Environmental Pollution 118 (2002) 259–272
www.elsevier.com/locate/envpol
Atmospheric nitrogen deposition on the east coast of Spain:
relevance of dry deposition in semi-arid Mediterranean regions
M.J. Sanz*, A. Carratalá, C. Gimeno, M.M. Millán
Fundación CEAM, Parque Tecnológico, c/Charles Darwin 14, 46980 Valencia, Spain
Received 10 January 2001; accepted 31 August 2001
‘‘Capsule’’: N deposition patterns on the east coast of Spain were characterized with special emphasis on dry deposition.
Abstract
Bulk deposition composition and pine branch washing were measured from April 1999 to March 2000 on the east coast of Spain.
The main objective was to characterise N deposition patterns with special emphasis on dry deposition. Bulk deposition in the region
is dominated by neutralisation processes by Ca2+ and HCO
3 , ClNa of marine origin and a high correlation between NO3 and
2
2
SO4 . SO4 concentrations show a decrease with respect to previous studies in the region in agreement with generalized sulfur
emission decreases while the remaining ions, including NO
3 , are higher due to their general increase as well as to the inclusion of
dry deposition in bulk collectors in the present study. An enrichment in NO
3 has been observed in dry deposition composition
(branch washing) with respect to bulk deposition, while an impoverishment has been observed in the case of NH+
4 . Annual bulk
deposition varies between 7.22–3.1 and 3.5–1.8 Kg ha1 year1 for S- SO2
4 and N- NO3 , respectively. N total deposition goes from
9.78 to 6.8 Kg ha1 year1 at most stations, with the lowest deposition at the control station and Alcoi. The relative dry deposition
with respect to the total was over 40% at most stations, going up to 75 % at the southern station. N-deposition is expected to be
higher considering that N-NH+
4 deposition has been underestimated in this study. # 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Sulfate; Nitrogen; Bulk deposition; Dry deposition; Mediterranean
1. Introduction
Recent emissions inventories have shown that N
emissions are increasing in many areas of the world,
suggesting that N saturation of terrestrial ecosystems
may occur. It has been hypothesised that in the Western
Mediterranean Basin the quantity of inorganic nitrogen
deriving from the atmosphere may be much more
important than estimated. With the growing industrialization and traffic increase in this region, some
environmental problems have appeared which were
unknown before the 1970s. Among them are the formation of ozone, nitric acid, nitrates and other nitrogenous compounds, including aerosols and particulate
material, which generate from the emissions of NOx
* Corresponding author. Tel.: +34-96-131-8227; fax: +34-96-1318190.
E-mail address: mjose@ceam.es (M.J. Sanz).
and organic vapors. For most of the year the regional
climate is dominated by local atmospheric processes
(sea breezes and up-slope winds), which cause the air
mass to re-circulate over the same area and keep it
much warmer than in other European regions (Millán et
al., 1997). These conditions promote photochemistry
and ozone formation, so that the values detected in this
area greatly exceed European directives for vegetation
and crop damage (Millán et al., 1992, 1997).
Thus, to the list of environmental concerns in this
region, from eutrophication of coastal areas and drinking water contamination to the problem of water pollution by nitrates employed in ‘‘intensive’’ agricultural
practices (Mueller et al., 1995), we must now add the
possible ‘‘extensive’’ problems arising from ozone
damage and the deposition of nitrogenous compounds
via the atmosphere. In Spain, the areas with the greatest
identified problems, for both air pollution (Millán et al.,
1992) and nitrate leaching produced by intensive agriculture practices (Varela, 1991), are the Mediterranean
coastal fringe and parts of the central plateau.
0269-7491/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0269-7491(01)00318-9
260
M.J. Sanz et al. / Environmental Pollution 118 (2002) 259–272
Nitrogen deposition in terrestrial ecosystems where
photochemical pollutants dominate the pollution climate
may be high or at least persistent. Thus, chronic nitrogen inputs are expected in remote sites, which can lead
to various negative effects, including deficiencies, soil
acidification, altered species composition, decreased
mycorrhizal infection, increased susceptibility to environmental stresses, and elevated nitrate concentrations in
soils, ground water and streams (Bytnerowicz and Fenn,
1996; Fenn et al., 1998; Fenn and Poth, 1999) in natural
ecosystems and forests. Nevertheless, initial positive
effects can be detected, such as enhanced tree growth
when N deposition is not excessive. The other side of
the problem, as earlier mentioned, is that intensive
agriculture and the large N inputs result in heavy
nitrate-leaching to the ground watersheds in some areas,
such as the deltas and lower valley plains of the east
coast of Spain where nitrate concentrations are very
high (Varela, 1991; Ramos, 1996).
Generally speaking, in Mediterranean Ecosystems the
magnitude of the impact of nitrogen deposition and
the susceptibility of specific ecosystems to dry deposition remain largely unknown. The greater magnitude
of dry deposition is due to the temporal coincidence of
high atmospheric pollutant levels and drought, a fact
already evidenced in the Mediterranean ecosystems of
California where N dry deposition can increase to 35–45
kg N ha1 year1 (Fenn, 1991; Bytnerowicz and Fenn,
1996). The objective of the present study is to evaluate
atmospheric (Dissolved Inorganic Nitrogen, DIN)
deposition on the east coast of Spain, where recirculatory processes dominate the air pollution dynamics, and
dry deposition may be as high or even higher than wet
deposition. Newly obtained data are compared to older
data to see the time evolution, and sampling problems
are also discussed.
2. Material and methods
2.1. Sampling network description
In the Mediterranean Basin, the atmospheric air
motions at the mesoscale level are strongly linked to
topography and it is very well documented that recirculatory processes are present most of the year (Millán et
al., 1997) and are responsible for the observed air pollution (Photochemical smog) patterns in the air quality
networks (Seufert, 1997; Millán et al., 2000). Sampling
stations are located along valley transects combined
with north/south transects (Fig. 1) in order to characterize deposition patterns on the East coast of Spain.
Co-ordinates and brief descriptions of each location can
be found in Table 1. Sampling stations 4 and 7 are regular stations on the Valencian Community’s Air Quality
Network, and station 5 is a MEDEFLU-Project site.
