Environmental Pollution xxx (xxxx), xxx-xxx
Biomass fires in eastern Europe during spring 2006 caused episodic
high deposition of ammonium in northern Fennoscandia
Per Erik Karlsson
a*
, Martin Ferm a, Hans Tømmervik b, Lars Hole c, Gunilla Pihl
Karlsson a, Sofie Hellsten a, Cecilia Akselsson d, Tuija Ruoho-Airola e, Wenche Aas f,
Teis Nørgaard Mikkelsen g, and Bengt Nihlgård h.( final author order depending on
contributions)
a
IVL Swedish Environmental Research Institute, Box 5302, SE-400 14 Gothenburg,
Sweden
b
Norsk institut for naturforskning (NINA), Norway
c
Norwegian Meteorological Institute, Norway
d
Lund University
e
Finnish Meteorological Institute, Finland
f
NILU, Norway
g
Department of Chemical and Biochemical engineering, Technical University of
Denmark, Denmark
h
Lund University
 Corresponding author:
Per Erik Karlsson
IVL Swedish Environmental Research Institute,
Box 5302, SE-400 14
Gothenburg, Sweden
Telephone
+46 31 7256207
Fax
+46 31 7256290
E-mail
pererik.karlsson@ivl.se
Abstract (144 words)
Episodic high air concentrations of ammonium were detected at low and high altitude
sites in Sweden, Finland and Norway during the summer 2006, coinciding with
polluted air from biomass burning in eastern Europe passing over northern
Fennoscandia. Outstanding high values for throughfall deposition of ammonium were
detected at one low altitude site and several high altitude sites in north Sweden. The
occurrence of the high ammonium in throughfall differed between the summer
months 2006, most likely related to the timing of precipitation events. Unusual visible
injuries on the shrub vegetation in northern Scandinavia occurred during 2006. High
ammonia dry deposition might have contributed to these injuries, together with high
ozone concentrations which also occurred in the same area during the summer 2006.
It is concluded that long-range transport of ammonium from large-scale biomass
burning may contribute substantially to the nitrogen load at northern latitudes.
Key words: ammonium, air concentrations, deposition, biomass burning, vegetation
damage, Russia.
Research highlights:

...
1. Introduction
The Arctic and sub-Artic ecosystems are experiencing a considerable change in
climate, both during summer and winter (Bokhorst et al., 2009, Karlsen et al. 2009).
At the same time, the air nitrogen concentrations and deposition together with other
agents as ozone (Maninnen et al., 2009) and SO2 (Tømmervik et al. 2003) may be
significant at high latitudes and can exacerbate secondary and biotic stresses in
heathland and bog systems, increasing the likelihood of ecosystem damage (Aber et
al., 1989, Bobbink et al., 1998, Hole et al., 2008, Kühnel et al., 2011, Phoenix et al.
2012, more refs?). Responses are apparent at modest N deposition rates. Given future
climate scenarios of more extreme weather patterns, or climate change that may result
in greater pathogen or herbivore damage, these stresses likely represent increasing
threats to semi-natural systems receiving greater rates of N deposition (Phoenix et al.
2012). Reactive nitrogen is considered as a major, global environmental problem
(Sutton et al., 2011). Nitrogen deposition represents a threat to biodiversity (Dise et
al., 2011) as well as to soils in general (Velthof et al., 2011). The highest risks for
negative impacts of N deposition on vegetation biodiversity are for regions with a
historically low nitrogen load, such as e.g. European northern latitudes (Nordin et al,
2005, Dise et al., 2011, Phoenix et al., 2012, more ref). Northern ecosystems are
especially vulnerable to nitrogen deposition as bryophytes and lichens are important
parts of these ecosystems and as bryophytes and lichens take the major part of their
nutrition directly from the air (Cornelissen et al., 2001, Gordon et al., 2001, Dise et
al., 2011, Bate, 2002, Phoenix et al., 2012 ). Furthermore, nitrogen may increase
primary productivity of the ecosystems and above a certain level it is common that a
few competitive species are able exploit the available N and to dominate other species
by shading (Dise et al., 2011, Stevens et al., 2011, Phoenix et al., 2012 more ref).
Nitrogen impacts on vegetation at far northern latitudes has not been well studied but
indication of effects like vegetation type transition and composition are reported
(Tømmervik et al., 2004, Stevens et al., 2011). On the other hand negative effects of
ozone have been reported (Maninnen et al. 2009). For instance, the nitrophilous
plant, Trientalis europaeus (Bertils & Näsholm 2000), was more frequent in
Finnmark in 2010 than in 1998 as well as the cover of vascular plants increased
(Tømmervik et al. 2011, Tømmervik et al., 2012). The ecosystems of alpine snowbeds
are apparently well supplied with N through high mineralization rates (Björk and
Molau, 2007). Add more text and references on N limitation of northern ecosystems.
