Darwin Harbour in good health
Westra Van Holthe, Willem
Media Releases for 12th Assembly 2012 - 2016; Media Releases; ParliamentNT
Made available by via the Publications (Legal Deposit) Act 2004 (NT)
Oceans; Marine life
Northern Territory Government
Issued as a Media Release
Northern Territory Government
47 6. Conclusion For the reporting period (mid-2013 to September 2014) the water quality of the Darwin Harbour region was very good to excellent with the exception of Myrmidon and Buffalo Creeks. West Arm, the Elizabeth River estuary, Blackmore River estuary and Middle Harbour were graded A, excellent water quality. Shoal Bay, the Outer Harbour and East Arm were graded B, very good water quality. Myrmidon Creek and Buffalo Creek were respectively graded C (good) and D (poor). No waters were graded E (very poor) this reporting year. Improvements in the Buffalo Creek system were observed for dissolved oxygen. Day time DO levels were slightly better than the previous reporting year with the annual median meeting designated water quality objectives. However, DO levels typically decrease in the upper reaches of the creek during the night. The Middle Harbour reporting zone also indicated improvements. Dissolved oxygen revealed better agreement with WQOs in the 2014 reporting year. However previous departures did not pose any need for further investigation and were more indicative of natural variation typically observed with tidal and spatial changes (Mauraud, 2013). There has been no major change in the water quality of Darwin Harbour since 2009. The system overall remains largely in very good condition with only small localised areas subject to degradation. Potential sources of pollution to the waterways of Darwin Harbour include sediments, nutrients and other human-related pollutants. All these compounds can come from both point and diffuse sources, coming from a specific location (i.e. sewage treatment plant) or from a wide area (i.e. stormwater during the wet season). The influence of the sewage treatment plant wastewater discharge is clear with the highest values for total nitrogen, total phosphorus, ammonia and filterable reactive phosphorus measured at sites adjacent to respective outfalls, and in Buffalo Creek. These systems represent the extremes in water quality, however their influence is localised and not detected more broadly in the harbour. Seasonal variations (dry vs wet season) and spatial variations (upper vs outer sites) have been previously identified as important factors driving water quality, amongst others. Results from previous years have varied slightly but differences may be due to the location and the number of the sites sampled, the frequency and the time of the sampling event, the method and parameters used for the grade calculation and natural ecological processes affecting the environment. Conclusion
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