Estimation of Atmospheric CO2 Pressure from River and Ground Water Composition

Abstract

The carbon cycle has important applications in monitoring global climate change. Atmospheric CO2-pressure is a major component of this cycle. It is possible to calculate the partial pressure of CO2 in the atmosphere from a geochemical interpretation of temperature, pH and bicarbonate alkalinity of a river. This is known as the “effective” or “apparent” CO2 pressure. Such calculations across the world have shown that rivers have pCO2 higher than the atmospheric value which varies from 300 to 400 ppm i.e. logpCO2 is between -3.5 and 4.0. Many suggestions have been made to explain this paradox. The major ones are: (a) perennial rivers have a Base Flow which is essentially high-CO2 groundwater, (b) the rate of dissolution of CO2 in river water is faster than the rate of release of excess CO2 back to the atmosphere, (c) human activities like burning of fossil fuels and deforestation have resulted in an increase of CO2 in the atmosphere which in turn has favored photosynthesis and given more plant cover on land. It is obvious that interaction between various sinks and sources of CO2 has resulted in the lack of equilibrium between rivers and the earth’s atmosphere. This effect is possibly temporary but deserves further investigation. Data recently collected along the course of the Mahanadi river in Odisha show that the apparent logpCO2 in this river ranges from -3.4 to -2.8 at temperature 25.0 to 32.5 °C. In other words, the pCO2 is slightly higher than the atmospheric value. At those stations where earlier data were available, there is a decreasing trend over the past few years. This paper attempts to verify this observation in terms of the different hypotheses listed above.