trends in atmospheric deposition fluxes of sulphur and nitrogen in czech forests

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Trends in atmospheric deposition uxes of sulphur and nitrogen in Czech forests Iva H unová * , Jana Maznová, Pavel Kurfürst Czech Hydrometeorological Institute, Na Sabatce 17, 143 06 Prague 4 e Komo rany, Czech Republic article info Article history: Received 17 January 2013 Received in revised form 3 May 2013 Accepted 7 May 2013 Keywords: Atmospheric deposition Czech Republic Nitrogen Sulphur Forests abstract We present the temporal trends and spatial changes of deposition of sulphur and nitrogen in Czech forests based on records from long-term monitoring. A statistically signicant trend for sulphur was detected at most of the sites measuring for wet, dry, and total deposition uxes and at many of these the trend was also present for the period after 2000. The spatial pattern of the changes in sulphur deposition ux between 1995 and 2011 shows the decrease over the entire forested area in awide range of 18.1e0.2 g m 2 year 1 with the most pronounced improvement in formerly most impacted regions. Nitrogen still represents a considerable stress in many areas. The value of nitrogen deposition ux of 1 g m 2 year 1 is exceeded over a signicant portion of the country. On an equivalent basis, the ion ratios of NO 3 /SO 4 2 and NH 4 þ /SO 4 2 in precipitation show signicantly increasing trends in time similarly to those of pH. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Atmospheric deposition has decreased in the recent two de- cades in Europe (EEA, 2011) substantially due to a combination of several reasons as being: More stringent legislation with consequent implementation of effective countermeasures at large sources and decreasing emission of sulphur dioxide (SO 2 ) and to lesser extent of oxides of nitrogen (NO x ), Restructuring of industry and economic activities after pro- found political and economic changes in the 1990s, and Economic crises of recent years. Nevertheless, the deposition values in many European regions still remain far from satisfactory (EEA, 2011). The long-term moni- toring of precipitation chemistry and ambient air pollution is essential for quantication of both wet and dry deposition and revealing the time trends and spatial patterns under major envi- ronmental and climate change, and to link these with potential environmental impacts (Skefngton and Hill, 2012). In contrast to many other European countries, the national network for monitoring of ambient air quality and chemical composition of precipitation over the CR has operated for a fairly long time (H unová, 2001). The reason is that ambient air quality belonged to the most prominent envi- ronmental issues in the former Czechoslovakia and was negatively perceived by the public (Moldan and Schnoor, 1992). It was consid- ered an important factor contributing essentially to forest dieback (Fanta, 1997), and also had the most negative consequences for hu- man health which manifested, for example, in life expectancy decrease (Bobak and Leon, 1992). Sulphur dioxide (SO 2 ) as the rst pollutant started to be measured in ambient air in the CR in 1960s. The oldest records of precipitation chemistry date back to 1978. The major emission source of SO 2 was the combustion of poor local lignite with high sulphur content. The daily mean concentrations of SO 2 in the Czech part of the so called Black Trianglereached very high values, e.g. 1600 mgm 3 in January 1982 (CHMI unpublished data). Annual means reached hundreds of mgm 3 in the most polluted areas (Bridgman et al., 2002). Severe air pollution, ranking the former communist Czecho- slovakia in the most polluted European countries (Moldan and Schnoor, 1992), has decreased substantially. Profound socio- economic changes in Central Europe in 1989 resulted in signi- cant improvement of many environmental indicators, including industrial emissions. The trend in SO 2 , NO x and NH 3 emissions from the Czech sources is shown in Fig. 1 . The aim of the paper is to present the temporal trends and spatial patterns of sulphur and nitrogen deposition uxes in Czech mountain forests for the entire period between measurement commencement * Corresponding author. E-mail address: [email protected] (I. H unová). Contents lists available at SciVerse ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.envpol.2013.05.013 Environmental Pollution 184 (2014) 668e675

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Environmental Pollution 184 (2014) 668e675

Contents lists available

Environmental Pollution

journal homepage: www.elsevier .com/locate/envpol

Trends in atmospheric deposition fluxes of sulphur and nitrogenin Czech forests

Iva H�unová*, Jana Maznová, Pavel KurfürstCzech Hydrometeorological Institute, Na �Sabatce 17, 143 06 Prague 4 e Komo�rany, Czech Republic

a r t i c l e i n f o

Article history:Received 17 January 2013Received in revised form3 May 2013Accepted 7 May 2013

Keywords:Atmospheric depositionCzech RepublicNitrogenSulphurForests

* Corresponding author.E-mail address: [email protected] (I. H�unová).

