Toxic Waters
A freshwater Harmful Algal Bloom (HAB) is 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, however scientific documentation has proven that nitrogen including ammonia can trigger HAB’s in the form of a cyanobacteria bloom. This can be compounded by the addition of road salt, heavy metals and increased water temperature.
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 of nutrients (biologically available, inert, etc) and other environmental conditions including temperature, light and wind. 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. 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. While HAB’s have been controlled by phosphorus supply, it is not phosphorus alone that causes the bloom. Many forms of cyanobacteria respond to nitrogen. HAB’s are able to get nitrogen from nitrates, nitrites or ammonium. Research has indicated that algal abundance can be traced to ammonia. This is important to note for current research utilizing algae in biomonitoring, targeting faulty septic systems. Any addition of ammonia to waterways with increased nutrient levels and elevated sodium chloride levels from road salt application can spur excessive algal growth, forming HAB’s. Ammonia enters the environment from urea, both animal and human waste, wastewater effluent, lawn and garden fertilizers, urban runoff, atmospheric deposition and within products applied to agricultural fields.
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 algal 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. Some forms of chlorophyta (green algae) produce taste and odor causing issues in drinking water and can form extensive, thick mats of algae within littoral zones of lakes and within streams smothering substrate and fish breeding habitat in addition to decomposing along shorelines and decreasing property values (who wants to swim in decayng, smelly muck).
Bodies of water with increased acidification are more susceptible to HABs. The carbonic balance, which is linked to the increased Co2 concentrations, can also increase the growth rate of all forms of algae while reducing the overall nutritional value, thereby causing a trophic imbalance. Recent studies have shown that bodies of water with reduced calcium levels can also lead to trophic impaction. Large bodied zooplankton need adequate calcium levels to reproduce, without it smaller bodied zooplankton can dominate causing a trophic cascade affect. The trophic cascade can be amplified by invasive and introduced species to a body of water.
Cyanobacteria HABs are unique, as zooplanktons generally do not graze on cyanobacteria, preferring diatoms
MXLLS
and filamentous forms of chlorophyta that are more nutritious. Smaller forms of zooplankton can actually be impacted by the toxins produced by the cyanobacteria. There is a complex relationship between cyanobacteria HABs and zooplankton, toxins produced can alter zooplankton population dynamics. The production of toxins can be a direct relationship and response to zooplankton populations feeding on the algae.
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 and other nutrients. The release of phosphorus during spring and fall turn-over from these sediments can contribute a significant portion of nutrients which can delay water quality recovery. In addition, increased water temperatures from climate change can cause higher occurrence of harmful algal blooms (HABs), increasing intensity, frequency and distribution. Warming waters coupled with increased nutrient addition can favor cyanobacteria.
(This article is an updated version of a previous publication, that includes new information.) - C. Parnapy 2017
