Ocean Deoxygenation Conference | Kiel 2018

Dissolved oxygen concentrations in natural water bodies are governed by the balance between oxygen production, consumption, and exchange with the atmosphere. The occurrence of coastal hypoxia/anoxia can be natural, human influenced, or result from the interaction between natural and anthropogenically induced processes. Naturally occurring hypoxia/anoxia is found: in bottom waters of silled basins and fjords with restricted circulation
This study originated from the need to manage the extension of the anoxic water layers, from deeper to shallower environments, aiming to control the consequences in environments with great economic and ecological values. Two Greek coastal basins, the anoxic Aitoliko lagoon and the hypoxic Amvrakikos Gulf were used as case studies as both are systems where fresh water discharges are human controlled, and this is directly correlated with the development of hypoxic/anoxic conditions in their bottom layers.
The deep basin of Aitoliko (~27.5m) is connected with the adjacent Messolonghi lagoon (~2m deep) through shallow and narrow openings (mean depth ~1.2m). The interaction between the two lagoons is interrupted by the fresh water that inflows into Aitoliko lagoon by the function of a pumping station, near the connecting sill. The Amvrakikos Gulf is an enclosed basin as its only link to the open Ionian Sea is a narrow strait. It receives fresh water from two Rivers, Arachthos and Louros. The rivers’ discharges are controlled by Hellenic Electricity Company, disturbing the seasonal density variations in the water column of Amvrakikos Gulf.
Samplings were conducted on seasonal basis at an extensive sampling net in both basins. Continuous profiles of temperature, salinity and dissolved oxygen were measured in situ. Water column stability was estimated and seasonal changes were brought out. An attempt to understand the influence of the human controlled fresh water discharges on density profiles and consequently on the seasonal changes on the water column stability was made, for both basins.