Chesapeake Bay Underwater Grasses Make a Comeback: How Plants Managed to Thrive

It turns out that the Chesapeake Bay may be making a comeback. Scientists have found that the Susquehanna Flats, a large bed of underwater grasses that virtually disappeared more than 40 years ago, is now one of the biggest and healthiest in the bay. Now, researchers are finding out the story behind this comeback.

Underwater grasses are crucial to the Bay. They provide habitat for juvenile fish and enhance water clarity by trapping and removing sediment from the water. That's why monitoring these grasses is crucial for assessing the health of the Bay.

"Underwater grasses are sensitive to water quality so they are a direct indicator of the Bay's health," said Cassie Gurbisz, lead author of the new study, in a news release. "The fact that they came back means something good is happening. It's important, however, for us to understand how they came back so we can use that information to support restoration in other areas."

The underwater grasses in question at the Susquehanna Flats were already stressed by pollution. When Tropical Storm Agnes hit in 1972 and dumped sediment on the grasses, it was the final straw. The plants virtually disappeared from the area for nearly three decades. Then in the early 2000s, the grasses began to grow once more.

In order to find out what caused these plants to regrow, the researchers analyzed data from the timer period. They found that a combination of drought and reductions in nutrient pollution had a lot to do with the recovery.

"Exceptional growing conditions during the drought period allowed the system to overcome turbid water and served to kick start a rapid resurgence," said Gurbisz. "Light availability is the most important factor in the growth of submersed plants."

The plants then took over with a process called positive feedback, which allowed them to improve their own growing conditions by helping sediment drop to the bottom and stay there.

"These processes and patterns are not unique to Susquehanna Flats," said Michael Kemp, one of the researchers. "Similar trends have been suggested for the Mid-Atlantic Coastal Bays and Northern Europe alike. Our broader motivation lies in the idea that the methods and models used here can be applied elsewhere to explore similar plant bed dynamics around the world."

The findings are published in the journal Limnology and Oceanography.