2005 Progress Report: Attenuation of Non-Point Source Nitrogen Pollution in a Coastal Watershed: Implications for Nutrient Management

EPA Grant Number: R830652
Title: Attenuation of Non-Point Source Nitrogen Pollution in a Coastal Watershed: Implications for Nutrient Management
Investigators: Piehler, Michael F. , Band, L. R. , Paerl, Hans , Whalen, Stephen C.
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Hiscock, Michael
Project Period: January 20, 2003 through January 19, 2006 (Extended to January 19, 2007)
Project Period Covered by this Report: January 20, 2005 through January 19, 2006
Project Amount: $737,555
RFA: Nutrient Science for Improved Watershed Management (2002) RFA Text |  Recipients Lists
Research Category: Water , Water and Watersheds

Objective:

The objectives of this project are to provide detailed field and experimental data on transformations of nitrogen (N) in agricultural and forested coastal catchments. These data will be organized into a process-based spatial model to predict the quantity and form of N exported.

Progress Summary:

Human activity in coastal regions has affected the sources, transport, and effects of nutrients in estuarine systems. Interactions of the anthropogenic and climatic forcing features pose significant challenges to nutrient management in coastal watersheds. We compared the nutrient (nitrogen and phosphorus) load from two sub-watersheds (agricultural and silvicultural) and assessed the response of estuarine water quality parameters in the South River (a tributary of the Neuse River Estuary, North Carolina) during an 18 month period. Distinct patterns in the delivery, chemical composition, and the magnitude of the nutrient load were seen in the different land uses. More than 75% of the nutrient load from the agricultural watershed was delivered during periods of elevated discharge; there was a much lower percentage from the silvicultural watershed. Phytoplankton nutrient bioassays in the adjacent creeks and the South River revealed nitrogen limitation, with a few examples of compound specific impacts. Clarifying the relative importance of land use and hydrologic variability in this tractable system will advance the understanding of small watershed dynamics and their connectivity to larger estuarine complexes.

Denitrification is the sole mechanism of permanent nitrogen removal along the riverine to estuarine continuum, but its contribution to nitrogen attenuation in the system is not well understood. Denitrification rates measured seasonally in stream bed sediments were variable but showed a distinct spring maximum, which was likely associated with rising temperatures and added nitrogen from fertilizer application (0–150 μmol N m-2 h-1 during the summer, fall, and winter and 150–300 μmol N m-2 h-1 in the spring). Reach-scale uptake experiments showed the potential for 65–98% retention of the watershed dissolved inorganic nitrogen (DIN) load in ephemeral drainage ditches. Results indicated that nitrogen retention was high despite low hyporheic exchange that is typically associated with channelized streams with low gradients, straight channels, and homogenous stream bed sediments. Comparison of direct denitrification rate measurements to reach-scale uptake rates and a watershed mass balance showed considerable potential for nitrogen removal via denitrification in agricultural stream sediments.Nitrogen retention by plants and algae has been shown to be an important uptake mechanism. However, the ultimate fate of the assimilated N has not been extensively studied. As plant biomass is decomposed by bacteria, remineralized N and particulate and dissolved organic N fractions are released. Plant biomass is also a labile carbon and energy source for denitrifiers. In experiments, we found that 5–20% of the N in an algal leachate was denitrified, which has important implications for export of watershed derived N.

Budgetary expenditures for the reporting period were in line with the level of work that has been completed.


Journal Articles on this Report : 5 Displayed | Download in RIS Format

Other project views: All 23 publications 8 publications in selected types All 8 journal articles
Type Citation Project Document Sources
Journal Article Ensign SH, Doyle MW. In-channel transient storage and associated nutrient retention: evidence from experimental manipulations. Limnology and Oceanography 2005;50(6):1740-1751. R830652 (2004)
R830652 (2005)
  • Full-text: ASLO PDF
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  • Abstract: ASLO Abstract
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  • Journal Article Ensign SH, McMillan SK, Thompson SP, Piehler MF. Nitrogen and phosphorus attenuation within the stream network of a coastal, agricultural watershed. Journal of Environmental Quality 2006;35(4):1237-1247. R830652 (2005)
  • Abstract from PubMed
  • Journal Article Paerl HW, Valdes LM, Piehler MF, Stow CA. Assessing the effects of nutrient management in an estuary experiencing climatic change: the Neuse River Estuary, North Carolina. Environmental Management 2006;37(3):422-436. R830652 (2004)
    R830652 (2005)
    R828677C001 (Final)
  • Abstract from PubMed
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  • Journal Article Paerl HW, Piehler MF, Valdes LM, Dyble J, Moisander PH, Pinckney JL, Steppe TF. Determining anthropogenic and climatically-induced change in aquatic ecosystems using microbial indicators: an integrative approach. Verhandlungen Internationale Vereinigung fur Theoretische und Angewandte Limnologie 2005;29(1):89-133. R830652 (2005)
    R828677C001 (Final)
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    Journal Article Valdes-Weaver LM, Piehler MF, Pinckney JL, Howe KE, Rossignol K, Paerl HW. Long-term temporal and spatial trends in phytoplankton biomass and class-level taxonomic composition in the hydrologically variable Neuse-Pamlico estuarine continuum, North Carolina, USA. Limnology and Oceanography 2006;51(3):1410-1420. R830652 (2005)
    R828677C001 (Final)
  • Full-text: ASLO - Full Text PDF
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  • Abstract: ASLO Abstract
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  • Supplemental Keywords:

    chemical transport, estuary, ecological effects, ecosystem, Mid-Atlantic, agriculture,, RFA, Scientific Discipline, Air, INTERNATIONAL COOPERATION, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Water & Watershed, Environmental Chemistry, climate change, Air Pollution Effects, Aquatic Ecosystem, Water Quality Monitoring, Environmental Monitoring, Terrestrial Ecosystems, Ecological Risk Assessment, Atmosphere, Watersheds, anthropogenic processes, nutrient transport, anthropogenic stress, bioassessment, watershed classification, biodiversity, watershed management, ecosystem monitoring, nutrient flux, conservation, biota diversity, diagnostic indicators, ecosystem indicators, Mystic Lake, aquatic ecosystems, water quality, bioindicators, watershed sustainablility, biological indicators, ecosystem stress, watershed assessment, nitrogen uptake, conservation planning, aquatic biota, land use, restoration planning, watershed restoration

    Relevant Websites:

    http://www.unc.edu/~mpiehler Exit
    http://www.marine.unc.edu/Paerllab/ Exit

    Progress and Final Reports:

    Original Abstract
  • 2003 Progress Report
  • 2004 Progress Report
  • Final