SHORT COMMUNICATION THERMAL PROFILES WITHIN RIVER BEDS

This pilot study uses a chemical technique (KEtX) to establish vertica l profiles of average monthly water temperature within river beds: the hyporheic zone at the interface between surface water and groundwater . Data are presented for two gravel-bed sites and one sand-bed site on the River Wissey, Norfolk, UK. From February to October 1992, average monthly temperatures were determined at 10 cm intervals down Im profi les. A strong seasonal pattern was defined at all sites with hyporheic temperatures being relatively warm in winter and cool in summer. Isot hermal periods occurred in March-April and September-October. Temperat ure ranges within the hyporheic were decreased (4.6-7.7 degrees C) com pared with those of surface waters (10 and 10.9 degrees C). Temperatur e profiles were similar at all sites during winter, but the sand-bed s ite had relatively low temperatures at a standard depth within the hyp orheic during summer and the temperature gradient became isothermal la ter in the autumn at this site. It is suggested that the influence of flows and substratum characteristics on temperature patterns, especial ly in regulated rivers, may have significant ecological implications, for example for determining the timing of salmonid fry and invertebrat e emergence.