TY - JOUR
T1 - Biogeomorphic recovery of a river reach affected by mining
AU - Dawson, Martin
AU - Gurnell, Angela
AU - Lewin, John
N1 - Funding Information:
This research has benefitted from the ongoing interest and encouragement of several people including Mark Macklin, Paul Brewer and Paul Edwards. The constructive suggestions from the anonymous reviewers are gratefully acknowledged. Janet Baxter kindly provided permission to use her photography of the reach and provided useful insights into vegetation change in the area. Assistance with the fieldwork was given by Ronald Dawson, Gary Higgs and others. Laboratory assistance was provided by Natalie Ludgate. The water quality data were made available courtesy of Natural Resources Wales. The research undertaken in 1986–1987 was supported by a NERC Post‐Doctoral Fellowship GT5/F85/AAPS/1 held by the corresponding author at Aberystwyth University.
Publisher Copyright:
© 2022 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.
PY - 2022/12/12
Y1 - 2022/12/12
N2 - Environmental changes are impacting river systems worldwide. These arise from factors such as flood magnitude–frequency changes, direct human management interventions, inadvertent human impacts on sediment supply and fluvial regimes and landscape-scale changes in climate. Historical and active metal mining is significant in this regard. Here, we investigate morphodynamic changes within a reach of the River Ystwyth, Wales, since 1845. We analyse historical and contemporary information derived from maps, river flow records (1962–2021), metal analyses of sediment samples (1970s and 2021), ground geomorphological surveys (1970s and 1986–1987) and remotely sensed imagery (2001–2021) to investigate changes during a period of active metal mining followed by a century of post-mining recovery. During the studied period, an initially meandering river was transformed into a braided one, subsequently reverting to a single sinuous channel. Sinuosity reduced from 1.31 in 1845 to 1.09 in 1982 before recovering to 1.39 in 2019. Inversely, the braiding index reduced from a maximum of 2.0 in 1987 to 1.5 in 2021. Evolution in planform was associated with a change from expansive bar formation and avulsion under braided conditions to lateral bar accretion and associated bank erosion along a sinuous single channel. The initial 19th-century channel pattern and floodplain instability seems to have been related to mining sediment toxicity effects rather than a response to high sediment volumes, with recent recovery and channel style reversion being attributable to vegetation encroachment and biomass stabilization of the floodplain. Causal factors of recent recovery appear to be colonization by gorse (Ulex europeaus) in the absence of physical control measures and a reduction in grazing by the native rabbit population because of a disease-induced decline in their numbers. These results highlight the importance of riparian vegetation in addition to sediment balance and hydrological processes in controlling fluvial responses to environmental changes.
AB - Environmental changes are impacting river systems worldwide. These arise from factors such as flood magnitude–frequency changes, direct human management interventions, inadvertent human impacts on sediment supply and fluvial regimes and landscape-scale changes in climate. Historical and active metal mining is significant in this regard. Here, we investigate morphodynamic changes within a reach of the River Ystwyth, Wales, since 1845. We analyse historical and contemporary information derived from maps, river flow records (1962–2021), metal analyses of sediment samples (1970s and 2021), ground geomorphological surveys (1970s and 1986–1987) and remotely sensed imagery (2001–2021) to investigate changes during a period of active metal mining followed by a century of post-mining recovery. During the studied period, an initially meandering river was transformed into a braided one, subsequently reverting to a single sinuous channel. Sinuosity reduced from 1.31 in 1845 to 1.09 in 1982 before recovering to 1.39 in 2019. Inversely, the braiding index reduced from a maximum of 2.0 in 1987 to 1.5 in 2021. Evolution in planform was associated with a change from expansive bar formation and avulsion under braided conditions to lateral bar accretion and associated bank erosion along a sinuous single channel. The initial 19th-century channel pattern and floodplain instability seems to have been related to mining sediment toxicity effects rather than a response to high sediment volumes, with recent recovery and channel style reversion being attributable to vegetation encroachment and biomass stabilization of the floodplain. Causal factors of recent recovery appear to be colonization by gorse (Ulex europeaus) in the absence of physical control measures and a reduction in grazing by the native rabbit population because of a disease-induced decline in their numbers. These results highlight the importance of riparian vegetation in addition to sediment balance and hydrological processes in controlling fluvial responses to environmental changes.
KW - bar morphology
KW - channel change
KW - grazing
KW - mining
KW - vegetation succession
UR - http://www.scopus.com/inward/record.url?scp=85138328793&partnerID=8YFLogxK
U2 - 10.1002/esp.5470
DO - 10.1002/esp.5470
M3 - Article
SN - 0197-9337
VL - 47
SP - 3497
EP - 3514
JO - Earth Surface Processes and Landforms
JF - Earth Surface Processes and Landforms
IS - 15
ER -