Biogeochemistry and weathering in a forest catchment and an arable field in central Sweden

Abstract

Fluxes of base cations, nitrogen and phosphorus were investigated in a long‐term study at a forest site and a nearby arable site in central Sweden. At both sites soil mineralogy was reflected in the stream water concentrations, especially during base‐flow. Weathering rates for the major base cations and natrium (SBC + Na) in the forest soil calculated from empirical relationships and quartz distribution in the soil profile were 0.4 and 0.3 kmol_c ha⁻¹ year⁻¹, respectively. Simulations using the PROFILE model of forest soil predicted a weathering rate of 0.6 kmol_c ha⁻¹ year⁻¹ Net vegetation uptake of base cations was calculated to be larger, at 0.8 kmol_c ha⁻¹ year⁻¹ In the soil of the arable site biogeochemical fluxes resulting from weathering and biomass removal were one order of magnitude faster. Budget calculations for the arable land indicated that a weathering rate of 7 kmol_cha ⁻¹ year ⁻¹ was needed to keep the system in balance. Weathering of Mg was estimated to be equal to the amount applied as fertilizer based on the quantities supplied during a 15‐year period of conventional farming. For K the ratio of weathering to the need for fertilization was estimated at 1.5.

Key words:

• Budgets
• fluxes of base cations
• modelling
• water chemistry