Comparison of three mapping procedures developed for river macrophytes

SUMMARY. Three methods of mapping macrophytes on short sections of river are described and compared. All methods involve setting up a 1‐m grid system over the site using permanent stakes to locate a series of temporary strings. The first method (detailed mapping), which generates a map, uses the grid system to locate accurately the position of macrophytes and substrata on the river bed. It is very time consuming and objectivity in mapping is difficult to achieve. The second method (points method) involves recording the macrophytes and substratum below each intersection of the 1‐m grid system covering the study site. This method is fast, capable of giving estimates of percentage cover for the different substrata and macrophytes but does not produce a map. The third method (rectangles method) is regarded as both the most efficient and also the most objective of the three mapping procedures. The substratum or macrophyte dominating each 50 × 100 cm rectangle of river bed is recorded together with additional substrata and macrophytes present. The procedure is rapid to use in the field, provides a simplified map of the study site and is more amenable to detailed analysis than the two previous methods. All three mapping methods are best suited to rivers less than 20 m wide where safe wading and good visibility can be guaranteed.