Abstract
Temporary streams are characterized by the alternation of dry and wet hydrological phases, creating both a harsh environment for the biota as well as a high diversity of opportunities for adaptation. These systems are eminently microbial-based during several of these hydrological phases, and those growing on all solid substrata (biofilms) accordingly change their physical structure and community composition. Biofilms experience large decreases on cell densities and biomass, both of bacteria and algae, during dryness. Algal and bacterial communities show remarkable decreases in their diversity, at least locally (at the habitat scale). Biofilms also respond with significant physiological plasticity to each of the hydrological changes. The decreasing humidity of the substrata through the drying process, and the changing quantity and quality of organic matter and nutrients available in the stream during that process, causes unequal responses on the biofilm bacteria and algae. Biofilm algae are affected faster than bacteria by the hydric stress, and as a result the ecosystem respiration resists longer than gross primary production to the increasing duration of flow intermittency. This response implies enhancing ecosystem heterotrophy, a pattern that can be exacerbated in temporary streams suffering of longer dry periods under global change.
Highlights
THE RELEVANCE OF TEMPORARY STREAMS IN THE WORLDFlow intermittency is part of the natural hydrology for streams and rivers, especially in arid and semi-arid landscapes
Reviewed by: Stéphane Pesce, Institut National de Recherche en Sciences et Technologies pour l’Environnement et l’Agriculture, France Jean Luc Rols, Université Toulouse III, France
A decrease in bacterial diversity during non-flow may affect up to half of the Operational Taxonomic Units (OTUs) present (Timoner et al, 2014a), and affiliated taxa related to Firmicutes, Actinobacteria, and Alphaproteobacteria incorporated on the bacterial communities
Summary
Flow intermittency is part of the natural hydrology for streams and rivers, especially in arid and semi-arid landscapes. Decreased water flow may lead to the transformation of the habitat character of rivers in the direction from lotic (moving waters) to lentic (standing waters), a process that can be termed as lentification (Sabater, 2008), usually associated with higher water temperatures, greater evaporative losses, and relevant changes in the biogeochemical processes as well as in the biological community inhabiting the river. This drying may continue for longer or shorter periods of time until there is complete flow interruption, when the water vanishes and there is complete streambed desiccation. These biogeochemical phases offer a variety of ecological niches for fast-growing, well adapted organisms, especially to those that may be favored by repeated drying-wetting cycles
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