For the Chesapeake, 2018 was a year of mud, trash and sewage as unrelenting rainfall washed across its vast watershed, sending unusually high amounts of freshwater runoff into the Bay month after month.The Susquehanna River, laden with debris, overflows its banks at Port Deposit, MD, during a high flow period in September 2018. By early December, 3,400 tons of debris were collected upriver at the Conowingo Dam, ranging from beverage containers to floating docks. That haul dwarfs the 600 tons normally gathered there. (Dave Harp)

The water-fouling nutrients and sediment that were also flushed into the Bay by record-setting rainfall throughout the region will test the staying power of recent water quality improvements to the nation’s largest estuary.

At risk are improving trends for the Chesapeake’s fish-stressing “dead zone” and the restoration of its vital underwater grass beds and oyster populations.

Some cleanup efforts seemed to withstand the repeated downpours, but others faltered. Farmers struggled to plant pollution-absorbing cover crops, for instance.

It will be months before anyone can fully gauge the impact of higher-than-normal river flows that began flooding the Chesapeake in May and persisted through the rest of the year. August, September and November all set records for freshwater flows into the Bay, and December flows were running far above normal in its three largest tributaries, the Susquehanna, Potomac and James rivers.

“It’s very unusual to have seven months of above average flows,” said Scott Phillips, Chesapeake Bay Coordinator with the U.S. Geological Survey, “especially during this period of time.”

Extended periods of high flows are more common earlier in the year, when winter snow melts and spring rains arrive.

Not only did the year end wet, but scientists said high flows were almost a certainty for early 2019 because the ground is so saturated that water will continue to work its way into streams for months. Further, with the onset of winter, there’s little vegetation to absorb the moisture.

“Even if we don’t have rain, I think we’re going to have above average stream flows just because of the amount of groundwater draining after almost year-long high precipitation,” Phillips said.

Rainfall — and the associated increase in river flows — is often bad news for Bay water quality because it washes large amounts of nutrients and sediment from fields, parking lots and lawns that foul water quality.

Stormwater overwhelms a leaf-choked drain near the Choptank River in Cambridge, MD. (Dave Harp)The ensuing cloudy water can cause dramatic diebacks for underwater grass beds, and the sediment can bury bottom-dwelling creatures, while nutrients fuel algae blooms that draw oxygen out of the water, which leads to “dead zones.” Prolonged spells of freshwater inputs can also kill oysters and other salt-loving creatures that cannot move.

How many nutrients reached the Bay last year won’t be known for some time. But more than 500 million pounds of nitrogen were washed into the Chesapeake in other years with similarly high river flows, Phillips said. That’s more than two-and-a-half times the region’s cleanup goal for an “average” year.

Last year’s deluge will be the greatest test to the staying power of Bay restoration efforts since flooding associated with Tropical Storm Lee in late summer 2011. Since then, the Bay has experienced six years of normal or below average river flows. That led to noticeable improvements in its health, including the near-disappearance of anoxic water — areas with no oxygen at all — and a widespread comeback in underwater grasses.

Bay advocates point to such improvements as evidence that the multibillion-dollar cleanup effort is producing tangible results. They are optimistic that a healthier Chesapeake is better able to withstand periodic high-flow events, which inevitably leave the Chesapeake awash with pollutants.

“The Bay is resilient,” said Bruce Michael, director of the resource assessment service for the Maryland Department of Natural Resources. “We’ve made tremendous progress and success in reducing our nitrogen and phosphorus.”

Rainy as it was, 2018 could have been worse. Very high flows on the Susquehanna River — source of half of the Bay’s freshwater — can scour sediment that has built up behind Conowingo Dam and send it into the Chesapeake, adding even more misery to the ecosystem.

But flows at Conowingo peaked at 375,000 cubic feet per second in July — less than half of the highest flow caused by the 2011 tropical storm. USGS scientists said they saw little evidence last year of significant sediment scouring from behind the dam.

Although flows weren’t extraordinarily high, they were unusual in that they remained higher than normal for months at a time, including when it is usually dry. Those conditions are making it hard for scientists to predict their impact.

Not only were high river flows prolonged, but rains were so pervasive that they soaked the entire watershed — from southern Virginia to New York, and from West Virginia to Delaware. The District of Columbia’s record wet year resulted from measurable rain falling on more than one in three days throughout 2018.

