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Journal of Environmental Quality 31:547-556 (2002)
© 2002 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America

TECHNICAL REPORT
Ecosystem Restoration

Leaching from Organic Matter–Rich Soils by Rain of Different Qualities

I. Concentrations

L. T. Strand*, G. Abrahamsen and A. O. Stuanes

Agricultural University of Norway, Department of Soil and Water Sciences, P.O. Box 5028, N-1430 Ås, Norway

* Corresponding author (line.strand{at}ijvf.nlh.no)

Received for publication March 12, 2001.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
Soil monoliths from an area exposed to acid precipitation and from an unpolluted area were used in a lysimeter experiment to study effects of different rain qualities on the chemical composition of the leachate from shallow soils rich in organic matter. The vegetation was either dominated by moorgrass [Molinia caerulea (L.) Moench] or heather [Calluna vulgaris (L.) Hull]. The lysimeters received either "acid rain" (pH 4.3) or "normal rain" (pH 5.3). High concentrations of dissolved organic carbon (DOC) were characteristic of the leachate. The different "rain" qualities had no significant influence on the DOC concentration. More DOC was, however, leached from lysimeters with heather vegetation. Roughly 50% of the aluminum (Al) was in complex with organic material and the Al charge was calculated to be between +1.4 and +2.0. Sulfate (SO2-4) was the only component that was significantly influenced by the treatment, as more was leached from lysimeters receiving "acid rain." Sulfate was poorly correlated with pH, suggesting that reduced SO2-4 input would not necessarily lead to reduced acidity. Differences in the pH of the leachate due to the treatments were less than 0.15 pH units. Nitrate (NO-3) was only leached in very low concentrations and of little consequence for the leachate acidity. Some observations do, however, suggest that NO-3 may contribute to acidification in episodes with high precipitation. High concentrations of Cl- in the leachate and a significant positive correlation between Cl-, H+, and base cations indicate that sea salt episodes may be important for soil acidification and acidity of the leachate.

Abbreviations: DOC, dissolved organic carbon


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
IN SOUTHERN NORWAY areas either with shallow soils or barren nutrient-poor crystalline bedrock correspond with the areas receiving the most acid precipitation. It is also here that freshwater acidification has been most severe. The shallow soils are acid, rich in organic matter, have a low content of exchangeable base cations, and a low ability to sorb sulfate (SO2-4) and nitrate (NO-3). This suggests that the soils are particularly vulnerable to acidification and have little ability to influence the rainwater quality before it reaches adjacent freshwater systems.

Recently, great effort has been made to reduce sulfur and to some extent nitrogen components in the precipitation. This reduction in SO2-4 deposition (Tørseth and Semb, 1995) has been followed by a restoration of the surface waters in these areas (Skjelkvåle and Henriksen, 1995). However, there is no 1:1 relationship between the reduction in deposition of SO2-4 and the decrease in freshwater acidity (Abrahamsen and Stuanes, 1980; Wright et al., 1986, 1988a; Skjelkvåle and Henriksen, 1995). The present study aims to examine the effects of an increase or a decrease in SO2-4 and NO-3 deposition on the chemical concentrations of the leachate from shallow soils rich in organic matter. Soils from two sites, one pristine and one that has been subject to long-term acidification, were chosen for this lysimeter study.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 
Soil and Lysimeters
Soils from two different sites were chosen: Storgama (8°32' E, 59°01' N, altitude 560 m) in Telemark county, an area that has received acid precipitation for a long period (Overrein et al., 1980), and Kårvatn (8°52'E, 62°45'N, altitude 280 m) in Møre and Romsdal county, an area with low depositions of anthropogenic air pollutants (Overrein et al., 1980) (Fig. 1) . The amount and composition of the precipitation collected at the two sites for the periods 1980–1983 and 1995–1999 are given in Table 1. There are clear differences between the two sites with regard to the concentration of H+, NH+4, NO-3, and SO2-4, components that partly have an anthropogenic origin. Geographic location, particularly the distance from the sea, influences the concentration of sea salts and amount of precipitation. The higher amount of precipitation at Kårvatn implies that the differences in deposition between the two sites are smaller than the differences in concentrations. Also, the reduction in H+ and SO2-4 deposition from the 1980s to the 1990s is reflected in the data.



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  		Fig. 1. Map of Norway showing the site where the soil was collected.

