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WETLANDS ASSESSMENT REPORT
Increasing urbanization continues to degrade or eliminate wetlands. This study was undertaken to find out exactly where and how many of these natural storm water storage, water filtration and biohabitat features are left, and to evaluate their quality and ability to function.
The Cuyahoga River Remedial Action Plan, Kenyon College and the Ohio EPA recently completed an evaluation of the ecological condition of wetlands in the 800 square mile Cuyahoga River watershed.
Our goal was to assess wetlands using the Ohio Rapid Assessment Method (ORAM) to determine their ecological condition and report on how ecological condition changes as surrounding land-use changes (urban, agricultural, natural). Sample sites were randomly selected using wetlands mapped by the Ohio Wetland Inventory.
Of the 366 sites visited, we determined that 243 points (66.4 %) were wetlands while the remainder (16.4 %) were either non-wetlands (n = 60) or duplicate points (n = 18). For the remaining 12.3% of the cases (n = 45), field crews were unable to access to the site.
Across the watershed, 9.1% of wetlands were in poor condition, 13.2% in fair condition, 51.0% in good condition, and 26.7% in very good condition. There was dramatic decline in the numbers of Superior condition (Category 3) wetlands from the upper parts of the watershed in Geauga county (where 49.3% of all wetlands sampled were Category 3), to the middle parts of the watershed in Portage (18.5% and Summit (19.6%) counties, and the near disappearance of Category 3 wetlands in Cuyahoga county (8.3%). This is related to increasing urban development in the lower portion of the watershed.
Using a measure of land use intensity called the Landscape Development Index (LDI), we measured the relationship between land-use and ORAM scores over different buffer distances. ORAM scores tend to decrease as the intensity of land use (high LDI scores) increases for depressional, riverine, and slope, particularly when buffer distances are small (i.e., 100 m). This implies that protecting a buffer around a wetland is crucial to maintaining its’ ecological health, even in urban environments.
Overall, watershed-wide land use intensity can be characterized as in "low" to "moderately-low". Wetlands in Geauga County had significantly lower LDI scores across most buffer distances than wetlands in Cuyahoga, Summit, and Portage Counties. We also found that wetland size is also a strong predictor of wetland condition, as wetlands decrease in size, ecological condition tends to deteriorate. This is probably a by-product of landscape fragmentation.
A secondary objective of this project was to explore key wetland functions through soil analysis. Soil samples were collected at 202 of the wetland sites. Although soil data showed no consistent trends with condition category we did find that depressions contained significantly higher nutrient concentrations (total nitrogen, total phosphorus and total carbon) than riverine sites. These are important sites for water quality improvement since they act to store nutrients in the watershed, reducing nutrient runoff.