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Using an Intensive Assessment Method to Calibrate a Rapid Wetland Assessment Method: an Example from the Nanticoke Basin, Delaware and Maryland

Alan T. Herlihy 1,Amy D. Jacobs 2, and Mary E. Kentula 3

1 Department of Fisheries & Wildlife, Oregon State University, Corvallis, OR
2 Delaware Department of Natural Resources and Environmental Control, Water Resources Division,, Dover, DE
3 U.S. Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Corvallis, OR

The development of rapid assessment methods has become a priority for many organizations that want to report on the condition of wetlands at larger scales requiring many sampling sites. To have faith in these rapid methods, however, requires that they be verified with more comprehensive intensive methods. Wetland condition was quantified using both rapid and intense methods from a probability sample of 191 sites from three wetland types (riverine, flat, and depression) in the Nanticoke Basin located in the Mid-Atlantic Coastal Plain, USA. A single overall indicator of wetland condition (IWC) was developed from the intensive method by combining the scores of a number of hydrogeomorphic variables after removing variables that were redundant and/or not responsive to stressor gradients. The Delaware rapid assessment method involves a stressor checklist of 75 stressors that can be summed into one overall rapid condition score based on best professional judgement weightings of the effect of each stressor. Initial comparison showed good agreement for all wetland types between the intense IWC score and the rapid score but there was a distinct non-linearity in the flat and riverine data. We used a multiple linear regression approach to calibrate the rapid score to the IWC (based on the intensive method) using the regression coefficients as stressor weights and eliminating non-responsive stressors. The resulting calibrated rapid score was highly correlated to the IWC for all wetland types (rsquare=0.81 to 0.89) and showed very little evidence of non-linearity. The calibration step provides a more solid foundation for the use of the rapid method and a verifiable linkage to a more rigorous assessment of condition.

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