Ecological Issues Related to Wetland Preservation, Restoration, Creation and Assessment

The Science of the Total Environment 240Ž. 1999 31᎐40

Ecological issues related to wetland preservation, restoration, creation and assessment

Dennis F. WhighamU

Smithsonian En¨ironmental Research Center, Box 28, Edgewater, MD 21037, USA

Received 15 May 1999; accepted 18 May 1999

Abstract

A wide range of local, state, federal, and private programs are available to support the nationalŽ. USA policy of wetland ‘No Net Loss’. Implementation of programs, however, has resulted in the continued loss of natural wetlands on the premise that restored or created wetlands will replace the functions and values lost by destruction of natural wetlands. What are the ecological implications and consequences of these programs from a biodiversity and ecosystem perspective? From a biodiversity perspective, ongoing wetland protection policies may not be working because restored or created wetlands are often very different from natural wetlands. Wetland protection policies may also be inadequate to preserve and restore ecological processes such as nutrient cycling because they mostly focus on individual wetlands and ignore the fact that wetlands are integral parts of landscapes. Wetland mitigation projects, for example, often result in the exchange of one type of wetland for another and result in a loss of wetland functions at the landscape level. The most striking weakness in the current national wetlands policy is the lack of protection for ‘dry-end’ wetlands that are often the focus of debate for what is and what is not a wetland. From an ecological perspective, dry-end wetlands such as isolated seasonal wetlands and riparian wetlands associated with ﬁrst order streams may be the most important landscape elements. They often support a high biodiversity and they are impacted by human activities more than other types of wetlands. The failings of current wetland protection and mitigation policies are also due, in part, to the lack of ecologically sound wetland assessment methods for guiding decision making processes. The ecologically based HydrogeomorphicŽ. HGM approach to wetland assessment has the potential to be an effective tool in managing biodiversity and wetland ecosystem function in support of the national ‘No Net Loss’ policy. Published by Elsevier Science B.V.

Keywords: Wetlands; Biodiversity; Ecosystem function; ‘No Net Loss’; Wetland policy; Restoration; Creation; Mitigation; Assessment; Hydrogeomorphic; HGM; Landscape

Tel.: q1-410-798-4424, ext. 226; fax: q1-301-261-7954. U E-mail address: [email protected]Ž. D.F. Whigham

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1. Introduction without seriously considering the impacts of the losses under the guise of the ‘No Net Loss’ policy. Most historical wetland losses that have oc- One consequence of continued wetland losses, as curred in the US resulted directly or indirectly described below, is that they will have a negative from programs supported by government policy. impact on wetland associated species. Only in recent decades have policy debates and Wetland loss can be viewed in several ways. administrative programs resulted in a significant The most obvious type of wetland loss is the decrease in the rate of wetland lossŽ Dahl et al., conversion of a jurisdictional wetland to a non- 1991; Dahl and Allord, 1996; Opheim, 1997; jurisdictional status. Some areas may be classified Tzoumis 1998.Ž . In some states e.g. Ohio and as wetlands based on biota, soils, and hydrology California. , protection and restoration efforts but are not considered to be jurisdictional be- came only after most wetlands were lostŽ e.g. cause they are specifically excluded by state or Sibbing, 1997.Ž. . In other states e.g. Florida , his- federal regulations. Conversion of these types of torical policies related to water and wetland man- wetlands also represents a wetland loss. Finally, it agement resulted not only in considerable wet- could be argued that conversion of one type of land losses, but, in threats to entire landscapes. In wetland to another represents a net loss of wet- south Florida, for example, the Everglades and lands. The point that needs to be made, indepen- other hydrologically linked ecosystems are threat- dent of how one defines wetland loss, is that ened primarily because of historical policies that wetland losses continue for many reasons. In allowed widespread wetland conversion and alter- Minnesota adequate wetland legislation does not ation of local and regional hydrologic regimes protect wetland resources because political deci- Ž.Gunderson et al., 1995; Harwell, 1997 . Cur- sions resulted in regulatory structures that ‘lead rently, most types of wetlands are protected to a perpetuation of degraded wetland and up- through a variety of federal and state programs land habitat that is unrecognized but so prevalent Ž.