Harmful Algal Blooms

This year has seen a substantial amount of fall freshwater Harmful Algal Blooms or

(HABs) 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. The concern is when they are made of blue-green algae or cyanobacteria, which can cause toxic conditions. Any HAB is 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 (phosphorus or nitrogen) 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, like present within Lake Champlain.

When a body of water experiences additional sodium chloride from nearby road salt application practices, it can shift the forms of algae within a waterbody from more nutritious forms like diatoms and chlrophyta (green algae) to cyanobacteria. Adding nitrogen to the body of water will only shift the forms of algae within the bloom to non-nitrogen fixing cyanobacteria and chlorophyta. If the bloom is comprised of certain forms of Cyanobacteria the addition of Nitrogen will cause toxins to be produced. The same can be said for adding aeration, it will only shift the composition of forms of algae within the bloom. Targeting the source of excessive nutrients is the only way to stop the bloom from forming.

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, dominant alga species, 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 that are more nutritious. 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 during spring and all turn-over from these sediments can contribute a significant portion of phosphorus which can delay water quality recovery.

In October 2017, the Winooski Natural Resources Conservation District noted a cyanobacteria bloom in Lake Champlain near Shelburne. The HAB was identified as being dominated by Anabaena a potentially toxin producing cyanobacteria.

If you are interested in having algae identified, or help to identify projects to reduce nutrients from entering local waterways on your own property, please email: info@winooskinrcd.org