JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION VOL. 33, NO.5 AMERICAN WATERRESOURCES ASSOCIATION OCTOBER 1997 DISTINGillSHING BETWEEN WATERSHEDS AND ECOREGIONSl JamesM. Omernik and Robert G. Bailey2 ABSTRACT: In an effort to adopt more holistic ecosystem To accomplishthis redirection, the need for a spa- approaches to resource assessment and management, many state and federal agencies have begun using watershed or ecoregion tial framework is obvious.The problem is which one. frameworks. Although few would question the need to make this Do we use existing frameworks, or do we need to move from dealing with problems and issues on a case by case or developone to fit this particular purpose?Many have point-type basis to broader regional contexts, misunderstanding of felt that watershedsprovide the spatial tool necessary each of the frameworks has resulted in inconsistency in their use for effective research, assessment,and management and ultimate effectiveness. The focus of this paper is on the clarifi- cation of both frameworks. We stress that the issue is not whether of ecosystems(Water Environment Federation, 1992; to use watersheds (or basins or hydrologic units) or ecoregions for Armitage, 1995; Montgomery et al., 1995; Parsons, needs such as developing ecosystem management and non-point 1985; USFWS, 1995; Cannon, 1994; Lotspeich, 1980; source pollution strategies or structuring water quality regulatory FEMAT, 1993; Maxwell et al., 1995; CoastalAmerica, programs, but how to correctly use the frameworks together. Defmi- 1994; USEPA, 1996a). However, publications recom- tions, uses, and misuses of each of the frameworks are discussed as well as ways watersheds and ecoregions can be and have been used mending use of the watershed framework do not all together effectively to meet resource management needs. agree on how and at what scales this use should be (KEY TERMS: ecoregions; basins; watersheds; hydrologic units; undertaken. For example, Montgomery et al. (1995) ecosystem management.) and the report by the Forest EcosystemManagement AssessmentTeam (FEMAT, 1993) suggestthe water- shed (or basin) framework is applicable at two middle hierarchical levels, with physiographic regions or eco- BACKGROUND logical regions (also known as ecoregions),such as we have developed (Omernik, 1995; Bailey, 1995a, Much of the recent popularity with the terms 1995b), being appropriate at the broadest level, and "watershed" and "ecoregion"has come about because project or site delineations being most useful at the of the attempt by government agencies at regional, more detailed levels (largest scales).Others, such as state, national, and international levels to adoptmore the U.S. Fish and Wildlife Service (USFWS), recom- holistic approaches to research, assess, monitor, mend use of watersheds,basins, or hydrologic units at inventory, and manage their resources. The intent all hierarchical levels (USFWS, 1995). appears to be to shift from dealing with single issues, There have been warnings regarding the potential point-sourceproblems, and micro scales,to a broader misuse and misunderstanding of watersheds for approachthat considers spatial patterns of the aggre- structuring ecological research and management gate of natural and anthropogenic interrelationships (Omernik and Griffith, 1991; Hughes and Omernik, involving ecosystemsand their components.This no 1981; Hughes et al., 1994), but unfortunately such doubt stems from a growing realization of the insidi- caveatsare often veiled (Cannon,1994; Born and Son- ous nature of increased human population and modifi- zogni, 1995; Water "Environment Federation, 1992). cation of environmental resources(Holling, 1994). At the Watershed'93 Conference,John Cairns (1994) IPaper No. 96178 of the Journal of the American Water ResourcesAssociation (formerly Water ResourcesBulletin). Discussions are open until June 1, 1998. ZRespectively, Research Geographer, U.S. Environmental Protection Agency, National Health and Environmental Effects Research Labora. tory, Western Ecology Division, 200 SW 35th St., Corvallis, Oregon 97333; and Leader, Ecosystem Management Analysis Center, USDA For. est Service, 3825 East Mulberry St., Fort Collins, Colorado 80524. JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 935 JAWRA Omernik and Bailey gave a plenary presentation titled "The Current State management strategies. We stress that it is not an of Watersheds in the United States: Ecological and "either/or" argument. Both frameworks have impor- Institutional Concerns." Except for its appearancein tant purposes and are complementary when used the title, the word "watershed" canbe found only once together correctly. in the proceedingsmanuscript. The bulk of the paper was aptly focused on the complexities