Banking on Mitigation
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Banking on Mitigation New regulations might change the landscape of national wetlands policy Although the Clean Water Act protects U.S. wetlands, e\'ery year thousands of acres of swamps and marshes are legally destrtiyed and con\erted into golf courses, shopping malls and other forms of dry, lucrative ground. Since 1989, the goal of wetlands policy has been to ndiieve "no net loss," but that remains an elusive target. Under cur- rent guidelines, developers whose proj- ects will impinge on natural wetlands can receive permits allowing constaic- tion in return for agreeing to offset the damage through a process known as compensator)' mitigation. The two most common fonns of this practice are in- dividual mitigation, in which de\el- opers build compensatory wetlands themselves, and mitigation banking, in which developers puidiasecredits frtim companies (mitigation banks) that have restored or created wetlands nearby. In theory, it's a pretty straightfor- ward system—for each acre of natural wetland lost there should be at least one acre created or restored. But a 2001 study by the National Research Coun- cil concluded that despite mitigation efforts the country was losing about AO,[X)O acres of wetlands annually. Last spring, in an attempt to improve the pnKess, the U,S. Army Corps of Engi- neers proposed new regulations that would force developers to meet strict- er—that is, more expensivt'—standards for individual mitigation sites, which might make mitigation banks seem like a bargain in comparison. According to tlie Corps, increased use of mitigation banking will address many of tlie prc^iblems tliat have kept "no net loss" from being realized. But a number of studies, and quite a few scientists, dis- pute the benefits of mitigation banks— and question whetlier it's even possible to engineer successful wetlands. "How do you re-create something that ttx>k nature a tliousaiid years to de- vek>p?" asks Joy B. Zedler, an ecologist at the University' of Wisconsin-Madison and one of the authore of the NRC re- port. "You don't" At least not, she says, within the tbnescale imposed by the Corps. Most mitigation sites are subject to no more than five years of oversight, but some wetlands, particularly foisted At a mitigation-banking site in North Carolina, workers convert former agricultural land to wetlands. (Photograph courtesy of George Howard, Restoration Systems.) areas, might take decades to replace ad- equately tiie land lost to development. According to Zedler, the primary ob- stacle is that although scientists know that welands help regulate water cy- cles, serve as water filters and provide habitat for diverse flora and fauna, even specialists don't always know how they do it. William M. Lewis, Jr., an ecologist at tlie University of Colo- rado at Boulder, believes that for now "we don't have any reliable way of rep- licating fimctions and values." A study published last year by Ohio's Environmental Protection Agency supports these concerns. The agency studied 12 mitigation-ban king sites across the state to determine how well they mimicked natural conditions. The results weren't particularly prom- ising. Twenty-eight percent of the area surveyed consisted of shallow ponds lacking rooted vegetation and could not be considered functioning wet- lands. Most of this acreage, however, had either already been sold as credits or approved for Siile. Tlie Ohio EPA also found that plant communities were generally of lower quality than natural wetlands and more likely to be home to invasi\'e species. The banking sites scored even worse when judged by the presence of am- phibians. None provided habitat for either wood frogs or spotted salaman- ders, which the report called indicative of successftil sites, and all were domi- nated by JList a few species of frogs. Of course, individual mitigation sites face all of these same difficulties. But two factors add to the risks of banks. Eirst, if one small individual mitigation site fails, the effects on the surrounding landscape should be minimal. Tlic col- lapse of a large bank site is a much more costly mistake. Second, whereas devel- opers who create their OUTI mitigation sites are usually required to do so in the immediate vicinity of tlie destroyed wetlands, mitigation banks tend to be Itxrated farther from the impact sites. At the same time, mitigation bank- ing has a number of points in its favor. Eor one thing, purchasing credits from a bank that has already restored or cre- ated wetlands can reduce or eliminate the time lag between the impact of de- \ elopment and tlie construction of new wetlands. According to George How- ard, co-founder of Restoration Systems, a mitigation-banking company based in North Carolina, there's another ad- vantage to mitigation banks: "Unsuc- 122 American Scientist, Volume 'iS
Transcript of Banking on Mitigation
Banking on Mitigation
New regulations might change the landscapeof national wetlands policy
Although the Clean Water Act protectsU.S. wetlands, e\'ery year thousandsof acres of swamps and marshes arelegally destrtiyed and con\erted intogolf courses, shopping malls and otherforms of dry, lucrative ground. Since1989, the goal of wetlands policy hasbeen to ndiieve "no net loss," but thatremains an elusive target. Under cur-rent guidelines, developers whose proj-ects will impinge on natural wetlandscan receive permits allowing constaic-tion in return for agreeing to offset thedamage through a process known ascompensator)' mitigation. The two mostcommon fonns of this practice are in-dividual mitigation, in which de\el-opers build compensatory wetlandsthemselves, and mitigation banking, inwhich developers puidiasecredits frtimcompanies (mitigation banks) that haverestored or created wetlands nearby.
