Precipitation quality stations operated by CHMI, ČGÚ, VÚV, VÚLHM and HBÚ AV ČR from which data on precipitation quality and atmospheric deposition were processed in 2001, are plotted in Fig. 3.1. Information on individual stations and on measuring methods is listed in Table 3.4. In 1996, most of the CHMI stations switched over to weekly sampling intervals in line with the EMEP methodology. In 1997 the special weekly bulk sampling for heavy metals was introduced at these stations. At the stations of ČGÚ, VÚV and VÚLHM there are taken bulk samples in monthly intervals.

Tables 3.5 and 3.6 contain average values of the chemical composition of atmospheric precipitation and the values of the 2001 annual wet deposition.

Wet deposition charts were compiled for selected ions on the basis of all-round chemical analyses of precipitation samples, specifically for SO₄^2- - S, NO₃^- - N, NH₄⁺ - N, H⁺ (pH), F^-, Pb²⁺, Cd²⁺, and Ni²⁺.

Deposition charts for chlorides are not included, as their concentrations do not show any systematic local fluctuations, and some VÚV and VÚLHM stations have constantly higher values (Podbaba, Lužnice, Kamýk�). The interpretation of such diverse results is rather problematic.

The above ions were selected to represent deposition fields with regard to their considerable impact on the various spheres of the environment. Wet deposition charts for each of the ions were derived from the field of ion concentrations in precipitation (based on annual mean concentrations weighted by precipitation totals calculated from the data observed), and from the field of annual precipitation totals which was generated on data from 750 precipitation gauging stations, taking into account the altitude�s effect on precipitation amount. When constructing wet deposition fields, results of wet-only samples are preferred to bulk samples and weekly samples are preferred to monthly samples. Data from the stations operated by ČGÚ, VÚV and VÚLHM which are based on monthly bulk sampling (see Table. 3.4) are modified by empirical coefficients expressing the individual ions� ratios in bulk and wet-only samples (values for each of the ions from 0.94 to 1.35) for the purpose of the development of the wet deposition charts. To optimize the production of maps based on the results from various sources and obtained through various methodology and with various sample intervals individual stations were weighted relatively in correspondence with reliability of the measured data from 0.6 to 1.0.

In addition to wet deposition, also dry and total deposition charts are included for sulphur, nitrogen and hydrogen ions. Dry sulphur and nitrogen deposition was calculated using fields of annual mean SO₂ and NO_x concentrations for the Czech Republic, and the gas deposition rates found in [18] for SO₂ 0.7 cm.s^-1/0.35 cm.s^-1, and NO_x 0.4 cm.s^-1/0.1 cm.s^-1, in case of forested/unforested area. Total deposition charts were produced by adding S and N wet and dry deposition charts. The wet hydrogen ion deposition chart was compiled on the base of pH values measured in precipitation. Dry hydrogen ion deposition reflects SO₂ and NO_x deposition based on stechiometry, assuming their acid reaction in the environment. The total hydrogen ion deposition chart was developed by summation of wet and dry deposition charts.

The average deposition fluxes of S, N and H are presented in the following table:

Tab. 3.1 Average deposition fluxes S, N and H in the Czech Republic, 2001

Throughfall sulphur deposition chart was generated for forested areas from the field of sulphur concentrations in throughfall and a verified field of precipitation, which was modified by a percentage of precipitation amounts measured under canopy at each station (40 to 100 % of precipitation totals in 2001). Throughfall deposition generally includes wet vertical and horizontal deposition and dry deposition of particles and gases in forests; in case of sulphur, circulation of which within the forests is negligible, throughfall deposition is considered to provide a good estimate of total deposition.

Heavy metal wet deposition charts for Pb, Cd and Ni were derived from concentrations of these metals in bulk precipitation samples at individual stations. The field of deposition flows of Pb and Cd contained in SPM (dry Pb and Cd deposition) were derived from the fields of these metals� concentrations in the ambient air (Chapter 2.3). The deposition rate of Cd contained in SPM was taken as 0.27 cm.s^-1 for a forest and 0.1 cm.s^-1 for unforested terrain; the figures for Pb are 0.25 cm.s^-1 for a forest and 0.08 cm.s^-1 for unforested terrain [18].

