ASSESSING WETLAND CONDITION ON A WATERSHED BASIS IN THE MID-ATLANTIC REGION USING SYNOPTIC LAND-COVER MAPS ROBERT P. BROOKS*, DENICE H. WARDROP, and JOSEPH A. BISHOP Penn State Cooperative Wetlands Center, 302 Walker Building, Pennsylvania State University, University Park, PA 16802 USA (*author for correspondence, phone: 814-863-1596, fax: 814-863-7943, e-mail:[email protected]) Abstract. We developed a series of tools to address three integrated tasks needed to effectively manage wetlands on a watershed basis: inventory, assessment, and restoration. Depending on the objectives of an assessment, availability of resources, and degree of confidence required in the results, there are three levels of effort available to address these three tasks. This paper describes the development and use of synoptic land-cover maps (Level 1) to assess wetland condition for a watershed. The other two levels are a rapid assessment using ground reconnaissance (Level 2) and intensive field assessment (Level 3). To illustrate the application of this method, seven watersheds in Pennsylvania were investigated representing a range of areas (89–777 km2), land uses, and ecoregions found in the Mid-Atlantic Region. Level 1 disturbance scores were based on land cover in 1-km radius circles centered on randomly-selected wetlands in each watershed. On a standardized, 100-point, human-disturbance scale, with 100 being severely degraded and 1 being the most ecologically intact, the range of scores for the seven watersheds was a relatively pristine score of 4 to a moderately degraded score of 66. This entire process can be conducted in a geographic information system (GIS)-capable office with readily available data and without engaging in extensive field investigations. We recommend that agencies and organizations begin the process of assessing wetlands by adopting this approach as a first step toward determining the condition of wetlands on a watershed basis. Keywords: wetlands, watersheds, land cover, condition assessment, Mid-Atlantic Region 1. Introduction The need for strategic restoration of aquatic ecosystems was strongly supported by the National Research Council (NRC) (1995) which called for integrated approaches. A more recent report by the NRC (2001) provided advice on how to implement and improve the wetlands mitigation process on a watershed basis, a process that includes restoration as one element of many options. To conduct watershed-based management of aquatic ecosystems, or “waters” as defined by the Clean Water Act, one must integrate information obtained at various scales, from site-level assessments of stream, lake, and wetland conditions to landscape-level land uses. The objectives of a project conducted by the Penn State Cooperative Wetlands Center (CWC) were to develop, evaluate, and integrate a series Environmental Monitoring and Assessment 94: 9–22, 2004. c 2004 Kluwer Academic Publishers. Printed in the Netherlands. 10 BROOKS ET AL. of tools for use in inventorying, assessing, and restoring the ecological condition of wetlands and associated riparian areas. To comprehensively manage wetlands on a watershed basis, these three integrated stages need to be addressed (Brooks et al., 2002). If assessment of wetland condition as a function of human disturbance is considered in a watershed context, restoration potential of those same wetlands also can be considered be- cause the proportion of wetlands falling below an acceptable level of con- dition, and their spatial location can be determined. For the purposes of this paper, we define condition as the state or quality of the wetland or watershed being studied as a function of physical, chemical, or biological parameters. Depending on the objectives of the assessment, the availability of re- sources, and the degree of confidence required in the results, there are three levels of effort available to address these tasks. In developing these assessment tools, the CWC has formulated a matrix that shows how con- ducting the three tasks over three levels of assessment is an integrated process (Figure 1). That is, an effort is made to relate information across tasks at an appropriate level of effort. In this paper we confine our discussion to assessing the condition of wetlands at Level 1, which is designed to produce a coarse assessment of wetland condition across a set of watersheds from remote-sensing imagery. An assessment conducted only from remote-sensing data is appropriate primarily for planning purposes (Figure 1). If one applies the collective Level 1 and 2 assessments and detects a problem or irregular “signal” within a specific area relative to an established reference condition, then an intensive Level 3 assessment using Hydrogeomorphic (HGM) Func- tional Models (Brinson, 