 

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  		Table 1. Annual precipitation and annual mean weighted solution concentrations in the precipitation. (Data are extracted from reports from the Norwegian State Pollution Control Authority.)

 
Both areas have nutrient-poor crystalline bedrock, which either is exposed or covered by shallow soils rich in organic matter. The soil profiles showed O horizons with increasing mineral soil content with depth and classify as Folic Histosols or Dystric or Lithic Leptosols according to FAO–UNESCO (1990). At each site eight relatively undisturbed soil monoliths with intact vegetation cover were taken down to the lithic contact. The depth varied between 15 and 25 cm for the Storgama monoliths and between 20 and 30 cm for the Kårvatn monoliths. The monoliths were cut to a size of 35 by 55 cm to fit the lysimeters. Four monoliths from each site had a vegetation cover dominated by moorgrass and will be referred to as the moorgrass lysimeters. Four others were dominated by heather and had little moorgrass, these will be referred to as the heather lysimeters. As it was impossible to find big enough areas with only moorgrass vegetation at Kårvatn, some heather was always present in these lysimeters. This was not the case for the Storgama moorgrass lysimeters. The pH of the moorgrass lysimeters was somewhat higher than that of the heather lysimeters and the pH of the Storgama soil appeared to be slightly higher than those from Kårvatn (Table 2). The content of organic matter (SOM) was fairly similar for the soil from both places. The lysimeters were placed in a "cold" greenhouse to achieve full control of the precipitation. The lysimeters were given an adjustment period of 30 d.


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  		Table 2. Soil organic matter (SOM) and pH of the soils in the lysimeters, analyzed prior to the experiment and sorted by site, vegetation, and layers. na = Not analyzed.

 
Treatments
Two lysimeters with moorgrass vegetation and two lysimeters with heather vegetation from each site received simulated "acid rain" (pH 4.3) or simulated "normal rain" (pH 5.3) (Table 3). The "normal rain" was close to the quality of the precipitation at Kårvatn except for a higher concentration of NH+4. The "acid rain" had the same H+ and SO2-4 concentration as the Storgama rain but higher concentrations of "sea salts."


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  		Table 3. Chemical characteristics of the artificial rainwater used in the experiment.

 
The experiment with the Storgama lysimeters started and ended one year before the Kårvatn lysimeters; however, lysimeters from both sites were run for four years. The first, third, and fourth year rain was applied regularly twice a week in equal amounts and of equal quality. The lysimeters received simulated rain in amounts comparable with the average annual amount of precipitation in Storgama and Kårvatn, respectively (Table 1). Rain was applied once a week by watering can and no rain was applied when the soil was frozen. The amount of water that should have been applied during the frost periods was used to simulate snowmelt flushes in the spring. The second year the rain was applied episodically in order to simulate a natural precipitation pattern. The episodes were determined by the weekly precipitation pattern registered at Storgama and Kårvatn the previous year. For the "normal rain" lysimeters only the amount of rain varied episodically; for the "acid rain" lysimeters both the pH (varying from 3.8 to 5.3 with a mean of 4.3) and amount of rain varied episodically (Table 3).

Sampling and Analyses
Generally, the leachate from each lysimeter was measured and sampled once a week, but twice a week in the summer to minimize chemical changes in the leachate. Two subsamples were taken from each weekly leachate sample. On one subsample pH, chloride (Cl-), and dissolved organic carbon (DOC) were analyzed immediately. To the second subsample 1% 8.4 M HCl was added and stored at 4°C. These samples were bulked by volume each month and analyzed for nitrate (NO-3), ammonium (NH+4), sulfate (SO2-4), total phosphorous, sodium (Na+), potassium (K+), magnesium (Mg2+), calcium (Ca2+), and total aluminum. Soil organic matter (SOM) was analyzed as loss on ignition and pH of the soil was measured in water (1:2.5 [v/v]). All analyses were done according to methods and procedures described by Ogner et al. (1975). Pearson's correlation analysis was used to reveal relationships between the concentrations of the components in the leachate. Effects of treatments, vegetation, and sites were assessed by analysis of variance based on the volume-weighted averages for the whole period. Annual treatment effects were also assessed by analysis of variance of volume-weighted averages for each treatment year.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSION
 REFERENCES
 
