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Lag Times' Impact on Bay Cleanup No Drop in the Bucket


A cold, gray dawn gives way to an eruption of light over the Blackwater River on December 21, 2012, the Winter Solstice. Groundwater moves more slowly on the Bay's Eastern Shore, slowing the effects of cleanup actions. Photo by Dave Harp.

The following first appeared in Bay Journal News earlier this month. 

Actions may take days to decades to show results depending on where they are taken.

Pull a bucket of water from the Chesapeake, and each drop will most likely be from a different place and tell a different story about how it got there.

For some, it's been a pretty short trip that started as a drop of rain that smacked into a parking lot, then flushed quickly into a local stream and reached the Bay a few days later.

Some may have soaked into Piedmont soil a decade ago and only recently emerged in a stream after traveling through groundwater.

Some drops from the Eastern Shore may have fallen as rain when John F. Kennedy was president, seeped into the Delmarva's slow-moving aquifers, and now, after 50 years, made it to the Bay.

A few may have even started their journey before the United States was a country.

Collectively, they offer more than a history lesson; they also provide a cautionary tale about how rapidly people should expect to see significant water quality improvements in the Chesapeake.

All of the drops of water absorbed nitrogen, which readily dissolves in water. But they likely all contain different amounts of nitrogen, because they absorbed the nitrogen at different times, in different places, when more or less was being applied to fields and when nitrogen-reducing management practices might not have been in place.

For example, the "youngest" water in the bucket might carry reduced amounts of nitrogen because cover crops, an effective nitrogen reducing practice, were in place when it fell as rain. But older water that predates cleanup actions may contain higher levels of nitrogen.

Those older waters are, in effect, time capsules that reflect activities that took place on the land years ago. In extreme cases, the nitrogen levels entering streams from groundwater that is many decades old could get worse before they get better, because it comes from a period when the amounts of nitrogen being applied to fields was rapidly increasing and often exceeded the amount that plants could use, meaning more nitrogen entered the groundwater.

"It's really a mixture of water ages that ends up in a stream," said Scott Phillips, Chesapeake Bay coordinator for the U.S. Geological Survey. "Some water travels over the land as storm runoff and is really young. Even the groundwater discharged into the stream is a mixture of ages. It is a complicated situation of many ages of water and associated nitrogen going into a stream."

That mixture complicates efforts to sort out overall water quality trends because improvements are often masked by "old"—often dirtier—water that is still moving through the system.

Scientists refer to the delay from when a pollution control action is taken to when it actually results in a water quality improvement as a "lag time." The concept is not new, but recent reports suggest lag times may delay the attainment of Bay cleanup goals longer than previously recognized—bedeviling efforts to show that billions of dollars of investments are reaping significant benefits to the Bay and its tidal rivers.

"The potentially long periods of these lag times do not constitute an excuse for inaction, but they do constitute a reason for being patiently realistic about the time scale for observing results," said a recent report from the Bay Program's Scientific and Technical Advisory Committee.

A new study from U.S. Geological Survey scientists showed just how much patience may be needed. It found that so much of the rainfall on the Delmarva Peninsula soaked into the groundwater, and its groundwater moved so slowly, that roughly a third of that water is more than half a century old.

That means much of it still predates the spike in agricultural fertilizer use that occurred in the 1960s and '70s. As a result, even though some "young" groundwater is part of the mix, the overall nitrogen concentrations reaching Eastern Shore rivers through groundwater are continuing to rise, and in many places it will take decades for that "old" groundwater with high nitrogen concentrations to be flushed from the aquifers.

The study, led by USGS scientist Ward Sanford, concluded that a 13 percent reduction today in the amount of nitrogen reaching groundwater was needed simply to keep overall nitrogen levels steady in 2050.

A diet with lag times?

A bucket of water pulled from the Bay in 2025 will likely be cleaner than one pulled out today—just as one pulled out today would, in most areas, be cleaner than one in 1990. But it likely will have far more nitrogen, phosphorus, and sediment than was prescribed by the Chesapeake Bay pollution diet.

