Biogeochemical Cycling following Planting to Red Pine on a Sandy Prairie Soil

Abstract

Native prairies in the Lower Wisconsin River Valley provide a means of comparing nutrient cycling patterns across undisturbed and managed ecosystems. Bulk precipitation, throughfall, and soil solutions at three depths were collected from August 1991 to December 1993 at three study sites (native prairie and native prairie planted to 30 and 40-year-old red pine, Pinus resinosa Ait.). Elemental input-output balances were calculated from water chemistry data and from water balances using chloride as a tracer. Concentrations of cations and dissolved organic carbon (DOC) in soil solution were greater in the conifer plantations than in the prairie ecosystem. Inorganic acid concentrations were only slightly higher under pine than under prairie, suggesting that the greater cation leaching under pine vegetation was dependent on DOC contributed by throughfall and leaching from the forest floor. There was a small net gain in Mg and losses in Ca, K, and S in the prairie ecosystem. There was a net loss in all elements from the pine ecosystem, and losses were greater than from the prairie. The greater losses in Mg, K, and S from the pine ecosystem are attributed to interception of dry deposition by the tree canopy. Sulfur contributed by dry deposition to the pine ecosystem was mainly returned to the forest floor as organic S and oxidized to SO2−4 as solutions passed through the soil profile. In contrast, greater Ca losses under pine than under prairie are attributed to increased weathering due to afforestation.