Bioavailable dissolved organic carbon serves as a key regulator of phosphorus dynamics in stream biofilms

Phosphorus (P) dynamics at the sediment-water interface of aquatic ecosystems are receiving increasing attention due to their implications for water quality. P uptake by microbial biofilms can serve as a mechanism to control and mitigate the risk of eutrophication. Microbial biofilms capture P both intracellularly and extracellularly. While the significance of extracellular P entrapment in biofilms in engineered systems has recently been established, little is known about its dynamics in aquatic ecosystems. Current research on eutrophication control predominantly emphasizes nitrogen, phosphorus, or nitrogen-phosphorus ratio-based approaches, often overlooking the potential indirect influence of bioavailable dissolved organic carbon (DOC) on P uptake by heterotrophic microorganisms.

In this study, we tested the effect of bioavailable DOC on P entrapment patterns in biofilms and in biofilm P-regulation mechanisms such as polyphosphate accumulation and alkaline phosphatase activity in semi-natural flow-through experimental flumes. Our results show that intracellular P entrapment, is limited by bioavailable DOC, while extracellular P entrapment is independent of bioavailable DOC and potential to offset intracellular P saturation.

We further demonstrate that DOC bioavailability influences benthic P cycling and that its implications may extend into critical areas of ecosystem functioning such as river self-purification, competitive resource utilization and organic P cycling.