Influence Of Top-Down And Bottom-Up Forces On Sediment Organic Matter Dynamics In An Experimental Eelgrass (Zostera Marina)

EPA Grant Number: F5E11084
Title: Influence Of Top-Down And Bottom-Up Forces On Sediment Organic Matter Dynamics In An Experimental Eelgrass (Zostera Marina)
Investigators: Spivak, Amanda C.
Institution: College of William and Mary
EPA Project Officer: Lee, Sonja
Project Period: July 1, 2005 through May 1, 2007
Project Amount: $108,395
RFA: STAR Graduate Fellowships (2005) RFA Text |  Recipients Lists
Research Category: Academic Fellowships


This research will experimentally test how top-down and bottom-up perturbations interact with benthic biodiversity and food chain length to alter sediment carbon pools, pathways, and transformation rates in an experimental eelgrass (Zostera marina) system. Conclusions from this work will be useful in predicting how estuaries will respond to anthropogenic food web alterations and nutrient loading. In addition, these results will provide insights regarding the effects on estuarine carbon and nitrogen cycling.

The proposed research will experimentally test the interactive effects of eelgrass bed community structure (diversity and food chain length) and bottom up forcings (nutrient loading) on the sources and quality of sediment organic matter (SOM) and resultant OM remineralization (sediment carbon and nitrogen fluxes).


To test the effects of benthic community structure on carbon cycling I will use a suite of complementary studies, including two mesocosm experiments and one field experiment. The first mesocosm experiment tested the effects of grazer diversity and trophic structure on SOM quantity and quality. The second mesocosm experiment will test the interactive effects of grazer diversity, food chain length, and nutrient loading on carbon deposition, ecosystem production, and sediment nutrient fluxes. The field experiment will test the interactive effects of food chain length and nutrient loading on SOM quantity and quality in an eelgrass bed. The response of eelgrass systems to manipulations will be evaluated to determine:

  1. amount and composition of carbon delivered to the sediments (C:N, lipid biomarkers, bulk C isotopes),
  2. sediment microbial community response to altered SOM composition (lipid biomarkers, CSIA),
  3. and changes in dissolved organic and inorganic carbon and nitrogen fluxes from the sediments (DO, DIC, DOC, DIN).

Expected Results:

Since grazing invertebrates consume different primary producers (epiphytic algae, macroalgae, benthic microalgae, vascular plants) the identity of invertebrates in a benthic community is important to the composition and quantity of OM delivered to the sediments. The strength of top-down (predator presence) and bottom-up (nutrient availability) forces can affect both grazer feeding behavior and the delivery of OM to the sediments. Changes in SOM composition or quality could have significant impacts on rates of sediment microbial remineralization.

Supplemental Keywords:

seagrass, Zostera marina, blue crab (Callinectes sapidus), diversity, trophic structure, carbon, sediment organic matter (SOM), lipid biomarkers, remineralization, ecosystem,, RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Aquatic Ecosystem, Environmental Monitoring, Ecology and Ecosystems, dissolved organic matter, anthropogenic stress, nutrient dynamics, biodiversity, food web, nutrient loading, food chain, ecosystem monitoring, aquatic food web, sediment organic matter, anthropogenic impact, aquatic ecosystems, carbon supply, seagrass

Progress and Final Reports:

  • 2006
  • Final