Defining a Wetland and the Hydrogeomorphic (HGM) Method
Introduction
To fulfill the requirements of the nationally accepted no-net-loss standard for both wetland acreage and function (which are not necessarily related), the Army Corps of Engineers has been charged with quantifying both wetland acreage and function. This is necessary for society to know how much wetland acreage and function is being lost or gained from the total stock. Measuring acreage is politically sensitive because the definition of wetland boundaries goes on to hold legal status. Quantifying function produces great controversy because the "objective" science behind an institutionalized functional assessment method like the hydrogeomorphic method will further define (in a way many will not understand) the legal dimensions of the no-net-loss policy.
Acreage
Ultimately, the four agency agreement on the definition of a wetland and how to delineate it in the field determines wetland acreage determines the exact reach of section 404 of the Clean Water Act. A wetland is defined by a minimum number of days the soil is saturated during a normal year. Not surprisingly, the technical definition of wetland boundaries has become the focus of a political tug-of-war. On one side, property rights groups and developers pull for a higher number of saturated days, while conservationists and the majority of ecologists pull for a lower number of saturated days to qualify. The history of this political struggle has gone from seven to twenty-one days. Today, a jurisdictional (under sec. 404) wetland is soil that is saturated at least fourteen days in a normal year. Unfortunately for not-net loss of wetland function, the definition of wetland boundaries and the ability to quantify acreage is the first and easier step. Recently, the Corps has begun to act on the ecological reality that while acreage is a useful, accessible statistic, it does not address the purpose of section 404 of the Clean Water Act--protecting wetlands for the beneficial functions that they are universally acknowledged to provide.
Function and the Hydrogeomorphic (HGM) Method
The HGM method groups wetlands together according to their abiotic, structural characteristics. The main three categories are geomorphic setting, water source, and hydrodynamics. Geomorphic setting is the landscape position of the wetland, and the largest categories are depressional, slope-flat, peatland, riverine, and fringe. Water source main categories are precipitation, groundwater discharge, and surface or near-surface inflow. Hydrodynamics are differentiated into three qualitative categories: vertical fluctuation of water table, unidirectional flow, and bidirectional flow. Further groupings and classifications occur at regional and local levels. Wetlands under regulatory scrutiny (potentially impacted, restored, or created) are compared to extensively studied and functionally evaluated "reference" sites. The end result is a functional capacity index.
Func. Cap. Index = Func. Cap. Altered or Created / Func. Cap. Natural
This ratio can then be used to determine either how much mitigation is required, or how much credit a mitigation bank has generated. Such a system gives higher priority to intact wetlands and gives incentive for higher quality in mitigation projects.
Impact of the HGM Method
The functions that the HGM method assesses are self-sustaining ecosystem functions, not functions that wetlands provide to society that are valuable. "The present classification [HGM] stops short of discussing values.... By limiting the analysis to science, issues can be avoided that deal with which value is more important than others (Brinson, 1993, p.3)." However, limiting a discussion to science does not necessarily make the discussion value-neutral. The built in biases of quantitative science apply. This objective scientific method will be used in a politically charged atmosphere to determine mitigation requirements and credits. The emphasis on relatively easy quantifiable characteristics automatically de-emphasizes complex or unquantifiable characteristics. The HGM method is a sophisticated improvement on acreage assessment alone, and the further development and application of the HGM method will ensure more rational and successful mitigation efforts. However, the social value question cannot go on unanswered or unaddressed.