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Presented at the NABS Annual meeting, Vancouver, British Columbia, 2004
in Land-water Interfaces 1
Change in floodplain lateral habitat physical structure mediated by floodwater recession
M.L. Anderson, J.A. Stanford, and F.R. Hauer. Flathead Lake Biological Station, Division of Biological Sciences, The University of Montana, Polson, MT 59860–9659, USA.
The flood–pulse mediated expansion–contraction cycle of aquatic habitat inundation has dramatic implications for benthic organisms inhabiting floodplain “lateral” river–edge environments. We examined spatial and temporal change in biophysical structure of shallow shoreline, backwater, and spring channel lateral habitats along the descending limb of the annual hydrograph on the Middle Fork Flathead River (MT). We found high rates of change in lateral habitat dimensionality, position, and persistence as the hydrograph descended to base flow. Temperatures fluctuated considerably on a daily and seasonal basis within and between shallow shoreline and backwater environments, in contrast to low spatial and temporal temperature variability in groundwater fed spring channels. Percent cover by course woody debris decreased from summer to fall as wood was abandoned by receding floodwaters. Percent cover by aquatic vegetation decreased in shallow shorelines and backwaters, but increased slightly in springbrooks. Late summer periphyton samples yielded average chlorophyll a value of 13.42 mg/m2 from shallow shorelines, 54.51 mg/m2 from spring channels, and 84.91 mg/m2 from backwaters. Large variations between individual sample chlorophyll a values existed within and between sites (0.80-397.16 mg/m2 range across sites). Our work highlights the need for integrating highly dynamic lateral aquatic habitats into investigations of riverine ecology.
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