Long-term investigations of trophic relationships in southern chalk streams

1. An understanding of the feeding relationships of organisms is fundamental to our capability to conserve and manage aquatic systems. At one extreme we must study the cyclic and erratic physical processes which govern the reproduction, survival and growth of consumers and their‘prey’and at the other the rates of food consumption, the assimilation of nutrients and the energetic interactions of plants, animals and micro‐organisms. 2. Since the commencement of freshwater science in this country, our understanding of the mechanisms by which producers and consumers interrelate has increased greatly. Information is required basically on three levels: (1) Short‐term laboratory and field studies designed to provide detailed data on aspects such as habitat selection, growth, feeding behaviour, etc. (2) Investigation of patterns of change which show periodicities of weeks, months or even a few years associated with the life cycles of many plants and animals and with the seasonal variations in physical and chemical parameters. (3) Long‐term surveillance and monitoring, often in a superficial manner, of particular aspects of river ecology in order to detect trends of change or patterns of variation over tens or hundreds of years and, if possible, to relate these to recorded climatic changes. 3. Long‐term data collection, in the scale of human longevity, is most appropriate to phenomena which show readily indentifiable periodic maxima or minima or which occur at well defined times (for example the discharge of a river or the start and finish of flow in a winterbourne). Alternatively, information which is amenable to automatic or semi‐automatic monitoring (temperature, water chemistry, fish migration) or integrated sampling (insect abundance, annual removal of cut water weeds) may also provide valuable evidence of long‐term change.