DIFFERENCES IN SOIL CHEMICAL WEATHERING AND NUTRIENT FLUXES ALONG AN EARTHWORM INVASION CHRONOSEQUENCE IN A MINNESOTA SUGAR MAPLE FOREST

Over the past several decades invasive European earthworms have been introduced through agricultural and fishing activities, which accelerated their invasion into soils of the Great Lakes Region that had been earthworm-free since the last glaciation. Soil mixing by earthworms reduces forest productivity by altering nutrient availability and physical properties of the rhizosphere. This study examines mineral weathering and inorganic nutrient dynamics across an earthworm invasion chronosequence in a Northern Minnesota sugar maple forest. The transect includes a gradient of invasion from high earthworm density to non-invaded soils over a distance of 200 m. Soils in the A and E horizons have a sandy loam texture and are underlain by a clay loam Bt. X-ray diffraction data show that quartz, feldspars, and plagioclase account for ~95% of the minerals. Earthworms vertically relocate minerals and elements, which is consistent with the depth profiles of 137-Cs and 210-Pb activities. Elemental profiles show a reduction of Ca, Mg and P concentrations in 0-7cm depths as earthworms invade the soil, while Na, K, Si, Al, and Fe concentrations increase. Earthworm mixing results in the reduction of cation exchange capacity and exchangeable calcium in the 0-5 cm depths but increases in 5-15 cm. Fractional mass loss values (tau) show that Ca, relative to the soil’s parent material, is enriched by up to 14 times in pre-invasion A horizons, but is reduced to 2 in earthworm invaded soils. Contrarily, the level of Fe enrichment in A horizon soils is significantly elevated with earthworms. Crystalline Fe oxides were found to increase with invasion, which provides additional mineral specific surface area to complex carbon and may cover reactive mineral surfaces, inhibiting mineral dissolution. Magnetic susceptibility measurements have been made to understand the speciation of iron along the transect. We are also examining soil water and litter chemistry data to understand the degree that increased soil mixing affects element redistribution. Integrating soil mineral weathering processes with nutrient dynamics will enhance our capacity to predict ecological changes as invasive earthworms continue to invade northern forests.