September 1, 2016

Coastal Resilience, Invasive Species, and Carbon Cycling in Coastal Dune Habitat

A coastal storm in 2008 caused extensive erosion at the Cape Cod National Sea Shore’s Coast Guard Beach exposing an odd black woody deposit at the base of the eroded dune. Scientists identified these deposits as peat, buried long ago at a time when sea level was lower and this area was a freshwater cedar swamp. Deposits like this are formed when extremely productive systems sequester carbon dioxide from the atmosphere for use in building plant material. The plant material is deposited annually as litter and roots, building soil carbon deposits over time. Lack of oxygen in wetland sediments slows microbial decomposition of the buried plant material resulting in deep peat deposits that function as efficient carbon sinks for the planet. Before the dune erosion the carbon rich peat was safely stored under the dunes, but now that it is exposed, the carbon will likely be broken down, releasing greenhouse gasses into our atmosphere. MIT Sea Grant coastal ecologist, Rob Vincent, is working with the EPA and National Park Service to characterize carbon cycling in coastal dune habitat. The information generated by this work will be included in the EPA “Blue Carbon” coastal carbon cycling model currently under development.

When Vincent took a closer look at the peat, he also found evidence of roots and rhizomes from a well-known invasive species, Phragmites australis (Common Reed), growing in the peat. It appears as though the peat layers intercept ground water flow, providing a source of water and nutrients for the invasive plant. This is unusual because robust patches of Phragmites are not typically found in a dune environment where water and nutrients are limited. The appearance of Phragmites had been a mystery, but with the exposure of the peat deposits scientists were able to confirm that by tapping into historic wetland peat layers deep below the dune surface, Phragmites are provided with a competitive advantage, allowing them to survive in an otherwise stressful environment. This information will aid resource managers in their efforts to control invasive species.

Vincent is working with the EPA and National Park Service to study the carbon cycling of this unique dune environment, as well as the effects of peat deposits on the establishment and persistence of invasive Phragmites plants. With the increased risk of erosion from coastal storms exposing the once buried peat deposits, and the challenge of controlling an aggressive invasive species, this dynamic system has a lot going on. The research findings from this study will inform future conservation efforts in the region as well as allow us to gain a deeper understanding of carbon cycling in coastal dunes.