2.2. Sampling protocol
2.2.1. Bulk deposition
To collect rain for chemical analysis, we used a 10-l
bulk collector composed of a polypropylene bucket connected by a U-bend, to prevent evaporation, to a funnel
with a 707 cm2 horizontal interception surface. The rim
of the funnel was positioned at 1.5 m above ground level
to avoid ground contamination. In addition, a device to
prevent bird contamination was set up. Before collecting
the sample, the funnel was rinsed with 300 ml of deionised water to wash away any matter deposited between
the last rain episode and the collection time. Thus, such
samples represent a combination of dry+wet deposition,
with the dry component being mostly coarse particulate
matter (Krupa, 2000). The sampling period was 2 weeks
(14 days). At two sites, ‘‘El Saler’’ and Morella, precipitation amounts were continuously recorded by a
precipitation gauge (ARG100, SKY), and most of the
other sites were near National Institute of Meteorology
precipitation rain gauges, which was useful to compare
the precipitation volumes collected and the number and
date of the rain events. Once in the lab, pH (Crison
micropH 2002, Ag/AgCl electrode), conductivity (Crison microCM2201) and alcalinity (colorimetric tritiation) were measured for each composed sample.
Afterwards, the samples were filtered with a Sartorious
cellulose filter (0.45 mm pore size) and frozen (18 C)
for a period of no longer than 2 weeks.
2.2.2. Branch washing
Because of the inadequacy of any single method to
evaluate dry deposition, we measured deposition to pine
branchlets to be compared with the bulk deposition
data. A leaf-washing technique developed by Lindberg
et al. (1984) and modified by Bytnerowicz et al. (1987)
was used. Aleppo pine (Pinus halepensis Miller) was
selected as one of the most common conifer species on
the East coast of Spain and in the Western Mediterranean Basin. Three 7-year-old potted trees supplied by
the National Forestry Department (DGCN, Ministry of
Environment) were placed on each sampling location.
Four branches (5–8 cm long), one from each geographic
quadrant, at about 1–1.5 m above ground level, were
thoroughly washed at the beginning of the experiment
and rinsed every 2 weeks with 50 ml of deioniseddistilled water dispersed from polypropylene spray bottles. Extended series of washes were done to check leaf
efficiency for removing deposited ions, and it was found
that the first 50 ml of wash removed more than 90 % of
the deposited ions. The rinsing solutions were collected
into a funnel in 50 cc polyethylene bottles and immediately placed in cool boxes at 4 C. Once in the lab, a
composed sample of 200 ml was obtained for each tree,
and the same analytical procedure as for bulk deposition samples was followed.
M.J. Sanz et al. / Environmental Pollution 118 (2002) 259–272
261
Fig. 1. Map of the locations.
Total surface area exposed was calculated by measuring the two main axes of each needle, approaching
half of the cylinder surface. The surface of the stems
was calculated from the stem diameter and length
measurements.
2.2.3. Surrogate surfaces
Three Teflon filters (Whatman PTFE, 47 mm, 1 mm
pore-size) were held in PVC double rings at a height of
about 1.5 m above ground to avoid soil-dust contamination. Surfaces were exposed in a horizontal position. The filters were collected at the same time the
conifer branches were rinsed. The exposed and blank
filters were placed in 47 mm diameter Petri dishes
(Poliestilen, Millipore) and additionally enclosed in zip
plastic bags. Immediately after collection, bags were
placed in cool-boxes filled with ice. Once in the lab, bags
were kept at 18 C. Prior analysis filters were rinsed
with 25 ml of deionised-distilled water (Milli-Q), shaken
for 30 min and submitted to the same analytical procedure as the bulk deposition samples.
2.3. Analytical methods
After samples were filtered and prior to freezing
(18 C), the subsample for ammonium was acidified
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M.J. Sanz et al. / Environmental Pollution 118 (2002) 259–272
Table 1
Sampling stations (see footnotes for other available information)a
Transect
Co-ordinates and altitude (m)
Stations and distance to the coast line (km)
North-south coastal transect
To characterise heterogeneity in the deposition along
the coastal bend, background air mass at the mouth
of the valley
(0 90 5800 W, 38 580 22N)/12
(0 180 3900 W, 39 200 5000 N)/2
7. Gandı́a (Alicante)a
5. El Saler (Valencia)b,c
(0 240 2300 E, 40 250 1000 N)/30
2. Benicarló (Castellón)/2.7b
–
2. Benicarló (Castellón)
(0 10 3600 E, 40 320 4900 N) / 700
(0 50 2800 , 40 380 1600 N)/1156
3. Vallivana (Castellón)/40b
4. Morella (Castellón)/51a
–
5. El Saler (Valencia)/0.5
(0 260 3000 W, 39 170 1300 N)/32
6. La Peira (Valencia) 6.4a
–
7. Gandı́a (Valencia)/3.2
(0 320 1700 W, 38 300 5800 N)/ 1014
8. Alcoi (Alicante)/29.6a
(0 380 000 W, 38 280 2200 N)/503
9. Agost (Alicante)/17.4
(1 210 4600 W, 41 10 200 N)/895
1. Burbáguena (Teruel)/164
Valley transect I
To characterise deposition along the sea breeze penetration
path (Servol Valley). Gradients due to coastal cell
penetration and deposition in areas influenced by reservoir
layers (top of the mountain)
Valley transect II
To characterise deposition along sea breeze penetration
path (Turia Valley) on the coastal plain of a wide valley
with intensive agriculture
Valley transect III
To characterise deposition along sea breeze penetration
path (Serpis Valley)
Semi-arid area
Southern semi-arid area where dry deposition is the most
important component
Control
Non-influenced by coastal recirculatory cells
a
b
c
Temperature, speed and wind direction, distance to the sea, O3, NO, NO2, rainfall, RH.
Temperature, speed and wind direction.
Rainfall.
with sulfuric acid and the one for cations with nitric
acid, to prevent volatilisation and precipitation, respectively. Concentrations of anions were determined by ion
chromatography (Dionex DX500 Ion Chromatograph,
IonPac ASII 2mm and ASRS Ultra 2 mm suppressor
column), concentrations of cations were determined by
ICP (Optima 3000) and the concentration of ammonium was determined spectrophotometrically by the
indophenol blue method (Eaton et al., 1998).
