Backwater habitats and their role in nature conservation on navigable waterways

In Britain, lightly trafficked canals frequently contain diverse, productive macrophyte communities. These represent important habitats for macroinvertebrates and fish while having a high intrinsic value in nature conservation terms. As recreational boat traffic increases, fragile macrophytes are progressively eliminated and the biomass of the remaining species is greatly reduced, thereby adversely affecting weed-associated animals and ultimately simplifying the structure of the whole ecosystem. From the viewpoint of aesthetics, nature conservation and fisheries management, ecological enhancement of these traffic impacted ecosystems is desirable but options are limited by channel size and the intensity and type of disturbance. Backwater areas connected to the main channel but apparently remote from traffic influences ought however, to provide a minimally-disturbed refuge for macrophytes and dependent organisms. An extensive field survey was undertaken to test this hypothesis and evaluate the potential for exploiting backwater sites as 'off-line' nature reserves. Principal determinants of vegetation structure 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.