Do antibiotics affect methane production in eutrophic lakes? A comparative study in Lake Taihu and Lake Chaohu, China

Eutrophic lakes are sinks for pharmaceutical contaminants, especially antibiotics, and are crucial sources of methane (CH₄). This study investigated four antibiotics commonly used in human and veterinary medicine. Sediment samples were collected from two eutrophic lakes, Lake Taihu and Lake Chaohu, to construct water-sediment systems. A 120-day cultivation experiment was conducted, revealing that: (1) The inter-phase distribution of the antibiotics in the water-sediment systems is mainly affected by the nature of the drugs; (2) CH₄ accumulation in the Lake Taihu group was higher than that in the Lake Chaohu group probably owing to the higher organic matter content of the Lake Taihu sediments; (3) In the Lake Taihu group, CH₄ production in the tetracycline (TC) treatment increased by 27-53 % relative to the control, whereas the Sulfamethoxazole (SMZ) treatment showed a 17-39 % enhancement. In contrast, in the Lake Chaohu group, except for ciprofloxacin (CIP), treatments with TC, SMZ, and Trimethoprim (TMP) considerably suppressed CH₄ production, with reductions ranging from 12 % to 62 %. (4) The dominant methanogenic archaea in both systems belonged to the genus Methanobacterium, and the relative abundance of methanogenic archaea, such as Methanosphaera and Methanoregula, fluctuated to different degrees. The aim of this study is to further provide a theoretical basis for the mechanism of antibiotic effects on CH₄ production in eutrophic lakes and a scientific basis for the effects of pharmaceutical pollutants on global warming.