2.4. Attribution of marine source
The major source for Chlorides is marine aerosols.
Considering that there is no fractionating in sea salt
aerosols and all chlorides in the samples come from
marine origin ([Clm]=[Cl]), the percentage of marine
source (%MS) at each station could be calculated using
the marine ratios. In this case the ratios from the review
of Keene et al. (1986; in meq), have been used in the
following expression.
2þ
%MS ¼ ½Cl m þ Naþ m þ SO2
4 m þ Mg m
P
P
þ Ca2þ m þ ½K mÞ= ½cat þ ½ani
¼ð1 þ 0:86 þ 0:10 þ 0:21 þ 0:038
P
P
þ0:018Þ½Cl = ½cat þ ½ani :
P
P
where
½cat þ ½ani are the total meq of cations plus
anions and 1, 0.86, 0.1, 0.21, 0.038 and 0.018 are the
of
ratios
the different ions to marine chlorides, i.e
Naþ m =½Cl m ¼ 0:86.
2.5. Quality control/quality assurance
The evaluation of the ionic balance and the estimation
of conductivity were applied as quality checks for all
samples: bulk deposition, branch washes and surrogate
surface washes (Mosello et al., 1999). Na+/Cl ratios
were also calculated. Assuming that sea salt is the
dominant source of both ions, the ratio should resemble
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M.J. Sanz et al. / Environmental Pollution 118 (2002) 259–272
the sea-water ratio, being close to 0.858 (Keene et al.,
1986; Ivens, 1999). To assure reproducibility, 10 % of
the samples were randomly selected and re-analyzed;
2
differences in the main anions (NO
3 , SO4 , Cl ) and
cations were less than 10%. Ammonium differences
ranged between 2 and 15 %.
3. Results
3.1. Average concentrations in bulk deposition and
branch washing
The volume-weighted means (VWM) for each location was calculated for bulk samples (Table 2). VWM
for nitrates and sulfates in bulk samples is higher in sites
with lower volumes of precipitation, with the highest
being in Agost (106 and 144 me l1, respectively) and the
lowest in Burbáguena (34 and 58 me l1, respectively).
For ammonium the control site shows relatively high
VWM values, although Agost presents the highest
values. To compare with concentrations and ratios from
this study, Table 3 shows previous data from studies on
the chemical composition of rain at 27 locations in the
Valencian Community in 1990–1991 (Carratalá, 1993),
at other locations in the Mediterranean (Carratalá,
1993; Escarré et al., 1999) and in central-northern Europe (Pedersen et al., 1992).
4. Variations in dry deposition with respect to bulk
deposition concentrations
Table 4 presents the VWM of the dry deposition
measured on pine needles during periods without rain.
Its greatest interest is in verifying whether there is
enrichment in any of the ions with respect to the bulk
deposition, since in themselves the concentrations are
dependent on the volume of wash used and on the area
of the surface. Said volume was approximately the same
in all the washes (200 ml), with surfaces of between 129
and 1470 cm2.
The relation between both types of deposition was
determined by using a linear adjustment between all the
stations for each ion, and it is shown in Fig. 2 for Ca2+,
2
Na+, K+, NH+
and NO
4 , SO4
3 . To compare the
results with those of bulk deposition, a comparison of
the slopes of these linear adjustments was performed. In
general, the best regressions are found for NO
3 and
2
+
2
SO2
(with
r
=0.7),
followed
by
Na
with
r
=0.6
4
+
2+
and by K and Ca . Finally, in the case of ammonium, no correlation is found between the dry and the
bulk deposition concentrations. Worth noting is the fact
that in the case of NH+
4 , the concentration values in the
washes are clearly lower (slope51). For the remaining
ions, the slopes obtained are greater than 1, with the
nitrates showing the maximum slope (3.2). The significance here lies not so much in the slope values as in
the differences between them which are indicative of the
enrichment or the impoverishment of some ions with
respect to others in each type of deposition.
Taking sulfate and calcium as references, both of
which present a slope ffi 1, it can be seen that sodium
and nitrate have bigger slopes, implying their enrichment in dry deposition with respect to bulk deposition.
In the case of ammonium, the slope is less than 1 and
thus shows an impoverishment.
5. Main sources of ions in bulk deposition and branch
washing
The percentage of marine sea salt (Tables 2 and 4, %
MS) has been calculated using marine ratios as described
in the Section 2. In bulk deposition it goes from 5% at
station 1 (Burbáguena), the location farthest from the
Table 2
Volume weighted mean (VWM in meq l1) for major ions in bulk deposition for this study (1999)a
Site
1.BUR
2.BEN
3.VAL
4.MOR
5.SAL
6.PE
7.GAN
8.ALC
9.AGO
Rainfall
(mm)
382
530
570
436
464
361
369
238
184
Volume weighted mean in bulk deposition (meq l1)
Ca2+
K+
Mg2+
Na
NH+
4
Cl
NO
3
SO2
4
b
SO2
4 nm
HCO
3
184
286
189
203
212
379
342
440
483
6
10
3
7
11
11
12
11
14
14
34
17
18
46
46
64
41
38
20
103
35
34
178
127
195
94
92
55
48
38
48
33
34
28
40
80
12
95
29
30
168
139
198
76
114
34
44
44
51
40
58
52
57
106
58
70
63
75
72
104
122
81
144
56
60
59
72
54
89
101
73
132
145
191
122
156
156
303
219
336
381
%IMB
%MS
5.67
8.96
4.11
0.63
4.60
0.62
4.01
6.30
2.70
5.0
24.0
12.0
10.8
40.6
25.7
35.6
14.4
17.4
P
P
P
P
The volume of rainfall collected is also presented (prec.). % IMB (% Imbalance) correspond to the ratio ( cat- ani)/( cat+ ani), and %
MS (% marine ions) correspond to the sum of ions of marine origin using marine ratios from the literature (Keene et al., 1986).
b
SO2
4 nm correspond to non-marine sulphates.
