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

This paper presents details of the methodology developed by the United King dom's Environmental Change Network for the long-term monitoring of macrophy tes in rivers and streams. The methodology is based on techniques first pro posed by the Standing Committee of Analysts (1987) and later adapted by the National Rivers Authority (NRA) and Environment Agency, but differs in spl itting the surveyed 100 m stretch of water into sections to provide an obje ctive measure of the frequency of occurrence of individual species in place of the more subjective estimation of cover. A pilot study of the ECN metho dology took place at five sites in 1997. The results of this study, includi ng a few practical difficulties in the application of the methodology, are presented and discussed. For all but one of the sites strong associations w ere found between the number of species observed and the physical character istics of the watercourse. The most important characteristics were degree o f shading, substrate type, depth and clarity. The frequency of occurrence o f individual species within sections of the watercourse was found to be str ongly related to the log of the overall estimates of cover. Because the use of sections, rather than a single overall cover estimate, enables variatio n in the pattern of vegetation over surveyed stretches to be detected and r elated 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 fou nd 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.