Analyzing the Impacts of Off-Road Vehicle (ORV) Trails on Watershed Processes in Wrangell-St. Elias National Park and Preserve, Alaska

Christopher D Arp,Trey Simmons

doi:10.1007/s00267-012-9811-z

Abstract

Trails created by off-road vehicles (ORV) in boreal lowlands are known to cause local impacts, such as denuded vegetation, soil erosion, and permafrost thaw, but impacts on stream and watershed processes are less certain. In Wrangell-St. Elias National Park and Preserve (WRST), Alaska, ORV trails have caused local resource damage in intermountain lowlands with permafrost soils and abundant wetlands and there is a need to know whether these impacts are more extensive. Comparison of aerial photography from 1957, 1981, and 2004 coupled with ground surveys in 2009 reveal an increase in trail length and number and show an upslope expansion of a trail system around points of stream channel initiation. We hypothesized that these impacts could also cause premature initiation and headward expansion of channels because of lowered soil resistance and greater runoff accumulation as trails migrate upslope. Soil monitoring showed earlier and deeper thaw of the active layer in and adjacent to trails compared to reference sites. Several rainfall-runoff events during the summer of 2009 showed increased and sustained flow accumulation below trail crossings and channel shear forces sufficient to cause headward erosion of silt and peat soils. These observations of trail evolution relative to stream and wetland crossings together with process studies suggest that ORV trails are altering watershed processes. These changes in watershed processes appear to result in increasing drainage density and may also alter downstream flow regimes, water quality, and aquatic habitat. Addressing local land-use disturbances in boreal and arctic parklands with permafrost soils, such as WRST, where responses to climate change may be causing concurrent shifts in watershed processes, represents an important challenge facing resource managers.

Highlights

Off-road travel across boreal lowlands is challenging in the summer because of expansive mosaics of lakes, muskeg, bogs, and forest that occur atop permafrost soils with poor and uneven drainage
Elias National Park and Preserve (WRST), Alaska, off-road vehicles (ORV) trails have caused local resource damage in intermountain lowlands with permafrost soils and abundant wetlands and there is a need to know whether these impacts are more extensive
There are seven major ORV trail systems spanning 114 km that can be accessed from the Nabesna Road in WRST (Fig. 1; Table 1)

Summary

Introduction

Off-road travel across boreal lowlands is challenging in the summer because of expansive mosaics of lakes, muskeg, bogs, and forest that occur atop permafrost soils with poor and uneven drainage. Land uses potentially impacting soil erosion, channel initiation, and runoff patterns typically relate to resource extraction or recreational activities and associated road or trail networks (Montgomery 1994) Disturbances resulting from such activities can impact watershed processes by modifying both surface and subsurface flowpaths, resulting in the expansion of source areas during runoff events (Knighton 1998); (Winter 2007) and potentially causing greater fluxes of water, sediment, and nutrients downstream with consequent effects on riparian and benthic habitat (Freeman and others 2007); (Wipfli and others 2007). Discontinuous or sporadic permafrost is already susceptible to a variety of natural thermokarst processes because of warm permafrost temperatures and variable icecontent (Jorgenson and Osterkamp 2005), which further complicates drainage network evolution and makes land surfaces more sensitive to local land-use disturbances

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