Abstract
Lord Howe is a small subtropical volcanic island approximately 700km north east of Sydney. Its degrading groundwater resources due to growing population and tourist numbers combined with highly permeable soils, over-extraction, and inappropriate waste disposal systems typify many islands in the south west Pacific region. This study was undertaken to better understand the hydrogeochemistry and quality of the Lord Howe groundwater system and to recommend options for groundwater management. Three distinct groundwater bodies, attributed to geology and land-based inputs, were identified. Over-extraction is causing salt water intrusion beneath the northern portion of the settlement area. Nitrate, nitrite, and phosphate concentrations ranged from 49 g. L-1 to 12753 pg. L-1 pg. L-1 to 3 pg. L-1, and 30 pg. L-1 to 305 pg., respectively. Highest concentrations were found in the northern portion of the settlement area due to higher population densities and low retention capacity of the soils. Ammonium concentrations ranged from 10 pg. L-1 to 34 pg. L-1, with highest concentrations in the southern portion of the settlement area attributed to slightly lower dissolved oxygen levels. A number of management recommendations are given, including monitoring of salt water intrusion and alternative effluent disposal systems. Further detailed studies are needed to better assess seasonal variations and potential flushing to sensitive marine waters.