![]() In South Korea a clay called “yellow loess” has been used since 1996 to control blooms of a HAB species called Margalefidinium polykrikoides that have caused millions of dollars of damage to fish farms. Today, both South Korea and China routinely use clay to control algal blooms. In deeper water, darkness, prolonged contact with the clay, and eventual burial in sediments on the seafloor can also kill the algae cells.The practice of using clay to control algal blooms in the ocean is not new, with mentions in scientific literature dating back 30 years or more. In some cases, as with the fragile cells of the Florida red tide organism Karenia brevis, the flocculation and sinking process can rupture cell membranes, killing the cell. As these flocs fall, they capture additional particles, clearing the water as they descend. ![]() As these aggregations, known as “flocs,” grow, they sink through the water until they reach the bottom. The process of flocculation is common in approaches to purifying drinking water as well as sewage treatment. When sprinkled on surface waters during an algal bloom, the tiny but dense clay particles will “flocculate” or combine with other particles in the water, including the HAB cells. The oldest and most widely used approach to controlling HABs involves the application of a certain types of clay during blooms.
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