Lead author and PhD candidate Edwina Tanner in the University of Sydney's School of Geosciences, said although the Sydney Harbour was a net carbon emitter, during periods of high rainfall it became a carbon sink, as coastal waters filtered runoff from the highly urbanised catchment. The research is published in the 5 June edition of the international journal Estuarine, Coastal and Shelf Science. Sydney is also predicted to become a megacity - with a population of 10 million - by 2100. Sydney's emissions measured at a similar, albeit lower level, to other natural drowned river valleys in the United States such as the Hudson River, which flows through New York. Sydney's emissions were found to be significantly less than China's major dammed river, the Yangtze, which is adjacent to megacities including Shanghai.
The emissions from Sydney Harbour - including from urban runoff, leaf litter, soil decomposition and sewage overflow - were found to be very low compared to the highly polluted estuaries of Europe and Asia, which can emit up to 76,500 car CO 2 equivalents each year.
The research, by the University of Sydney's Marine Studies Institute and the Centre for Coastal Biogeochemistry at Southern Cross University, is the first long term study of such a large and important Southern Hemisphere system referred to as a drowned river valley, which in Sydney spans estuaries from Middle Harbour to Lane Cove and Parramatta.
That is the message of new research that has quantified CO 2 emissions from the Harbour for the first time - found to be 1000 tonnes annually - equivalent to the pollution from about 200 cars.