There has been a steady increase in NOx and NHy deposition at northern latitudes
since 1860 (Hole et al. 2009) as a result of industrialization and intensified farming.
After the 1980s there has been a decline as a result of emission reduction measures
such as the UN-ECE Gothenborg protocol. The general trend with an accelerating
deposition during the 19th century and a decline in the last 20 years, corresponds well
with ice core observations such as Weiler et al., 2005. There were some stations with
reduced deposition in Fennoscandia, but also some with increasing trends in the same
area (Hole et al., 2008, 2009). It has earlier been suggested that decreasing NHydeposition in continental Europe due to lower surface NHy affinity will lead to higher
NHy-concentrations in more remote areas (e.g. Sutton et al., 2003), but this was not
confirmed (Hole et al. 2008, 2009).
Hole and Engardt (2008) showed that changes in precipitation patterns due to climate
change will have a significant influence on the deposition of sulphur and nitrogen
compounds in northern regions in the next 50-100 years, with a strong increase of
NHy deposition (40%) along the Norwegian coast. In other regions of Scandinavia
changes will be moderate.
Aas et al. (2008) made deposition maps for Norway based on data from
approximately 700 precipitation stations and air and precipitation concentrations
measured at a limited number of sites. The depositions of NOx and NHy in the
interior of northern Norway (Finnmarksvidda) area were estimated 0.6 and 0.7 kg N/
ha, respectively. Aas et al. (2010) showed that the annual mean air concentration of
NHy in air in Karasjok was about 0.12 μg m-3, about 20% of other stations on the
Norwegian mainland. Add deposition measurements in northern Sweden...
The alkaline NH3 reacts readily with acidic substances in the atmosphere to form
ammonium salt particles, such as (NH4)2SO4, NH4NO3 and NH4Cl, that occur
predominantly in the fine particle fraction (Finlayson-Pitts and Pitts, 1999, Hertel et
al., 2011). (NH4)2SO4 can under certain meteorological conditions be transported over
very long distances (Brosset et al., 1975, Irwin and Williams, 1988, Krupa, 2003). In
the absence of sulphate, NH3 will mainly react with HNO3 and form NH4NO3.
NH4NO3 has a higher deposition velocity as compared to (NH4)2SO4, (ref). Hence the
presence or absence of sulphate in the atmosphere has a large impact on the longrange transport of NH3/NH4 (Fowler et al., 2007, Fagerli and Aas, 2008, Hertel et al.,
2011).
On important component of the hemispheric air pollution is emissions from the largescale biomass burning (Yurganov et al., 2004, Simmonds et al., 2005). Biomass
burning is the second most important source for ammonia in the atmosphere after
agricultural activities (Krupa, 2003). During the last decade there have been several
large-scale biomass burning events in eastern Europe. Russian fire statistics are
available over the four past decades but, until recently, these statistics are considered
very unreliable. Over the past decade, improved remote sensing has permitted a more
accurate assessment of the annual fires in Russian boreal forest, revealing that Russia
generaly has the largest area burned among boreal forests (Goldammer 2010).
Comparative fire statistics for total vegetated area and forest area burned in the
Russian Federation in the period 2000-2007 are presented in Figure 1, based on
agency reports and remote sensing. The number and extent of forest fires in Russia
have increased from an annual average of 17 800 fires in the period 1986-1990 to 21
700 fires in the period 1991-1995, with a subsequent increase to more than 29 000
fires in the period 1996-2005 (Goldammer 2010). For the year 2006, Goldammer
(2010) reports 36000, 1306 and 3800 fires in Russia, Belarus and Ukraine,
km2/ yr
respectively (Goldammer 2010).
200000
180000
160000
140000
120000
100000
80000
60000
40000
20000
0
1998
Agency, Total area
burned
Agency, Forest area
burned
Satellite, Total area
burned
Satellite, Forest area
burned
2000
2002
2004
2006
2008
Figure 1. Comparative fire statistics for total vegetated area and forest area burned in the Russian
Federation in the period 2000-2007 based on agency reports and remote sensing (Source: Goldammer
2010).
If polluted air from biomass burning in eastern Europe will affect the air quality over
Scandinavia depends on the weather situation during the period of burning. In the
beginning of May 2006, there were large areas on Svalbard where the snow was
coloured black (Stohl et al, 2007). There were also record high ozone concentrations
on Svalbard as well as on Iceland. This highly polluted air originated from biomass
burning in eastern Europe and it was estimated that approximately 2 M ha burnt
during May and June 2006 (Stohl et al, 2007).
Figure 2. Trajectory analysis for air masses arriving at Zeppelin, Svalbard, on May 2nd 2006. Arrow
indicate the county of Jämtland, Sweden. From Stohl et al., 2007. Atmos. Chem. Phys., 7, 511-534.
