The effect of acid rain and altitude on concentration, δ34S, and δ18O of sulfate in the water from Sudety Mountains, Poland

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Chemical Geology 249 (2008) 36 – 51 www.elsevier.com/locate/chemgeo

The effect of acid rain and altitude on concentration, δ 34 S, and δ 18 O of sulfate in the water from Sudety Mountains, Poland Anna Szynkiewicz a,⁎,1 , Magdalena Modelska a , Mariusz Orion Jędrysek a , Maria Mastalerz b a

b

Wrocław University, Institute of Geological Sciences, Cybulskiego 30, Wrocław, Poland Indiana Geological Survey, Indiana University, 611 North Walnut Grove, Bloomington, IN 47405, USA Received 28 October 2006; received in revised form 7 November 2007; accepted 24 November 2007 Editor: D. Rickard

Abstract The analyses of sulfate content, δ34S and δ18O of dissolved sulfate, and δ18O of water were carried out in a 14 km2 crystalline massif located in the Sudety Mountains (SW Poland) to 1) assess the amount of the sulfate delivered to the surface and groundwater systems by modern atmospheric precipitation, 2) determine the effect of altitude on these parameters, and 3) investigate their seasonal variations. In April and November of 2002, August 2003, and March and September of 2005, samples of water were collected from springs and streams of the massif. During these seasons, sulfate contents and δ18O(SO2− 4 ) values varied from 5.80 to 18.00 mg/l and from 3.96 to 8.23‰, respectively, showing distinctively higher values of δ18O(SO2− 4 ) in wet seasons. The δ34S(SO2− 4 ) values had a relatively narrow range from 4.09 to 5.28‰ and were similar to those reported for organic matter in soil and the canopy throughfall in the Sudety Mountains. 18 18 2− Sulfate content, δ34S(SO2− 4 ), δ O(SO4 ), and δ O(H2O) values revealed a remarkable dependence on the altitude. The calculated altitude effects for five season averages of these parameters were − 1.00 mg/l/100 m, −0.18‰/100 m, − 0.27‰/100 m, and − 0.17‰/100 m, respectively. This dependence on the altitude resulted mainly from the mixing of sulfates of different origins such as anthropogenic sulfate, sulfate produced in the soil within the weathered zone of the massif, and that one from the tree canopy. The oxygen isotope mass balance indicates that, in the study area, about one third of the sulfate delivered to the surface and groundwater by modern precipitation comes from anthropogenic pollution. Further interaction of meteoric water within the weathered rocks causes a continuous decrease of δ18O(SO2− 4 ) values resulting from biological transformation of the sulfate due to plant vegetation and decomposition of organic matter. © 2007 Elsevier B.V. All rights reserved. Keywords: Freshwater sulfate; Sulfur isotopes; Oxygen isotopes; Sudety Mountains

⁎ Corresponding author. Tel.: +48 71 3759 236; fax: +48 71 3759 371. E-mail addresses: [email protected] (A. Szynkiewicz), [email protected] (M. Modelska), [email protected] (M.O. Jędrysek), [email protected] (M. Mastalerz). 1 Now at: Indiana University, 1001 E 10th St, Bloomington, IN 47405, USA. 0009-2541/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.chemgeo.2007.11.006

1. Introduction Recently stable isotope methods have found a wide application in hydrological studies. They are commonly used to understand the water cycles in freshwater

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environments, with special emphasis on the direction of water flow, sources of water, time of water residence, and the extent of water–rock interactions. The isotopic mass balance, moreover, is an important tool for quantitative evaluations of freshwater resources. Among stable isotopes, sulfur and oxygen isotopic compositions of sulfate dissolved in waters are the most suitable for isotope mass balance calculations, because sulfate ions have shown high thermodynamic stability and very low half-time (104–107 years) of isotopic exchange between other sulfur and oxygen-bearing compounds dissolved in waters (Lloyd, 1968; Chiba and Sakai, 1985). Because of the dynamic water cycle on the earth's surface and the relatively short time of water residence in many shallow aquifers, the isotopic exchange between sulfate and water has been accepted as negligible. Therefore, any change in primary sulfate isotope composition implies that chemical transformation or mixing of different origin sulfates has taken place. Observed large variations of sulfur isotopic composition (δ34S values from c.a. − 50 to c.a. + 30‰) in the lithosphere, in addition to the spatial–temporal dependence of oxygen isotopic composition of precipitation, leave a significant fingerprint on sulfate dissolved in waters (e.g. Clark and Fritz, 1997). For that reason, sulfate isotopic composition has been used in many studies to examine the sulfate sources and processes affecting its content during the hydrological cycle (e.g. Gélineau et al., 1989; Dowuona et al., 1993; Van Stempvoort et al., 1994; Groscheová et al., 1998; Eckardt and Spiro, 1999; Dogramaci et al., 2001; Berner et al., 2002; Cortecci et al., 2002; Massmann et al., 2003; Kirste et al., 2003; Trembaczowski et al., 2004; Edraki et al., 2005; Novák at al., 2005a,b; Schiff et al., 2005; Bottrell and Newton, 2006; Jezierski et al., 2006; Ryu et al., 2006). It was shown that sulfate isotopic composition in freshwater systems might be controlled by local conditions including geological and hydrological settings, precipitation, biological activity (controlled by dissimilatory sulfate reduction), and geographical location. Therefore, the study of sulfate isotopic composition is a powerful tool for tracing, quantitatively and qualitatively, the water flows and water–rock interaction in a distinctive environment. The main goal of this work was the qualitative and quantitative assessment of the amount of sulfate delivered by modern atmospheric precipitation to the surface water and groundwater systems in the mountainous crystalline massif. It is of relevance for the area of the crystalline massif located in the Sudety Mountains, because this area has been affected by precipitation contaminated by emissions from the combustion of fossil

