Interrelations of river ship traffic with aquatic plants in the River Nile, Upper Egypt

Abstract

Multivariate analysis of data from a 1997 survey of submerged vegetation at 3 locations on the River Nile in Upper Egypt showed that hydrochemical factors (total oxidised nitrogen, sulphate and sodium) were the most important environmental variables explaining the distribution and the abundance of submerged plant species. The kinetic energy of waves produced by tourist ship wash (measured using an index incorporating measured wave height at shore, depth of sampling site and distance between ship channel and sampling site) was next in importance, and explained more of the variation in submerged plant abundance and distribution than did river flow rate. Classification using TWINSPAN identified 5 major groups of sites characterised by differing plant community composition (and having significant inter-group differences in wave index and flow rate). Ship wave effects are likely to be an important factor contributing to differences observed in hydrosoil texture and organic matter content at different depths at one study location (Aswan) heavily used by ship traffic. Coarse sand and gravel fragments with low organic matter content, were predominant in the shallow water zone, most heavily impacted by ship waves; while finer sand with high organic matter content formed the hydrosoil in deeper water. Such variation in sediment characteristics is also likely to influence macrophyte growth. The environmental disturbance effects of ship traffic in the Nile in Upper Egypt currently appear to play a significant role in the ecology of the river's submerged vegetation. Given the long-term trend towards tourism use of the Nile for cruise holidays, it is likely that ship traffic intensity will increase over the next decade, adding to the impacts on aquatic vegetation.