The rain flushed huge volumes of debris off the landscape, in addition to the nutrients and sediment. By early December, Exelon Corp., operator of Conowingo, reported that it had collected 3,400 tons of debris at the dam, ranging from beverage containers to floating docks. That haul dwarfs the 600 tons normally gathered there. But it wasn’t the only place awash with junk: The updated stormwater management system in the District captured more than 700 tons of trash and debris flowing off streets last year.

Flows at Conowingo peaked at 375,000 cubic feet per second in July — less than half of the highest flow caused by the 2011 tropical storm — but USGS scientists said they saw little evidence of significant sediment scouring from behind the dam. (Dave Harp)

Still, a lot of debris went uncollected, creating a hazard for boaters during much of the summer. The waterborne clutter was so bad at times that charter boat captains canceled fishing trips.

Chronic downpours caused a rash of sewage spills throughout the watershed, releasing hundreds of millions of gallons of wastes into rivers and streams.

The downpours posed other challenges as well for restoration efforts.  Here are brief reports on some of the bigger issues the drenching of 2018 posed for the Bay:

Underwater grasses

One of the biggest concerns is how submerged grass beds fared. These underwater meadows provide important habitat for juvenile fish and crabs, plus many types of waterfowl.

Because they, like all plants, depend on sunlight to survive, their abundance is considered a prime indicator of the Bay’s overall water quality. After six “normal,” or low-flow years in a row, grass beds passed the 100,000-acre mark in 2017, the most seen in decades.

But heavy rains can turn water cloudy with sediment, blocking the sunlight the plants need to grow. But scientists are cautiously optimistic many beds were large and robust enough to survive a setback, though they may be smaller next year. “We had so much grass in 2017, that you kind of reach the points of resilience,” said Brooke Landry, a biologist with the Maryland DNR.

Grass beds survived an initial test early last year when, after a wet spring, many beds appeared to be in good condition. “We had probably the best water clarity that we’ve ever seen in the Tangier-Smith Island area since we started the imagery,” said Bob Orth of the Virginia Institute of Marine Science, who has overseen an annual aerial survey of underwater grasses since it started in 1984.

But after river flows picked up in mid-July, much of the Bay couldn’t be surveyed because of rain and clouds. On days when the sky was clear, the water was often too murky to spot grass beds. “All you would see is mud,” Orth said.

Still, the aerial survey yielded glimpses of robust grasses surviving even late into the summer in places such as the upper Chester, the Severn, the upper Patuxent and the Pamunkey rivers, Orth said. In other places, photos showed patches of grass still popping up through expanses of muddy water.

The massive grass beds in the Susquehanna Flats, where the river empties into the Bay also seemed intact. Landry said satellite photos showed a plume of muddy river water splitting when it reached the underwater meadow there.

Cassie Gurbisz, an assistant professor of environmental studies at St. Mary’s College, was doing field work in the flats when the river ran high in August and said, “the water was crystal clear in the middle of the flats. It was just amazing. It was like there was no flood at all.” On the outer edges of the grass bed, she added, “I couldn’t even see my hand in front of my face underwater.”

Heavy rains can turn water cloudy with sediment, blocking the sunlight that underwater grass beds need to grow. (Dave Harp)

But even where the beds persisted, there is a danger they may not bounce back next year. In late summer and fall, many underwater grass species found in the Bay typically use photosynthesis from the sun to build up energy reserves, which are stored in tubers and rhizomes in the bottom sediment. They need that stored energy to survive winter and start growing in spring.

“If there is chronic light limitation from all of this flooding, then those tubers and rhizomes are not going to be as big and robust,” Gurbisz said. “So, you might have problems the following year where the grasses might not come back in certain places.”

Oxygen levels & ‘dead zones’

Dissolved oxygen levels in deep waters of the Bay were poor during much of the summer, but not record-setting, despite the massive input of nutrients delivered by the rains. Strong winds accompanying some of the midsummer storms helped by mixing oxygen-rich freshwater on the surface with oxygen-starved saltwater on the bottom.

But the chronically high flows and murky water reduced algae growth, which also helped. Algae blooms deplete oxygen levels when they die and sink to the bottom. They decompose there in a process that draws the oxygen out of the water, leading to so-called dead zones.

Strong flows dispersed algae blooms before they could grow large, while murky water blocked the sunlight that microscopic aquatic plants need to grow.

