Q&A on salt marshes: Massachusetts’ thriving communities

With over 10,000 acres of salt marsh, the Great Marsh is the largest salt marsh in New England. Photo courtesy of Flickr

By Mikayla Heiss
BU News Service

Salt marshes provide important areas of high diversity to saltwater ecosystems in Massachusetts, but these historically threatened coastal grasslands are at risk.

Jennifer Bowen, an associate professor of marine and environmental sciences at Northeastern University, studies the effects of human activities, such as adding excess nutrients like nitrogen to water for nutrient pollution, and the structure of microbial communities within these critical habitats. Recently, she returned from a trip to the west coast with a cold. 

Bowen talked about her work and the general status of salt marshes throughout Massachusetts through her sniffles and sneezes. An edited and condensed version of the conversation follows. 

What drew you to salt marshes?

I’ve always wanted to work in the coastal zone. Salt marshes are really important in terms of the services that they provide to coastal communities. That combination of thinking that they’re really beautiful and how important they are to all aspects of sustainability is ultimately why I decided to spend most of my time focusing on marshes.

Tell me about the benefits of salt marshes.

There are quite a huge number of services these habitats provide to coastal communities. Salt marshes intercept water coming from the land either through groundwater or through rivers. Because they intercept that water, they can remove a lot of the pollutants and nutrients coming from agricultural run-off, golf courses, fertilizers and septic systems. 

They are also really important in terms of attenuating storms. It’s going to slow down the rate that the storm is moving.  

What are some threats to salt marshes?

Before humans, as sea levels naturally rose and fell, marshes would move inland because as upland habitats get inundated with salt water, those plants can’t survive. The marsh grasses that are able to survive move into that space where they now have a competitive advantage. 

Humans have also built structures. A marsh could migrate inland in areas where there’s open space for them. But if people have built sea walls and houses, the marsh can’t migrate to where it normally would.

What is the general status of salt marshes in the Greater Boston area?

The Great Marsh up in Plum Island is the largest existing salt marsh in New England. Closer to the city itself, in Revere there’s the Rumney Marsh, which is a pretty large marsh complex. There are some parts of the Neponset watersheds where they have done restoration efforts that have pretty decent salt marshes, but then there’s this huge other area that has been taken over by an invasive reed.

In a paper you co-authored, you mentioned that about 81% of salt marshes in the Boston Harbor were destroyed. What are some of the implications of this loss?  

The implicants today are that the Prudential Center is sitting on top of what used to be a salt marsh. Back Bay was a salt marsh that was filled by the late 1800s, early 1900s. Wetlands have been historically viewed as wasteland that could be either converted into agricultural land or could be filled and developed. Now, we have to focus on remediating or preventing future marsh loss in areas where there are existing marshes and be smart about picking degraded marshes that we can help restore.

Some of your work focuses on microbial communities. What are these communities like in salt marshes?  

The microbial communities in salt marshes are incredibly diverse and surprisingly so. Salt marshes are every bit as diverse as soils. Microbes can do a whole bunch of other things to survive that we can’t do. They can use things other than air to breathe, like nitrates or sulfate. Because of that and dynamic gradients, there is a huge amount of space for microbes to survive. What’s amazing is that we know very little about the microbes that live in salt marshes. My graduate student is working on reconstructing genomes of microbes from salt marshes. Of these genomes that he’s recovering, easily half of them are not closely related to other bacteria that we know about.  

Are these microbe communities different based on the time of the day?  

Yes and no. The communities basically stay the same. It’s more a question of who’s doing what and when they’re doing it. In an experiment, the microbes who were actively doing things in the sediment stayed the same, but in the water, they changed a lot. That change was due to having cyanobacteria that become active during the day and died at night. A whole bunch of taxa become really active at night to decompose the microbes that died during the day. You can see this cycle of growth, death and rebirth over the course of a day-night cycle in the water.

In your opinion, what is the best part of a salt marsh? 

I’m a nerd. So I think that the fact that there are microbes in the marsh and we have no idea how they’re doing these things and that they have this repertoire of metabolic possibilities that is so unique. It’s really fascinating. That aside, I think that the light in salt marshes is amazing, especially in the late afternoon. It’s just spectacular. They’re really beautiful and calming.

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