title: Impact of water abstraction on storage and breakdown of coarse organic matter in mountain streams.
abstract: Water abstraction is a prevalent impact in streams and rivers, which is likely to increase in the near future. Because abstraction reduces discharge, the dimensions of the wetted channel and water depth and velocity, it can have strong influence on stream ecosystem functioning. Although the impacts of large dams on stream and river ecosystems are pretty well known, the effects of diversion schemes associated with low dams are still poorly understood. Furthermore, the remote location of many diversion schemes and the lack of collaboration by power companies often make it difficult to know the volume of water diverted and its environmental consequences. To assess the impact of water abstraction on the storage and breakdown of coarse particulate organic matter in streams we compared reaches upstream and downstream from five low dams that divert water to hydropower plants in mountain streams in N Spain. We measured the storage of organic matter and the breakdown of alder leaves in winter and spring, and calculated the results at the patch (i.e., per square meter of bed) and at the reach scale (i.e., per lineal meter of channel). Water diversion significantly reduced discharge, and the width and depth of the wetted channel, but did not affect water quality. Diversion significantly reduced the storage and breakdown of organic matter in winter but not in spring. The number of shredders colonizing litter bags was also significantly reduced. The results point to an important effect of water abstraction on the storage and breakdown of organic matter in streams at least in some periods, which could affect downstream reaches, global carbon fluxes, and associated ecosystem services.
authors.affiliation: Faculty of Science and Technology, The University of the Basque Country, PO Box 644, 48080 Bilbao, Spain. Electronic address: maite.arroita@ehu.es.
authors.forename: Maite
authors.initials: M
authors.lastname: Arroita
authors.affiliation: Faculty of Science and Technology, The University of the Basque Country, PO Box 644, 48080 Bilbao, Spain.
authors.forename: Ibon
authors.initials: I
authors.lastname: Aristi
authors.affiliation: University College of Teacher Training, The University of the Basque Country, Juan Ibañez de Sto. Domingo, 1, 01006 Vitoria-Gasteiz, Spain.
authors.forename: Joserra
authors.initials: J
authors.lastname: Díez
authors.affiliation: Faculty of Engineering, The University of the Basque Country, 48013 Bilbao, Spain.
authors.forename: Miren
authors.initials: M
authors.lastname: Martinez
authors.affiliation: University of Pau and Pays de l'Adour, UFR Sciences and Techniques, 64600 Anglet, France.
authors.forename: Gorka
authors.initials: G
authors.lastname: Oyarzun
authors.affiliation: Faculty of Science and Technology, The University of the Basque Country, PO Box 644, 48080 Bilbao, Spain.
authors.forename: Arturo
authors.initials: A
authors.lastname: Elosegi
mesh_terms: D000818:Animals; D001673:Biodegradation, Environmental; D018533:Biomass; D017753:Ecosystem; D004784:Environmental Monitoring; D007448:Invertebrates / Q000502:physiology*; D045483:Rivers / Q000737:chemistry*; D013030:Spain; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D014873:Water Pollutants
keywords: Abstraction; Decomposition; Diversion; Ecosystem functioning; Low dam; Organic matter