Effects of a decomposing drift algal mat on sediment pore water nutrient concentrations in a Florida seagrass bed

A rapid increase in sediment pore water nutrient concentrations, from 300 to 900 µM ammonium-N and 20 to 200 µM dissolved reactive phosphate-P, followed by an equally rapid decline to initial concentrations, was noted between May and July 1978 in the Indian River lagoon, Florida, USA. These events coincided with the occurrence and physical state of a drift algal mat composed of Microcoleus lyngbyaceus and various seagrasses. It is suggested that the sinking and decomposition of the algal mat over the sample site reversed the nutrient concentration gradient and caused a buildup of nutrients in the sediment.