Abstract
SUMMARY: Measurements of dissolved inorganic nutrients (NH 4 +, NO 2 -+NO 3 -, HPO 4 -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 9.68-16.85 ∝mol m-2 d-1 for NH 4 +, NO 2 -+NO 3 , HPO4 -2 and SiO2 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.
Highlights
Nutrients are minor constituents of the seawater that are of great importance for the growth of primary producers and small heterotrophs, such as bacteria (Bodungen, et al, 1985)
FIG . 4. – Average nutrient fluxes from the sediments pore waters (PW) to the water column calculated for NH4+, NO2- + NO3, HPO4-2 and SiO2 across the study sites (MSS and Industrial Complex Zone (ICZ)) along the Jordanian coast of the Gulf of Aqaba
Found to be within the typical range reported for oligotrophic tropical oceans (e.g. Tribble et al, 1990; Bell, 1991; Charpy-Roubaud et al, 1996; Rasheed et al, 2002) and for the water column and surface water during the season in the Gulf of Aqaba in particular (Badran and Foster, 1998; Badran, 2001)
Summary
Nutrients are minor constituents of the seawater that are of great importance for the growth of primary producers and small heterotrophs, such as bacteria (Bodungen, et al, 1985). Reef-building corals are distributed in oligotrophic tropical waters devoid of essential nutrients, yet they represent the most productive coastal marine ecosystem (D’Elia, 1988; Sorokin, 1993). This paradox is best explained by the rapid recycling of nutrients within the system (Richter et al, 2001; Rasheed et al, 2002). The recycling process, is not confined to the reef itself. There is a significant exchange of nutrient elements between the coral reef framework, the underlying sediments and the surrounding water (Capone et al, 1992). Nutrient exchange is controlled by physical and biological processes and is strongly dependent on the ambient nutrient concentration and distribution
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