Carbon Characteristics in Restored and Reference Riparian Soils

In the prairie pothole region of Canada, wetlands once utilized for agricultural purposes are being restored in an attempt to return them to their preexisting hydrologic state. The overall objective of this research was to assess differences in riparian soil organic matter (SOM) quality and quantity between reference wetlands, which had never been cropped, and restored wetlands of varying times since restoration. Samples (0–6 cm) were taken from 15 reference and 28 restored sites, and SOM fractions were isolated using a combination of acid hydrolysis and physical separation techniques. Climatic variables (moisture deficit and effective growing degree days) were the primary influence on the chemical composition of the light fraction (LF), as characterized using ramped-cross-polarization 13C nuclear magnetic resonance spectroscopy. The younger restored soils (1–3 yr) showed significantly lower C concentrations than the reference soils in the bulk samples and both size separates (sand and silt + clay size). There also was an enrichment in 13C in the LF and acid-unhydrolyzable residue fractions of these younger restored soils compared with the older restored (7–11 yr) and reference soils, suggesting that this material was more decomposed. Total C concentrations in the restored soils increased with time and reached levels comparable to reference soils after 7 to 11 yr. The C distribution among soil fractions remained different from the reference soils even in the older restored soils, however, indicating that restoration was not complete in terms of C characteristics.