| Abstract: | Policy demands informed decisions about the consequences for the physical, chemical and biological environment within a river catchment. This represents a significant challenge to scientists since many of the determining factors operate at relatively small spatial scales. Summarizing the effects of land-use change on the environmental aspects at a river-catchment scale demands the integration of complex information collated at the smaller spatial scales. This introduces both complexity and uncertainty into modelling approaches because these factors operate over different time periods; for example, in addition to current management practice, the inheritance factor means that the history of previous land uses will also impact on the nutrient status or animal species composition. This requires the development of a biophysical framework in addition to the more commonly used catchment-based definition for organizing these data. The implications of land-use change on nutrient cycling are reviewed by contrasting the properties of nitrogen and phosphorus. In addition, the possible linkages that exist between patterns of species composition and nutrient availability are explored. The general effect of increasing nutrient availability for increasing productivity but decreasing species richness is discussed using examples from a contemporary study of the River Earn in Scotland. |
