Territory Stories

Darwin Harbour in good health



Darwin Harbour in good health


Westra Van Holthe, Willem

Political affiliation

Country Liberals


Media Releases for 12th Assembly 2012 - 2016; Media Releases; ParliamentNT






Made available by via the Publications (Legal Deposit) Act 2004 (NT)




Oceans; Marine life

Publisher name

Northern Territory Government

File type



Issued as a Media Release

Copyright owner

Northern Territory Government

Parent handle


Citation address


Related items

https://hdl.handle.net/10070/528211; https://hdl.handle.net/10070/528213

Page content

7 Dissolved oxygen. Water contains small amounts of oxygen which is needed by animals. Storm water and industrial waste can lower the amount of the oxygen in the water to levels that could be harmful to aquatic animals. Chemical reactions and microbial activity that determine the amount and type of nutrients in the harbour are affected by low oxygen (hypoxia). Dissolved oxygen (DO) is measured as a concentration (mg/L). Oxygen saturation is the amount of oxygen compared to the amount water naturally holds when in equilibrium with the air (assuming no biological processes), expressed as percentage and varying with temperature and salinity. The amount of oxygen at 100% saturation decreases with temperature. The lower holding capacity of warm waters, as well as the higher microbial activity of warm temperatures that use oxygen, makes Darwin Harbours waters vulnerable to low dissolved oxygen. Water clarity. Clear water allows sunlight to reach plants to grow, such as seagrass and algae (macroscopic and microscopic) that live on the seabed. Water clarity is affected by the tides, being clearest during neap tides and during the turn of the tides. Water clarity can also be affected by storm water, dredging activity and large amounts of algae. To assess the water clarity, total suspended solids (TSS) can be used. Also known as total suspended sediment, this is a measure of the amount of particulates in the water column. TSS concentrations were estimated from turbidity using a TSS-turbidity relationship. Algae. Algae are aquatic plants. Microscopic algae can gather together in colonies to be visible to the naked eye in either the water or on the sediments and other seabed substrates. Algae are a natural part of the ecosystem and provide food for large (e.g. mangrove snails) and small animals (zooplankton). However, when waters become polluted with nutrients, the amount of algae can be too much and can adversely affect the marine ecosystem. The types of algae will also be affected by pollution. Sometimes though, large amounts of algae can occur naturally, such as the Trichodesmium blooms that occur during the build-up months. To assess the quantity of algae, we measure chlorophyll a (Chl a), a green pigment of aquatic plants, used in the process of photosynthesis. Nutrients. Nitrogen and phosphorus are plant nutrients. Pollution by nutrients can produce too much algae, and affect the ecosystem. The nutrients measured were nitrogen oxides (NO; nitrate and nitrite), ammonia, total nitrogen (TN), total phosphorus (TP) and filterable reactive phosphorus (FRP). 4.1. Water quality parameters The following water quality parameters were monitored to assess water quality in the Darwin Harbour region. 4.1.2. Parameters used in the Report Card