CO₂ emissions from German drinking water reservoirs

Area of Science:

• Environmental Science
• Climate Change Research
• Water Resource Management

Background:

• Reservoirs significantly contribute to atmospheric carbon dioxide (CO2) globally.
• Accurate quantification of greenhouse gas emissions from drinking water reservoirs remains a challenge at regional and national scales.

Purpose of the Study:

• To quantify total CO2 emissions from German drinking water reservoirs.
• To identify the primary drivers influencing these emissions.

Main Methods:

• Utilized routine monitoring data from 39 German drinking water reservoirs spanning 22 years (1991-2013).
• Calculated CO2 fluxes and analyzed relationships with water chemistry (pH, alkalinity, dissolved organic carbon) and catchment land use.

Main Results:

• All studied reservoirs were net CO2 sources, with a median flux of 167 gCm-2y-1.
• CO2 emissions exhibited seasonal variation, peaking in autumn.
• Emissions were primarily driven by surface water CO2 concentration, water pH, and total alkalinity, rather than gas transfer coefficients or dissolved organic carbon.
• Catchment land use showed a significant correlation with CO2 emissions.

Conclusions:

• German drinking water reservoirs emit approximately 44,000 tons of CO2 annually.
• These emissions constitute a negligible portion (<0.005%) of Germany's national CO2 emissions.
• Water chemistry, particularly low pH and alkalinity, and catchment land use are key factors controlling CO2 emissions from these reservoirs.