Abstract:
Stream biofilms play a vital role on structure and function of agricultural streams. In many lowland
streams, macrophyte vegetation is abundant and functions as an important substrate for biofilm
(epiphyton) in addition to the gravel and stone substrate for epilithon on the stream bed. We expect
that reach-scale habitat conditions in streams (e.g., nutrient availability, hydraulic conditions) affect
the epiphyton and epilithon biomass and composition, and that this effect will be substrate-specific
(macrophytes and stones). The objectives of our study were (i) to describe concurrent changes in
epiphyton and epilithon biomass and composition over a year in agricultural streams, and (ii) to
determine the substrate specific reach-scale habitat drivers for the epiphyton and epilithon
structure. We monitored epiphyton and epilithon biofilm biomass and composition at three-week
intervals and reach-scale environmental conditions daily during a year for two agricultural steams.
The results showed that epiphyton and epilithon communities differed in biomass, having high
substrate specific biomass in epilithon compared to epiphyton. Epiphyton was mainly composed of
diatom and green algae, while cyanobacteria were more important in epilithon, and the diatom
species composition varied between the two biofilm types. Epiphyton structural properties were less
influenced by reach-scale hydrology and nutrient availability compared to epilithon. Our study shows
that control of biofilm structure is substrate specific, indicating that the distribution of substrate in
streams will be important to biofilm structural and functional properties on the reach-scale.
Knowledge of biofilm control in agricultural streams is important in order to improve management
strategies, and future studies should improve the understanding of micro-scale habitat conditions,
interactive relationships within biofilms and between the biofilm and the substrates.