Predicting Reacidification of Calcite Treated Acid Lakes

Abstract

A mathematical model (acid lake reacidification model, ALaRM) for predicting reacidification times of calcite treated acid lakes has been calibrated and field tested using data from two Lake Acidification Mitigation Project (LAMP)) lakes (Woods Lake and Cranberry Pond, Big Moose, N.Y.) The model is based on dynamic water column and sediment mass balances of acid neutralizing capacity (ANC) and dissolved inorganic carbon (DIC). Inclusion of a sediment submodel that includes sediment–pore water proton exchange, production of DIC through sediment respiration, ANC generation or utilization through redox reactions, long-term dissolution of calcite deposited in the surface sediments during application, and pH adjustment through an equilibrium proton balance, permits the deterministic simulation of sediment response to whole-lake liming and its subsequent effect on water column reacidification. Application of ALaRM to the postliming response of the two lakes demonstrated that reacidification was controlled primarily by hydrologic flushing and secondarily by sediment–water ANC transfer. Cranberry Pond, which has a mean hydraulic retention time of 2 mo, reacidified to near 0 ANC and pH < 5 within 6 mo after treatment. Woods Lake, which has a mean hydraulic retention time of almost 6 mo, still had an ANC > 20 μeq∙L−1 and a pH > 5.6 just prior to its reliming 15 mo after its initial treatment.