Nitrogen processing by biofilms along a lowland river continuum

Abstract

Abstract 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 (C 2 H 2 ) block technique and assessing changes in NH , NO x and N 2 O. Unlike microbial community structure, N dynamics were spatially heterogeneous. Nitrification, determined from the difference in accumulation of NH before and after addition of C 2 H 2 , 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 C 2 H 2 could be accounted for by denitrification. Copyright © 2005 John Wiley & Sons, Ltd.