Impact of ecotourism on the diversity of bacteria, archaea, and fungi in the freshwater stream of the Agua Azul Waterfalls in southeastern Mexico

Natural freshwater streams harbor diverse microbial communities that support ecosystem functioning. Due to their great biodiversity and geomorphological characteristics, these ecosystems are often very attractive ecotourism destinations, which makes them highly vulnerable to anthropogenic disturbances. The Agua Azul Waterfalls (Cascadas de Agua Azul, in Spanish), a major ecotourist destination located in Indigenous territories of southeastern Mexico (Chiapas, Mexico), offer a unique setting to investigate how sustained human activity influences microbial diversity and quality of water and sediments, as well as the role of local management in conserving biodiversity. To determine the ecological sensitivity of this freshwater stream to tourism pressure, we sampled sites spanning gradients of ecotourist activity and performed an integrated analysis of the physicochemical properties, elemental composition and microbial community composition (bacteria, archaea and fungi) of water and sediment samples. Areas associated with ecotourism activities showed notable changes in physicochemical parameters and microbial community composition, indicating localized human-induced impacts on this ecosystem. Although no significant differences were observed between zones, the detection of anaerobic methanogenic archaea and ammonia-oxidizing archaea in shallow sediments suggests that oxygen availability, methanogenesis (both acetoclastic and hydrogenotrophic), and nitrogen metabolism may play important roles in shaping the functioning of this ecosystem. Our findings highlight the potential of microbial diversity in combination with physicochemical parameters as a tool to detect early stages of human impacts on freshwater ecosystems and establish a basis for future monitoring and conservation efforts.