Grimm Nancy B.

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Nancy B.

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  • Preprint
    Stream denitrification across biomes and its response to anthropogenic nitrate loading
    ( 2007-06-06) Mulholland, Patrick J. ; Helton, Ashley M. ; Poole, Geoffrey C. ; Hall, Robert O. ; Hamilton, Stephen K. ; Peterson, Bruce J. ; Tank, Jennifer L. ; Ashkenas, Linda R. ; Cooper, Lee W. ; Dahm, Clifford N. ; Dodds, Walter K. ; Findlay, Stuart E. G. ; Gregory, Stanley V. ; Grimm, Nancy B. ; Johnson, Sherri L. ; McDowell, William H. ; Meyer, Judy L. ; Valett, H. Maurice ; Webster, Jackson R. ; Arango, Clay P. ; Beaulieu, Jake J. ; Bernot, Melody J. ; Burgin, Amy J. ; Crenshaw, Chelsea L. ; Johnson, Laura T. ; Niederlehner, B. R. ; O'Brien, Jonathan M. ; Potter, Jody D. ; Sheibley, Richard W. ; Sobota, Daniel J. ; Thomas, Suzanne M.
    Worldwide, anthropogenic addition of bioavailable nitrogen (N) to the biosphere is increasing and terrestrial ecosystems are becoming increasingly N saturated, causing more bioavailable N to enter groundwater and surface waters. Large-scale N budgets show that an average of about 20-25% of the N added to the biosphere is exported from rivers to the ocean or inland basins, indicating substantial sinks for N must exist in the landscape. Streams and rivers may be important sinks for bioavailable N owing to their hydrologic connections with terrestrial systems, high rates of biological activity, and streambed sediment environments that favor microbial denitrification. Here, using data from 15N tracer experiments replicated across 72 streams and 8 regions representing several biomes, we show that total biotic uptake and denitrification of nitrate increase with stream nitrate concentration, but that the efficiency of biotic uptake and denitrification declines as concentration increases, reducing the proportion of instream nitrate that is removed from transport. Total uptake of nitrate was related to ecosystem photosynthesis and denitrification was related to ecosystem respiration. Additionally, we use a stream network model to demonstrate that excess nitrate in streams elicits a disproportionate increase in the fraction of nitrate that is exported to receiving waters and reduces the relative role of small versus large streams as nitrate sinks.
  • Article
    The changing landscape : ecosystem responses to urbanization and pollution across climatic and societal gradients
    (Ecological Society of America, 2008-06) Grimm, Nancy B. ; Foster, David R. ; Groffman, Peter M. ; Grove, J. Morgan ; Hopkinson, Charles S. ; Nadelhoffer, Knute J. ; Pataki, Diane E. ; Peters, Debra P. C.
    Urbanization, an important driver of climate change and pollution, alters both biotic and abiotic ecosystem properties within, surrounding, and even at great distances from urban areas. As a result, research challenges and environmental problems must be tackled at local, regional, and global scales. Ecosystem responses to land change are complex and interacting, occurring on all spatial and temporal scales as a consequence of connectivity of resources, energy, and information among social, physical, and biological systems. We propose six hypotheses about local to continental effects of urbanization and pollution, and an operational research approach to test them. This approach focuses on analysis of “megapolitan” areas that have emerged across North America, but also includes diverse wildland-to-urban gradients and spatially continuous coverage of land change. Concerted and coordinated monitoring of land change and accompanying ecosystem responses, coupled with simulation models, will permit robust forecasts of how land change and human settlement patterns will alter ecosystem services and resource utilization across the North American continent. This, in turn, can be applied globally.