0269-7491/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.envpol.2013.05.013

a b s t r a c t

We present the temporal trends and spatial changes of deposition of sulphur and nitrogen in Czech forestsbased on records from long-term monitoring. A statistically significant trend for sulphur was detected atmost of the sitesmeasuring forwet, dry, and total deposition fluxes and atmany of these the trendwas alsopresent for the period after 2000. The spatial pattern of the changes in sulphur deposition flux between1995 and 2011 shows the decrease over the entire forested area in a wide range of 18.1e0.2 g m�2 year�1

with the most pronounced improvement in formerly most impacted regions. Nitrogen still represents aconsiderable stress inmanyareas. The value of nitrogen deposition fluxof 1 gm�2 year�1 is exceeded over asignificant portion of the country. On an equivalent basis, the ion ratios of NO3

�/SO42� and NH4

þ/SO42� in

precipitation show significantly increasing trends in time similarly to those of pH.� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Atmospheric deposition has decreased in the recent two de-cades in Europe (EEA, 2011) substantially due to a combination ofseveral reasons as being:

� More stringent legislation with consequent implementation ofeffective countermeasures at large sources and decreasingemission of sulphur dioxide (SO2) and to lesser extent of oxidesof nitrogen (NOx),

� Restructuring of industry and economic activities after pro-found political and economic changes in the 1990’s, and

� Economic crises of recent years.

Nevertheless, the deposition values in many European regionsstill remain far from satisfactory (EEA, 2011). The long-term moni-toring of precipitation chemistry and ambient air pollution isessential for quantification of both wet and dry deposition andrevealing the time trends and spatial patterns under major envi-ronmental and climate change, and to link these with potentialenvironmental impacts (Skeffington and Hill, 2012). In contrast tomanyother Europeancountries, thenational network formonitoringof ambient air qualityandchemical compositionof precipitationover

All rights reserved.

the CR has operated for a fairly long time (H�unová, 2001). The reasonis that ambient air quality belonged to the most prominent envi-ronmental issues in the former Czechoslovakia and was negativelyperceived by the public (Moldan and Schnoor, 1992). It was consid-ered an important factor contributing essentially to forest dieback(Fanta, 1997), and also had the most negative consequences for hu-man health which manifested, for example, in life expectancydecrease (Bobak and Leon, 1992).

Sulphur dioxide (SO2) as the first pollutant started to bemeasured in ambient air in the CR in 1960s. The oldest records ofprecipitation chemistry date back to 1978. The major emissionsource of SO2 was the combustion of poor local lignite with highsulphur content. The daily mean concentrations of SO2 in the Czechpart of the so called “Black Triangle” reached very high values, e.g.1600 mg m�3 in January 1982 (CHMI unpublished data). Annualmeans reached hundreds of mg m�3 in the most polluted areas(Bridgman et al., 2002).

Severe air pollution, ranking the former communist Czecho-slovakia in the most polluted European countries (Moldan andSchnoor, 1992), has decreased substantially. Profound socio-economic changes in Central Europe in 1989 resulted in signifi-cant improvement of many environmental indicators, includingindustrial emissions. The trend in SO2, NOx and NH3 emissions fromthe Czech sources is shown in Fig. 1.

The aim of the paper is to present the temporal trends and spatialpatterns of sulphur andnitrogen depositionfluxes inCzechmountainforests for the entire period between measurement commencement

Fig. 1. SO2, NOx and NH3 emissions from Czech emission sources, 1990e2011.

I. H�unová et al. / Environmental Pollution 184 (2014) 668e675 669

and 2011. The trends of sulphur and nitrogen deposition for valuesmeasured until 2001 at selected Czech rural sites operated by theCHMI have already been published (H�unová et al., 2004). Neverthe-less, generally high inter-annual variations in meteorology canconfound attempts to detect trends in deposition through measure-ment. Long term data series of wet deposition of some two decadesare therefore required to measure deposition trends (Matejko et al.,2009). For approximation of the most recent deposition trends,however, we also separately checked the data after 2000.

2. Methods

2.1. Atmospheric deposition of sulphur and nitrogen

For our analysis, we used the data from 15 Czech sites (Table 1) operated by theCzech Hydrometeorological Institute collected in a nation-wide ambient air qualitydatabase (Ostatnická, 2012). The sites are situated as far away as possible andpractical from local sources to meet a demand for regional representativeness. Totaldeposition was calculated as a sum of wet and dry deposition fluxes. The evolutionof the atmospheric deposition measurements over the Czech rural area, thebeginning of precipitation composition measurements at individual sites andaccessibility of ambient air pollution concentration for dry deposition flux estima-tion is summarized in Table 2.