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fuels in the Black Triangle, one of the largest polluted areas in SW Poland. Jezierski et al. (2006) suggested, however, that modern anthropogenic sulfate input to the freshwater system in the Sudety Mountains might be negligible, and that, instead, factors of geo-and biogenic origin affect the isotopic composition of sulfate during downward flow. Nevertheless, in their study (Jezierski et al., 2006), multiple sulfate sources and, consequently, varying isotopic composition of the sulfate made the quantitative calculations of the anthropogenic sulfate input problematic. Therefore, for more reliable assessment of the quantity of anthropogenically-derived sulfate, we selected another catchment in this area, where sulfate inputs are controlled by a limited number of factors. In this case, two isotopically distinctive factors are dominant: 1) precipitation and 2) the presence of a relatively shallow zone of weathered rocks. In Fig. 1, we present a simplified model showing expected interactions between sulfur reservoirs of geogenic, biogenic and atmospheric origin in the studied region. During five different seasons between 2002 and 2005, the isotopic (S, O) analyses of sulfate and its concentration in surface waters and groundwater were carried out to describe seasonal and spatial relationship between anthropogenic and biologically transformed sulfate. 2. Geological background The Kamienica Catchment is located in the central part of the Sudety Mountains (SW Poland) and geographically belongs to the Śnieżnik Massif (Fig. 1). This is a crystalline massif composed of different types of gneisses, mica schists, and lenses of Ca-rich silicates (Fig. 2). There are no significant occurrences of sulfurbearing minerals on the surface that would importantly control the sulfate inputs from the surrounding rocks. The crystalline rocks are covered by the weathered rocks of varying thickness (from 1 to 10 m), consisting mainly of weathered debris, slope clays, and river alluviums (Tarka, 1997). In the Śnieżnik Massif, Staśko and Tarka (2002) distinguished three major systems of water flow (Fig. 3): 1) local — within the near-surface weathered rocks (1–10 m deep), 2) transitional — in the fractured rock zone (10–50 m deep), and 3) regional — including the zone of deep faults (100–500 m deep). The water flow systems in the Kamienica Catchment greatly influence the geochemistry of the water. Modelska (2004) showed statistically that the water flows within the zone of fractured rocks in transitional and regional systems were dominantly responsible for variations in water chemistry, including HCO3−, Ca2+, Mg2+, Na+ ions and SiO2 concentrations, followed by the flows within

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Fig. 1. A simplified model showing the expected interaction between sulfur reservoirs of geogenic, biogenic and atmospheric origin in the Kamienica Catchment.

the zone of weathered rocks (controlling K+, SO42− and SiO2 concentrations), whereas precipitation was responsible for only 10% variations in the water chemistry (controlling NO3−and Cl− ions). The observed significant relationships between sulfate concentration and the local flow system, and the lack of sulfur-bearing mineralization in this area led to the conclusion that, in the Kamienica catchment, sulfate content might be, to large extent, controlled by in-situ processes related to a biogeochemical sulfur cycle on the mountain slopes rather than to acid rain, a common phenomenon in this area (Modelska, 2004; Modelska et al., 2006). In the area studied, there is no industrial activity, and small villages constitute the majority of settlements. Nevertheless, in the 1980s and 1990s, the Kamienica Catchment was added to the sulfate anomaly. At that time, the sulfate concentration in the surface water and groundwater reached 28 mg/l (Ciężkowski et al., 1997a). Recently, however, the sulfate concentration has not exceeded 18 mg/l in this area. It was suggested that acid rain generated in the Black Triangle region (located about 120 km NW of the investigated area, Fig. 2) was the main cause of the elevated sulfate content. The Black Triangle is one of the main sources of anthropogenic pollution in the Sudety Mountains due to the burning of lignite. Because

of western-dominated wind directions, a large portion of the emissions generated in the Black Triangle is deposited through the central and east parts of the Sudety Mountains, including the Kamienica Catchment (Fig. 2). The acid rain in the study area has also caused a significant decrease in the pH of surface and groundwater, particularly at higher altitudes (Jezierski, 2002). 3. Methods 3.1. Sampling Analysis of sulfate concentration, δ 18 O(H2O), δ O(SO42− ), and δ34 S(SO42− ) values were conducted during different seasons: April and November of 2002, August 2003, and March and September of 2005 in surface water (5 sampling points along the Kamienica River) and groundwater (5 sampling points on the west slope of Kamienica River). Three sampling points for the groundwater represent natural springs (K1, K6, K15) and the other two points are from a main gallery of the old uranium mine (ST) and a 20 m deep well (So3), respectively (Fig. 2). All sampling points of groundwater were located in the major dislocation extended from N to S and from NW to SE (Fig. 2). Springs under study mostly represent the local 18

A. Szynkiewicz et al. / Chemical Geology 249 (2008) 36–51

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Fig. 2. A geological sketch of Kamienica Catchment and sampling locations. Samples of groundwater — K1, K6, K15, ST, SO3; Samples of surface water — R0, R8, R10, R11, R12.

system of water flow, whereas streams constitute the base of drainage, with the dominant transitional and regional water flow systems. Nevertheless, in all places of the

Kamienica Catchment drainage, the mixing processes between local, transitional, and regional systems of water flow have been observed (Modelska, 2004).

Fig. 3. A cross section showing the major systems of water flow in the Kamienica Catchment (after Staśko and Tarka 2002), with localization of sampling points. Samples of groundwater — K1, K6, K15, ST, SO3.

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In April and November of 2002, the springs and river under study were characterized by a high water level. In these seasons, sampling of water was carried out after almost complete snow melt and after the autumn rain, respectively. In August 2003, low water levels were observed in all sampling points. This was due to a significantly dry summer season with relatively high air temperatures and limited precipitation. In March 2005, water was sampled when the snow began melting following relatively long and snowy winter. At the time of the sampling, there was still about 0.5 m of snow cover at higher altitudes and water level was low. In September 2005, the lowest water level in all sampling points was observed, resulting from a dry summer period. In summer 2005, however, relatively lower air temperatures and more abundant precipitation, compared to the summer of 2003, were noticed. Nevertheless, the spring K1 was completely dry in September 2005. This might have resulted from a general decrease in the spring discharges and water level in streams from the Kamienica Catchment during a few previous years. In the Kleśnica Catchment, located 2–3 km northwestern from the Kamienica Catchment, samples of rain water were collected. Rain water for H–O and S–O isotopic analyses was sampled in 50 ml and 5 l polyethylene bottles, respectively, using the rain-gauge located at 800 m above sea level (asl) in an open space area. Before arrival at the laboratory, the rain water intended for sulfate isotopic analyses was acidified by 10 ml of 10% HCl. The samples of fresh snow were taken in 10 l plastic boxes in the Kamienica Catchment at 780 m asl, close to the R0 sampling point. After arrival at the laboratory, snow melted in room temperature. The melted water was filtered and prepared for chemical and isotopic analyses (see Sections 3.2 and 3.3).

