A Comparison of Soil Characteristics Observed in Farmed, Restored and Natural Closed Depressions on the Des Moines Lobe of Iowa.

Extensive artificial soil drainage systems, including subsurface tiles and surface ditches, have been installed throughout the agricultural Midwest to remove excess water from perennially wet soils.  Factors of soil formation, such as soil climate and biota, have been substantially altered by artificial drainage.  Efforts to restore wetlands are ongoing but success has been limited in some cases by poor characterization of soil properties.  The objectives of this study were to 1) quantify alterations of wetland soils due to artificial drainage in the recently glaciated, Des Moines Lobe region of north-central Iowa; and 2) compare the quality of drained wetland soils to those undergoing restoration efforts and those considered natural (undrained).  Wetland soils in thirteen Des Moines Lobe closed depressions were sampled during this study representing three distinct populations: artificially drained, restored and undrained soils.  Farmed wetland depressions had significantly higher soil nutrients (NO₃, P and K) than restored or natural depressions.  There were distinct visual differences in soil morphological characteristics between farmed and restored wetland types, including evidence of plow layers, depth of A horizons and gleying, color and structure.  Fewer differences were noted between restored and natural sites, implying that restoration of wetlands was returning soils to a more natural state in a relatively short time (15-20 years) compared to the time since they were initially artificially drained (50-100 years).  These preliminary study results provide clear indication of soil alteration due to artificial drainage and important context for establishing realistic timeframes for wetland soil restoration in closed depressions located on the Des Moines Lobe.  Better understanding soil restoration processes will help quantify the success of wetland restoration programs and measure the progress made toward achieving greater soil sustainability.