July 28: A new study has found that a small group of highly adaptable microbes plays a critical role in maintaining the chemical stability of deep water reservoirs, even as the overall microbial community changes significantly over time.
Researchers studied Xiaowan Reservoir, one of the world’s deepest reservoirs located on China Lancang River, over a three year period from 2017 to 2019. The findings suggest that ecosystem stability depends less on preserving the same microbial species and more on maintaining essential biological functions performed by a few versatile “keystone” microbes.
The reservoir which exceeds 650 feet in depth, develops distinct warm surface waters and cold, oxygen poor deep waters during summer. Scientists collected water samples from different depths in both winter and summer to examine how microbial communities changed over time.
Using advanced genetic sequencing techniques, researchers identified which microbes were present and reconstructed the genomes of individual organisms to understand their metabolic functions.
The study revealed that microbial communities changed more from year to year than they did between shallow and deep water layers. Dominant bacterial species shifted significantly, with Brevundimonas leading in 2017 and 2019, while Acinetobacter became dominant in 2018.
Despite these shifts, the overall chemical functions performed by the microbial community remained remarkably stable. This phenomenon, known as functional redundancy, allows different microbial species to perform the same ecological roles, ensuring continuous nutrient cycling.
Researchers reconstructed the genomes of 671 microbes and identified 46 keystone microorganisms that linked the broader microbial network. These microbes were capable of carrying out multiple biochemical processes, including carbon, nitrogen, sulfur and iron cycling, enabling them to adapt to changing environmental conditions.
The study also found increasing microbial capacity to process urea and sulfur compounds over the three year period, likely reflecting nutrient runoff from nearby agriculture and fish farming. Scientists warned that excess urea entering reservoirs could promote algal blooms and reduce water quality.
Dissolved organic carbon emerged as the strongest factor influencing the distribution of keystone microbes, outweighing temperature, oxygen levels and nutrient concentrations.
Researchers said monitoring what microbes can do, rather than simply identifying which species are present, could provide a more effective way to detect early signs of oxygen depletion, algal blooms and declining reservoir health.
The findings highlight the importance of microbial functions in maintaining drinking water quality and supporting hydropower reservoirs as climate change and land use pressures continue to alter freshwater ecosystems.