Relative Soil Aeration in a Cultivated Prairie Pothole

摘要

Many small prairie potholes receive surface runoff from their catchments and serve as a focal point of ground water recharge. Soil aeration controls the solubility and form of many soil chemicals. Platinum electrodes are sensitive to oxygen and provide a very sensitive indicator of its presence. Electrodes were installed at the 15-, 30-, and 45-cm depth across two transects within a shallow, cultivated depression which serves as a recharge site for groundwater. Soils on the rim of the depression remained aerobic throughout two consecutive cropping years even at 45 cm. Soils within the depression became anaerobic briefly in the first year and very intensely anaerobic in the second year. Electrode potentials decreased with depth. Values of -250 mV were measured at 45 cm and these values suggest that sulfate-S was reduced to sulfide-S within the depression. Because the subsoil was anaerobic, all nitrate-N should be reduced to nitrogen gas. Thus, leaching of nitrate-N into the groundwater during the growing season is a very unlikely event. The degree of anaerobiosis was sufficient to dissolve iron and manganese oxides; organic chemicals adsorbed to these oxide surfaces may be at increased risk of leaching into groundwater.