Measuring nutrient and pesticide movement in soils: benefits for catchmentmanagement

The movement of nutrients, especially NO3- and H2PO4-, and pesticides from soils into receiving waters can pose problems for the management of water q uality in catchments. This paper briefly reviews the reactions of these mat erials in soil, and the processes involved in their transport by water over and through soils in the field. The natural heterogeneity of soils, and fl uctuations in the source strength of pesticides and nutrients due to biophy sical factors and environmental conditions, have a profound effect on measu rements. Preferred techniques are discussed for measuring losses from drain ed systems (sampled as point sources, which provide an integration of spati al and temporal variability in the areas drained) and undrained systems (sa mpled as diffuse sources, where the reliability of areal averaging depends on the efficiency of the sampling strategy). Pathways of nitrogen, phosphor us and pesticide movement from soil into receiving waters (surface and grou ndwater) are identified, and examples given of the quantities lost in solut ion and solid phases under various land uses. The importance of recognising the likelihood of 3-dimensional flow of water and entrained solutes in the landscape is emphasised. Techniques to obtain representative samples are discussed and sampling prot ocols for good quality assurance-quality control are identified. The concep ts of precision, accuracy, completeness and comparability are defined. Samp ling equipment is reviewed and procedures for preventing contamination in t he field and laboratory, and the preservation of samples, are recommended. The application of techniques is illustrated by case histories for pesticid e monitoring. The role of models for integrating the various processes that determine the fate of nutrients and pesticides under a specific management practice is discussed. The scope and current limitations for extrapolating the results of site-specific measurements to larger areas, such as whole c atchments, through simulation modelling are briefly discussed.