Wet depositionwas calculated based on automated wet-only samples onweeklybasis, analysed by standard methods with comprehensive QA/QC procedures,described in detail by H�unová et al. (2011). Dry deposition was estimated using theinferential method, combining measurements and modelling. This method,

Table 1Stations used for the analysis ranked according to increasing altitude.

Site Characterization Altitude[m a.s.l.]

Ostrava-Poruba Suburban site 242Hradec Králové Suburban site 276Praha-Libu�s Suburban site 301Kucha�rovice Agricultural area, south Moravia 334Ústí n.L.-Ko�ckov Suburban site 367Kocelovice Agricultural area,

St�redo�ceská hilly area519

Ko�setice Agricultural area,Czech-Moravian Highlands

535

Svratouch Agricultural area,�Z�dárské vrchy

735

P�rimda �Ceský Les 740�Cervená Nízký Jeseník 749Sou�s Jizerské hory Mts. 771Rudolice v Horách Mountain site, Kru�sné hoty Mts. 840Luisino údolí Mountain site, Orlické hory Mts. 875Bílý K�rí�z Mountain site, Moravsko-Slezské

Beskydy Mts.890

Krkono�se-Rýchory Mountain site, Krkono�se Mts. 1001

recommended by Fowler et al. (2009), is based on the assumption of a steady-staterelationship F ¼ c. vd, where the dry deposition flux (F) is a product of the meanconcentration (c) and of the dry deposition velocity (vd). Dry deposition velocitiesused were as follows: for SO2: vd ¼ 0.7 cm s�1 for forest (0.35 cm s�1 for areasoutside the forest), for NOx: vd ¼ 0.4 cm s�1 for forest (0.1 cm s�1 for areas outsidethe forest), for NH3: vd ¼ 0.66 cm s�1 for forest (0.44 cm s�1 for areas outside theforest). Deposition velocities for SO2, NOx and NH3 were calculated using theresistance analogy based on meteorological and land use data for the CR (Dvorakovaet al., 1995; Fiala et al., 2001). Annual mean concentrations of SO2, NOx and NH3wereused as recorded at the sites. If these were not available, we used an expert esti-mation based on the measurements from the neighbouring sites of the same typeaccording to EoI classification (EC, 1997). For SO2 direct measurements were avail-able for 12 out of 15 sites. For NOx, the availability of direct measurements was muchpoorer. Ambient NH3 concentrations were measured only at three sites in total overthe CR. After rejection of one site which represented an area highly impacted bychemical industry, we used the mean calculated from the recorded values of the tworemaining sites as a rough approximation for all sites in the CR. To summarize, totalsulphur deposition was calculated as a sum of dry SeSO2 and wet SeSO4

2� deposi-tion. Total nitrogen deposition was calculated as a sum of dry NeNOx, NeNH3, andwet NeNO3

� and NeNH4þ deposition.

In the dry deposition calculationwe did not account for particulate SeSO42�, and

NeNO3�, neither for NeHNO3(g) due to the unavailability of measured data.

Currently, particulate NeNO3� and gaseous HNO3 is not measured in the CR. For

particulate SeSO42� the only data available are from three sites (two rural and one

city-background). According to these records and using the vd ¼ 0.25 cm s�1 (Fialaet al., 2001) we estimated the annual mean particulate SeSO4

2� deposition to be0.18 g m�2 year�1. When compared to the total deposition, this portion canreasonably be considered negligible.

We also did not account for occult deposition as the data is not available.

2.2. Temporal trends

Different methods are used for detecting trends in atmospheric deposition(Marchetto et al., 2013). We analysed the data for temporal trends using the ManneKendall non-parametric test, recommended by the WMO for this kind of data andused in similar studies (Salmi et al., 2002; Sicard et al., 2007; Bashir et al., 2008). Thistest is used to identify the monotonous trend in data-series which does not showany seasonal variation or cycles. Atmospheric chemistry data, however, usually havedistinct seasonal variability and the ManneKendall test is thus applied to annualvalues to overcome the problem of seasonality and autocorrelation. Non-parametricmethods generally have the advantage of being insensitive to outliers, missingvalues are allowed, and data do not need to be normally distributed (Gilbert, 1987;Salmi et al., 2002), which was appropriate for the analysed data set. For calculationwe used software produced by the Finnish Meteorological Institute (Määttä et al.,2002). We analysed both nitrogen and sulphur deposition with respect to contri-bution of wet and dry deposition fluxes, and additionally the wet deposition of Hþ.Apart from deposition fluxes, we also checked the ratios of major ions in precipi-tation e nitrate to sulphate, and ammonia to sulphate e on an equivalent basis. Alltrends were detected for the entire period of measurement which differed amongindividual sites (see Table 2).

