Effects of physical disturbance on phosphorus uptake in temperate stream biofilms

Microbial biofilm nutrient uptake kinetics can provide insight into assimilative mechanisms that regulate stream primary productivity. While kinetic experiments are often performed, little work has estimated uptake in connection with disturbance (removal) or detailed the effects that common scour events may have on benthic microbes; therefore, the goal of this study was to evaluate physical disturbances on benthic stream biofilms to determine effects on phosphorus (P) uptake rate, physiological capability, and abiotic sorption. Artificial substrata were collected from 2 reaches along a temperate stream; resident biofilms were either removed via abrasion (disturbed) or left intact. A series of short-term radiotracer (H³³₃PO₄) experiments were then conducted to measure P uptake. In vivo autofluorescence was measured as a proxy of algal physiological condition. The experiments showed no difference in P-uptake rates (μgP/μgChl/d) between disturbed (x= 0.77 ± 0.11 [SE] μgP/μgChl/d) and intact (x= 0.91 ± 0.17 μgP/μgChl/d) biofilms (t = 0.69, p = 0.492, df = 33). Further, microbial physiology was not depressed by physical disturbance. While killed samples yielded significantly lower uptake compared to live biota (F = 17.51, p = 0.001), abiotic sorption still accounted for a moderate fraction (range = 0.021-0.038 μgP/μgChl/d) of total uptake and thus warrants estimation in metabolic studies. Overall, these findings lend credence to numerous experiments that investigate benthic microbial physiologic responses post-disturbance and highlight the importance of uptake following common physical disturbances that occur in turbulent environments. In addition, our work measured several kinetic constants across both disturbance and temporal gradients, and we discuss their significance within a physiological framework.