with double-distilled water to remove chlorine ions and dried at 130 °C. The sulfur from BaSO4 was converted to SO2 gas during combustion with V2O5 at 900 °C (Yanagishava and Sakai, 1983). The oxygen from BaSO4 was converted to CO2 gas during reaction with graphite at 1400 °C. All CO gas produced parallel to CO2 was converted directly to CO2 by oxidation in the platinum rod due to glue discharge (Mizutani, 1971). The isotope equilibration between CO2 and H2O was used to determine the oxygen isotope composition of water (e.g. Mills and Urey, 1940). The sulfur and oxygen isotopic compositions were measured in MI3 and Finnigan Mat Delta E mass spectrometry, respectively. The sulfur isotopic composition was expressed as δ34S relative to CDT and the analytical precision was ±0.10‰. The oxygen isotope ratios of sulfate and water were expressed as a δ18O value relative to V-SMOW, respectively, and the analytical precision was ±0.15‰. 3.4. Statistical analysis The method of non parametric Spearman's rank correlation was used for correlation analyses. This method is a non-parametric equivalent of Pearson's linear correlation method. (Norcliffe, 1982). The non-parametric correlation analysis was applied because of the small number of data and the difficulties with standarization of their distribution. The significance level (p) of 0.05 was usually considered. Because of limited number of samples (only 10 sampling points in each season), however, it was necessary to increase the significance level up to 0.39. All numbers calculated for the significance level are presented in graphs (Fig. 5, 6). The method of linear regression analysis was used to calculate the Eqs. (1)–(8) (see Sections 4 and 5). 4. Results

3.2. Chemical analysis The samples of surface and groundwater were collected into 5 l polyethylene bottles. The concentration of sulfate was measured instantaneously using the spectrophotometer HACH DR 2010 (8015 method). Additionally, sulfate concentration was calculated from the amount of precipitated barium sulfate. These two methods have yielded comparable results within ±1 mg/l. 3.3. Isotopic analysis Immediately after arrival at the laboratory, the water was filtered, heated to 80–90 °C and BaCl2 + HCl were added to precipitate BaSO4. The precipitate was washed

4.1. Seasonal changes in chemical and isotopic composition During wet seasons, relatively higher values of sulfate concentration in November 2002 (8.39 to 14.85 mg/l) and March 2005 (9.00 to 18.00 mg/l) compared to April 2002 (7.02 to 14.06 mg/l) were observed. During dry seasons, the sulfate concentration reached the lowest values, in August 2003, from 5.80 to 11.40 mg/l, and in September 2005, from 6.00 to 12.70 mg/l (Table 1, Fig. 4). In general, variations of sulfate content in surface water paralleled those in groundwater (Fig. 4). The δ18O(H2O) values in wet seasons varied in a narrow range from − 11.97 to − 10.63‰ in April 2002,

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Table 1 Variations in the SO2− 4 concentration Location

surface water

δ S [‰]

δ O [‰]

780 640 640 640 740 980 820 755 870 820

8.75 10.63 10.69 14.06 7.10 10.77 9.13 7.02 8.21 8.30

4.60 4.82 4.73 5.08 4.50 4.75 4.30 5.24 4.70 5.05

5.42 5.31 5.23 7.09 5.41 7.38 7.29 6.19 5.22 5.27

− 10.69 − 11.73 − 11.97 − 10.82 − 11.55 − 10.63 − 10.96 − 11.25 − 10.76 − 11.06

November 2002

R0 R8 R10 R11 R12 K1 K6 K15 ST SO3

780 640 640 640 740 980 820 755 870 820

8.39 9.86 10.30 14.85 9.94 10.74 12.52 10.51 8.85 11.66

n.a. 4.70 5.22 4.66 4.53 4.56 4.54 4.92 4.59 4.64

6.76 5.07 6.45 8.23 5.12 5.71 6.17 7.36 4.60 5.99

− 10.65 − 10.39 − 11.05 − 11.11 − 10.98 − 11.26 − 11.45 − 11.29 − 11.01 − 11.28

August 2003

R0 R8 R10 R11 R12 K1 K6 K15 ST SO3

780 640 640 640 740 980 820 755 870 820

7.80 8.40 8.10 11.40 7.10 8.80 9.40 9.10 5.80 10.00

4.62 4.52 4.93 5.26 4.52 4.37 4.09 4.84 4.36 5.28

5.07 4.79 3.96 5.27 4.63 4.13 5.64 5.43 4.14 5.45

− 9.91 − 9.93 − 9.86 − 10.31 − 11.04 − 10.34 − 10.51 − 10.85 − 10.24 − 10.05

March 2005

R0 R8 R10 R11 R12 K1 K6 K15 ST SO3

780 640 640 640 740 980 820 755 870 820

11.00 12.00 11.00 18.00 10.00 11.00 16.00 13.00 9.00 12.00

4.25 4.38 4.31 4.57 4.33 4.30 4.24 4.86 4.42 4.38

4.92 4.74 5.01 5.82 4.62 5.44 5.61 4.76 5.44 4.93

− 11.85 − 11.81 − 11.46 − 11.53 − 11.57 − 12.62 − 12.79 − 12.61 − 11.33 − 12.43

August 2005

R0 R8 R10 R11 R12 K1 K6 K15 ST SO3

780 640 640 640 740 980 820 755 870 820

7.10 9.55 8.95 10.55 7.65 Dry 10.70 12.70 6.00 9.95

4.42 4.72 4.47 4.96 4.57 Dry 4.19 4.84 4.40 5.03

5.79 4.46 5.16 5.38 6.16 Dry 4.95 4.82 5.87 5.53

− 11.61 − 11.34 − 10.75 − 11.12 − 10.99 Dry − 11.84 − 11.34 − 11.67 − 11.38

ground water

surface water

ground water

surface water

ground water

Water δ18O [‰]

R0 R8 R10 R11 R12 K1 K6 K15 ST SO3

ground water

surface water

Sulfate

April 2002

ground water

surface water

Altitude above the sea level [m]

SO2− 4

[mg/l]

34

18

18 18 2− δ34S(SO2− 4 ), δ O(SO4 ), and δ O(H2O) values in the surface and groundwater from the Kamienica Catchment. In August 2005 the point K1 was completely dry.

