Newsletter August 2012

August 2012

Additional atmospheric deposition of nitrogen caused by shipping completed
Final results of additional atmospheric deposition of nitrogen caused by shipping have been completed. The task of WP3 was to assess the degree of inter-annual variability of spring and summer phytoplankton blooms and nitrogen fixation in response to a ship nitrogen deposition on the background of natural variability of environmental conditions in the Gulf of Finland. Two 10-year runs with coupled 3D physical and biological-chemical model were performed using atmospheric deposition of NOx without ship deposition and including ship deposition (2008).

Annual atmospheric NOx deposition was 13.7 kton and ship NOx deposition 1.6 kton to the Gulf of Finland area in 2008. Annual ships NOx deposition is about 12% from total atmospheric deposition. Ship NOx deposition is highest in May, June, July and August (20-30%). Ship NOx deposition caused the increase of spring bloom and post bloom biomass phytoplankton biomass (~1%) reducing at the same time phosphate resources. Ship NOx deposition causes the decrease of nitrogen fixation about 2-6%. Thus the increase of the Gulf nitrogen pool caused by the additional ship NOx deposition to the Gulf was partly compensated by the decrease of nitrogen fixation. The effect of ship NOx deposition on cyanobacteria bloom was larger in the western and central Gulf of Finland. No trend in phytoplankton primary production and nitrogen fixation due to accumulation of ship NOx deposition in the Gulf water column was observed.

Due to the phytoplankton composition (green algae + cyanobacteria) the annual total biomass in the Gulf is actually limited by phosphorus, i.e. the increase of green algae primary production is practically compensated by the decrease of nitrogen fixation by cyanobacteria.

Summer measurement campaign in the Harmaja island
The summer campaign in the Harmaja island continued during the summer. Particle number concentrations and size distributions were measured at two altitudes of a 10 m tall tower in order to find the gradients of the concentrations when the ships were passing the island. Data analysis of the summer campaign continues still.

Collection and preprocessing of meteorological data has been continued. Years 2008 and 2009 have been re-simulated for calculation of the one hour concentrations. Results have been checked and analysed. Model-measurement inter-comparison has been started with EMEP measurements.