PNW 98 Session - Full AbstractsPNW 98 Session - Full AbstractsA different assumption, being used in Washington State, is that level of function is determined by conditions found in a wetland. The A-teams use their judgement to identify the highest performing wetlands in a regional subclass to set the reference standards, without regard to how severely it has been altered. The decision to use a different assumption was made by two assessment teams, and a statewide technical committee, after examining the data collected in 86 reference wetlands in the lowlands of western Washington.
Data were collected on 60 environmental characteristics of each wetland. These characteristics represented the variables chosen for the draft assessment models that were developed following the procedural steps of the HGM Approach. In addition, an assessment team judged wetlands for severity of alteration and level of performance. Severity of alteration to water regime, soils, vegetation, buffers, and contributing basin were judged on a qualitative scale of 1-5. Performances of 16 functions were judged on a qualitative scale of 1-7.
The data indicate that high levels of performance of a function were not correlated with lack of alteration. Least altered wetlands were judged to perform individual functions at levels that spanned the entire qualitative range of 1-7. At the other end of the scale, wetlands with the severest alterations performed many functions at high levels. Furthermore, altered wetland were not judged to perform functions at levels that were significantly higher (and thus might be "unsustainable") than levels found in the least altered wetlands. In the depressional class, for example, the average indices of performance of 16 functions for the 6 least altered wetlands were 2.5, 4.2, 5.5, 4.1, 5, and 3.6 out of 7. The three most severely altered wetlands had average indices of performance of 5, 3.6, and 4.7.
The HGM approach also stipulates that conditions in the least altered wetlands be used to set the standards for individual variables. Calibrating models using this criterion, however, resulted in "function capacity indices" of 1 for over 90% of the reference wetlands assessed. Reducing the size of the region did not significantly change this conclusion. Using the second assumption to calibrate the models provided a much better fit between the data and model results. In general, the average deviation between the score a wetland received using the models and its performance as judged by the A-team was between 0.1 and 0.2 when the scores were normalized to the range of 0-1.