Dissolved Organic Carbon and Phosphorous
Irrespective of site, vegetation, or treatment, DOC was an important component in the leachate (Table 4). The DOC concentrations in the leachate were much higher than those found in most rivers, streams, and lakes in southern Norway (Skjelkvåle and Wright, 1998). However, the DOC concentrations were comparable to those found in other studies of shallow soils rich in organic matter and from O horizons of mineral soils (Christophersen et al., 1982b; McDowell and Wood, 1984; Vance and David, 1989; Dai et al., 1996; Raastad and Mulder, 1999). The concentrations of DOC were higher in the leachate from the Kårvatn lysimeters than from the Storgama lysimeters, particularly during the first year (Table 4, Fig. 2) . Other studies have shown that even small disturbances in soils rich in organic matter may cause unnaturally high DOC values in the leachate (Christophersen et al., 1982b; Wright et al., 1988a). Greater disturbances due to higher amounts of coarse heather roots and a thicker soil column may have prolonged the installation effects for the Kårvatn lysimeters compared with that of the Storgama lysimeters.


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  		Table 4. Volume-weighted concentrations of components in the leachate from the lysimeters for the whole period (mean of two repli-cates). DOC = dissolved organic carbon.

 


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  		Fig. 2. Concentrations of dissolved organic carbon (DOC) (µM) for lysimeters from both sites shown as mean of two replicates: {circ} Heather "normal rain," • Heather "acid rain," {star} Moorgrass "normal rain," * Moorgrass "acid rain," F = frost, D = drought.

 
More DOC appeared to be leached from the Storgama lysimeters receiving "normal rain" than from the lysimeters receiving "acid rain." Increased acid input has been found to lower the concentrations of DOC in the leachate (Vance and David, 1989; Tipping and Woof, 1991; Guggenberger, 1992). However, similar results were not found for the Kårvatn lysimeters (Table 4, Fig. 2).

The DOC concentrations were generally negatively correlated with the water fluxes (Table 5); this has also been shown in several other studies, for example, McDowell and Wood (1984). The lowest concentrations occurred in the spring during the simulated snowmelt. This has also been found in other studies (Herbert and Bertsch, 1995; Currie et al., 1996). Particularly for the Kårvatn lysimeters (Fig. 2), high concentrations occurred immediately after frost periods before being diluted by the simulated snowmelt. This confirms that freezing and thawing influence the decomposition and disintegration of organic matter (Arthur and Fahey, 1993; Hobbie and Chapin, 1996). The Storgama moorgrass lysimeters did not follow the same pattern as described above, since DOC concentrations were positively correlated with the water flux (Table 5). The DOC concentrations from these Storgama moorgrass lysimeters generally showed little seasonal variation with exception for the year with episodically application of rain, where increased DOC concentrations appeared to follow the increase in water fluxes (Fig. 1). This appears to be an effect of increased mineralization. Controls on the seasonality of DOC concentrations in the leachate from organic horizons are related to both timing of decomposition and of litter input and may therefore differ according to different vegetation types (Currie et al., 1996). Currie et al. (1996) also found that there were small differences in DOC concentrations between different vegetation types in the spring; however, greater divergence occurred during the growing season, culminating in the autumn. The DOC concentrations from the Storgama heather lysimeters were much higher than from the moorgrass lysimeters and comparable with those of the Kårvatn lysimeters. This difference between the vegetation types persisted throughout the experiment (Fig. 2). The same was not observed for the Kårvatn lysimeters, although toward the end of the experiment a similar difference occurred (Fig. 2). The lack of difference between the moorgrass and heather for the Kårvatn lysimeters could be due to less difference between the vegetation types.


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  		Table 5. Correlations between some components in the leachate from the Storgama (S) and Kårvatn (K) lysimeters. M = moorgrass lysimeters, H = heather lysimeters, N = normal rain (pH 5.3), and A = acidic rain (pH 4.3). A plus sign = positive correlation, while a minus sign = negative correlations at a significance level p < 0.05. The analyses are based on the mean of two replicates. DOC = dissolved organic carbon.

