Nutrient diffusive fluxes from sediments in the northern Gulf of Aqaba, Red Sea

Abstract

SUMMARY: Measurements of dissolved inorganic nutrients (NH-2 and SiO 2 ) in pore waters (PW) and overlying bottom waters (OBW) were carried out in sediments of two reefs on the Jordanian coast of the Gulf of Aqaba at different water depths down to 30 m. One of the two sites was a marine reserve in front of the Marine Science Station (MSS) and the other hosted an Industrial Complex Zone (ICZ). The PW samples were retrieved using specially designed interstitial water traps. The concentrations in the OBW were within the typical range reported for oligotrophic tropical oceans. They showed minor variations with depth due to a well-mixed water column. Higher nutrient values were found at the ICZ compared to MSS suggested anthropogenic nutrient inputs. Our results showed significantly higher nutrient concentrations in the PW than in the OBW. The average concentrations in PW were about 16, 6, 9 and 5 times higher than the average values reported in the OBW for NH 4 + , NO 2 -+NO 3 -, HPO 4 -2 and SiO 2 respectively. Average fluxes of the dissolved inorganic nutrients were estimated in this study using the pore water gradient concentration across the sediment-water interface. Average diffusion fluxes were in the ranges 1. 41-46.44, 2.68-18.25, 0.04-0.60 and 9.68-16 , HPO 4 -2 and SiO 2 respectively. Flux of all nutrients was higher at the MSS. This can be attributed to higher sediment organic matter content and high biological activity. The results of this study demonstrate (i) the importance of coral reef sediments in recycling nutrients for coral reef communities and (ii) the effect of pumping cooling water on the nutrient regeneration process. -2 y SiO 2 ) del agua intersticial (PW) de sedimentos de dos arrecifes y de las capas del agua profundas (OBW). Uno de los dos lugares era una reserva marina en frente de la Marine Science Station (MSS) y el otro estaba enclavado en la zona de un complejo industrial (ICZ). Las muestras del PW se recogian utilizando unas trampas especiales diseñadas para aguas intersticiales. Las concentraciónes de nutrientes en la OBW estaban dentro del rango típico que se reporta para oceanos trópicales oligotróficos. Estas mostraban pequeñas variaciones con la profundidad debido a que la columna de agua estaba mezclada. Los valores mas elevados de nutrientes fueron hallados en la ICZ comparados con los de la MSS, lo que sugeria que los vertidos de nutrientes eran de origen antropogé-nico. Nuestros resultados mostraban concentraciones de nutrientes significativamente mas elevadas en las PW que en las OBW. Las concentraciones medias en la PW eran alrededor de 16, 6, 9 y 5 veces mas altas que el promedio de los valores alcanzados en las OBW para NH 4 + , NO 2 -+NO 3 -, HPO 4 -2 y SiO 2 respectivamente. El promedio del flujo de los nutrientes inorgánicos disueltos fueron estimados en este estudio utilizando un gradiente creciente de la concentración del agua intersticial a través de la interfase agua-sedimento. El promendio del flujo de difusión oscilaba entre 1. 41-46.44, 2.68-18.25, 0.04-0 -2 y ...

Exchange of nutrients across the sediment–water interface in intertidal ria systems (SW Europe)

“…Otherwise, in the Ria of Ortigueira the thicker oxic-suboxic sediment layer in spring act as retention to the upward diffusive phosphate flux while at summer this layer is reduced due to the increase of organic matter mineralization rates (Ishikawa and Nishimura, 1989;Falcão et al, 2006). Phosphate and silicate diffusive fluxes were low compared with the fluxes of important river-dominated estuaries (Watson et al, 1993;Mortimer et al, 1999), but similar to those found by Al-Rousan et al (2004) in coral reef along the Jordanian coast of the Gulf of Aqaba.…”

Oceanographic forcing of nutrient uptake and release over a fringing coral reef

“…Data are mean 6 SE, showing the number of values used in the calculations (n). See Table 2 focusing on specific habitats such as sediments (Capone et al 1992;Rasheed et al 2002;Al-Rousan et al 2004), coral cavities (Gast et al 1998;Scheffers et al 2004;Rasheed et al 2006), or micro atolls (Steven and Atkinson 2003), but the relevance of these habitat-specific rates at the scale of a reef community or ecosystem remains difficult to discern (Table 6). The release rates that were estimated in the present study, by assuming gross nutrient uptake was mass-transfer limited (J 2 MTL ), were on the same order as those documented in coral cavities and micro atolls, but were an order of magnitude higher than observed over carbonate sediments (generally a net sink; Wild et al 2005;Eyre et al 2008).…”

Community metabolism in temperate maerl beds. II. Nutrient fluxes

“…DO concentration may influence nitrification and denitrification, since oxygen penetration into the sediment stimulates the aerobic process of nitrification (Al-Rousan et al 2004). Community respiration during dark incubations may cause depletion in DO at the end of the incubation, especially in summer and autumn, when the DO concentrations are the lowest and the respiration rates the highest.…”