COMPARING THE EFFECTS OF AGRICULTURAL LAND DISTURBANCE ON WEATHERING AND SOIL DEVELOPMENT IN LOESS SOILS OF EASTERN IOWA AND NEBRASKA

Land disturbance from agriculture is widespread throughout the Midwestern United States but the effects of such land use on weathering and soil formation, especially at depth, are not well understood. Clear Creek watershed, part of the Intensively Managed Landscapes Critical Zone Observatory (IML-CZO) located in eastern Iowa, and Glacier Creek Preserve, located in eastern Nebraska, are two watersheds intensively modified by agriculture that also contain small fragments of restored prairie. Soils at both sites are formed in thick last-glacial Peoria Loess overlying glacial till but differ in mean annual precipitation, providing contrasting conditions to study the effect of disturbance on soil and solute geochemistry. Meteorological stations at the study sites record baseline atmospheric and soil parameters, including soil moisture, temperature, and electrical conductivity at four depths down to 120 cm. At both sites deep cores (5 – 9 m) were collected from ridgetop soils under agricultural land use, while the Nebraska site has a similarly deep core in a 45-year old prairie restored from corn-soybean agriculture. Soil core analyses include bulk geochemistry (ICP-AES, XRF and portable XRF), total C and N, pH and particle size distribution. Porewater samplers were also installed at four depths down to 120 cm to determine soil porewater chemistry under agricultural and restored prairie land use. Preliminary results of bulk soil geochemistry reveal little elemental depletion in loess at the Nebraska (drier) site but up to 200% enrichment of Ca and Mg between 2 – 7 m depth under agricultural land use. The Iowa site (wetter) shows significant Ca and Mg depletion in the upper 3m and smaller enrichment from 3.5- 7m depth relative to the Nebraska site. In contrast, Ca and Mg enrichment is smaller and only present from 4 – 7 m depth in the Nebraska restored prairie soil. Bulk geochemistry studies at a restored prairie in Iowa are underway. Soil porewater chemistry collected from these sites will help determine solute fluxes in relation to bulk soil geochemistry and provide insight into how agricultural disturbance may be altering weathering and water movement through the critical zone.