Carbon dioxide dynamics of Bhalswa Lake: a human-impacted urban wetland of Delhi, India

Urban lakes in developing economies face tremendous anthropogenic pressure which tends to modify their role in the regional carbon cycle. This makes it imperative to quantify their carbon budget and identify the underlying factors and processes. Present study aims to understand the seasonal carbon dioxide (CO2) dynamics of an urban lake in a semi-arid subtropical region and identify major controls operating on it. Systematic sampling of Bhalswa lake waters was undertaken in winter and summer of 2017–2018. The hydrochemical data generated were used to determine partial pressure and evasion flux of CO2 using pH and total alkalinity couple. The lake waters show CO2 supersaturation with respect to atmospheric equilibrium and act as a source of CO2 to the atmosphere in both seasons. The average partial pressure of carbon dioxide (pCO2) and CO2 evasion flux observed is 1033.73 ± 229.07 µatm and 6.33 ± 2.23 mmol m−2 d−1, and 1034.99 ± 187.37 µatm and 11.65 ± 3.42 mmol m−2 d−1 during winter and summer, respectively. Neither pCO2 nor CO2 evasion flux shows any significant seasonal difference. For yearly dynamics, dissolved organic carbon, dissolved inorganic carbon and dissolved oxygen act as strong controls on lake water pCO2. While for individual seasons, pH and water temperature act as significant controls. Among various pollution sources, untreated sewage and dairy waste, seepage of polluted groundwater and atmospheric dust impact the lake's carbon dynamics. The present study will help better understand the role of freshwater wetlands of ever-expanding urban areas in the regional carbon cycle of developing economies.