The role of highly sratified nutrient-rich small estuaries as a source of dissolved inorganic nitrogen to coastal seawater, the Qishon (SE Mediterranean) case

We studied the role of small, highly stratified, sulfate and nutrient enriched estuaries, as a source or sink of inorganic nitrogen species, using the Qishon estuary at the Mediterranean coast of Israel, as a case study. Measurements of nutrient concentrations, δ¹⁵N and δ¹⁸O of nitrate+nitrite, δ¹³CDIC and δ¹⁸OH₂O were performed during 2008-2009 along the upper-fresh and lower-saline water masses, as well as sediment porewater depth-profiles. Such estuaries are characterized by relatively low removal flux of NO3- (via sedimentary denitrification) and enhanced (×3) upward flux of NH4+ (via sulfate reduction), attributed to the penetration of seawater of low NO3- and high dissolved oxygen and sulfate concentrations. The role of such small estuaries in releasing dissolved inorganic nitrogen, especially in sensitive oligotrophic areas as the Levantine basin and in the long-term, as a result of enhanced seawater penetration due to the expected sea level rise, has important environmental policy implications.