The impact of livestock-farming on welsh streams: the development and testing of a rapid biological method for use in the assessment and control of organic pollution from farms

Organic wastes from intensive agriculture are a major cause of surface-water pollution in Great Britain. There are a large number of possible sources for such pollution, and there is a need to target the efforts of pollution-control authorities to the worst-affected parts of catchments. This paper describes the development of a rapid method for the identification of polluted streams based upon the macro-invertebrate fauna. An indicator key was developed by TWINSPAN classification of data from benthic sampling at 55 sites in West Wales. The key requires assessment of the abundance of four macroinvertebrate taxa and of the extent of 'sewage-fungus' growth, all of which can be determined by examination in the field. The key can separate sites into three groups representing different levels of pollution impact as indicated by differences in biotic indices and chemical data. The system was tested successfully at a further 146 sites in West Wales resulting in the notification of 49 farms to the pollution-control authorities. Non-biologists were able to use the key efficiently after a short period of training. A further test involving 51 sites in Devon indicated that the technique may be adaptable to other parts of Great Britain. It is envisaged that indicator systems designed to suit local fauna may have a major role in a pro-active strategy developed to combat pollution from farms because they have potential advantages over more complex biological methods currently in use.