Expansive, positive changes to habitat diversity following the formation
of a valley plug in a degraded desert river
Abstract
Widespread hydrologic alterations have simplified in-stream habitats in
rivers globally, driving population declines and local extirpations of
many native fishes. Here, we examine how rapid geomorphic change in a
historically degraded desert river has influenced habitat
diversification and ecosystem persistence. In 2010, a large reach of the
degraded and simplified lower San Rafael River (SRR), Utah, was impacted
by the formation of a valley plug and began to shift from a homogenous,
single-thread channel to a complex, multi-threaded riverscape. We
combined field measurements and drone-collected imagery to document
habitat changes due to the valley plug. Our results demonstrate that in
2021, the valley plug reach was more diverse than any other stream reach
along the SRR, containing 641% more diverse habitat (e.g., pools,
riffles, backwaters) than what was measured in 2015. The plug reach also
retained water for periods beyond what was expected during seasonal
drying, with the total extent of inundation within the riverscape
increasing by over 2,800%. Since the formation of the valley plug,
riparian habitat has increased by 230% and channel networks have
expanded to more than 50 distinct channels throughout the zone of
influence. Our results provide evidence of successful self-restoration
in a formerly highly degraded reach of desert river, and encourage new
methods of desert river restoration. We aim to inform the use of
large-scale, disruptive restoration actions like intentional channel
occlusions, with the goal of mitigating the impacts of simplification
and increasing habitat persistence in the face of exacerbated aridity in
the desert Southwest.