Harmful Algal Blooms
As the summer season is on us and temperatures are rising, a freshwater Harmful Algal Bloom (HAB) could form in nearby lakes, ponds and reservoirs. HABs are any excessive amount of algae that causes negative or harmful impacts on other organisms, water quality, recreation or the economy. HABs are an indicator of nutrient enrichment, primarily phosphorus within that given body of water.
All bodies of water are unique and not every HAB is the same. It will depend on the limiting nutrient within the given body of water, forms (biologically available, inert, etc) of nutrients available and other environmental conditions. If a low nitrogen: phosphorus ratio occurs, then nitrogen fixing cyanobacteria will become dominant. Adding nitrogen to the body of water will only shift the forms of algae within the bloom to non-nitrogen fixing cyanobacteria and chlorophyta. The same can be said for adding aeration, it will only shift the composition of forms of algae within the bloom.
Not all HABs/ algal blooms will produce toxins. Within the scientific community there is still much conjecture as to what will trigger toxin production within a HAB. Many factors contribute to the forming of toxins; including weather, temperature, nutrient availability, cell density, salinity, and light. Not all toxin producing HABs are comprised of cyanobacteria, some forms of diatoms and dinoflagellates can create toxic conditions as well.
Cyanobacteria HABs are unique, as large bodied zooplanktons generally do not graze on cyanobacteria, preferring diatoms and filamentous forms of chlorophyta. There is a complex relationship between cyanobacteria HABs and zooplankton, toxins produced can alter zooplankton population dynamics, favoring smaller bodied forms. The production of toxins can be in direct relationship and response to zooplankton populations.
Once long term water quality protection measures have been put in place and phosphorus reduction is started, an immediate reduction in HABs is not certain. Bodies of water that regularly experience HABs will also contain sediment that is rich in phosphorus. The release of phosphorus from these sediments can contribute a significant portion of phosphorus which can delay water quality recovery.
