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Warmer waters cause challenges for Bay restoration

Warmer waters cause challenges for Bay restoration

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This is excerpted from a longer article that first appeared in the January/February 2023 issue of the Bay Journal.

by KARL BLANKENSHIP, Bay Journal News Service

Warming water is threatening to undo decades of efforts aimed at improving aquatic habitat in the Chesapeake region, from headwater streams to the open water of the Chesapeake Bay itself.

The increasing water temperatures, which threaten species like brook trout and striped bass, already are offsetting some of the habitat benefits of the multi-billion-dollar Bay restoration effort, a new report warns. Worse, some actions taken to reduce pollution are actually contributing to warmer, more stressful, stream conditions for fish.


“We’re behind the eight ball right now in considering this in our major policies,” said Rich Batiuk, a former senior science official with the state-federal Bay Program partnership, who helped organize a 2022 workshop focused on the region’s rising water temperatures.

Batiuk was a leading architect of the current Bay cleanup strategy for reducing nutrient and sediment pollution to clear the Bay’s water and shrink its oxygen-starved “dead zone.” The resulting water-quality improvements were intended to boost aquatic life. But some of the assumptions underlying that effort didn’t account for the negative impact that rising water temperatures would have on fish, crabs and even worms and algae.

Now, a report from the Bay Program’s Scientific and Technical Advisory Committee, stemming from last year’s workshop, warns that those changes could undermine progress toward Bay Program goals for “fisheries management, habitat restoration, water-quality improvements and protecting healthy watersheds.”

Batiuk and other scientists, as well as government and nonprofit organization representatives who participated in the workshop, stressed the urgent need to save areas that can still be protected from rising temperatures while mitigating harm to places where changes are inevitable.

“We’ve got to be thinking about temperatures in the same way we talk about nitrogen, phosphorus and sediment,” Batiuk said.

The failure to account for such impacts has resulted in the widespread use of nutrient-control devices, such as detention ponds, which increase stream temperatures. At the same time, actions that would help reduce the threats from warming water – such as planting trees along streams and in urban areas – are far off track.

“We are behind on our goals that may most help this,” said Rebecca Hanmer, a former Bay Program director who helped organize the workshop. “To say that we have to take rising water temperatures into account is not to say that’s a new goal for the Bay Program. It’s a new reality.”

In the Chesapeake, the average summer water temperature has increased about 1.8 degrees since 1995, driven primarily by warming air temperatures.
Across the watershed, a U.S. Geological Survey analysis found that stream temperatures increased 2.52 degrees on average from 1960 to 2020. That increase stems not only from warming air, but land-use changes that warm stream temperatures.

These increases have already impacted aquatic life. Nearly a century ago, when pioneering crab biologist Reginald Truitt was working with the Bay’s blue crabs, the crustaceans spent nearly five months burrowed into mud as they hibernated during cold months.

Typically, the crabs would begin digging in by early December and remain until late April. Today, the crabs usually don’t bed down until mid to late December, and they emerge by late March or early April.

Such changes could have implications for the winter survey of hibernating blue crabs, which assesses their population each year. It could also factor into future harvest management.

Meanwhile, eelgrass beds, one of the Bay’s most important underwater habitats, have been declining for decades. Scientists fear that the heat-sensitive plant, which is the only underwater grass species in many portions of the Lower Bay, will largely disappear in coming decades, dramatically reducing important habitat for juvenile blue crabs and fish, waterfowl and other species.

In the headwaters, brook trout, which typically do not tolerate water warmer than 68 degrees, also have been declining for decades. Other cold-water dependent species, such as the checkered sculpin, a small fish, are facing similar habitat losses. Many less-studied fish, mussels and amphibians may also be at risk.
As water warms, it holds less oxygen, creating problems for species like sturgeon, which require high oxygen concentrations. In the summer, low-oxygen levels in bottom areas of the Bay force striped bass toward warmer surface waters, which are stressful to the fish and cause increased mortality when the fish are handled.

Warmer temperatures also increase the toxicity of some heavy metals and other chemicals, promote the growth of bacteria and harmful algal blooms, and spread pathogens that can infect fish.

Scientists are also concerned that warming temperatures could disrupt predator-prey relationships that have existed for millennia.

That could be especially worrisome for migratory fish, which evolved to spawn in specific habitats at certain times so their young can take advantage of abundant food. As temperatures change, food sources may no longer be available at the right place or right time.

“Those rising temperatures could affect spawning, other prey relationships, nonnative species or pathogens [and] diseases,” said Stephen Faulkner of the U.S. Geological Survey Eastern Ecological Science Center in Leestown, W.Va. “There’s a whole suite of potential indirect effects related to rising temperature.”

Karl Blankenship is editor-at-large of the Bay Journal. You can reach him at kblankenship@bayjournal.com.

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