Study of biogeochemical processes in an intermittently anoxic coastal system (Gulf of Elefsis) under simulated ocean acidification conditions

• Main Authors: Kapetanaki, Natalia, Καπετανάκη, Ναταλία
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: National and Kapodistrian University of Athens 2018
• Subjects: σύστημα ανθρακικών; Θρεπτικά; πειράματα μικροκόσμων; Οξίνιση των θαλασσών; Άνθρακας; carbonate chemistry; microcosm experiment; Carbon; Nutrients; Ocean acidification; Φυσικές Επιστήμες; Γεωεπιστήμες και Επιστήμες Περιβάλλοντος; Natural Sciences; Earth and Related Environmental Sciences; Ocean acidification
• Online Access: http://hdl.handle.net/10442/hedi/44495; https://doi.org/10.12681/eadd/44495

There has been a focus recently, on the common co-occurrence of oxygen depletionand ocean acidification (OA) and their concurrent effects on ocean biogeochemistry.Normally atmospheric CO2 is the major driver of OA; however, naturally occurringmicrobial decomposition of organic matter (OM) in coastal marine environments causeincreased acidity in deeper layers similar or even exceeding the future predictions forglobal OA. Experimental studies in coastal areas with increased inputs of OM andnutrients, coping with intermittent hypoxic/anoxic conditions, provide betterunderstanding of the mechanisms affecting nutrients and carbon biogeochemistry underthe emerging effects of coastal pH decrease. Two laboratory CO2-manipulatedmicrocosm experiments were conducted using seawater and surface sediment from thedeepest part of Elefsis Bay (Saronikos Gulf, Eastern Mediterranean) focusing to studythe co-evolution of processes affected by the decline of dissolved oxygen and pHinduced by (a) OM remineralization and (b) the future anthropogenic increase ofatmospheric CO2. Under hypoxic and more acidified conditions, a significant increase oftotal alkalinity was observed mainly attributed to the bicarbonate ions produced in favorof CO32- to buffer the CO2 increase and the reactive nitrogen species shift towardsammonium. Νitrate and nitrite decline, in parallel with ammonium increase,demonstrated a deceleration of ammonium oxidation processes along with decrease innitrate production. Additionally, the decreased DIN:DIP ratio, the prevalence of organicnutrient species against the inorganic ones, the observations of constrained DONdegradation and the higher DOC concentrations possibly reveal inhibition of OMdecomposition under lower pH values. Similarly, dissolved As and V seemed to berestricted due to inhibition of OM; Ni, Cu, Co and Pb were found to incorporate incarbonate bonds and Fe/Mn oxyhydroxides, increasing their dissolved fraction underlower pH. During severe hypoxic and more acidified conditions, nutrients were ...