River restoration: unexpected consequences of excessive disturbance

Langford, T. E., Jones, J. G. and Shaw, P. J. (2007) River restoration: unexpected consequences of excessive disturbance. Change in Aquatic Ecosystems, Plymouth, UK. 04 - 06 Jul 2007.

Abstract

River temperature regulates nearly all bio-chemical processes and is a key parameter of water quality. Aquatic organisms respond to the entire temperature regime, including the absolute value, seasonal and diel ranges, rate of change and the timing and duration of significant thermal events. In recent summers, stream water temperature in unshaded locations across the New Forest has repeatedly exceed 24 oC making them unsuitable habitat for vulnerable species such as Brown Trout. Although fish are known to use cool water refuges during the summer, low flows can restrict migration and reduce the accessible habitat. The stress caused by overcrowding and the potential increased exposure to disease may also be harmful. The shade cast by riparian vegetation can exert a major influence on the freshwater thermal regime particularly in small rain-fed streams and therefore affect the ability of sensitive species to withstand extreme high temperatures. Observations across the New Forest in recent summers, have shown that water temperatures in the shaded reaches were as much as ten degrees cooler than the open sections. The problem of high temperatures is expected to get worse as a consequence of climate change; with drier summer resulting in reduced flows and average summer/autumn temperatures predicted to rise by 4 to 5 oC in southern England. Thus the cooling influence of riparian shade is likely to become increasingly important across England and Wales to protect vulnerable stenothermic species such as trout and salmon from thermal stress. This project was devised to determine the influence of riparian shade on stream temperature and behaviour and ecology of woodland streams in the New Forest. We will present details of riparian shade, water temperature, fish populations and community structure in three streams. We will illustrate how riparian shade affects the thermal regime and the volume of suitable habitat within the stream. Quantify the influence of land use, land cover and riparian shade on the response of water temperature to air temperature and model the impact of climate change predictions on the probably suitability of these rivers as habitat for vulnerable/threatened fish species. Habitat restoration and the removal of riparian shaded from a previously shaded stream will also be discussed.

This record has no associated files available for download.

Contributors

Author: P. J. Shaw

Download statistics