ŽVottler and Muir, 1996 and some programs e.g. on the landscape’Ž. Svoboda, 1998 . Some wetlands Wetlands Preserve Program. provide funding to are not legally protected. Programs such as the support wetland protection and restoration. US Army Corps of EngineersŽ. COE Nationwide We are currently in the era of ‘No Net Loss’. Permit 26Ž Albrecht and Connolly, 1998; Sibbing, Some argue that we have achieved the goal of ‘No 1998. allow wetlands, especially intermittently Net Loss’ of wetlands because the rate of wetland flooded headwater and isolated wetlands, to be loss has slowed and because many wetlands are converted to non-wetland habitats without any being restored or createdŽ. e.g. Tolman, 1997 . mitigationŽ. Caputo, 1997 . The COE has pro- Others argue that, while wetland losses have posed to replace many of the nationwide permits slowed, wetlands losses continue at an unaccept- with new permits, which would almost certainly able rateŽ. Heimlich et al., 1997 . The debate allow for the continued loss of headwater and related to ‘No Net Loss’ is most often a numbers isolated wetlands. The proposed COE changes in game and what is usually lost in the debate is the nationwide permits were proposed even though a fact that wetlands continue to be lost or degraded National Academy of Sciences studyŽ National and wetlands designed to replace themŽ e.g. re- Research Council, 1995. concluded that ‘the sci- stored, enhanced, or created wetlands. often have entific basis for special permitting of wetlands in lower biodiversity and do not function similarly to headwaters or isolated wetlands is weak’. the natural wetlandsŽ. Kentula, 1996; Street, 1998 . Undoubtedly debates will continue over issues Many wetlands, and the functions that they per- such as: what is a wetland, how do you delineate form, are gone forever because a large number of the boundaries of a wetland, and how effective is wetland losses are never reported and restoration the national ‘No Net Loss’ policy? While these projects are often never completed or are failures debates continue I contend that because of the Ž.Smith, 1997 . The scenario that emerges is one in politically contentious nature of wetlands that which the US continues to lose natural wetlands ‘No Net Loss’ will remain a stated national goal D.F. Whigham rThe Science of the Total Enïronment 240() 1999 31᎐40 33 but we will continue to lose natural wetlands. I likely have a negative impact on the nation’s also believe that wetland losses will continue to biodiversity. One possible way to avoid the cont- occur, this is based on the assumptions that de- inued loss of wetland-dependent species is to stroyed wetlands can be replaced by restored, conserve more wetlands. Can wetland preserva- enhanced, and created wetlands. tion be used as a management tool at a national What are the potential impacts of a continua- scale? I believe that wetland preservation will tion of the present wetland policy? I submit that always be a desirable goal but that it is not likely wetland losses and associated declines in biodi- to be a viable approach for conserving wetland- versity and ecosystem function will continue for dependent species at a national scale. Noss and two primary reasons. First, the continued destruc- PetersŽ. 1995 identified areas of the country that tion of wetlands, particularly dry-end wetlands, contain ecosystems which contain federally will result in a loss of biodiversity and a reduced threatened species. Most of the ecosystems iden- ability of wetlands to provide important landscape tified by Noss and Peters occur over extensive values such as water quality improvement. Sec- geographic areas and it seems highly unlikely that ond, the continued failure of the majority of it will be possible to preserve large areas in any of wetland restoration efforts will result in a contin- themŽ e.g. the entire state of Florida, riparian ued loss of wetland functions which directly or forests and wetlands throughout California, wet- indirectly influence biodiversity. The purpose of lands distributed across several Mid-western this paper is to discuss four related topics that states. . Noss and Peters found, for example, that influence biodiversity and ecosystem function. many federally threatened species are associated First, I consider the issue of conservation of wet- with the nation’s large rivers and streams. Large land-dependent species through efforts to pre- rivers and streams are all involved in interstate serve wetlands. Second, I consider the ecological commerce and there is no possibility that