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 tempora l and spatial variability of the pore-water chemistry of an experiment ally acidified seepage lake (Little Rock Lake, Wisconsin) Were determi ned. 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 s urficial 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 meas urements also reveal significant seasonal changes in solute fluxes, in cluding a sudden change in sediment metabolism following a springtime algal bloom. Spatial differences in particle deposition caused pore-wa ter fluxes of ammonium and alkalinity to be almost an order of magnitu de higher at a hypolimnetic site than at epilimnetic sites. After 2 yr of acidification, pore-water gradients of sulfate, calcium, and alkal inity showed only minor changes, and the pore-water pH in the acidifie d basin remained within 0.5 pH units of preacidification pH.