Long-term changes in forest soils of Maine and Illinois

Soil formation is a complex process that varies with climate, relief, parent material, organisms, and time. Most soil genesis and weathering experiments are short-term and focus on addressing primarily climate, relief, parent material, or organism as a single factor. Long-term soil genesis experiments are rare and are designed to evaluate the factor of time. There is a need to apply experimental designs of long-term soil studies to different ecosystems such as forests due to their crucial role in carbon sequestration and to maintain forest productivity. The overall objective of this study was to understand how forest soils change on a long-term basis by utilizing ecosystems in Maine and Illinois. Specific objectives were to: 1) determine chemical changes in an upland forest soil in central Illinois in response to reduced acidic deposition inputs; 2) assess chemical changes in a bottomland floodplain soil in central Illinois that receives periodic sediment inputs; and 3) examine soil formation processes in a Maine spruce-fir soil. This thesis is divided into two parts based on field site locations and experimental designs from previous studies: 1) a study utilizing buried soil-bags at Howland, Maine, and 2) a resampling of soils at Robert Allerton Park, Monticello, Illinois. A study of organic matter quantity and quality in 1992 was utilized for the buried soil-bags study in a commercial spruce-fir forested plot at Howland, Maine. Soils at the study site have thick organic horizons and well developed E horizons. Sixty soil-bags were constructed in 1992 using C horizon material from a large soil pit in the plot, and placed directly beneath the Oa horizon in groups of five at 12 locations (sampling was planned to occur five times). Additional bags were placed in the center of the Bhs horizon. Another set of bags filled with acid-washed commercial sand were also installed at that time at the same locations. A total of thirty-six incubated soil-bags were retrieved in 2009 from beneath the Oa horizon and within the Bhs horizon. Compared to the acid-washed sand material, changes that occurred in the soil-bags containing the C horizon material were more evident. Soil-bags buried beneath the Oa horizon experienced more changes compared to the ones buried within the Bhs horizon. Leaching of the organic acids from the surface horizons led to an increase in exchangeable cations and a decrease in CaCl2 soil pH in the soil-bags buried beneath the Oa and Bhs horizon. Compared to the original C material, soil-bags containing C horizon were enriched with C and N, S was relatively unchanged, and P was slightly depleted. Soil-bags buried deeper within the Bhs horizon accumulated much less C, about the same N, lost some S, and gained P, compared to the original C horizon material. Soil-bags containing acid-washed sand buried under the Oa horizon, compared to the original sand material, were enriched with C and N but slightly depleted in S and P. Compared to the original acid-washed sand material, soil-bags buried within the Bhs horizon accumulated less C and N but had greater S and P depletion. The majority of the changes that occurred in the incubated soils-bags could be explained by the translocation of the organic acids, as would be expected in an acidic Spodosol. Bartel-Ortiz and David (1986) established two study sites at Robert Allerton Park in Monticello, Illinois; one in the bottomland and one in the upland. The dominant soils are classified as Cumulic Endoaquolls at the bottomland site and Typic Hapludalfs at the upland site. These sites were resampled in 2009 using the same protocol used in 1986 by Bartel-Ortiz and David. Soils in the bottomland site, in general, changed much less during the past 23 years than those at the upland site. Bulk density as measured, decreased in the top 60 cm but increased from 60-80 cm at both sites. Soil pH increased at both sites during the past 23 years. Total C, N, and S were relatively unchanged at both sites, with greater concentrations found at the bottomland site. Exchangeable cations increased at both sites during the past 23 years, with the largest increase found in exchangeable Ca and Mg. This increase could be attributed to the decrease in acidic deposition in the region. Sediment inputs in the bottomland site were not a major factor in contributing to soil change overtime, but likely maintained the high elemental concentrations of the soils. Soils are ever changing. The availability of long-term soils experiments allow researchers to monitor how soils interact with different environmental factors. The results from these studies not only are excellent records of how soils form and change but also can assist scientists to determine the most sustainable management practices to protect this important resource