 
As 50 to 70% of the total P in organic soil horizons generally is found to be bound in organic form (Vaithiyanathan and Correll, 1992; David et al., 1995), the concentration of total P in the leachate is likely to be closely linked to the leaching of DOC. The significantly positive correlation between DOC and total P in the present study supports this (Table 5). The concentrations of total P were low (Table 4). The higher concentrations in the leachate from the Kårvatn lysimeters were due to high concentrations the first year of treatment. Values for total P in the leachate from uncultivated soils given in Arthur and Fahey (1993) and Qualls and Haines (1991) are comparable or slightly lower than our values. The treatments did not appear to have any effect on total P in the leachate.

Inorganic Anions
Based on the volume-weighted average for the whole experimental period inorganic anions were leached from the soil in the following order of magnitude (by charge) irrespective of sites, vegetation, or treatment:

The dominance of Cl- in the leachate was to be expected as the concentrations of Cl- in the rain applied were relatively high and soils generally have a low ability to sorb Cl-. Compared with the natural precipitation in the Storgama area the Cl- concentrations in the rain applied were particularly high (Tables 1 and 3). The Cl- input was comparable with Kårvatn's more sea salt–influenced rain. The input ratio of [Na] to [Cl] was 0.73 while the ratios in the leachate were between 0.5 and 0.7, suggesting that Cl- was more mobile than Na+. Chloride showed a significantly positive correlation with H+ in all lysimeters except the Kårvatn moorgrass lysimeters (Table 5). This points to the importance of sea salt episodes for acidification and to Cl- as an important cause of acidity in runoff (Skartveit, 1980; Christophersen et al., 1982a; Wright et al., 1988b; Hindar et al., 1995).

The concentrations of SO2-4 were significantly higher in the leachate from the Storgama lysimeters than from the Kårvatn lysimeters, regardless of treatment (Table 4). For the Storgama lysimeters receiving "acid rain" the amount of SO2-4 in the leachate was by charge almost equal to the amounts of Cl- leached. This difference between the two sites may be attributed to the longer exposure to acid precipitation with higher doses of SO2-4 of the Storgama soil. Despite the low sorption capacity of these soils they must have retained some SO2-4, which subsequently was leached. Dahl et al. (1979) showed by using radioactive SO2-4 in minicatchments with similar soils as in this study that although the input on average equaled the output of SO2-4, some of the radioactive SO2-4 was retained. This implied that the radioactive SO2-4 had replaced some previously retained sulfate. Generally, the highest concentrations of SO2-4 were found in the leachate in the early spring and late autumn (Fig. 3) . The same patterns have been found in other lysimeter and catchment studies (Likens et al., 1977; Gjessing et al., 1976; Dovland and Semb, 1978; Dahl et al., 1979; Christophersen and Wright, 1980; Wright et al., 1986). The seasonal variation was less evident the second year of treatment when the rain was applied in episodes. However, SO2-4 concentrations were then particularly high after periods of drought (Fig. 3). Similar observations were made by Bergseth (1978), Christophersen and Wright (1980), Christophersen et al. (1982a), and Wright et al. (1986), and they explained this by increased sulfur mineralization.



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  		Fig. 3. Concentrations of SO2-4 (µM) for the Storgama lysimeters shown as mean of two replicates: {circ} Heather "normal rain," • Heather "acid rain," {star} Moorgrass "normal rain," * Moorgrass "acid rain," F = frost, D = drought.

 
Sulfate was the only chemical component that showed any significant (p < 0.05) difference due to treatment for the whole experimental period and both sites. Comparisons between the leachate from the Storgama lysimeters receiving "acid rain" and "normal rain" showed that the differences in concentrations of SO2-4 rapidly approached the differences between the "rain" qualities applied. This difference was maintained throughout the experiment. During the simulated snowmelt and in the year with episodic application of rain, the differences in the SO2-4 concentrations in the leachate between treatments appeared to be enhanced (Fig. 3). This was probably due to less contact time between soil and water. This applied to lysimeters from both sites, although for the Kårvatn lysimeters the differences in the leachate generally were less than between the applied rain. For the Kårvatn lysimeters the difference was smallest the first year but increased as the experiment proceeded. Sulfate was significantly positively correlated with most base cations in the leachate. This suggests that a reduction in SO2-4 input would reduce the loss of particularly Ca2+ and Mg2+, and thereby reduce the rate of soil acidification. However, while there was a positive correlation between SO2-4 and H+ for the Storgama heather lysimeters there was no correlation or even negative correlations for all the other lysimeters (Table 5). This suggests that a reduction of SO2-4 in the precipitation does not necessarily lead to a reduction in the H+ concentrations of the leachate, at least not in the short term. There was no correlation between SO2-4 and total Al, except for the Storgama heather lysimeters receiving "normal rain" (Table 5).

