Carbon dioxide concentration in Lakes

Carbon dioxide concentration sources and forms in Lakes

Like oxygen, carbon dioxide (CO₂) exchange happens at the interface between atmospheric air and water. Unlike oxygen the decomposition of organic sediment- soil respiration increases the concentration of carbon dioxide, CO₂ in lakes also comes from the decomposition of organic sediments (soil respiration). As seen in oxygen, carbon dioxide also dissolves in water, and the concentration of CO₂ in water increases compared to the atmosphere.

The phytoplankton populations tend to consume carbon dioxide, the high consumption of CO₂ lead to a decrease in carbon dioxide concentration in water, hence water pH increases (while, the dissolve of carbon dioxide in water decreases the pH of water leading to an increase of acidic condition of lakes, and carbon dioxide consumption by phytoplankton increase the pH of lakes). Seasons also contribute the change of CO₂ concentration, during ice-covered season, CO₂ builds up inside lakes. Once the ice melts and stratification happens, a sharp decrease in the CO₂ levels in the surface of water happens that reverse again during autumn turnover due to CO₂ high air-water exchange during strong wind weather (Cole, 1998).

Carbon dioxide concentration can be correlated to the trophic state of lakes during different seasons, the study of clean-water oligotrophic lakes (Riera, 1999) showed a significant decrease in the CO₂ levels in water column following ice-out. The state of CO₂ under-saturation persisted till autumn turnover. In the same study, two bog lakes showed supersaturated CO₂ levels during the ice-free season where the level of CO₂ increased again during autumn turnover (Riera, 1999). 

Balmer et.al investigated the carbon dioxide concentration in eutrophic lakes. Their study showed that the sediment influences CO₂ concentration in the water column. For shallow eutrophic lakes, the large sediment interface increased the consumption of CO₂ compared to deep lakes. CO₂ flux was linked to photosynthesis in eutrophic lakes, the high consumption of CO₂ during the summer made the eutrophic lakes suitable sites for atmospheric CO₂ uptake _{(Balmer, 2011)}.

References

Balmer, M. a. D. J., 2011. Carbon dioxide concentrations in eutrophic lakes: undersaturation implies atmospheric uptake. Inland Waters, 1(2), pp. 125-132.

Cole, J. a. C. N., 1998. Atmospheric exchange of carbon dioxide in a low‐wind oligotrophic lake measured by the addition of SF6. Limnology and Oceanography, 43(4), pp. 647-656.

Riera, J. S. J. a. K. T., 1999. Seasonal dynamics of carbon dioxide and methane in two clear-water lakes and two bog lakes in northern Wisconsin, USA. Canadian Journal of Fisheries and Aquatic Sciences, 56(2), pp. 265-274.