a
264
M.J. Sanz et al. / Environmental Pollution 118 (2002) 259–272
Table 3
Volume weighted mean (VWM) precipitation chemistry (meq l1) in nine localities on the Mediterranean seaboard (1–9) and six localities from the
European Network (EMEP; 10–15a)
Reference
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
a
Site
Rainfall
(mm year1)
Morella (S)
Vinaroz (S)
Torrent (S)
Gandia (S)
Alcoi (S)
Elx (S)
Monseny (S)
Prades (S)
Almeŕa (S)
Iraty (FR)
Ispra (I)
Birkenes (N)
Witteveen (NL)
Braganza (P)
Kamernicki (Y)
677
628
555
829
522
186
876
551
675
668
1233
1861
844
420
5287.6
Volume weighted mean of rainfall samples (meq l1)
Ca2+
K+
Mg2+
Na+
NH+
4
Cl
NO
3
SO2
4
127
226
212
144
320
201
57
59
123
21
17
7
19
34
82
12
12
26
18
22
10
4
9
15
1
2
4
–
4
19
16
48
48
58
29
38
10
11
34
8
4
17
25
11
26
23
109
95
137
69
60
23
26
37
13
7
76
113
12
53
42
38
75
40
41
51
23
29
32
57
71
33
139
18
87
34
134
123
180
87
75
29
30
34
13
10
91
132
11
69
24
34
34
33
32
38
21
23
19
22
62
34
51
10
36
75
118
105
90
122
99
46
56
58
23
35
27
87
25
75
pH
HCO
3
(meq l1)
5.7
5.8
6.0
5.3
5.7
6.2
4.8
4.9
5.7
5.1
4.3
4.4
4.9
5.4
5.1
133
163
235
126
296
186
14
23
–
–
–
–
–
–
–
Source: 1–6 (Carratalá, 1993), 7–9 (Escarré et al., 1999) and 10–15 (Pedersen et al., 1992).
Table 4
Volume weighted mean (VWM in meq l1) for major ions in pine branch washing for this study (1999)a
Site
Volume weighted mean of branch washing samples (meq l1)
2+
1. BUR
2. BEN
3. VAL
4. MOR
5. SAL
6. PE
7. GAN
8. ALC
9. AGO
+
Ca
K
69
359
128
79
164
294
516
141
526
5
12
7
6
10
13
25
8
17
2+
+
Mg
Na
7
41
19
12
45
42
149
14
66
15
137
57
34
143
113
508
33
201
NH+
4
13
12
9
7
10
14
13
9
12
Cl
NO
3
SO2
4
b
SO2
4 nm
HCO
3
12
133
30
23
151
121
556
37
179
22
97
60
36
69
77
187
47
275
12
67
19
17
40
56
166
20
118
10
53
16
14
24
43
107
16
98
54
210
87
57
97
162
169
95
226
%IMB
%MS
5.36
4.53
5.49
1.17
1.93
6.47
5.57
0.38
1.26
12.1
27.6
16.0
18.6
45.7
30.0
53.7
20.3
24.5
a
Also presented is the, % IMB (% imbalance) corresponding to the ratio (catani)/ (cat+ani), % marine ions corresponding to the sum
of ions of marine origin using marine ratios from the literature (Keene et al. 1986).
b
SO2
4 nm mm correspond to non-marine sulphates.
seashore, to 40.6% at station 5 (Saler), the closest to
the seashore. In branch washing the %MS were slightly
higher, going from 12% in Burbáguena to 53% in
Gandı́a. The relationship between marine source and
distance to the sea can be seen in Fig. 3 and follows a
clear potential gradient from seashore high values
towards inland low values.
Typical ions of terrestrial origin are associated with
CO3Ca. Several ions such as Mg2+, K+, and SO2
4 also
have a certain terrestrial origin. The amount of calcium
and carbonates in this study is quite large. There is a
+
strong correlation between Ca2+ and HCO
3 and K
2
(r =0.98 and 0.80, respectively). These two ions
(Ca2+ and HCO
3 ) show a strong negative correlation
with volume (0.80 and 0.87, respectively) indicating
their predominantly local origin. They are washed in the
first fractions of rain and then diluted. A quite strong
correlation has also been found between Ca2+ and
2
SO2
and NO
4
3 (r =0.79), as a consequence of neutralisation processes.
The strong correlation between nitrates and sulfates
of non-marine origin (r2=0.8 for bulk samples and 0.9
for branch washing samples), shown in Fig. 4, indicates
their common anthropogenic origin. The differences
between the two samples (bulk and branch washing) is
that nitrates are enriched with respect to sulfates in
branch washing. Ammonium shows a certain correlation with nitrates only in bulk samples (r2=0.5) and no
correlation with the remaining ions from bulk and
branch washing.
M.J. Sanz et al. / Environmental Pollution 118 (2002) 259–272
265
2
Fig. 2. Relationship between the VWM concentrations of Ca2+, Na+, K+, NH+
4 , SO4 and NO3 in both types of deposition (bulk deposition and
pine branches washing ) calculated by using a linear adjustment of all the stations in the study. The different slopes indicate the preferential way of
deposition strategy for each ion.
Fig. 3. Relationship between marine source (represented by Cl concentration) and distance to the sea (Km). Branch washing (p) and bulk
samples (pl) shows the same potential relationship. Higher concentrations in branch washing are an effect of washing volume.
6. Deposition of sulfate and nitrogenous compounds
6.1. Bulk deposition
The bulk deposition data for S-SO2
4 , N-NO3 and
+
1
1
N-NH4 in kg ha year corresponding to this study
are shown in Table 5. In order to compare them with
previous data, Table 6 shows data corresponding to
Mediterranean and European stations, taken from the
literature. The annual precipitation at each locality is
also included. In the case of S-SO2
4 , deposition is
around 5.5 kg ha1 year1, oscillating between 7.22 kg
ha1 year1 at Gandı́a and 3.1–3.5 kg ha1 year1 at
Alcoi and Burbáguena. The lowest values are found at
the control station and at the Alcoi station. N-NO
3
deposition oscillates between 3.5 kg ha1 year1 at
Vallivana and 1.8–1.9 kg ha1 year1 at Burbáguena
and Alcoi. The contributions from bulk deposition are
quite homogeneous by valleys (Table 5), as is the precipitation (Table 2). It is interesting to note that the
Burbáguena station (control station), while showing
precipitation levels on the order of the El Saler and La
Peira stations, presents a lower deposition, pointing to
the lower average NO
3 levels in the area. With respect
to N-NH+
4 deposition, the behavior is similar to that
of N-NO
3 , excepting the fact that for ammonium, the
Burbáguena station does not behave like a background station. With this exception the levels oscillate
around 3 kg N-NH+
ha1 year1 in the northern
4
1
valley and from 2 to 1 kg N-NH+
year1 in the
4 ha
other valleys. Comparing our results with the values in
Table 6, we find similar results in Spanish and European Mediterranean stations with similar environments
and precipitation volumes. The stations with the highest ammonium deposition are those located in areas
with high ammonium emissions and high annual precipitation, for example sites in the Netherlands
(Table 6).
