CO2 emissions from hydroelectric reservoirs in the Tigris River basin, a semi-arid region of southeastern Turkey

Three hydroelectric reservoirs (Kralkizi, Dicle and Batman) in the Tigris River basin (Turkey) were sampled monthly during one year in order to reveal spatial and seasonal changes in aqueous partial pressure of CO2 (pCO(2)) and to estimate diffusive fluxes of CO2 from the reservoirs' surface water. pCO(2) concentrations did not show significant spatial differences, while they showed significant seasonal variations. Temperature, precipitation and biological CO2 uptake through photosynthesis controlled pCO(2) seasonality in the reservoirs, with maximal concentrations in the winter (ranging from 516.9 mu atm in Kralkizi to 1299.2 mu atm in Dicle) and minimal concentrations in the spring (ranging from 47.7 mu atm in Batman to 140.7 mu atm in Kralkizi). Most studies reported that reservoirs worldwide are net sources of CO2 to the atmosphere. However, the reservoirs in this study were sinks for atmospheric CO2 during the spring, summer and autumn seasons, while they were CO2 sources to the atmosphere during the winter. Air-water CO2 fluxes in Kralkizi, Dicle and Batman dam reservoirs were 2.39, 32.88 and 8.12 mmol/m(2)/day in the winter, respectively. On an annual basis, all three reservoirs acted as a sink for atmospheric CO2. These estimated CO2 fluxes were in the lower range for temperate reservoirs, despite the potential for winter conditions that shifted the reservoirs from sink to net source for atmospheric CO2.