Soil carbon dioxide content, temperature, and moisture were measured biweekly for one year at Pigeon Mountain, GA. Levels of soil CO2 ranged from 0.04% to 2.4% and were highest during the growing season, lowest during the winter. Soil temperature correlated positively with soil CO2, accounting for 90% of CO2 variation. Soil moisture variations decreased CO2 concentration at times of high soil water content when CO2 was flushed downward, and also at times of low soil moisture content when CO2 production was inhibited. A predictive model of logistic form using 14‐day means of daily actual evapotranspiration fit the data well (R2= 0.83). The model also tested well against soil CO2 data acquired in the coastal plain at Rocky Point, NC. If actual evapotranspiration rates are known, the model permits estimation of soil CO2 without preliminary field work, and can be used for studies of karst denudation, which require soil CO2 data for seasonal and regional comparison of solution rates.

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Time patterns of karst denudation in northwest Georgia (U.S.A.) were investigated at three spring sites for 12 months and at five stream sites for 10 years. Rainfall was evenly distributed and showed no significant seasonality. At the springs, as well as the streams, water hardness was largely controlled by discharge. At the springs, soil pC02 and water pH were strongly correlated (r = -0.69 to -043). Solute transport in spring waters was highly seasonal, with two conduit flow springs removing more limestone in the winter, and the diffuse flow spring removing more during the growing season. At the stream sites, most denudation occurred during the winter and spring seasons, and least during the summer.Fourier analysis showed that variations in denudation occur on deterministic (long-wave) as well as stochastic (shortwave) time scales. As contributing variables, discharge varied in short-wave and long-wave cycles, whereas soil pCOz showed only a long-wave cycle. The 12 month deterministic cycles were the most important, with changes in discharge taking precedence over soil pC02. Time series regression explains up to 69 per cent of changes in denudation through rain and soil pCOz. Time cycles in available water are the key controlling factor of denudation, and amounts of available soil C 0 2 may not be as important in the temporal patterns of karst downwearing as has been believed previously. KEY WORDS Karst denudation Seasonality Soil COz U.S. southeast Dissolved load R. H. KIEFERavailable for karst denudation, so that the high latitudes should have greater potential for dissolution of the rock. Additionally, C 0 2 is more soluble at lower temperatures; lower water temperatures, according to Corbel, would therefore also cause higher denudation rates.The controversy between these two opposing viewpoints has not been resolved yet. Smith and Atkinson (1976) examined 232 values of mean hardness, grouped by climate, as well as 134 erosion rates. Differences in water hardness by climatic region were significant, but differences in annual erosion rates were not. The role of climatic control over denudation rates thus remains uncertain. Nevertheless, recent years have seen a general rejection of Corbel's theories, and emphasis has been placed on the dominant role of soil COz concentrations in determining karst denudation (Gerstenhauer, 1960;Lehmann, 1970;Atkinson, 1977).Carbon dioxide is produced in the soil through root respiration and microbial decomposition, becomes dissolved in percolation water and forms carbonic acid (Adams and Swinnerton, 1937), rendering the water more aggressive. Levels of soil C 0 2 can be largely explained through soil temperature, but daily actual evapotranspiration may be used as a tool for prediction (Kiefer, 1990). Crowther (1983) warned that mean C02 concentrations in tropical karst soils probably underestimate the true solution potential of percolation water in the tropics, because the highest C 0 2 is found during times of recharge during wetter periods. In temperate regions, most recharg...

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