Salt Marsh Macrophyte Rhizosphere Effects on Microbial Biotransformation of Halogenated Estuarine Contaminants

EPA Grant Number: U916218
Title: Salt Marsh Macrophyte Rhizosphere Effects on Microbial Biotransformation of Halogenated Estuarine Contaminants
Investigators: Ravit, Elizabeth A.
Institution: Rutgers, The State University of New Jersey
EPA Project Officer: Lee, Sonja
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $128,000
RFA: STAR Graduate Fellowships (2003) Recipients Lists
Research Category: Academic Fellowships , Aquatic Ecosystems , Fellowship - Aquatic Ecology and Ecosystems


The objective of this research project is to address the links between salt marsh emergent macrophyte vegetation, associated sediment microbial communities, and xenobiotic biotransformation. This link between structure and function is a central question in analyzing the role and importance of maintaining estuarine wetland ecosystems. The question is particularly important in light of the extensive wetland creation and restoration projects currently underway in U.S. estuarine and coastal systems. Typically, the primary focus of these projects is the plant community; better understanding of the links between macrophyte species and sediment microbial function is vitally important. My research will apply an analysis of microbial diversity versus function relationship to biotransformation processes that have great value to human populations as well as value within the natural environment.


Synthetic halogenated aromatic hydrocarbons are extremely stable organic compounds linked to several environmental and public health concerns including cancer, liver damage, and reproductive disorders. These substances are persistent in estuarine environments because they are hydrophobic and tend to sorb to particulate matter. Because of sorption of these contaminants onto particles and subsequent particle incorporation into sediment profiles, contaminant fate is strongly linked to the activity of sediment microbiota. The ability of sediment microorganisms to biotransform pollutants is the primary factor regulating the accumulation of contaminants in salt marsh ecosystems. It is believed that reductive dehalogenation activity is widespread in anaerobic estuarine sediments, and there is a need for further study of factors affecting metabolism and growth of anaerobic dehalogenating organisms.

Living plants have accelerated the decomposition of organic material in wetland soils. The rhizosphere is a dynamic heterogeneous environment, and a general increase in microbial cell numbers and activity in the rhizosphere has been well documented. Macrophyte rhizospheres affect sediment microorganisms by providing substrates for microbial growth, increasing synergistic microbial communities on root surfaces, and altering sediment chemical and physical conditions including redox potential, pH, and inorganic nutrient availability. It is likely that rhizosphere effects vary for not only different xenobiotics, but also for different plant species, depending on specific sediment conditions and characteristics of the indigenous microbial communities. I will study the effect Spartina alterniflora and Phragmites australis vegetation have on microbial communities found in salt marsh sediments, specifically microorganisms with the potential to biotransform xenobiotics. This research has important implications for the environmental effects of replacing P. australis with S. alterniflora during salt marsh restoration projects.

Supplemental Keywords:

fellowship, salt marsh, macrophyte rhizosphere, microbial biotransformation, halogenated estuarine contaminants, Spartina alterniflora, Phragmites australis, halogenated aromatic hydrocarbons, HAHs, estuarine wetland ecosystems, anaerobic dehalogenating organisms, reductive dehalogenation, anaerobic estuarine sediments, hydrophobic, estuarine contaminants, wetland, particulate matter, PM, organic compounds, soils, microbial communities.

Relevant Websites:

2004 STAR Graduate Fellowship Conference Poster (PDF, 1p., 80.5KB, about PDF)

Progress and Final Reports:

  • 2003
  • 2004
  • Final