HR: 12:05h
AN: OS12A-08    [Abstracts]
TI: Large Phytoplankton Blooms Fuelled by Agricultural Runoff Into Especially Vulnerable Ocean Waters
AU: * Beman, J
EM: beman@stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305 United States
AU: Matson, P A
EM: matson@stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305 United States
AU: Arrigo, K R
EM: arrigo@pangea.stanford.edu
AF: Department of Geophysics, Stanford University, Stanford, CA 94305 United States
AB: In large areas of the ocean, primary productivity is controlled by supply of nutrients to surface waters. The relative balance between supply and removal of nutrients-such as nitrogen, phosphorus, and iron-determines which nutrient is most limiting to phytoplankton growth. Areas with high rates of microbial denitrification exhibit large nitrogen deficits relative to other nutrients. These regions are particularly vulnerable to inputs of nitrogen from other sources, as we demonstrate here for the Gulf of California, where nitrogen in agricultural runoff fuels large (54-577 km$^{2}$) phytoplankton blooms. Despite naturally high nutrient concentrations and rates of primary productivity agricultural nitrogen exerts a surprisingly strong and consistent effect on phytoplankton biomass, stimulating blooms only days after irrigation and fertilization of agricultural fields. Because these blooms can be transported rapidly over long distances, their ecological effects are likely felt across the Gulf. As fertilized agriculture intensifies and expands globally, these findings highlight the sensitivity of the world's oceans to runoff, particularly in the developing tropics and subtropics.
DE: 1615 Biogeochemical processes (4805)
DE: 1635 Oceans (4203)
DE: 1640 Remote sensing
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting