Impacts of an inter-basin water transfer: Distribution and abundance of Micronecta poweri (Insecta : Corixidae) in the River Wear, north-east England

I. Micronecta poweri (Insecta: Corixidae) is potentially sensitive to changes in river flow. A field experiment was designed to assess the impact of an inter-basin water transfer on the distribution and abundance of M. poweri in the receiving River Wear, north-east England.

2. The transfer increased river discharge threefold for a period of 1 h; the transfer discharge was then reduced to a rate equivalent to double the receiving flow. Velocity changes were variable: some parts of the river channel were subjected to order of magnitude increases in near-bed velocity, others suffered no perceptible change. Losses of fine particulate organic material were associated with the areas of greatest velocity increase.

3. Downstream of the transfer outlet, average total M. poweri abundance in replicate samples was reduced by approximately 50% during the transfer. Losses were variable within the 250 m reach monitored, with some areas gaining and some losing animals. Differences could not be explained simply as a function of proximity to the transfer outlet.

4. Results suggest that transfer impacts are location specific, varying greatly even over short (250 m) distances. For flow sensitive taxa, even relatively minor flow changes (increasing discharge to the 50 percentile flow value) may be considered as disturbance events when viewed at the patch or reach scales.

5. Despite the impacts identified for M. poweri, transfers are generally viewed as having a beneficial effect on the conservation of aquatic habitat in the River Wear. They ensure that water abstractions for potable and industrial supply can continue during the summer months without reducing the availability of suitable salmonid habitat. However, there remains a need to assess the possible transfer of biological material from the donor River Tyne to the receiving River Wear. Copyright (C) 2000 John Wiley & Sons, Ltd.