An anti-cyclonic weather system over Russia transported this polluted air towards
west and north ending up from Scotland to Finland (Anttila et al., 2008, Whitham &
Manning, 2007). Significant concentrations of several pollutant, among them
ammonia, were detected in the polluted snow on Svalbard (Stohl et al, 2007). High
amounts of ammonia were also detected in the PM10 particles sampled in eastern
Finland during May 2006 (Anttila et al., 2008). A trajectory analysis (Figure 2)
showed that some of these polluted air masses were transported across the county of
Jämtland in northern Sweden.
Visible injuries of air pollution like SO2, heavy metals etc. have been recorded in
northern Fennoscandia (Aamlid & Venn; 1992,; Tømmervik et al., 2003). Visible
injuries of O3 on herbaceous vegetation have been repeatedly observed in
Fennoscandia over the last decades, at ambient O3 exposure concentrations that are
lower than those in Central and Southern Europe (e.g. Pihl-Karlsson et al., 1995;
Pleijel et al., 1991; Harmens et al., 2005, Manninen et al., 2009). This is likely to be
due to the climatic conditions in Fennoscandia, which promote relatively high rates of
O3 uptake into the leaves (Matyssek et al. 2007). NH3 can cause direct foliar injury on
higher plants as well as alterations in growth and productivity, drought and frost
tolerance, responses to insect pests and pathogens (Krupa, 2003).
The aims of this study were to analyse occurrence of high amounts of ammonia in the
air and in deposition at northern latitudes in Scandinavia, to examine links to large
scale biomass burning events and to analyse the possible role for the nitrogen load at
northern latitudes as well as for the occurrence of visible damage on the vegetation.
2. Methods
Sites
In this study, results were used from monitoring sites within different networks in
Finland, Sweden and Norway. Air concentration values were used from the sites
Virolahti and Utö in Finland, Bredkälen, Esrange and .... in Sweden and from
Tustervatn and Karasjok in Norway. Oulanka, Utö, Bredkälen, Esrange, Tustervatn
and Karasjok are EMEP (European Monitoring and Evaluation Program) sites. The
sites ... are positioned at high elevation in the Swedish mountain region and were
operated within a special project financed by the Swedish Environmental Protection
Agency.
Procedure for the air concentration sampling...
Results from bulk- and throughfall deposition measurements were analysed for the
sites ... in Finland, Nymyran, Sör-Digertjärn, Hundshögen, Fiskåfjället in Sweden and
Tustervatn and Karasjok in Norway. As stated above, ... Tustervatn and Karasjok are
EMEP sites. The Swedish sites Nymyran, Sör-Digertjärn, Hundshögen, Fiskåfjället
are part of The Swedish Throughfall Monitoring (SWETHRO) network, which has
been described in detail (Pihl Karlsson et al., 2011). In brief, SWETHRO is a
regionally financed network, that includes measurements of air concentrations, bulk
deposition (BD) in open areas, throughfall deposition (TF) and soil water chemistry
inside forest stands. Monitoring sites are positioned in closed, mature managed forests
with no major roads or other pollution sources in the vicinity. During summer, TF is
measured in polyethylene bottles lined with plastic bags with polyethylene funnels
(Ø=15.5 cm) threaded into the lid. The plastic bags are replaced at each sampling
occasion. Ten TF collectors are placed in an L-shaped pattern with five bottles at each
side or in some cases as a cross-shaped pattern (30 x 30 m) in a homogeneous part of
the forest. The bottles are wrapped with aluminium foil to minimize the effect of heat
and sunlight (Ferm, 1993). To prevent contamination by insects and forest litter, a
piece of nylon netting is attached between the funnel and the bottle. The ten TF
samples are merged to one composite sample. BD is measured in an open area
adjacent to the TF measurements, using a similar type of collectors as was used for TF
(Ø=20.3 cm). Samples of TF and BD deposition are collected monthly throughout the
year.
The measurements at Swedish high altitude sites Katterjock (515 m a.s.l), Tjärnberg
(500 m a.s.l.), Skorvfjället (808 m a.s.l) and Prästbodarna,were part of a special
project lasting 2001-2007. The measurements at these sites were similar to those
described above for the SWETHRO network, with the difference that due to the low
density of trees close to the timber line, only five throughfall collectors were used at
each site and the collectors were all positioned under the branches of single trees.
Chemical analysis
Methods for analysing air concentrations samples...
Martin: Filterpack, Sweden? Lars: Tustervatn? Tuija, air concentrations Utö/Virolahti
When the water samples from deposition measurements arrived at the laboratory pH,
alkalinity and conductivity were measured directly. The water sample was then
filtered using a cellulose acetate filter (0.8 µm). Subsamples were preserved with
sulphuric acid (H2SO4), to be analyzed for Kjeldahl-N and NH4-N, and with nitric
acid (HNO3) for analysis of Fe and Al. The remaining sample volume was not
preserved and used for analyses of SO4-S, NO3-N, Cl, Ca, Mg, Na, K, Mn, by Ion
Chromatography and of NH4-N, analysed by Flow Injection Analysis (FIA). Kj-N
was measured according to Foss-Tecators method AN 52212002-10-24.
