SS3.05 Land-use, Groundwater and Lotic Ecosystems
Date: Monday, June 10, 2002
Time: 11:00:00 AM
Location: Colwood
 
LamontagneS, CSIRO Land & Water, Adelaide, Australia, sebastien.lamontagne@csiro.au
Herczeg, A, , CSIRO Land & Water, Adelaide, Australia, andrew.herczeg@csiro.au
 
GROUNDWATER DELIVERY RATE OF NITRATE AND PREDICTED CHANGE IN NITRATE CONCENTRATION IN BLUE LAKE, SOUTH AUSTRALIA
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Blue Lake, the principal water supply for the City of Mount Gambier (South Australia), is contaminated with nitrate from polluted groundwater. The lake has a very small surface catchment (the crater of an extinct volcano) but is a part of the large Gambier Limestone aquifer. Nitrate concentration in the Blue Lake has increased slowly but steadily from 2.7 to 3.5 mg N/L between 1970 and 1997. A simple mass-balance analysis demonstrated that groundwater is the principal input of nitrate to the lake (17 to 22 metric tons N per year) and that both pumping withdrawal (10 to 14 t/year) and in-lake consumption (7 to 10 t/year) are important losses. The slow increase in nitrate concentration in the lake appears to be caused by a similar slow increase in nitrate concentration in the groundwater entering the lake. A forecast suggests that the lake water nitrate concentration will remain within recommended drinking water guidelines for the next few decades but may exceed the guideline at the scale of centuries. The slow rate of change for nitrate concentration in the Blue Lake highlights that large aquifers and their associated groundwater-dependent ecosystems may require centuries to adjust to changes in land-use.