Cyanobacteria blooms induced precipitation of calcium carbonate and dissolution of silica in a subtropical lagoon, Florida Bay, USA

Abstract

In recent decades, annual cyanobacteria blooms in Florida Bay displayed spatial and temporal patterns that are consistent with changes in alkalinity and dissolved silicon in water. In early summer, the blooms developed in the north–central bay and spread southward in fall. The blooms drew down dissolved inorganic carbon and increased water pH, causing in situ precipitation of calcium carbonate. Dissolved silicon concentrations in these waters were at minimum in spring (20–60 µM), increased during summer, and reached an annual maximum (100–200 µM) during late summer. The dissolution of silica as a result of high pH in bloom water was first observed in this study. During the peak of blooms, silica dissolution in Florida Bay varied from 0.9 × 107 to 6.9 × 107 mol per month over the study period, depending on the extent of cyanobacteria blooms in a given year. Concurrent calcium carbonate precipitations in the cyanobacteria bloom region are between 0.9 × 108 and 2.6 × 108 mol per month. It is estimated that 30–70% of atmospheric CO2 uptake in bloom waters was precipitated as calcium carbonate mineral and remainders of CO2 influx were used for the production of biomass.