What are they?
Harmful algal blooms are caused by toxin producing blue-green algae species (Cyanobacteria) and basically characterise the advanced stage of eutrophication. Eutrophication is a process of nutrient enrichment that occurs naturally over centuries, but has been accelerated by human changes to land use that result in more nutrient runoff.
Microcystis wesenbergeii (photo by Wendy Paul)
Anabaena planktonica (photo by Wendy Paul)
Inputs of nutrients to lakes occur as external loads exported from lake catchments and as internal loads released from bottom sediments. These inputs stimulate algal growth, so that at high concentrations, blooms occur. A bloom occurs when there is rapid growth of phytoplankton and specifically when there is an accumulation into dense, visible patches near the surface of the water. In deeper lakes decay of blooms can lead to the removal of oxygen from bottom waters as algae settle out. This loss of oxygen in turn reactivates nutrients in the bottom sediments that were previously 'locked up' when there was plentiful oxygen. Sediment nutrient release may again trigger rapid deterioration of lake water quality, as evidenced by even greater deoxygenation of bottom waters, increased lake water nutrient concentrations and greater frequency and intensity of algal blooms.
Unfortunately, some species of cyanobacteria produce potent natural toxins that can be transferred through the food web where they affect and even kill the higher forms of life such as zooplankton, shellfish, fish, birds, mammals, and even humans that feed either directly or indirectly on them.
How is LERNZ involved?
LERNZ aims to restore the indigenous biodiversity in New Zealand lakes by 2015 by developing new models and technologies to effectively manage harmful algal blooms.
This Intermediate Outcome focuses on enhancing the resilience of lake ecosystems through reducing the incidence of harmful algal blooms (HABs), applying integrated predictive models, and overcoming impediments to technology transfer, policy and planning.
Emphasis must be placed on the control of nutrients from lake catchments in order to stabilise any trend of increasing oxygen consumption in bottom waters of lakes, and thereby preventing seasonal loss of oxygen from promoting rapid deterioration in lake water quality.
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