SEDIMENT PORE-WATER DYNAMICS OF LITTLE-ROCK LAKE, WISCONSIN - GEOCHEMICAL PROCESSES AND SEASONAL AND SPATIAL VARIABILITY

The nature of sediment alkalinity generation processes and the temporal and spatial variability of the pore-water chemistry of an experimentally acidified seepage lake (Little Rock Lake, Wisconsin) Were determined. Analysis of vertical gradients of solutes near the sediment-water interface indicates that sulfate reduction and base cation production were the major mechanisms of alkalinity generation. A comparison of surficial accumulation rates and burial rates indicates that the major source of cations to the pore water occurred by release of organically bound and exchangeable cations through decomposition. Pore-water measurements also reveal significant seasonal changes in solute fluxes, including a sudden change in sediment metabolism following a springtime algal bloom. Spatial differences in particle deposition caused pore-water fluxes of ammonium and alkalinity to be almost an order of magnitude higher at a hypolimnetic site than at epilimnetic sites. After 2 yr of acidification, pore-water gradients of sulfate, calcium, and alkalinity showed only minor changes, and the pore-water pH in the acidified basin remained within 0.5 pH units of preacidification pH.