Rice husk as a potential source of silicate to oceanic phytoplankton

Lead/cadmium impacts on zeolite-tobermorite: Nutrient release and sediment stability

To realize the comprehensive utilization of large amounts of high-ash coal slime and comprehensively understand the excellent performance of nutrient release and lead and cadmium adsorption of high-ash coal slime silicon composite materials, green and safe mild hydrothermal conditions (200 °C) were used to prepare the rich-rich coal slime. Zeolite/tobermorite composites (Z-TOBs) were used in this study. Batch adsorption tests and repeated extraction tests were used to determine whether silicon, potassium, and calcium nutrients of Z-TOBs have sustained release properties and are affected by pH. Through temperature gradient analyses, batch adsorption experiments at the water-soil interface, and density functional theory (DFT) calculations, the nutrient release mechanisms and the passivation of lead (Pb) and cadmium (Cd) by Z-TOBs were comprehensively investigated. The findings indicated that the release of silicon, calcium, and potassium nutrients from Z-TOBs was influenced by both ambient temperature and Pb and Cd concentrations. As the ambient temperature increased, the release patterns of different nutrients from Z-TOBs varied significantly, and the release of Pb and Cd was enhanced; however, the adsorption capacity for Pb consistently exceeded that for Cd. The passivation effect of soil amended with Z-TOBs on Pb remained stronger than that on Cd, significantly impacting the release of silicon. Characterization results revealed that silicon participated in the formation of silicon-containing compounds such as Cd2SiO4, CdAl2Si3O12, and Pb3Si2O7. The skew density calculated using DFT indicated that the silicic acid compounds formed with Pb and Cd exhibited greater stability than those formed with CO32- and SO42- groups, with Pb compounds demonstrating superior stability compared to Cd compounds. This study offers both practical and theoretical insights for the comprehensive utilization of high-ash coal slime in mild environments, presenting an alternative pathway for sustainable agricultural development.

Water column properties associated with massive algal bloom of green Noctiluca scintillans in the Arabian Sea

An algal bloom of Noctiluca scintillans (NS) was monitored for 20 days in the Arabian Sea during February 2017. The stations under the influence of NS had low temperature and high salinity compared to outside indicating influence of convective mixing. The microscopic cell count of NS reached a value of 52,600 cells l-1. The surface variability in oxygen and pCO2 measured alongside showed a strong disconnect. Modest supersaturation of surface waters (ΔpCO2 = 3-75 μatm) was observed around the NS bloom compared to outside. However, as these stations were under the influence of convective mixing, the observed change in pCO2 due to subsurface ventilation cannot be ruled out. From the viewpoint of climate change and its influence on oceanic processes, constant monitoring of this bloom becomes essential due to its survival strategy in nutrient-depleted conditions and light of the present observations.