Spatial Variability in Palustrine Wetlands

Wetlands are complex ecosystems having considerable spatial variability. Understanding soil spatial relationships in wetlands is difficult because of the number of factors that affect soil properties. We established a nested sampling design within five small, forested and scrub-shrub palustrine wetlands in Virginia to examine soil spatial variability within and among sites. Sampling was based on relative elevation intervals within each wetland and soil depth within each sampling unit. Soils were analyzed to determine variability in nutrient status, pH, organic C content, and particle-size distribution (PSD). Elevation contributed the least amount to the total variability (variability among sites) for nearly every parameter. Depth from the soil surface explained the most total variability in regard to PSD, indicating that parent material stratification in these alluvial wetlands strongly influences soil physical properties. Most of the total variability in the soil chemical parameters was explained by site. Within sites, elevation trends were observed for particle-size and chemical parameters in most of the wetlands. Elevation trends were related to water table levels and the depositional environment. Within elevation sampling units, particle-size and chemical parameters were shown to be significantly related to depth from the soil surface (at the 0.05 level). These relationships could be attributed to the stratified nature of alluvial soils and the accumulation of organic matter at or near the soil surface. Pedon sampling locations were spaced ≈1 m apart and therefore showed less random variability than elevation sampling locations spaced throughout the 0.25- to 0.35-ha study areas. Soils were classified as Endoaquepts, Humaquepts, Dystrudepts, Endoaquents, and Fluvaquents, depending on the wetland site.