Abstract
This study was undertaken in order to investigate the capacity of floating reed beds to remove algae. The development of algae in eutrophic raw water storage reservoirs adversely affects the operational efficiency and economics of drinking water treatment downstream processes. In wastewater treatment using lagoons algal growth adversely affects discharge consent compliance and can cause practical problems when attempting agricultural reuse of effluents. Floating reed bed root systems were studied in stored lowland river water in the River Thames basin in England and in tertiary sewage effluent lagoons in tropical Australia. Whereas many research studies have been undertaken in recent years on the performance and ecology of constructed (reed bed) wetlands, almost nothing is known about the ecology of floating reed beds or their performance. Thus the objectives of this study was to obtain insights into the principal ecological mechanisms operating within submerged root matrices and to assess their potential for efficient algal removal. The results of cultivating a range of reed species suggest that the root morphology and development is strongly influenced by nutrient concentration and that lower nutrient levels encourage more vigorous root growth. Macrophytes with a fibrous roots system such as Phalaris arundinaceous should be selected for floating reed beds applications to filter algae as they provide a relatively homogeneous filter medium. In order to understand the dominant ecological mechanisms operating a preliminary study of the feeding behaviour of the main herbivores living within the root system was undertaken. This requires more prolonged and detailed study to identify the maximum capacity of floating reed beds in removing algae, in terms of quantity (chlorophyll a concentration) and quality (algae species). The study showed that the floating reed beds root system was able to intercept and retain algae in suspension in the water column. The adhesion of algae to the biofilm was observed with cell degradation in some cases. The main organisms recorded living within the fibrous root system were herbivore oligochaete worms. Although more results are required, these preliminary findings highlight the potential for the invertebrate community to permanently remove trapped algae from the water column through secondary grazing.