Algal blooms are a major environmental problem in many urbanized and altered waterways. In the Sydney Olympic Park, algal blooms persist in patches of isolated or poorly-flushed wetlands, causing odours and other problems. Locally, blooms are caused by a combination of algal growth and mortality, plus the rates at which algae arrive from elsewhere, or are removed by flowing water. It is important to distinguish among the factors to ensure relevant and cost-effective management of this problem.
This project examined growth of algae in three degraded wetlands plus relevant control sites in the Sydney Olympic Park. In addition, levels of dissolved nitrogen and phosphorus in the water were measured. There was more algal growth in the Waterbird Refuge and in the Saltwater Billabong than in their relevant control sites, but, at Nuwi wetland, algal growth was similar in the waters downstream from the wetland to that in the wetland itself. There was no clear pattern between algal growth and levels of nutrients in the water and, in fact, there were generally smaller amounts of nutrients in the Waterbird Refuge and the Saltwater Billabong, suggesting that these may have been depleted by the algae. The patterns of nutrients and growth at Nuwi were more complex, although no clear relationships could be identified.
Both algal growth and concentrations of nutrients were very patchy, at scales of metres to 100s of metres, suggesting that very local processes affect each of these variables. More importantly, they also indicate the complexity of spatial scales needed in any sampling or monitoring programme, if differences or changes in these variables are to be precisely measured. Similarly, the repeated experiment at Nuwi, showed that these variables can change markedly over a matter of only a few weeks and that these changes differ at scales or 10s to 100s of metres.
