Effects of past fly ash deposition on the forest floor humus chemistry of pine stands in Northeastern Germany

Forest Ecology and Management 183 (2003) 113–126

Effects of past fly ash deposition on the forest floor humus chemistry of pine stands in Northeastern Germany Susanne Klose*, Franz Makeschin Faculty of Forest, Geo and Hydro Sciences, Institute of Soil Science, Dresden, University of Technology, P.O. Box 1117, D-01735 Tharandt, Germany Received 27 February 2002; received in revised form 26 November 2002; accepted 11 February 2003

Abstract Humus morphology and chemical characteristics of forest soils subjected to long-term deposition of alkaline and acid air pollutants were studied in pine forests on sandy substrates in Northeastern Germany. High emission rates of fly ash in the past caused an accumulation of mineral particles and ferromagnetic fly ash constituents in the organic layer. Mass and total ash content of organic horizons and magnetic susceptibility measurements suggested that fly ash was mainly accumulated in the F and H horizons of the forest soil. Total mass of organic layers at sites with heavy deposition loads were as high as 132 t ha
1. The F and H horizons of fly ash affected forest soils showed mineral contents of up to 59 and 79%, respectively. By measurements of magnetic susceptibility, it was shown that magnetic fly ash particles were found in the fine fractions (125–63 and <63 mm). Fly ash deposition significantly increased the pH values in the L, F and H horizon and mineral topsoil (0–10 cm). Lower pH values in the L layer compared to F and H horizons indicated a re-acidification of these forest soils due to reduced depositions of alkaline ash. Significantly higher concentrations of NH4Cl extractable cations (i.e. ‘effective cation exchange capacities’) and ‘base saturations (BS)’ of >90% were found in the humic horizons at sites where pH was increased due to high fly ash emissions. Stocks of basic cations were dominated by Ca2þ and decreased significantly along the fly ash deposition gradient from 46.33 to 6.91 kmol IE ha
1. Proportions of water extractable cations on NH4Cl extractable cations increased in the forest soil with decreasing deposition loads. Particularly monovalent cations (i.e. K and Na) are more mobile in fly ash influenced soils than bivalent cations (i.e. Ca, Mg). Stocks on organic C and total N decreased along the deposition gradient from 26.7 to 17.5 t C ha
1 and from 1.257 to 0.792 t N ha
1. In contrast, C/N ratios of the organic horizons increased from about 20 to 22 for F and H horizons. Measurements of hot water and cold water extractable organic C suggest that the availability of soil organic matter is reduced in soils with high historical fly ash loads. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Forest soils; Fly ash; Emissions; Humus morphology; Acid neutralization capacity; Ca stocks; Carbon and nitrogen budgets

1. Introduction * Corresponding author. Present address: Department of Vegetable Crops, University of California at Davis, 1636 East Alisal Street, Salinas, CA 93905, USA. Tel.: þ1-831-755-2805; fax: þ1-831-755-2898. E-mail addresses: [email protected], [email protected] (S. Klose).

In former East Germany the use of lignite as the main source of energy resulted in heavy air pollution as emission control was inadequate. Consequently, considerable amounts of acid (i.e. SO2, NOx) and alkaline (dust, fly ash) compounds were deposited

0378-1127/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0378-1127(03)00099-9