In theory, it's a pretty straightfor-ward system—for each acre of naturalwetland lost there should be at leastone acre created or restored. But a 2001study by the National Research Coun-cil concluded that despite mitigation
efforts the country was losing aboutAO,[X)O acres of wetlands annually. Lastspring, in an attempt to improve thepnKess, the U,S. Army Corps of Engi-neers proposed new regulations thatwould force developers to meet strict-er—that is, more expensivt'—standardsfor individual mitigation sites, whichmight make mitigation banks seem likea bargain in comparison.
According to tlie Corps, increased useof mitigation banking will address manyof tlie prc iblems tliat have kept "no netloss" from being realized. But a numberof studies, and quite a few scientists, dis-pute the benefits of mitigation banks—and question whetlier it's even possibleto engineer successful wetlands.
"How do you re-create somethingthat ttx>k nature a tliousaiid years to de-vek>p?" asks Joy B. Zedler, an ecologistat the University' of Wisconsin-Madisonand one of the authore of the NRC re-port. "You don't" At least not, she says,within the tbnescale imposed by theCorps. Most mitigation sites are subjectto no more than five years of oversight,but some wetlands, particularly foisted
At a mitigation-banking site in North Carolina, workers convert former agricultural land towetlands. (Photograph courtesy of George Howard, Restoration Systems.)
areas, might take decades to replace ad-equately tiie land lost to development.
According to Zedler, the primary ob-stacle is that although scientists knowthat welands help regulate water cy-cles, serve as water filters and providehabitat for diverse flora and fauna,even specialists don't always knowhow they do it. William M. Lewis, Jr.,an ecologist at tlie University of Colo-rado at Boulder, believes that for now"we don't have any reliable way of rep-licating fimctions and values."
A study published last year byOhio's Environmental ProtectionAgency supports these concerns. Theagency studied 12 mitigation-ban kingsites across the state to determine howwell they mimicked natural conditions.The results weren't particularly prom-ising. Twenty-eight percent of the areasurveyed consisted of shallow pondslacking rooted vegetation and couldnot be considered functioning wet-lands. Most of this acreage, however,had either already been sold as creditsor approved for Siile.
Tlie Ohio EPA also found that plantcommunities were generally of lowerquality than natural wetlands and morelikely to be home to invasi\'e species.The banking sites scored even worsewhen judged by the presence of am-phibians. None provided habitat foreither wood frogs or spotted salaman-ders, which the report called indicativeof successftil sites, and all were domi-nated by JList a few species of frogs.
Of course, individual mitigation sitesface all of these same difficulties. Buttwo factors add to the risks of banks.Eirst, if one small individual mitigationsite fails, the effects on the surroundinglandscape should be minimal. Tlic col-lapse of a large bank site is a much morecostly mistake. Second, whereas devel-opers who create their OUTI mitigationsites are usually required to do so inthe immediate vicinity of tlie destroyedwetlands, mitigation banks tend to beItxrated farther from the impact sites.
At the same time, mitigation bank-ing has a number of points in its favor.Eor one thing, purchasing credits froma bank that has already restored or cre-ated wetlands can reduce or eliminatethe time lag between the impact of de-\ elopment and tlie construction of newwetlands. According to George How-ard, co-founder of Restoration Systems,a mitigation-banking company basedin North Carolina, there's another ad-vantage to mitigation banks: "Unsuc-
122 American Scientist, Volume 'iS
cessful projects could bankrupt me per-sonally," he says, "and that's a greatincentive to succeed."
Perhaps the biggest problem withindividual mitigation is that no oneknows just how well it works. In 2005,the Govemment Accountability Officeissued a report showing that the Corpsrarely visited sites to ensure that re-qu i i^ mitigation was being completed.And in most cases, annutil monitoring
reports from the permit recipients (usu-ally a condition of approval) were neverfiled. "Until tlie Corps takes its over-sight responsibilities more seriously,"the report concluded, "it will not knowif thousands of aa"es of compensatorymitigation have been performed."
So altlioLigh many wetlands ecologistsdon't share Howard's enthusiasm forbanking, there is agii^ment that, as heputs it, "tlie alternatives are a sad, sad
story." According to the Corps, the draft-ed regulations aix* unlikely to diange sig-nificantly befoa' being finali/ed later thisyear, which means that mitigation bankswi]] soon become an increasingly im-portant part of national wetlands policy.Whether that's a step toward "no netloss" remains to be seen. As Zedler says,"tliere's a lot of promise in mitigationbanking, but it all depeiids on how it'sdone."—Amos Esti/
Sensitive Cells
Stem cells take their cue from their physical surroundings
Our choice of careere as adults isn't de-termined by whetlier we slept on a cotor a featlier mattress as a child. But then,we're not stem ceils (at least, not anymore). A pair of recent reports showsthat when scientists grow stem ceils inthe laboratorv', the physical properties ofthe cells' cLiJture-dish homes influencewhen tliey wiU adopt a distinct path inlife and what that path will be.