they consequences of the continued destruction of dry- can be preserved or would we want them to be end wetlands. Third, I ask whether or not there is preserved in their current condition. Restoration any scientific justification to support the conclu- of large rivers and streams is a more important sion that restored and created wetlands function issue than preservationŽ. e.g. Sparks et al., 1998 . similarly to natural wetlands from the perspective Even if large areas associated with rivers could be of biodiversity and nutrient cycling? Fourth, I preserved, it is unlikely that treats to wetland-de- describe the HydrogeomorphicŽ. HGM approach pendent species could be eliminated because most to functional assessment to develop the argument landscapes associated with large rivers have been that most wetland mitigation will continue to fail highly fragmentedŽ. e.g. Gosselink et al., 1990 . unless they are based on sound ecological princi- Even where large areas of an ecosystem type ples that include the use of reference wetland have already been preserved in national parks systems. Ž.e.g. Everglades National Park or preserved by a variety of conservation and planning mechanisms Ž.e.g. Pine Barrens of New Jersey many wetland- 2. Wetland preservation dependent species remain threatened because wetlands are impacted by indirect human activi- More than 50% of the nation’s original wetland ties such as changes in water quality, invasion of area has been lost and while the rate of wetland alien speciesŽ. Flack and Benton, 1998 , and physi- loss has declined, we continue to lose most types cal alterations of watersheds which supply surface of wetlandsŽ. Opheim, 1997 . Will the continued and groundwater to wetlandsŽ Zampela and Bun- loss of wetlands have a negative impact on biodi- nell, 1998. . I conclude that wetland preservation versity? Boylan and MacleanŽ. 1997 have esti- should be viewed as only one part of our national mated that 46% of the nation’s endangered effort to conserve wetland biodiversity. Conserva- species are wetland-dependent suggesting that the tion of wetland-dependent species will be most continued loss or degradation of wetlands will successful when the species in question have small 34 D.F. Whigham rThe Science of the Total Enïronment 240() 1999 31᎐40 geographic ranges or their life history needs can breeding success of migratory waterfowlŽ Weller, be met by preservation of specific areas. 1998; Kantrud et al., 1989. . Vernal pools in Cali- fornia play an important role in the maintenance of regional biodiversityŽ. Zedler, 1987 . 3. Dry-end wetlands Dry-end wetlands associated with first order streams are the most abundant types of wetlands Wetlands occur over a wide range of hydrologic in watersheds and they are the first wetlands in conditions and many wetlands occur in areas the landscape to intercept runoff of surface and where flooding is intermittent or where the subs- groundwater from source areas such as agricul- trate may be saturated to the surface for a rela- tural fieldsŽ Holland et al., 1990; Lowrance et al., tively short period of time. These types of wet- 1995. . Several studies have demonstrated that lands are often referred to as ‘dry-end’ wetlands. riparian forestsŽ including wetland and non-wet- Many dry-end wetlands occur in headwater posi- land habitats. play an important role in removing tions of drainage systems while others are dis- sediments in nutrients from agricultural runoff tributed across landscapes, often as isolated de- ŽPeterjohn and Correll, 1984; Jacobs and Gilliam, pressional wetlands. Examples of isolated dry-end 1985; Cooper, 1990. . Boundaries between uplands wetlands are vernal pools and playas in the arid and depressional wetlands have also been shown west and southwest, potholes in the Prairie Pot- to play an important role in the maintenance of hole region, seasonally flooded depressional wet- biodiversity of plant and animal speciesŽ Kirkman landsŽ. e.g. Carolina Bays and seasonally wet flats et al., 1998. . Connectivity between habitats is also in the southeast. Many dry-end wetlands are an important component of biodiversity mainte- isolated or are maintained by fluctuating ground- nance in landscapes and fragmentation of land- water and are not part of or adjacent to the scapes has been shown to result in the decline of surface tributary system of waters of the US. even common speciesŽ. e.g. Jules, 1998 . The avail- Dry-end wetlands are often not protected be- able data, while still scarce for most types of cause they can fall under the umbrella of the wetlands and landscapes, demonstrates that every COE Nationwide Permit 26Ž. Caputo, 1997 and effort should be made to retain and restore head- they will likely remain unprotected by any permit water and isolated wetlands rather than allow that replaces the Nationwide Permit 26. Final their continued conversion to non-wetland habi- decisions have not been made on the specific tats. nature of future COE nationwide permits but proposals, to date, appear to be based more on streamlining the regulatory bureaucracy rather 4. Wetland restoration and creation than on scientific knowledge. The argument is also made that dry-end wetlands are not impor- Wetland restoration and creation are growing tant because they are typically small and perform fields of scientific endeavor and societiesŽ e.g. few important ecological functions. There is no Society for Ecological Restoration.