That diet, or total maximum daily load, sets limits on the amount of nitrogen, phosphorus, and sediment that can enter the Bay from each state and major tributary. Those limits are intended to help the Bay and tidal portions of its tributaries meet water quality standards for dissolved oxygen, water clarity, and chlorophyll a (a measure of algae). Those standards are aimed at protecting aquatic life.

The TMDL calls for all actions needed to reduce pollution levels to acceptable levels to be in place by 2025. But because of lag times, the TMDL made no prediction of when water quality standards would actually be met throughout the Chesapeake.

The suite of environmental models and other tools used by the state-federal Chesapeake Bay Program to establish the TMDL and to guide the states' development of watershed implementation plans—the strategies that guide nutrient and sediment reduction efforts—do not factor in lag times.

Failure to account for lag times can have consequences in making such decisions. Modeling done for the TMDL showed that, pound for pound, nutrients from the Eastern Shore have a greater impact on dissolved oxygen levels in deep waters of the Bay than a pound from any other river except the Susquehanna. But time lags were not a factor in the allocation decision. To the extent that nutrient reductions from the Eastern Shore are necessary, full attainment of Bay water quality standards (as well as those in Eastern Shore tributaries themselves) will be delayed.

While the practical impact on the Bay is small—total nutrient loads from the Eastern Shore are dwarfed by those from the Susquehanna and other rivers—it illustrates the potential effect of not accounting for time lags when making nutrient reduction allocations among river basins.

If lag times are not factored into decision-making and better communicated with the public, support for cleanup efforts could be undermined, the Scientific and Technical Advisory Committee report cautioned. "We have to do a better job of communicating that these anticipated lags are in the system and that improvement is not going to happen overnight," said Gene Yagow, a senior research scientist in Virginia Tech's Biological Systems Engineering Department, and one of the lead authors of the STAC report.

The report noted that the lag times impact fundamental activities of the Bay Program. While installing best management practices to control runoff has been a priority for years, the Bay Program lacks a complete inventory of installed practices—particularly when it comes to those installed without government funding which often are not reported to agencies. It also often lacks precise information about where those practices are located. Practices near streams tend to yield benefits more quickly than those farther away.

Without that information, it is hard to fully estimate the extent to which lag times are delaying water quality improvements. "You can't estimate the lag time of something that you can't quantify," Yagow said.

The Bay Program has embarked on an effort to better account for BMPs in the watershed with a focus on nongovernment-funded practices.

Lag times have other implications as well. The STAC report noted that lag times complicate nutrient trading. In a trade, a wastewater treatment plant operator may want to offset increased discharges by paying farmers to do more. But the increased discharge would be immediate, while the nutrient reductions from BMPs may not result in water quality benefits in the Bay until many years in the future. Trying to factor the impact of lag times into a trade, the report said, "would add an extra layer of complexity making point-to-nonpoint source trading even more difficult to implement."

"A lot to ask"

The extent to which lag times will influence future Bay decision-making remains to be seen. The Bay Program partnership is planning a "midpoint assessment" of progress toward meeting the 2025 nutrient reduction goals that is to be completed by the end of 2017.

But the "principles and priorities" that have been established to guide the reassessment focus on ensuring that nutrient reduction practices will be in place by 2025—not when those practices will achieve the TMDL's water quality goal.

That could change. "Given this new information coming out, we are going to bring forward time lags and see how our partners want to tackle that issue in the context of the midpoint assessment," said Rich Batiuk, associate director for science with the EPA's Bay Program Office.

New tools being developed, including new groundwater models by USGS scientists, can help better predict where nutrient control actions will have less of a lag time than others. Targeting BMPs that become effective quickly toward those areas could help reduce lag times.

Still, as a practical matter, there are only so many places with shorter lag times, and while they can be prioritized for implementation, it would also require landowners to want to implement the practices that produce the fastest results.

"That is a lot to ask," Batiuk acknowledged.

The issue is further complicated because some of the places with the greatest lag times—the Eastern Shore and, to a lesser degree, Western Shore—are, ironically, those closest to the Bay. Asking places farther upstream from the Bay to do more would be, at best, challenging.

"The politics of that would be difficult," said Beth McGee, senior scientist with the Chesapeake Bay Foundation. "And the decision more politics than science."