Storulvsjön
Katterjåkk
Tjärnberg
Skorvfjället
Bredkälen
Prästbodarna
Figure 3. Maps showing the positions of the different monitoring sites in Norway,
Sweden and Finland.
Maps to be replaced...
The results from the throughfall measurements during spring and summer 2006 at the
site Nymyran, within the Swedish SWETHRO network, were central to this article.
Therefore, some detailed information is given in Table 1 for the monthly sampling
periods May through August 2006.
Meteorological information
Meteorological information for the different sampling sites in Sweden were from the
weather service (“LuftWeb”) provided by the Swedish Meteorological and
Hydrological Institute (SMHI). Estimates can be obtained for each position in Sweden
based on interpolated weather data.
Vegetation survey
The episode of high concentrations of ozone and other pollutants reaching northern
Fennoscandia during April and May 2006 initiated a series observations of the
vegetation in Troms county, Norway, later in the spring. Discolouration and injury to
leaves of rowan (Sorbus aucuaparia) were observed in Tromsø. Sample leaves were
sent to a forest pathologist in Norway and the conclusion was that the chlorosis on the
leaves might have been caused by air pollution such as ozone or other pollutants
(Børja I. 2006., personal communication). These initial observations were followed by
a campaign were leaf samples were collected near air pollution monitoring stations
(EMEP, NILU etc.) in the northern Fennoscandia. Leaf samples of birch and rowan
were collected at Øverbygd-Målselv (Veltvatn-Dividal) in Troms county (Norway),
Karasjok in Finnmark county (Norway) and Esrange in northern Sweden. Further
samples were collected during summer 2006 in Tromsø and Nordreisa (Troms
county). These leaves were inspected in-situ using diagnostics in (Vollenweider &
Gunthardt-Goerg, 2005), dried and stored for further investigations. Leaves were
further examined using microscopic analysis.
Phenological observations of birch of rowan were conducted common used methods
in the Nordic countries (Wielgolaski 1999 and Pudas et al. 2008) and assessed against
observations done in the region (e.g. Phenology of the North Calotte:
http://sustain.no/projects/northcalotte/map/ and the Plant Phenologcial Network in
Finland, www.metla.fi/metinfo/fenologia).
3. Results and discussion
Air concentrations of pollutants over Finland, Sweden and Norway
NH4, low altitudes
Concentrations of black carbon are an indicator for polluted air originating from
biomass burning (Hyvärinen et al., 2001). Daily mean air concentrations of black
carbon during 2006 are shown in Figure 4 for the EMEP monitoring site Bredkälen,
positioned in the middle of the county of Jämtland, Sweden. The concentrations of
black carbon started to rise above the baseline level around April 26 and maximum
daily mean concentration, 12 µg/m3, was measured on May 2. The concentrations
Bredkälen Daily mean air concentrations of black
carbon
14
12
10
8
6
4
2
02-dec
02-nov
02-okt
02-sep
02-aug
03-jul
02-jun
03-maj
02-apr
03-mar
31-jan
0
01-jan
Air concentrations (ug/m3)
returned to baseline levels around May 9.
Date 2006
Figure 4 Daily mean air concentrations of black carbon during 2006 for the EMEP monitoring site
Bredkälen, positioned in the middle of the county of Jämtland, Sweden
Daily mean air concentrations of NH3/NH4+ (gaseous+particle) and SO42- during 2006
are shown in Figure 5 for three different sites, Utö in Finland, Bredkälen in Sweden
and Tustervatn in Norway. All three sites were positioned so that the polluted air
masses from eastern Europe during the beginning of May (Figure 2) would have
passed over. There was a period between xx April and xx May 2006 with consistantly
high air concentrations of NH3/NH4+ and SO42- at all three sites. At Utö, the highest
daily air concentration of NH3/NH4+ for the year 2006 was measured on May 3rd, even
if there were nearly as high concentrations also for other days during 2006. The high
concentrations of NH3/NH4+ at Utö were accompanied by fairly high cocnentrations
of SO42-, even if there were days with higher concentrations of SO42- during other
parts of the year. Also at Bredkälen, the highest daily air concentration of NH3/NH4+
for the year 2006 was measured on May 3rd, and also here this was accompanied by
high concentrations of SO42-. At Tustervatn ...