Results

• Wet sulphur deposition decreased after 1997 in comparison with the levels from the period 1994–1997 by 40 %. Since 2000 the profound decrease has not continued and the values remained at the level of 1999. In 2001 the sulphur deposition showed a slightly increase in comparison with the year 2000, for instance in the Beskydy Mts. Dry sulphur deposition decreased even by 60 % in 1998–1999 and in 2001 it stagnated, which is coherent with SO₂ concentrations in the ambient air. The field of total sulphur deposition is the sum of wet and dry depositions and it shows the total sulphur deposition amounting to 77,800 t for the Czech Republic�s territory for the year 2001 (see Table 3.2). After the decrease from the values above 100,000 t, in the period 1999–2001 the sulphur deposition remains at the level about 75,000 t per year. Sulphur deposition reached the maximum values in the Krušné hory Mts., the Jizerské hory Mts., the Krkonoše Mts. and the Orlické hory Mts., and newly also in the Železné hory Mts. and the Beskydy Mts. The lowest values were recorded in the foothills of the Šumava and Český les Mts.
• The throughfall sulphur deposition field shows maximum values in the same areas as the total deposition calculated with the use of another method. Throughfall deposition reaches higher values in mountainous areas in comparison with total deposition. The contribution can be attributed to horizontal deposition which is not included in total summary deposition because of uncertainties. Hoarfrost, icing and rime, and fog are normally highly concentrated and may significantly contribute to sulphur and other elements� deposition in mountainous areas. The problem is in a very erratic character of this type of deposition from place to place where some uncertainties may occur when extrapolating to a wider area. In such case, the field of throughfall deposition can be considered as illustrative for what values the total sulphur deposition might reach. Table 3.3 shows the values of total and throughfall deposition for the forested areas of the Czech Republic in recent years. The values confirm the already mentioned decline of total sulphur deposition in the previous years and stress the significance of throughfall deposition as the method for determination of total sulphur deposition.
• The fields of wet and dry nitrogen deposition are generally the same as in the past years. After the slight decrease of dry deposition of oxidized nitrogen forms by 10–20 % in the second half of the 90�s stagnation has been reached; the total deposition is 48,000 t of N-ox per year (see Table 3.2). In 2000–2001 further decrease of dry nitrogen deposition was recorded which however apparently reflects the specification by modelling the field of NO_x concentrations in the ambient air.
• The charts and values of both wet and dry deposition of hydrogen ions have shown stagnation since 1999. In the second half of the 90�s both wet and dry depositions of hydrogen ions decreased by 50 % per the whole area of the Czech Republic, the decrease of dry deposition of hydrogen ions values was in coherence with the already mentioned decrease of dry deposition of SO₂ - S and NO_x - N.
• The field of wet �bulk� deposition of lead ions illustrates general stagnation to a slight increase of deposition in 2001 after the decrease by up to 20 % recorded in 1998–1999. Less significant is the lead anomaly in the area of the Jizerské hory Mts. and the Krkonoše Mts., i.e. in the area with the marked anomalies of both wet and dry cadmium deposition.
• After the decrease of wet deposition of a number of elements in the second half of the 90�s, the development of annual wet deposition of the main elements as measured at selected stations in the Czech Republic (Fig. 3.20) shows sulphur, nitrogen and lead deposition stagnation instead. The decrease of sulphate deposition was substantial not only at the exposed stations as Ústí nad Labem, Prague-Libuš or Hradec Králové but it was also obvious at the background stations Košetice and Svratouch. The marked decrease of sulphur deposition is directly linked with the change of the proportion of sulphur and nitrogen at the stations. The deposition of both elements has been balanced since the second half of the 90�s, at the background stations the nitrogen deposition is slightly higher (Košetice). The decrease was substantial at the station Ústí nad Labem where the wet sulphate deposition decreased by 60 % after 1995 and where the decrease of other substances (NO₃^-, NH₄⁺, Pb) was also obvious. The decrease of sulphur and nitrogen deposition was the direct output of the programme aimed at the reduction and desulphurization of electric power stations in northwest Bohemia (1994 – Počerady, 1995 – Prunéřov). The decrease in wet deposition of hydrogen ions in recent five years by 50 % can be observed at all stations.

Tab. 3.2 Estimate of the total annual deposition in the Czech Republic (78,841 sq. km) in tonnes, 2001

Tab. 3.3 Estimate of the total annual deposition of sulphur on the forrested part of the Czech Republic (16,990 sq. km) in tonnes, 1997–2001

Tab. 3.4 Station networks monitoring precipitation quality and atmospheric deposition, 2001

Tab. 3.5 Mean annual concentrations of principal pollutants in precipitation at given stations, 2001

Tab. 3.6 Annual wet atmospheric deposition at given stations, 2001

Fig. 3.1 Station networks monitoring precipitation quality and atmospheric deposition, 2001

Fig. 3.2 Fields of annual wet deposition of sulphur (SO₄^2- - S), 2001

Fig. 3.3 Fields of annual dry deposition of sulphur (SO2 - S), 2001

Fig. 3.4 Fields of annual total deposition of sulphur, 2001

Fig. 3.5 Fields of annual throughfall deposition of sulphur, 2001

Fig. 3.6 Fields of annual wet deposition of nitrogen (NO₃^- - N), 2001

Fig. 3.7 Fields of annual wet deposition of nitrogen (NH₄⁺ - N), 2001

Fig. 3.8 Fields of annual total wet deposition of nitrogen, 2001

Fig. 3.9 Fields of annual dry deposition of nitrogen (NO_x - N), 2001

Fig. 3.10 Fields of annual total deposition of nitrogen, 2001

Fig. 3.11 Fields of annual wet deposition of hydrogen ions, 2001

Fig. 3.12 Fields of annual dry deposition of hydrogen ions corresponding to SO₂ and NO_x deposition, 2001

Fig. 3.13 Fields of annual total deposition of hydrogen ions, 2001

Fig. 3.14 Fields of annual wet deposition of fluoride ions, 2001

Fig. 3.15 Fields of annual wet deposition of lead ions, 2001

Fig. 3.16 Fields of annual dry deposition of lead, 2001

Fig. 3.17 Fields of annual wet deposition of cadmium ions, 2001

Fig. 3.18 Fields of annual dry deposition of cadmium, 2001

Fig. 3.19 Fields of annual wet deposition of nickel ions, 2001

Fig. 3.20 Annual wet deposition at selected stations between 1990 and 2001, the Czech Republic