Measuring nutrient and pesticide movement in soils: benefits for catchment management

Abstract

Summary. The movement of nutrients, especially NO₃^- and H₂ PO₄^-, and pesticides from soils into receiving waters can pose problems for the management of water quality in catchments. This paper briefly reviews the reactions of these materials in soil, and the processes involved in their transport by water over and through soils in the field. The natural heterogeneity of soils, and fluctuations in the source strength of pesticides and nutrients due to biophysical factors and environmental conditions, have a profound effect on measurements. Preferred techniques are discussed for measuring losses from drained systems (sampled as point sources, which provide an integration of spatial and temporal variability in the areas drained) and undrained systems (sampled as diffuse sources, where the reliability of areal averaging depends on the efficiency of the sampling strategy). Pathways of nitrogen, phosphorus and pesticide movement from soil into receiving waters (surface and groundwater) are identified, and examples given of the quantities lost in solution 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 protocols for good quality assurance–quality control are identified. The concepts of precision, accuracy, completeness and comparability are defined. Sampling equipment is reviewed and procedures for preventing contamination in the field and laboratory, and the preservation of samples, are recommended. The application of techniques is illustrated by case histories for pesticide 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 catchments, through simulation modelling are briefly discussed.