114

S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

into ecosystems surrounding the power stations. In 1989, 5.3 Mt of SO2 and 2.1 Mt of alkaline dusts were emitted in total in East Germany (Finkbeiner et al., 1993). At point sources in the industrial region Leipzig–Halle–Bitterfeld more than 100 kt SO2 were emitted annually. Peak concentrations of 2800 mg SO2 m
3 (Bitterfeld) to 4500 mg SO2 m
3 (Leipzig) were recorded during meteorological inversions (Bellmann and Grote, 1998). Thus, the Du¨bener Heide, a forested area of about 450 km2 located to the east of the industrial centre, is most severely influenced by atmospheric depositions. The deposition of air pollutants within the Du¨bener Heide forest area followed a steep gradient with highest concentrations close to the industrial centre, and decreasing concentrations towards the north-east according to the prevailing wind direction (i.e. south-west). In the mid 1980s, the annual SO2 concentration varied from about 150 to 70 mg m
3 from the western to the eastern border of the Du¨bener Heide, while background concentrations of 37 mg m
3 where obtained from Neuglobsow located in northern Brandenburg (Bellmann and Grote, 1998). Unfortunately, no data about the temporal development of fly ash, dust, NOx and NH3 concentrations in the region before the German reunification in 1990 are available. A significant decrease in SO2 and alkaline dust depositions was observed after 1990, where industrial complexes were either closed or modernized. During 1989 and 1996, annual emissions of SO2 and fly ash decreased from 1200 and 600 kt to 100 and 0.2 kt, respectively (Neumeister et al., 1997). In contrast, NOx emission from agriculture, industry and traffic slightly increased in the same time period. Thus, the buffer mechanism of alkaline dust in the atmosphere was disrupted and ‘‘acid rain’’ was observed for the first time in the Du¨bener Heide forest area after the German reunification. Atmospheric dust emitted in the Du¨bener Heide region contained substantial amounts of SO3, CaO, SiO2, Al2O3, Fe2O3 and MgO, and to a much lesser content, other oxides, such as MnO2, P2O5, TiO2, Na2O, and K2O. Furthermore, anions, such as Cl
and F
and heavy metals (i.e. Cu, Cr, Mo, Pb) were detected in dust sediments in this region (Baronius, 1992). Generally, the deposition gradient of the acid component of these emissions, i.e. SO3, increased with distance from the industrial source from 0.5 to 14.0 km, whereas main proportions of the alkaline

constituents (CaO, MgO, Fe2O3) with coarser particle sizes (>20 mm diameter) were transported only over short distances (Erhard and Flechsig, 1998). First symptoms of a wide-ranging forest damage due to air pollution were observed at the beginning of the 1970s where crown structures were examined. It is well known that, during the past decades, soil chemical properties in German forest ecosystems were rapidly changing (Ulrich et al., 1979; Hildebrand, 1986; Matzner, 1987; Kopp and Kirschner, 1992; Konopatzky and Freyer, 1996). At the end of the 1960s, base saturations (BS) varying between >65% and 20–35% were mapped in the organic layers in the Du¨bener Heide. With regard to soil pH, two contrasting developments were observed: (1) an alkalization and (2) a re-acidification. Until the mid-1960s, the pH values of the topsoils increased due to the deposition of fly ash with large amounts of basic cations. As a result of the installation of dust filters in power plants, the deposition of basic cations decreased, whereas acid deposition remained constant or even increased until the mid-1980s. Subsequently, a re-acidification of the forest surface soils started (Bellmann and Grote, 1998). Forest soils in the Du¨bener Heide area were limed until the 1960s and fertilized with urea from the end of the 1960s until the mid-1980s, generally at total amounts of 300–1000 kg N ha
1, distributed over 3–12 years, to mitigate soil acidification and nutrient imbalances caused by acid deposition (Baronius, 1992; Bellmann and Grote, 1998). As a consequence, increases in total nitrogen stocks, decreases in C/N ratios of the humus layer, and changes in humus forms were observed between 1967 and 1989 (Bellmann and Grote, 1998). The main objectives of this field study were to estimate humus morphology, physico-chemical properties and element budgets in five forest stands along a 90-year fly ash deposition gradient. The results of this study should provide useful tools for risk assessment in such forest ecosystems resulting from the current soil conditions and the future development of soil properties.

