PARENT SESSION
Symposium 1: In the Footsteps of Lewis and Clark: Rediscovering Earth From Land to Sea - A Biogeoscience Perspective.
Organized by: PV Sundareshwar and J Elser
Monday, August 2, 8:00 AM to 11:30 AM, Oregon Ballroom 202.
Do nitrogen transformations differ qualitatively across biomes?
Howarth, Robert*,1, 2, Townsend, Alan 3, Marino, Roxanne1, 2, Gettel, Gretchen1, Bettez, Neil1, Boyer, Elizabeth4, 1 Department of Ecology & Evolutionary Biology, Ithaca, NY, USA2 Ecosystems Center, Woods Hole, MA, USA3 Institute for Arctic and Alpine Research, Boulder, CO, USA4 School of Forestry and Environmental Science, Syracuse, NY, USA
ABSTRACT- In the symposium on Rediscovering Earth from Land to Sea, a Biogeoscience Perspective, speakers are challenged to determine if diverse biomes differ qualitatively in their biogeochemical cycling. We will address this for nitrogen by examining rates and controls on two key processes: nitrogen fixation and denitrification. We will also examine how human alteration of the nitrogen cycle affects nitrogen fluxes in rivers at the scale of large watersheds. For nitrogen fixation, rates differ greatly across biomes, for example often being high in tropical forests and eutrophic lakes but low in temperate forests and pelagic-dominated estuaries. The specific controls on nitrogen fixation differ among biomes, but a common theme is that a combination of both physiological (biogeochemical) and ecological controls (such as grazing and competition) seem to interact to regulate rates. Patterns in rates of nitrogen fixation across biomes cannot be understood based simply on consideration of physiological controls alone. For denitrification, rates also differ across biomes and tend to be much higher in aquatic ecosystems than in terrestrial ecosystems. The controls on denitrification, however, are probably the same across biomes; high rates occur whenever nitrate is found in anoxic conditions, which generally result from waterlogging and high organic carbon content in soils and sediments. Human activity has altered the nitrogen cycle more than that of any other major element cycle. The extent of this alteration varies greatly across regions, but the responses of regions to alteration of the nitrogen cycle are remarkably similar, at least as seen in riverine nitrogen fluxes. Across the temperate zones of Earth, nitrogen fluxes in large rivers are a relatively simple function of nitrogen inputs from human activity and river discharge, with roughtly 25 percent of inputs to the watershed exported in the river.
Key words: denitrification, biogeochemistry, nitrogen fixation, nitrogen