Monitoring of aquatic macrophytes for detection of long-term change in river systems.

This paper presents details of the methodology developed by the United Kingdom's Environmental Change Network for the long-term monitoring of macrophytes in rivers and streams. The methodology is based on techniques first proposed by the Standing Committee of Analysts (1987) and later adapted by the National Rivers Authority (NRA) and Environment Agency, but differs in splitting the surveyed 100 m stretch of water into sections to provide an objective measure of the frequency of occurrence of individual species in place of the more subjective estimation of cover. A pilot study of the ECN methodology took place at five sites in 1997. The results of this study, including a few practical difficulties in the application of the methodology, are presented and discussed. For all but one of the sites strong associations were found between the number of species observed and the physical characteristics of the watercourse. The most important characteristics were degree of shading, substrate type, depth and clarity. The frequency of occurrence of individual species within sections of the watercourse was found to be strongly related to the log of the overall estimates of cover. Because the use of sections, rather than a single overall cover estimate, enables variation in the pattern of vegetation over surveyed stretches to be detected and related to watercourse characteristics, the precision with which change can be detected is increased, and the possibility of determining the causes of change is thereby enhanced. Moreover the use of sections allows within-site variation to be calculated and hence the accuracy of estimated changes to be quantified. In general implementation of the ECN methodology was not found to be particularly onerous or difficult. As a result of the pilot study some changes in the ECN methodology have been made, primarily to reduce the workload so that sites can be surveyed comfortably in a single day.