2. Material and methods 2.1. Site conditions The field study was carried out in the Du¨bener Heide forest area, which is directly influenced by

S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

115

Table 1 Selected site and stand characteristics of the five sites along the fly ash deposition gradient in the Du¨ bener Heide forest district, NE Germany Site and stand characteristics

Site 1

Description Geographical location Distance to Bitterfeld (km) Annual precipitation (mm) Annual temperature (8C) Stand age (year)a Soil type Humus form a

2

3

Burgkemnitz Schkoena 518400 8900 N 518400 5400 N 128240 3000 E 128320 3300 E 8 16 520–560 8.5–9.0 P. sylvestris (86) P. sylvestris (86) Q. petreae (26) Eutric Cambisol (with relictic albic Fine humus-rich raw humus-type moder

4

5

Buchholz 518430 9300 N 128300 8700 E 14

Eisenhammer Grosswig 518380 4300 N 518410 3000 N 128370 2100 E 128400 5500 E 18 25 580–650 8.0–8.5 P. sylvestris (96) P. sylvestris (89) P. sylvestris (98) F. sylvatica (39) P. sylvestris (73) properties) Eutric Cambisol Albic Cambisols Fine humus-poor raw humus-type moder

In 1999.

the emissions of the former major industrial centre Halle–Leipzig–Bitterfeld. With an extent of 450 km2, 75% of the area is covered by forests, about 50% of them even-aged stands of Scots pine (Pinus sylvestris L.). The Du¨ bener Heide is located in the loess-free Pleistocene region between the rivers Elbe and Mulde in the northeastern German lowlands. The experimental sites are situated at an altitude of 80–190 m along a deposition gradient from the southwestern (Burgkemnitz) towards the northeastern (Grosswig) direction of the industrial complex of Bitterfeld–Wolfen–Zschornewitz. Geographical location, site and stand characteristics are summarized in Table 1. 2.2. Soil sampling and pre-treatment Four composite samples from the L (Oi), F (Oe) and H (Oa) horizon and the uppermost mineral horizon (0–10 cm) were taken at all five sites in Spring and Fall of 1999 and 2000. Composites were made from five to eight random samples from an area of 400 cm2 each from the northern, eastern, southern and western directions from the center of the plot (total plot size: 400 m2) to obtain site-representative surface samples. Samples of the forest floor were collected on a volume basis in order to calculate total mass of organic layers and element stocks. Samples were sieved through a 5 and 2 mm meshes size for organic and mineral soils, respectively. Prior to chemical analyses, samples were dried at 60 8C for 96 and 48 h for humic and mineral soils, respectively.

2.3. Parameters Total ash content was measured by the loss-onignition method that includes the combustion of the oven-dried soil at 430 8C until the weight of the sample remained constant (about 16 h). Particle size separation was done on selected samples of the H and F horizons and mineral topsoil of site 1 to detect the particle sizes of accumulated fly ash. The procedure for the recovery of fly ash from these samples has been described in Klose et al. (2003). Briefly, particle size separation was carried out by a combination of wet sieving and sedimentation following ultrasonic treatment. Four sand fractions were separated by wet sieving of the soil suspension (1:8 w/v). One mixed silt-clay fraction <63 mm was recovered after centrifuging and drying of the remaining sample at 105 8C. Magnetic susceptibility measurements were conducted on all five particle size fractions. Magnetic susceptibility is a measure for the induced magnetization of a sample brought into contact with a magnetic field. Ferromagnetic susceptibility was analysed on dried and ground samples (<180 mm) by the method described by To¨ lle and Raasch (1989). This method is based on the determination of changes in frequency Df, when 5 cm3 of soil is inserted into the alternated magnetic field of a coil generated by an oscillator in the Ferromagnetic Analyser FMA 5000 (Forgenta, Berlin). The pH was determined by a combination glasselectrode in 0.01 M CaCl2 solution and in H2O after