2.3. Spatial patterns

A fine resolution maps were developed to study the spatial patterns of atmo-spheric deposition. For construction of maps of total deposition we used all sites

Table 2Beginning of precipitation composition measurements at individual sites andaccessibility of ambient air pollution concentrations for dry deposition fluxestimation.

Site Hþ S/SO42� S/SO2 N/NO3

� N/NH4þ N/NOx

Wet Wet Dry Wet Wet Dry

Ostrava-Poruba 1995 1996 1996 1995 1995 1995Hradec Králové 1983 1983 1983 1983 1983 1984Praha-Libu�s 1986 1985 1992 1986 1988 1988Kucha�rovice 2002 2002 2002 2002 2002 2002Ústí n.L.-Ko�ckov 1991 1980 1991 1991 1991 1995Kocelovice 1997 1997 1997 1997 1997 e

Ko�setice 1990 1990 1990 1989 1990 1993Svratouch 1978 1978 1985 1978 1989 1994P�rimda 1990 1989 1991 1990 1990 1994�Cervená 1995 1995 1995 1995 1995 1997Sou�s 1996 1996 1993 1996 1996 1993Rudolice v Horách 1996 1996 1996 1996 1996 1996Luisino údolí 2003 2003 2003 2003 2003 2003Bílý K�rí�z 1989 1989 1989 1989 1989 1994Krkono�se-Rýchory 2002 2002 1995 2002 2002 1995

I. H�unová et al. / Environmental Pollution 184 (2014) 668e675670

classified as background according to the EoI classification, EC 1997 (Fig. 2). Thoughthere were more measuring sites at our disposal for the CR, we excluded localitiesclassified as urban, industrial and traffic. Their spatial representativeness is fairlysmall and so they were not considered in our spatial analysis.

The spatial pattern of wet-only deposition was derived from the data of pre-cipitation composition from sites operated by the CHMI, the Czech Geological Sur-vey, the Forestry and Game Management Institute and T.G. Masaryk Water ResearchInstitute. For improving the interpolation in border regions we benefited from dataprovided by the German LfULG and Polish WIOS and IMGW. To be specific: inaddition to 15 measuring sites operated by the CHMI (used also for temporal trendanalysis as described above), we used 28 other rural sites (22 for the Czech area, and6 for the Polish and German border regions), resulting in 43 sites in total forinterpolation. Maps were prepared using the Inverse Distance Weighted (IDW)spatial interpolation technique (e.g. Issaks and Srivastava, 1989). Important infor-mation on precipitation totals was gained from a map based on 750 precipitationgauging sites recorded by standard gauges by the CHMI. Due to the high density ofthe precipitation monitoring network, this map was prepared using universal linearkriging taking into account the dependence of precipitation totals on altitude (Tolaszet al., 2007).

The fields of annual concentrations of SO2 and NOx, essential for estimation ofdry deposition, were constructed using IDW interpolation of values from themeasuring sites in combinationwith the Gaussian dispersionmodel SYMOS 97 (EEA,2010) which adheres to the referencemodelling method of the CR. SYMOS 97 annualconcentrations were calculated using detailed emission inventories for the CR and

Fig. 2. Station network for precipitation composi

relevant meteorological data (Ostatnická, 2012). The maps were derived usingassimilation of measured and modelled data with subsequent interpolation ofresiduals.

The final deposition maps were produced by adding sulphur and nitrogen wetand dry deposition flux maps having a fine spatial resolution of 1 � 1 km. Themethod was described earlier in detail by H�unová et al. (2011). A digital map ofCzech forests produced from the European digital Land Use map (CORINE LandCover 2000, http://etc-lusi.eionet.europa.eu/CLC2000) was used. All maps wereprepared with ArcGIS Geostatistical Analyst (Johnston et al., 2001). The maps ofdifferences in deposition fluxes were prepared using the tools for map algebra. Weinvestigated the differences between the current situation and 1995 because for thisyear the first spatial patterns, both for sulphur and nitrogen atmospheric depositionfluxes, were possible to prepare. Before 1995 the measuring sites were sparse andtheir results did not allow derivation of the maps due to an insufficient number ofmeasuring points in space.

