The influence of riparian woodland on stream temperatures: implications for the performance of juvenile salmonid

Stream temperature was monitored at five mainstem locations and one tributary location on the Girnock Burn, a 31-km(2) tributary catchment of the Aberdeenshire Dee in north-east Scotland. Stream temperature was recorded at 15-min resolution between April 2003 and March 2006 to investigate the influence of semi-natural riparian woodland on the spatial and temporal variability of stream temperature and the influence that this had on the performance of juvenile Atlantic salmon (Salmo salar). Two upstream sites were located in open moorland locations, while three downstream sites were located in areas of mixed deciduous/coniferous woodland areas at progressive distances of 0.75, 1.5 and 2.0 kin from the upstream edge of continuous riparian tree cover. The effects of riparian woodland on stream temperature varied through the year, increasing during the spring to a maximum in summer, before decreasing once again in autumn. Maximum, mean and diel temperature amplitude were lower and minimum temperatures higher at woodland sites when compared to those located in open moorland. Although significant differences in fish performance were detected between sites, the influence of temperature variability was unclear due to confounding factors, some of which could not be measured during the study. It is recommended that future studies should combine advances in field-based temperature monitoring with those in hydroclimatology to develop realistic process-based models that can be used for stream temperature prediction. Further advances are needed in understanding the relationship between naturally variable thermal regime and fish performance in order that ecological predictions can be usefully made from field and modelled temperature data. (C) Crown Copyright 2008. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.