Nitrogen species distribution in groundwater: A review of historical data with recent sampling in the Gippsland, Victoria (Australia

Michael Adelana1, Michael Heaven2, Mark Holmberg3, Matt Kitching4, George Croatto4

Agriculture Victoria, Department of Economic Development, Jobs, Transport and Resources

1 32 Lincoln Square North, Parkville, Victoria 3053, [email protected] 

2 1301 Hazeldean Road, Ellinbank, Victoria 3821, Australia

3 Cnr Taylor Street & Midland Highway, Bendigo, Victoria 3554

4 Terrace 4, Ernest Jones Drive, Macleod, Victoria 3085

Abstract

In agricultural regions diffuse pollution by nitrate is considered one of the main causes of groundwater quality deterioration. For agricultural systems that are pasture based, the input loads (e.g. fertiliser, cow dung and urine) can result in loss of nutrients.  Hence, shallow groundwater aquifers in agricultural areas are susceptible to nitrate contamination from losses of N by leaching. A review of historical data, together with recent sampling, was carried out in the Gippsland region of Victoria to map distribution of N-species in shallow aquifer systems. This review revealed that there is limited routine monitoring of nitrate in groundwater.  Nevertheless, based on the limited historical spatial and temporal groundwater chemistry data available, the concentrations of nitrate and ammonium are generally below Australian water quality (ANZECC) limits in the shallow unconfined aquifer in West Gippsland. However, localized clusters of values higher than the ANZECC limit exist in alluvium near Mitchell River, East Gippsland.  In all confined deep aquifer samples the concentrations were found to decrease further. An analysis of groundwater chemistry could not identify a correlation between land use or soil and the concentrations of groundwater nitrate and total nitrogen. Only shallow piezometer samples at Willow Grove, West Gippsland suggested high nitrate reductions under intensely grazed dairy soils.  Site-specific piezometer studies would be required to determine the depth of influence below the soil zone for reduction of nitrate to acceptable concentrations.