3. Results

Table 3 summarizes the temporal trends in sulphur and nitrogendeposition fluxes assessed separately for individual constituents(dry, wet and total). The results show that most sites recorded sig-nificant decreasing trends for sulphur. Apart fromwet deposition, asignificant decreasing trend for dry SeSO2 deposition flux was alsodetected for the period after 2000. For nitrogen the situation ismorecomplex. For NeNO3

� wet deposition a significant decreasing trendwas detected at only five out of fifteen assessed sites and for one ofthese five sites the significant decrease was detected also for theperiod after 2000. Three of these sites are classified as rural, two assuburban. For NeNOx dry deposition the statistically significantdecreasing trendwas recorded at six sites, four of these classified asrural, two of them as suburban. The only site with an increasingtrend for dry deposition of nitrogen (NeNOx) observed since 2000 isKrkono�se-Rýchory. Wet NeNH4

þ deposition decreased at two sitesonly, one of these recorded a decreasing trend only after 2000. Dueto the lackofmeasuring sites, dry depositionofNeNH3was assessedonlyas amean for the entireCRbasedon recordsof tworural sites, asmentioned above. No significant trend was found in those mea-surements. A significant decreasing trend for total N depositionwasfound only for four sites (two rural: Rudolice, Sou�s, and two sub-urban: Praha-Libu�s and Hradec Králové) and for two sites (Sou�s andOstrava-Poruba) after 2000.

The pH, an important indicator of precipitation acidity,increased steadily (Fig. 3a). Fig. 3b and c show the ratios between

tion and atmospheric deposition monitoring.

Table 3Trends of deposition fluxes of sulphur and nitrogen, Czech Republic, 1990e2011.

I. H�unová et al. / Environmental Pollution 184 (2014) 668e675 671

the major ions in precipitation. On an equivalent basis, the ratio ofnitrate to sulphate significantly increased over time (by 3% annu-ally) reflecting the changes in emissions. The same applied for theammonium to sulphate ratio, which was found to have significantlyincreased by 4% annually.

The analysis of spatial pattern shows that currently the sulphurload reaches less than 1 g m�2 year�1 over 90% forested area, with2e3 g m�2 year�1 over 0.1% of Czech forested area (Fig. S1 ofSupplement). The temporal change in spatial patterns of theannual total deposition flux of sulphur between 1995 and 2011 wasconsiderable (Fig. S2 of Supplement). It is obvious that sulphurdeposition decreased over the entire forested area during theperiod under study. This decrease was not uniform over the CR. Itranged widely between 18 g m�2 year�1 and 0.2 g m�2 year�1. Themost pronounced improvements we observed were in the regionsof north-western Bohemia in the Kru�sné hory, the Jizerské hory, theLu�zické hory and the Krkono�se Mts., in the �Ceskosaské �SvýcarskoNational Park and Ralská pahorkatina region. The analysis of spatialpattern of the annual total deposition flux of nitrogen in 2011(Fig. S3 of Supplement) reveals that currently portions of the Czechforests with highest deposition levels receive 2 g N m�2 year�1.According to our results, 71% of the forested area experienced totalN deposition higher than 1 g m�2 year�1, the value considered acritical load for European forests (Bobbink and Roelofs, 1995).Nevertheless, this represents an improvement as compared to thepast e in 1995 100% of forested area received a total N depositionhigher than 1 gm�2 year�1. The temporal change in spatial patternsof the annual total deposition flux of nitrogen between 1995 and2011 is minor (Fig. S4 of Supplement). In contrast to sulphur, thechanges in nitrogen deposition flux over time were more complex.We observed a certain decrease in total annual deposition duringthe period under investigation, though much milder in comparisonto sulphur, with a peak value of 2.5 g m�2 year�1. In some areas werecorded stagnation of the change in nitrogen deposition flux(some areas in southern and northern Moravia) and even an in-crease up to 0.4 gm�2 year�1 north of the Jizerské horyMts, close tothe Polish and German border.