McGee, like others, said she is concerned about maintaining public support if tangible progress is slow. "How are you going to maintain momentum when currently we are hard-pressed to point to many success stories?" she asked. "I think the solution is to look for success stories, to find areas where we have done a lot of implementation and where we expect things to turn around."

Bay officials are seeking to bolster their communication of the difficult issue. The Bay Program is working to complete a "lessons learned" report that highlights how local actions influence local water quality responses. They are also looking to highlight other areas of rivers or shallow waters of the Bay that may be more likely to show early responses to cleanup actions.

The Bay Program has developed a new water quality indicator to better highlight incremental water quality improvements around the Bay, rather than simply showing whether or not water quality standards are being fully attained. "Obviously, water quality standards attainment is the ultimate goal," said Jon Capacasa, director for water quality protection with EPA Region III. "But the public can derive a lot of benefits from the incremental reductions in nutrients and sediments to the Bay along the way. It is not one big on/off switch in 2025."

EPA officials are also pushing efforts to better quantify the level of water quality improvement that can realistically be expected in 2025. While the Bay wouldn't fully attain water quality standards by then, such predictions could help show that actions are having expected responses.

Water quality efforts should get a boost in coming years. Efforts to upgrade wastewater treatment plants have progressed rapidly, and officials expect most to be upgraded by the end of next year.

But after 2014, most of the nutrient reductions will have to come from nonpoint sources—mainly runoff from farms, urban and suburban areas and other land uses. With each passing year, smaller portions of the nutrient control actions being implemented will be fully felt in the Bay and tidal rivers by 2025. Portions of those improvements will continue to be offset by "old" nutrient pollution emerging from slow-moving groundwater.

But over time, the hypothetical bucket of water drawn from the Bay should increasingly reflect improvements from the nutrient controls efforts now underway—and those that will be taken in the near future.

"People like myself, we wouldn't be in this business we are in if we didn't have some level of optimism," Batiuk said. Lag times, he said, provide a reason to keep taking action—not to give up.

"Two generations back, they didn't see the level of degradation that would be caused by high nitrate levels in the groundwater," he said. "Yes, it might be a future generation that is actually going to see the full effect of what we do today. But we have to do it."


The only constant thing about lag times is that they are not the same

Lag times vary from place to place, by type of pollutant and by the routes pollutants take to the Bay.


Nitrogen readily dissolves in water, and the time it takes to reach the Bay is closely related to water flow.

In much of the Bay watershed, about half of the rain makes it to streams within a year, either quickly running off the land after a rain or by traveling through shallow groundwater. About a quarter of the precipitation travels through deeper groundwater, taking anywhere from a couple of years to a decade to reach the stream. The rest can take one or more decades. The exact time varies from place to place, and is heavily influenced by geology.

On the flat Coastal Plain soils of the Eastern Shore, for example, the lag time is much longer. About 90 percent of the rain travels through groundwater, and because the land is so flat, it moves slowly. While the average groundwater travel time in the Piedmont and Ridge and Valley region is a decade, the average on the Eastern Shore is 20–40 years.

Portions of the Western Shore which, like the Eastern Shore, are also located in the sandy Coastal Plain—generally an area south and east of Interstate 95—and are characterized by slow-moving groundwater. The flow here, though, is probably not quite so slow as the Eastern Shore because the region is hillier.


Much of the phosphorus running off the land is attached to fine particles of clay and silt. It is washed into streams by rainfalls that are heavy enough to cause erosion. Once in the stream, it moves downstream, step by step, during heavy rains that resuspend those particles and carry them farther downstream until they settle on the bottom, waiting to be moved by the next storm.

Where in the watershed the particles originate and how far they have to go affects how long it takes them to reach the Bay, but it can take years or decades. Again, the trip can be longer on the Eastern Shore, despite its proximity to the Bay, simply because it is so flat, the particles do not move so far.

Phosphorus lags are also created when high concentrations build up in soils over time. Areas with high phosphorus soil “reservoirs” can continue to lose phosphorus to water for years or decades.


