Weiss, Tristan听1听;听Covino, Tim P听2听;听Brooks, Alex C听3听;听Wohl, Ellen听4
1听Colorado State University
2听Colorado State University
3听Colorado State University
4听Colorado State University
Fluvial networks of mountain landscapes alternate between narrow and wide alluvial valley segments. Wide valley segments are regions of high biodiversity and storage in otherwise narrow, transport dominated reaches1. In North America, beaver (Castor canadensis) engage in dam building that enables the establishment of beaver meadow complexes (hereafter 鈥渕eadows鈥�), characterized by extensive riparian corridors, multi-thread channels, and high levels of river-floodplain connectivity2. However, human land-use and the widespread removal of beaver in these regions has caused many of these systems to shift to a simplified state with limited riparian corridors, high levels of incision, and low river-floodplain connectivity3. In this study, we examined how the hydrology, biogeochemistry, and ecosystem functioning (i.e. instream metabolism) differs between meadows (n=4) of varying beaver activity on the eastern slope of Rocky Mountain National Park. Study sites consisted of a beaver meadow complex (0.38 km2), a smaller active beaver meadow (0.19 km2), a recently abandoned meadow (<10 years, 0.1 km2), and a long-abandoned meadow (>40 years, 0.38 km2), listed in order of decreasing channel complexity. We hypothesized that (1) abandoned meadows would exhibit hydrologic and dissolved organic carbon (DOC) characteristics similar to upstream narrow segments (e.g. little hydrologic attenuation, low levels of carbon transformations, etc.), and (2) complex active meadows would show hydrologic attenuation, variable sink source dynamics of DOC across flow states, and have greater organic matter complexity. Using a combined approach of hydrometric, weekly grab samples, and measurements of dissolved oxygen, we explored seasonal shifts in water, carbon and ecosystem functioning (i.e. instream metabolism). We observed streamflow attenuation at the most complex meadow while the long-abandoned meadow showed water loss to groundwater seepage. Patterns in DOC export and quality at the active meadows remained virtually the same as their narrow reference segments. Alternatively, both abandoned meadows showed increases in DOC export and concentrations and shifts in carbon composition and quality across all flow states relative to their reference segments. Lastly, the two end-member sites (complex-active: simplified-abandoned) showed differences in net ecosystem productivity (NEP), with the complex site sustaining high rates of NEP and the abandoned meadow showing lower more variable NEP. Our results suggest that active beaver meadows have more hydrologic buffering, maintain stable DOC export patterns (flux, concentration and character), and sustain higher rates of ecosystem metabolism relative to abandoned beaver meadows.
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