4. Discussion

The presented study is based on the results of long-termmonitoring of atmospheric deposition in Central Europe, heavilyaffected by ambient air pollution in the past. For our analysis weused the concept of “total deposition” derived from wet and drydeposition fluxes (H�unová et al., 2011). We are aware however, thatthis total deposition does not equal the “real deposition”. It isunderestimated by not accounting for the contribution of severalcomponents which are likely to contribute considerably to the realatmospheric deposition. One of these components is occult depo-sition which varies widely and might be substantial particularly inmountain forested areas (Bridges et al., 2002; Seinfeldt and Pandis,1998). Such complexity has been shown earlier for sulphur depo-sition over the CR (H�unová et al., 2011). We also did not account forgaseous HNO3 due to the unavailability of data. HNO3 due to highdeposition velocity resulting from its high reactivity (Wesely andHicks, 2000) may, however, contribute significantly to the drydeposition of nitrogen even in regions with relatively low con-centrations (Flechard et al., 2011). We accounted only partly forNH3 using scarce information at disposal to get a rough approxi-mation of its contribution at measuring points, it was not consid-ered in developing spatial patterns. To measure the dry depositionfor HNO3 and NH3, the components which might contribute sub-stantially to the dry deposition of nitrogen, is costly and labourintensive. Dry deposition of nitrogen thus generally has high un-certainties and usually is estimated by different models (Suttonet al., 2011). Currently we work on estimation of gaseous HNO3

contribution to dry deposition of nitrogen over the CR using anEularian photochemical dispersion model CAMx, the Comprehen-sive Air Quality Model with extensions (ESSS, 2011), coupled with ahigh resolution regional numerical weather prediction modelAladin.

We used a fixed deposition velocity for the entire period of ourlong-term analysis. We are aware, however, that it is a roughapproximation with consequent high uncertainity in this aspect. Ithas been recognized that long term (1 year) average deposition

Fig. 3. Annual means of pH (a), the ratio of NO3�/SO4

2� (b) and NH4þ/SO4

2� (c) in precipitation, Czech mountain forest sites, 1989e2011.

I. H�unová et al. / Environmental Pollution 184 (2014) 668e675672

velocities change with time due to the change in the chemicalclimatology at the regional scale (Fowler et al., 2009; Zhang et al.,2003).

Not accounting for occult deposition, gaseous HNO3, NH3, andusing fixed deposition velocities for our analysis constitute themajor weaknesses of the presented study. It is likely to result inunderestimation of nitrogen deposition which might be substan-tial. It is urgently needed to work on these issues to further refine

the quantification of deposition fluxes over the CR. Nevertheless,the study presents a valuable indication of changes of spatial pat-terns and long-term trends of deposition based on componentsmeasured during the entire duration of long-term monitoringprogram.

The decrease of sulphur emissions in Europe and consequentprompt decrease of sulphur air pollution and deposition present asuccessful story in ambient air quality management. In the CR,

I. H�unová et al. / Environmental Pollution 184 (2014) 668e675 673

major decreases of sulphur deposition were recorded in areasadjacent to large emission sources (H�unová et al., 2004). Incontrast, the control of nitrogen emissions has not been as suc-cessful as yet (EEA, 2011).

Relatively profound changes in emissions of SO2, NOx, and NH3recorded during last two decades in the CR were also recordedelsewhere (Fowler et al., 2007). The large changes in emission re-gimes in Europe (EEA, 2011) have led to changes in the atmosphericresidence time of nitrogen.

Both sulphur and nitrogen play an important role in thebiogeochemistry of forests as essential plant nutrients and indis-pensable substances for many reactions in living cell. However, theincrease in sulphur and nitrogen deposition cannot be consideredas universally beneficial for ecosystems (Kravitz et al., 2009). Thebiogeochemical cycles of sulphur and nitrogen are not independentof each other, but are coupled, even when considering only fluxesinto and out of the atmosphere (Jarvie et al., 2012). A changingchemical climate significantly effects transformation and removalrates and thereby the sourceereceptor relationship (Rodhe, 1981;Fowler et al., 2007). Increasing emissions of NOx may reduce theatmospheric concentration of the OH radical and thereby slowdown the gas phase oxidation of SO2 (Rodhe et al., 1981). The un-even decrease of emissions is assumed to shift the equilibriumbetween nitric acid and ammonium nitrate towards particulatephase (Fagerli and Aas, 2008). The observed changes in sulphateand nitrate deposition fluxes over time induced by changes inemissions might have many important implications for soil, waterand biota (Bell and Treshow, 2002; Bobbink and Roelofs, 1995;Forsius et al., 2005; Galloway et al., 2008). For example Savva andBerninger (2010) reported a large scale decrease in growth ofScots pine significantly related to sulphur deposition in low-pollution pristine environments of boreal Eurasia, with an addi-tional effect of higher sensitivity to drought. Nitrogen deposition atcurrent rates is known to cause widespread loss of specie richnessin a wide range of ecosystem types in Britain (Maskell et al., 2010).Van Dobben and De Vries (2010) found a small but significant effectof anthropogenic atmospheric deposition on the floral diversity offorests in Europe that is additional to the effect of major factorswhich are soil, climate, and tree species, and indicated a slight shifttowards nitrofytic species at high N deposition. Oulehle et al. (2011)reported that, based on their results from Nacetin, a site repre-senting a typical Czech and in broader sense a Central Europeanforested area, reducing sulphur deposition resulted in major im-pacts on forest organic matter cycling, causing a reversal of nitro-gen enrichment of ecosystems, cessation of nitrate leaching, and amajor loss of accumulated organic soil carbon and nitrogen stocks.Recent, wide-spread rising trends in dissolved organic carbon(DOC) in the surface waters on glaciated, acid-sensitive regionsacross Europe and North America are likely to be related to changein deposition chemistry and catchment acid-sensitivity (Monteithet al., 2007).

