South Riverkeeper Diana Muller has documented three species of underwater grasses in the river this summer around South River Farm Park and in Glebe Bay.

"This is thick as snot!" Muller exclaimed as she paddled through the grass beds last week.

She had first discovered the grasses earlier in the summer while paddling with two new South River Federation employees.

Muller took the employees out on a kayaking trip to help them get to learn about the river. She chose to paddle near South River Farm Park, a wooded county-owned property that has a restored "living shoreline."

The group found themselves paddling through patches of sago pondweed, widgeon grass and Eurasion water milfoil.

On the return trip last week with Chesapeake Conservation Corps intern Carol Wong, Muller found the sago pondweed was thicker and more expansive, while there was less widgeon grass and milfoil.

At low tide, the tops of the grasses poked through the surface of the water, making it look like there were millions of tiny needles on the surface.

"This is the thickest I've ever seen it," Muller said. She used a small rake to pull up samples of the grasses and photographed them with a waterproof camera.

Muller said South River Farm Park and the area around it represent how a restored Chesapeake Bay should look.

A bald eagle and numerous blue herons and ospreys flew by.

"This is perfect: tree canopy, living shoreline and grasses," Muller said.Role in ecosystem

Underwater grasses are technically called "submerged aquatic vegetation," or SAV.

They grow in shallow areas, usually near shorelines.

They calm wave action and serve as places for fish and crabs to swim and hide. Many ducks and waterfowl eat underwater grasses.

Underwater grasses help suck up the nutrients nitrogen and phosphorus that fuel the growth of algae blooms that cause the Chesapeake's infamous oxygen-deprived dead zones.

Underwater grasses can be harmed by sediment-laden stormwater runoff that smothers grass beds.

Tropical Storm Agnes in 1972 "dealt a final blow" to many grass beds with its huge amounts of runoff and rainfall, according to the Virginia Institute of Marine Science.

A team from VIMS conducts the official annual grass survey each summer.

They fly in a plane, taking aerial photographs of the bay and its rivers. Those photographs are compared to maps and past photos.

For the past three years, the VIMS team has not documented any grasses in the South, West and Rhode rivers.

The Severn and Magothy rivers have some grasses, but they've been declining each year.

The last time the area around South River Farm Park had documented grasses was 2001, Muller said. That year, the South River had 10.74 hectares (26.5 acres) of grasses in the South River Farm Park area and in Glebe Bay.

'A positive thing'

It's difficult to tell why exactly the grasses are growing back in the South River.

Peter Bergstrom, a biologist and grass expert for the National Oceanic and Atmospheric Administration in Annapolis, said grasses can fluctuate from year to year.

The factors that contribute to grass growth can't always be pinned down.

For example, sago pondweed - the dominant species in the South River - usually does well when the water is saltier. But the bay's waters have been less salty this year because there has been so much rain, Bergstrom said.

Another puzzling factor is that the South has seen sago pondweed this year, and so has the Magothy River. But the Severn River in between them has more widgeon grass.

In general, anything that improves water quality and makes the water more clear will help grasses grow. If the water is murky with lots of sediment in it, sunlight can't reach underwater grasses for photosynthesis.

Waterfowl can contribute to the spread of underwater grasses as they eat the grass and then release the seeds through their excrement.

And even when there were no documented grass beds in the South, it's possible that there were small "relic beds" still surviving that expanded this year.

However the grasses returned to the South River, it's a rare positive development in the ongoing struggle to restore the health of the Chesapeake Bay.

"You can't count on it being there next year - that's the frustrating thing," Bergstrom said. "But it's a positive thing."

Copyright © Capital Gazette Communications LLC, 2011.