Insights into microbial actions on hydraulic concrete structures: Effects of ammonia and sulfate on community structure, function and biofilm morphology

Microbial corrosion of hydraulic concrete structures (HCSs) has received increasing research concerns. However, knowledge on the morphology of attached biofilms, as well as the community structures and functions cultivated under variable nutrient levels is lacking. Here, biofilm colonization patterns and community structures responding to variable levels of ammonia and sulfate were explored. From field sampling, NH₄⁺-N was proven key factor governing community structure in attached biofilms, verifying the reliability of selecting target nutrient species in batch experiments. Biofilms exhibited significant compositional differences in field sampling and incubation experiments. As the nutrient increased in batch experiments, the growth of biofilms gradually slowed down and uneven distribution was detected. The proportions of proteins and β-d-glucose polysaccharides in biofilms experienced a decrease in response to elevated levels of nutrients. With the increased of nutrients, the mass losses of concretes exhibited an increase, reaching a highest value of 2.37 % in the presence of 20 mg/L of ammonia. Microbial communities underwent a significant transition in structure and metabolic functions to ammonia gradient. The highest activity of nitrification was observed in biofilms colonized in the presence of 20 mg/L of ammonia. While the communities and their functions remained relatively more stable responding to sulfate gradient. Our research provides novel insights into the structures of biofilms attached on HCSs and the metabolic functions in the presence of high level of nutrients, which is of significance for the operation and maintenance of hydraulic engineering structures.