1993; Smith et al., 1995) and Indices of Biologi- cal Integrity (IBIs) can be used to diagnose specific stressors (Karr and Chu, 1997) and provide design guidance for specific restoration projects. The use of reference sites has become increasingly more common as ecologists and managers search for reasonable and scientifically based methods to measure and describe the inherent variability in natural aquatic systems (Hughes et al., 1986; Kentula et al., 1992). The primary reasons to include reference sites in a regional assessment and restoration effort are the need to compare impacted or degraded sites to a least impaired set of attributes or benchmarks. The primary criterion for selecting reference sites involves choosing sites that represent ideal, near-pristine conditions represented by the least disturbed sites available, which is common for ASSESSING WETLAND CONDITION USING SYNOPTIC LAND-COVER MAPS 11 stream assessments (Karr and Chu, 1997), or choosing sites that repre- sent the best attainable conditions for a particular region even though they may not be pristine (Smith et al., 1995). Although reference sites often represent areas of minimal human disturbance (i.e., reference standards in HGM parlance; Smith et al., 1995), in many instances it is more useful to represent a range of environmental conditions across a landscape. It is also possible, as we propose in this paper, to designate reference standard watersheds based on similar criteria. Whether individual wetlands or entire watersheds are being considered, we define a reference set as a gradient of conditions, not just the least impacted elements. INVENTORY ASSESSMENT RESTORATION Level 1 Use existing map Map land uses in watershed; Produce synoptic watershed resources (NWI) of compute landscape metrics map of restoration potential wetlands Level 2 Enhance inventory using Rapid site visit and stressor Select sites for restoration; landscape-based decision checklist; preliminary examine levels of threat from rules condition assessment surroundings Level 3 Map wetland zones Apply HGM and IBI models Map specific sites for abundance using verified to selected sites for condition restoration; design projects inventory based on reference with reference data sets Figure 1. Integrated tasks for wetland monitoring by watershed at three levels of effort. 2. Methods A synoptic map provides an overall visual representation of the watershed and can be used to help interpret decisions regarding site selection for sampling, protection, and restoration. We have modified the synoptic approach developed by Leibowitz et al. (1992) where geographic information system (GIS) data were used to locate watersheds or wetlands with specific characteristics. We were not able to acquire the necessary data layers (e.g., county-level digital soils data, sufficient hydrologic gauging stations) to apply this approach. We recommend that synoptic maps display at a minimum the most current land-use and land-cover data available. Although land-use patterns do not completely describe disturbance levels, they are usually highly correlated with landscape and wetland condition (O’Connell et al., 1998; Wardrop et al., 1998). During discussions with state environmental managers early on in this project, land use was identified as a preferred factor to portray in watershed maps used for assessing wetland condition. 12 BROOKS ET AL. A synoptic map provides a set of baseline conditions for comparing long-term changes, whether these changes involve degradation or restor- ation. The map can help identify potential landscape-level threats to parts of the watershed. Targeting of major projects, such as mitigation banks can be facilitated. Using a digital database for creating a synoptic map, a set of metrics for spatial analysis can be generated from GIS software programs to characterize the patterns of the landscape (e.g., proportional land cover, connectivity, Miller et al., 1997). Recommended resources for developing synoptic maps include the listed parameters, although only the first three items were required for the analyses presented here. The other parameters can be useful in other geographic regions and for Levels 2 and 3. • current land use and land cover from Thematic Mapper (TM) satellite imagery • stream network (digitized 1:24,000 blue line database) • wetlands and water bodies (National Wetlands Inventory [NWI] digitized 1:24,000 base maps) • road network (digitized 1:24,000 database) • topography (Digital Line Graph [DLG] database) • hydric and non-hydric soils (digitized county soil surveys as available, STATSGO) • trends data (indicators of expected change, such as land-use conversion rates, population growth rates, intensity of landscape use) Assessment at Level 1 serves as a screening