Improved dissolved oxygen status following removal of exotic weed mats in important fish habitat lagoons of the tropical Burdekin River floodplain, Australia

The Burdekin delta floodplain, north Queensland, is highly modified for agricultural purposes. Riparian condition is very poor and exotic aquatic weeds dominate waterways. Historically, most streams and lagoons were highly seasonal, but those now used for the delivery of irrigation water maintain elevated flows and increased turbidity and nutrient loading. These factors have aided exotic weed growth and many major lagoons are covered by dense water hyacinth (Eichhornia crassipes) mats which greatly reduce dissolved oxygen levels, one of the most important water quality variables for aquatic fauna. Mechanical harvesting of water hyacinth from several of these lagoons resulted in rapid and substantial increases in dissolved oxygen saturation, and improved suitability of the habitat to support fish species. Decrease in dissolved oxygen as water passes sequentially through weed-infested lagoons, justified the approach of harvesting upstream lagoons first, however, the channels that connect these lagoons remain weed-infested and are still impacting upon downstream oxygen levels.