Did multiple sediment-associated stressors contribute to the 1999 lobster mass mortality event in Western Long Island Sound, USA?

Near-bottom hypoxia during summer months has been a documented recurring phenomenon for decades in western Long Island Sound (WLIS); this temperate estuary has also supported, until 1999, a substantial American lobster (Homarus americanus) fishery. In response to a dramatic mass die-off of lobsters that began in WLIS in the late summer of 1999, a benthic habitat survey using a sediment-profile imaging (SPI) camera was conducted in October 1999. Follow-up surveys involving SPI and simultaneous measurements of dissolved oxygen (DO), hydrogen sulfide and ammonia within 10 cm of the bottom were conducted in August, September and November 2000. The SPI images revealed black sediments at or just below the sediment-water interface at a high proportion of stations in both 1999 and 2000, suggesting strongly reducing conditions and elevated levels of sulfides and other reduced end-products in sediment pore-water. Visual redox depths were relatively shallow (less than 2 cm) and spatially variable, and benthic communities appeared to be dominated by small, surface-dwelling opportunists. In August 2000, near-bottom DO concentrations < 2 mg I⁻¹ coincided with shallow redox depths at stations in the Western Narrows region. As DO levels increased from August to November 2000, visual redox depths remained shallow. Both sulfide and ammonia were detected in samples of bottom water taken within about 10 cm of the seafloor in all three 2000 surveys. The results suggest that anaerobic decomposition processes within the organic-rich sediments of WLIS strongly influence conditions at the sediment-water interface during late summer-early fall, the time of year that the lobster mortality event of 1999 began. Releases of reduced end-products (e.g., sulfide and ammonia) into overlying waters, combined with low DO levels and abnormally high water temperatures, represent multiple environmental stressors that may have physiologically weakened the lobsters and increased their susceptibility to deadly pathogens.     

Reinventing rice husk ash: derived NaX zeolite as a high-performing CO<Subscript>2</Subscript> adsorbent

In this work, rice husk ash was used as silica source to synthesize NaX zeolite potentially suitable for CO₂ adsorption. The produced material, denoted NaX-RHA, was characterized employing X-ray diffraction, scanning electron microscopy and gas adsorption porosimetry, in order to verify the occurred production of well-crystallized NaX zeolite with a significant degree of purity. CO₂ adsorption isotherms on NaX-RHA were volumetrically evaluated in the 298–348 K temperature range up to standard pressure, revealing performances that are higher than those reported for commercial similar substrates. The experimental data regarding CO₂ adsorption on NaX-RHA were very satisfyingly fitted by the semiempirical Sips model. Analyzing the best fitting values of model parameters allowed to conclude that the synthesized adsorbent could be quite suitable for applications like CO₂ capture from flue gas.