EFFECTS OF HYDROLOGIC FLOWPATH ON SEEP BIOGEOCHEMISTRY IN SANDSTONE PAVEMENT JACK PINE BARREN ECOSYSTEMS

Oligotrophic jack pine (Pinus banksiana) barrens ecosystems with thin, organic soils occupy sandstone pavements in isolated stands in northeastern New York. Event-level solute chemistry was evaluated by daily sampling between March and June of 2002 in an intermittent seep draining a small watershed (0.28 ha) to investigate the effects of hydrologic flow path on biogeochemical fluxes. The thin, organic soils produce extremely acidic waters (mean pH=4.20; alkalinity=-64 ueq/L) with high mean concentrations of Al (0.91 mg/L; n=70) and Fe (0.83 mg/L) exceeding all of the base cations except Ca (1.23 mg/L). Analysis of a single event showed that Al concentrations declined during the rising limb of the hydrograph (dilution and flow through surface O horizons), then increased to a maximum during the falling limb (contact with surficial mineral soils in fissures), and then declined to low levels as baseflow was approached (contact with deeper mineral soils). Calcium concentrations showed a near mirror image to Al, except during peak flows as dilution also reduced concentrations. Comparison of seeps to bulk precipitation showed almost complete retention of nitrate through several events, except during the largest event when overland flow of precipitation probably carried rainwater to the seep with minimal contact with the organic soils.