Atmospheric wet deposition of soluble macro-nutrients in the Cilician Basin, north-eastern Mediterranean sea

Abstract

In order to estimate wet deposition atmospheric fluxes of macro-nutrients into the eastern Mediterranean coastal waters, soluble inorganic phosphate (PO₄³⁻), nitrate (NO₃⁻) and nitrite (NO₂⁻) concentrations in precipitation (from February 1996 to June 1997) have been measured at a coastal sampling site, Erdemli, Turkey. Water-soluble inorganic PO₄³⁻-P, a reactive, bioavailable, limiting macro-nutrient in the oligotrophic waters of the eastern Mediterranean was studied with respect to its contribution to biological productivity. Reactive PO₄³⁻-P and NO₂⁻ + NO₃⁻-N concentrations were found to be highly variable in rainwater samples. One of the aims of the study was to determine the contribution of dust transport to the soluble macro-nutrient budget of the eastern Mediterranean. No differences were found between the mean reactive P and NO₂⁻ + NO₃⁻-N concentrations of “red rain” and normal rain events. Most likely as a result of low solubility of crustal phosphorus, dust episodes were not found to be important sources of reactive P, in terms of wet deposition. The annual wet deposition fluxes of reactive PO₄³⁻-P and NO₂⁻ + NO₃⁻-N into the Cilician Basin were respectively estimated to be 0.010 g P m⁻² per year and 0.23 g N m⁻² per year, which are comparable to the fluxes from land-based sources in the north-eastern Mediterranean. The incorporation of water soluble bioavailable PO₄³⁻-P and NO₂⁻ + NO₃⁻-N delivered via atmospheric wet deposition could be responsible for approximately 3.3% (0.40 g C m⁻² per year) and 11.0% (1.31 g C m⁻² per year) respectively, of the mean annual new production in the north-eastern Mediterranean.