IN NATURAL RESOURCES

Few lake studies have used a method that directly measures dissolved carbon dioxide (CO2). Direct measurements are dissolved carbon dioxide estimates obtained with an analyzer or sensor, such as the headspace analysis method that uses gas collection syringes and an ion chromatography CO2 analyzer (Cole and Caraco, 1998). In lake studies summarized in Sobek et al. (2005) for the period 1968 to 2005, the vast majority of estimates of dissolved carbon dioxide were indirectly derived from measurements of pH and dissolved inorganic carbon (DIC) or pH and acid neutralizing capacity (ANC). Traditional direct measurements are difficult to obtain. However, indirect measurements can under or overestimate the carbon dioxide concentration due to uncertainties associated with pH, DIC and ANC. Recently, a new field based technology called pumping induced ebullition (PIE) was developed for the direct measurement of carbon dioxide (Browne, 2004a). This approach simplifies direct carbon dioxide measurements by using a process that mechanically induces ebullition of a dissolved gas in a water sample, traps th