Experimentally altered groundwater inflow remobilizes acidity from sediments of an iron rich and acidic lake.

To study the impact of changes in groundwater flow and chemistry on acidity export from sediments in acid mine drainage (AMD) polluted lakes, a column experiment was carried out. Schwertmannite rich sediment was subjected to three different flow rates (0, 5, and 20 L m(-2) a(-1)), two percolate chemistries (1/1 mmol L(-1) vs 10/15 mmol L(-1) sulfate/ferrous iron, pH 5), and DOC input (approximately 2.5 mmol C L(-1)). Percolation induced acidity export in all percolated treatments (8.8-40.4 mol m(-2) a(-1)) by accelerated proton generation from schwertmannite transformation (18.0-35.9 mol m(-2) a(-1)) and ferrous iron release (3.8-11.6 mol m(-2) a(-1)) from the sediment matrix. Mobilization increased with flow rate and decreased with sulfate and iron concentrations. Unspecifically bound ferrous iron contents increased within the sediment (up to 40.5 mol m(-2) a(-1)) when iron concentrations in the percolate were high. Reduced sulfur species formed following raises in pH, but acidity consumption through this process (0.3-6.6 mol m(-2) a(-1)) and the formation of carbonates (0.11-0.45 mol m(-2) a(-1)) remained small. The study thus suggests that increases in groundwater inflow remobilize acidity from AMD polluted sediments.