States in the Chesapeake Bay region are spending billions of dollars to stem the flow of nutrients that foul the Bay’s water — but just how “clean” must the Bay be to declare victory?

Computer models show that, even if all planned nutrient reductions are achieved, some areas of the Bay would still fall short of oxygen goals at certain times. Is that important? The answer could impact both the Bay cleanup and its cost. (Dave Harp)

The answer is a complex mix involving a lot of science topped off with some policy decisions, as well as one that could be subject to debate in coming months. 

In fact, a handful of places around the Bay were always likely to fall short of prescribed cleanup goals even if all of the actions to support the Bay’s “pollution diet” were fully enacted. Those places were given variances that allowed their dissolved oxygen levels, at specific times and locations, to fall short of established minimum levels.

New computer model projections show that some of those areas may no longer need such variances if current pollution reduction goals are met. But the deepest area in Maryland’s portion of the Bay, between the Bay Bridge and the mouth of the Patuxent River — a segment known as “CB4” — may be even more problematic.

The state-federal Bay Program’s computer models show that, even if all planned nutrient reductions are achieved, CB4 would still miss its oxygen goal by 6 percent during an average summer — up from the 2 percent previously projected.

Whether that’s important or — like horseshoes — close enough, is hard to say. The answer could have far-reaching implications for the cleanup and its cost.

The background

The Bay’s primary water quality problem is too much of the nutrients nitrogen and phosphorus, which spur an overabundance of algae in the Bay. When the algae die, they’re consumed by bacteria in a process that draws large amounts of oxygen out of the water.

That’s especially a problem in deepwater areas, where oxygen levels cannot easily be recharged with oxygen from the atmosphere. During the summer, it often leads to oxygen-starved “dead zones” that can be lethal for fish, crabs and bottom-dwelling worms. 

Those organisms require different amounts of oxygen, and to ensure they have enough oxygen at the right places and right times, the cleanup effort has divided the Chesapeake into a mosaic of areas with different oxygen requirements based on the species they support.

The Bay is divided into 92 water quality segments, but the deep portion of one of them – CB4 – would miss oxygen goals 6 percent of the time even if pollution reduction targets are achieved. (Chesapeake Bay Program)

Overall, the Bay and the tidal portions of its tributaries are divided into 92 segments, most of which are further subdivided into different “designated uses,” (shallow water, open water, deepwater, deep channel, and migratory and spawning areas) each of which have their own specific oxygen requirements. 

Those were translated into enforceable state water quality standards more than a decade ago that set minimum oxygen requirements for each use within each segment.

Spawning and nursery areas for migratory fish may need 6 parts per million of oxygen to protect spawning fish, their eggs and the juvenile fish that are produced. The deep channel of the Bay, though, needs just 1 ppm of oxygen — enough to support worms and other bottom-dwelling organisms that serve as the base of the food chain. But during the summer, even that small amount of oxygen can be a struggle to maintain.

The Bay cleanup plan, formally known as the Chesapeake Bay Total Maximum Daily Load, was established in 2010 and set the maximum amount of nitrogen and phosphorus that can enter the Bay and still ensure the minimum required oxygen condition levels, from the surface to its deepest water.

Those “maximum loads” are about 196.5 million pounds of nitrogen and 13.75 million pounds of phosphorus. Achieving those targets requires more than a 40 percent reduction from the nutrient loads that reached the Bay in 1985, when cleanup efforts started.

Not quite there

The nutrient levels established by the TMDL in 2010 were designed to attain necessary oxygen levels in the vast majority of the Bay and its tidal tributaries — but not quite all of them. They would not achieve the prescribed minimum levels at all times in parts of four segments, including deep portions of CB4, the deepest parts of the Patapsco and lower Chester Rivers, and the deepest parts of the Eastern Bay, according to projections from the Bay Program computer models. 

Instead, the water quality standards submitted by the state and approved by the EPA contained variances that allowed those areas to miss oxygen goals by 2 to 7 percent in time and space.

The most problematic, and largest, area was segment CB4, a patch of deepwater south of the Bay Bridge that includes a shipping channel. In that location, the variance allowed the 1 ppm minimum oxygen standard to be missed 2 percent of the time and still be considered in attainment with water quality standards.

Today, as the Bay Program completes its midpoint assessment of progress toward the 2025 cleanup deadline, updated computer models show a slightly different picture.

In the updated projections, current cleanup levels would eliminate the need for variances in the Patapsco and Chester rivers. That’s good news. 

But in the deep channel of the Mid Bay — historically the hardest place to meet oxygen goals — the latest computer model projections show the same level of nutrient load reductions won’t achieve the same level of oxygen benefit. Therefore, the variance in that area — the amount of time and space the oxygen levels in that area could be exceeded —would need to increase from 2 percent to 6 percent.

How close is close enough? 

Rich Batiuk is the associate director for science with the EPA’s Bay Program Office and was pivotal in the development of the Bay’s dissolved oxygen criteria. Batiuk said the variance provides a needed “release valve” in policy making.

Water quality segments are divided into “designated uses,” each of which has specific dissolved oxygen requirements based on the types of species they support. (Chesapeake Bay Program)If planned nutrient reductions are achieved, the other 91 segments of the Bay would fully achieve their oxygen goals. But getting 1 ppm of oxygen in the deep channel portion of the remaining segment to fully comply with Maryland’s water quality standards would require a huge additional effort by all of the watershed states that would cost billions of additional dollars, Batiuk said. 

“Just that little push, you’re talking another 10 million pounds of nitrogen loads that must be reduced,” he said. “That’s not a small chunk of change.”

But 6 percent seems to be the upper limit, Batiuk said. If the variance for CB4 were allowed to increase by more than that to accommodate greater nutrient loads, other areas would begin to miss their oxygen goals as well.

“Then there are two or three other segments that start to come into non-attainment,” he said. “All of a sudden you have opened up the dam.”

The decision rests with Maryland, which has to adopt any variance into its water quality standards, seek public review and comment, and then submit them to the U.S. Environmental Protection Agency for approval.

Maryland Environment Secretary Ben Grumbles said that he wants to see additional analysis, but right now, a 6 percent variance for CB4 looks like the “sweet spot” as it eliminates the need for most other variances while keeping a similar level of cleanup effort. 

Increasing the variance by more than 6 percent just to make the job easier, Grumbles said, “would be unacceptable from our perspective.”

Likewise, Beth McGee, a water quality scientist with the Chesapeake Bay Foundation, said her organization supports the change to 6 percent because of its technical basis and noted that the deep channel variance is supposed to be temporary and will be reviewed every three years.

Still, she cautioned that increasing a variance can be perceived as “moving the bar” by making standards easier, and may result in “a little pushback” by others in the environmental community, she said. 

In any case, McGee noted, the CB4’s deep channel area is far from meeting water quality standards today. If other nutrient controls are implemented, she said, it may trigger better-than-predicted water quality responses — as has been seen in some parts of the Bay — that are not accounted for in the model projections.

“Let’s continue to implement,” she said, “and if we get to the point where that 2 percent to 6 percent actually matters, then let’s talk about it.”

As with horseshoes, close just might be good enough.