In the CR, ranking among the regions with the highest loads ofacid deposition in Europe in the past (H�unová et al., 2004),numerous activities e empirical research, modelling studies, andlong-term monitoring e were and still are carried out to elucidatethe geochemical and biological implications for forests. Czechforested area accounts for about 33% (representing 26 430 km2) ofthe entire surface area. Norway spruce (Picea abies) an importanttimber tree, is the dominant tree species covering nearly 48% of thetotal forested area. Pine trees (Pinus spp), with 14%, rank second.The coniferous forests accounts for 67% of the Czech forested area.Oak (Quercus spp) with 7.4% and beech (Fagus sylvatica) with 7.2%are the most common deciduous species (ÚHÚL, 2007).

During the last 50 years, ambient air pollution has been aserious threat for Czech forests. Large-scale forest damage, mainly

on Norway spruce in mountain and lower mountain areas, hasnegatively influenced the functions of forest ecosystems (Vaceket al., 2013). In spite of substantial improvement in air quality, at-mospheric deposition still remains a negative factor for forests(Bohá�cová et al., 2010).

Long-term research in Czech mountain forests showed that soilacidification presents a serious problem, being caused by a com-bination of both natural and antropogenic factors including acidbedrocks (esp. granites), acid deposition, soil leaching by relativehigh precipitation totals, and forest species composition, leading tothe development of poor, acid or strongly acid soils e Cambisols,and Podzols (Bor�uvka et al., 2005). Particularly sensitive to acidi-fication is topsoil (Hédl et al., 2011).

In highly acidified regions in Central Europe, the commonforestry practice of planting Norway spruce has probably largelycontributed to soil acidification (Oulehle and Hru�ska, 2005). Theacidification leads to soil depletion. The basic cations e mostlycalcium and magnesium are leaching from the soil horizons, andincreased mobility of aluminium ions, toxic to the root systems, isobserved (Vacek et al., 2013). Lomský et al. (2012) who evaluatedlong-term changes in the forest health as a result of the pollutionloads and mineral nutrition indicated, that ongoing nitrogendeposition resulted in unbalanced nutrition and disturbed N:P andN:Mg ratios in the needles and soil. They proposed that acidifica-tion of soil and the phosphorus and magnesium deficiency arepotential limiting factors to the forest nutrition in the future.Nutritional imbalance in trees imposes lower resistance to bioticand abiotic factors (Hru�ska and Ciencala, 2002). Some naturalmitigation of described processes, at least during the growingseason, is reported by T�uma et al. (2012). The tall fern (Athyriumdistentifolium Tausch ex Opiz) spreading over clearings particularlyof Norway spruce forests at altitude above 1100 m a.s.l. andcovering large areas in mountainous regions of Central Europetakes up nutrients in large amounts and immobilizes them in bothliving and dead plants. The release of accumulated nutrients andrecycling of elements is very slow, however.

Hru�ska et al. (2002) reported only a very slow acidificationrecovery in Czech forests, and predicted that severely damagedsites, under continued pressure from intensive forestry respon-sible for approximately one third of the net base cation lossthrough accumulation in harvested biomass, would not return toa good environmental shape in the near future. The future re-covery of soil water is predicted to be significantly better in beechcomparing to spruce forests (Oulehle et al., 2007). Oulehle et al.(2012) presented a new version of the biogeochemical modelMAGIC simulating C/N dynamics indicating that despite recentdeposition reductions and recovery, progressive nitrogen satu-ration at coniferous-forested sites in the CR would result inincreased future nitrate leaching, ecosystem eutrophication andre-acidification.

