BACKWATER HABITATS AND THEIR ROLE IN NATURE CONSERVATION ON NAVIGABLEWATERWAYS

In Britain, lightly trafficked canals frequently contain diverse, prod uctive macrophyte communities. These represent important habitats for macroinvertebrates and fish while having a high intrinsic value in nat ure conservation terms. As recreational boat traffic increases, fragil e macrophytes are progressively eliminated and the biomass of the rema ining species is greatly reduced, thereby adversely affecting weed-ass ociated animals and ultimately simplifying the structure of the whole ecosystem. From the viewpoint of aesthetics, nature conservation and f isheries management, ecological enhancement of these traffic impacted ecosystems is desirable but options are limited by channel size and th e intensity and type of disturbance. Backwater areas connected to the main channel but apparently remote from traffic influences ought howev er, to provide a minimally-disturbed refuge for macrophytes and depend ent organisms. An extensive field survey was undertaken to test this h ypothesis and evaluate the potential for exploiting backwater sites as 'off-line' nature reserves. Principal determinants of vegetation stru cture and species diversity are identified and discussed and are used to prescribe a set of ideal characteristics for prospective backwater nature reserves and to forecast likely management problems.