Effects of recreational land use on an urban fringe stream ecosystem

Background/Question/Methods

The emerging science of urban ecology has raised awareness of the impacts of urbanization on stream ecosystems, as well as the importance of these ecosystems for the ecological services they provide. Direct impacts of urbanization on streams are well documented, whereas less is known about indirect impacts that take place in the urban fringe and are part of the total urban footprint.  Recreational activity, in particular, is often overlooked because it is perceived as a low impact land use that occurs in a more “natural environment.”  We assessed the effects of high intensity recreational land use on City Creek, a watershed located in the urban fringe of Pocatello, Idaho.  We compared City Creek to a nearby, paired watershed (Gibson Jack Creek) that experiences only low intensity recreational use, with a focus on the potential impacts on fine sediment delivery to the stream and its ecological consequences.  In addition, we conducted measurements along the length of City Creek to identify spatial patterns in transported and stored sediment and investigate potential sources associated with land use features (e.g., trails, bridge crossings).

Results/Conclusions

To assess whether high intensity recreational activity in the City Creek watershed has significantly increased the fine sediment levels in the stream we compared measurements of turbidity and total suspended solids (TSS) from City Creek to Gibson Jack Creek, which experiences much lower recreational activity.  Turbidity and TSS were, on average, more than an order of magnitude higher in City Creek than in Gibson Jack Creek (p< 0.001 and p<0.02, respectively) indicating intensity of recreational land use has consequences for fine sediment delivery to the stream.  Comparisons of stream ecosystem function and structure between the two streams to determine ecological consequences of high sediment levels in City Creek also showed significant differences (e.g., leaf decomposition rates were higher in Gibson Jack than City Creek, p<0.0073).  Measurements of spatial patterns in transported and stored sediment indicated areas that contribute large amounts of sediment to the stream which can then be redesigned to mitigate for these inputs.