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34 2− Fig. 4. Seasonal variation in sulfate content, δ18O(H2O), δ18O(SO2− 4 ), and δ S(SO4 ). Seasons 1, 2, 3, 4, 5 are April 2002, November 2002, August 2003, March 2005, September 2005, respectively.

from − 11.45 to − 10.39‰ in November 2002, and from − 12.79 to − 11.33‰ in March 2005 (Table 1, Fig. 4). In August 2003, the δ18O(H2O) had the highest values, ranging from − 11.04 to −9.86‰. Regardless of the dry

season in September 2005, the δ18O(H2O) showed lower values, from − 11.84 to − 10.75‰; these values correspond more to values observed for the wet seasons. During all seasons, variation in δ18O(H2O) values in

A. Szynkiewicz et al. / Chemical Geology 249 (2008) 36–51

surface water paralleled δ18O(H2O) of groundwater with a small deviation for three surface water samples (points R8, R10, R12) in April 2002 (Fig. 4). The δ 18 O(SO42− ) values had a wider variation compared to the δ18O(H2O) values, and ranged from 5.22 to 7.38‰ in April 2002, 4.60 to 8.23‰ in November 2002, 3.96 to 5.64‰ in August 2003, 4.62 to 5.82‰ in March 2005, and from 4.46 to 6.16‰ in September 2005 (Table 1, Fig. 4). In April and November of 2002, δ 18 O(SO42− ) values were, on average, 0.90‰ higher as compared to those observed in August 2003 and March and September of 2005. In general, among all seasons, the variation of δ18O(SO42−) values in surface waters did not follow the variation in groundwater for sampling points K6 and ST, in contrast to what was observed for δ18O(H2O) values (Fig. 4). δ34S(SO42−) values had the most narrow and consistent range, from 4.09 to 5.28‰, during all seasons. There is no apparent distinction between δ34S(SO42−) values and the seasons or the type of water. Only in March and September of 2005, for all surface water, was there a parallel shift (on average 0.26‰) of δ34S(SO42−) from lower to higher values, respectively (Fig. 4). 4.2. Variations in chemical and isotopic composition relative to altitude Variations in sulfate contents showed remarkable changes with a change of altitude in all studied seasons. Based on average values of sulfate content from five seasons, two groups of waters were distinguished (Fig. 5); 1) surface water with low sulfate content (except of R11), and 2) groundwater with higher (on average by 2.58 mg/l) sulfate content (except of ST) compared to the surface water. The altitude effect for sulfate content is expressed by the following equations: surface water : SO2
4 conc: ¼ 16:44
0:0103d Altitude; R ¼
0:87; p ¼ 0:05

ð1Þ

groundwater : SO2
4 conc: ¼ 18:52
0:0089d Altitude; R ¼
0:82; p ¼ 0:09 ð2Þ Based on Eqs. (1) and (2), it was calculated that sulfate concentration increased with decreasing altitude (expressed in meters above the sea level) by an average value of 1 mg/l per 100 m. In all seasons under study, δ18O(H2O) values in surface water and groundwater paralleled the line defined by the Sudety Altitude Effect (SAE) (Fig. 5). The SAE line was calibrated based on 40 measurements of δ18O

43

(H2O) values in shallow groundwater (springs and wells) and for the altitude range between 180 and 1400 m above the sea level (asl) during two seasons: July 1986 and January 1987 (Ciężkowski and Kryza, 1989). The reported increase of δ18O(H2O) values by 0.17‰ per 100 m by Ciężkowski and Kryza (1989) is consistent with values obtained for the Kamienica Catchment (Table 1, Fig. 5). In general, cold seasons showed the lowest values of δ18O(H2O) compared to distinctively higher values of δ18O(H2O) noted for warm seasons. The average value of δ18O(SO42−) for all seasons revealed a statistically important relationship with altitude expressed by the following equation:
d18 O SO2
¼ 7:5887
0:0024d Altitude; 4

ð3Þ

R ¼
0:58; p ¼ 0:17 Based on Eq. (3), the altitude effect for δ18O(SO42−) is −0.24‰. The increase of δ18O(SO42−) values with altitude was similar to the SAE line defined for δ18O(H2O) values (Fig. 5). Three samples of surface water (R8, R10, R12) placed outside a linear correlation line. Independent chemical and hydrodynamic modelling done for Kamienica Catchment (Ciężkowski et al., 1997b; Staśko and Tarka, 2002; Stępień et al., in press) showed that these points were the most susceptible to mixing processes as they represent the base of the drainage. δ34S(SO42−) values showed the altitude dependence for all seasons under study (Fig. 5). Based on average values of δ34S(SO42−) for all seasons, two groups of water have been distinguished: 1) surface water characterized by low values (except of R11); and 2) groundwater with higher (on average by 0.22‰) values (except of K6). This altitude dependence may be expressed as follows: surface water : d34 SðSO2
4 Þ ¼ 5:9774
0:0020d Altitude; R ¼
0:97; p ¼ 0:005 ð4Þ

groundwater : d34 SðSO2
4 Þ ¼ 5:9312
0:0015d Altitude; R ¼
0:80; p ¼ 0:10

ð5Þ

Based on Eqs. (4) and (5), it was calculated that δ 34 S(SO42− ) increases with decreasing altitude with an average value of − 0.18‰ per 100 m. 4.3. Precipitation δ18O(SO42−) values from precipitation varied from 11.31 to 14.84‰, with an average of 12.91‰ in March 2005 (Table 2). They were distinctly higher, on average by 7.42‰, than δ18O(SO42− ) values observed in surface

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Fig. 5. Values of δ18O(H2O), δ18O(SO4), δ34S(SO4), and SO4 concentrations relative to altitude. The circled field is out of linear fit and represent samples of surface water (R8, R10, R12) that have been affected the most by mixing processes of water from different altitudes (see Section 4.2. for more details). The values for each sampling point represent averages for all five seasons. Seasonal variations for each sampling point are shown in Fig. 4.