Ž , journals e.g. ecological basis for these conclusionsŽ National Restoration Ecology, Wetlands, Wetland Journal., Research Council, 1995. and they may be more booksŽ e.g. Kusler and Kentula, 1990; Hammer, valuable than other types of wetlands because of 1992; Kentula et al., 1992; Kadlec and Knight, important landscape and biodiversity functions 1996.Ž and annual meetings e.g. Society of Wet- that they perform. Several examples of the impor- land Scientists, Hillsborough Community College tance of dry-end wetlands serve to support these Ecosystem Restoration and Creation meeting. are contentions. devoted partially or completely on the topic of Small isolated wetlands are often important wetland restoration. While the science of wetland from the perspective of landscape hydrology and restoration and creation is young, one can ask biodiversity. In the Prairie Pothole region, seaso- whether or not enough information is known nal wetlands are important sites for feeding and about wetlands to restore or create them with a D.F. Whigham rThe Science of the Total Enïronment 240() 1999 31᎐40 35 high degree of success. Success in the context of 1. Large systems support and maintain the high- wetland restoration and creation is a relative term est biodiversity. Thus, restoration work with and it depends, in part, on the goals of each large systems should have greater potential restoration project. If the purpose is to create for sustaining regional biodiversity; wetland habitat without regard to any particular 2. Coastal wetlands support greater biodiversity objective other than to provide more wetland if there are good linkages with adjacent area, the answer is yes as long as hydrologic ecosystems and few barriers to water flow and conditions are present to support wetland biota. movement of animals. Restoration projects The answer is also yes if the objectives are fairly should remove barriers and improve connec- broad in scope and if the hydrologic conditions tivity; are appropriate. The Olentangy River Wetland 3. Specific ecosystem types will develop best if Restoration Research Park on the campus of the located near or adjacent to an existing ecosys- Ohio State University is a good example of a tem of the same type; and successful wetland creation project with broad 4. Small habitat remnants are likely to have objectivesŽ. Mitsch, 1997 . The project objectives reduced resilience and less resistance to natu- were to:Ž. 1 create riverine wetland habitat for ral and man-made perturbations. purposes of conducting research on ecological processes in constructed and natural wetlands;Ž. 2 Restoration of non-tidal habitats may be more conduct research for the development of proper problematic because it is harder to restore hydro- design criteria for wetland restoration and cre- logic conditions, particularly when wetlands are created or restored in topographic locations which ation efforts;Ž. 3 develop criteria for measuring are different than those in which the natural the success of wetland restoration and creation wetland occurred. After 3 years, restored wet- efforts;Ž. 4 teach wetland ecology to a wide range lands in Iowa had fewer species than natural of audiences; andŽ. 5 demonstrate wetland cre- wetlands in all zones but the submersed zone ation and restoration techniques. If the restora- Ž.Galatowitsch and van der Valk, 1996 . They also tion goals are directed toward emplacement of found that many species guilds were different specific wetland biodiversity and functionŽ. s at between natural and restored wetlands and con- Ž mitigation sites, success is possible e.g. Marcus, cluded that the seed bank is an important source .Ž 1998 but failures far outnumber successes e.g. of colonizers and that fewer species occurred in . Street, 1998 . the seed bank of restored wetlands. Brown and Ž. Zedler 1997 found that many restoration and BedfordŽ. 