Monterey Bay Aquarium Research Institute

Per Hall, Ph.D

Deparment of Chemistry
University of Gothenburg, Sweden

Biogeochemistry of Marine Systems with Anoxic Basins and Plans for Oxygenation via Ecological Engineering


Wednesday — March 3, 2010
Pacific Forum — 3:00 p.m.

The Baltic Sea is a eutrophic semi-enclosed brackish sea. About 70,000 km2 of its bottom area is today anoxic, i.e. overlain by oxygen-free bottom water. Oxygen exists typically to a depth of around 100 m in the central basin of the Baltic Sea. High phosphate release from anoxic sediments together with fixed nitrogen removal through denitrification and anammox at the oxic-anoxic interface in water column and sediment create low N/P ratios of nutrients. The low nutrient N/P ratios, in turn, create massive blooms of N fixing cyanobacteria during summer. These blooms can be toxic, are a serious environmental problem, and are a real nuisance for tourism. Cyanobacteria have existed in the Baltic Sea for at least 7,000 years, but the massive blooms are  a “modern” phenomenon and thought to be triggered by anthropogenic activities, especially discharge of nutrients from land, which stimulates algal growth, sinking of organic matter, and oxygen consumption in bottom water and sediment. Depletion of oxygen stimulates both P release and N removal. The solution to this problem may be oxygenation of Baltic deep water through ecological engineering. Wind powered pumps are planned to transport oxygen-rich water from about 50 m to anoxic deep water at about 130 m depth.

I will present results on influence of bottom water oxygen and bottom type on benthic nutrient and dissolved inorganic carbon (DIC) fluxes in different basins of the Baltic Sea, and in a west-Swedish marine anoxic fjord. The benthic fluxes were measured in-situ using a benthic chamber lander. Plans for basin-wide oxygenation through ecological engineering will be presented together with preliminary predictions on how the benthic release of nutrients may be influenced by oxygenation.

Next: March 10 - George Jackson