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Table 2 Variations of sulfur and oxygen isotopic composition in sulfate coming from precipitation (rain water and snow) Period

Type of precipitation

SO2− 4 concentration [mg/l]

δ34S [‰]

δ18O [‰]

References

1995 Jan 1999 Feb 2002 Aug 2005 Mar 2005 Mar 2005 Mar 2005

Rainfall Snow Snow Rainfall Rainfall Snow Rainfall

4.60 1.40 6.50 n.a. 1.07 0.33 n.a.

5.70 7.55 6.08 7.37 5.15 7.63 3.27

n.a. n.a. 8.74 n.a. 12.57 11.31 14.84

Groscheová et al. (1998)⁎ Jędrysek et al. (2002) Jezierski et al. (2006) this study this study this study this study

Samples of precipitation for this study were taken 2–3 km northwestern from the Kamienica Catchment (rain water) and close to the R0 sampling 34 point at 780 m asl (snow). ⁎ the mean annual values for SO2− 4 concentration and δ S. n.a. — not analysed.

water and groundwater (average 5.49‰). In contrast, δ34S(SO42−) values had a smaller range of variations from 3.27 to 7.63‰, with an average of 5.86‰. These values were slightly higher, on average by 1.23‰, than δ34S(SO42−) values in surface water and groundwater (average 4.63‰), but in good agreement with data reported by Groscheová et al. (1998), Jędrysek et al. (2002) and Jezierski et al. (2006) for other areas of the Sudety Mountains located closer to the Black Triangle (Table 2). 5. Discussion 5.1. Seasonal changes in chemical and isotopic composition For all seasons, δ18O(H2O) values of surface water and groundwater are comparable to previous data reported for the Sudety Mountains by Ciężkowski (1990), Ciężkowski and Kryza (1989), and Staśko and Tarka (2002). For all seasons, the δ18O(H2O) values are in good correspondence to the Sudety Altitude Effect (SAE), which defines a − 0.17‰ altitude effect for the Sudety Mountains (Fig. 5). This indicates that the surface water and groundwater in the study area are dominantly fed by infiltration of atmospheric precipitation at different altitudes. Additionally, higher values of δ18O(H2O) in warmer seasons compared to cold seasons (Fig. 4) show the role of seasonal isotopic effects in the Kamienica Catchment, as rainwater becomes more enriched in 18O isotopes during summer compared to autumn and winter (e.g. Sigenthaler and Oescheger, 1980; Clark and Fritz, 1997). This, in turn, results from kinetic isotopic fractionation during condensation and precipitation at different altitudes. Generally, the effect of seasonal variations in water isotopic composition is suppressed with time and, after two years of water residence in the aquifer, is unnoticeable (e.g. Gat and Ganfiantini, 1981). Therefore, pronounced seasonal

variations of δ18 O(H2O) values in the Kamienica Catchment indicate a short time (less that two years) of water residence. The seasonal variations in precipitation may directly influence the concentration of ions dissolved in surface water and groundwater, as rain and snow-melting waters have low mineralization. This, in turn, results in a significant dilution of dissolved ions in surface and groundwater, including sulfate ions. The importance of this process was observed by Jezierski et al. (2006) for another catchment in the Sudety Mountains. In the Kamienica Catchment, however, during the rainy period in November 2002 and after the snow melting in March 2005, a significant increase of sulfate content was observed compared to dry seasons of August 2003 and September 2005 when the lowest sulfate content was observed (Fig. 4). This suggests that precipitation (rain and snow) supplies additional sulfate into the surface water and groundwater under study. Generally, an interaction of precipitation with trees, soil, and bedrocks results in the leaching of sulfate from different sources. Tree canopies affected by precipitation are one of these sources. Groscheová et al. (1998) showed that interaction of precipitation with tree canopies resulted in a significant increase of sulfate content in the throughfall by the scavenging of sulfate from plant surfaces, compared to the precipitation from the open space area. This is an especially important factor in polluted areas, because the coniferous species assimilate SO2 by needles (e.g. Horn et al., 1989; Gebauer et al., 1994). The SO2 input in polluted areas is usually higher than the amount of SO2 that can be assimilated by conifers. The excess SO2 undergoes a transformation to the sulfate (e.g. Turner and Lambert, 1979) which is deposited on the surface of spruce needles. Thus, tree canopies are a temporary reservoir of atmospherically derived sulfur modified via plant vegetation. Additionally, the snow load on tree canopies during the winter season may accumulate the sulfate

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coming directly from acid precipitation and dry deposition, and may result in an increase in the total anthropogenic sulfate input when snow melting begins in early spring. The Kamienica Catchment is extensively forested at all altitudes and coniferous and deciduous trees are the most dominant tree groups. The sulfate fluxes from throughfall are unknowh for this catchment, however, we expect that large amounts of sulfate from tree canopies may be washed out by rain water. This is inferred from higher sulfate contents observed after rain that occurred in late autumn of November 2002 (Fig. 4). Because the anthropogenic sulfate shows significantly higher values of δ18O(SO4) (11.31 to 14.84‰, Table 2), the highest values of δ18O(SO4) noted for that period, particularly in surface waters (Fig. 4), may indicate a larger input of sulfate directly from atmospheric pollution. During the winter, a large snow cover from tree canopies is transported downward by intense winds and deposited on the forest floor. This process increases the amount of spruce needles and leaves in the snow cover. Therefore, the highest sulfate content was observed in March 2005 (Fig. 4), directly after the initial snow melt.

