(Spring Algal Bloom, Me-Kwa-Mooks Park, Seattle, Wa, USA)
Algal Blooms, A Synopsis:An algal bloom occurs when there is a high abundance of microscopic phytoplankton suspended in the water column. Phytoplankton fall into two categories: diatoms, calciferous plated photoautotrophs without individual means of locomotion, and dinoflagellates, microscopic algae with propelling flagella. These photosynthesising organisms are the very basis of the aquatic food web providing the link between atomic elements and subsequent consumers (copepods, fish, humans, etc). Primary producers are responsible for most of the available dissolved oxygen in the water column and thus they provide a habitable environment for creatures that respire oxygen. The two factors that most affect algae population growth are the availability of light and nutrients. Phytoplankton "bloom" in spring and summer as daylight hours increase allowing for a greater period of photosynthesis. While most blooms cause minimal negative impact if there is an overabundance of available nutrients, known as eutrophication, in the water column this can cause the bloom to multiply so fast that the sheer mass of micro-algae blocks light penetration which can inhibit the solar energy absorption of other photosynthetic organisms. This high concentration of micro algae can also induce low oxygen conditions in bodies of water due to a lack of secondary predation. The decomposing remains of dead algae increase the activity of bacterial decomposers that use up the remaining oxygen inducing low oxygen zones. These zones are known to experience fish kills and low diversity volume considering how few species can persist with low dissolved oxygen concentrations. Some species of algae cause respiratory problems for fish as the algae concentrated water is flushed through the gills. These algae often have spiny shapes that cause small cuts and accumulations of algae in the gills.
Impacts of Algal Blooms on Humans:
As low oxygen zones become more prevalent the decrease of biodiversity can impact commercially important fisheries. These fish kills can also affect areas that rely on tourism as their economic means. Some algal blooms produce toxins that can have serious human health affects if ingested. Not only does shellfish poisoning cause illness, but in some cases deaths. This can impact economically important bivalve fisheries, as well. The species of Karenia brevis is known to cause respiratory irritation in humans due to the inhalation of an aerosol created by the bloom. Aphanizomenon flow-aquae species of algae blooms in Upper Klamath Lake, Oregon during the summer months where it is harvested by humans and used as a dietary supplement. The genus of spirulina algae is another phytoplankton harvested and cultivated by humans as a dietary supplement.
Human Impacts on Algal Blooms:
The biggest anthropogenic impact on algal blooms in the increase of land runoff. Many nutrients, such as, nitrogen and iron are in very limited supply in the ocean even though these are extremely abundant on land. Even with the much higher concentration of these nutrients on land some areas are heavily supplemented with additional nutrients to increase plant growth. Farms and lawns are two heavily fertilised areas that when watered the excess water runoff takes the same nutrients into the watershed and, ultimately, to the ocean where they begin their second life by increasing the growth of aquatic algae. Sewage runoff from human outputs, septic tank overflow and animal farming add a similar abundance of nutrients to the watershed and produce the same nutrient loaded results.
Citations:
Eutrophication and harmful algal blooms: A scientific consensus
The diversity of harmful algal blooms: a challenge for science and management
The diversity of harmful algal blooms: a challenge for science and management
