INVESTIGATING EFFECTS OF GEOLOGIC MATERIALS AND LAND-USE ON NUTRIENT EXPORTS FROM THE CRITICAL ZONE – A DEERFIELD RIVER CASE STUDY

Surficial geologic material and human manipulation control the chemistry of the Critical Zone and identifying their effects be difficult to distinguish. For example, macro (P, Ca, K, Mg) and micronutrients (Zn, Cu, Mn) in soils and streams may be controlled by weathering and precipitation reactions in the Critical Zone, or may be added to soils from agricultural activities. Here, we explored four subwatersheds of the Deerfield River in Massachusetts with contrasting surficial geology and land-uses to separate their effects on the sourcing, retention, and export of macro and micronutrient. We hypothesized that watersheds dominated by shallow soils formed from lodgment till would have less retention and greater export of macro and micronutrients compared to the deeper soils formed from fluvial deposits. Further, we hypothesize that land-use has also increased export of macronutrients. Shallow, glacial till soils had lower macronutrient concentrations than deeper glaciofluvial soils. Further, agricultural soils had comparable or higher base cation concentrations than forested glaciofluvial soils. Monitoring dissolved macro and micronutrient concentrations in stream water in the watersheds indicated that deeper glaciofluvial deposits had 2x higher export of base cations. Human land-use further increased macronutrient export. Export of secondary oxide forming elements (Al, Fe) and micronutrients was also greater in the shallow, glacial till systems. When considering mineral dissolution, glaciofluvial systems have >4x silicate dissolution rates than glacial till systems. These results highlight weathering of geological materials controls macronutrient availability in soils and export to surface waters, which are further augmented by human activities.