The concentrations of NO-3 in the leachate were very low compared with Cl- and SO2-4 (Table 4). This applied to all lysimeters, except one of the Storgama heather lysimeters receiving "acid rain." Between 30 and 70% of the ingoing NO-3 was leached from this lysimeter. The seasonal variation in the leachate of NO-3 from the Kårvatn lysimeters is reflected in the significant positive correlation between the NO-3 and amount of water (Table 5). This shows that the nitrate leaching is lowest in the growing season. However, for the Storgama lysimeters, NO-3 showed a negative correlation with the water flux. The second year when the rain was applied episodically, the leaching pattern of NO-3 from the Storgama lysimeters became highly irregular and the difference between the treatments increased (Fig. 4) . Drought periods appear to cause peaks in the NO-3 concentrations. Drought was more frequent for the Storgama lysimeters than for the Kårvatn lysimeters, mainly because of more "rain" applied to the Kårvatn lysimeters. Nitrate was poorly correlated to other components in the leachate but the concentrations were low. For the Storgama lysimeters, however, a significant positive correlation was found between NO-3 and the base cations (Table 5). Except for the Storgama moorgrass lysimeters receiving "acid rain," which showed a significant positive correlation, NO-3 was not significantly correlated to H+ (Table 5). This suggests that although some NO-3 is leached, it does not contribute much to the acidity of the percolating water.



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  		Fig. 4. Concentrations of NO-3 (µM) for the first two years for the Storgama lysimeters shown as mean of two replicates: {circ} Heather "normal rain," • Heather "acid rain," {star} Moorgrass "normal rain," * Moorgrass "acid rain," F = frost, D = drought.

 
Acidity and Aluminum
Total Al appears to be more readily leached from the moorgrass lysimeters than from the heather lysimeters (Table 4). There were no significant differences in Al concentrations in the leachate due to treatment. However, slightly more Al was leached from the lysimeters receiving "acid rain" (Table 4). This is in accordance with several other studies that show that acidification may cause increased Al concentrations in the leachate by solubilization of organo–metallic complexes (Krug and Isaacson, 1984; Cronan et al., 1986; Mulder et al., 1989; Walker et al., 1990; Berggren and Mulder, 1995; Wesselink et al., 1996). A more moderate response of Al release with decreasing pH will be expected compared with a solubility controlled by Al(OH)3 (Bloom and Grigal, 1985). Total Al is positively correlated with DOC (Table 5). It is well documented that Al solubility in acid soils is controlled by complexing mechanisms with soil organic matter (Driscoll et al., 1985; Cronan et al., 1986; Mulder et al., 1989; Walker et al., 1990; Berggren and Mulder, 1995; Wesselink et al., 1996). No analytical speciation of Al has been carried out but speciation calculations were done by use of the ALCHEMI equilibrium model (Schecher and Driscoll, 1987) including a triprotic acid model. For the model calculation default parameters (Schecher and Driscoll, 1987), a DOC correction factor of 0.043 was used, along with the following assumptions: pCO2 = 3.50, temperature = 10°C, F = 2.0 x 10-6 M, and Si = 6.0 x 10-5 M. We consider the chosen assumptions to be fairly realistic for the two sites. The calculations indicate that 22 to 45% of the total Al is in the form of Al3+ and 36 to 65% as organically complexed Al (Table 4). This leaves 12 to 24% of the total Al as inorganic forms other than Al3+. The percentage of Al3+ is higher for the Storgama lysimeters (24–45%) compared with the Kårvatn lysimeters (22–28%). This gives a higher percentage of organically complexed Al for the Kårvatn lysimeters (56–65%), since the percentages of other inorganic forms are quite similar for the two sites (10–24%). The calculated saturation index (log Kso = 7.74) (Wesolowski and Palmer, 1994) indicates that the moorgrass lysimeters from Storgama are closest to equilibrium with gibbsite due to a higher pH for these lysimeters (Table 4). Based on the calculated Al charge (Table 4), the contribution of Al to the cationic charge of the leachate is about 8% for the heather lysimeters and about 15% for the moorgrass lysimeters from Kårvatn and about 14% for the heather lysimeters and between 17 and 30% for the moorgrass lysimeters from Storgama. James and Riha (1986) studied pH buffering in a forest soil organic horizon and found that the contribution of Al to total cationic charge in solution was <1%, while Nätscher and Schwertmann (1991) found the contribution to be between 5 and 10% for various organic horizons in acid forest soil. Results from these studies are lower or in the lower range of what we found based on the model calculations.

