One Small Step for Bugs

Restoring benthic communities

Restoring benthic communities

Credit: iStock/scubaluna

Like the inhabitants of the tragically fated Roman city of Pompeii, which fell victim to fallout from the Vesuvius volcano, benthic macroinvertebrate organisms in long-established communities along the river bottom received no warning of the oncoming catastrophe. They, like their human counterparts separated by millennia (and phylum), may have seen a few dark clouds but had no means of escape. It is likely the sudden disturbance killed many resident benthic organisms outright; others were probably washed away into a downstream lake known as the Mill Pond, which itself became mired with sediment. A large fish kill erupted in the blackened water, with fish showing signs of “abraded and plugged gills. . . . Mussel and macroinvertebrate colonies were rapidly buried under the silt and sand.”

Continuous Change
John Jackson, senior research scientist at the Stroud Water Research Center in Pennsylvania, says two big changes affecting aquatic ecosystems occur whenever urbanization takes place: “The land use changes and the water use changes.”

Straightening stream channels to accommodate properties, or burying streams in pipes and conduits to make way for structures, graphically simplifies meandering brooks and floodplains into linear conveyances for water. Replacing woods and meadows with impermeable surfaces for homes, offices, roads, and other facilities directs water toward these conveyances with extreme efficiency, often bypassing or overrunning formerly vibrant ecological niches. Well-manicured lawns complete the transformation of complexes of bog or glade into orderly subdivisions of uniform landscapes with well-defined drainage schemes.

It’s not only the hydrology that changes when urbanization takes place, but also the quality of the water itself, as drastically as the reshaped land it courses over.

Automobiles, simplifying life for us, put enormous pressure on aquatic ecosystems. Victoria Mills, executive director of the Doan Brook Watershed Partnership, a watershed restoration advocate in Cleveland, OH, says the amount of pollution spread over developed landscapes that can be attributed to drips from gas pumps, roadside car repairs, and other leakage from motor vehicles alone amounts to two Exxon Valdez–size oil spills every year.

And lawns are almost as troublesome. In accordance with its status as arguably the third-largest crop in the nation, the spreading monoculture of grass lawns contributes nutrients to the environment at an accelerating pace, says Mills. With the impacts of urbanization flowing to the streams and rivers, the streambed at the bottom of the food chain suffers the brunt. Something is being lost; in fact, entire worlds are vanishing before our eyes. Perhaps because of their minute, sometimes nearly microscopic, status, the inhabitants of these worlds largely go unnoticed. However, an expanding group of researchers, technicians, and other allies of the natural world say the vanishing benthic communities and aquatic macroinvertebrates would have a lot to tell us about the waters of our wider world, if we were to listen.

Guidelines and Lifelines
Assessing the health of 1,107,002 miles of streams and rivers in the United States, EPA listed 614,000 miles of those river and stream reaches as impaired. That amounts to more than 55% of all streams examined. Jackson, who studies urban stream health, says the proportion of urban streams suffering degradation is even greater. He says he has “not found an a single stream in an urban watershed that was not degraded in some way.”

However, Jackson says, his standard for what constitutes degradation is somewhat different from the criteria EPA uses in listing waterways for impairment.

Jackson focuses his research on benthic organisms and freshwater macroinvertebrate ecology. While EPA uses the designation of impairment as a regulatory measure triggering Clean Water Act provisions, Jackson says that definition of impairment is the result of an administrative decision where to draw the regulatory guideline. “The line has to be drawn somewhere,” he notes.

Jackson believes it is likely there are many streams that are significantly degraded that fall just outside the parameters of EPA’s listing authority relative to designated uses for the water, whether for drinking, for swimming, for fishing, or for non-contact recreation. He says some of these borderline streams may be just as desperate for attention as those on the 303(d) list. Jackson explains that there are a number of alternative ways to measure and talk about stream health that can help direct attention to the broader range of streams in need of healing.

As an objective measure, he says, stream health is directly correlated with the presence or absence of diverse benthic communities. That’s not because having diverse aquatic organisms in residence generates healthy conditions on its own, but the other way around. His suggestion mirrors the US Geological Survey’s (USGS) observation in its 2013 National Water-Quality Assessment program report Ecological Health in the Nation’s Streams, which states “aquatic biological communities are a direct measure of stream health because they indicate the ability of a stream to support life.”

Jackson says one way to tell if a stream is degraded is by comparing it to more pristine reference streams in the same geographic region of a similar hydrology and geology. He says a stream that “lacks an organism” or community of organisms that is present in the nearby reference waterway can be regarded as degraded. In other words, it may lack an element of vitality and possibly functionality because of disturbances caused by human activity.


