HR: 0800h
AN: B31A-0065    [Abstracts]
TI: Understanding nitrogen removal processes within river networks over annual time scales: implications of saturation.
AU: * Wollheim, W M
EM: wil.wollheim@unh.edu
AF: Complex Systems Research Center, Morse Hall, University of New Hampshire, Durham, NH 03824, United States
AU: Vorosmarty, C J
EM: charles.vorosmarty@unh.edu
AF: Complex Systems Research Center, Morse Hall, University of New Hampshire, Durham, NH 03824, United States
AU: Fekete, B
EM: balazs.fekete@unh.edu
AF: Complex Systems Research Center, Morse Hall, University of New Hampshire, Durham, NH 03824, United States
AU: Milly, P
EM: cmilly@usgs.gov
AF: USGS, P.O. Box 308 GFDL/NOAA, Princeton, NJ 08542, United States
AU: Findell, K L
EM: Kirsten.Findell@noaa.gov
AF: GFDL/NOAA, P.O. Box 308, Princeton University, Princeton, NJ 08542, United States
AU: Peterson, B J
EM: peterson@mbl.edu
AF: Marine Biological Laboratory, Water St., Woods Hole, MA 02543, United States
AB: River networks are an important control of nutrient exports between terrestrial and coastal systems. We explored how this control is simultaneously influenced by runoff variability, elevated N inputs, and aquatic process saturation using a daily time step river network N removal model. The model assumes a saturating denitrification function derived from recent denitrification measurements in headwater stream channels experiencing a range of loading rates. We assumed the denitrification function could be applied over the entire range of stream sizes within a full river network-drainage basin context, and over time assuming rates vary only with temperature. The model was applied to a single suburbanizing watershed (Ipswich River, MA, 400km2 watershed area) using specified runoff conditions and at the global scale using runoff from the Land Model (LM) of the GFDL AM2/LM2 supplemented by a new river discharge and mass-transport model. We used a frequency analysis to characterize the distribution of river network N removal over annual time scales as a function of flow conditions. Percent of inputs removed can be significant under low flow conditions (>70%) but is constrained over annual time scales because most nonpoint N inputs enter the network when hydraulic conditions limit removal capacity. The effects of N saturation within the river system are most evident at moderate flows below mean annual discharge where the relative influences of biological activity and hydraulic factors on removal are balanced. Both increasing runoff conditions and increasing N inputs shift N removal to larger downstream systems. Greater climate variability and N inputs to river systems would lead to disproportionate changes in N exports to the coastal zone.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting