HR: 0800h
AN: GC31A-0107    [Abstracts]
TI: Changes in nitrogen cycling during the past century in a northern hardwood forest
AU: * McLauchlan, K K
EM: mclauch@ksu.edu
AF: Kansas State University, Department of Geography 118 Seaton Hall, Manhattan, KS 66506, United States
AU: Craine, J M
EM: jcraine@ksu.edu
AF: Kansas State University, Division of Biology 116 Ackert Hall, Manhattan, KS 66506, United States
AU: Oswald, W W
EM: w_wyatt_oswald@emerson.edu
AF: Emerson College, 120 Boylston Street, Boston, MA 02116, United States
AU: Leavitt, P R
EM: peter.leavitt@uregina.ca
AF: University of Regina, Department of Biology, Regina, SK S4S 0A2, Canada
AU: Likens, G E
EM: likensg@ecostudies.org
AF: Institute of Ecosystem Studies, 65 Sharon Turnpike P.O. Box AB, Millbrook, NY 12545, United States
AB: Nitrogen availability, defined here as the supply of nitrogen to terrestrial plants and soil microorganisms relative to their demands, limits the productivity of many temperate zone forests and in part determines ecosystem carbon content. Despite multidecadal monitoring of nitrogen in streams, the long-term record of nitrogen availability in forests of the northeastern United States is largely unknown. Therefore, although these forests have been receiving anthropogenic nitrogen deposition for the past few decades, it is still uncertain whether terrestrial nitrogen availability has changed during this time and subsequently whether forest ecosystems have responded to increased nitrogen deposition. Here, we reconstructed changes in vegetation and other ecosystem characteristics using a millennial-scale lacustrine sediment record and high-intensity sampling of wood from living trees in the watershed of Mirror Lake, New Hampshire, USA. In particular, we used stable nitrogen isotopes in wood and lacustrine sediments to demonstrate that nitrogen availability in a northeastern forest has declined over the past 75 years, likely due to ecosystem recovery from EuroAmerican land use. We determined a presettlement trajectory of ecosystem change, and found the forest nitrogen availability has only recently returned to levels forecast from these trajectories, rendering the trajectory of future forest nitrogen cycling uncertain. Our results suggest that chronic disturbances caused by humans, especially logging and agriculture, are major drivers of terrestrial nitrogen cycling in forest ecosystems today, even a century after cessation.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 1632 Land cover change
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting