Increased methane emission associated with anthropogenic activities in a highly urbanized tropical reservoir
摘要
Pollution in reservoirs affects the water quality, ecosystem services, and CH4 emissions. High temperatures and eutrophic conditions in a tropical urban reservoir can potentially increase CH4 fluxes. To investigate the interference of pollution on CH4 fluxes in Guarapiranga, a highly urbanized tropical reservoir (Brazil), four sampling stations (G1 to G4) with different degrees of pollution were evaluated. The sampling campaigns occurred from May (2018) to March (2019), considering spatio-temporal dimensions and water and sediment characteristics. Chemical analysis for these compartments were carried out followed by statistical analyzes and Random Forest modeling to understand the relationship between water and sediment characteristics on CH4 fluxes and to rank the most important predictors for CH4. Statistical analysis showed differences on CH4 fluxes (Kruskal–Wallis, p < 0.01), except between May and August (p < 0.05). The highest CH4 fluxes were observed during March (G3 = 722.0 mg m−2 d−1, and G2 = 439.2 mg m−2 d−1). Carbon, phosphorus, and nitrogen, both in the water and sediment, showed anthropogenic impact in all stations. The Random Forest model pointed temperature, pH and DOC as the main predictors of CH4 fluxes in Guarapiranga reservoir. We observed an increase on CH4 fluxes in warmer waters (above 29 °C) during March and with pH close to 7.0. This is the first study that quantified and associated CH4 fluxes in the Guarapiranga reservoir with limnological variables in the most populous region in South America. Our results provide an advance on main factors which governs CH4 fluxes in tropical urban reservoirs.