At the 2006 annual meeting of the.American Society for Cell Biology inSan Diego last December, ChristopherJ. Murphy of the University of Wis-consin-Madison presented data show-ing that embryonic stem cells are morelikely to keep theiv pluripotency—theirability to become any type of ceil—when they are grown on a surfacestamped with a pattern of tijiy ridges.The effect was independent of tlie scaleof the ridges, which ranged from nano-meters to micrometers in width. Tra-ditionally, cultured cells are grown onsmooth glass or plastic surfaces.
Tliis finding challenges the ingrainedculture of cell cu]ture, whidi has longasSLmied that the molecules dissolvedin the liquid medium tliat batlies cells,including growth factors and otherdiemical signals, had the last word indetermining ceil physiology. Murphydisagrees, citing work in his laboratorythat shows physical properties of thesurface to be "as fundamental an ele-ment [in determining cell behavior] ashaving growth factors in the media,"
So what exactly docs the physical to-pography do to tlie cell? "What doesn'tit do?" asks Murphy. "It changes ev-erything—adhesion, migration, pro-liferation, differentiation." From his
systems-engineering perspective, theresearch offers potential benefits forthe large-scale production of embryon-ic stem cells, wliidi have tlie theoreticalability to divide indefinitely but oftenlose pluripotency for reasons that arepoorly Lmderstocid.
The Wisconsin team's findings eciioprevious work by sdendsts at the Uni-versity of Pennsylvania. In the August25, 2006, issue of the journal Cell, thePenn group showed that the fate of mes-enchymal stem cells could be directedby the stiffness of the sutetrate on whichthey were grown. Mesenchymal stemcelis come fnim adult bone marrow.
A research team led by Dennis E.Discher found that stem cells grown onthe stiffest matrix became bone precur-sors. Those grown on the softest surface-became nerve cells, and those grownon a medium-stiff substrate assumedthe characteristics of muscle ceils. Thesha}.">es of the cells and the suite of activegenes contained within confirmed theirnew identities. Previous studies hadshown that chemical cues could effectthis kind of differentiation, but Disch-er's paper was tiie first to demonstratethat cell lineage could be controiied inthe absence of soiuble stimuli.
This property' makes sense, Dischersays, given the role of such cells in tissueregeneration and repair. "Tliese [mesen-chymal stem] cells leave the bone mar-row and end up in different places—muscle, bone, fat." But to repair muscle,or become a neumn in the brain or car-tilage at the end of a bone, tlie stem cellmust become anchored and "physicallyengage the niicrt>environment" beforebecoming one of the gang.
Sudi differences in the relative stiff-ness of animal tissues are easy to ap-preciate, according to Discher. "Youcan feel it. You know brains, calf'sbrains, how soft they are? I take youto the supermarket, you can feel thedifference between steak and bone, orbetween fat and calf's brains."
But groceries aside, how exactlydoes a cell "feel" the surface it growson? "It starts with attachment and con-traction," explains Discher. Cells createwhat are cahed focal adhcsiotis—pointsof attachment on the substrate—thatprovide a foundation for the cytoskel-eton. A type of motor protein known asnonmuscle niyosin 11 applies tension tothe actin filaments of the cytoskeleton.At the end of the line, a complex of pro-teins near the focal adhesion appears toact as a "mechantvtransducer," trans-lating physical forces into intracellularsignals. In the Cell paper, Discher andhis colleagues showed that inhibitingmyosin prevented the substrate-baseddifferentiation.
The strong effect of physical prop-erties on cell beiiavior in these experi-ments doesn't mean that sdentists wen?wrong before about soluble signals. Onthe contrary, the two types of stimuliseem to work together. But Discherstates—using language similar to Mur-phy's—that "physical cues are just asinfluential [on celi fate] as chemicalcues. It's a balance." In his mesenchy-mal stem ceiis, differentiation was morecomplete when diemicai and physicalcues pointed in tiio same dii^nrtion.
Tile potential implications of this workfor cell biologists are profound, giventhat ever^'thing scientists know about theway cells l^ehave in culture comes fromexperiments on hard, smtxith surfaces.For this reason, Discher cautions tliat bi-oiogists need to "take tJiose data [fromrigid substrates] with a grain of salt"Given the tens of tliousands of rtsearchpapers that include sucii methods, that'sa lot of salt.—Chris Btvdie
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