The H+ concentrations were generally negatively correlated with the water flux (Table 5), which means that the acidity decreased when greater amounts of water passed through the soil. For the Storgama lysimeters there was a significantly higher pH in the leachate from the moorgrass compared with the heather lysimeters (Fig. 5) . This is connected to higher DOC concentrations in the leachate from the heather lysimeters. Slightly higher concentrations of H+ were found in the leachate from the lysimeters receiving "acid rain." Differences in H+ concentrations between treatments were generally more pronounced in periods with simulated snowmelt and higher percolation (Fig. 5). Cracks and macropores, which are more pronounced after periods of frost and drought, allow water to pass through the soil more rapidly, leaving less opportunity for buffering reactions to take place. There was, however, no significant difference between the treatments for the experiment as a whole. However, differences between the treatments appeared to increase as the experiment proceeded (Fig. 5). On average, the treatments caused differences between 0.05 and 0.15 pH units in the leachate, with moorgrass giving the greatest differences (Table 4). Wright et al. (1988a) studied exclusion and addition of acid precipitation in minicatchments with soils comparable with those of this study and found effects on the pH of the leachate in the same range as in our study. The pH of the precipitation at Storgama has improved in the last decade from 4.3 in the period 1980–1983 to 4.5 in the period 1995–1999 (Table 1). Our study suggests that this improvement will have a minor effect on the pH of the leachate from the soil in this area.



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  		Fig. 5. pH variations for lysimeters from both sites shown as mean of two replicates: {circ} Heather "normal rain," • Heather "acid rain," {star} Moorgrass "normal rain," * Moorgrass "acid rain," F = frost, D = drought.

 
Base Cations and Ammonium
The leaching of base cations and ammonium ranked by charge for the whole period were as follows:

Storgama: Moorgrass:Na+ > NH+4 > K+ > Ca2+ > Mg2+ Heather:"Normal rain": NH+4 > Na+ > K+ > Ca2+ > Mg2+"Acid rain": Na+ > NH+4 > K+ > Ca2+ > Mg2+Kårvatn: Moorgrass:Na+ > NH+4 > Mg2+ > K+ > Ca2+ Heather:Na+ > NH+4 > K+ > Mg2+ > Ca2+

The site, vegetation, and treatment appeared to have little influence on the ranking of the base cations in the leachate. If Al is given a charge of +1.5 the contribution to the total cationic charge will be between 25 and 36% for Na+, 18 and 30% for NH+4, 9 and 18% for K+, 6 and 13% for Mg2+, and 7 and 8% for Ca2+. The dominance of Na+ among the base cations in the leachate may be explained by the relatively high amounts of Na in the rain applied (Table 3) along with a low retention of Na+ in the soil (Christophersen et al., 1982a).

Depletion of divalent base cations from soil exposed to acid precipitation is well documented due to exchange of H+ against the base cations and the high mobility of sulfate (Abrahamsen et al., 1994). Though there were no significant differences, higher amounts of base cations were leached from the lysimeters receiving "acid rain" (Table 4). If each year is considered separately the Storgama lysimeters showed significantly (p < 0.05) higher concentrations of Ca2+ from the lysimeters receiving "acid rain" the first year. This suggests that Ca2+ was rapidly leached from the system and that weathering or biological cycling of Ca could not compensate for this loss. For the Kårvatn lysimeter the Mg2+ concentrations were significantly (p < 0.05) higher from the lysimeters receiving "acid rain" the fourth year of the experiment. Magnesium dominated over calcium in the leachate from Kårvatn, probably reflecting the influence of sea salt. The lag in time before the treatment had any significant effect on leachate of divalent cations for the Kårvatn lysimeters may be due to changes in the organic matter and protonation of weak organic acids (James and Riha, 1986).