Natural systems are being affected by climate change, particu-larly temperature increases, changes in precipitation patterns, andincreasing frequency of extreme events (IPCC, 2007). The acidifi-cation processes have not been investigated in relation to IPCCpredicted changes for altered rainfall patterns in Europe e

increased extreme events, decreased summer precipitation,increased winter precipitation. The projections to future anticipateincreased frequency of extreme events, such as heat waves, heavyprecipitation, drought, wind storms, and storm surges in Europe(Beniston et al., 2007), the effects of which can be critical for forests(Fuhrer et al., 2006). The major anticipated impact of projectedclimate change assumes that drought would become a key limitingfactor for Czech forests at lower altitudes, while increased tem-perature along with the prolonged vegetation season at higher al-titudes might be beneficial to forest vegetation (Hlásny et al., 2011).

I. H�unová et al. / Environmental Pollution 184 (2014) 668e675674

The urgent need to address the knowledge gaps in interaction be-tween air pollution, climate change and forests, has been recentlystressed (Serengil et al., 2011; Matyssek et al., 2012).

5. Conclusions

Our results reveal some significant changes over the periodobserved. Our analysis of trends in atmospheric deposition fluxes ofsulphur and nitrogen in Czech forests can be concluded as follows.

1. Trends of S and N deposition fluxes at individual sites analysedfor the entire measuring period (different for individual sites):

A statistically significant decreasing trend for sulphur wasdetected at most of the 15 measuring sites for wet (SeSO4

2�), dry(SeSO2), and total deposition fluxes. At many of these sites statis-tically significant decreasing trends for S were recorded also for thelatest period, after 2000.

The results for N are more complex. At 1/3 out of 15 sites sta-tistically significant decreasing trends for N were detected for N-oxidized (wet: NeNO3

�, dry: NeNOx), at few of them this trendapplies also for the recent period after 2000. One site (mountainlocality Krkono�se-Rýchory) was even found to have experiencedstatistically significant increasing trend for NeNOx after 2000. ForN-reduced (wet: NeNH4

þ) only two sites recorded a statisticallysignificant trend, one of these after 2000. Trends for dry NeNH3were not calculated because the data are not available. For total Ndeposition flux a statistically significant decreasing trend wasrecorded at five sites, for two of them after 2000.

2. Changes in spatial patterns of S and N deposition fluxes overthe last 17 years:

The spatial pattern of the changes in sulphur deposition fluxbetween 1995 and 2011 shows the decrease over the entire forestedarea in fairly wide range of 18.1e0.2 g m�2 year�1 with the mostpronounced improvement in the north-western Bohemia, infa-mously known as a part of the so-called Black Triangle in the past.

Nitrogen still represents a considerable stress inmany areas. Thevalue of nitrogen deposition flux of 1 g m�2 year�1 (the critical loadset up for Central European coniferous forests) is still exceeded oversignificant portion of the country. In contrast to sulphur, thechanges in the spatial pattern of nitrogen deposition flux are muchmore complex. The improvement is not that big, with the highestdecrease in deposition flux a mere 2.5 g m�2 year�1 in north-western Bohemia (the Kru�sné hory and Krkono�se Mts.), stagna-tion in some areas in southern and northern Moravia and even amild increase by 0.4 g m�2 year�1 in the area north of the Jizerskéhory Mts. close to the Polish and German borders.

It is urgently needed to work on further refinement of thequantification of deposition fluxes over the CR.

3. Changes in ion ratios in atmospheric precipitation:

On an equivalent basis, the ion ratios of NO3�/SO4

2� and NH4þ/

SO42� in precipitation show a statistically significant decreasing

trend due to the changes in emissions indicating the changes inatmospheric chemistry patterns with likely implications for theenvironment. The acidity indicated by pH shows significantlyincreasing trend over the period under review.

4. Possible geochemical and biological implications of the re-ported findings are numerous and have been investigated inempirical research, modelling studies and long-term moni-toring. The elucidation of meaning of the observed changes in

the framework of global climate change remains a scientificchallenge and is yet to be established.

Acknowledgements

We would like to acknowledge the grant QI112A168 (ForSoil) ofthe Czech Ministry for Agriculture for partial support of thiscontribution. The input data on meteorology and precipitationchemistry used for the analysis have been provided by the CzechHydrometeorological Institute. We thank our colleague, LintonCorbet, who revised the English for style and commented the finalversion of the manuscript. We also highly appreciate comments oftwo anonymous reviewers to the earlier version of the manuscript.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.envpol.2013.05.013.

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