1997 and Stauffer and Brooks Ž. 1997 construction projects are not successful or are had suggested that restoration of soil conditions only partially successful because of failures to is important in restoration efforts in non-tidal recognize that wetlands are parts of larger land- wetlands. They found that vegetation recovery scapes. She demonstrated that failed attempts at occurred faster when restored wetlands received restoration and creation were often due to design salvaged wetland soils that contained propagules parameters that excluded important features of of wetland species compared to sites, which had natural wetlands. Scatolini and ZedlerŽ. 1996 no soil remediation. AshworthŽ. 1997 found simi- found that invertebrate species assemblages were lar results in a Wisconsin study. She used a multi- different in constructed coastal wetlands com- variate approach to evaluate the success of a pared to natural reference wetlands. They sug- restoration and found that, while revegetation gested that the differences were mostly due to the occurred in the restored wetlands, that the domi- fact that the substrates in the constructed wetland nant genus in the restored site was Salix while were coarser and had lower organic matter, which Carex aquatilis and Calamagrostis canadensis were resulted in a lower rate of colonization by plants. the dominant vascular plant species in the natural Zedler provided four principles that should be reference site. Ashworth concluded that vegeta- used to guide coastal wetland restoration efforts: tion dissimilarities between restored and natural 36 D.F. Whigham rThe Science of the Total Enïronment 240() 1999 31᎐40 sites were due to differences in soil depth and scribe and quantify specific wetland functions such hydrology. as maintenance of groundwater recharge, nutri- The literature now contains several studies in ent cycling, and biodiversity. The six classes of which characteristics of restored wetlands have wetlands that are used to develop HGM models been compared to natural wetlands that are often are riverine, depressional, slope, flats, estuarine referred to as reference wetlandsŽ e.g. Keddy et fringe, and lacustrine fringe. Wetland functions al., 1993; Scatolini and Zedler, 1996; Streever et for each class are based primarily on position of a al., 1996; Brown and Bedford, 1997. . The use of wetland in the landscape, the dominant source of reference wetlands in restoration efforts is highly water to the wetland, and the direction of water desirable for at least three reasons. First, infor- movement within the wetland. mation from reference wetlands can be used in HGM is still under development but several planning restoration efforts to decrease the likeli- publications are available which describe and hood of failure and partial successes. Second, evaluate the strengths and weaknesses of the data from natural reference wetlands can be com- approachŽ Brinson et al., 1994, 1995, 1997, 1998; pared to restored wetlands to determine the de- Brinson, 1995, 1996; Brinson and Rheinhardt, gree to which restoration efforts are successful in 1996; Hruby, 1997, 1998; Rheinhardt et al., 1997. . restoring biodiversity and ecosystem functioning. In the context of the present paper, HGM is Third, when restorations have failed or have been relevant because the methodology that underpins only partially successful, information from natural the approach can be used to provide solutions to reference wetlands can be used to guide efforts to many of the problems and issues related to wet- make the restoration successful. These and other land biodiversity and ecosystem functioning that I uses of reference information are an integral have described. component of the ecologically based Hydrogeo- As an example, I return to problems associated morphicŽ. HGM approach to wetland functional with dry-end wetlands. I provided evidence to assessment. demonstrate that dry-end wetlands are important and that efforts should be made to change the regulatory environment that permits their contin- 5. The Hydrogeomorphic() HGM approach to ued destruction. While there is a clear need for wetland functional assessment policy change and for additional research on the ecology of dry-end wetlands, it is unlikely that In this section I provide a brief overview of the either will occur quickly. Decisions will continue HydrogeomorphicŽ. HGM approach to wetland to be made on the fate of dry-end wetlands with- assessment that is currently being developed in out a complete understanding of their ecology. the USA. HGM is different from previous assess- The HGM approach provides input into the deci- ment systems because it is based on ecological sion making process by offering quantitative in- principles and on the use of reference wetland formation on the ecological status of wetlands. systems. The use of reference wetland systems is The approach, thus, provides the