Credit: iStock/GordZam

A Bug’s Life
Sara Burns, a researcher in benthic ecology at Indiana ­University Bloomington, explains the role of benthic ­macroinvertebrates in the environment, noting that benthic organisms are themselves a central component of stream health and not merely ­indi­cators. “Benthic organisms are an integral part of the energy system. They filter water, feed on decaying organisms, and process energy.”

Depending on their species and taxa, macroinvertebrates typically occupy themselves within small ranges of the river where they scavenge, graze, and browse. Their source of nutrition is mainly leaf litter flowing downstream, Burns says, and by browsing in discrete areas of habitat, they become a storehouse of energy for the particular section of river they inhabit.

For instance, “They aid in decomposition, by shredding leaf matter into ever-smaller fragments.” By dining on decaying plant and animal matter, they keep nutrients and energy cycling locally through living systems rather than allowing material to flow downstream to degrade slower-moving bodies of water.

Because they forage over a very narrow spatial range, the nutrient load and energy content benthic organisms consume stays in that area of the river, where they in turn may become the food of fish or aquatic vertebrates, moving energy up the food chain. Burns says that if they survive long enough to complete the cycle of metamorphosis, a process that can take up to five years, to eventually fly off as adult mayflies, dragonflies, or caddisflies, they then become “a huge source of food for birds and bats and riparian animals that eat them as they emerge.” As such, they represent a significant source of energy at the base of aquatic and terrestrial food chains. Although it may sound like a hapless condition, benthic macroinvertebrates have long been part of the most successful orders of life, at least until they encountered humans.

Fawn River Meltdown
Every now and then events occur that are so unprecedented and so extraordinary that the only way they could be approximated would be in a laboratory. Sometimes such events create the perfect conditions to test out an important theory. Some people refer to these events as natural experiments; these are the exceptional occurrences that because of their unusual and well-defined circumstances can be used to “prove the rule.” But they are, in many instances, not of the most fortunate nature; in fact, they often display the character of catastrophic accidents.

One such event occurred on the Fawn River in Indiana in 1998, when the operators of a state fish ­hatchery in Orland, IN, opened the floodgates, causing a rapid drawdown of the reservoir. Up to that time, the river had avoided the major negative impacts of encroaching human activity. According to a guide to resources in the state written prior to the opening of the gates, the 5-mile stream reach that received the discharge that day rivaled “any other in the state for combined biological interest and feasibility.”

All of that changed when the water came in. Flowing from the depths of the fish hatchery, it was not just water that entered the river, but also tons sediment that had settled out behind the dam over the years the hatchery had been functioning. According to the Fawn River Restoration and Conservation Charitable Trust (FRRCT), “the quantity of the sediment discharge was magnified by two prior herbicide applications in the reservoir, spaced one year apart, followed by three years in which additional sediments destabilized as anchoring vegetation and root masses rotted.” The wall of water rushing from impoundment carried with it a slurry of 100,000 cubic yards fine sediment, silt, and mud and sent it barreling down the previously pristine Fawn River channel.

Robin Sears, an area resident and staff member of the FRRCCT, says the force of the sediment billowing down the river uplifted the pebbled bottom and replaced it with mud and silt, and when the displaced gravel finally resettled to the bottom, an additional new layer of silt and more fine sediment heaped on top of that.

According to the FRRCCT, “The hyper-concentrated flow of sediments ( > 60% solids) deformed and buried the gravel bottom, filled the deep pools and cuts with silts and sand, and reduced connectivity to the underlying aquifer by plugging the hyporheic pores.”

In an instant, the formerly vibrant streambed habitat was transformed into a muddied, inhospitable mire. The sudden destruction wreaked upon the benthic communities, in miniature, the doom of Pompeii a thousand times over.

Although it happened very rapidly and in a rural location, Burns says, the disaster on Fawn River in many ways mirrored what’s been happening, gradually, to urban waterways everywhere. “Sedimentation, to varying degrees, is a problem in both urban and agricultural regions.”

However, shielded by a generous riparian zone of wooded wetlands and prairie and otherwise nearly undisturbed landscape, the Fawn River disaster and restoration would make an almost ideal test tube to shed some light on how benthic ecosystems can be restored to viability, even after severe insult. Burns led the data collection team studying the response of the Fawn River macroinvertebrate communities to restoration via fine sediment removal.

