title: Regulation causes nitrogen cycling discontinuities in Mediterranean rivers.
abstract: River regulation has fundamentally altered large sections of the world's river networks. The effects of dams on the structural properties of downstream reaches are well documented, but less is known about their effect on river ecosystem processes. We investigated the effect of dams on river nutrient cycling by comparing net uptake of total dissolved nitrogen (TDN), phosphorus (TDP) and organic carbon (DOC) in river reaches located upstream and downstream from three reservoir systems in the Ebro River basin (NE Iberian Peninsula). Increased hydromorphological stability, organic matter standing stocks and ecosystem metabolism below dams enhanced the whole-reach net uptake of TDN, but not that of TDP or DOC. Upstream from dams, river reaches tended to be at biogeochemical equilibrium (uptake≈release) for all nutrients, whereas river reaches below dams acted as net sinks of TDN. Overall, our results suggest that flow regulation by dams may cause relevant N cycling discontinuities in rivers. Higher net N uptake capacity below dams could lead to reduced N export to downstream ecosystems. Incorporating these discontinuities could significantly improve predictive models of N cycling and transport in complex river networks.
authors.affiliation: Catalan Institut e for Water Research, Carrer d'Emili Grahit, 101, 17003 Girona, Spain. Electronic address: d.vonschiller@ehu.eus.
authors.forename: Daniel
authors.initials: D
authors.lastname: von Schiller
authors.affiliation: Faculty of Science and Technology, University of the Basque Country, P.O. Box 644, 48080 Bilbao, Spain. Electronic address: ibon.aristi@ehu.eus.
authors.forename: Ibon
authors.initials: I
authors.lastname: Aristi
authors.affiliation: Catalan Institut e for Water Research, Carrer d'Emili Grahit, 101, 17003 Girona, Spain. Electronic address: lponsati@icra.cat.
authors.forename: Lídia
authors.initials: L
authors.lastname: Ponsatí
authors.affiliation: Faculty of Science and Technology, University of the Basque Country, P.O. Box 644, 48080 Bilbao, Spain. Electronic address: maite.arroita@ehu.eus.
authors.forename: Maite
authors.initials: M
authors.lastname: Arroita
authors.affiliation: Catalan Institut e for Water Research, Carrer d'Emili Grahit, 101, 17003 Girona, Spain. Electronic address: vicenc.acuna@icra.cat.
authors.forename: Vicenç
authors.initials: V
authors.lastname: Acuña
authors.affiliation: Faculty of Science and Technology, University of the Basque Country, P.O. Box 644, 48080 Bilbao, Spain. Electronic address: arturo.elosegi@ehu.eus.
authors.forename: Arturo
authors.initials: A
authors.lastname: Elosegi
authors.affiliation: Catalan Institut e for Water Research, Carrer d'Emili Grahit, 101, 17003 Girona, Spain; Institute of Aquatic Ecology, University of Girona, Campus de Montilivi 17071, Girona, Spain. Electronic address: ssabater@icra.cat.
authors.forename: Sergi
authors.initials: S
authors.lastname: Sabater
mesh_terms: D017753:Ecosystem; D019083:Mediterranean Region; D009584:Nitrogen / Q000032:analysis*; D058458:Nitrogen Cycle; D010758:Phosphorus; D011210:Power Plants; D045483:Rivers / Q000737:chemistry*; D014872:Water Movements; D014881:Water Supply / Q000706:statistics & numerical data*
chemical_list: D010758:Phosphorus; D009584:Nitrogen
keywords: Cycling; Dam; Ecosystem functioning; Flow regulation; Nitrogen; Nutrient; River; Uptake