The influence of swales on the spatial variability of soil properties in Southern Louisiana, U.S.A

Soil physicochemical properties vary among different landscapes and elevations. The spatial variability of soil properties in a 1.66 ha pasture exhibiting artificial swales was evaluated near Bayou Wikoff, Louisiana to identify relationships between particle size (clay %), organic carbon (OC %), and soil reaction (pH), with elevation. High density sampling was conducted in the field, geo-located via global positioning system (GPS), and subjected to physicochemical lab analysis. Results showed high clay % (μ = 27.95%), high OC % (μ = 2.38%), and strongly acidic soils (μ = 5.15). Results were spatially georeferenced and interpolated across the landscape with the ArcGIS spatial analyst tool. Three interpolation methods (spline, inverse-distance weighting [IDW], and regression kriging) were evaluated to determine values between sampled points. Spline interpolation showed strong relationships between elevation and OC %, pH, and clay %; all linked to swale location. The regression kriging also produced acceptable results and provided a good estimate of soil properties between sampled points. This method is more applicable to small datasets and is directly weighted on adjacent points, versus the entire dataset. For sampled points, significant correlation coefficients (p < 0.05) were found between elevation and clay % (r =-.61), pH (r = -.32), and OC % (r = -.64). All three measured soil properties were inversely proportional to elevation as it decreased towards the bayou. Best management practices should focus on swale lows to reduce total suspended solids (colloidal clay) as means of improving water quality entering nearby bayous.