The Effects of Floods on Estuarine Fisheries and Food Webs

Floods are extreme events that can rapidly alter water and habitat quality in receiving estuaries. Because floods are unpredictable, they are more difficult to study, so have received less research attention than freshwater flow studies, resulting in a paucity of information on their ecological effects in the coastal zone. Previous studies have shown correlations between high flow periods and increased fisheries catches, which suggests that floods stimulate productivity in receiving waters. However, there have been no studies providing direct links between floods and increased productivity responses in fisheries species. In addition, the long-term effects of deposited flood sediment on food webs in estuaries are poorly understood. Floodwaters can carry high loads of fine sediment, which settles at the most offshore portion of the estuary delta, known as a prodelta. Nutrients, trace elements and other substances are also exported from the catchment dissolved in floodwater or attached to fine sediment particles and are deposited in estuaries. However, the processes of nutrient release from suspended sediments and settled sediments, and uptake of nutrients and trace elements into the food web in receiving estuaries are not well understood. Therefore, this thesis used laboratory experiments (Chapter 2 & 3) to study these processes with the aim of gaining a better understanding of the mechanisms underpinning measured ecological flood responses using field studies (Chapter 4 & 5). This study used catchment soils formed from three distinct rock types (granite, basalt and sandstone) from the Brisbane River (Queensland, Australia) catchment in a flood simulation experiment to quantify the rates of nutrient release during flooding (Chapter 2). In the laboratory, the fine fraction (