Model systems examine the effect of several treatments simultaneously, but how well do they simulate natural lake systems? In our studies at Little Rock Lake, Wis., we measured sediment–water fluxes of sulfate in laboratory sediment–water microcosms, in situ limnocorrals, and the whole lake. Treatments in the laboratory sediment–water microcosm experiment included sediment type, temperature, pH, and [SO42–]; sulfate fluxes were determined by mass balance. Treatments in the field mesocosms (4 m diameter × 1.5 m depth, open to sediment) included (in duplicate): control (pH 6.0), pH 5., 5.0, and 4.5 (H2SO4) and pH 5.0 (HCl). Weekly additions of acid maintained treatment pH throughout the summer. Results from these experimental systems are compared with sulfate fluxes measured in the lake (by porewater profiles and a whole-lake budget). Potential problems associated with experimental systems are discussed in the context of these experiments.