Greenish, cloudy, and with a smell like rotten eggs, “pistachio tides” are causing concern among residents who live along the Magothy River.
Magothy River Association member Bob Moyer said he went out to photograph a particularly large pistachio tide on Cattail Creek in October, and was so overwhelmed by the sulfur smell that he collapsed to his hands and knees and had to crawl off the pier.
Pistachio tides occur when bacteria in the river produce hydrogen sulfide, which depletes the oxygen in the water and creates a rotten smell. The bacteria produce a bright green color, which is where the name comes from.
Working with the river association, Johns Hopkins University is researching the bacterial booms in Cattail and Old Man creeks this summer to identify where and when they occur. Pistachio tides usually develop between August and October, and Hopkins started collecting water samples in early July to get ahead of the blooms.
That classic rotten egg smell is an ancient evolutionary mechanism to help us avoid hydrogen sulfide, which is a deadly poison, on the order of hydrogen cyanide. Interestingly, people rapidly get habituated to the smell, and so poisonings from hydrogen sulfide do occur occasionally.
Sulfate reducing bacteria, which produce sulfide from sulfate (a major salt in salt water) are obligate anaerobes and are totally inhibited by even low concentrations of oxygen. The process is quite common in sediments, but rare in the water column, and usually only in the bottom water. Something is seriously wrong if the surface water in the Magothy are going anoxic even occasionally.
The Wombat has Rule 5 Sunday: Gother Than Thou up and garnering clicks at The Other McCain.
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