A Cascade of Degradation
In the new, post-event benthic environment on the Fawn River, the challenges were many. The accumulated sediment was densely packed down, sealing the porous interstitial spaces on the gravel bed, disrupting the connection between the stream and the underlying cold-water aquifer. The formerly cold-water reach, fed by groundwater, had been suddenly transformed into a warmer environment dominated by surface flow, inhospitable to the previous inhabitants. At the same time, dissolved oxygen in the stream was depleted by the replacement of riffles and pools by silt and sand bars, reducing the turbulence and mixing that would otherwise facilitate aeration. The once variegated oxygen-rich ecosystem had been reshaped into an anoxic flatland environment. Among other aftereffects, the sediment itself encouraged more erosion. With the streambed raised, in some areas by feet, the flow had been pushed outward and upward from the original thalweg. The raised and widened stream began scouring the original riverbank, damaging streamside habitat unaccustomed to inundation, continually washing additional sediment into the streambed.

Through this one incident, the once-prolific stretch of river had been reduced to hosting only the most disturbance-tolerant taxa. Absent were almost all traces of the pollution-intolerant families of macroinvertebrates, which, says Burns, include molting insects and those with complex life cycles, sometimes extending five years or longer. “Some only lay eggs under very specific conditions; others may have laid eggs despite the existing conditions, but they would not have survived long enough to emerge as adult flying insects capable of repopulating the stream.”

In response to lawsuits and advocacy by residents neighboring the river, a settlement was obtained in compensation for the damages caused by the 1998 release from the hatchery. A portion of those financial resources was directed to fund restoration activities and to study the outcome of the effort.

In spite of the challenges, the solution appeared straightforward: In theory, if the sediment could be removed, the river could be returned to its once-near-pristine condition, prepared for the succession of species and the return and recolonization by flora and fauna typical of the region. The FRRCCT set about a major project that would prove or disprove that theory. After a decade as an underwater wasteland, in 2011, the plan to restore the vitality of Fawn River went into action.

Breaking the Mold
The standard technique employed to remove sediment from water bodies has long relied upon massive dredging operations involving heavy equipment dragged to the streamside and invasive plowing of the stream. The FRRCCT, however, desired a lighter footprint and made the decision not to use heavy equipment in the river and riparian corridor. This led to the use of the low-impact, human-operated Sand Wand technology from Streamside Environmental LLC. Using the Sand Wand, operators could wade the stream and selectively jet and suction fine material within an enclosed shroud, pumping the slurry out of the riparian corridor to dewatering pits located on former agricultural fields, with gravel and cobble left in place.

According to Streamside Environmental, the Sand Wand has a much smaller footprint than dredging, requiring merely a narrow path cleared from the waterway to the discharge location to allow access for the stream team and equipment placement. Designed to minimize the impact of sediment removal, the device supplies a jet of water to stir up particulate matter from the gravel bed, and it can be calibrated to selectively extract sediment and particles that float up into the water. As with a vacuum cleaner going over a carpet, the rocks and the gravel and other objects that don’t make it through the Sand Wand’s filter are left relatively undisturbed on the streambed.

After treating a series of test plots at the beginning of the restoration project, the FRRCCT determined that simply removing the sediment from the streambed would not eliminate the ongoing threat of excessive sedimentation. The test plots rapidly filled in with new sediment soon after treatment. The restoration team tracked that problem down to continued sedimentation from the streambanks made susceptible to erosion in the initial incident.

To address this ongoing sediment deposition, in addition to deploying the Sand Wand, the restoration team installed large woody debris at strategic locations along the stream as an adaptive management tool to direct the flow away from the bank and toward the thalweg, to manage the momentum of the flow, and to use the forces of the river itself to keep excessive sediment deposits from building up in the streambed. Burns observes that as the river cleans itself with the help of this redirected current, the fine particulate matter is lifted from the interstitial spaces in the cobble, eventually restoring this inviting habitat for some of the more sensitive macroinvertebrates.

“As the gravel in the thalweg of the river is cleaned, the hyporheic habitat—that is, the habitat in the gravel and centimeters below the gravel, where the river water exchange happens—would be improved significantly,” explains Burns. “There would be more oxygen exchange, more groundwater would be entering the river, there would be a temperature change, and there wouldn’t be mud clogging everything up.” As conditions evolve toward this ideal, she says, “If there are more sensitive taxa as adults that come to lay their eggs, we would expect to see the river be recolonized over time.”

Looking at data from the study that accompanied the restoration, Burns says, “We found that very quickly over the course of the three-year study period, in areas where the sediment had been cleared only from the thalweg, that there were already more burrowing macroinvertebrates.”

That finding, she says, indicates that, “in a restoration project, if you know what your target is, and in this case it was heavy sedimentation, and you can reverse or remove that particular insult to the system, there is a chance that there will be some recovery.”