opportunity to especially relevant to the current discussion be- make decisions that are based on ecologically cause they provide the information needed to sound principles. In the Prairie Pothole Region, make ecologically based decisions related to wet- for example, teams of experts working on a regio- land conservation, restoration, and creation. Brin- nal HGM guidebook identified 11 ecological sonŽ. in press provides a useful summary of the functions for temporary and seasonal dry-end rationale and uses of reference wetlands. wetlands:Ž. 1 maintain static surface water storage; The HGM approachŽ. Smith et al., 1995 is Ž.2 maintain dynamic surface water storage; Ž. 3 based on the premise that wetland can be catego- retain particulates;Ž. 4 maintain elemental cy- rized into distinct classesŽ. Brinson, 1993 and that cling;Ž. 5 remove imported elements and com- characteristics of the classes can be used to de- pounds;Ž. 6 maintain characteristic plant commu- D.F. Whigham rThe Science of the Total Enïronment 240() 1999 31᎐40 37 nity;Ž. 7 maintain habitat structure within the 5.3. Variables relating a wetland to surrounding wetland;Ž. 8 maintain food webs within the wet- wetlands in the landscape land;Ž. 9 maintain habitat interspersion and connectivity among wetlands;Ž. 10 maintain taxa rich- ness of invertebrates; andŽ. 11 maintain distribu- Ž.a Ratio of total area of temporary and seaso- tion and abundance of invertebrates. nal wetlands to the total area of semi-permanent To quantify the 11 functions, a team of wetland and permanent wetlands within a 1-mile radius of experts developed a list of variables that could be the wetland.Ž. b Absolute density of wetlands used to assess ecological conditions at any wet- within a 1-mile radius of the wetland. land assessment site. Short descriptions of the 15 The scalingŽ. e.g. quantification of the variables variables follow and examination of them demon- listed above is done by collecting information strates that most can be easily measured or from a series of wetlandsŽ. Reference Wetlands observed in the field. Other variables can be that represent the range of conditions found in quantified by collecting data that are readily nature for a given class of wetlands within a available on aerial photographs. The list of vari- defined geographic area. The collection of mate- ables also demonstrates that the team of experts rial from the reference wetlands includes infor- decided that it was important to assess each wet- mation that can be used to develop descriptive land in a landscape context. The 15 variables fall profiles of the wetland subclass and data that are into three categories. used to develop and scale HGM models. The entire set of information collected from reference 5.1. Variables related to conditions within an wetlands is called a Reference Wetland System. indiïdual wetland The reference concept is a cornerstone in the HGM approach but reference sites have been used successfully in other assessment approaches. Ž.a Presence of litter in several stages of de- The Index of Biological IntegrityŽ. IBI approach composition;Ž. b presence or absence of a natural to stream assessment is based on conditions in or constructed outlet;Ž. c abundance of woody relatively unaltered or pristine reference sites. and herbaceous plants in all vegetation zones;Ž. d IBI has been used to assess the ecological health physical integrity of the soil;Ž. e ratio of native to of fishŽ. Karr, 1981; Angermeier and Karr, 1986 non-native plant species; andŽ. f dominant land- use and condition in the wetland. and invertebrate communities in stream ecosys- temsŽ Karr and Kerans, 1992; Kerans and Karr, 1994.Ž. . Zampela and Bunnell 1998 have used 5.2. Variables related to relationships between a components of IBI and reference in the HGM wetland and surrounding upland areas context to compare fish assemblages in degraded streams in the New Jersey Pinelands. The term Ž.a Condition of the grassland buffer surround- ‘reference’ in the context of HGM is used as a ing the wetlands.Ž. b Continuity of the grassland basis for comparison. The common property of buffer surrounding the wetland.Ž. c Width of the wetland reference systems, defined as a group of grassland buffer surrounding the outermost wet- two or more wetlands of the same class or sub- land edge.Ž. d Extent of sediment delivery to class, is that they represent examples of a particu- wetland from anthropogenic sources including lar type or complex of wetlands independent of agriculture.Ž. e Area surrounding the wetland that their ecological conditionsŽ Brinson and Rhein- defines the watershed of the wetland.