Detection of polymeric silicate in the pore water of freshwater lakes

Understanding the formation mechanisms of polymeric silicates is essential to the study of microbiology and biogeochemistry. It has implications for the growth of diatoms and dinoflagellates and studying the processes that control the dissolution, precipitation, and biological uptake of different silicates species can provide an understanding of the occurrence of toxic blooms. This study examines the seasonal distribution of monomeric and polymeric silicates in the brackish and freshwater lakes of Japan. Inductively coupled plasma atomic emission spectroscopy was used to detect and quantify total dissolved silicates (TSi) and the spectrophotometric molybdenum blue method was used to detect molybdate reactive silicates (monomers to tetramers). The difference between the concentrations obtained via these two methods was used to determine the concentrations of polymeric silicates. Polymeric silicates were detected in anoxic-reducing pore waters from sediments of the freshwater Lake Biwa and Lake Kawaguchi in Japan, with a maximum concentration of 0.42 mmol L −1 . Polymeric silicate was continuously detected as long as the lake bottom environments remained under anoxic-reducing conditions. It provides insights on the formation mechanisms of polymeric silicates in freshwater lakes. The polymerization of silicates is understood to occur during the adsorption reaction between monomeric silicates and Fe(OH) 3 precipitate. Furthermore, this polymerization is deemed to be a dehydration condensation reaction because the silicates adsorbed on Fe(OH) 3 precipitate are situated at short distances from each other. In the anoxic-reducing environments, these monomeric and polymeric silicates are released from ferric hydroxide (Fe(OH) 3 ) precipitate by reacting with hydrogen sulfide.