PRE-BARRAGE AND POST-BARRAGE SCENARIOS OF THE RELATIVE PRODUCTIVITY OF BENTHIC AND PELAGIC SUBSYSTEMS OF THE BRISTOL CHANNEL AND SEVERN ESTUARY

The relative importance of benthic and pelagic production within the e cosystem energy cycle, varies considerably for different regions of th e Bristol Channel and Severn Estuary. In regions of high turbidity, pe lagic primary production is negligible whereas, in the clearer waters of the Outer Channel, the much higher pelagic production contributes t o both benthic and pelagic secondary production, The construction of a tidal power scheme would most probably reduce turbidity, so increasin g the overall productivity of the enclosed estuary. A range of scenari os, and their implications, are discussed.