of ecosystems, what we do not know about them, and ecosystem management and restoration scenarios. Cairns DEFINITIONS stressed that although lip service is given to it, little understanding exists of ecosystems and ecosystem Ecoregions management in a holistic sense.He stated that cur- rent efforts to emphasize watershed management remain focused on componentssuch as water quality. The most glaring difference betweenthe definitions When discussing the spatial extrapolation of ecosys- of watersheds and ecoregionsconcerns the degree of tem level restoration activities, Cairns referred to agreement on the definitions. Whereas the definition of the term watershed is fairly widely accepted,there ecoregions rather than watersheds. Repeatedly, Cairns made the point that there has been a reluc- are marked differences of opinion regarding ecore- tance to deal with that in which few have experience gions and how they can or should be delineated. and understanding, i.e., ecosystem-leveldecisions. Much of the difference in approachesto define ecore- Jonathan Cannon (1994), in another paper in the gions sterns from a lack of agreement on a definition of that which we are attempting to regionalize - proceedingsof the Watershed'93 Conference,strongly ecosystemsin aggregate (Born and Sonzogni, 1995). endorsed the U.S. Environmental Protection Agency Allen et al. (1993)claimed that the conceptof ecosys- (EPA)watershed approachand cited the "Water Qual- ity 2000" report which stated that watershedsprovide tem is both widely understood and diffuse and the appropriate spatial framework for total environ- ambiguous. Some question the concept itself (Calli- mental and economic planning (Water Environment cott, 1995;Fitzsimmons, 1996). In discussingthe com- plexities of this problem, Kay and Schneider (1994) Federation 1992).He acknowledgedthe caveatburied stated that most North American ecologicaljournals in "Water Quality 2000" stating: "In some water- sheds, planning and management activities may be (particularly U.S. journals) do not consider holistic more effective in attaining water quality goals if they ecosystemresearch a fit topic because it does not fol- low traditional scientific methods in that there are are organized by ecologicalregions (sub-watersheds). not observer-independent ways of defining ecosys- This is because the natural differences in climate, tems. The definition of "ecosystem" as it relates to geology,soil, land form, and vegetation may not con- form strictly to hydrologic regions.These features can regionalization and ecosystemmanagement (versus individual lakes, streams, wetlands, forests, etc., com- determine the ecological character of surface water and near-surfacegroundwater." Notice, however, that prising ecosystems)appears to be evolving (Haeuber and Franklin, 1996; Grumbine, 1994; Barnes, 1993). in this statement ecoregions are considered "sub- Originally the definition was centered on the biota watersheds," indicating at least an imprecise use of and then becamethought of as subsuming biotic and terms, if not a lack of understanding of the difference abiotic characteristics but in the absence of humans. between ecoregionsand watershedsand their hierar- More recently the term has taken on a more holistic chical nature. meaning that considershumans as part of the biota The purpose of this paper is to clarify the difference (McDonnell and Pickett, 1993; Barnes, 1993;Rowe, between watersheds and ecological regions and to 1990, 1992). The definition has also evolved some- explain some appropriate and inappropriate uses of what regarding scale. It is now commonto consider these spatial frameworks. We will not present a dis- ecosystemsin a multi-scale sense, from specific sites cussion of the different techniques for defining ecore- to global regions, as opposed to mostly relatively gions. Although we are not in complete agreement homogeneoussmall areas. Some of the difference in regarding the delineation of ecoregions,we share the definition is the result of our different educational concern that a spatial framework of watersheds, backgrounds and experiencesand differences in the basins, or hydrologic units has very different purposes missions of the agencieswe work within. than one of ecologicalregions, and that there is an Although the authors of this paper have employed urgent need to clarify the differences to reduce the dissimilar approachesin developingecological regions misuse of each framework. We also wish to address (Bailey, 1995a; Omernik, 1995), our objectives have some common misconceptions about watersheds, been similar, and as we revise our understandings of ecoregions,and hydrologic units that are germane to the meaning of the term "ecosystems"the products of their utility for the regionalization