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AbstractThe paper describes the approach and methods used during a three‐year programme to improve river‐water quality in an area seriously affected by agricultural pollution.Low base‐flow river systems serving clay catchments exhibit flash characteristics which required long‐term permanent solutions to ensure improved river water quality under all weather conditions. The approach which was used needed to identify polluters and convince them (a) that effective remedies had to be found and implemented within a reasonable time scale, and (b) that there would be serious consequences of failure to undertake improvements. The initial contact with dischargers, the attitudes adopted and responses received are considered and discussed. Progress throughout each phase of the programme, the solutions used and the degree of improvement achieved are assessed. Legislative changes during the period of the programme, other factors influencing agricultural pollution of watercourses, and likely future implications of these, are discussed.The success of the programme resulted in the elimination of all major sources of agricultural pollution.

Cone and Seismic Cone Penetration Tests (CPT and SCPT) have been carried out at a total of 101 sites in the Porirua and Lower Hutt regions of New Zealand, initially (from 1975 to 1987) as government-funded public- good science, and later as part of a multi-disciplinary microzoning project under contract to Wellington Regional Council. The shear wave velocities and depths determined in the study were successfully used to predict small-signal resonant frequencies for two sediment-filled basins, and the inferred cohesions were used qualitatively to predict the importance of nonlinearities in limiting ground motion amplification. The major results were the identification and shear wave characterisation of a surface layer (depth 12 m, diameter 600 m) of cohesive flexible sediment in the Porirua basin and a successful prediction of the associated basin resonant frequency, identification and shear wave characterisation of a thick surface layer (depth 30 m, length 2 km, width 500 m) of cohesive flexible sediment in the Wainuiomata basin which explained an observed resonance, identification and shear wave characterisation of a wedge of flexible sediment, cohesive below and uncohesive above, in the lower part of the Hutt Valley, and identification of a pocket of flexible sediment in the Naenae area.

Improving stream water quality in agricultural landscapes is an ecological priority and a legislative duty for many governments. Ecosystem health can be effectively characterised by organisms sensitive to water quality changes such as diatoms, single-celled algae that are a ubiquitous component of stream benthos. Diatoms respond within daily timescales to variables including light, temperature, nutrient availability and flow conditions that result from weather and land use characteristics. However, little consideration has been given to the ecological dynamics of diatoms through repeated seasonal cycles when assessing trajectories of stream function, even in catchments actively managed to reduce human pressures. Here, six years of monthly diatom samples from three independent streams, each receiving differing levels of diffuse agricultural pollution, reveal robust and repeated seasonal variation. Predicted seasonal changes in climate-related variables and anticipated ecological impacts must be fully captured in future ecological and water quality assessments, if the apparent resistance of stream ecosystems to pollution mitigation measures is to be better understood.

Improving stream water quality in agricultural landscapes is an ecological priority and a legislative duty for many governments. Ecosystem health can be effectively characterised by organisms sensitive to water quality changes such as diatoms, single-celled algae that are a ubiquitous component of stream benthos. Diatoms respond within daily timescales to variables including light, temperature, nutrient availability and flow conditions that result from weather and land use characteristics. However, little consideration has been given to the ecological dynamics of diatoms through repeated seasonal cycles when assessing trajectories of stream function, even in catchments actively managed to reduce human pressures. Here, six years of monthly diatom samples from three independent streams, each receiving differing levels of diffuse agricultural pollution, reveal robust and repeated seasonal variation. Predicted seasonal changes in climate-related variables and anticipated ecological impacts must be fully captured in future ecological and water quality assessments, if the apparent resistance of stream ecosystems to pollution mitigation measures is to be better understood.