Consequences of the increasing iron concentration in catchments draining into the Baltic Sea
Iron concentrations in marine waters are often very low (0,07-0.23 nM in the North Atlantic) and iron has received attention as the possible limiting factor of primary production in vast areas of the global ocean. Nevertheless, iron is not scarce in the Baltic Sea (15 nM-144 nM Bothnian Sea to the Baltic Proper). During the last four decades the iron concentration has constantly increased along the Swedish coastline. The positive trends for iron in river waters result in increasing coastal export. For the Swedish coast as a whole, iron export has increased by 70% over four decades. In freshwater, interactions with organic matter (OM) maintain iron in solution where it would otherwise precipitate and sediment. In estuaries, iron is known to behave non-conservatively and it has been estimated that at least 95% of the iron in “the average world river” aggregates and sediments in estuaries. However, due to a lower salinity in the Baltic Sea more iron is expected to reach the open water. The relatively high iron concentration might be one reason explaining the success of nitrogen fixing cyanobacteria in the Baltic Sea, and to the extent that riverine iron reaches the open water the increasing iron export may enhance nitrogen fixation and blue-green algae blooms even further. To better understand the role of iron and the ensuing consequences the following questions will be examined during my PhD:
- Is the increase in riverine iron export resulting in a higher iron concentration along the Baltic Sea salinity gradient?
- How does the speciation of iron and the interaction with OM of different quality determine the transport capacity of iron in the salinity gradient?
- Are the riverine waters important in providing bioavailable iron to the receiving system?
To address these questions iron speciation, OM characteristics and the interactions between iron and OM will be characterized in great detail. Non-standard methods as Synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy, Flow injection analysis for iron (FeLUME instrument) and Infrared IR spectroscopy will be applied within the project.