Circulation and the nutrient budget in Myall Lakes
A two-dimensional model is used to study transport of material within Myall Lakes and is coupled to the ocean using a one-dimensional model of Lower Myall River. Runoff from the catchment is calculated from water levels and compares favourably with rainfall assuming an average runoff yield of 28% and a runoff coefficient of 47% for events above the 90th percentile. Most of the runoff enters Bombah Broadwater which is also the only basin connected to the ocean. Intermittent runoff events rapidly displace water from Bombah Broadwater into Boolambayte Lake and from Boolambayte Lake into Myall Lake. Displaced water is mixed within basins by wind-driven circulation within the time scale that levels fall as water drains from the lakes to the ocean. Only 7% of the nutrient load entering Bombah Broadwater becomes resident Myall Lake. About 40% of the nutrient load entering Boolambayte Lake becomes resident in Myall Lake. Median time scales for loss of conservative material entering each basin with the runoff are: 140 days for Bombah Broadwater, 118 days for Boolambayte Lake, and 535 days for Myall Lake. Salinity fluctuates greatly in Bombah Broadwater but is stable in Myall Lake. Material loss from Bombah Broadwater is characterized by many time scales associated with runoff from the catchment and low-frequency changes in ocean water level. Comparison of observed distributions of total nitrogen with simulations indicates that there are sources of total nitrogen in Boolambayte Lake and Myall Lake and sinks of total nitrogen in Bombah Broadwater. There appear to be sinks of total phosphorus throughout the Myall Lakes.
Key wordsFlushing Runoff Currents Nutrient Source Sink
The author thanks J. Wilson, A. M. Redden, T. Asaeda, and G. Coade for sharing measurements that inspired and underpin this work. Wind measurements were provided by the Bureau of Meteorology and water level measurements by Manly Hydraulics Laboratory. Comments by anonymous reviewers helped the author identify and correct a substantive error in the first draft.
- Arakawa, A. & V. R. Lamb, 1977. Computational design of the basic dynamical processes of the UCLA general circulation model. Methods of Computational Physics 17: 174–265.Google Scholar
- Cohen, D., 2004. An examination of planktonic processes in the Myall Lakes. B.Sc. Honours Thesis, University of Newcastle, Newcastle.Google Scholar
- Dasey, M., A. Raine, N. Ryan, J. Wilson & N. Cook, 2004. Understanding blue-green algaeblooms in Myall Lakes NSW. New South Wales Department of Infrastructure Planning and Natural Resources, NSW Government, ISBN 0 7347 5498 1Google Scholar
- Elliot, W. P., 1958. The growth of the atmospheric internal boundary-layer. Eos, Transactions, American Geophysical Union, 39: 1048–1054.Google Scholar
- Fischer, H. B., E. J. List, R. C. Y. Koh, J. Imberger, & N. H. Brooks, 1979. Mixing in Inland and Coastal Waters. Academic Press, New York.Google Scholar
- Flett, I., 2003. The History of Algal Blooms in Myall Lakes. Department of Environmental Sciences. Undergraduate Thesis. Sydney, University of Technology: 1–69.Google Scholar
- Leonard, B. P., 1996. Bounded higher-order upwind multidimensional finite-volume convection-diffusion algorithms. In Minkowicz, W. J. & E. M. Sparrow (eds) Advances in Numerical Heat Transfer, Vol. 1, Taylor and Francis, Washington DC: 1–57.Google Scholar
- Okubo, A., 1970. Horizontal dispersion of floatable particles in the vicinity of velocity singularities such as convergences. Deep Sea Research 17: 445–454.Google Scholar
- Paerl, H. W., 1992. Growth and reproductive strategies of freshwater blue-green algae (cyanobacteria). In Sandgren, C. D. (ed.), Growth and Reproductive Strategies of Freshwater Phytoplankton. Cambridge University Press, Cambridge: 261–315.Google Scholar
- Palmer, D., D. J. Fredericks, C. Smith, G. Logan & D. T. Heggie, 2000. Benthic Nutrient Fluxes in Bombah Broadwater, Myall Lakes. Australian Geological Survey Organisation, Professional opinion, No. 2000/33.Google Scholar
- Sanderson, B. G., T. Asaeda, L. Rajapakse & A. M. Redden, 2008. Mechanisms affecting biomass and distribution of Charophytes and Najas marina in Myall Lake, New South Wales, Australia. Hydrobiologia. doi: 10.1007/s10750-008-9373-5.
- Wilson, R. E. & A. Okubo, 1978. Longitudinal dispersion in a partially mixed estuary. Journal of Marine Research 36: 427–447.Google Scholar