By boat or by air, environmentalists in Anne Arundel County are making an effort to map horned pondweed, an underwater grass that appears in the spring but dies ahead of the survey scientists have long used to measure sea grass growth in the Chesapeake.

South Riverkeeper Jesse Iliff, of the Arundel Rivers Federation, said there has been a resurgence of the grass in recent years, anecdotally — but there isn’t enough data about where the grass is growing and how much of it there is. Grasses that grow in the spring can die before the annual survey, conducted between August and September, but Iliff and others are finding ways to map the seasonal grass and share their data nonetheless.

The spring grass is important because it provides habitat, lessens shoreline erosion and could help break through thick, dark mayonnaise-consistency mud caused by excess sediment and nutrients, according to Iliff.

He said in some parts of the South River, that layer of mud can be a foot deep. Oysters can’t live in it — the mud is anaerobic, which means it doesn’t have any oxygen. They suffocate. He said grasses such as horned pondweed can break through that layer, providing needed oxygen and eating up extra nutrients.

The hope is the creek beds can be sandy again, eventually.

“It’s been a long time getting here, it’ll be a long time getting back out of it,” Iliff said.

Scientists don’t leave out the spring grasses in surveys because of a lack of interest, but a lack of time and manpower, according to Brooke Landry, chair of the Chesapeake Bay Program’s Submerged Aquatic Vegetation Workgroup. Horned pondweed prefers colder water, she said, so it peaks in the spring before temperatures get hot, and can also come back later in the year when the water cools again.

The Virginia Institute of Marine Sciences conducts an aerial survey each year which is timed to match up with the peak of biological activity, Landry said, which is May for the lower bay, late June to early August for the mid-bay and August and September for the upper bay. Annapolis is in the mid-bay, Landry said, and grasses typically peak around July.

While that work can capture some of the horned pondweed, Iliff and Jeff Holland, the West and Rhode Riverkeeper, have said that in years past while they noticed horned pondweed in the spring, the VIMS survey showed no grass in the rivers.

“It’s up to us if we want to capture horned pondweed,” Iliff said.

And they’ve been making an effort.

Landry is asking environmental groups such as the Severn River Association to collect data through a citizen science project called Chesapeake Bay SAV Watchers. As part of the effort the Severn River Association launched a “SAV Navy” in 2017, through which people on paddle-powered watercraft mapped the edges of grass beds using GPS equipment. They have been trained to identify plant species and collect water quality information as well.

This year for the first time the SAV Navy will start mapping spring grasses like horned pondweed, from late April until June. Landry said the data they capture is sent to VIMS, where it is added to a map of SAV, submerged aquatic vegetation, beds under a layer called “observations.”

One river down, Iliff is taking a technical approach to mapping the spring grass.

In the past, he said he has tried to map the edges of beds with a boat and Map My Run, a phone app typically used by joggers to track exercise. That wasn’t very effective.

Now, he has a drone and a fish finder. The fish finder can show him where underwater grass is, just as it uses sonar to spot rockfish for anglers.

Using the drone, he hopes to capture aerial shots of the grass beds that he can then stitch together digitally and analyze.

He recently went into Church Creek with the drone. Despite being the most polluted creek on the South River, with more than 50 percent of its watershed covered in impervious surfaces such as parking lots or buildings, he has spotted grass growing there in the past, he said.

The drone was grounded by wind, however. With fairer winds, maybe he and others can finally quantify spring underwater grass.

rpacella@capgaznews.com