In 2008, the U.S. Army Corps of Engineers issued the Interim Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Midwest Region with the intent of increasing the regional sensitivity of wetland delineation procedures. Included in the Midwest Supplement are new procedures for determining wetland hydrology. To assess the effects of the changes in methods, we compared the new wetland hydrology determination procedures to those in the 1987 Manual to quantify wetland hydrology acreage at 20 Illinois wetland mitigation sites during the 2009 and 2010 growing seasons. We also applied the new procedures retroactively at selected sites with at least 4 years of hydrologic data to provide a long-term context for changes in wetland hydrology acreage. As previously reported, the 2009 wetland hydrology acreage was unchanged at 9 sites, decreased at 6 sites, and increased at 2 sites, although springtime precipitation was well above average. Retroactive application at 7 long-term monitoring sites showed that median annual acreage decreased at 4 sites, increased at 1 site, and did not change at 2 sites. We will also present preliminary data from the 2010 growing season. Given that peak surplus moisture and flooding in Illinois typically occurs during April and May, the increased duration required to satisfy the wetland hydrology criteria in the Midwest Supplement is not offset by advancing the start of the growing season into March. Therefore, decreases in acreage are expected as a result of changes in methodology from the 1987 Manual to the 2008 Midwest Supplement.
|Original language||English (US)|
|Title of host publication||Peaks to Playas|
|State||Published - 2010|