PARENT SESSION
Oral Session # 27: Wetland Ecology II: Amphibians, Chemical Cycling, and Tidal Forests.
Presiding: D Jenkins
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 101.
Using Mantel tests to investigate spatial variability, soil properties, and phosphorus sorption in riparian wetlands.
Bruland, Gregory1, Richardson, Curtis1, 1 Duke University, Durham, NC
ABSTRACT- Soils of forested riparian wetlands are highly effective at phosphorus (P) sorption. However, these soils exhibit extreme spatial variability across riparian zones. We used a spatially-explicit sampling design in two forested riparian wetlands in North Carolina to better understand the relationships among P sorption, soil properties, and site variability. Our objectives were to quantify spatial variability of P sorption and related soil properties, to determine which soil properties best explained the variability in P sorption after accounting for spatial autocorrelation, and to compare parametric Pearson correlations to non-parametric Mantel correlations. We measured bulk density, pH, soil organic matter (SOM), texture (% clay, % silt, % sand), oxalate extractable Al (Alo), Fe (Feo), and the P sorption index (PSI). The two sites had substantially different mean PSIs due to differences in Alo, Feo, and % clay. We also found considerable differences in the spatial variability of soil properties at each site. For example, pH, Alo, Feo, and PSI exhibited autocorrelation at site one (S1), while Alo, Feo and PSI exhibited autocorrelation at site two (S2). Kriged maps illustrated that soil properties at S1 appeared to vary at smaller scales than those at S2. After accounting for the effects of autocorrelation, we determined Alo to have the highest Mantel correlation with PSI at both sites. While Pearson correlations would have led us to conclude that PSI was significantly related to most of our selected soil properties, partial Mantel correlations revealed several of these relationships to be spurious. We believe the Mantel approach is robust and could also serve as a model for research of controls on other biogeochemical processes such as denitrification. This type of spatially-explicit P sorption research provides insight on how to develop more accurate landscape-scale water quality models and on how to reproduce natural variation in mitigation of wetlands.
Key words: phosphorus sorption, wetland, Mantel test, spatial variability