Salt Marsh Drowning in Long Island Sound: Causes and Biogeochemical Consequences

EPA Grant Number: FP917098
Title: Salt Marsh Drowning in Long Island Sound: Causes and Biogeochemical Consequences
Investigators: Hill, Troy Derek
Institution: Yale University
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2010 through August 31, 2013
RFA: STAR Graduate Fellowships (2010) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Water Quality: Coastal and Estuarine Processes


Healthy marshes accumulate pollutants in their sediments, including heavy metals brought in with the tides or deposited atmospherically. In Long Island Sound, some marshes are gradually converting to unvegetated mud flats, a poorly understood process that may compromise their role as sediment and pollutant sinks. If drowning marshes erode and begin exporting the metals stored in their sediment profiles, they could be unrecognized and potentially important non-point sources of pollution, a circumstance with serious implications for environmental and human health.


Salt marshes serve as long-term repositories of toxic trace metals, a critical function in urbanized estuaries such as Long Island Sound. Salt marsh drowning, and the potential for drowning marshes to erode and export pollutants, merits serious concern. In hopes of understanding marsh loss and its implications for trace metal storage, this project combines sediment profile analyses with aerial photography and high-resolution monitoring of pollutant fluxes in marshes along the Connecticut coast.


One explanatory mechanism for marsh drowning is sediment deprivation; marshes may not be receiving adequate sediment loads. This study will investigate the sediment deprivation hypothesis by constructing long- and short-term sediment budgets for drowning and healthy marshes using a combination of dated sediment cores, sediment traps, and sediment supply measurements. In addition to understanding causes, this research evaluates the consequences of marsh loss by coupling volumetric changes in marsh sediments with pollutant depth profiles to estimate historic trends in metal storage over the last 35 years. Metal concentrations in sediments and in tidal waters also will be measured to discern the current direction and magnitude of metal flux between marshes and the estuary. By studying long- and short-term trends in metal fluxes and accumulation, my research will detail the role of healthy marshes in pollutant sequestration.

Expected Results:

The project will focus on marshes in western Long Island Sound, an area exposed to intensive anthropogenic stress and elevated ambient metal levels. The accumulation of metals in salt marsh sediments in the western basin has been understudied, despite the high local population densities and the prevalence of marsh drowning in western Long Island Sound. This research provides information about the causes and consequences of marsh decline, information that is critical for salt marsh conservation efforts. This work also will use a novel approach to conduct detailed metal inventories for marshes in Long Island Sound and advance our understanding of the capacity of healthy marshes to sequester metals—a valuable contribution to the community of researchers interested in monitoring material fluxes and budgets in intertidal ecosystems.

Potential to Further Environmental/Human Health Protection:

This research will contribute important information to the management and policy communities by establishing inventories of pollutants stored in marsh sediments and by studying the potential for deteriorating marshes to become non-point sources of metal pollution. The public health, conservation, and scientific communities all will benefit from a finely-detailed assessment of the role healthy marshes play in retaining metals, and the functional losses associated with marsh drowning. Understanding the fate of sediment-derived pollutants helps guide monitoring and mitigation programs aimed at reducing public exposure to metal pollution.

Supplemental Keywords:

salt marsh, mass balance, trace metal, sediment budget, Long Island Sound,

Progress and Final Reports:

  • 2011
  • 2012
  • Final