This phenomenon is defined as an altitude effect and expressed as the total increase of δ18O(H2O) value per 100 m (eg. Sigenthaler and Oescheger, 1980). The altitude effect of shallow groundwater in the Sudety Mountains was calculated as − 0.17‰, which means that δ18O(H2O) value increases by 0.17‰ with each 100 m decrease in altitude (Ciężkowski and Kryza, 1989). Generally, the variation of δ18O(H2O) values relative to altitude in the Kamienica Catchment followed this trend during all seasons (Fig. 5). Based on the average value of δ18O(SO42−) from all seasons, an altitude effect of − 0.24‰ was noted for sulfate. This effect was slightly larger than the one observed for waters (− 0.17‰/100 m). This difference was probably caused by higher values of δ18O(SO42−) observed in April and November of 2002 compared to lower values noted in August 2002 and March and September of 2005. Because of this difference, in the next step, the regression lines for seasons with higher and lower values of δ 18 O(SO42− ) were calculated separately as follows (Fig. 6):
Apr and Nov 2002 : d18 O SO2
¼ 13:23
0:0091d Altitude; 4 R ¼
0:58; p ¼ 0:17 ð6Þ

5.2. Variation in isotopic composition relative to altitude


Aug 2003Mar and Sep 2005 :d18 O SO2
4 ¼6:42
0:0015d Altitude; R ¼
0:35; p ¼ 0:39 ð7Þ

5.2.1. Oxygen isotopes in water and sulfate In the mountain regions, oxygen isotope composition of surface water and shallow groundwater fed by atmospheric precipitation is, to a large extent, dependent on the altitude at which the precipitation occurs. In general, in all mountain regions the increase of δ18O (H2O) values with a decreasing altitude is observed.

Eqs. (6) and (7) imply that altitude effect for δ 18 O(SO42− ) values may significantly differ between seasons, reaching the lowest values of −0.91‰ for seasons with high water level (April and November 2002) and the highest values of −0.15‰ for seasons with low water level (August 2003 and March and September 2005).

Fig. 6. Variations of δ18O(SO2− 4 ) values relative to altitude. Average values for A) April + November of 2002 and B) August 2003 + March 2005 + September 2005. The circled fields are out of linear fit and represent samples of surface water (R8, R10, R12) and groundwater (K1) that have been affected the most by mixing processes of water from different altitudes and precipitation, respectively.

A. Szynkiewicz et al. / Chemical Geology 249 (2008) 36–51

Sulfates from April and November of 2002 had significantly higher values of δ18O(SO42− ) compared to other seasons (Fig. 4). While April and November showed higher water levels and the spring discharges in all sampling points (resulting from the intensive snow melting in April and heavy rains in November 2002), the sulfate coming from canopy throughfall and anhropogenic pollution could have controlled more intensively the δ18O(SO42−) value in that time (see Sections 5.1 and 5.3). In fact, Jędrysek et al. (2002) reported, for the other part of Sudety Mountains, the significant increase of δ18O(SO42−) values with decreasing altitude for sulfate coming from the surface of spruce needles in tree canopy. Based on those data, the altitude effect for sulfate coming from canopy througfall may reach values even up to − 0.56‰ according to the following equation:
d18 O SO2
¼ 5:8719
0:0056d Altitude; 4 R ¼
0:58; p ¼ 0:025

ð8Þ

This effect is 0.40‰ smaller than we observed in the Kamienica Catchment in April and November 2002. It should be pointed out, however, that sulfate from acid rain in the Sudety Mountains is significantly enriched in 18 O isotopes (Table 2). Therefore, even small inputs of the precipitation derived sulfate may influence the increase of δ18O(SO42−) values in the water under study and, in turn, increase the total altitude effect, up to − 0.91‰, due to mixing with rainwater and snow melting water. It is generally accepted that δ18O(SO42−) value in freshwater sulfate is controlled by oxygen isotope composition of water and dissolved O2 (e.g. Everdingen and Krouse, 1985). Dissolved O2 in freshwater aquifers comes mainly from dissolution of atmospheric oxygen which is enriched in heavy isotopes (δ18O = +23.5‰, Kroopnick and Craig, 1972). For that reason, the formation of sulfate in O2-rich environment produces higher values of δ18O(SO42−). Depending on the organic and/or inorganic oxidation pathway, the contribution of atmospheric oxygen to sulfate ions might vary widely (Taylor et al., 1984). In the Kamienica Catchment, the significantly higher δ18O(SO42−) values (4.13 to 8.23‰) compared to the negative values of δ18O for the water (− 12.79 to− 9.86‰) implies that atmosphericallyderived O2 was an important constituent of the total sulfate pool. However, the observed similar altitude effect for δ18O between water (− 0.17‰) and sulfate (− 0.15‰) in August 2003, and March and September 2005 suggests that δ18O(SO42−) values were, to a large extent, controlled by the δ18O(H2O). Statistical modelling showed that the main sulfate load in the studied

47

waters comes from the shallow zone of weathered rocks and the local system of water flow (Modelska, 2004). This implies that during those seasons large inputs of sulfate probably came from in-situ processes such as rock weathering and/or biological activity. The sulfur inventory of the crystalline rocks of the Kamienica Catchment is unknown, because no sulfurbearing minerals were detected on the surface. Nevertheless, gneissic rocks, the most common in this area, may contain accessory minerals such as sulfides. Chemical analysis of the total sulfur content showed, however, that sulfur concentration in those rocks is very small, less than 0.01% which is consistent with similar data for other gneissic catchments in the Sudety Mountains (Novák et al., 2005b). For that reason, we conclude that weathering of crystalline rocks would have provided the negligible amounts of sulfur, especially considering the relatively short time period of this study. Consequently, the biological transformation of sulfate within the weathered zone was likely the most important factor controlling the variations of δ18O(SO42− ) values relative to altitude. Gélineau et al. (1989) showed that a large portion of sulfate coming from precipitation might undergo biological transformation and be recycled in the soil during water movement to the watershed followed by the general decrease of δ18O(SO42−) values. Because δ18O(SO42−) values in the water under study represent the sum of all processes taking place during downward water flow, we propose that lower values of δ18O(SO42−) during dry seasons indicate a bigger influence of biological transformation of sulfate in the soil and weathered zone. March 2005 represents a time of sampling during the first episode of snow melting after a relatively long winter. While during the winter all precipitation is temporarily stored in the snow cover, it may be expected that sulfate isotopic composition of the soil and weathered zone is also significantly affected by biological activity during the cold seasons. Consequently, the δ18O(SO42−) might show lower values after the first episode of snow melting because of the washing out of sulfate from the soil and weathered zone; this is consistent with lower values of δ18O(SO42−) in March 2005. 5.2.2. Sulfur isotopes in sulfate The observed narrow range of δ34S(SO42−) values, from 4.09 to 5.28‰, implies that sulfur sources for freshwater sulfate in the Kamienica Catchment were isotopically homogenous during the analyzed seasons. Jezierski et al. (2006) found in the adjacent area that δ34S of organic sulfur in soil had values of 4.08 and 4.90‰ for coniferous and deciduous forests, respectively.

