No abstract

Northern peatlands are important terrestrial carbon stores, and they show large spatial and temporal variation in the atmospheric exchange of CO 2 and CH 4 . Thus, annual carbon balance must be studied in detail in order to predict the climatic responses of these ecosystems. Closed-chamber methods were used to study CO 2 and CH 4 in hollow, Sphagnum angustifolium lawn, S. fuscum lawn, and hummock microsites within an ombrotrophic S. fuscum bog. Micrometeorological tower measurements were used as a reference for the CH 4 efflux from the bog. Low precipitation during May-August in 1994 (84 mm below the long-term average for the same period) and a warm July-August period caused the water table to drop by more than 15 cm below the peat surface in the hollows and to 48 cm below the surface in high hummocks. Increased annual total respiration exceeded gross production and resulted in a net C loss of 4-157 g/m 2 in the different microsites. Drought probably caused irreversible desiccation in some lawns of S. angustifolium and S. balticum and in S. fuscum in the hummocks, while S. balticum growing in hollows retained its moisture and even increased its photosynthetic capacity during the July-August period. Seasonal (12 May-4 October) CH 4 emissions ranged from 2 g CH 4 -C/m 2 in drier S. fuscum hummocks and lawns to 7 and 14 g/m 2 in wetter S. angustifolium-S. balticum lawns and hollows, respectively. Aerodynamic gradient measurements at the tower showed slightly higher CH 4 flux rates than the average estimates for the whole bog obtained by closed-chamber methods. Winter C efflux comprised 30 g CO 2 -C/m 2 and 1 g CH 4 -C/m 2 out of a total loss of 90 g C/m 2 on average in the bog, and there was an estimated annual loss of 7 g C/m 2 by leaching. This study shows how delicately the boreal bog's C balance in different microsites depends on climatic variations, especially the distribution of precipitation. It also confirms that severe C losses can occur in boreal bogs during extended summer droughts, even in years with annual temperatures close to the long-term average and with precipitation clearly greater than the long-term average.

Abstract. Four measurement campaigns were performed in two different environments -inside the harbour areas in the city centre of Helsinki, and along the narrow shipping channel near the city of Turku, Finland -using a mobile laboratory van during winter and summer conditions in 2010-2011. The characteristics of gaseous (CO, CO 2 , SO 2 , NO, NO 2 , NO x ) and particulate (number and volume size distributions as well as PM 2.5 ) emissions for 11 ships regularly operating on the Baltic Sea were studied to determine the emission parameters. The highest particle concentrations were 1.5 × 10 6 and 1.6 × 10 5 cm −3 in Helsinki and Turku, respectively, and the particle number size distributions had two modes. The dominating mode peaked at 20-30 nm, and the accumulation mode at 80-100 nm. The majority of the particle mass was volatile, since after heating the sample to 265 • C, the particle volume of the studied ship decreased by around 70 %. The emission factors for NO x varied in the range of 25-100 g (kg fuel) −1 , for SO 2 in the range of 2.5-17.0 g (kg fuel) −1 , for particle number in the range of (0.32-2.26) × 10 16 # (kg fuel) −1 , and for PM 2.5 between 1.0-4.9 g (kg fuel) −1 . The ships equipped with SCR (selective catalytic reduction) had the lowest NO x emissions, whereas the ships with DWI (direct water injection) and HAMs (humid air motors) had the lowest SO 2 emissions but the highest particulate emissions. For all ships, the averaged fuel sulphur contents (FSCs) were less than 1 % (by mass) but none of them was below 0.1 % which will be the new EU directive starting 1 January 2015 in the SO x emission control areas; this indicates that ships operating on the Baltic Sea will face large challenges.

The CO 2 dynamics were measured in an organic soil in eastern Finland during the growing season and wintertime, and the annual CO 2 balance was calculated for plots where barley or grass was grown. During the summer, the CO 2 dynamics were measured by transparent and opaque chambers using a portable infrared gas analyser for the CO 2 analyses. During the winter, the CO 2 release was measured by opaque chambers analysing the samples in the laboratory with a gas chromatograph. Statistical response functions for CO 2 dynamics were constructed to evaluate the annual CO 2 exchange from the climatic data. The net CO 2 exchange was calculated for every hour in the snow-free season. The carbon balance varied extensively depending on the weather conditions, and type and phenology of vegetation. During the growing season, the grassland was a net source while the barley ®eld was a net sink for CO 2 . However, both soils were net sources for CO 2 when autumn, winter and spring were included also. The annual CO 2 emissions from the grassland and barley soil were 750 g CO 2 -C m ±2 and 400 g CO 2 -C m ±2 , respectively. The carbon accumulated in root and shoot biomass during the growing season was 330 g m ±2 for grass and 520 g m ±2 for barley. The C in the aboveground plant biomass ranged from 43 to 47% of the carbon ®xed in photosynthesis (P G ) and the proportion of C in the root biomass was 10% of the carbon ®xed in photosynthesis. The bare soils had 10±60% higher net CO 2 emission than the vegetated soils. These results indicate that the carbon balance of organic soils is affected by the characteristics of the prevailing plant cover. The dry summer of 1997 may have limited the growth of grass in the late summer thus reducing photosynthesis, which could be one reason for the high CO 2 release from this grass ®eld.

No abstract