Model of internal alkalinity generation: Sulfate retention component

Internal alkalinity generation is modeled by an input-output approach in which equations to describe budgets for sulfate, nitrate, ammonium, and base cations are linked to an alkalinity budget equation. Calibration of the sulfate model using ion budgets for 14 softwater lakes shows that the sulfate sink coefficient is reasonably uniform (mean = 0.46 m yr^-1) and can be used to predict sulfate retention. Model predictions show that internal sulfate sinks are needed to correctly predict lakewater [SO₄^2-] and that in-lake sulfate sinks can account for over 50% of input. For experimentally acidified Little Rock Lake, Wisconsin, the sulfate model predicts 90% recovery of [SO₄^2-] 13 years after acid additions stop.