| Elevated phosphorus (P) concentrations in streams are frequently linked with eutrophication and diminished water quality. Stream biofilms appear to play important roles in P assimilation thus representing a valuable transformation of nutrients in aquatic ecosystems. However, little work has identified parameters explaining variation in uptake rates, evaluated the effect of common disturbance techniques, addressed how increasing P-loads affect assimilative abilities, or estimated the influence of initial assimilatory processes on biofilm P dynamics. Therefore, there were four central approaches (chapters) to this dissertation: 1) perform an assessment of peer-reviewed literature reporting aquatic microbial P-uptake rates, 2) evaluate the effect of physical disturbance techniques commonly used in benthic biofilm metabolic studies, 3) measure P-uptake rates for benthic biofilms along an experimental and natural nutrient gradient, and 4) evaluate spatio-temporal P fluxes in biofilms. Regarding the first research approach, several ecological/experimental parameters were found significant in describing and explaining observed variation in published aquatic P-uptake rates: microbial group (benthic, planktonic), source (culture, wild), and sample time (long, short). This underscored the varied nature of microbial assimilatory kinetics and provided a quantitative synthesis of uptake rates thereby advancing nutrient dynamic models. The second chapter showed that common biofilm sampling techniques (physical disturbance) caused no differential effects on kinetic parameter estimates (t= 0.69, p= 0.492, df= 33), lending credence to numerous metabolic studies on benthic microbes post-abrasion and highlighting the potential for microbial uptake following scouring events. The third chapter identified the occurrence of P saturation in some stream biofilms and quantified its effect on the uptake of new P additions, and further concluded that nitrogen was a synergistic nutrient for resident benthic biofilms, particularly in streams of higher productivity (P legacy effect). Lastly, the fourth chapter demonstrated rapid P exchange processes occurring at early time periods (i.e., ≤ 5 minutes), the magnitude of which seems to diminish over longer periods (i.e., 15 - 30 minutes), further suggesting that experimental time periods scaled to hours or longer obscure such fundamental short-term responses. Overall, the studies conducted here employ both empirical and experimental techniques and help to explain ecological and biological variation in biofilm P-uptake rates. |
