Spatial Autocorrelation of Denitrification in a Restored and a Natural Floodplain

Abstract

Floodplain wetlands have the potential to act as significant nitrogen (N) sinks through both assimilatory uptake and denitrification. However, the methodological constraint of making denitrification measurements at the point scale makes estimating field-scale rates difficult without a good understanding of how point measurements might be extrapolated. To address this issue, we compared spatial heterogeneity and scale of spatial autocorrelation of soil denitrification and its potential drivers (moisture, total N, nitrate and organic matter) in neighboring natural and restored floodplain systems of the Wisconsin and Baraboo Rivers in Wisconsin, USA at two spatial scales (large 81 m2 plot, and small 5 m2 plot). At the coarser scale, the range of autocorrelation was shorter at the restored site for 4 of the 5 soil parameters including denitrification (range = 9 m, vs. 21 m at the natural site). At the finer spatial scale, significant autocorrelation was detected for 4 of the 5 variables at the natural site, but only 1 variable (NO3-N) at the restored site. We suggest that high variability in spatial distribution of denitrification could render some interpolation techniques inappropriate.