Sunscreen mixing with salt water and sand creates a smell that can only mean summertime at the beach. But those who live and work near the ocean know that sometimes the beach stinks. There’s the putrid smell of low tide, the fishy smell of live bait and lobster pots waiting to be put out. And for some there is a smell of rotten eggs, signaling danger.
When certain types of seaweed decomposes it releases hydrogen sulfide, a colorless, toxic flammable gas, into the air causing an odor that smells like rotting eggs.
The gas can cause fatigue, sinus infections, sore throats, headaches, and vomiting. People most at risk are those with respiratory problems, the elderly, children and pregnant women. Some animals such as dogs are also easily affected. In 2006 in France the release of hydrogen sulfide on a beach is thought to have caused the death of a horse and caused the horse rider to lose consciousness.
According to the Marine Sciences Department at the University of Connecticut the green sheets of algae and green strings of algae are the seaweed most likely to release the hydrogen sulfide. What happens is that when seaweed collects in piles, still wet, sometimes only a few millimeters thick, hydrogen sulfide forms below a white crust as the seaweed decomposes. Hydrogen sulfide gas is released into the air when the white crust is broken either by waves, wildlife or people.
The problem is occurring more frequently due to high levels of nitrogen in the waters. Nitrogen from acid rain, waste water treatment plants and fertilizers that end up in the water can cause low oxygen in the water and allows algae to grow in higher than normal amounts. According to the University of Connecticut, it doesn’t matter if fertilizer is organic or not it will still contribute to the problem. Warm winters are also to blame because a mild climate allows the algae to live through the winter so more seaweed builds up along beaches.
There are rarely easy solutions to the problem. In France they’ve had to close beaches to keep people safe and in New Jersey residents have formed committees to monitor and remove the buildup of seaweed. Other communities, such as one in Groton, Connecticut solved the problem in a cove by relocating a wastewater treatment plant, but it still took about 12 to 15 years for the water system to recover from the nitrogen.
The simplest short-term solution is for communities to pay to have the seaweed removed or for them to remove it themselves. In Washington state in 2007 the legislature passed a law that set funds aside specifically to remove seaweed at select beaches.
The long-term solution of lowering the levels of nitrogen in the water isn’t something that most communities can do by themselves as waterways are so connected.