Abstract
Temporary streams are submitted to high seasonal hydrological variations which induce habitat fragmentation. Global change promotes longer non-flow periods, affecting hydrological continuity and the distribution of biological assemblages in river networks. We aimed to investigate the effects of hydrological discontinuity on phototrophic biofilm assemblages in a Mediterranean stream, at both network and habitat scales. At the network scale during basal flow conditions, mostly nitrate and DOC concentrations were associated to the taxonomical and trait distribution of algae and cyanobacterial assemblages. Cyanobacteria dominated at the upstream and downstream sites of the network, while green algae and diatoms were abundant in its middle part. At the habitat scale, hydrological discontinuity promoted large changes in biofilm composition between riffles and pools, where pools were inhabited preferentially by green algae and riffle habitats by cyanobacteria. Our findings emphasize the myriad of factors affecting the spatial distribution of phototrophic biofilms, which become more heterogeneous according to water flow interruption. Under the predicted climate change scenarios, spatial heterogeneity in temporary streams may increase, which will lead to change phototrophic biofilm assemblages.
Highlights
Temporary streams characteristically cease to flow at some point in space and time (Boithias et al, 2014), experiencing cycles of expansion, contraction and fragmentation (Acuna et al, 2005)
DOC concentrations reached 1.47–2.2 mg C l-1 in the A9 site and 0.987–1.44 mg C l-1 in A3; differences were not observed between riffles and pools (‘‘Appendix B’’, Table 4)
Phototrophic biofilm assemblages changed in composition and abundance driven by the local conditions of conductivity, nutrients, DOC and cation concentrations, which accentuated their differences downstream probably favoured by the base-flow conditions during the sampling
Summary
Temporary streams characteristically cease to flow at some point in space and time (Boithias et al, 2014), experiencing cycles of expansion, contraction and fragmentation (Acuna et al, 2005). Phototrophic epilithic biofilms (developing mostly on the upper parts of cobbles and rocks) are usually dominated by eukaryotic algae and cyanobacteria (Lock, 1993; Romani & Sabater, 2000) These are involved in the biogeochemical cycling of nutrients and organic matter (Von Schiller et al, 2007; Lange et al, 2011; Battin et al, 2016), and provide a good quality food source for consumers (Bott & Kaplan, 1990; Stevenson, 1996; Graba et al, 2013) within river networks
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