Management actions mitigate the risk of carbon dioxide emissions from urban lakes

Lakes are recognized as important sources of carbon dioxide (CO₂) emissions, which vary greatly across land use type. However, CO₂ emissions from lakes in urban landscapes are generally overlooked despite their daily connections to human activity. Furthermore, the role of management actions in CO₂ emissions remained unclear mostly because of the lack of long-term observations. Here, the CO₂ partial pressure (pCO₂) from two urban lakes (Lake Wuli and Lake Donghu) in eastern China were investigated based on 16-year (2002-2017) field measurements. This long-term measurements showed the annual mean pCO₂ were 1150 ± 612 μatm for Lake Wuli and 1143 ± 887 μatm for Lake Donghu, with corresponding estimated flux of 21.12 ± 19.60 mmol m^-2 d^-1 and 16.42 ± 20.39 mmol m^-2 d^-1, respectively. This indicates significant CO₂ evasion into the atmosphere. Strong links between CO₂ and human-derived nutrients (e.g., ammonium) and dissolved organic carbon, dissolved oxygen, and trophic state index were found. Although pCO₂ was relatively uniform across sites and seasons in each lake, substantial inter-annual variability with significant decreasing trends were found. The decrease in annual CO₂ can be partly explained by the reduction of pollutant loadings with management actions, which held the hypotheses that management actions mitigated the CO₂ emission risks. Overall, management actions (e.g., ecological restoration and municipal engineering) should be considered for better understanding the roles of anthropogenic aquatic ecosystems in carbon cycle.