Rotting seaweed poses no danger
By Ashley Mackin
In a recent letter to the La Jolla Light, Bird Rock resident Karyn Meyer asked about the rotting seaweed found on the beach near her home. Her concerns included the cleanup of said seaweed and whether the gases emitted were toxic and dangerous to breathe. The area she specified was near Searidge Drive and Chelsea Street, north of Tourmaline beach.
As promised, The Light did some investigating about her concerns.
Dr. Russ Vetter, Director of the Fisheries Resources Division of the National Oceanic and Atmospheric Administration, said it is common for large amounts of organic debris, such as seaweed and kelp, to die this time of year. However, he added, “This year there has been a large pulse in organic debris.”
Speaking of behalf of the Scripps Institute of Oceanography, assistant director of communications, Mario Aguilera, confirmed through his sources that the gas emitted from rotting seaweed is hydrogen sulfide, which is classified as toxic. An SIO scientist, who asked not to be named, said the higher temperatures of the summer months in- crease the rate of bacterial decay, therefore more of a ”rotten egg smell” is emitted. He said that Scripps does not monitor or study the level of hydrogen sulfide in the air.
The San Diego Air Pollution Control District also does not monitor hydrogen sulfide concentration levels along the beaches because it focuses on factories and businesses. Air Pollution Control Officer Robert Kard said he has experience with hydrogen sulfide through other avenues, and ex- plained that the conditions at Bird Rock do not yield harmful levels. He explained hydrogen sulfide has a “low-odor threshold,” meaning humans can smell it, even in low concentrations.
He also said in open, ventilated space, such as at Bird Rock beach- es, the concentration of hydrogen sulfide in the air is not harmful.
Acknowledging the “rotten egg smell,” Kard said in closed spaces, such as sewers, hydrogen sulfide could be harmful, but not in a beach setting.
Dan Daneri, District Manager for Shoreline Parks, a division of San Diego Park and Recreation, said the rocky area where much of the seaweed rots cannot be accessed with parks’ machinery; therefore Shoreline Parks does not clean that area. Seaweed and other debris are removed from areas to which they have access.
However, Daneri said the smell becomes less of a problem when the temperature drops, and the rate of decay decreases.
Vetter’s advice is to not disturb or move the seaweed to avoid the release of more hydrogen sulfide. Additionally, he said, it is the wave patterns in San Diego that disturb the seaweed in the water, furthering the release and carrying it to shore.
“Our typical onshore flows, the ones that make San Diego so pleasant, carry the hydrogen sulfide to shore,” Vetter said.
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