Morphological Changes in Soils Produced When Hydrology Is Altered by Ditching

Abstract

A soil's hydrology (seasonal saturation occurrence) must be estimated in the field to delineate jurisdictional wetlands and to evaluate soil suitability for on‐site waste disposal. It is difficult to predict soil hydrology on lands that contain ditches, because the areal extent of hydrologic alteration by an individual ditch is generally unknown. This study evaluated whether morphological changes occurred in soils after a drainage ditch had been installed. Four transects of plots were established parallel to a ditch with plots at distances of 7, 30, 60, and 80 m from the ditch. Each transect contained plots in the following soils: Aquic Paleudults, Aeric Paleaquults, and Typic Paleaquults. Soils within 30 m of the ditch had a significantly (0.10 level) greater volume of Fe masses at depths of 40 to 100 cm than soils further from the ditch. Duration of saturation did not vary significantly with distance from the ditch, but within 30 m of the ditch water tables fluctuated more frequently than those in soils further away. Concentrations of Fe(II) in groundwater at a depth of 60 cm were higher at 7 m from the ditch than at 60 m, but redox potentials at a depth of 60 cm were <500 mv for shorter periods of time at 7 m than at greater distances from the ditch. We hypothesized that groundwater flowing into the soils within 30 m of the ditch introduced Fe(II) into the Bt horizons. The Fe(II) oxidized and formed Fe masses as the water table fell. Our results indicate that soil colors can change within 30 yr as a result of ditching. We suggest that the major area of soil influenced by the ditch can be identified by where the Fe masses in the argillic horizons increase as one approaches the ditch.