Nitrogen processing by biofilms along a lowland river continuum

While numerous studies have examined N dynamics along a river continuum, few have specifically examined the role of biofilms. Nitrogen dynamics and microbial community structure were determined on biofilms at six sites along a 120 km stretch of the lowland Ovens River, South Eastern Australia using artificial substrates. Terminal restriction fragment length polymorphism (T‐RFLP), chlorophyll a and protein analyses were used to assess biofilm microbial community composition. N dynamics was determined on the biofilms using the acetylene (C₂H₂) block technique and assessing changes in NH, NO_x and N₂O. Unlike microbial community structure, N dynamics were spatially heterogeneous. Nitrification, determined from the difference in accumulation of NH before and after addition of C₂H₂, occurred mostly in the upper sites with rates up to 1.4 × 10^?5 mol m^?2 h^?1. The highest rates of denitrification occurred in the mid‐reaches of the river (with rates up to 1 × 10^?5 mol m^?2 h^?1) but denitrification was not detected in the lower reaches. At the very most, only 50% of the observed uptake of NO_x by the biofilms following addition of C₂H₂ could be accounted for by denitrification. Copyright © 2005 John Wiley & Sons, Ltd.