Influence of riparian shade on stream thermal regime (New Forest 2010)

River temperature is a key parameter of water quality. Most bio-chemical processes and physical characteristics of a water body are functions of temperature. Aquatic organisms including fish are polikothermic and respond to the entire temperature regime; the absolute value, seasonal and diel ranges, rate of change and the timing and duration of extreme thermal events. Salmonids are cold water species with high metabolic rates and oxygen demand, they thrive in temperatures below 20oC and have an upper thermal limit of 24 - 28oC. In recent summers water temperatures in excess of 25oC have been recorded in streams across the New Forest. High water temperature is associated with low flow, reduced oxygen level and increased ammonia concentration. Fish are able to move to cooler water but the stress caused by crowding and potential exposure to diseases can led to fish deaths. The shade cast by riparian vegetation has a significant influence on river habitat quality and with climate change predicted to lead to warmer, drier summers the role of riparian shade may become important across England and Wales to protect vulnerable species from the threat of high water temperatures. Objectives (1) to monitor stream water temperature in shaded and unshaded sections of three streams in the New Forest and (2) investigate the relationship between water temperature and riparian shade levels. Additional resource: Broadmeadow, S., Jones. J.G., Langford, T.E.L., Shaw, P.J. and Nisbet, T., (2010). The influence of riparian shade on lowland stream water temperatures in Southern England and their viability for Brown Trout. River Research and Applications DOI: 10.1002/rra.1354 Jan (2010).