
%0 Journal Article
%A Lamontagne, Sébastien 
%T Groundwater delivery rate of nitrate and predicted change in nitrate concentration in Blue Lake, South Australia
%J Marine and Freshwater Research
%D 2003/01/31
%V 53
%N 7
%P 1129-1142
%K 
%R https://doi.org/10.1071/MF01239
%U https://www.publish.csiro.au/paper/MF01239 
%X Blue Lake, the principal water supply for the City of Mount Gambier (South Australia), is contaminated with nitrate (NO3&#8211;) from polluted groundwater. Using existing data, a study was undertaken to determine the past load of NO3&#8211; from groundwater entering the lake and to forecast future trends in lake NO3&#8211; concentration. Groundwater NO3&#8211; loads for the 1971&#8211;1997 period were estimated with an inverse model, which combined the long-term record for NO3&#8211; concentration in the lake with a simple NO3&#8211; mass-balance. Model results show that the load of NO3&#8211; from groundwater (18&#8211;24 metric tons (t) year&#8211;1 as N) was by far the largest source to Blue Lake between 1971 and 1997. Sinks for NO3&#8211; included pumping withdrawal (10&#8211;14 t year&#8211;1), in-lake consumption (7&#8211;10 t year&#8211;1), and groundwater outflow (0&#8211;1.8 t year&#8211;1). The NO3&#8211; concentration in incoming groundwater (4&#8211;7 mg N L&#8211;1) appears to have increased slowly but steadily during the 1971&#8211;1997 period (at a rate varying between 0.037 and 0.070 mg N L&#8211;1 year&#8211;1). By assuming that the rate of increase in groundwater NO3&#8211; concentration will remain constant, a forecast for lakewater NO3&#8211; concentration was made for the 1998&#8211;2028 period. Lakewater NO3&#8211; concentration should increase from the contemporary &#126;3.5 mg N L&#8211;1 to 4 or 5 mg N L&#8211;1 by 2028. In the short term (decades), the rate of pumping withdrawal will be the main determinant of NO3&#8211; concentration in the lake through its impact on the rate of groundwater inflow and the lake water residence time. Although the drinking water guideline for NO3&#8211; (11. 3 mg N L&#8211;1) may not be exceeded in the short term (decades), it may be exceeded in the longer term (centuries) as NO3&#8211; concentration in the neighbouring aquifer adjusts to the contemporary land use. 
