Seasonal CO₂ flux dynamics in tropical constructed Lakes: comparative insights from wet and dry zones of Sri Lanka

Abstract

Tropical man-made freshwater systems are increasingly recognized as significant yet understudied contributors to atmospheric carbon dioxide (CO₂) emissions. It is hypothesized that CO₂ fluxes in reservoirs located in different climatic zones of Sri Lanka would exhibit distinct seasonal patterns due to contrasting environmental drivers. This study examined seasonal CO₂ flux dynamics in Thalangama Tank (wet zone) and Huruluwawa Tank (dry zone). Monthly six hour CO₂ flux measurements were conducted for six months using automated floating chambers. Simultaneously, monitoring of water quality and meteorological parameters performed. In Thalangama Tank, CO₂ flux remained consistently positive. Turbidity shows the strongest positive correlation (r = +0.53), indicating sediment resuspension, reduced solar radiation for aquatic photosynthesis and organic matter decomposition as dominant processes. One-way ANOVA revealed marginal seasonal variation (F = 2.42, p = 0.052), suggesting stable CO₂ emissions across months. In contrast, Huruluwawa Tank exhibited a significant seasonal shift from net CO₂ emission to uptake (F = 3.90, p = 0.008).Negative correlations were observed between CO₂ flux and wind speed (r = –0.56), turbidity (r = –0.53), and dissolved organic carbon (r = –0.35), implying enhanced mixing and primary productivity promoted CO₂ sequestration. These findings highlight distinct CO₂ flux patterns across climatic zones and highlight the necessity of zone-specific carbon assessments. Further, detailed investigations are essential to accurately identify the environmental controls governing CO₂ fluxes in tropical freshwater reservoirs, particularly in the context of climate change mitigation and ecosystem management.