title: Methane and nitrous oxide emissions from a subtropical estuary (the Brisbane River estuary, Australia).
abstract: Methane (CH4) and nitrous oxide (N2O) are two key greenhouse gases. Their global atmospheric budgeting is, however, flout with challenges partly due to lack of adequate field studies determining the source strengths. Knowledge and data limitations exist for subtropical and tropical regions especially in the southern latitudes. Surface water methane and nitrous oxide concentrations were measured in a subtropical estuarine system in the southern latitudes in an extensive field study from 2010 to 2012 and water-air fluxes estimated using models considering the effects of both wind and flow induced turbulence. The estuary was found to be a strong net source of both CH4 and N2O all-year-round. Dissolved N2O concentrations ranged between 9.1 ± 0.4 to 45.3 ± 1.3 nM or 135 to 435% of atmospheric saturation level, while CH4 concentrations varied between 31.1 ± 3.7 to 578.4 ± 58.8 nM or 1210 to 26,430% of atmospheric saturation level. These results compare well with measurements from tropical estuarine systems. There was strong spatial variability with both CH4 and N2O concentrations increasing upstream the estuary. Strong temporal variability was also observed but there were no clear seasonal patterns. The degree of N2O saturation significantly increased with NOx concentrations (r(2)=0.55). The estimated water-air fluxes varied between 0.1 and 3.4 mg N2O m(-2)d(-1) and 0.3 to 27.9 mg CH4 m(-2)d(-1). Total emissions (CO2-e) were N2O (64%) dominated, highlighting the need for reduced nitrogen inputs into the estuary. Choice of the model(s) for estimation of the gas transfer velocity had a big bearing on the estimated total emissions.
authors: Advanced Water Management Centre (AWMC), the University of Queensland, Brisbane, Qld 4072, Australia.
authors: Ronald S
authors: RS
authors: Musenze
authors: Advanced Water Management Centre (AWMC), the University of Queensland, Brisbane, Qld 4072, Australia.
authors: Ursula
authors: U
authors: Werner
authors: Advanced Water Management Centre (AWMC), the University of Queensland, Brisbane, Qld 4072, Australia; School of Civil Engineering, the University of Queensland, Brisbane, Qld 4072, Australia.
authors: Alistair
authors: A
authors: Grinham
authors: Healthy Waterways Ltd, P.O. Box 13086, George Street, Brisbane, Qld 4003, Australia.
authors: James
authors: J
authors: Udy
authors: Advanced Water Management Centre (AWMC), the University of Queensland, Brisbane, Qld 4072, Australia. Electronic address: z.yuan@awmc.uq.edu.au.
authors: Zhiguo
authors: Z
authors: Yuan
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D004784:Environmental Monitoring; D063366:Estuaries; D008697:Methane / Q000032:analysis*; D009609:Nitrous Oxide / Q000032:analysis*; D011793:Queensland; D045483:Rivers / Q000737:chemistry
chemical_list: D000393:Air Pollutants; D009609:Nitrous Oxide; D008697:Methane
keywords: Aquatic emissions; Estuary; Greenhouse gas; Methane; Nitrous oxide; Subtropical