sampling near the Hobet Mining Complex in West Virginia, this research finds that annual mass flux of nitrate in mined catchments was 9 to 61 times greater than at a reference catchment. Further, the project finds that high levels of nitrate export during active mining declines after reclamation but can remain significantly elevated for at least several decades post mining. Analysis of nitrate isotopes from stream water finds baseflow at mined sits to be highly enriched in both δ15N and δ18O compared to the reference site. These isotopic values do not match the signature of any known potential nitrate source but do match with the results of fractionation from denitrification occurring in large pools of NO3-. A developed watershed nitrogen budget identifies mining explosives as a sizable mining input of N that could export 9 to 3716 kg N ha-1 but also suggests other sources including fertilizer, weathering derived rock N, and soil mineralization all may play a role in elevated export. Finally, an analysis of regional water quality and surface mining extent indicate a significant correlation between the cumulative extent of surface mining and annual mean nitrate concentrations in the mostly heavily mined regional basin.
Open Access
Pattern and Variation in Development of Small Urban Watersheds
(2014-04-25) Allen, Diane Mary
Increased urbanization has been correlated with hydrologic, chemical, geomorphologic, and biologic changes to receiving streams. Therefore, the status quo in watershed management has been to control the amount of impervious surface area. However, because various measures of development and impervious surface area are correlated, it is hard to discern what aspects of development cause adverse ecological impacts: impervious surface area is correlated with stormwater infrastructure, natural vegetation cover, road density, and so on. In practice, the level of variability in any of these parameters can be high at any intensity of development. We can take advantage of that variability to choose landscape configurations that minimize watershed impacts for any given level of urbanization. To do so, we must understand how watershed land cover parameters co-vary with development intensity (percent impervious surface) and which aspects of configuration most directly impact urban streams. To this end, I examined 14 specific aspects of development configuration and stormwater infrastructure for 235 small watersheds in the Piedmont region of North Carolina. For both landscape metrics and infrastructure features, there was a high degree of variability at almost any level of development intensity. In the case of road density for central ranges of development, there was so much variation that the expected positive correlation of roads with development was no longer significant. Our results set the stage for future exploration of the hydrologic and chemical processes that are altered in urban streams. Relation of development pattern to ecological process in this way will support more nuanced methods for management of watershed development so that hydrologic impacts might be minimized for any given level of development intensity.
Open Access
Restoring Farmland to Wetlands: The Potential for Carbon Credits in Eastern North Carolina
(2008-04-22T03:01:58Z) Neely, Hayes
Rising atmospheric CO2 levels and the resulting global warming have created interest in storing carbon in land and biomass. Wetlands that are currently drained for agriculture have lost much of their historically stored carbon through soil oxidation. One solution to this problem is to restore farmland to wetlands in order to store carbon. This study 1) creates a model of carbon storage in restored wetlands in the Southeast, 2) identifies land where restoration may occur in eastern North Carolina, and 3) determines the price of CO2 necessary for the revenue from carbon credits to equal the revenue from farming in eastern North Carolina. Restoration of all the 40,756ha of marginal farmland in the lower Pasquotank Basin could store approximately 9,651,428 tons of carbon over 90 years. In order for restoration to be profitable from selling CO2 credits alone, current CO2 trading prices would need to increase to between $29.49 and $72.16 ton-1 CO2. While CO2 prices are currently not at this level, schemes such as unbundling credits from multiple ecosystem services provided by wetlands could affect the tipping point of restoration profitability.
Open Access
The Biogeochemical Consequences of Saltwater Intrusion to Freshwater Wetland Sediment
(2013-04-26) Glodzik, Katie
Saltwater intrusion driven by water extraction, coastal modifications, and climate change may alter the biogeochemical cycling of freshwater coastal wetlands. Anaerobic respiration in freshwater wetlands is typically dominated by methanogenesis, leading to a high methane (CH4) flux, but the availability of sulfate (SO42—) in seawater may shift the dominant pathway to SO42— reduction, decreasing CH4 flux. Seawater may also impact nitrogen cycling by releasing ammonium (NH4+) from soil and causing salinity and hydrogen sulfide stress to nitrifiers and denitrifiers. This experiment tests the soil biogeochemical impacts of artificial seawater amendments to intact sediment cores taken from a freshwater coastal wetland on the Albemarle Peninsula of North Carolina. Intact cores were assigned to one of four experimental treatments designed to compare the impact of surface and subsurface saltwater exposure on sediment biogeochemistry. Cores received surface water treatments 2-3 times per week and were exposed continuously to subsurface treatments. Gas flux and porewater were sampled 9 times over the 20-week experiment. Saltwater added to the soil surface raised soil solution to 10.4 ppt average salinity by the end of the experiment and led to significant increases in NH4+ concentration and significant declines in dissolved organic carbon (DOC). In surface saltwater exposed cores we measured a significant increase in nitrous oxide (N2O) production but no significant change in carbon dioxide (CO2) or CH4 flux. Surface exposure treatments led to significant reductions in microbial biomass, and all salinity treatments (regardless of direction of exposure) had significant reductions in carbon mineralization and respiration efficiency by the end of the experiment. Our results suggest that saltwater exposure altered microbial biomass and function, and that surface water salinization will have more immediate and measurable impacts on biogeochemical cycling in these soils than exposure to saline ground water.

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Browsing Nicholas School of the Environment by Advisor "Bernhardt, Emily S"