Beaver ponds' impact on fluvial processes (Beskid Niski Mts., SE Poland) Dorota Giriat a, ⁎, Elżbieta Gorczyca b , Mateusz Sobucki b a Department of Geomorphology, Faculty of Geography and Regional Studies, University of Warsaw ul. Krakowskie Przedmiescie 30, 00-927 Warsaw, Poland b Department of Geomorphology, Institute of Geography and Spatial Management, Jagiellonian University, ul. Gronostajowa 7, 30-387 Cracow, Poland HIGHLIGHTS • Beavers came back to the Carpathian rivers after an over three hundred year absence. • Beavers' dam cascade system changed fluvial erosion, transport and sedimentation. • Beaver activity changed the headwater valley morphology. • Beaver damming and ponding affect fluvial systems in montane regions. GRAPHICAL ABSTRACT abstract article info Article history: Received 6 June 2015 Received in revised form 19 November 2015 Accepted 21 November 2015 Available online xxxx Editor: D. Barcelo Beaver (Castor sp.) can change the riverine environment through dam-building and other activities. The European beaver (Castor fiber) was extirpated in Poland by the nineteenth century, but populations are again present as a result of reintroductions that began in 1974. The goal of this paper is to assess the impact of beaver activity on montane fluvial system development by identifying and analysing changes in channel and valley mor- phology following expansion of beaver into a 7.5 km-long headwater reach of the upper Wisłoka River in south- east Poland. We document the distribution of beaver in the reach, the change in river profile, sedimentation type and storage in beaver ponds, and assess how beaver dams and ponds have altered channel and valley bottom morphology. The upper Wisłoka River fluvial system underwent a series of anthropogenic disturbances during the last few centuries. The rapid spread of C. fiber in the upper Wisłoka River valley was promoted by the valley's morphology, including a low-gradient channel and silty-sand deposits in the valley bottom. At the time of our survey (2011), beaver ponds occupied 17% of the length of the study reach channel. Two types of beaver dams were noted: in-channel dams and valley-wide dams. The primary effect of dams, investigated in an intensively studied 300-m long subreach (Radocyna Pond), was a change in the longitudinal profile from smooth to stepped, a local reduction of the water surface slope, and an increase in the variability of both the thalweg profile and sur- face water depths. We estimate the current rate of sedimentation in beaver ponds to be about 14 cm per year. A three-stage scheme of fluvial processes in the longitudinal and transverse profile of the river channel is proposed. C. fiber reintroduction may be considered as another important stage of the upper Wisłoka fluvial system development. © 2015 Elsevier B.V. All rights reserved. Keywords: Beaver ponds Fluvial processes Land use change Silting Grain size Fluvial system Science of the Total Environment 544 (2016) 339–353 ⁎ Corresponding author. E-mail addresses: dagiriat@uw.edu.pl (D. Giriat), elzbieta.gorczyca@uj.edu.pl (E. Gorczyca), mateusz.sobucki@uj.edu.pl (M. Sobucki). http://dx.doi.org/10.1016/j.scitotenv.2015.11.103 0048-9697/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv