Spatial variability in the hyporheic zone refugium of temporary streams |
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Authors: | Rachel Stubbington Paul J Wood Ian Reid |
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Institution: | (1) School of Science and Technology, Nottingham Trent University, Clifton Campus, Nottingham, Nottinghamshire, NG11 8NS, UK;(2) Department of Geography, Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK |
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Abstract: | A key ecological role hypothesized for the hyporheic zone is as a refugium that promotes survival of benthic invertebrates
during adverse conditions in the surface stream. Many studies have investigated use of the hyporheic refugium during hydrological
extremes (spates and streambed drying), and recent research has linked an increase in the abundance of benthic invertebrates
within hyporheic sediments to increasing biotic interactions during flow recession in a temporary stream. This study examined
spatial variability in the refugial capacity of the hyporheic zone in two groundwater-dominated streams in which flow permanence
varied over small areas. Two non-insect taxa, Gammarus pulex and Polycelis spp. were common to both streams and were investigated in detail. Hydrological conditions in both streams comprised a four-month
period of flow recession and low flows, accompanied by reductions in water depth and wetted width. Consequent declines in
submerged benthic habitat availability were associated with increases in population densities of mobile benthic taxa, in particular
G. pulex. The reduction in the spatial extent of the hyporheic zone was minimal, and this habitat was therefore a potential refugium
from increasing biotic interactions in the benthic sediments. Concurrent increases in the hyporheic abundance and hyporheic
proportion of a taxon’s total (benthic + hyporheic) population were considered as evidence of active refugium use. Such evidence
was species-specific and site-specific, with refugium use being observed only for G. pulex and at sites dominated by downwelling water. A conceptual model of spatial variability in the refugial capacity of the hyporheic
zone during habitat contraction is presented, which highlights the potential importance of the direction of hydrologic exchange. |
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