A Regional Guidebook for Applying the Hydrogeomorphic Approach to Assessing Wetland Functions of Prairie Potholes

Abstract

ABSTRACT:The Hydrogeomorphic (HGM) Approach is a method for developing functional indices and the protocols used to apply these indices to the assessment of wetland functions at a site-specific scale. The HGM Approach was initially designed to be used in the context of the Clean Water Act, Section 404 Regulatory Program, permit review to analyze project alternatives, minimize impacts, assess unavoidable impacts, determine mitigation requirements, and monitor the success of compensatory mitigation. However, a variety of other potential uses have been identified, including the determination of minimal effects under the Food Security Act, design of wetland restoration projects, and management of wetlands.This report uses the HGM Approach to develop a Regional Guidebook to (a) characterize ponded, herbaceous marshes of the glaciated Prairie Pothole Region, (b) provide the rationale used to select functions of the ponded, herbaceous depressional marsh subclass, (c) provide the rationale used to select model variables and metrics, (d) provide the rationale used to develop assessment models, (e) provide data from reference wetlands and document its use in calibrating model variables and assessment models, and (f) outline the necessary protocols for applying the functional indices to the assessment of wetland functions. DISCLAIMER:The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.

Signatures of human impact: size distributions and spatial organization of wetlands in the Prairie Pothole landscape

“…The complexity of the wetland perimeter described above can be quantified in terms of the SI, calculated as the ratio of the actual wetland perimeter to the perimeter of a circle of equivalent area, as shown in (Merendino and Ankney 1994, Gilbert et al 2006). A comparison of the SI between current and historical wetlands shows a value of 2.43 ± 1.28 for historical wetlands and 1.56 ± 0.60 for current wetlands; all means are presented ±standard deviation.…”

“…In a study of multiple wetland ponds in Saskatchewan, Canada between 1963 and 1969, observed a strong linear correlation between infiltration losses from ponds and the P : A ratio. These findings suggest that rates of water loss, and thus the potential for recharge, from prairie potholes will vary directly with the P : A ratio and hence inversely with the size of individual wetlands (Gilbert et al 2006). Accordingly, the reduction in the P : A ratio that has occurred between historical and current wetlands translates to disproportionate losses in their recharge function.…”

“…Perimeter : area relationships for both historical and current wetlands were calculated using perimeter and area values for the wetland polygons obtained through ArcGIS. The complexity of the wetland perimeter was quantified in terms of the shoreline irregularity index (SI), a measure of shoreline irregularity expressed as a ratio of the wetland perimeter to the perimeter of a circle of equal area (Merendino and Ankney 1994, Gilbert et al 2006). The dimensionless SI metric was calculated using the following equation: where P is the wetland perimeter in m and A is the wetland area in m 2 .…”

Restoration guidelines for wetlands of the western Prairie Pothole Region /

“…Several assessment protocols are available. Protocols in wide use in Montana range from rapid assessments of Proper Functioning Condition (Pritchard, 2003) to the Montana Department of Transportation's Montana Wetland Assessment Method for highway projects (Berglund and McEldowney 2008) to Army Corps of Engineers' Hydrogeomorphic (HGM) Method for Prairie Potholes (Gilbert et al 2006). Over the past several years, the Montana Natural Heritage Program (MTNHP) has been refining a protocol for assessing the ecological integrity of wetlands, using the three-tiered approach recommended by the U.S. Environmental Protection Agency: 1) a landscape-level assessment using GIS; 2) a rapid, semi-quantitative multimetric field assessment of wetland condition; and 3) a quantitative, vegetation-based method used to calculate indices of biological integrity.…”

Effect of hydrogeomorphic setting on calcareous fen hydrology

“…A wetland's position in the landscape (e.g., riparian, depressional, and lacustrine) is referred to as its hydrogeomorphic setting, which imparts controls on the relative sources of water (precipitation, groundwater, and surface water) to a wetland and their inherent hydrodynamic energies (Brinson, ). This approach is frequently adopted for wetland classification and assessment of hydrological, biogeochemical, and ecological functions, largely in a regulatory context (Smith, Ammann, Bartoldus, & Brinson, ; Cole & Brooks, ,b; Gilbert, Whited, Clairain, & Smith, ; Hill, Neary, & Morgan, ). Because the hydrogeomorphic setting is a strong control on the hydrology and soil physics and chemistry of a wetland, it also influences vegetation composition (Mitsch & Gosselink, ; Rheinhardt, ).…”