The two basins of this seepage lake were separated by a vinyl curtain in August 1984 after a year of background studies, and acidification of one basin with H2SO4 began at ice-out in 1985. Chemical and biological responses measured during successive 2-yr periods at pH ~5.6, 5.1, and 4.7 verified some but not all impacts predicted at the outset. Changes in major, minor, and trace ions generally agreed with predictions. Internal alkalinity generation (IAG) increased at lower pH, and sulfate reduction eliminated ~50% of added H2SO4. Sediment cation exchange was important in IAG and acidified surface sediments, possibly diminishing the lake's ability to counteract further H+ inputs. Mass loss of oak leaves was reduced at pH 5.1 (birch leaves at pH 4.7). Population parameters were more sensitive than community measures for plankton. Species composition changed at each pH, especially at pH 4.7. Many changes in zoopiankton and benthos were indirect responses to an algal mat that developed at lower pH or to food web interactions; these were not predicted accurately. Sensitivity of major fishes to lower pH was Ambloplites rupestris > Micropterus salmoides > Pomoxis nigromaculatus > Perca flavescens. Fish production was reduced at pH's above those resulting in population decreases.

No abstract

No abstract

No abstract

Ion budgets for the two basins of experimentally acidified Little Rock Lake (Vilas County, WI, U.S.A.) indicate that Ca2+, Mg2+, and K+ were released from the bottom sediments to the water column during 1984-1994, and NH4+, NO3-, and SO4(2-) were removed for a net internal alkalinity generation (IAG). Sulfate removal contributed approximately 50% of the IAG in the reference basin, and cation production generated approximately 40%. In-lake processes in the reference basin removed approximately 38% of the sulfate input; 58% was lost to outflow, and 4% remained in the water column. As a result of acid additions that stimulated sulfate reduction and lower pH that enhanced ion exchange, sulfate removal and Ca2+ production were more important for IAG in the treatment basin. During 1984-1994, sulfate removal contributed about 61% of the IAG, and Ca2+ production contributed about half of the IAG from cation production. In the treatment basin, in-lake processes removed about 46% of the total input of sulfate (including acid additions); 36% was lost to outflow and 18% remained in the water column (representing approximately 25% of the added acid). In both basins of LRL, NH4+ consumption roughly balanced NO3- consumption, and net N transformations provided only 3-12% of the IAG. Overall, Na+ and Cl- were conservative in both basins during 1984-1994. Most ion budget components, including calculated internal reaction terms, showed fairly large interannual variations; e.g., ion inputs (dominated by atmospheric deposition) varied by a factor of about two. Over the 10-year period, ANC terms calculated from the budgets as the difference between base cation and acid anion terms agreed well with measured ANC terms for the budget components, indicating that the budgets accounted for all important IAG constituents.