A
NH3.NH4 æg(N)/m3
SO4-- æg(S)/m3
2
1
27-dec
27-nov
28-okt
28-sep
29-aug
30-jul
30-jun
31-maj
01-maj
01-apr
02-mar
31-jan
0
01-jan
Air concentrations (ug/m3)
Utö. Daily mean air concentrations
3
Date 2006
B
3
NH4-N_TOT
SO4-S
2
1
02-dec
02-nov
02-okt
02-sep
02-aug
03-jul
02-jun
03-maj
02-apr
03-mar
31-jan
0
01-jan
Air concentrations (ug/m3)
Bredkälen Daily mean air concentrations
Date 2006
C
Lars/Wenche, can you provide me with daily mean concentrations of (NH3+NH4) and SO4 for
Tustervatn 2006?
Figure 5. Daily mean air concentrations of NH3/NH4+ (gaseous+particle) and SO42- during 2006 at
three different sites, Utö in Finland (A), Bredkälen in Sweden (B) and Tustervatn in Norway (C).
NH4, high altitudes
At the high altitude sites in northern Sweden air concentrations of pollutants were
measured on a monthly basis. High monthly mean air concentrations of ammonia
were detected at high elevation in northern Sweden during May 2006 (Figure 6).
Eventhough the air concentrations for May 2006 were not always record high, there
were high values also in particular during 2003, the values for May 2006 were always
among the highest during the period of measurements. Also high sulphur, potassium
and calcium concentrations were detected. High concentrations of calcium were
record high at all sites during May 2006.
0.6
Katterjock. Monthly mean air concentrations.
NH3+NH4-N
0.4
SO4-S
0.2
0.0
2003
2004
2005
2006
Air concentrations
(ug/m3)
Air concentrations
(ug/m3)
A
0.2
Ca2+
K+
0.1
0.0
2003
2007
Katterjock. Monthly mean air concentrations.
2004
2004
2006
2007
1.0
Tjärnberg. Monthly mean air concentrations.
NH3+NH4-N
SO4-S
0.5
0.0
2003
2004
2005
2006
2007
C
Air concentrations
(ug/m3)
Air concentrations
(ug/m3)
Air concentrations
(ug/m3)
B
0.2
Tjärnberg. Monthly mean air concentrations.
K+
Ca2+
0.1
0.0
2003
2004
2004
2006
2007
Not available
1.0
Skorvfjället. Monthly mean air concentrations.
NH3+NH4-N
SO4-S
0.5
0.0
2003
2004
2005
2006
2007
0.8
Prästbodarna. Monthly mean air concentrations.
NH3+NH4-N
0.6
SO4-S
0.4
0.2
0.0
2003
2004
2005
2006
2007
Air concentrations
(ug/m3)
Air concentrations
(ug/m3)
D
0.2
Prästbodarna. Monthly mean air concentrations.
K+
Ca2+
0.1
0.1
0.0
2003
2004
2004
2006
2007
Figure 6. Air concentrations measured at high altitudes in northern Sweden, 2003-2007. Monthly mean
total air concentrations of NH4+(gas+PM), SO42-, K+ and Ca2+. Unit µgN/m3. A, Katterjock, 515 m
a.s.l.; B, Tjärnberg, 500 m a.s.l.; C, Skorvfjället, 808 m a.s.l.; Prästbodarna, 710 m a.s.l. Values for
May 2006 are marked with a symbol.
Ozone, low altitudes
Ozone
Deposition
Throughfall, low altitudes
A comparably very high monthly value for ammonia deposition in throughfall was
detected at Nymyran in June 2006, a site with a 75-year-old Norway spruce forest at
an altitude of 300 m a.s.l (Figure 7). Sample volume was average but NH4
concentration in the sample was high. The sample was carefully checked for
contamination, but there was no sign of bird droppings such as e.g. high pH or high
phosphorous concentrations. Analysis of Kj-N showed that the sample content of
organic N was relatively low. The low sample volume in April and May 2006,
indicated that the precipitation in April and June was low at the site. The precipitation
patterns are analysed further in the next section below.
A
B
Nymyran, NH4-N concentrations
800
2.0
600
1.5
mg/l
g/ha/month
Nymyran, NH4-N deposition
400
0.5
200
1999
2001
2003
2005
2007
0.0
1997
2009
Figure 7. Monthly ammonia deposition in
throughfall at the low altitude site Nymyran, 75-yearold Norway spruce forest at an altitude of 300 m a.s.l.
Data is shown for the calculated deposition (upper),
the sample ammonia concentration (middle) and the
sample volume (lower). A symbol is shown for the
value for June 2006.
1999
2001
2003
2005
2007
2009
C
Nymyran, sample volume
35000
30000
25000
ml/month
0
1997
1.0
20000
15000
10000
5000
0
1997
1999
2001
2003
2005
2007
2009
Throughfall measurements at two sites nearby, Sör-Digertjärn under Scots pine and
Storulvsjön under Norway spruce, did not show elevated NH4 or Kj-N deposition
during 2006 (data not shown).
It is well known that a large fractions of the nitrogen deposition to forests can be
taken up directly to the canopies (e.g. Parker, 1983, Ferm, 1993, Adriaenssens m. fl.,
2012), in particular in regions with comparably low deposition. This means that the
NH4 deposition during the spring 2006 most likely was considerably larger than the
throughfall deposition values that were actually measured.
