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River vegetation and pollution. 1975. In Science, Technology and Environmental Management. (Eds) R.D. Hey, T.D. Davis, pp. 137—44. Saxon House/Lexington. ISBN 0-347-01087-3



12.1 INTRODUCTION

 

The factors determining the distribution and performance of watercourse macrophytes (larger plants) can be grouped into three categories: (a) catchment geology and flow regime, the latter depending on topography, geology and climate; (b) management practices such as canalisation, dredging, cutting, flow regulation and spraying; and (c) man-made alterations to the chemical or physical quality of the river (not included in (b) as they are not intended for the benefit of the watercourse or its users). This diverse group of factors will be considered in this chapter.

Vegetation can, therefore, be predicted from flow pattern and geology (and management). When the general type of plant community does not conform to prediction, the vegetation is damaged, e.g. by trampling or accidental toxic spillages; or is polluted, frequently eutrophically; or is eliminated by severe damage or pollution.

Macrophytes are common in lowland and some highland rivers. They are easier to record than fish or invertebrates, as they are large and stationary, and there are only about fifty common species. The species present at a site can usually be seen from a bridge, though more detailed sampling may be required.

Macrophyte species are closely correlated with their habitat. Stream habitats are complex, and different species tend to be best correlated with different variables. Callitriche spp., for example, are related to shallow water; mosses to stable substrates; Myriophyllum alterniflorum to soft waters; M. spicatum to harder ones; Potamogeton pectinatus to high concentrations of various solutes; and Ranunculus fluitans (in highland regions) to large volumes of water. Consequently, much information on a stream habitat can be deduced from a list of the species present in it. Macrophytes can, therefore, be used for monitoring.