NUTRIENT CYCLING BY BIOFILMS IN RUNNING WATERS OF DIFFERING NUTRIENT STATUS

The autotrophic and heterotrophic nature of attached algal and bacterial populations in streams was investigated in July and August 1986. Glass slides were colonized in two rivers in Algonquin Park, Ontario, that differed in their concentration of bioavailable phosphorus (P). The importance of three abundant algal species was demonstrated by considering their activities on a cellular level using nuclear track autoradiography (NTA). Community biomass accrual, carbon fixation, and phosphate uptake were monitored at bi-weekly intervals and were generally reflective of that of the dominant algal species in each river. It has been proposed that, in running waters, nutrients do not cycle in place but are continually translocated downstream before being re-used by attached organisms. This mode of recycling was demonstrated by monitoring biotic incorporation, release, and subsequent downstream re-incorporation of radiolabelled P and carbon (C) metabolites at the community and cellular levels. The river with less bioavailable P re-assimilated the P metabolites more quickly, but C re-assimilation was similar in the two rivers. This may account for observations that biomass development in running waters may exceed that predicted from empirical P-biomass relationships. Data presented also provide evidence that the species succession, and consequently the tiered development of a biofilm, was the result of the differing abilities of species to sequester and recycle organic and inorganic nutrients from overlying waters.