REASSESSMENT OF WETLAND SOIL QUALITY USING SPATIAL VARIABILITY FACTORS

The Ellison Park wetland is a delta-type coastal wetland covering over 423 acres in an urban area adjacent to Rochester, NY. The wetland extends for about 3 km with a main channel and secondary channels through the wetland. Levees along main channels are up to 1 m higher than the water level of the adjacent channel. In downstream sections of the wetland, these levees diminish in height as the channel moves through the wetland and are essentially absent. For over a decade, surveys have been completed to assess the impact of urban runoff on soil quality and the wetlands ability to store excess nutrients and toxic metals. Samples were collected along two 300 m long transects located in the upper and lower portions of the wetland. Soil samples were collected at 30 m intervals. Individual sample results were averaged along a given transect and used to represent that portion of the wetland. Although it is known that variations in wetland soil properties are interrelated to site hydrology and landscape elevation, the location of sampling sites has not actively taken this into consideration.

Recent studies have shown systematic variations in soil properties with respect to elevation above the local water table. Two soil groups, levee and depressed area, are observed to be statistically different. Samples collected along the Ellison Park transects may be classified using these groups. The lower wetland is composed of depressed area soils only. The upper wetland contains both groups. Samples are initially grouped based on water level at the sampling site at the time of sampling. This grouping is checked using organic matter content as this parameter shows the most distinct variation between the two groups. For the upper wetland, organic matter in the levee group ranged from 7.2% to 9.9% while the depressed area samples ranged from 23.5% to 39.9% for the 2001 survey. A similar trend is seen for most other chemical parameters. For example, P ranges from 11.3 to 12.9 mg/kg in levee samples, and from 12.3 to 18.2 mg/kg in depressed area samples. Using this grouping scheme in the upper wetland, soil quality averages were recalculated using a weighted average for the 1999 and 2001 surveys. The weighted average takes into account the area represented by each group. Recalculation shows differences between the average and weighted average results.