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M.J. Sanz et al. / Environmental Pollution 118 (2002) 259–272
6.2. Dry deposition over Pinus halepensis leaves
Dry-deposition contributions are calculated from the
14-day measurement period of deposition to pine foliar
surfaces and taking into account the days of exposition
since the last day of rain within the fortnight. A rain
event is considered to wash the pine leaves completely,
which means a reset to 0 in terms of deposition. In this
way, the dry deposition only accounts for several dry
periods of 14 days and several periods with 1–14 days of
dry deposition. The days prior to the rain event are lost;
thus it must be kept in mind that branch washing
underestimates the annual dry deposition when rain
events are present within a collection period.
Table 5 also shows the results obtained for dry
deposition measured in the yearly period considered in
the present study (drym). As has been mentioned, the
2
1
Fig. 4. Relationship between NO
3 and SO4 (meq l ) in both types of
deposition (bulk deposition, pl) and pine branches washing, p). AH
high correlation indicates their common origin (anthropogenic). The
higher slope in pine branch washing indicates that dry deposition is
more effective than wet deposition for NO
3.
dry deposition calculations use the data from the date
on which the precipitations occurred, and this is
obtained from the pluviometric data registered at the
regional meteorological network stations located near
the stations in this study. Concordances between precipitation volumes at homologous stations are shown in
Table 7. The agreement observed is quite good (slope 1,
r2=0.8), taking into account the great spatial heterogeneity in the precipitation of the region. Table 7 also
shows the number of days with precipitations and the
number of available days for estimating dry deposition
to needle surfaces.
The dry deposition measured for sulfates, including
sulfates of marine origin, is seen to be quite variable
and, in contrast to the bulk deposition, to follow no
clear pattern. The lowest value is registered at the control station (Burbáguena, 0.16 kg ha1 year1) and the
highest value is measured at the Gandı́a station (3.10 kg
ha1 year1). In general, the levels are substantially
lower than those obtained for bulk deposition; the percentages associated to dry deposition range from 5 to
37%. However, it should be pointed out that in Table 5
the annual dry deposition (drym) is underestimated
and the bulk deposition includes dry deposition,
although over a much less efficient collection surface. In
fact, the dry deposition estimated over surrogate surfaces like teflon filters (data not shown) is also lower
than for branches.
The dry deposition of N-NO
3 oscillates between 5.17
kg ha1 year1 at the Agost station and 0.26 kg ha1
year1 at the control station (Burbáguena). In this case a
greater homogeneity can be seen between the transects:
from 1 to 1.6 kg ha1 year1 in the north followed by 1–
2.3 kg ha1 year1 in the Turia valley (middle transect);
the southern transect shows the most heterogeneity, with
Table 5
+
+
Annual deposition of S-SO2
4 , N-NO3 , N-NH4 and N-(NO3 +NH4 ) thorough bulk and dry (over pine branches) deposition measured in this
a
study
Site
Bulk deposition (kg ha1 year1) and dry deposition (kg ha1 year1)
S-SO2
4
1. BUR
2. BEN
3. VAL
4. MOR
5. SAL
6. PE
7. GAN
8. ALC
9. AGO
a
N-NO
3
+
N-(NO
3 +NH4 )
N-NH4
Bulk
Drym
Drye
Bulk
Drym
Drye
Bulk
Drym
Drye
Bulk
Drym
Drye
Bulk+Drye
3.52
5.98
5.71
5.23
5.33
5.99
7.22
3.10
4.24
0.16
1.32
0.38
0.66
0.73
1.95
3.10
0.57
2.46
0.29
2.37
0.76
1.56
1.27
2.79
5.00
0.91
3.33
1.81
3.30
3.52
3.09
2.59
2.93
2.69
1.89
2.73
0.26
1.61
1.04
1.27
1.14
2.29
2.98
0.93
5.17
0.48
2.89
2.09
3.01
1.97
3.28
4.81
1.49
6.99
2.94
3.54
3.07
2.93
2.14
1.72
1.46
1.35
0.94
0.16
0.18
0.14
0.23
0.15
0.43
0.25
0.21
0.28
0.31
0.32
0.29
0.53
0.26
0.61
0.40
0.33
0.37
4.75
6.83
6.59
6.02
5.66
4.65
4.15
3.24
3.67
0.42
1.79
1.19
1.49
1.30
2.72
3.23
1.13
5.44
0.78
3.20
2.38
3.55
2.23
3.89
5.21
1.82
7.37
5.5
10.0
9.0
9.6
7.9
8.5
9.4
5.1
11.0
Bulk deposition covers the period April 1999–March 2000 (less that 5% of samples have been lost). Dry deposition covers the same period;
however, two values are presented for the annual dry deposition: Drym which only accounts for the deposition on the days after rainy events where
dry deposition could have been measured (the exact number of days included in each station are in Table 6) and Drye which has been extrapolated to
the total number of dry days in the yearly period.
267
M.J. Sanz et al. / Environmental Pollution 118 (2002) 259–272
Table 6
+
1
Annual deposition of S-SO2
year1 from the literature at seven localities in Spain and seven from the EMEP networka
4 , N-NO3 , N-NH4 in kg ha
Reference
Site
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Rainfall
(mm year1)
Pyrenees (S)
Montseny (S)
Prades(S)
Roquetas (S)
Morella (S)
Valencian C. (S)
Almerı́a (S)
Deuselbach (G)
Iraty (F)
Ispra (I)
Birkenes (N)
Witteveen (NL)
Braganza (P).