116

S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

4 h (1:10 and 1:2.5 (w/v) for mineral and organic soils, respectively). Total C and N contents were analysed on <180 mm samples by a flame photometrical method using a CNS-Analyzer (model Foss Heraeus). For estimation of short-term available C and N fractions (cold-water extractable C and N; CWC and CWN, respectively) field-moist soil was extracted with H2O (1:5 and 1:20 (w/v) for mineral and organic soils, respectively) by shaking at 180 rev min
1 for 24 h, centrifuged for 15 min at 4000 rev min
1, and measured with a multi N–C-analyzer (Jena Analytics). The medium-term available C and N fractions were obtained by boiling a soil–water solution for 1 h by the method described by Bronner and Bachler (1979). Soil–water ratio and procedure following boiling was in accordance with cold water extracts. For estimation of H2O extractable cations (water extracts, WE), 25 g of mineral soils and 5 g of organic soil were suspended in 50 ml of deionised water and shaken horizontally at 180 rev min
1 for 24 h. The extracts were filtered through a 0.45 mm membrane filter, H concentration was determined by a pH electrode, concentrations of Ca, Mg, Na, Mn, Fe, Al by a ICP-OES and K by AAS. NH4Cl-extractable cations (salt extracts, SE) were determined after extraction with 0.5 M NH4Cl-solution (1:40 and 1:80 (w/v) for mineral and organic soils, respectively). Samples were shaken at 180 rev min
1 for 2 h in the evening before and for another 30 min in the morning of filtration. Concentrations of cations were analysed as described for WE cations. 2.4. Data analyses The data presented in this paper are median values of all four occasions to exclude seasonal and annual effects. Bulk densities (g cm
3) and dry weight of organic horizons (t ha
1) were used for calculation of element stocks (kg ha
1). The data are expressed on an oven-dry basis. Moisture was determined from weight loss after drying at 105 8C for 48 h. Statistical analysis, including multivariate data analysis (MANOVA), separation of means by the Kolmogorov–Smirnov test and correlation analysis by Spearman were performed by the Statistical Package for the Social Sciences (SPSS version 10.0.7 for Windows).

3. Results 3.1. Mass of the organic horizons, total ash content and magnetic susceptibility Total weight of organic layers decreased with distance to the emission source from 132 to 73 t ha
1 at sites 1 and 5, respectively (Fig. 1). Differences in weight of organic layers between the five sites were mainly caused by variations in the F and, to a much lesser degree, in the H horizon. The total ash contents of the forest floor in the Du¨ bener Heide region were unusually high, ranging between 12 and 24% in L horizon, 39 and 59% in F horizon, and 73 and 79% in the H horizon (Fig. 2). A tendency for decreasing ash contents from site 1 to 5 was observed for the L and F horizons. The Kolmogorov–Smirnov test revealed that differences in ash content in the L horizon were significant for the following comparisons: site 1 and 3, site 1 and 5, site 2 and 3, site 2 and 5, site 3 and 4 and site 4 and 5 (P < 0:05). In the F horizon significant (P < 0:05) differences were observed between site 1 and sites 3, 4 and 5, and between site 2 and sites 3, 4 and 5. Significant differences in ash content of the H horizon were found between site 1 and sites 2 and 5, and between sites 2 and 4 (P < 0:05). Accumulation of fly ash in forest soils can be monitored by magnetic susceptibility measurement (Klose et al., 2001, 2003). Fly ash from lignite-fired power plants surrounding the study area showed strong magnetic properties varying between 350 and 601  10
8 m3 kg
1 for the power stations Lippendorf and Zschornewitz, respectively. Magnetic susceptibility values were highest in the fine fractions (125–63 mm and <63 mm) of the F and H horizons with values up to 669  10
8 m3 kg
1 and lowest in the mineral soil with values of <10  10
8 m3 kg
1 (Table 2), indicating that high total ash contents of the H and F horizons in this study were mainly attributed to fly ash accumulations. 3.2. Soil pH, effective cation exchange capacity (ECEC) and base saturations (BS) Fly ash deposition significantly increased pH values in the L, F and H horizons and mineral topsoil (0– 10 cm) along the fly ash deposition gradient (Table 3).

