Abstract:
Stream biofilms play an important role in the structure, functioning, and integrity 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. The overall explanatory power of the measured environmental variables was low, probably
due to micro-scale habitat effects and interactive processes within stream biofilms. 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.