Oxygenation of Large Volumes of Natural Waters by Geo-Engineering: with Particular Reference to a Pilot Experiment in Byfjorden

Abstract

Deeper parts of enclosed natural water bodies may at times be depleted in oxygen because consumption is higher than supply. When the oxygen concentration becomes less than 2 ml O₂ l⁻¹ the water is said to be hypoxic, and many animal species will have problems with the oxygen supply. If the water becomes completely depleted in oxygen, i.e. anoxic, no higher forms of life are possible. Since the 1950s, the Baltic proper is usually hypoxic in the semi-permanent halocline and below this the deepwater is often anoxic for long periods. There is then a lack of biomass as compared to a hypothetic case when anoxia and hypoxia do not occur (Diaz and Rosenberg 2008), a problem of increasing global concern. Hypoxia and anoxia influence the biogeochemistry. For instance, hypoxia stimulates the loss of nitrate and nitrite to nitrogen gas by denitrification and anoxia inhibits the binding of phosphorus to iron and manganese. Conley et al. (2002) showed that there is a correlation between decreased phosphorus content in the water and decreased area of anoxic bottoms in the Baltic proper. Stigebrandt and Gustafsson (2007) estimated that earlier anoxic bottoms in the Baltic proper that become overlain by oxic water may more or less instantaneously bind 4 tons P per square kilometer. The process is reversible why phosphorus will dissolve again if the bottom water becomes anoxic.