S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

117

Fig. 1. Total mass of organic horizons along the fly ash deposition gradient in the Du¨ bener Heide forest area (results are median values of four field reps taken at four occasions in 1999 and 2000). Sites were located 8, 16, 14, 18, and 25 km from the Bitterfeld industrial area, respectively.

Fig. 2. Total ash content of the organic horizons and mineral soil (0–10 cm) along the fly ash deposition gradient in the Du¨ bener Heide forest area (results are median values of four field reps taken at four occasions in 1999 and 2000). Sites were located 8, 16, 14, 18, and 25 km from the Bitterfeld industrial area, respectively.

118

S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

Table 2 Particle size distribution and magnetic susceptibility of selected samples from F and H horizons and mineral topsoil (0–10 cm) in the Du¨ bener Heide forest district, NE Germany Horizon

Particle size (mm)

Relative contribution mass (%)

Magnetic mass susceptibilitya (10
8 m3 kg
1)

F (Oe)

2000–630 630–200 200–125 125–63 <63

25.9 33.3 18.1 9.3 13.3

332 83.7 69.4 539 669

H (Oa)

2000–630 630–200 200–125 125–63 <63

20.0 42.3 17.0 9.2 11.5

295 78.3 108 403 546

0–10 cm

2000–630 630–200 200–125 125–63 <63

12.9 56.3 16.9 5.6 8.2

8.25 3.03 4.48 32.3 123

a

Magnetic mass susceptibility ¼ magnetic volume susceptibility/bulk density. Magnetic volume susceptibility ¼ FMA value ðmHzÞ  ð0:7  10
5 Þ (Klose et al., 2003).

Differences between the five forest sites became most evident in the F and H horizons. The pH (CaCl2) followed the same distinct gradient as the pH (H2O) (data not shown). Separation of means by the Kolmogorov–Smirnov test revealed that pH differences were, in general, significant (P < 0:05) between site 1 and all other sites, and between site 2 and all other sites. In the H horizon and 0–10 cm of mineral soil, pH values differed significantly (P < 0:05) between all sites, with exception for the comparison between site 4 and 5 in the mineral soil (Table 3). The soil acidification potential (SAP, i.e. difference between pH (H2O) and (CaCl2)) was, in general, higher at sites that formerly received higher fly ash (i.e. Ca and Mg) loads than less influenced sites (Table 3). The ‘effective cation exchange capacities’ (ECEC) decreased significantly from site 1 to site 5 and within one site from the L horizon to the mineral soil (0– 10 cm) (Table 3). Differences in ECEC were significant over the 2-year investigation period for the comparison of site 1 and all other sites for the F and H horizons, between sites 2 and 3 in the F horizon, and between sites 2 and 5, sites 3 and 5, and sites 4 and

