Development of Habitat Suitability Criteria and In‐Stream Habitat Assessment for the Benthic Cyanobacteria Phormidium

Global demand for freshwater has led to unprecedented levels of water abstraction from riverine systems. This has resulted in large alterations in natural river flows. The deleterious impacts of reduced flows on fish and macroinvertebrate abundances have been thoroughly investigated; in contrast, there is a limited understanding of the potential for changes in the abundance of nuisance benthic algal/cyanobacterial blooms. In New Zealand, Phormidium sp. blooms are common in numerous rivers during summer low flows. In this study, an in‐stream habitat assessment is used to examine the relationship between Phormidium habitat availability and reducing flows. Over 650 observations of Phormidium mats, from seven sites (Hutt River, lower North Island, New Zealand), were used to construct habitat suitability curves for depth, velocity and substrate. Preference curves were fitted using both the ‘forage ratio’ and ‘quantile regression’ methods. Phormidium growth, observed at all seven sites, increased significantly from upstream (uppermost site, 5.2% mat cover) to downstream (63.5%). The habitat suitability curves revealed Phormidium had a large tolerance to velocity, depth and substrate type. Consequently, decreases in flow had only negligible effects on available Phormidium habitat. During periods of stable flow, Phormidium abundance positively correlated with increased nitrogen concentrations, potentially explaining the large variation in Phormidium cover from upstream to downstream. Quantile regression generated habitat suitability criteria were a more accurate predictor of available Phormidium habitat than the forage ratio criteria. Copyright © 2013 John Wiley & Sons, Ltd.     

Tertiary treatment of wastewater with Phormidium bohneri (Schmidle) under various light and temperature conditions

Experiments were carried out on secondary effluents under different conditions of light and temperature with the aim of evaluating the potential and limits of the epilithic filamentous cyanobacterium Phormidium bohneri (Schmidle) for biotreatment of domestic wastewaters. Aerated cultures were incubated at 10 and 30°C in a chamber fitted with a photic gradient plate receiving 120 and 720 μE/m²s. Results indicate that the strain used prefers elevated temperatures, and can withstand considerable variation in light intensity. Response at 30°C with regard to NH₃ and PO₄⁻³ removal agrees with that reported for unicellular chlorophytes. A complete exhaustion of these nutrients was obtained after 3 and 5 days, respectively. It appears that NH₃ stripping contributed substantially (38–100%) to the overall NH₃ removal efficiency observed in the system. In addition, the protein and carbohydrate content of the biomass produced suggests potential feedstock use.     

Removal of phosphate by foam-immobilized Phormidium laminosum in batch and continuous-flow bioreactors

Free-living and polyvinyl foam-immobilized cells of Phormidium laminosum were studied for their phosphate uptake characteristics. Initial phosphate uptake rates yielded hyperbolic curves when plotted against the external phosphate concentration, indicating the existence of a saturatable transport system. The phosphate uptake rates of N-starved free-living cyano-bacteria were also examined and showed that N-starvation led to lower uptake rates. The addition of nitrate to N-starved cyanobacteria markedly increased phosphate uptake. Phosphate uptake by free and immobilized cyanobacteria was inhibited in the dark and stimulated by the presence of calcium ions or bicarbonate. No phosphate uptake was observed when a chelating agent, such as ethylenediaminetetraacetic acid (EDTA), was added to the cultures. Several bioreactors were established for initial studies in using immobilized cyanobacteria for the removal of phosphate from water. Three different types of batch fluidized-bed, as well as two continuous-flow bioreactors (i.e. fluidized- and packed-bed), were examined. Although cyanobacteria immobilized on the polymer foams did not show high phosphate uptake efficiencies, simultaneous removal of nitrate and phosphate from water by means of N-starved immobilized cyano-bacteria appeared to be a promising possibility for future development.