The Ranger uranium mine adjacent to Kakadu National Park in the Northern Territory has ceased operations and the mine site is currently in its rehabilitation phase. Billabongs in the Park have been identified as potential off-site ecosystem receptors (of magnesium, metal and nutrient contaminants) from mine water discharged from the rehabilitated site, and two billabongs on the mine-site are key features the Traditional Owners want to see protected to a standard that meets cultural amenity. There are currently insufficient baseline data for the off-site billabongs to assess for future changes in water quality and limited knowledge of how their phytoplankton communities vary seasonally, and in response to contaminants. Given the long-term requirement for monitoring of contaminants arising from the mine-site, the Supervising Scientist’s long-term goal is to transition to an aquatic monitoring system that can be carried out independently by Indigenous Ranger Groups. Consequently, there has been an emphasis on employing aquatic monitoring techniques that are inexpensive, rapid, robust, and performed in situ with portable instrumentation.
The aim of this work was to establish a baseline water quality dataset for two of the off-site billabongs (chlorophyll a, nutrients, metals, major ions, physicochemical parameters), and a reliable phytoplankton monitoring method, which could be used for rapid assessment of primary productivity status and the potential for harmful algal blooms. For the latter, laboratory and in situ measurements of chlorophyll a were compared with algal cell counts (flow cytometry and microscopy) to determine a relationship between algal density and chlorophyll a. Seasonal patterns in water chemistry were detected and the hand-held in situ fluorometer was found to be a suitable, low-maintenance method for detecting potential changes in billabong productivity.