Gustafsson, B.G. & Stigebrandt, A. (2007) Dynamics of nutrients and oxygen/hydrogen sulfide in the Baltic Sea deep water. Journal of Geophysical Research – Biogeochemistry 112: G02023, doi:10.1029/2006JG000304.

The water in the deepest basins of the Baltic Sea are only intermittently renewed. The interval between water renewals, so-called stagnation periods, are typically several years during which only turbulent diffusive exchange of matter occurs with overlying water. The diffusive fluxes of nutrients, oxygen and hydrogen sulfide through the 150 m level in the Eastern Gotland deep Basin were computed from high quality hydrographic and hydrochemical observations, Comparing with observed storage changes in the basin water, the residual corresponding to the net source or sink due to biogeochemical transformations could be obtained. It is found that decomposition rates of organic matter vary by a factor of about 3.5 mostly due to variations in redox conditions. On average 15.8 gC m-2yr-1 are decomposed in the deep basin. No trend is found in the investigated period 1965 - 2005. The variability of the phosphate source is dominated by release of dissolved phosphate from particulate iron-bound phosphate at oxic to anoxic transitions. It is found that the deep sediments release about 3 gP m-2 when overlying water turns anoxic. Denitrification rates are on average 2.6 gN m-2yr-1, but also these are highly variable depending on redox conditions. Comparing with observations of organic matter and nutrient accumulation in the sediments, we conclude that the supply of organic matter through the 150 m horizon is about 30.6 gC /m2/yr. Further, the results corroborates that the nutrient content of the organic matter supply follows approximately the Redfield ratio.

Stigebrandt, A. & Gustafsson, B.G. (2007) Improvement of Baltic proper water quality using large-scale ecological engineering. Ambio 36: 280-286

Eutrophication of the Baltic proper has led to impaired water quality, demonstrated by e.g. extensive blooming of cyanobacteria during premium summer holiday season and severe oxygen deficit in the deepwater. Sustainable improvements of water quality, by reduction of phosphorus (P) supplies, will take several decades before giving full effects because of large P storages both in soils in the watershed and in the water column and bottom sediments of the Baltic proper. In this paper it is shown that drastically improved water quality may be obtained within a few years using large-scale ecological engineering methods. Natural variations in the Baltic proper during the last decades have demonstrated how rapid improvements may be achieved. The present paper describes the basic dynamics of phosphorus, organic matter and oxygen in the Baltic proper. It also briefly discusses advantages and disadvantages of different classes of methods of ecological engineering aiming at restoring the Baltic proper from effects of eutrophication.

Preliminary computations show that the P content might be halved within a few years if about 100 kg O2 s-1 are supplied to the upper deepwater. This would require 100 pump stations, each transporting about 100 m3 s-1 of oxygen-rich so-called winter water from about 50 to 125 metres depth where the water is released as a buoyant jet. Each pump station needs a power supply of 0.6 MW. Off-shore wind power technology seems mature enough to provide the power needed by the pump stations. The cost to install 100 wind-powered pump stations, each of 0.6 MW power, at about 125 metres depth seems to be about 200 million Euros.  

The BACC Author Team (2008) Assessment of Climate Change fron the Baltic Sea Basin. Regional Climate Studies, Springer Verlag, 473pp.

About this book
This book offers an up-to-date overview of the latest scientific findings in regional climate research on the Baltic Sea basin. This includes climate changes in the recent past, climate projections up until 2100 using the most sophisticated regional climate models available, and an assessment of climate change impacts on terrestrial, freshwater and marine ecosystems.

The authors demonstrate that the regional climate has already started to change, and will continue to do so - projections show that the region will become considerably warmer and wetter in some parts, but dryer in others. Terrestrial and aquatic ecosystems have already shown adjustments to increased temperatures, and are expected to face further changes in the near future.

The BACC Author Team consists of more than 80 scientists from 13 countries covering various disciplines related to climate research and related impacts. BACC is a project within the BALTEX (Baltic Sea Experiment) Programme and a contribution to the World Climate Research Programme.