Particulate matter filtration and seasonal nutrient dynamics in permeable carbonate and silicate sands of the Gulf of Aqaba, Red Sea

Abstract

This study compares mineralization in permeable silicate and carbonate sands in the shallow shelf of the Gulf of Aqaba. From July 1999 to March 2000, we monitored concentrations of inorganic nutrients in water and pore water at two neighboring sites, one dominated by silicate, the other by carbonate sand. Although the carbonate was coarser than the quartz sand, organic matter, dissolved inorganic nitrogen (DIN), and ortho-phosphate concentrations in the biogenic carbonate sediment always exceeded those in the terrigenic silicate sands (factor 1.5–2.0 for organic matter, 1.7–14.0 for nutrients). Higher nutrient concentrations in the water column during winter months caused increases in pore-water nutrient concentrations in both sediments down to 10 cm depth with no significant delay, emphasizing the effect of advective transport of solutes and particles into permeable sands. An experiment was conducted where sieved clean quartz and carbonate sands of same grain size (250–500 µm) were incubated in-situ. Although exposed to the same water and boundary current conditions, the sieved carbonate sand accumulated more organic matter and developed higher nutrient concentrations than the incubated silicate sediment. We conclude that the mineralogical characteristics of the carbonate sand (higher porosity, sorption capacity and pH buffer capacity) enhance the filtration capacity, and the biocatalytic conversion efficiency relative to the smooth crystalline quartz grains.