CONWOY is a multi-disciplinary project with the aim to investigate the regional effects of global climate change on Danish freshwater and marine ecosystems. DHI has been involved in several subprojects within this framework and some of the highlights are shown below. The general CONWOY webpage can be found at www.conwoy.ku.dk .
Consequences of climate change have been assessed by projects at both large regional scale and on local meso-scale. The knowledge from these projects has been compiled and linked to the operational Waterforecast model to give an indication of how the oceanography and water quality in Danish waters for the years 2070-2100 would look like in a future climate.
The project is drawing to an end and publications are on the way for each of the projects below – abstracts and links will appear as they become available.
Stratification and oxygen depletion in the Danish Waters
The operational Waterforecast model, which describes the present day conditions and produces 5 daily forecasts, has been put into climate mode. It has been run for two periods; 1960-1990 and 2070-2100, with the meteorological and fresh water forcings predicted by the 
regional atmospheric climate model.
The modelled results of the predicted climate changes show an increased and prolonged period of stratification in the waters connecting the North Sea and the Baltic Sea. Furthermore, temperature increases in the bottom waters. These two features favours low oxygen concentrations, and model results indicate a future doubling of the area affected by anoxia (here defined as concentrations less than 4 mg/l).
Mechanisms behind and consequences for the Major Baltic Inflows (MBI)
Around New Year 2003 conditions for the onset of a medium sized inflow were present. This event was the first of its kind in 10 years.
The inflow gave a much needed “breath of fresh air” to the deep basins in the Baltic proper.
The model results show the progression of the inflow through the Great Belt and the Sound, and how it continues through the Bornholm basin to the narrow Stolpe Channel. The model resolution is not sufficient to follow the very dense but narrow intrusion past the Stolpe Channel.
Because MBIs are such irregular events and climate models describe trends and not necessarily detailed events – this analysis is at best an indication of a trend.
As can be seen from the the figures, there is a small tendency to the future MBI’s being stronger but fewer.
However, there is no evidence of a break down of Major Baltic Inflows in the future.
Impact of climate change on plankton dynamics
Global climate models all have in common predictions of changes in the future climate. For the northern hemisphere, there is a good agreement between the majorities of the global models that the temperature is going to rise and more extreme events of storm and rainfall will occur - changes that will impact on the entire biological structure and functioning of the aquatic ecosystem.
Through mesocosms experiments and 3D hydrodynamic and bio-geochemical modelling efforts analyses of the potential effects of increasing temperature in the future have been conducted.
A temperature increase implies a potential shift towards a more heterotrophic ecosystem, because the heterotrophic organisms have higher Q10 than the autotrophic ones.
The overall conclusion of the analyses was a lower spring bloom biomass, and the remineralisation was shifted from the bottom layer to the water column leading to a reduced sedimentation.
|
Phytoplankton gC m-2 |
Zooplankton gC m-2 |
Primary production gC m-2day-1 |
Sedimentation gC m-2day-1 |
1960-1990 |
2,71 |
0,07 |
0,52 |
0,02 |
2070-2100 |
2,03 |
1,38 |
0,47 |
0,01 |
Changes in summer conditions for blooms of toxic blue-green algae
With increasing temperatures and decreasing salinities (due to increasing river run-off to the Baltic Sea system) the growth conditions improve for the potential toxic blue-green algae. Today the Danish beaches experience occasional occurrences of blue-green algae, but in a changing climate we might experience pronounced spatial distributions of these algae compared with the situation today.
Red: high risk of blue-green algae, Orange: middle risk, White: no risk of blue-green algae.
| 1960-1990 |
2070-2100 |
 |
 |
Thermal stratification in a freshwater lake – consequences of climate changes
In deeper (temperate climate) lakes, a thermocline develops during summer resulting in anoxic conditions in the bottom layers. Model results indicate that a changing climate with increasing temperatures and changing wind regime will strengthen the stratification and prolong the anoxic period with up to one month per year.