Soil, silt, and sand particles largely move in episodic events. But how fast they travel depends on the weight of the particles. Fine sediments, those typically associated with phosphorus, are lighter and stirred up by smaller storms; they travel farther before they settle to the stream bottom. Heavier particles, like sand, are moved by larger storms and typically travel shorter distances. So heavier sediments can take longer—potentially many decades—to reach the Bay.

Also contributing to the sediment lag time is that material can be stored in stream banks or trapped behind dams for long periods of time before being dislodged by particularly severe storms. For heavy particles, the travel time to the Bay can range from decades to centuries.

Implementation lags

Various runoff control actions, usually called best management practices or BMPs, can also have lag times before they become fully effective. For instance, a stream forest buffer may take years to develop the root system it needs to intercept nitrogen moving through the ground. But fencing livestock out of streams can result in quick nutrient reductions.

So even when a best management practice is installed, it may take several years before it begins affecting the amount of nutrients leaving a field. A recent Bay Program Scientific and Technical Advisory Committee report said that when transport lag times associated with various geological settings are combined with lags for various BMPs to become fully effective, "lag times of one-to-three decades [are] common."

That doesn't mean that there are no quick benefits. Even on the slow-moving Eastern Shore, a portion of the benefit of an action can quickly be seen—about 10 percent of the rainfall runs off the surface rather than going through groundwater. And while a forest buffer may not become fully effective for years, the mere step of transforming a field into a buffer will produce benefits before trees take root. It's just that achieving the full benefit becomes a drawn-out process—and it is more drawn-out in some places, and with some practices, than others.

Some actions produce almost immediate results, such as wastewater treatment plant upgrades. Wastewater treatment plant discharges go straight into rivers, where they reach tidal waters in hours, or days, depending on their location. So when a plant is upgraded, there is no lag for water-quality benefits. Recent studies also suggest air pollution reductions can result in rapid nutrient reductions.

In places like the Western Shore, which has many large wastewater treatment plants, upgrades can help counter the lengthy groundwater lag times that delay the effectiveness of runoff control efforts. Unfortunately, across the Bay on the Eastern Shore, wastewater treatment plants are fewer and smaller, limiting their ability to counter lag times.

What happens in 2025?

In 2025, it is possible that all of the nutrient and sediment control actions outlined in state watershed implementation plans will be implemented. But it's probable that much of the Bay will fall short of water quality standards because of lag times, which delay the beneficial effects of many pollution control efforts.

In that event, any portions of the Bay that fail to meet water quality standards will remain on the federal impaired waters list. Waters can only be removed from the so-called "dirty waters" list based on water quality monitoring—not the predicted future benefits of actions put in place.

As long as it is on that list, the Chesapeake Bay Total Maximum Daily Load would remain in place. But whether states would be asked to do more to attain standards, or be allowed to wait to see whether water quality goals are eventually met, is uncertain.

"I think it is really premature to say exactly what the Chesapeake Bay Program partnership would do in 2025," said Jon Capacasa, director for water quality protection with EPA Region III.

Determining whether the Bay has met its water quality goals is not simply an "on/off proposition," he said. In fact, the Bay TMDL is not a single TMDL but a compilation of individual TMDLs for nitrogen, phosphorus and sediment covering 92 individual "segments" that make up the Bay and the tidal portions of its rivers. Some of those have better water quality than others.

Every two years, states are required to assess each tidal Bay segment to see whether they attain water quality standards and then file reports with the EPA. In the case of the Bay, the water quality standards are for specific levels of dissolved oxygen; for water clarity and underwater Bay grasses; and for chlorophyll a (a measure of algae).

"We are not waiting until 2025," Capacasa said. "If a segment is meeting standards, it is taken off the list sooner than that. We fully expect to see more segments in attainment of water quality standards before 2025."

But segments with the most severe water quality problems—particularly deep waters with chronic low oxygen problems or shallow water sites with very poor water clarity—would likely remain on the list until greater nutrient and sediment reductions are achieved.

Continued monitoring will help determine whether segments with the most stubborn problems are on the right track, Capacasa said. If not, he said, "Bay Program partners, as well as EPA, can take stock of what segments remain impaired and if there is anything more that we could be doing, or should be doing."

Karl Blankenship  


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