Dominique O'Brien1, Stephen Lewis1, Aaron Davis1, Christie Gallen2, Chris Paxman2, Rachael Smith3, Ryan Turner3, Michael Warne3, Jochen Mueller2, Jon Brodie1
1Catchment to Reef Research Group, TropWATER, James Cook University, Townsville
2National Research Centre for Environmental Toxicology, The University of Queensland, Coopers Plains
3Department of Science, Information Technology, Innovation and the Arts (DSITIA)
Barratta Creek constitutes one of the major upstream catchments and drainage lines in the watershed of the Bowling Green Bay Ramsar wetland. The Barratta Creek catchment has been considerably altered following the development of the Burdekin-Haughton Water Supply Scheme (BHWSS) in the late 1980s largely for sugarcane cultivation, which led to the establishment of perennial flow within the creek after it became the main distributary channel for irrigation tailwater runoff. As such, pesticide concentrations within the creek prior to the undertaking of this project were elevated compared to most streams of the Great Barrier Reef catchment area. This study has utilised a combination of passive samplers deployed at monthly intervals and grab samples at four sites along the Barratta Creek Complex over two years to examine the persistence, concentration, pesticide use in the catchment area, seasonality and spatial variation of the multiple pesticide residues detected. In addition, this study further assesses the utility of passive sampling techniques vs grab sampling when undertaking water quality monitoring. This project initially proposed a 12 month monitoring program at four sites within the Barratta creek system. Additional resources were obtained and the project was continued for an additional twelve months so that at the conclusion of the monitoring program, 24 months of continuous monthly pesticide monitoring had been undertaken. During this study period, two changes in the regulated use of diuron by the sugarcane industry were introduced by the Australian Pesticides and Veterinary Medicines Authority (AVPMA).
A total of 37 different pesticide residues (which does not include metabolites of some of these pesticides) were detected in the Barratta Creek Catchment during the two year research program, although a number of these residues were detected infrequently (< 5 occasions of the 27 deployments) and at low concentrations (i.e. below available ecological guidelines). Since pesticide usage data are unavailable in the upstream catchment area, this research program provides valuable insights on the pesticides in common use in this region. Moreover, long-term programs provide insights into changing patterns in pesticide usage. This study found increasing levels of metribuzin and metolachlor in Barratta Creek which likely reflects the wider adoption of these 'alternative' herbicides to diuron and atrazine in the lower Burdekin region. The herbicides diuron and atrazine regularly exceeded ANZECC and ARMCANZ (2000) ecological protection guidelines for several months (five to seven months of the year) at all four sites including in the Ramsar wetland in Bowling Green Bay. While concentrations of both atrazine and diuron progressively decrease towards the lower reaches of the Creek system (e.g. in the Ramsar wetland site concentrations were approximately a third to a half of the values measured at the upper site), they still exceeded the 99% species protection value for six months of the year.
The change in the types of pesticides and their concentrations detected throughout this monitoring program has provided a valuable record of the pesticides employed by the local industry and how the usage of pesticides by the industry has changed in response to regulatory action. As such it is advisable that the monitoring of pesticide residues within the Barratta Creek is continued. This monitoring program will ensure that any future changes in pesticide usage are captured so that pesticides used by local industries are not being transported into the receiving environments at concentrations likely to put valuable species or ecosystems at risk.