Kamernicki (Y).
1640
876
551
428
678
518
675
691
668
1233
1861
844
420
527
Deposition (kg ha1 year1)
S-SO2
4
N-NO
3
N-NH+
4
+
N-( NO
3 + NH4 )
13.4
6.4
4.8
3.3
8.1
12.3
6.3
2.5
2.5
6.9
8.0
11.7
1.7
6.3
4.1
2.6
1.7
2.8
2.3
3.1
1.8
2.9
2.1
10.7
8.9
6.0
0.6
2.7
5.1
2.8
2.3
3.2
4.0
4.1
3.0
3.2
5.3
12.3
8.6
16.4
1.1
6.4
9.2
5.4
4.0
5.9
6.3
7.2
4.8
6.1
7.4
23.0
17.5
22.5
1.6
9.1
a
References: (1), Camarero and Catalan (1993); (2, 3 and 7), Rodà et al. (1993); (5 and 6), Carratalá et al. (1993); and (4, and 8–14), Pedersen et
al. (1992).
Table 7
Rainfall (mm) collected in the sampling period (1 year) in this project
and at the closest station to a National Institute of Meteorology
(INM) stationa
Site
1. BUR
2. BEN
3. VAL
4. MOR
5. SAL
6. PE
7. GAN
8. ALC
9. AGO
Rainfall (mm)
Number of days
Sampled
INM
Wet deposition
Dry deposition
382
530b
570b
436b
464b
361
368b
238b
184
371
687
509
509
471
320
457
277
196
86
66
111
111
70
35
49
37
32
149
167
127
107
171
231
196
204
246
a
Also presented are the number of days with rain and the number
of the days in which it was possible to measure the dry deposition.
b
1–2 fortnight periods have been lost.
oscillations of between 2.98 kg ha1 year1 at Gandı́a
and 0.93 kg ha1 year1 at the Alcoi station, which
could be under special meteorological conditions. On
the other hand, Agost presents the highest values (5.17
kg ha1 year1). The percentage of dry deposition with
respect to bulk deposition is higher than in the case of
the sulfates; it oscillates between 65% at the driest station and 12% at the control station.
In the case of ammonium, very low deposition values
were found in dry deposition: between 0.43 and 0.14 kg
ha1 year1. Compared to the bulk deposition (0.94–
3.54 kg ha1 year1), ammonium values are considerably lower, in most cases below 10% of the bulk
deposition values.
7. Estimation of annual dry deposition and comparison
to annual bulk deposition
As we stated above, the dry deposition data (drym) in
Table 5 do not correspond to the set of annual dry days.
This data was used to calculate the average daily
deposition (Table 8), which, taking into account the
annual number of dry days per station (365 minus
the number of rainy days), was then used to obtain the
annual dry deposition, drye (also shown in Table 5).
These calculations show the largest deposition rates to
2
be for N-NO
3 , followed by S-SO4 , with ammonium
levels very much lower. The calculated deposition rates
between stations are relatively homogeneous; for total
N they vary between 0.76 and 2.213 mg m2 day1. The
minimum is found at the control station (Burbáguena)
followed by Alcoi. The station showing the highest rates
is Agost which has been shown to have the highest
concentrations and the maximum number of days without rain.
When annual dry deposition, drye, is calculated by
applying the above-calculated rates, S-SO2
yearly
4
deposition ranges from 0.29 to 5 kg ha1 year1. The
minimum appears at the control station and the maximum at Gandı́a. For N-NO
3 yearly deposition, the
minimum also appears at the control site (0.48 kg ha1
year1), but the maximum is at Agost (6.99 kg
ha1 year1). The northern valley transect shows small
differences between stations from the seashore to the
upper valley stations (0.92 kg ha1 year1). The Turia
valley transect shows slightly larger differences even
though the distance between the sites is smaller (1.21 kg
ha1 year1). On the other hand, the southern valley
transect shows even larger differences (3.32 kg ha1
268
M.J. Sanz et al. / Environmental Pollution 118 (2002) 259–272
Table 8
Annual average of daily dry deposition rate of S-SO2
4 , N-NO3 , N
+
2
1
and
N-tot
(N-NO
+
N-NH
)
in
mg
m
day
calculated
NH+
4
3
4
from drym, and taking into account the days of dry deposition measured (in Table 7)
Site
1. BUR
2. BEN
3. VAL
4. MOR
5. SAL
6. PE
7. GAN
8. ALC
9. AGO
Daily deposition rate (mg m2 day1)
S-SO2
4
N-NO
3
N-NH+
4
N-tot
0.104
0.792
0.301
0.612
0.430
0.844
1.583
0.279
1.000
0.172
0.967
0.822
1.186
0.668
0.993
1.522
0.454
2.100
0.109
0.105
0.113
0.210
0.089
0.186
0.127
0.101
0.112
0.281
1.072
0.935
1.397
0.758
1.179
1.649
0.556
2.213
Table 9
Estimation of the percentages of wet and dry deposition of N-tot (N+
a
NO
3 +N-NH4 ) considering dry deposition over pine branches
Site
Surface
efficiency (%)
Wet and total atmospheric deposition
N (kg ha1 year1)
1. BUR
2. BEN
3. VAL
4. MOR
5. SAL
6. PE
7. GAN
8. ALC
9. AGO
N-DB/DP
N-WET
N-TOT
WET/TOT
82%
29%
44%
36%
47%
16%
23%
66%
17%
4.10
5.90
5.55
4.74
4.61
4.03
2.95
2.04
2.42
4.89
9.11
7.92
8.29
6.85
7.92
8.16
3.86
9.78
84%
65%
70%
57%
67%
51%
36%
53%
25%
a
Wet deposition has been calculated by subtracting dry deposition
to bulk collectors, and dry deposition to bulk collectors has been
estimated with the use of data from fortnight periods with no rain
occurring.
year1). Ammonium causes the total N (N-NO
3 + NNH+
4 ) dry deposition to increase by a small fraction
(0.26–0.61 kg ha1 year1). Thus, the total N (bulk plus
dry, Table 5) deposition ranges from 5.53 kg ha1
year1 at the control station to 11.04 kg ha1 year1 at
the Agost station. It should be noted that the total N
deposition may be overestimated due to the inclusion of
a small fraction of dry deposition in the wet fraction.
