Posted by Rick Civelli | 10.23.2012 | Marine Science
Where have all the salt marshes gone?
There’s nothing like the view from a salt marsh in the morning. Green Spartina grasses blowing in the wind as red-winged blackbirds fly in and out. Fiddler crabs dodging the incoming tide. A great egret spearing fish in the shallows. And of course, there’s that one-of-a-kind smell wafting up from the muddy depths.
All our campers learn the importance of these habitats. They collect crabs, oysters, and juvenile fish, showing the need for nursery habitats in commercial fisheries. They swim in coastal waters where salt marshes rim heavily populated areas – a testament to the marsh’s ability to remove harmful chemicals such as pesticides and fertilizers. Putting it mildly, salt marshes are important. That is why it has been alarming that salt marshes have been disintegrating, dying, and disappearing from the East Coast for the last two decades.
The cause of the decline had remained a mystery until recently. There are some instances where a rise in sea level is responsible, but that didn’t explain the vast majority of cases. After a nine year study, scientists at the Marine Biology Lab in Wood’s Hole have found the culprit. Not surprising, it’s us.
Scientists sought to replicate the environments where this habitat loss was occurring. They did so by adding nitrogen and phosphorus in concentrations similar to what are released by sewer and septic systems. Originally, it was hypothesized that this increase in nutrients would actually enhance salt marsh grass growths, and it did, to a point.
Over the first few years the Spartina grasses did grow taller and greener, but the growth was primarily at the top. They developed fewer roots and rhizome systems, making them unstable. After a few years of this top heavy growth, the unsupported grasses eventually topple over, pulled down by the tides.
It is these grasses and their root systems that provide the stability for the entire salt marsh. These roots stretch and hold the soil in place, thereby holding the entire creek bank in place. Once the Spartina grasses go, so does the bank, sliding into the creek. Cracks form and widen and higher parts of the marsh subsequently slide down. So slowly the salt marsh is converted into a mud flat. Mud flats only have a fraction of the diversity and productivity as salt marshes, so all animals and plants suffer.
The researchers of this study were very much surprised by the results. “Now we really understand that there are limits to what salt marshes can do,” says Linda Deegan, one of the scientists on the study. Prior to this it was thought the marsh and its inhabitants could soak up most of what was thrown at them, now we know that we have to help them in the future. Please remember there’s always a marsh downstream, and stem the spread of chemical treatments in your area.