HR: 16:15h
AN: NB14A-04    [Abstracts]
TI: Top-down Feedback Exacerbates Effects of Nutrient Enrichment in Detritus-based Ecosystems via Increased Loss of Basal Carbon
AU: * Rosemond, A D
EM: rosemond@uga.edu
AF: Institute of Ecology, University of Georgia, Athens, GA 30622 United States
AU: Suberkropp, K
EM: KSUBERKP@biology.as.ua.edu
AF: Department of Biology, University of Alabama, Tuscaloosa, AL 35487 United States
AU: Cross, W F
EM: crosss@uga.edu
AF: Institute of Ecology, University of Georgia, Athens, GA 30622 United States
AU: Greenwood, J L
EM: greeenwood.jennifer@epa.gov
AF: Institute of Ecology, University of Georgia, Athens, GA 30622 United States
AU: Greenwood, J L
EM: greeenwood.jennifer@epa.gov
AF: present address: US Environmental Protection Agency, 26 W. Martin Luther King Dr., Cincinnati, OH 45268 United States
AU: Eggert, S L
EM: seggert@uga.edu
AF: Department of Entomology, University of Georgia, Athens, GA 30602 United States
AU: Taylor, N
EM: ntaylor@uga.edu
AF: Institute of Ecology, University of Georgia, Athens, GA 30622 United States
AU: Wallace, J
EM: bwallace@uga.edu
AF: Institute of Ecology, University of Georgia, Athens, GA 30622 United States
AU: Wallace, J
EM: bwallace@uga.edu
AF: Department of Entomology, University of Georgia, Athens, GA 30602 United States
AB: In primary producer-based food webs faced with chronic nutrient enrichment, increased plant biomass may ultimately be suppressed by consumers. Effects of chronic enrichment of detritus-based ecosystems may be fundamentally different, with consumers exacerbating, rather than suppressing, the effects of enrichment on basal resources. We have continuously enriched a headwater stream at the Coweeta LongTerm Ecological Research site (North Carolina, USA) with N & P (to ca. 400 ug/L dissolved inorganic nitrogen and 50 ug/L soluble reactive phosphorus) for 4.5 yrs and quantified leaf breakdown rates, microbial production, invertebrate production, and leaf litter standing crop in the enriched stream and in an adjacent reference stream. Whereas nutrient enrichment largely increases basal carbon in primary producer-based systems, detrital carbon in the treatment stream was drastically diminished relative to the reference stream. During each successive year of enrichment, rates of leaf breakdown were progressively faster and standing crops of detrital carbon were progressively lower. This `ramping up' of loss rates of carbon appear to be driven by increased consumption by invertebrates, rather than increased microbial activity. Our results illustrate that fundamentally different trophic feedback effects can potentially occur in detrital vs primary producer components of food webs in response to increased nutrient concentrations.
DE: 4815 Ecosystems, structure and dynamics
DE: 4817 Food chains
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly