The Impact of pH on pCO 2 Levels in Florida Lakes Jenney L. Kellogg Florida LAKEWATCH Florida LAKEWATCH Dept. of Fisheries and Aquatic Sciences University of Florida Gainesville, FL

Introduction Growing research dealing with supersaturation of carbon dioxide in freshwater systems. (Cole et al. 1994) Growing research dealing with supersaturation of carbon dioxide in freshwater systems. (Cole et al. 1994) Focus on heterotrophy in lakes. Focus on heterotrophy in lakes.

Objectives Evaluate pCO 2 levels in Florida Lakes. Evaluate pCO 2 levels in Florida Lakes. Examine factors that may influence pCO 2 levels in Florida Lakes. Examine factors that may influence pCO 2 levels in Florida Lakes.

Data Available 667 Lakes 667 Lakes 4730 samples taken 4730 samples taken year range year range

Summary of Lake Conditions

Methods Data were compiled from various studies conducted in Florida from (Canfield 1981, Canfield and Hoyer 1992, Florida LAKEWATCH 1993,1996, and Greis 1995) Data were compiled from various studies conducted in Florida from (Canfield 1981, Canfield and Hoyer 1992, Florida LAKEWATCH 1993,1996, and Greis 1995) Data included pH, Total Alkalinity, Specific Conductance, TP, TN, Chloride, Silicon, Sulfate, Calcium, Magnesium, Sodium, Potassium, Iron, Chlorophyll, Color, and Secchi Depth. Data included pH, Total Alkalinity, Specific Conductance, TP, TN, Chloride, Silicon, Sulfate, Calcium, Magnesium, Sodium, Potassium, Iron, Chlorophyll, Color, and Secchi Depth.

Methods pCO 2 measured indirectly using: Total Alkalinity (µequiv/L) Specific Conductance (µS/cm) pH Water Temperature (°C) pCO 2 measured indirectly using: Total Alkalinity (µequiv/L) Specific Conductance (µS/cm) pH Water Temperature (°C) Correlation Analysis Correlation Analysis Model the effects of changes in pH, Alkalinity, Temperature and Specific Conductance Model the effects of changes in pH, Alkalinity, Temperature and Specific Conductance

UndersaturatedSupersaturated Atmospheric Concentration

G. E. Hutchinson A treatise on limnology, volume 2, part 2. Wiley, New York. C. Juday, E. A. Birge & W. W. Meloche The carbon dioxide and hydrogen ion content of the lake waters of northeastern Wisconsin. Wisconsin Academy of Sciences, Arts, and Letters

Conclusions 80% of Florida lakes sampled were supersaturated with carbon dioxide. 80% of Florida lakes sampled were supersaturated with carbon dioxide. pH is the controlling factor for indirectly measured levels of pCO 2 in Florida freshwater lakes. pH is the controlling factor for indirectly measured levels of pCO 2 in Florida freshwater lakes.

Is pCO 2 controlling pH or is pH controlling pCO 2 ? pH is the controlling factor for measured levels of pCO 2.

Other Processes Leading to Excess CO 2 Net heterotrophy at the ecosystem scale. Net heterotrophy at the ecosystem scale. Injection of CO 2 rich groundwater. Injection of CO 2 rich groundwater. Precipitation of dissolved carbonates. Precipitation of dissolved carbonates. Mixing of an in-lake source of acidity with an input of bicarbonate. Mixing of an in-lake source of acidity with an input of bicarbonate. Emergent macrophytes Emergent macrophytes

Other Considerations Lakes supersaturated with pCO 2 may not be heterotrophic. Lakes supersaturated with pCO 2 may not be heterotrophic.

Acknowledgements Florida LAKEWATCH Florida LAKEWATCH NALMS Student Travel Grant NALMS Student Travel Grant Dr. Canfield, Mark Hoyer, Dr. Roger Bachmann, Department of Fisheries and Aquatic Sciences, University of Florida; Florida Lakewatch Dr. Canfield, Mark Hoyer, Dr. Roger Bachmann, Department of Fisheries and Aquatic Sciences, University of Florida; Florida Lakewatch Carlos Duarte, IMEDEA (CSIC-UIB), Instituto Mediterráneo de. Estudios Avanzados Carlos Duarte, IMEDEA (CSIC-UIB), Instituto Mediterráneo de. Estudios Avanzados Yves Prairie, Département des Sciences biologiques, Université du Québec à Montréal Yves Prairie, Département des Sciences biologiques, Université du Québec à Montréal

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