One reason the long-term health of the crab population in Maryland’s Chesapeake Bay is in jeopardy is that old traps set by watermen years ago remain on the bottom of the bay and continue to kill crabs, the Baltimore Sun reports.
From environmentalists’ point of view, these abandoned traps aren’t desirable, either. But Dana Lunkenheimer and Luke Andraka, both seniors at North County High School in Anne Arundel County, Md., have developed crab traps that are held together by zinc rings, which self-destruct after a while. By inventing the technology, they came in second place in the We Can Change the World Challenge—a contest run by Siemens and Discovery Education—and will split a $25,000 scholarship.
Their trap design means if the traps are abandoned by people who are licensed to take a legal catch of crabs from the Chesapeake Bay, they’ll fall apart on the bottom of the bay and not ensnare any crabs. Traps are most commonly lost or abandoned because of weather.
The Sun cited a 2008 study by the Chesapeake Bay Office of the National Oceanic and Atmospheric Administration, which estimated that more than 85,000 abandoned traps, known as “ghost pots,” were on the bottom of the Maryland portion of the Chesapeake Bay.
“A lot of people don’t know what a big issue it is,” the paper quoted Mr Andraka as saying. “It’s an incredible number of crabs that are dying every year, and the amazing part to me is that in Maryland, this is a huge issue, but in other areas, like in the Gulf of Mexico, this is an incredible problem.”
The destruction occurs after about eight months in Chesapeake Bay water, according to an extrapolation the students made from their experiments (they didn’t have a full eight months to test their design).
Why does the zinc dissolve?
Zinc is insoluble in water when the water is at a neutral pH of 7. However, the water in the bay is becoming more acidic due to increased levels of carbon dioxide from the atmosphere being dissolved. The same increase in acidity is affecting waters around the world, and the bay is not exempt.
Although the increase in acidity directly causes a few harmful effects on the environment and the Chesapeake Bay ecosystem, such as reducing rates of juvenile oyster shell formation, according to a University of Maryland Center for Environmental Science study, these students’ traps take advantage of the increase in acidity to do something good for the bay and the local economy.
In weak acids, such as dilute sulfuric acid, zinc dissolves to form Zn(II) cations:
Zn(s) + H2SO4(aq) → Zn2+(aq) + SO42-(aq) + H2(g)
The bay’s water is weakly acidic, but dissolving zinc is still a slow reaction in chemical terms, as there isn’t any real catalyst. The speed of this reaction supports the students’ claim that dissolving the zinc rings could take eight months.
