Time trends of nitrate in groundwaters under intensive agriculture in the Bundaberg region

Protecting groundwaters from contamination with nitrates leached below agricultural fields is an important element of sustainable farming practice. In the Bundaberg area, a groundwater system below sugarcane and horticultural land is a valuable source of urban water supply, and has links to surface waters and the coastal environment. A network of 49 domestic and production bores were monitored from 1994 to 1999 to determine temporal trends in nitrate concentrations of groundwater in the Bundaberg area. The network included all bores found to have high (> 50 mgIL) nitrate concentrations in a wider survey undertaken in 1993, and a selection of bores around three experimental sites where nitrate movement in the soil profile was studied. Monitoring revealed nitrate concentrations in 72% of bores were steady with another 26% falling in concentration from 1994 to 1999. Only one bore had increasing nitrate concentrations and this bore initially had a low « 20 mgIL) nitrate concentration. Of the bores with high nitrate in the 1993 survey, nitrate concentrations in 56% had fallen below 50 mgIL by 1999. Changes in nitrate concentration could not be associated with short-term rainfall patterns observed during the study. The results are positive for the Bundaberg community. However efforts to minimise nitrate leaching from urban and agricultural sources must be maintained.