Diatoms Found to be Good Indicators of Stream Health

The Clean Water Act was enacted to help prevent pollution of local freshwater systems. The scales for measuring pollution and ecosystem health, however, can be very vague. The authors of a recent study published in Science of The Total Environment have designed a more conclusive scale using microorganisms called diatoms.

Run-off from fertilizers, sewage, detergents, and other pollution can lead to an excess of nitrogen, phosphorous, and other nutrients. One consequence is something called eutrophication. In eutrophication, nutrient excesses lead to algal blooms. The algae block out light, preventing plant growth. They also suck up the oxygen, leading to dangerously low levels of dissolved oxygen in the water. The lack of oxygen can kill fish and the decay from dead plants and animals makes the situation even worse. Scientists need reliable scales in order to determine which freshwater systems are at risk of eutrophication and other problems.

Diatoms are a type of algae with a silica-based cell wall, leading to a glasslike appearance. The researchers found that diatom populations were great indicators of stream health. In healthy streams, the diatom population was dominated by surface-attached species. In an unhealthy ecosystem, most of the diatoms were motile species, able to move about freely. These population differences were good gauges as to the health of an individual stream. The authors note that other indicator species are already used for health measurements. The species used are normally fish or invertebrates, such as crayfish and insects. Using diatoms can provide a fuller picture while also being easier to work with and measure.

A current scale for measuring pollution levels is called the Biological Condition Gradient. The scale has six levels, from 1 (“natural”) to 6 (“highly disturbed”). The researchers found that the diatom population transitions happened right between level 3 and 4. These transitions were also consistent regardless of pH and other water conditions.

The authors found that diatom populations were a reliable way to measure water quality. Other indicator species are already used by researchers but diatoms are easier to measure. Diatoms can be added to current water tests to assess pollution levels, helping identify streams at risk of eutrophication.

REFERENCE

Sonja Hausmann et al. A diatom-based biological condition gradient (BCG) approach for assessing impairment and developing nutrient criteria for streams. Science of The Total Environment (2016).

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