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A. Szynkiewicz et al. / Chemical Geology 249 (2008) 36–51

Groscheová et al. (1998) found that the mean annual values of δ34S(SO42−) in the deciduous and spruce throughfall and the surface runoff were 5.1, 4.2 and 4.0‰, respectively. All these values are in agreement with our results for freshwater sulfate, and suggest that sulfate affected by biological transformation was probably the most important constituent of sulfate in the catchment under study. The negative altitude effect (−0.18‰) for δ34S(SO42−) values in the Kamienica Catchment, however, is in contrast to the positive altitude effect reported by Jędrysek et al. (2002) for δ34S in spruce needles. In that study, both organic sulfur and sulfate in spruce needles showed a similar altitude effect, +0.33 and +0.32‰, respectively. In contrast,Groscheová et al. (1998) showed that with a decreasing altitude, δ34S(SO42−) values decreased for bulk deposition, increased for the spruce throughfall, and showed no correlation in the deciduous throughfall. This suggests that the altitude effect for δ34S(SO42−) is strongly controlled by local conditions and may not be described by one variable only. Generally, the isotopic composition of the freshwater sulfate studied and its content represent the sum of all processes which have been taking place along the downward water flow in the massif. The biological sources of sulfate and the sulfate from precipitation have shown similar sulfur isotopic compositions to those observed in sulfate from surface water and groundwater in the Kamienica Catchment. Therefore, based on sulfur isotopic composition alone, it is difficult to discriminate and quantify the contribution of sulfate from each source. The altitude effect for δ34S(SO42−) values is relatively small in this area. The local precipitation showed slightly higher (on average by 1.23‰) values of δ34S(SO42−) compared to the δ34S(SO42− ) of surface and groundwater. Therefore, the altitude effect might have been additionally enhanced by mixing with isotopically heavier sulfate coming from precipitation, similar to the phenomenon observed for δ18O(SO42−) (see Section 5.2.1). Nevertheless, more detailed field observations are required to better understand the magnitude of this effect. 5.3. Precipitation–anthropogenic input The oxygen isotopic mass balance constrain is a relatively simple and accurate method for the quantitative estimation of the final δ18O of sulfate resulting from the mixing of two or more isotopically different sources. Based on relatively higher values of δ18O(SO42− ) during wet seasons and strong altitude dependence of δ18O(SO42−) values in the water under study, at least two isotopically different sources of sulfate may be distinguished: 1) pre-

cipitation and 2) biological activity. According to the mass balance equation, the evolution of δ18O(SO42−) resulting from mixing processes in the Kamienica Catchment may be expressed as follows:


18 2
d18 O SO2
¼ r1 *d18 O SO2
4 4 1 þr2 *d O SO4 2 ; ð9Þ in which r1 and r2 indicate the fraction of sulfate in sources 1 and 2, respectively, and r1 +r2 = 1. From 2002 to 2005, the sulfate concentration in precipitation varied from 0.33 to 3.21 mg/l. This sulfate represents about 20% of the total sulfate concentration noted in the surface and groundwater under study. Nevertheless, the effect of evapotranspiration may have caused a significant increase of sulfate concentration delivered by precipitation to the water. The concentration of Cl−ions has been used widely for calculations of the evapotranspiration factor, as chlorine is delivered to the hydrological systems mainly by precipitation, and the input from weathering is accepted as negligible (Apello and Postma, 1993). Based on 77 analyses of Cl−concentration in waters of the Kamienica Catchment and 5 analyses in the precipitation, the evapotranspiration factor has been estimated at 1.7 for 2002 and 2003 (Modelska, 2004). The sulfate input resulting from evapotranspiration may be calculated according to the equation given by Apello and Postma (1993) as follows:   2
CSO2
4ðwatersÞ
CSO4ðprecipitationÞ d Evapotran:Factor ð10Þ ¼ CSO2
4ðweatheringÞ ½mmol=L

where C is the sulfate concentration. Based on Eq. (10), the input of sulfate from precipitation due to evapotranspiration processes in the Kamienica Catchment was calculated to be from 20 to 56%, with an average value of 38%, (Modelska, 2004). This indicates that evapotranspiration may cause a significant increase of sulfate concentration dissolved in the surface water and groundwater under study. The uptake of sulfate by plants does not cause any measurable oxygen isotopic fractionation, whereas redox processes, occurring during organic matter decomposition, and dissimilatory sulfate reduction in particular, influence significantly the isotopic composition of sulfate. The water from the Kamienica Catchment is well aerated, and the aerobic oxidation of organic matter might be important in the active zone of weathered rocks. The reducing conditions, however, may appear in deeper parts of soil profiles. Lloyd (1968) has calculated the general evolution of δ18O(SO42−)