Precipitation and temperature at the site Nymyran during the sampling periods 2006
The collection of throughfall deposition is of course heavily dependent on
precipitation. Therefore we did a careful analysis of the daily precipitation events at
the site Nymyran (Figure 8). The analysis is based on data on daily precipitation for
the exact position of the Nymyran site, provided by the Swedish Hydrological and
Meteorological Institute (SMHI).
Nymyran, daily precipitation
Precipitation 2006
May period
June period
mm/day
20
10
0
92
30
123
153
day of year
184
214
Nymyran, daily mean temperature
Temperature 2006
oC
20
10
0
-10
92
123
153
day of year
184
214
Figure 8. Daily precipitation and daily mean temperatures at the site Nymyran for the period 1 April –
31 July. Values are for the year 2006 as well as means per year-day for the period 2001-2010 except
2006. The horizontal grey line indicates the sampling period for throughfall at Nymyran for May 2006
and the thick black horizontal bar the corresponding period June 2006. The thinner, vertical, black line
indicates the date 1 May 2006.
There was little precipitation during the period between the pollution event around 3
May 2006 and the end of the May sampling period for throughfall at Nymyran (Figure
8). Between May 1 and the shift of sampling period, May 22 2006, the accumulated
precipitation was only 15 mm and the daily maximum precipitation 5 mm. In contrast,
during the nine days between 22 May and 31 May 2006, the accumulated
precipitation was 49 mm. Hence, this analysis implies that the high amounts of NH4
found in the June 2006 throughfall sample from Nymyran might well have originated
from the highly polluted air masses that passed over Jämtland in the beginning of May
2006 if it was deposited a dry deposition, since there was little precipitation during the
remaining part of the May sampling period but substantial precipitation to wash out
the NH4 to the throughfall samplers during the June sampling period. The air
temperatures were elevated for more than a week in the beginning of May 2006
indicating a sunny weather condition.
Throughfall, high altitudes
Monthly ammonia deposition in throughfall is shown in Figure 9 for three sites at
high altitude (600-800 m a.s.l) in the county of Jämtland. These measurements were
made under Norway spruce, but with a slightly different methodology, as compared to
low altitude sites, due to the low stand density close to the timber line. All three sites
show high monthly ammonia deposition during summer 2006, but at different months,
also as compared to Nymyran. The relative ammonia deposition peak value for
Hundshögen is not as high compared to the other sites. No Kjelldahl-nitrogen
analyses are available for these sites.
A
B
800
1000
Throughfall deposition.
Sånfjället. NH4
August
600
400
200
g/ ha/ month
g/ ha/ month
1000
600
400
July
200
0
1998 2000 2002 2004 2006 2008
0
1998 2000 2002 2004 2006 2008
C
1000
g/ ha/ month
Figure 9. Monthly ammonia deposition in
throughfall at the high altitude sites in the county
of Jämtland (600-800 m a.s.l.) Fiskåfjället,
Hundshögen, Sånfjället. Throughfall deposition
measurements are made with a slightly different
methodology, as compared with low altitude
measurements. Peak values are shown as a grey
diamond together with an indication of the month.
Values for May 2006 are shown as an open tringle.
Throughfall deposition.
Hundshögen. NH4 dep
800
800
Throughfall deposition.
Fiskåfjället. NH4
600
July
400
200
0
1998
2000
2002
2004
2006
2008
Elevated NH4 deposition in throughfall at high altitudes was also evident at four other
sites outside the county of Jämtland (data not shown), one site south of Jämtland and
three sites north of Jämtland. At these sites the NH4 peak during 2006 occurred in
June or July. However, the peaks at these sites were not as pronounced during 2006 as
compared to peaks during other years.
Relation between ammonia deposition at high altitudes and precipitation events
The throughfall sample volumes to some extent indicate the precipitation volumes,
although interception and evaporation to weakens this relation. Monthly throughfall
sample volumes during 2006 are shown in Figure 10 for the high altitude sites
Sånfjället and Fiskåfjället. Hundfjället is not included the the NH4 peak was not as
prnounced for this site. The value for May 2006 is indicated with a thick arrow, while
the month with peak ammonia deposition is indicated for the respective site.
Regarding throughfall at Sånfjället, the sample volumes were very low for the months
May-July 2006 but considerably higher for August which was the month when the
high throughfall deposition of NH4 was detected. A similar situation appeared for
Fiskåfjället, where the sample volumes were low for May and June, but somewhat
higher for July when the high NH4 deposition was detected.
mm/ ha/ month
200
150
100
Throughfall deposition.
