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Influences of environmental conditions on macrophyte communities in drought‐affected headwater streams
Author(s) -
Westwood C. G.,
Teeuw R. M.,
Wade P. M.,
Holmes N. T. H.,
Guyard P.
Publication year - 2006
Publication title -
river research and applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.679
H-Index - 94
eISSN - 1535-1467
pISSN - 1535-1459
DOI - 10.1002/rra.934
Subject(s) - macrophyte , streams , environmental science , habitat , ecology , channel (broadcasting) , vegetation (pathology) , hydrology (agriculture) , streamflow , ordination , drainage basin , geography , geology , biology , medicine , computer network , geotechnical engineering , cartography , pathology , computer science , electrical engineering , engineering
A 10‐year study of groundwater‐dominated headwater streams in the chalklands of southern England has highlighted the major influence that stream flow has on the composition of in‐channel macrophyte communities. Macrophytes supply much of the physical structure within these headwater channels, as well as providing habitats for a rich assemblage of higher life forms, some of them specialized and rare. The overall influence of stream flow however, is modulated by many environmental factors operating at diverse spatial scales. Data describing the relevant environmental variables were accumulated for six chalk streams in the Thames basin and related directly to the vegetation record by means of Canonical Correspondence Analysis, correlation tests and other analyses, to reveal the circumstances in which communities would be likely to thrive and those in which they would be negatively impacted by variations in stream flow. It was found that local topography and channel dimensions had a direct influence on the composition of communities at local level and that land use and rates of water abstraction had an underlying, but no less important, influence at catchment level. The species most associated with positive species diversity were those of sluggish flow and damp margins indicating the importance of velocity and moisture gradients across the channel in producing a full manifestation of the flora. Strong negative correlations were produced by non‐aquatic grasses and herbs, which represent prolonged periods of channel desiccation. The environmental parameters most associated with positive diversity were high local water stages, wide channels and a high degree of semi‐natural land use within the catchment. Steep channel gradients were strongly associated with negative diversity. The results have confirmed that optimal channel conditions, as exemplified by the classic ‘winterbourne’ with its low‐flow channel, extensive margins, gently sloping banks and high seasonal inundation, will produce good conditions for species diversity and make communities more resistant to the effects of drought. These conditions can be enhanced through sensitive catchment management that encourages rainfall percolation, limits abstractions and seeks to maintain a low intensity of landcover management. Copyright © 2006 John Wiley & Sons, Ltd.