HR: 09:15h
AN: NB21D-04    [Abstracts]
TI: Community and Ecosystem-Level Impacts of an Emergent Macrophyte on the Ventura River, California.
AU: * Simpson, J
EM: simpson@lifesci.ucsb.edu
AF: Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AU: Leydecker, A
EM: al.leydecker@cox.net
AF: Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AU: Melack, J
EM: melack@lifesci.ucsb.edu
AF: Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AB: Ludwigia hexapetala is a pervasive, emergent vascular plant on the lower Ventura River. Presence of this plant appears to facilitate growth of shade-tolerant diatoms, while indirectly inhibiting filamentous green macroalgae. Four sites on the river were monitored during 2003; three downstream of a wastewater treatment plant, where Ludwigia is present, and one upstream site where it is absent. Filamentous algae occurred at all four sites, but declined rapidly at the below-treatment plant sites as growth and cover of vascular plants increased. By late summer, percent cover at these sites was dominated by Ludwigia, while the upstream site was consistently dominated by green macroalgae. Submerged plant parts provided substrate for diatom colonization, roughly doubling benthic diatom biomass (measured as chlorophyll a) at the downstream sites. Presence of the Ludwigia population also had strong ecosystem-level effects. The wastewater effluent produced typical stream water nitrate concentrations of 100-200 uM. Nitrate uptake rates downstream of the treatment plant inputs averaged 5 kg N/km/day, and direct uptake by Ludwigia could account for 20-40% of this nitrate drawdown. Further nitrate removal from the water column may be indirectly facilitated by the presence of Ludwigia through facilitation of diatom population growth.
DE: 1803 Anthropogenic effects
DE: 1806 Chemistry of fresh water
DE: 1851 Plant ecology
DE: 1871 Surface water quality
DE: 9901 NABS Student Award - Basic Research
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly