It would be convenient if the component activities of
agriculture could be simply and quantitatively related
to their impacts on freshwater systems. This would be
an ideal basis for creating legislation, for designing
incentive schemes to optimize agricultural practice and
for minimizing environmental consequences. However,
it is far from possible. Both agricultural and freshwater
systems are complex and the relationships between
them make a mesh of many dimensions. Not least there
are many sorts of agricultural system and a plethora of
natural waters and communities. The entire land
surface, much of which is agricultural, forms the
catchment area for one or other river system and
almost anything that happens on the catchment has an
effect on the freshwaters. The relationship between
catchment and receiving water is like that of a house
and its waste bin. Most of the activities in the house are
reflected in the contents of the bin. In 1979, the Royal
Commission on Environmental Pollution (RCEP)
published its Seventh Report, entitled Agriculture and
pollution (RCEP 1979). Its preoccupations then are
familiar still: pesticides, nitrogen fertilizers and organic
farm wastes, but the concept of ‘pollution’ has become
the much wider one of ‘impact’ as understanding has
increased of how systems function. Simply to consider
how substances emanating from agriculture affect
receiving waters, the old concept of pollution, is to
misunderstand most of the problem.