March 25, 2019
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Maine has a disappearing carbon sink for 10,000 cars in the ocean

George Danby | BDN
George Danby | BDN

Along the coast of Maine, from the Piscataqua River to Passamaquoddy Bay, eelgrass populations are declining. What is eelgrass and why should we care? Eelgrass is a flowering marine plant that essentially defines the coast of Maine. It grows in thick beds that provide shelter to commercially important fish and shellfish species and other organisms that make up nearshore food webs. The underground stems and roots of the plant help to stabilize bottom sediments, thus preventing erosion and promoting water clarity.

As if that weren’t enough, eelgrass also acts as a carbon sink. In other words, eelgrass uses CO2 in the process of photosynthesis and stores carbon in the ocean sediment. In Maine alone, eelgrass meadows sequester approximately 51,000 (+/-14,000) tons of carbon dioxide a year, or the equivalent of the carbon dioxide emitted from approximately 10,000 cars annually. Thus, eelgrass plays an important role in reducing the impact of human-made carbon dioxide emissions and mitigating ocean acidification in Maine’s coastal waters.

Equally important however, eelgrass plants can absorb excess nutrients that get into the ocean through polluted runoff. Nutrient runoff from fertilized lawns, farms and other sources, such as malfunctioning septic systems, is a larger contributor to ocean acidification than people think. Nutrients cause algal blooms in the ocean. When algae outgrow their environment, they die and sink to the ocean bottom. There, bacteria go to work, breaking down the algae. Under these circumstances bacteria can use up most or all of the oxygen in a cove or bay, leading to what is called a “dead zone.” In the process, bacteria produce carbon dioxide, a major culprit in coastal ocean acidification.

The Maine Commission to Study the Effects of Coastal and Ocean Acidification released a report on Feb. 5 recognizing the importance of shellfish resources and risks of ocean acidification to Maine’s economy. The commission made recommendations to the state of Maine regarding the threat of ocean acidification, and legislative members of the group introduced four bills to protect Maine’s marine ecosystem and coastal economy:

1) A bond proposal for a monitoring program to quantify acid from various inputs and chemical reactions affecting clam flats.

2) A measure to improve land for farming and implement best management practices for the watershed.

3) A measure to replace inadequate septic systems that impact nutrient loading and bacterial contamination of watersheds and bays.

4) A measure to continue the work of the ocean acidification commission.

We applaud this exciting development at the intersection of politics and the environment; however, a specific measure to protect and restore those habitats that are already absorbing CO2 from the water is missing.

Eelgrass can offset increasing CO2 levels from the atmosphere and absorb excess nutrients from polluted runoff, both of which can cause the acidity of the ocean to increase. So why not protect it?

A 2015 report on U.S. shellfisheries and ocean acidification by Julia Ekstrom and her colleagues in the journal Nature Climate Change ranks the Gulf of Maine third among regions in the United States most at risk for experiencing the devastating effects of rising ocean acidity. In recognition of the role of eelgrass in reducing ocean acidification, the Maine Commission to Study the Effects of Coastal and Ocean Acidification made the following recommendation: “Preserve, enhance, and manage a sustainable harvest of kelp, rockweed and native algae in bivalve areas and adjacent shoreline and preserve and enhance eelgrass beds.”

We must work at the community level to develop context-appropriate solutions to the problems posed by ocean acidification. On the coast of Maine, eelgrass is an available resource that has the potential to play an important role in the mitigation of ocean acidification, so we need to understand threats to eelgrass, protect eelgrass where we can and restore it where possible. Every property owner in every coastal watershed can do something to protect eelgrass, at the very least, by limiting the amount of fertilizer that is used on lawns and maintaining septic systems.

Eelgrass research and restoration efforts that are already under way in Maine need state support to be successful. Based on the recommendation of the commission, we suggest incorporating eelgrass into an existing measure or introducing an additional bill entitled: “A measure to support eelgrass research and restoration.”

Jane Disney of Salisbury Cove is a scientist at Mount Desert Island Biological Laboratory, and is president of Frenchman Bay Partners.


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