A. Szynkiewicz et al. / Chemical Geology 249 (2008) 36–51

49

18 2− Fig. 7. Model showing the evolution of δ18O(SO2− 4 ) values due to the mixing of sulfates coming from two sources, the biological source (δ O(SO4 ) ) values in the Kamienica Catchment varied from 11.31 values calculated by Lloyd’s equation) and wet atmospheric precipitation (the measured δ18O(SO2− 4 to 14.84‰). From line A to H, the contribution of sulfate from the biological source decreases, whereas the contribution of sulfate from precipitation increases. A — sulfate originated from redox processes calculated from Lloyd’s equation, B — mixing processes, minimal δ18O(SO2− 4 )precip.value when 20% of the sulfate come from the atmospheric precipitation and 80% is of biological origin, C — mixing processes, maximal δ18O(SO2− 4 )precip.value when 20% of the sulfate come from the atmospheric precipitation and 80 % is of biological origin, D — mixing processes, minimal δ18O(SO2− 4 )precip. value when 38% of the sulfate coming from the atmospheric precipitation and 62% is of biological origin, E — mixing processes, mean δ18O(SO2− 4 ) precip when 38% of the sulfate coming from the atmospheric precipitation and 62% is of biological origin, F — mixing processes, minimal δ18O(SO2− 4 ) precip, when 56% of the sulfate come from the atmospheric precipitation and 44% is of biological origin, G — mixing processes, maximal δ18O(SO2− 4 ) precip when 38% of the sulfate come from the atmospheric precipitation and 62% is of biological origin, H — mixing processes, maximal δ18O(SO2− 4 )precip value when 56% of the sulfate come from the atmospheric precipitation and 44% is of biological origin.

values due to redox processes during decomposition of organic matter as follows:
  ¼ 0:68d d18 OðH2 OÞ þ 0:32 d18 OðO2 Þ
8:7 d18 O SO2
4 þ4:6½x

ð11Þ

The above equation has been developed based on experiments with marine sediments but has also been applied to sulfate studies in freshwater environments (e.g. Gélineau et al., 1989, Trembaczowski 1991) to express oxygen isotopic fractionation during redox processes in general. Based on measured δ18O(H2O) values in the surface and groundwater in the Kamienica Catchment, and δ18O (O2) = +23.5‰ given by Kroopnick and Craig (1972) for atmospheric oxygen, the theoretical values of δ18O(SO42−) were estimated using Eq. (11) for all sampling points. These calculated theoretical values of δ18O(SO42−) are significantly lower (0.64 to 2.63‰, line A in Fig. 7) than the ones measured in the surface water and groundwater (3.96 to 8.23‰, Table 1). This difference suggests that contribution of sulfate coming from the soil and weathered rocks is minor. As sulfate coming from precipitation has significantly higher values of δ18O(SO42−), even a small input of this sulfate may increase δ18O(SO42−) values in the Kamienica Catchment due to the mixing with sulfate of

a biological origin. Based on Eq. (9), the expected values of δ18O(SO42− ), resulting from the mixing of sulfate from precipitation and production/transformation in-situ, were calculated and are presented in Fig. 7 (lines B to H). In our model three other factors were considered: 1) the oxygen isotopic composition of sulfate produced in-situ was mainly controlled by redox processes with δ18O(SO42−) values originating from Lloyd's Eq. (11); 2) the input of sulfate delivered by precipitation varied from 20 to 56% due to evapotranspiration (Modelska, 2004), and 3) δ18O(SO42−) values in precipitation ranged from 11.31 to 14.84‰ (Table 2). The seasons with high precipitation were expected to show the highest input of sulfate delivered by precipitation. In fact, for April and November of 2002 and March 2005, the best correlation between the calculated values (based on Eq. (9)) and those measured for δ 18 O(SO42− ) were observed when the average contribution of precipitation-derived sulfate was at least 38% (Fig. 7, lines D, E, G). This implies that sulfate coming directly from precipitation may control, on average, one third of the sulfate dissolved in the water of the Kamienica Catchment during wet seasons. August 2003 and September 2005 represent periods after relatively dry seasons, therefore, δ18O(SO42−) is shifted towards lower values compared to those calculated from Lloyd's equation (Fig. 7, line A). This

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A. Szynkiewicz et al. / Chemical Geology 249 (2008) 36–51

shift indicates a higher contribution of sulfate affected by biological activity in the soil and the zone of weathered rocks. The presented model is in agreement with calculations done by Trembaczowski (1991) for atmospheric groundwater system in southeastern Poland, in which it is estimated that about 30% of the sulfate is delivered by anthropogenic pollution.

composition of sulfate; A. Schimmelmann and A. Johnson for their help in manuscript preparation. This study was supported by grants: 2438/W/ING/02, S grants (1017/S/ING/03-05-IX), 2022/W/ING/05 and 2022/W/ ING/05-57. We also wish to thank Editor David Rickard and two anonymous reviewers whose comments and suggestions contributed to the improvement of the manuscript.

6. Conclusions

References

1. The observed dependence on δ18O(H2O) values on altitude suggests that the surface water and groundwater in the Kamienica Catchment were fed mainly by infiltration of atmospheric precipitation. The pronounced seasonal variations of δ 18 O(H2O) values suggest that the water residence time in the crystalline massif under study is less than two years. 2. The significant increase of sulfate contents in the waters under study in November 2002 and March 2005 (wet seasons) compared with lower sulfate contents in August 2003 and September 2005 (dry seasons) implies that sulfates coming from anthropogenic pollution and produced in-situ were washed out from the tree canopies, soil, and the zone of weathered rocks by precipitation derived water. 3. The altitude effect for δ18O(SO42−) values during dry seasons (− 0.15‰/100 m) is directly related to the altitude effect observed for δ 18 O(H 2 O) values (− 0.17‰/100 m). A bigger altitude effect (− 0.91‰/ 100 m) during wet seasons was probably caused by mixing at least two sulfate sources: 1) the scavenging of sulfate from tree canopy and 2) anthropogenic sulfate coming directly from precipitation. 4. Oxygen isotope mass balance suggests that sulfate coming from modern anthropogenic pollution may account for one third of the total sulfate in the waters under study. The input of this sulfate is the highest during wet seasons. With time, this sulfate is intensively recycled in the zone of weathered rocks, and this process results in a general decrease of δ18O(SO42−) values in waters of the Kamienica Catchment.

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