While this rebound in burrowing organism populations was not a surprise, neither could it be considered a foregone conclusion. “One of the reasons we decided to do this study was the assumption that habitat was key to restoring benthic communities and that if you built habitat you’d get restored organisms.” Burns says a number of recent studies indicate a more nuanced picture, and in fact data she collected on the Fawn River comparing benthic populations at various time scales after project implementation showed that some metrics of benthic vitality and diversity improved, while others seemed to be practically unaffected by the restoration. In some cases, benthic vitality by the selected measures seemed to decline in the months following restoration, weaving a complex scenario for future research to unravel.

Nonetheless, Robin Sears is able to report that anglers have since caught a 37-inch pike on the restored reach of the river, demonstrating progress. The fortunes of the creatures at the bottom of the pike food chain, the Fawn River’s benthic macroinvertebrate community, may still be up in the air.

Altered Waters
In an assessment of agricultural, mixed-use, and urban sites all across the mainland US, USGS found that 83% of stream biological communities studied had been altered by human activity, and a mere 17% had remained unaltered. In urban areas the USGS study data shows 89% of communities altered and only 11% intact and unaltered.

Jackson says degradation as a measure of stream health provides an objective standard based on statistical analysis of benthic communities living on the streambed. By those measures, the impact of human urban activity has been devastating.

During the process of urbanization there is no single triggering event that begins the slide towards stream quality degradation, says Jackson, but rather urban streams generally experience a “continuous gradient” of diversity loss and habitat disruption beginning with the first urban development.

“There is not just one first thing that happens to a stream” to begin the process of diversity loss, he says. Whether residential development, industrial development, or a mix among contributing factors to altering stream biological communities, USGS cites streamflow modifications, pesticides, and nutrients. In urban streams, says Jackson, “There is no smoking gun that if we fix that one thing it would restore the health of benthic communities.”

He observes that there has been some improvement in stream quality since the Clean Water Act went into effect. From the 1970s through the 1990s, he says, studies indicated “remarkable improvements in stream benthic ecological function.” He attributes these outcomes “to better control of industrial point-source discharges, better management of sewage through the implementation of separate sewer and stormwater systems, and better management of agricultural lands.”

He adds, however, “We have not seen a lot of additional progress in the last two decades.” According to Jackson, the rate of stream quality improvement has leveled off, leaving nearly 50% of freshwater streams impaired under regulatory guidelines and a much higher proportion functionally degraded relative to their natural preurbanized ecology.

“That means we’ve asked the waterway to handle our pollution and it couldn’t,” he says.

Nonetheless, Jackson believes it’s possible to begin to revitalize benthic ecological systems in two ways.

“One is prevention. Preventing things from getting worse. It’s not that water use and land use is static; we are always looking for more and different ways to use the land and use the water. There are always increasing demands, so the first step is making sure you don’t create more degradation.

“The second thing is restoration. In those places that are already degraded, how do we reduce the stressor loads to get it to a place where it is no longer degraded?”

For example, he says, White Clay Creek, where the Stroud Water Research Center is located, was historically not considered impaired, but it “was in a degraded condition in the 1960s” when the laboratory was built and restoration efforts undertaken. He says since that time the creek has shown remarkable progress.

“There are many species in the stream now that they didn’t collect back in the 1960s.” At the time the laboratory was built, “No one would have thought it was a bad stream; it was one of the better streams around here, but now we know there were things that were missing and they have come back.”

However, he concedes that, scientifically, there are a lot of unknowns. “What we don’t know is how much work it does take and what the time frames are.”

He says the science of benthic macroinvertebrate ecology is still in its infancy, particularly relating to applying that knowledge to model and predict how a stream ecosystem will respond to intervention. “Remember that a stream has 100 or 200—maybe more—species of macroinvertebrates, it might have 50 species of fish, it’s going to have 100 or 200 or even 300 species of algae. You’re talking about understanding the basic ecology for each of those species and then tying it to activities some distance from there. That’s a big lift; that’s a lot of information, and we’re just not there yet.”

Hydrological models are very successful able to make predictions about how water will behave under a wide range of influences, says Jackson, but modeling ecosystems is still a work in its early stages.

“We’re building the plane while we are flying it,” he says, “but if we don’t do it with that in mind we aren’t making enough progress to address what are always increasing needs to use the land and use the water.”

The important thing however, is to get the landing gear off the ground.

