Thursday, August 9, 2007
Exhibit Halls 1 and 2, San Jose McEnery Convention Center
Microtopography influences wetland hydrology and plant community composition, but the microtopographic variation found in natural wetland settings may not commonly be found in created wetlands. This study explores the relationship between microtopography, plant species richness/diversity and soil nutrients in wetlands, comparing results for two created wetlands with those for a mature reference wetland in northern Virginia. These attributes were measured along replicate multiscale tangentially-conjoined circular transects in each wetland. Microtopography was surveyed using a total station and used to derive three roughness indices: tortuosity, limiting slope, and limiting elevation difference. Plant species cover was measured in 0.2 m2 plots surveyed at peak growth and used to assess species richness and diversity. Soil samples taken at 80cm transect intervals were analyzed for total C and N, NH4-N and NO3-N, and Mehlich-3 extractable P, Ca, Mg, K, Al, Fe, and Mn, as well as moisture content. Soil parameters were examined in relation to microsite elevation and two indices of proximal roughness: tortuosity and limiting elevation difference. Differences in each attribute were examined among the wetland creation methods: disked, non-disked, and natural. Disked and non-disked created wetlands differed with regard to surface roughness, though neither strongly differed from natural wetlands. Disked and non-disked sites also differed in measures of plant diversity and species richness, and results demonstrate greater variability in plant species assemblages for disked wetlands. For soil nutrients, disked sites had higher NH4, Fe , and Mn , as well as moisture content . Variances differed among groups for total N, NO3, NH4, P, K, Mg, Fe, and Al, with the non-disked created sites consistently having the lowest variance among groups, suggesting minimal nutrient heterogeneity. Results suggest that disking increases water and nutrient and organic matter retention, and that it also establishes nutrient heterogeneity which is otherwise absent from non-disked created wetlands.