Oteramika trial catchment groundwater studies : studies into non-point source groundwater effects in Southland / prepared by Jens H Rekker.

"August 1998."

"Southland Regional Council; Oteramika Groundwater Studies."--Running footnote.

Includes bibliographical references (p. 83-84).

The Edendale Aquifer is an unconfined alluvial aquifer within Quaternary sandy gravel. The alluvium is capped by silty loess and silt loam soils. Overlying land uses include sheep and dairy grazing, cropping, horticulture, tree nursery, residential and industrial. All land uses affect the water quality of the underlying aquifer through leaching of dissolved contaminants. The aquifer has an extent of about 6,500 hectares. The Edendale Aquifer is recharged by infiltration of precipitation surplus, typically in the period May to October. Irrigation of dairy factory and dairy shed wastewater is practised over scattered parts of the Edendale terrace, which leads to enhanced infiltration and leaching of contaminants. Surveys and monitoring of groundwater quality within the aquifer and issuing from the aquifer as springs indicate the groundwater to be impacted by non-point source contaminants. These contaminants, principally nitrate nitrogen and phosphorus have potential to threaten potability of the groundwater, or exacerbate dissolved plant nutrient loads in downstream aquatic environments. Nitrate nitrogen presently rests at concentrations ranging between 2 and 12 gNO3-N/m3, with a three-year mean of 6.1 gNO3-N/m3 throughout most of the aquifergass extent. Dissolved reactive phosphorus is found at concentrations between 0.017 and 0.026 g/m3, which is elevated compared to the mean concentration of the Mataura River. The measured groundwater discharge from the aquifer averages 820 litres per second, which is equivalent to an annual recharge rate of about 400 millimetres across the surface of the terrace surface. Long term sampling of bore and spring waters; in addition, measurement of water table elevation provides sufficient information from which to calculate estimates of the mass load for various constituents. ... - Executive summary

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