“We didn’t have as many significant algae blooms this last year because the algae basically didn’t have time to set up with prolonged periods of sunny, warm conditions,” said DNR’s Bruce Michael. “They need light, and there’s not a lot of light with all that runoff.”

While oxygen levels have been worse in other years, poor conditions persisted longer into the fall than is typical, with a near-record amount of low-oxygen water — 1,200 cubic meters —  reported in Maryland’s portion of the Bay in October, Michael said. Only October 2011 had more, in the wake of Tropical Storm Lee.

Normally, the Bay has little “memory” from year to year when it comes to nutrients. Those that enter in a given year are usually either used up, buried or washed into the Atlantic Ocean, and do not feed water quality problems the following year.

With so many nutrients continuing to pour into the Bay late in 2018, though, scientists say it could promote an unusual growth of algae blooms this winter, and possibly into the spring, which could affect conditions this summer.

A torrent of rainwater from a parking lot and highway courses  its way  to a stormwater outfall pipe at Woods Road and Route 50 in Cambridge, MD. (Dave Harp)At a monitoring sensor near Annapolis, nitrate concentrations in the Bay in late October were nearly six times the normal levels, said Jeremy Testa, an assistant professor at the University of Maryland Center for Environmental Science.

“It suggests that the nitrate out there is really high right now, and having those concentrations is what can help support the bloom in the spring if they persist,” Testa said.

Scientists usually predict the amount of low-oxygen water they expect in the Bay each summer based on the amount of water that flows in from January through May. But the unusual nutrient spike late in 2018 may fuel an earlier-than-normal onslaught of hypoxia — or low oxygen — in the spring.

There’s not much precedent for this situation, but in 2012, the year after Tropical Storm Lee hit the Bay in late summer, hypoxic conditions did show up earlier than expected, Testa said.

Struggles for farmers

Besides causing problems for the Bay, the wet weather made it difficult for the region’s farmers to help reduce the flow of nutrients and sediment. Growers had to work in the mud to get smaller yields, and sometimes poorer quality crops as well. In some instances, fields couldn’t be harvested at all.

The ruts left in fields from working in the mud need to be addressed, or else erosion and runoff could increase next year, said Mark Dubin, agricultural technical adviser with the Bay Program. “It just touches every aspect of the agricultural industry,” he said.

The muddy fields that delayed harvests and ongoing rain also made it difficult for farmers to plant cover crops, Dubin said. Cover crops are a widely used practice that helps absorb excess nitrogen left on fields after crops are harvested.

Even where cover crops did get planted, they probably won’t soak up as much nitrogen as they would in a typical year, Dubin said. Heavy rains can push nitrogen deeper into the soil and beyond the root zones of the cover crops, so they can’t absorb the nutrient, he explained.

Farmers also had trouble installing new pollution controls such as streamside buffers, Dubin said. Some existing controls may have been washed away by flooding, or else didn’t perform as expected because of the sheer volume of rain. In some cases, he added, manure storage facilities are maxing out because farmers have had little opportunity to spread the animal waste as fertilizer on the fields.

“I don’t think its catastrophic, but I think it’s definitely stressing the system,” Dubin said.

An ‘awesome’ success

Not everyone was disappointed by the rain. “It was awesome!” exclaimed Carlton Ray, director of the Clean Rivers Project with DC Water, which manages stormwater and sewage in and around the nation’s capital. “We were hoping for wet weather, you know?”

Ray oversees a $2.7 billion effort aimed at capturing and treating effluent from the District’s antiquated combined sewer system, built more than a century ago, in which storm drains funnel rainfall runoff into sanitary sewers. In wet weather, the system typically overflows, sending diluted but raw human waste, into local rivers.

In a partial fulfillment of a federal consent decree to stop the overflows, seven miles of tunnels went online in March to capture and hold most of the stormwater and sewage that would normally spill into the Anacostia when it rains. After the storms pass, the stored wastewater gets treated at the Blue Plains Advanced Regional Wastewater Plant before being discharged into the Potomac.

Officials hoped the tunnel would capture and temporarily store 80 percent of the stormwater that normally flowed in the Anacostia. As of mid-December, it was outperforming that expectation, Ray said, capturing 89 percent, despite record rainfall in the District.

“This large source of pollution that’s been going on for years and years and years is now being taken off the table,” he said.

