Study: Susquehanna Flats natural resilient to storms, flooding

A recent study by scientists at the University of Maryland Center for Environmental Science has found the underwater grass beds in the Susquehanna Flats, which has only recently begun to make a comeback, are resilient to rough storms and flooding, like the hurricanes the area experienced in 2011.

EASTON — A University of Maryland Center for Environmental Science study found that underwater grasses in the Susquehanna Flats has a natural resiliency to rough storms and flooding.

Spanning nearly 20 square miles at the mouth of the Susquehanna River, scientists believe the Susquehanna Flats in the upper Chesapeake Bay to be one of the largest and healthiest in the Bay.

Underwater grasses are essential to the Bay’s ecosystem, according to UMCES.

“They pull harmful nutrients out of the water, cause sediments to settle to the bottom so sunlight can reach plants, protect the shoreline by reducing the impact of waves and currents, and provide habitat and food for a host of important organisms, including baby crabs,” UMCES stated in a press release.

But, it has not been without its share of threats. Tropical Storm Agnes in 1972 wiped out the bed, which according to UMCES was already weakened by decades of nutrient pollution. It had since made a comeback, but then came the two storms in 2011 that are at the center of UMCES’ study — Hurricane Irene and Tropical Storm Lee.

Scientists studied the two 2011 storms to find out how resilient the grasses in the Upper Bay had become, considering future threats like climate change that are slated to increase frequency and intensity of extreme storm events, according to UMCES. The results were good news for the grass beds.

“It’s proof that restored SAV beds have the capability to be resilient,” said study author Cassie Gurbisz of UMCES’s Horn Point Laboratory in Cambridge. “They can stick around for a while if you give them the right conditions.”

Scientists found that the 2011 storms did some damage to the grass bed at the Susquehanna Flats. The rush of water from the Susquehanna River tore up plants around the edge of the bed and deposited sediment that blocked the sunlight, which limited photosynthesis.

However, the bed was able to reduce the force of high flows sufficiently to prevent plant erosion at its inner core. In addition, although the floodwaters dumped a lot of sediment onto the SAV bed, it also dampened the waves driven by the winds, according to UMCES.

This decreased the amount of sediment that was later churned up and, as a result, increased water clarity. Clear water spilled over into adjacent regions during ebb tide, further improving the bed’s capacity for renewal by creating more favorable growing conditions in areas where plant loss had occurred, according to UMCES.

“Although there was substantial SAV loss in response to a major flood event, the system was also remarkably resilient, apparently owing to strong biophysical feedback processes carried out by a large, dense, healthy SAV bed,” said Gurbisz.

It’s called a positive feedback process. The plant beds alter physical conditions in ways that enhance their own growth, and it may help plant beds absorb the harmful impacts of storms, according to UMCES.

For instance, the plants create clear water in the middle of the bed, which promotes more plant growth, further improving water clarity. When that clear water spills out of the plant bed into the surrounding water, more light is available for new plants to grow, according to UMCES.

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