Tidal salt marshes have an amazing capacity to help the environment. In addition to providing a wildlife habitat and improving water quality, the marshes accumulate and sequester carbon in vegetation and soil. But what if the act of managing those marshes diminishes their capacity to better our environment or alters their carbon footprint, the balance between the carbon they absorb versus what they release? What if there is no net gain?
Four researchers associated with Indiana University set out to answer that question. They compared carbon sequestration at tidal salt marshes in the northeast U.S. managed with open marsh water management (OMWM) with unmanaged marshes at four U.S. Fish and Wildlife National Wildlife Refuges located in Maine, Massachusetts, New York and New Jersey.
Q. What is the role of wetlands and wetland management on carbon storage, greenhouse gas emissions and their contribution to global warming?
A. All wetlands sequester carbon (C), much more so than terrestrial ecosystems like forests and grasslands. However, freshwater wetlands also emit methane, a greenhouse gas that is about 25 times more potent or heat storing than carbon dioxide. In contrast, tidal salt marshes and other saline wetlands like mangroves sequester C but they release little methane. So, in addition to their well recognized value as habitat for finfish, shellfish and water birds and for water quality improvement, they help offset greenhouse gas emissions from human activities.
Managers of public lands such as the U.S. Fish and Wildlife Service oversee vast acreages of coastal wetlands and much of it is salt marsh. In the northeastern U.S., much this habitat was drained and ditched for mosquito control in the past. Activities such as Open Water Marsh Management (OWMM) whereby ditches are plugged to retain water on the marsh can enhance C sequestration and also improve access to the marsh by finfish and wading birds but with negligible release of methane. Other management activities such as breaching dikes or removing fill can provide the same benefits.
Q. One of the consequences of global warming is expected to be increasing sea levels as ocean surface waters warm and expand and ice sheets melt. How should coastal wetland managers prepare?
A. Sea level is expected to rise in the coming century and managers should be thinking about it now. Based on our findings, most salt marshes of the northeast are keeping pace with the current rate of sea level rise. That is the good news. The bad news is that some marshes along the New Jersey coast are not keeping pace with the current rate of sea level rise so they are certainly at risk if sea level rise accelerates.
The most important consideration for managers is to plan ahead, recognizing that sea level will continue to rise and set aside land upstream so tidal wetlands can migrate inland and upriver. Of course, this will be difficult in areas of the northeast that are densely populated and where the urban environment, sea walls and other man-made hard structures restrict their migration.
A. There is increasing interest in carbon trading programs, both in Europe and the U.S. However, there is a lot of reluctance on the part of policy makers to move forward with these programs though some states such as California are moving ahead on their own. Assuming carbon trading programs get traction, coastal land managers may be able to use the tools described above, OWMM and others, to increase carbon sequestration on their lands to offset their carbon footprint (e.g. their fossil fuel use) and still maintain other important ecosystem services like habitat and water quality improvement. They may even be able to sell carbon credits to others (which could help pay down the national debt. Unfortunately I don’t think it will be nearly enough).
The research is described in depth in the article “Carbon Sequestration in Tidal Salt Marshes of the Northeast United States” in the journal Environmental Management. It was authored by Katherine Drake, Holly Halifax, Susan Adamowicz and Craft. Drake is a 2015 graduate of IU’s Master of Science in Environmental Science program. She works with the Colorado Natural Heritage Program and, in the fall, will join the Nature Conservancy as a Restoration Specialist working with the Virginia Aquatic Resources Trust Fund. Halifax is an analyst at the U.S. Government Accountability Office. Adamowicz is the Land Management Research and Demonstration Biologist of the U.S. Fish and Wildlife Service stationed at the Rachel Carson National Wildlife Refuge in Wells, Maine.