Sample volumes
S
F
50
0
Jan
Apr
Jul
Oct
Month 2006
Figure 10. Monthly throughfall sample volumes during 2006 for the high altitude sites in Jämtland,
Sånfjället (black line) and Fiskåfjället (grey line). May 2006 is indicated with a thick, black arrow. The
months with peak value ammonia deposition at the two sites are indicated with thin arrows, together with a
letter indicating the site; F, Fiskåfjället; S, Sånfjället.
Bulk deposition measurements
There were no measurements of open-field, bulk deposition at Nymyran. However,
there were bulk deposition measurements available from the nearby site Storulvsjön
(Figure 3). There were no pronounced peaks in the monthly, bulk NH4 deposition
during 2006 at Storulvsjön (data not shown).
Summary of NH4 deposition events during 2006 in north Sweden
To summarize, there were several montly pronounced NH4 throughfall deposition
events during the summer of 2006, both at low and high altitudes, in particular in the
county of Jämtland, but also in other parts of north Sweden. These events occurred
during different months, probably related to the timing of precipitation events. It is
likely that the deposition to the forests occurred as dry deposition and then was
washed to the throughfall sampling collectors when there was enough precipitation.
The dry deposition at Nymyran most likely occurred during the pollution episode in
the beginning of May 2006, originating from biomass burning in eastern Europe, but
for the other sites the deposition might be related to other pollution episodes during
the summer 2006.
It is difficult to quantify the NH4 deposition to the forests in north Sweden, since a
large fraction of the nitrogen deposition generally is taken up directly to the canopies
and not included in the throughfall measurements (ref). However, since the fraction of
nitrogen taken up directly to the canopy is particularly large in low deposition regions,
such as northern Sweden, it is likely that the dry deposition of NH4 during the May
2006 by far exceeded 1 kg N/ ha. Since the normal yearly deposition of total inorganic
N in north Sweden is below 5 kg N/ ha (Pihl Karlsson et al., 2011), this NH4
deposition event is of considerable importance. It has been shown that nitrogen wet
deposition at Svalbard (Kuhnel et al., 2011) is strongly depending on a few episodic
“strong” events and a similar conclusion was made for sulphur deposition at remote
sites in finland (Ruoho-Airola and Salmi, 200x)
Leaf visible injury on vegetation during the summer 2006
During the summer 2006 unusual leaf visible injuries were observed in northern
Fennoscandia (Figure 11). Manninen et al. (2009) presumed these injuries to be
effects of unprecedented O3 concentrations and other pollutants. For example the
leaves in Figure 11 (A) indicate chlorosis and bronzing and was confirmed as
possibilities by I. Børja on 2006-06-18 (The Norwegian Forest and Landscape
Institute). The photograph B in Figure 11 shows leaves that are bronzed and this
indicate O3 injury following the diagnostics in Vollenweider & Gunthardt-Goerg
(2005). This tree was situated in a forest edge exposed to south-east. All observations
of the leaves which show injuries are summarized in Table 1. In order to assess these
injuries samples of leaves were examined and assessed using microscopy (Table 1).
A
B
Figure 11. A, Rowan (Sorbus aucuparia) leaves showing chlorotic and brown-reddish stippling and
red-brown necrotic areas in the leaf margins. Photographed in Tromsø (69°38’N, 18°55’E), NW Norway,
on 30 July 2006. B, Mountain birch red and bronze colored leaves, Karasjok (69°28’N, 25°31’E),
August 4th 2006. The tree was standing in a forest edge.
Table 1. Diagnostic characteristics of the injuries observed.
Site
Rowan
Date for
observation
and
sampling of
leaves
Tromsø
Indication of
chlorosis1, bronzing
and undeveloped
leaves (Fig.11-A)
2006-05-20
and
Indication of
chlorosis, bronzing
and undeveloped
leaves, may be O3 or
other pollutants
2006-06-15
(Norway)
VeltvatnØverbygdMålselv
(Norway)
Microscopy
Phenological
event (rowan)
Birch
Date for
observati
on and
sampling
of leaves
Microscopy
Phenological event (birch)
Bud burst:
Slight yellowing leaves
2006-0605
Concentric rings caused by basic
pollutants in combination with ammonia
and O3.
Bud burst:
2006-0615
Change of colors, marbling, injuries in
wax-layer (Fig.12) .. Small injuries and
brown spots, caused by air pollutants
(ammonia and O3)
2006-05-07
2006-06-10
Yellowing of
leaves:
2006-09-18
Small injuries and
brown spots (Fungiattacks caused by air
pollutants (ammonia
and O3).
Bud burst:
2006-05-08
Slight yellowing leaves
Yellowing of
leaves:
2006-05-06
Yellowing of leaves:
2006-09-20
Bud burst:
2006-05-06
Yellowing of leaves:
2006-09-25
2006-09-22
Nordreisa
(Norway)
Indication of
chlorosis, yellowing
and undeveloped
leaves
2006-07-01
Small injuries; dead
cells (browning).