In order to obtain an estimation of the total N
deposition and of the fractions of wet and dry
N deposition, we compared the deposition data from
several (3–6) rainless fortnight periods and found that
the N-NO
3 dry deposition to bulk collectors was 16–
82% of the deposition to pine branches (depending on
the stations). No estimations were made for N-NH+
4
due to the very low efficiency of the dry deposition.
Taking these percentages into account (Table 9), the dry
deposition to bulk collectors was discounted from the
bulk deposition to obtain the corrected wet deposition
(Table 9). Then the total deposition to pine leaf surface
was calculated (see also Table 9). The final estimated
values for total N deposition thus range from 3.86 to
9.78 kg ha1 year1, with the lowest at the Alcoi and the
control station (3.86 and 4.89 kg ha1 year1 respectively) and the highest at the Agost station (9.78 kg ha1
year1). The wet/(dry+wet) ratio for N deposition
ranges from 84% at the control station to 25% at the
Agost station (Table 9), with 60% being the average for
the northern transect and the Turia valley transect, and
44% for the southern transect, clearly linked to precipitation amount and number of wet days. Therefore,
N dry deposition accounts for more than 40% of the
deposition at most stations, increasing to 75% at
the driest station.
8. Discussion
In this work, higher ion concentrations in bulk samples than those reported by Carratalá (1993) are registered due to the fact that in the present study: (1) there
was less rainfall, producing higher values of ions associated to the washout process (Ca2+, HCO
3 and to a
2
+
lesser extent NO
3 , SO4 , NH4 ), (2) the dry deposition
after the rain events was also collected by washing the
collector funnel prior to the collection of the sample,
and (3) the deposition may have increased since 1992.
Thus, Burbáguena is confirmed as a background or
control site because it shows the lowest values for all but
ammonium whose levels are comparable to those of the
EMEP network (Table 4). With respect to the 1990–
1991 period (Table 3), sulfate levels in the area are
maintained or are slightly lower while nitrate levels
are considerably higher. The general decrease in sulfate
levels is in agreement with emission and overall deposition tendencies registered in recent years on the East
coast of Spain (Avila, 1996; Escarré et al., 1999). On the
other hand, NOx emissions are generally increasing in
western Europe due to a sharp increase in gas and oil
consumption (Dignon and Hameed, 1989; Pacyna et al.,
2000) and, as a consequence, higher nitrate concentration is expected. In fact, long-series for overall deposition are showing a slight increase for nitrates in remote
sites (Avila, 1996) with respect to previous studies in the
area. However, it should be noted that the inclusion of
dry deposition to the surface of the funnel resulted in a
definite increase in levels, indicating a possible earlier
underestimation of the dry deposition component in the
bulk deposition calculated by other studies in the area
(Carratalá, 1993).
Regarding ammonium, there is no clearly observable
tendency with respect to previous data, especially if we
take into account: (1) that locations do not coincide
M.J. Sanz et al. / Environmental Pollution 118 (2002) 259–272
exactly, (2) the primary character of this pollutant with
variations at the local level which may be important,
and (3) the difficulties in evaluating possible losses due
to volatilisation in our climate with long collection periods. Other studies have documented that the sampling
period is especially important for ammonium: long
sampling periods (week compared to event sampling)
resulted in lower NH+
4 concentrations and deposition
values of about 11% (De Pena et al., 1984). The most
significant differences in NH+
between weekly and
4
event samples were found by another group of authors
in Chicago (Sisterson et al., 1985) who attributed them
mostly to volatilisation, whereas researchers in Prague
attributed the differences they found to bioconsumption
(Vesely, 1990). Others concluded that biases are sitespecific (Ramundo and Seastedt, 1990). Thus, taking
into account our climatic conditions and the high pH in
the samples, the results of the present study suggest that
an even higher re-volatilisation than that mentioned in
the literature can be expected, and further experiments
are being developed to assess the problem for rain collectors and long collection periods.
Among the methods of surface analysis, dry deposition has usually been estimated on the basis of foliagerinsing (Bytnerowicz et al., 1987; Ross and Lindberg,
1994). It is important to note that branch washing
results are difficult to compare with the results from
throughfall studies because, in the latter, many layers of
leaves collect the pollutants. Still, the branch-washing
technique seems to be a simple and reliable method for
evaluating atmospheric dry deposition to plant surfaces
(Bytnerowicz et al., 1987; Bytnerowicz, 1994; Lindberg
et al., 1984), despite the fact that this method is affected
by: extraction of anions from foliage during washing,
uptake from foliage during collection periods (up to
39%, Stachurski and Zimka, 2000), and re-volatilisation
and re-suspension of deposition particles (Hosker and
Lindberg, 1982). All of this may explain the even lower
values for NH+
4 found in the branch washing samples
compared with the bulk collector. Nevertheless, branches continue to be more efficient than bulk collectors
and surrogate Teflon surfaces (data not shown) for collecting nitrates (Tables 2, 4 and 9). Other authors also
+
reported higher values of NO
3 than NH4 (about 2
times more) for Ceanothus leaf rinse data in California
(Riggan et al., 1985; Bytnerowicz et al., 1987). The
complex structure of the collecting device—natural
branch, branch coated with Teflon, artificial tree or
artificial branch—seems to condition efficiency even
more than the material itself. In fact, the Teflon-coated
branches showed an identical amount of deposition ions
to the uncoated branches (Bytnerowicz et al., 1991),
demonstrating the usefulness of the method.
