Ecology and water quality modelling
The natural water quality of a river is determined primarily by the prevailing climate together with catchment soil type and the underlying geology. These physical conditions determine the ecology of water courses since different plant and animal species have varying preferences/tolerances in the habitats that they colonise. For example, temperature regime has a marked influence upon the composition and health of freshwater ecology [Ozaki et al., 2003]. For many species, particular stages of a life cycle may only survive within preferred temperature ranges and thrive at optimum conditions. Water temperature is also linked to water chemistry through its effect on reaction rates, solubility and biological oxygen demand which, in turn, impact upon freshwater ecology. Furthermore, it has been shown that increases in water temperature can lead to increased suspended solids.
The ecological status of a river refers to its degree of modification from the natural or baseline ecological condition of the river in the absence of human impacts. We need to understand this relationship between the ecological status of rivers and the controlling environmental factors because deviations from natural baseline water quality are generally caused by the influence of people. This factor is recognised in the European Water Framework Directive [European Commission, 2000] whereby environmental standards have been developed to indicate, for example, the critical thresholds of maximum water temperature which would be expected to lead to an impact on the ecological health of a riverine habitat.
Concern over climate change is leading to improved modelling techniques to quantify the risk of significant ecological impacts. These have come about through advances in data collection, spatial modelling and the development of 2D hydraulic models, all aimed at habitat quantification and prediction at a scale appropriate to in-stream ecology.
References
Ozaki N, Fukushima T, Harasawa H, Kojiri T, Kawashima K and Ono M, 2003. Statistical analyses on the effects of air temperature fluctuations on river water qualities. Hydrological Processes, 17, 2837–2853.
European Commission 2000. Directive 2000/60/EC of the European Parliament of the Council of 23rd October 2000 establishing a framework for Community action in the field of water policy. European Commission, Brussels, Luxembourg.
