Monitoring effects of Southland demonstration farm on stream water nitrate

Abstract

The objective of this research work was to monitor the effects of the Southland Demonstration Farm on the concentration and amount of nitrate in the Tomoporakau Creek. The creek runs through the central area of the farm and drainage outfalls discharge directly into this stream. A detailed GPS topographical survey was conducted to confirm the drainage catchment area and hydrology of the site. Groundwater piezometers were established adjacent to the stream in order to monitor groundwater levels and compare those to stream water levels. Detailed surveys of the stream bed, stream surface, groundwater levels, and stream bank geometry were also conducted. Stream flow rate measurements were continuously monitored using “Sontek” Doppler flow equipment installed in concrete box culverts at „up-stream‟ and „down-stream‟ monitoring sites. Stream water was pumped continuously from the monitoring sites using submerged samplers that sent water to an instrument base-station at the dairy shed. The water nitrate concentration from each site was monitored in real-time using flow-through UV absorption spectrometer sensors. This system does not require any reagents as it measures the water nitrate concentration by detecting the UV light absorption by nitrate. These sensors also measure a full spectrum adsorption in order to automatically 'correct' for light absorption due to particulate material and/or other chemicals in the water.