The base cations from the heather lysimeters were generally negatively correlated to the water flux (Table 5). High concentrations were found in the very first leachate after the frost period. However, the concentrations decreased rapidly during the simulated snowmelt, followed by a gradual increase through the summer and a drop in concentrations in the late autumn and winter. The episodic application of rain the second year caused a more irregular leaching pattern, camouflaging the seasonal variation somewhat. The positive correlation between the base cations and SO2-4 and Cl- suggest that "acid rain" and sea salt episodes contribute to the depletion of base cations from the soil (Table 5).

The NH+4 concentrations in the leachate from the Kårvatn lysimeters were very high the first year of treatment but decreased gradually to very low values the last two years of the experiment. This suggests that in the first year of treatment the Kårvatn lysimeters were quite severely affected by increased mineralization caused by soil disturbances when the lysimeters were installed. Arthur and Fahey (1993) found that soil disturbances may have a long time effect, causing elevated concentrations of NH+4 in the leachate particularly from organic horizons. There was generally a peak in the concentration after the simulated snowmelt. The episodic application of rain caused an irregular leaching pattern both for the Kårvatn and Storgama lysimeters. For the Storgama lysimeters the episodic application also caused a greater leaching of NH+4 compared with the other years. This suggests that frost and drought have a large effect on decomposition and mineralization of organic matter and thereby the concentrations of NH+4 in the leachate.


   CONCLUSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
REFERENCES
 
The leachate quality from these shallow organic matter–rich soils was influenced by (i) the region from where the soils were collected, (ii) the vegetation type, (iii) the season of the year and the water fluxes, (iv) frost and drought periods, and (v) the quality of the "rain"

The soil in the Kårvatn lysimeters was slightly deeper and also these lysimeters received larger amounts of "rain" than the Storgama lysimeters. This may explain some of the differences in concentrations observed between the two sites. Site history also appears to influence the leachate quality. Kårvatn is a highly sea salt–influenced area while Storgama has received anthropogenic acid precipitation for a long period. The lysimeters from Storgama had clearer differences in vegetation than those from Kårvatn. This was probably the reason why there were more differences between the vegetation types in the leachate quality from the Storgama lysimeters than from the Kårvatn lysimeters.

Dissolved organic carbon is a very important component in the leachate from the soils studied and the concentrations were generally higher from the Kårvatn lysimeters than from the Storgama lysimeters. The heather lysimeters from Storgama had higher DOC concentrations than the moorgrass lysimeters. Dissolved organic carbon increased after frost and drought periods and was diluted by high water fluxes. Dissolved organic carbon was not obviously affected by the acidity of the "rain."

The molar charge concentrations of inorganic anions in the leachate decreased in the order Cl- > SO2-4 >> NO-3. The high concentrations of Cl- reflect that the "rain" used in this study had Cl- concentrations typical for precipitation in areas near the coast. The Kårvatn lysimeters had somewhat higher Cl- concentrations than those from Storgama, which probably reflect Kårvatn's proximity to the sea. The concentration of SO2-4 in the leachate reflected the differences in the concentrations in the two "rain" qualities. But also the historic pollution appeared to influence the SO2-4 concentrations in the leachate. Lysimeters from Storgama in southernmost Norway had higher concentrations than those from Kårvatn, and also greater differences between the two "rain" qualities.

The concentrations of cations in the leachate decreased in molar charge concentrations in the order Na+ >= H+ > NH+4 > K+ > Mg2+ >= Ca2+. Of the Al components only total Al was measured. Model calculations indicated that roughly 50% of total Al is complexed with organic matter. The Al charge varied between +1.4 and +2.0 and the contribution of Al to the cationic charge of the leachate varied from 7 to 30%. Sodium and Mg2+ were somewhat higher from the Kårvatn soil and this again reflects the proximity to the sea.

Correlation coefficients indicate that decreased SO2-4 concentrations in the precipitation will reduce the concentrations of NH+4 and base cations in the leachate more that those of H+ and Al. This implies that a reduction in SO2-4 concentration from 32 to 9 µM, corresponding to an increase in "rain" pH from 4.3 to 5.3, is not likely to influence the pH and Al concentrations in runoff from these soils very much. A pH change in the leachate of 0.05 to 0.15 units might be expected at the pH input levels used in this study.


   ACKNOWLEDGMENTS
 
The authors wish to thank Jan Mulder for his help with the ALCHEMI modeling.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSION
 REFERENCES
 





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