Precipitation quality stations operated by CHMI, ČGÚ, VÚV, VÚLHM, IFER, HBÚ AV ČR, IMGW and PIOS (Poland), from which data on precipitation quality and atmospheric deposition were processed in 2000, are plotted in Fig. 3-1. Data from LfUG (Germany) have not been supplied. 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 Black Triangle stations of LfUG and PIOS there is also implemented wet-only measurement in weekly intervals. 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 2000 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 - S, NO₃ - N, NH₄ - N, H⁺ (pH), Cl^-, F^-, Pb²⁺, Cd²⁺, and Ni²⁺. These 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 Tab. 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. Several markedly higher values of chloride ions recorded at VÚV and VÚLHM stations were not included while constructing the maps.

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 [7] 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 Table 3-1.

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 120 % of precipitation totals in 2000). 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 2.3.6). 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 [7]. The fields of throughfall Pb and Cd deposition charts were generated in a similar way as the fields of throughfall sulphur deposition.

Results

� Wet sulphur deposition decreased after 1997 in comparison with the levels from the period 1994–1997 by 40 %. In 2000 the profound decrease ceased and the values remained at the level of 1999. Dry sulphur deposition decreased even by 60 % in the previous years and this trend continued also in 2000, which is coherent with lower 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 decrease in sulphur deposition to the value of 70,400 t for the Czech Republic�s territory (see Table 3-2). Sulphur deposition reached the maximum values in the Krušné hory Mts., the Jizerské hory Mts., the Krkonoše Mts. and Orlické hory Mts. The lowest values were recorded in the foothills of the Šumava and Český les Mts.

� A marked maximum of the throughfall deposition field is, similarly as in the previous years, in a broader area of the Orlické hory Mts. Generally, a throughfall deposition reaches higher values in mountainous areas in comparison with a total summary 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 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 previous years. For the second half of the 90�s the slight decrease of oxidized nitrogen forms by 10–20 % mentioned in 1999 can be confirmed. In 2000 the decrease of dry nitrogen deposition was recorded which however apparently reflects further specification by modelling the field of NO_x concentrations in the ambient air.

� The charts and values of wet deposition of hydrogen ions show stagnation as compared with the year 1999, the decrease of dry deposition of hydrogen ions values is in a coherence with the already mentioned decrease of dry deposition of SO₂ - S and NO_x - N. 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 (see Tab. 3-1 and 3-2).

� After 1997 the decrease of wet �bulk� lead deposition by 20 % was detected, the level of the 2000 values remained the same as in 1999. The charts of wet �bulk� deposition of heavy metals show decline, as concerns both area and values; the highest deposition levels, similarly as in previous years, occurred in mountainous areas of the Krušné hory Mts., the Jizerské hory Mts., the Krkonoše Mts., the Orlické hory Mts. This territorial anomaly is accompanied by the deposition of fluoride ions.

� The development of annual wet deposition of the main elements as measured at selected stations in the Czech Republic (Fig. 3-23) shows the decrease of wet deposition of a number of elements in the second half of the 90�s. The decrease of sulphate deposition is substantial not only at the exposed stations as Ústí nad Labem, Prague-Libuš or Hradec Králové but it is also obvious at the background stations Košetice and Svratouch. This decrease is 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) is also obvious. The decrease of sulphur and nitrogen deposition is the direct output of the programme aimed at the reduction and desulphurization of electric power stations in northwest Bohemia (1994 – Počerady, 1995 – Prunéřov). The lower level of the wet deposition of lead is significant at all monitored stations. The decrease in wet deposition of hydrogen ions in recent five years by 50 % can be observed at all stations.

Tab. 3-1 Average deposition fluxes S, N and H in the Czech Republic, 2000

Tab. 3-2 Estimate of the total annual deposition in the Czech Republic (78,841 sq. km) in tonnes, 2000

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, 1997–2000

 Tab. 3-4 Station networks monitoring precipitation quality and atmospheric deposition, 2000

Explanatory notes:
M1 – monthly wet-only – autom. sampler
M2 – monthly bulk samples
M3 – monthly wet-only – daily cumulated samples
M4 – monthly throughfall
W1 – weekly wet-only – autom. sampler
W3 – weekly wet-only – daily cumulated samples
HM – weekly bulk for heavy metals analysis
(HM) – heavy metals analysis in mentioned sampling M1–W3
F2 – 14-day bulk samples
F4 – 14-day throughfall