Nitrogen saturation in streams and forests of the Maryland Piedmont

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dc.contributor.advisorPalmer, Margaret Aen_US
dc.contributor.authorCraig, Laura Shawnen_US
dc.contributor.departmentBehavior, Ecology, Evolution and Systematicsen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.date.accessioned2010-02-19T07:18:24Z
dc.date.available2010-02-19T07:18:24Z
dc.date.issued2009en_US
dc.description.abstractHuman activities have dramatically increased nitrogen (N) inputs to the landscape. Consequently, delivery of N to coastal waters, largely as nitrate (NO3-N), has increased, resulting in widespread eutrophication and harmful hypoxic conditions. The ability to mitigate the downstream effects of elevated N inputs requires a clear understanding of the transport and transformation of N in stream ecosystems. Here, I examine N processing in urban and forested watersheds of the Maryland Piedmont. I provide extensive evidence that three high-N streams draining urban and forested watersheds of the Maryland Piedmont are unable to remove NO3-N as a result of both N saturation and phosphorus limitation. My findings illustrate that when elevated NO3-N concentrations occur in the absence of other stressors that stimulate autotrophic activity (e.g. reduced canopy cover, increased nutrients) uptake cannot compensate for increased N loads. A review of the literature indicates that systems that are similarly unable to remove NO3-N vary widely in terms of land use and background N concentrations, highlighting the limitations of our understanding of N saturation in stream ecosystems. I also provide the first documentation of N saturation in both the aquatic and terrestrial components of an un-manipulated forested watershed. Detailed examination of N dynamics within the forested watershed reveals that the forest is severely N-saturated despite receiving atmospheric N inputs that are small relative to other parts of the Northeast and Mid-Atlantic. Because groundwater delivers a disproportionate fraction of the N load to the channel, in-stream N concentrations are elevated when deep groundwater flowpaths dominate, and the watershed is a source of N during dry periods, I hypothesize that hydrogeologic factors that control groundwater susceptibility to NO3-N contamination and promote delivery of NO3-N via subsurface flowpaths may exacerbate N-saturation response. My results suggest that we cannot rely on in-stream processing to reduce N loads even in minimally impacted watersheds. As a result, it is critical that management efforts reduce N loading to streams and take advantage of opportunities for increasing N removal in impaired systems only after other options have been exhausted.en_US
dc.identifier.urihttp://hdl.handle.net/1903/10041
dc.subject.pqcontrolledBiology, Ecologyen_US
dc.subject.pquncontrolledNitrogenen_US
dc.subject.pquncontrolledPiedmonten_US
dc.subject.pquncontrolledsaturationen_US
dc.subject.pquncontrolledStreamen_US
dc.subject.pquncontrolledwatersheden_US
dc.titleNitrogen saturation in streams and forests of the Maryland Piedmonten_US
dc.typeDissertationen_US

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