The effect of burrowing mammals on the hydrology of a drained riparian ecosystem Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/df65vb727

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  • Many species of rodents and insectivores live in subterranean burrows in soils throughout the world. The soil surface perforations of burrow entrances are often connected to complex, subsurface tunnel networks. Burrow entrances and associated subsurface tunnel networks represent a link between surface and subsurface ecological function. Anecdotal observations of surface-water run-off seen draining into these structures suggests rapid bypass of important biological and physical ecological functions necessary for maintaining the quality of both surface and subsurface water resources. Little documentation characterizing the nature of this phenomenon is seen in the literature. This study represents a pioneering effort to document the effects of soil-mammal activity on the hydrology of a perennial agricultural riparian ecosystem in Oregon USA. Using novel approaches, including Plaster of Paris as a subsurface tracer and digital video endoscopy, a detailed characterization of the geometry of surface and subsurface soil modifications by microtine rodents inhabiting an active dairy pasture revealed the extent, connectivity, and complexity of these structures. This knowledge allowed the design of a non-destructive, in situ, vertical transport dye tracer study to document the hydraulic significance of the environmental modifications by these soil mammals. Using a fluorescent dye tracer (Amino-G) and subsurface monitoring and sampling instrumentation, we demonstrated that under saturated conditions, the combined affects of surface and subsurface modifications by voles may enhance vertical transport though the effect is partly masked by a great variety of other bypass features found at this study site. The relative importance of bypass due to vole holes and tunnels appears to be a function of soil structure. The quantity of bypass features other than vole burrows may be sufficient to mask their impact. Additionally, we found that; when irrigating at run-off rates under dry soil conditions, the presence of burrow entrances appears to allow water to penetrate deeper and more rapidly into the soil profile bypassing the more bio-chemically active A-horizon. Under saturated soil conditions, transport to the subsurface appeared rapid but, the effect of burrow entrances on vertical transport could not be quantitatively distinguished from other bypass features natural to this area though suggestion of increased transport in the vole plot could be seen in the data. A destructive tracer analysis of the study plots revealed hydraulic connectivity between the tunnel networks and other transport features deeper in the profile. It appears that vole activity impacts local hydrology in two ways: (1) Surface pathways created by voles intercept and redirect surface runoff, (2) vole tunnels allow intercepted surface runoff to bypass the root zone. The study was inconclusive in two areas and suggests that future work is needed: (1) while speed of bypass transport was no greater below vole tunnel networks, it was not conclusively determined if percent mass transported is greater below such, and (2) whether what appears to be the biologically rich zone and far greater specific surface area of the vole tunnel system is sufficient to equal the bio-chemical activity of the root zone in degradation of solutes entering the vole tunnels
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