Ž. f Presence hardt, 1996. . of a constructed subsurface or surface outlet out- As indicated above, in HGM, assessments of side the outermost vegetated zone of the wet- wetland sites are based on application of models lands.Ž. g Dominant land-use of the upland water- of wetland functionsŽ. Rheinhardt et al., 1997 . shed. HGM models are developed from information 38 D.F. Whigham rThe Science of the Total Enïronment 240() 1999 31᎐40 compiled from a range of sites in a Reference existing conditions in the wetland in question and Wetland System that are chosen to represent the the impacts to ecosystem functioning that result range of conditions found for a particular class or from the proposed project. Comparisons of this subclass of wetlands in a defined geographic area. sort, to be effective and accurate, require infor- At the two ends of a continuum within a Refer- mation from and the possibility of visiting specific ence Wetland System used to development of wetland sites within a reference system. HGM models, are sites that are pristine or rela- Reference wetland systems can be used for tively undisturbed and sites that are highly al- training. Many wetland regulators are burdened tered or degraded. with large numbers of applications and wetlands One of the strengths of wetland reference sys- Že.g. dry-end wetlands and wetlands smaller than tems is that they have many potential uses beyond some critical area necessary to trigger wetland development and application of HGM models. assessment procedures. are not even visited prior BrinsonŽ. in press had identified four categories to issuance of permits. The availability of locally of uses: mitigation, education, research, and described reference wetlands, in conjunction with preservation. There are two sets of reasons or HGM models, would allow regulators to visit ac- justifications for the use of reference wetland tual wetland sites that span the range of ecologi- systems in HGM. First, data from reference sys- cal conditions that might be encountered. At tems allow everyone to use the same framework minimum, the availability of reference wetlands of comparison for assessment and the data can be would allow new untrained regulators to become standardized and scaled for better resolution and familiar with the resources that they are in charge comparison between sites. Development of refer- of protecting. ence systems for HGM models also allows for better efficiency in time for applying the assessment models, and greater consistency in applica- 6. Conclusions tion of the assessment methodology. Second, the application of federal, state, county or municipal Current wetland policy in the US will result in regulatory guidelines for assessment almost al- the continued loss of wetlands. From a landscape ways require comparisons of existing conditions at and biodiversity perspective, the focus of wetland a wetland site with conditions that will result regulation needs to be changed to provide greater from a proposed action. This type of comparison protection for dry-end wetlands. Dry-end wet- can not be adequately made unless it is possible lands need to be protected to a greater degree to compare the proposed project site in its exist- because they provide important ecological func- ing condition with similar types of wetlands that tions, including the maintenance of biodiversity, are relatively undisturbed and sites which repre- at the level of individual wetlands and, most im- sent a wide range of conditions, including those portantly, at the landscape level. It is difficult to activities that are proposed for the project site. In argue for greater protection of dry-end wetlands addition, regulation of activities in wetlands rou- without placing them in an appropriate ecological tinely calls for avoidance andror minimization of context. The development of reference wetlands impacts, for restoration design, and for moni- systems offers the potential to provide the neces- toring or contingency activities that document sary context to support conservation of biodiver- compliance. Each of these steps in the regulatory sity and ecosystem functioning. Reference wet- process require users to develop, articulate, and lands provide many opportunities beyond applica- defend reasonable conclusions concerning pro- tion in HGM models. They can be used in a posed activities that can be referenced directly to regulatory context as well as for training and wetlands on real propertyŽ e.g. reference wet- education. Currently, many decisions about the lands. . Furthermore, users of assessment methods fate of wetlands, particularly dry-end wetlands, need to be able to rapidly distinguish between are made in the absence of adequate ecological D.F. Whigham rThe Science of the Total Enïronment 240() 1999 31᎐40 39 knowledge. 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