From March 20 through mid-December, even though the system captured 4.48 billion gallons of stormwater and sewage, 540 million gallons still went into the Anacostia, Ray said.

But that should change when another tunnel segment is completed in 2023. Then, nearly all of the stormwater-diluted sewage that once went into the river will get treated. A future expansion will capture other overflows that now go into the Potomac.

“My neighbors probably didn’t want to see so much rain, but it was good for me because we got to test the tunnel, and the whole system,” Ray said.

Oysters take a hit

Oyster surveys in much of the Bay were still going on in December. But in the Potomac River, where they were complete, the news was bad.

Oysters on bars in low-salinity areas of the Potomac suffered mortality rates upward of 90 percent, and on one bar “they didn’t find a living oyster,” said Martin Gary, executive secretary of the Potomac River Fisheries Commission.

“The Potomac has a history of freshets, but this was a bad one,” Gary said. Bars farther downstream took hits as well, he said.

High flows can sometimes be good for spat sets — when oyster larvae settle on the bottom and begin growing. Good spat sets usually yield abundant oyster harvests a few years later.

But that wasn’t the case this year, at least not in the Potomac. Gary said oyster reproduction there last summer was “dismal.”

But oysters that survive the freshwater will face less of a chance of dying from two lethal oyster diseases, MSX and Dermo, which have devastated the Bay’s oyster population in the past, but prefer high salinities.

Ryan Carnegie, an oyster disease researcher with the Virginia Institute of Marine Science, said he is seeing “very low levels” of MSX, and infections by Dermo are the lowest observed since 1989.

“We’ve seen the parasites being basically knocked back,” Carnegie said. “So, if there is a silver lining, that’s one. If [oysters] can survive the freshwater, they are going to gain an added benefit from reduced disease pressure.”

A mixed bag for other species

The surge of freshwater lowered salinities throughout the Bay, essentially pushing stinging jellyfish out of most areas last summer — a relief for anyone trying to swim or work in the water.

“There have been some years where we had to go and get wetsuits,” said Dave Secor, a professor with the University of Maryland Center for Environmental Science. “But this year, it was an absolute zero. I’ve never encountered that before.”

Strong flows can also be beneficial to anadromous fish, which live in the ocean but return to freshwater to spawn. Maryland DNR surveys showed striped bass, American shad and blueback herring all had good reproduction and survival this year.

The status of blue crabs won’t be known until the annual winter dredge survey is complete, but fishery managers said some strong blue crab catches were reported in early fall, especially in the lower Bay. They think high flows may have pushed the crustaceans down the Chesapeake and helped to concentrate them.

But lower salinities associated with strong river flows could have other implications as well. Gary said fishermen were catching blue catfish, a nonnative species that doesn’t like high salinities, at the mouth of the Potomac late in the fall, when salinities were just 7 parts per thousand — less than half of what’s normal.

That’s bad news because the high freshwater flows may have enabled the blue catfish to escape the Potomac, where they are normally trapped by higher salinity water near its mouth, and spread throughout the Bay and into rivers where it hasn’t previously been reported.

Biologists have been concerned that the voracious predator could disrupt the Bay’s food chain. With salinities low almost everywhere last year, Gary said, “blue catfish have gone pretty much anywhere they wanted to go.”

Meanwhile, populations of dark false mussels, a native species that likes lower salinities, surged in several Western Shore rivers in Maryland. Clearer water was also reported in some of the areas where robust numbers of the water-filtering bivalves were found.

“In the past, when we’ve seen these mussel blooms in response to freshwater events, it has actually spurred underwater grass recoveries in a lot of cases,” said the DNR’s Landry.

That could help grasses bounce back in places like the Magothy, Severn and other rivers where the mussels were reported, she said.

Scientists say they aren’t surprised that last year’s deluge seems to have produced a mixed bag of results in the Bay.

“That’s the really interesting part,” said Peter Tango, monitoring coordinator with the state-federal Chesapeake Bay Program. “Estuaries by their nature are dynamic and experience these sorts of fluctuations.”

Indeed, estuaries are places where freshwater and saltwater meet and mix so the species that live in them tend to tolerate a range of conditions. Some fare better than others whatever the natural conditions, but most eventually bounce back from weather-related setbacks.

“It is going to be interesting in 2019, because it will be the test case of how resilient the Bay was with all of this fresh water runoff,” VIMS’ Bob Orth said.