Changes in the waxlayer on underneath
the leaves ).Most likely
O3 in combination with
ammonia
Bud burst:
2006-05-12
Yellowing of
leaves:
2006-0701
Bud burst:
2006-05-10
Yellowing of leaves:
2006-09-15
2006-09-18
Esrange
(Sweden)
Yellowing of leaves,
undeve-loped leaves
2006-08-03
Bud burst:
2006-05-08
Yellowing of
leaves:
2006-09-10
Karasjok
(Norway)
2006-08-04
Bud burst:
2006-05-20
Yellowing, mottling and bronzing
of leaves.
Indication of necrosis.
Change of colors, marbling, injuries in
wax-layer. Small injuries and brown
spots, caused by air pollutants (ammonia
and O3.
Yellowing, mottling and bronzing
of leaves (Fig. 11-B).
by I. Børja: 18-06-06 (The Norwegian Forest and Landscape Institute)
Bud burst:
2006-05-10
Yellowing of leaves:
2006-09-10
Some oxidative stress due to
prevailing ozone, ammonia, low
temperatures, pathogens and
nutrient imbalance
Some oxidative stress due to
Yellowing of prevailing ozone, ammonia, low
leaves:
temperatures, pathogens and
nutrient imbalance (lack of P)
2006-09-12
1Confirmed
2006-0803
2006-0804
Injuries in the wax-layer, brown spots,
might be a combination of ammonia and
O3. Concentric rings caused by basic
pollutants in combination with ammonia
and O3.
Bud burst:
2006-05-20
Yellowing of leaves:
2006-09-12
In Figure 12, microscopic injuries on leaves of Rowan and Birch collected during the
June 2006 in northern Norway. Similar injuries to these species, like we observed in
2006, have not been observed during other periods (Tömmervik, personal
communication). Hence, there may be a connection between these leaf injuries and
high ammonia episodes in combination with other pollutants like O3 or other
compounds. Microscopy revealed frequent injuries to the wax-layer. Marbling,
mottling, stipling, brown spots, fungi-attacks as well as change in coloration were also
frequent. According to Vollenweider & Gunthardt-Goerg (2005) mottling, stippling ,
brown spots may indicate influence of O3.Other drivers could also have reinforced the
injuries observed, such as climate conditions (frost in spring and drier weather
conditions). On the other hand, normal conditions due to precipitation were observed
in northernmost Sweden and in northern Norway during the spring and summer 2006
(www.met.no; www.smhi.se).
As can be seen in Table 1, the estimated bud burst in northern Fennoscandia occurred
in the beginning of May 2006, coinciding with the event of highly polluted air passing
over the area. Hence, the canopies of the deciduous shrubs were not fully developed
and it is uncertain to what extent the stomatal conductance had reach the maximal
values. On the other hand, there are several examples that leaves may be very
sensitive to air pollution at this stage of development (ref).
Figure 12. Rowan leaves (sampled June 2006) from Veltvatn-Dividal (ØverbygdMålselv), enhanced 10x. Small injuries and brown and yellow spots indicate influence
from air pollutants like ammonia and O3.
The significance of long-range transport of ammonia and the impacts on vegetation
1. Is there an increasing frequency of large-scale biomass burning?
2. How often have similar ammonia episodes influenced Fennoscandia?
3. How important could these events be for total nitrogen deposition to northern
ecosystems and for vegetation damage, for ?????
4. Conclusions
Several lines of evidences were found for frequent, episodic occurrence of
ammonia/ammonium in air concentrations in northern Scandinavia. Particularly high
air concentrations of particulate and gaseous ammonia at high altitudes were detected
during May 2006, coinciding with a well described event with highly polluted air
originating from large scale biomass burning in eastern Europe, passing over the
county of Jämtland, Sweden. High air concentrations of ammonia were detected in
areas over which this polluted air mass passed; at Utö, a small island between Finland
and Sweden, at Bredkälen in the county of Jämtland, Sweden and at Tustervatn, a
Norwegian site just north for Jämtland. At Bredkälen, also high air concentrations of
black carbon were detected.
Exceptional high values for throughfall deposition of ammonia were detected during
the summer 2006 at one low altitude site and several high altitude sites in Jämtland.
The occurrence of the high ammonia in throughfall in Jämtland varied between
different summer months most likely related to precipitation events.
Unusual visible injuries on the shrub vegetation in northern Scandinavia occurred
during 2006. High ammonia air concentrations and dry deposition might have
contributed to this, together with high ozone concentrations which also occurred in
the same area during the summer 2006.
Long-range transport of polluted air from large scale biomass burning might have an
important role for nitrogen deposition in northern Scandinavia as well as for the
occurrence of visible injuries on the vegetation in the region.
Acknowledgements
The contribution by Per Erik Karlsson to this study was financially supported by ....
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Figure Captions.
Figure 1.
Table 1. xxxx
of ozone over a threshold of 40 ppb.