Lysimeter experiment

One of our experiments to determine the beneficial reuse of Banks Peninsula’s wastewater uses lysimeters, which in this case are steel cylinders 50 cm in diameter and 70 cm deep. Each lysimeter contains an intact core of soil that was collected from Duvauchelle or Akaroa. The lysimeters receive measured amounts of irrigation, rainfall, and effluent. Lysimeters drain into a container allowing regular determination of the leaching volume, chemical composition, and pathogen load. Specifically, we seek to determine the effects of adding effluent at rates of 0 (control) 500, 1000, and 2000 mm per year on nitrate and pathogen leaching, soil structure and plant growth. Analyses of the growth and chemical composition of the pasture growing in the lysimeters indicates the effect of the effluent application on plant health. After two years of effluent application, the lysimeters will be deconstructed and the soil properties measured to reveal whether there is any soil degradation caused by the effluent application. The results from this experiment will enable the design of a land-based effluent disposal system with that promotes plant growth and does not lead to excessive runoff, nitrate leaching or pathogen entry into groundwater.

Dr Maria Jesus Guiterrez-Gines (behind) and PhD student Minakshi Mishra taking leachate samples from the lysimeters filled with soils from Duvauchelle and Akaroa.

Lysimeter diagram
A diagram of a lysimeter used in these experiments. The height is 70 cm and the width is 50 cm. The drainage is collected weekly and varies between 0 and 9 litres, depending on the treatment and rainfall. Drainage is collected more often during periods of high rainfall. A sample of the drainage is analysed for nitrate (a groundwater contaminant) and pathogens. The pasture is harvested periodically to simulate grazing. This is usually once every three weeks spring - summer - autumn and once every six weeks during winter.