The Influence of Macroalgal Blooms on Biogeochemical Processes in Shallow Coastal Lagoons: A Dual Isotope Tracer Approach

EPA Grant Number: F6E10284
Title: The Influence of Macroalgal Blooms on Biogeochemical Processes in Shallow Coastal Lagoons: A Dual Isotope Tracer Approach
Investigators: Hardison, Amber K
Institution: College of William and Mary
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2006 through September 1, 2008
Project Amount: $109,131
RFA: STAR Graduate Fellowships (2006) RFA Text |  Recipients Lists
Research Category: Aquatic Ecosystems , Fellowship - Oceanography and Coastal Processes , Academic Fellowships


In order to understand the effects of macroalgal blooms on nutrient retention within shallow coastal systems, the objectives of my research are:

  • To quantify the effects of macroalgae on water and sediment chemistry, focusing in particular on changes in the quantity and quality of sediment OM.
  • To determine the short-term fate of macroalgal organic matter within the water column and sediments during bloom and senescent periods across multiple nutrient loading rates
  • To quantify the uptake of carbon and nitrogen by macro- and microalgae across multiple nutrient loading rates and assess competition between autotrophs.


To trace the uptake and fate of macroalgal organic matter within a shallow coastal lagoon, my approach combines the use of lipid biomarkers, 13C and 15N labeling, and compound specific isotope analysis of microbial biomarkers both in field and laboratory (mesocosm) studies. Because macroalgal biomass within a lagoon is hypothesized to be closely associated with the lagoon’s degree of eutrophication, my research will contrast a pristine with an impacted coastal lagoon along the Delmarva Peninsula. The field monitoring will be used to contrast the effects of different nutrient loading rates and varied macroalgal abundances on water quality and sediment chemistry. However, with the monitoring efforts alone, the separate pathways of carbon and nitrogen and the causal mechanisms determining those pathways cannot be deduced. Two mesocosm experiments will be conducted to explicitly determine the short-term fate pathways of macroalgal carbon and nitrogen using isotopically labeled macroalgae. A third mesocosm experiment will follow the uptake of carbon and nitrogen by macroalgae in the presence of additional primary producers (phytoplankton, benthic microalgae).

Expected Results:

Shifts in land use resulting from population increases and associated development along the coasts have and will continue to accelerate delivery of nutrients to coastal bays. I predict that this will result in a continued shift towards macroalgal dominated systems, and as a result, nutrient cycles will be changed significantly. I expect that my research will demonstrate that macroalgaes act only as a temporary sink for incoming nutrients and effectively diminish the role of coastal lagoons as nutrient filters. With increasing nutrient loads, the macroalgal bloom and die-off will result in a positive feedback cycle resulting in increased nutrient cycling rates: the re-release of inorganic nutrients to the water column will fuel additional algal blooms, which will again die off, releasing additional nutrients to the water. This will result in expanded areas of hypoxia and anoxia and negative impacts on fisheries, aquaculture, and recreational activities.

Supplemental Keywords:

Coastal bay, eutrophication, macroalgae, Gracilaria vermiculophylla, Ulva lactuca, lipid biomarker, stable isotope tracer, D-amino acid, mineralization, nutrient cycling,, RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Aquatic Ecosystem, Biochemistry, Environmental Monitoring, coastal ecosystem, nutrient dynamics, landscape change, ecosystem monitoring, organic matter, biogeochemcial cycling, algal blooms, aquatic ecosystems, biochemical indicator , land use, biomarker

Progress and Final Reports:

  • 2007
  • Final