Flying Higher
For the Doan Brook Watershed Partnership (DBWP) in Cleveland, the prospect that urban streams’ benthic ecosystems can be restored through a watershed approach despite impacts too numerous to catalogue motivates a host of activities geared toward revitalizing streams feeding Lake Erie. When a new runway built at Cleveland Hopkins International Airport claimed 88 acres of wetland and more than a mile of Abram Creek in 2001, the Ohio Environmental Protection Agency ordered the city to mitigate the lost ecosystem through restoration activities on a separate Cleveland waterway known as Doan Brook. Originally slated as a $15 million project, it was intended to daylight and restore a naturalistic geomorphology to the stream by removing the walls of a manmade stone canyon built to protect the banks. Mills says there were various complications with this plan, some having little to do with hydrology. For example, the stone walls themselves were considered worthy of preservation. Built by workers with the Works Progress Administration during the 1930s, they had historical significance that precluded their removal, calling for an adjustment to the blueprints.

Subtracting the work that could not be authorized, however, left the Doan Brook improvement plan with $5 million to work with, and Mills says the funds helped accomplish a great deal along 2,000 linear feet of the brook. These improvements would allow the stream to flow more naturally while improving water quality and supporting fish populations.

Mills says the project, completed in 2011, implemented “nine to eleven in stream hydrologic solutions and nine habitat fixes throughout the stream to improve hydrology and restore habitat throughout the entire reach.” It restored the riparian corridor, reshaping and reinforcing steep eroding streambanks that were threatening infrastructure above, and replanting them with native plantings. In addition, as part of the project the Northeast Ohio Regional Sewer District (NEORSD) installed a rain garden to treat runoff from a parking lot that served a section of Rockefeller Park.

Along with the ecological benefits the project provides, Mills believes the effort may also help answer some important scientific and practical questions. “It’s great that they tried a number of different habitat modifications within the 2,000 feet, because then they can determine which approaches seem to work best.”

And, she views it as a beginning. “We consider that 2,000 feet to be one of the first steps to ultimately restoring the entire length of the stream up to the mouth at Lake Erie.”

In addition to its work with NEORSD to restore the Doan Brook within Rockefeller Park, the DBWP sponsors numerous outdoor events where naturalists share their insights into the watershed and its ecology with area residents. The watershed group has also implemented a wide range of other physical projects to restore ecological function on scales both small and large. “We have installed bioswales and rain gardens. We did a 400- to 500-foot restoration at a school, with plans for four or five other projects on the drawing board, and have a dam removal project in the works,” says Mills.

Dark Clouds, Bright Future
Mills believes restoring the vitality of waterways and their macroinvertebrate inhabitants will require caring for the entire watershed. “I don’t think any watershed work done today really looks at the stream in isolation. It is now common practice for the entire landscape that drains into any given water body to be considered fair game for restorative measures. For whatever project we’re doing in the stream, we do just as much work on the landscape to build back in any of the filtering and storage capacity that once existed before impervious pavements. Watershed perspective is it. It’s the only way.”

It’s an approach Burns endorses. “In terms of macroinvertebrate recovery, it’s about having more than one stretch of river that is healthy and restored,” she says. “It’s very important for the metapopulation of macroinvertebrates, because as adults they emerge from the water and fly around and mate and then lay their eggs somewhere else. If you have only one healthy stretch of river within a 20-mile radius, you’re not going to have a very diverse population, but if you have three healthy stretches within a 20- or 10-mile radius then those populations can move between the three rivers and you end up with more diversity.”

Regardless of the time or the amount of work it might require, Mills believes in the partnerships that DBWP has engaged in with groups such as the NEORSD. She says NEORSD has committed considerable resources and a timetable for replacing outmoded combined sewer systems that serve one half of the watershed, which she believes will greatly enhance the chance of success in restoring aquatic communities.

“If you’re working in a situation where you know the sewer district will correct the overflow problem, the habitat will already be in place when the bugs start being able to come back,” explains Mills.

Something seems to be working. Jackson says that by the 1950s “the Great Lakes were dead,” with mayfly populations decimated. As a result, he says, urban residents in the region are two decades removed from the phenomenon of the annual mayfly emergence, missing out on one of the great spectacles of the natural world.

But, Mills says things are changing, which has been frightening to some people. Since the late 1990s and 2000s, she has watched the mayflies stage a revival of sorts in the Cleveland area. Sometimes, she says, the insects take to the skies in such mass that “they create big clouds over the city.”

It’s encouraging, she notes, “when the six o’clock news has to report that there’s nothing to worry about, they don’t bite, and that they are actually a great sign of water-quality improvement.” SW_bug_web


Leave a Reply

Enter Your Log In Credentials