Heavy Metal Pollution and Algae

Heavy metal pollution poses a series threat to freshwater resources. Metals find their way into the aquatic ecosystem via weathering of rocks and soils, volcanic eruptions and from human activity. The most common means of entry is from mining activities. These metals which can include: mercury, lead, nickel, copper, chromium, and arsenic occur naturally in small amounts; their accumulation can impact both aquatic organisms and forms of algae.

Scientific studies have shown that forms of algae can be used as bioindicators of heavy metal pollution. Some forms of algae including; Stigeoclonium sp., Ankistrodesmus sp., and Scenedesmus sp., are tolerant of heavy metals. Other forms of algae under heavy metal conditions will have impacts to growth rates, and chloroplast production. The toxic impacts from heavy metals can interfere with essential nutrient uptake, cause changes in morphology and impact the reproduction of all aquatic organisms. Heavy metals are accumulated within cyanobacteria and can be released during decomposition following an algal bloom.

Soluble trace metals are controlled by the pH of the water. (see Acid Rain and Algae article) Most will settle into the sediments and accumulate. The water chemistry (water quality) will impact the rate of absorption of metals into the sediment. The lowering of the pH due to acid rain or mining activities, or the increase of salinity from road salt applications will release the sediment bound heavy metals back into the water column where bioassimilation can take place. Any decrease in oxygen from excessive algal growth can also release the metal ions from the sediment back into the water column.