Epiphyton in Agricultural Streams: Structural Control and Comparison to Epilithon

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.

Epipelic biofilms respond early to the impacts of urbanization in lowland streams

ABSTRACTMultiple structural and functional endpoints of stream biofilms are employed by water quality monitoring programs to detect both direct and indirect environmental impacts. Since multiple co-occurring stressors influence biofilm development, active biomonitoring (translocation experiments) could provide a useful monitoring tool that reflects the overall water quality of the urbanized sites. The aim of this research was to study the short-term responses of epipelic biofilms caused by their translocation to more polluted reaches in lowland urban streams. Fluvial sediment was translocated in three streams that run through urban areas following an urbanization gradient. The epipelic biofilms in the sediment were sampled to identify any fast occurring changes in their algal and bacterial biomasses, in their respiration and oxygen consumption. The results show that structural changes in the biofilm, such as an increased bacterial density and chlorophyll-a concentration, were measurable after two days of exposure to sites with impaired water quality. These immediate changes in the structure of the biofilm indicate that they are sensitive endpoints that can be employed in fast and inexpensive biomonitoring programs in urbanized streams.