Herbicides and Stream Macroalgae

round Spraying herbicides to kill weeds has become common practice among farmers to ensure space and nutrients for their crops. Streams receive most of the runoff that contains these weed killing chemicals, but little research has been done to look at the direct effects this has on key organisms in the water.

round1A recent article in Phycologia looked at a study in Brazil that examined the effects of glyphosate based herbicides on a type of green macroalgae that is common in streams around the world. The assumption was that the macroalgae would be sensitive to the chemicals thus affecting their photosynthesis, chlorophyll levels, and respiration. Macroalgae are perfect for monitoring the health and clarity of fast moving fresh water..in streams they are important organisms when it comes to cycling nutrients and increasing plankton. round3

The study tested several concentrations of technical grade glyphosate, Roundup weed killer, and AMPA and the effects on the algae were noted.  Algal photosynthesis was greatly reduced when glyphosate and roundup were used together. Concentration of the active ingredient and exposure time were considered.

AMPA boosted photosynthesis. Dark respiration , or respiration that occurs regardless of light , also increased with AMPA. Finally, the study found that when AMPA and certain  amounts of glyphosate were applied less chloropyll was found.

The end results found that the performance of algae was affected by herbicides. The form of the herbicide is crucial to determining the end effect, the algal productivity could shift visibly depending on the types of herbicide applied. Even legal amounts of herbicide can have an effect.

 

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