An Experiment with Forced Oxygenation of the Deepwater of the Anoxic By Fjord, Western Sweden

Abstract

In a 2.5-year-long environmental engineering experiment in the By Fjord, surface water was pumped into the deepwater where the frequency of deepwater renewals increased by a factor of 10. During the experiment, the deepwater became long-term oxic, and nitrate became the dominating dissolved inorganic nitrogen component. The amount of phosphate in the water column decreased by a factor of 5 due to the increase in flushing and reduction in the leakage of phosphate from the sediments when the sediment surface became oxidized. Oxygenation of the sediments did not increase the leakage of toxic metals and organic pollutants. The bacterial community was the first to show changes after the oxygenation, with aerobic bacteria also thriving in the deepwater. The earlier azoic deepwater bottom sediments were colonized by animals. No structural difference between the phytoplankton communities in the By Fjord and the adjacent Havsten Fjord, with oxygenated deepwater, could be detected during the experiment.Electronic supplementary materialThe online version of this article (doi:10.1007/s13280-014-0524-9) contains supplementary material, which is available to authorized users.

Consequences of artificial deepwater ventilation in the Bornholm Basin for oxygen conditions, cod reproduction and benthic biomass – a model study

“…They showed that pumping 800 m 3 s −1 of winter water from 40 to 90 m with a tenfold increase in the flow due to mixing at the outlet would have prevented the development of hypoxia and anoxia that occurred during a selected period starting in early May 2003 after a complete water exchange. The characteristics of the modeled pumped flow fit well with observations made in a comprehensive, long-term pilot experiment in the By Fjord, where 2 m 3 s −1 of surface water were pumped into the usually anoxic deepwater (Stigebrandt et al, 2014b). The pumped water had a speed of 2 m s −1 through the outlet orifices.…”

“…Preliminary estimates suggest a tenfold increase due to initial mixing and a further increase by a factor of 3 due to entrainment in the buoyant plume phase. Furthermore, the pumping in the By Fjord increased the rate of density reduction in the basin water by a factor of 100 and the frequency of water exchanges in the deeper parts of the basin by a factor of 10 (Stigebrandt et al, 2014b).…”

“…In a Swedish fjord, where the low oxygen concentrations caused mass mortality, but the near-bottom water was soon re-oxygenated, the recovery of the benthic fauna to pre-hypoxic compositions in this case took about 2 years , the reason being that the sediment was not over-enriched by organic matter. In an experiment with oxygenation of the basin water in the usually anoxic By Fjord, on the western coast of Sweden, colonization of the bottoms started after about 1 year, when the sediment surface had been oxidized (Stigebrandt et al, 2014b).…”

“…When the basin water resting in the Arkona Basin is eventually flushed by a new denser deepwater, parts of the flushed basin water will be entrained into the new deepwater, while the remainder is lifted above the sill level; cf. the process of water exchange in the By Fjord (Stigebrandt et al, 2014b). After the uplift, the flushed deepwater will be contained in a rather thin layer for topographical reasons.…”

How to combat cyanobacterial blooms: strategy toward preventive lake restoration and reactive control measures

“…In deep lakes, iron is less favorable due to release mechanisms at low oxygen concentrations (see ''Quantification of P loading'' section). If ample iron is already available, artificial oxygenation can be a way to increase the redox potential and thus the binding capacity of iron (Conley 2012;Stigebrandt and Kalén 2013;Stigebrandt et al 2014;Gerling et al 2014). Bormans et al (2015) reviewed the applicability of hypolimnetic oxygenation.…”