When the composition of the rain samples is considered, relationships between ion concentrations are
good indicators of their source (Losno et al., 1991;
269
Durand et al., 1992). The major ions are bicarbonate
and calcium, followed, depending on their marine character, by chloride or sulfate and nitrate, and sodium or
ammonium in the case of cations. Percentages found for
MS are in agreement with those found in other coastal
areas (Fujita and Kawaratani, 1988; Underwood et al.,
1988) and with previous studies in the area (Carratalá,
1993). They also follow a clear gradient from seashore
high values to inland low values, as was expected. Frequently, the anthropogenic origin of sulfates and
nitrates is associated with the acidity of the rain samples
(Zeng, 1989; Durand et al., 1992). However, the large
amount of calcium and carbonates in this study, the
strong positive correlation between them and with NO
3
and SO2
4 , and their negative correlation with precipitation volume which is in agreement with the type of
sampling (bulk), the calcareous nature of the soils (Gatz
et al., 1986; Khemani et al., 1987), and the high frequency of Saharan dust episodes (Avila, 1996; Carratalá
et al., 1996; Loye-Pilot and Martin, 1996) suggest
the existence of neutralisation processes occurring in the
atmosphere or in the collector (Casado et al., 1992;
Carratalá and Bellot, 1998). Acidity is thus unlikely to
occur. Another possible source of sulfates in bulk samples is gypsum-rich soils, but none of our sampling stations show this type of soils. On the other hand, the
strong correlation between nitrates and sulfates (r2=0.8
for bulk samples and 0.9 for branch washing samples)
indicates their common anthropogenic origin. The difference between the two samples is that nitrates are
enriched with respect to sulfates in branch washing
(Fig. 3), indicating a higher collection efficiency.
Ammonium shows a certain correlation with nitrates in
bulk samples only (r2=0.5), and no correlation with the
remaining ions from bulk and branch washing. This
points again to the possible existence of a higher revolatisation than for bulk samples, or to an uptake and/
or re-volatilization of ammonium in branch washing
samples.
When deposition is calculated from the measured
bulk values, S-SO2
4 deposition varies between 7.22 and
3.1 kg ha1 year1, showing a clear decrease when
compared with data from the same sites published in
previous studies (Carratalá, 1993). In the case of NNO
3 , bulk deposition varies between 3.5 and 1.8 kg
ha1 year1. The contributions are quite homogeneous
by zones and are linked to the precipitation in each
zone, i.e. to the atmospheric washing. It is interesting to
note that the Burbáguena station (control), while showing precipitation levels on the order of the El Saler and
La Peira stations, presents a lower deposition because it
is not influenced by heavily polluted air masses from the
coastal areas (Millán et al., 1997). With respect to
the literature and taking into consideration stations
with precipitation levels similar to those of this
study, similar deposition values are also observed. Only
270
M.J. Sanz et al. / Environmental Pollution 118 (2002) 259–272
stations in areas with elevated pollution levels and high
precipitation volumes show significantly higher bulk
deposition values (Birkenes, 1861 mm and 8.9 kg ha1
year1, Table 5).
With respect to N-NH+
4 bulk deposition, the behavior
is similar to that of N-NO
3 , excepting the fact that the
Burbáguena station does not react to ammonium like a
background station. With this exception the levels
oscillate around 3 kg N-NH+
ha1 year1 in the
4
1
northern transect and from 2 to 1 kg N-NH+
4 ha
1
year in the other transects. Comparing this case with
the literature, we can find similar results in Spanish and
European Mediterranean stations with similar environments and precipitation volumes (Pedersen et al., 1992;
Carratalá, 1993; Camarero and Catalán, 1993; Rodà et
al., 1993; Avila, 1996). The stations with the highest
ammonium deposition are those located in areas with
high ammonium emissions and high annual precipitation, as is the case of the stations in the Netherlands
(Table 5).
To prepare the dry-deposition estimations within a
14-day period, a rain event was considered to wash the
pine branches completely and it was assumed that
the gentle washing of the leaf surface would cause
minimal leaching from the leaf interior (Ondo et al.,
1984). In this way, dry deposition accounted for only a
few 14-day dry periods and several periods with 1–14
days of dry deposition. Thus, it must be kept in mind
that this is an underestimation of the annual dry
deposition. To avoid this, the dry deposition data were
recalculated by applying daily deposition rates to all the
rainless days in the collection period (Table 5). It should
be noticed that after applying this procedure, the total
N deposition was then overestimated because of the
overestimation of the wet deposition when assumed as
bulk deposition. A further correction was made by subtracting from the bulk deposition the dry deposition for
rainless days. This is to say that the fraction of dry
deposition estimated as branch washing and corrected
for surface efficiency as per Table 9 was subtracted from
the bulk deposition. However, since the bulk collector
resulted in a less efficient surface for dry deposition, and
there was a suspicion that NH+
4 dry deposition had
been underestimated, it is probable that even with this
correction the wet and total N deposition in Table 9 are
still underestimated. Dry deposition may go up to 75%
for N at the driest location (Agost).
The real values of total N deposition can be found
between the N-total deposition values of Table 5 and
those of Table 9. Thus, the maximum values of N total
deposition are obtained at Agost: 11.0 and 9.78 kg N
ha1 year1, respectively. Annual deposition rates in the
present study are similar to the annual N deposition
inputs (6–11 kg ha1 year1) found in southwestern
Sierra Nevada (Chorover et al., 1994), and they are
similar to N storage (4–10 kg ha 1 year 1) in the
vegetation increment of western forests (Johnson and
Lindberg, 1992), suggesting that current N deposition
rates may be near the assimilation capacity of the
overstory vegetation. Higher values for yearly inorganic
N-input have been reported in central Switzerland, with
a dry deposition of 16.8 kg N ha1 year1 and a bulk
deposition of 12.3 kg N ha1 year1(Schleppi et al.,
1998), and in the Alpine area of Austria, with 24–30 kg
N ha1 year 1, including dry and occult deposition, and
the wet component being approximately 14 kg N ha1
year 1 (Kalina et al., 2000).
Acknowledgements
This work has been financed by the Generalitat
Valenciana (Conselleria de Agricultura, Pesca y Alimentación) and Bancaixa. Thanks are given to Dr. Bea,
F. Sanz, C. Coll, P. Bornay, P. Vela, E. Calvo, S. Cosin
and J.J. Dieguez for helping us in the field and in the
laboratory. We are also indebted to Dr. Bytnerowicz
and Dr. Kruppa for their suggestions. J. Scheiding’s
corrections to the English text are appreciated.
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