5 in the H horizon. This trend was also significant for the L horizon, with exception for the comparison between sites 1 and 2, and sites 2 and 3. ECEC values in the L horizon differed significantly between site 1 and all other sites as well as between site 3 and sites 4 and 5 (Table 3). Nevertheless, ECEC values expressed relatively high spatial and temporal variations, especially at site 1. The high variations in the L horizon and mineral soil can partly be attributed to the composition of freshly fallen litter and to varying intensity of the pollution in the past, leading to a inhomogeneous mosaic of chemical soil properties. BS of more than 96% were detected in surface soils at site 1 (high fly ash loads), while those at site 5 (low fly ash loads) had BS between 23 and 48%, freshly fallen litter (L) excluded (Table 3). The development of BS along the deposition gradient separates site 1 (high fly ash load), from sites 2 and 3 (intermediate loads), and from sites 4 and 5 (low loads). The Kolmogorov–Smirnov test revealed that this trend was in general significant for the F and H horizons and the mineral soil. BS of the L horizon differed significantly for site 1 and all other sites (Table 3). Proportions of water extractable cations (WE) on salt extractable cations (i.e. NH4Cl extractable cations, SE) increased in the forest floor and in the mineral topsoil along the fly ash deposition gradient from site 1 to 5 (Table 3). The monovalent cations K and Na were more highly represented in the water extracts compared to the salt extracts, while those of the bivalent cations Ca and Mg were lower in the former. 3.3. Stocks of salt (NH4Cl) extractable and water extractable cations Stocks of salt extractable cations in the humus layer reflect the distinct differences in soil pH and ionic composition of the soil matrix and solution of the five sites studied. Stocks of SE basic cations in the humus layer decreased significantly along the deposition gradient from site 1 (46 kmol IE ha
1) to site 5 (7 kmol IE ha
1) (Table 4). The stratigraphical separation of the humus floor revealed that cations were mainly retained in the F and H horizons. The cation stocks were dominated by Ca2þ. Relative contributions of Ca2þ to the sum of salt extractable basic cations in the humic horizons ranged from 71% (F horizon, site 2) to 93% (H horizon, site 1) (Table 4).

S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

119

Table 3 Soil pH (H2O), SAP, ECEC and BS in organic horizons and mineral soils (0–10 cm) in the Du¨ bener Heide forest area (median of four field reps taken at four occasions in 1999 and 2000) Site

Horizon

pH (H2O)

SAPa pH units

ECEC (mmol IE g
1)

BS (%)

WE cations in percentage of SE cations Na

K

Ca

Mg

Sum

1

L F H 0–10 cm

5.12ab 5.19a 5.81a 5.88a

0.44 0.69 0.49 0.64

419.6a 412.3a 264.5a 91.9a

94.5a 96.6a 98.4a 96.7a

99 86 71 84

57 35 31 22

8 4 4 5

16 9 9 10

11 6 6 9

2

L F H 0–10 cm

4.80b 4.81b 4.64b 4.37b

0.44 0.43 0.55 0.57

303.2b 160.3b 149.0b 43.8a

92.9b 82.6b 88.2b 79.1b

91 69 73 96

35 72 39 20

8 5 9 9

17 12 22 20

11 6 14 17

3

L F H 0–10 cm

4.89b 4.92b 5.12c 5.21c

0.57 0.52 0.68 0.62

281.5b 241.4c 159.0b 46.7a

89.4b 76.6b 91.2c 83.2b

63 80 53 67

29 27 21 15

7 6 5 6

12 24 15 14

13 9 8 12

4

L F H 0–10 cm

4.80b 4.29c 4.31d 3.84d

0.51 0.45 0.52 0.44

318.4c 238.1c 156.6b 32.4b

79.1b 44.6c 29.2d 26.5c

97 65 91 47

56 55 56 27

13 6 12 14

27 16 29 34

19 10 13 23

5

L F H 0–10 cm

4.84b 4.53c 4.52e 4.19e

0.58 0.60 0.70 0.56

328.4c 240.6c 96.1c 22.0c

82.8b 47.7c 27.0e 22.5d

81 85 97 80

43 69 67 31

11 7 11 15

22 17 31 41

16 13 16 27

a

Soil acidification potential, calculated from the difference between pH (H2O) and pH (CaCl2). Separation of means by the Kolmogorov–Smirnov test. Different letters indicate significant differences in chemical properties between the five sites studied for a comparison of the same soil horizon (P < 0:05). b

Stocks of salt extractable acid cations, however, increased in the forest floor and mineral topsoil from site 1 (1.4 kmol IE ha
1) to site 5 (6.4 kmol IE ha
1). A similar trend was observed for the mobile fractions of cations (i.e. water extractable cations) in the soil solution. Stocks on mobile basic cations in the humus layer decreased 2.6-fold from site 1 to 5 (Table 4). In contrast, stocks on mobile acid cations increased 2.3-fold, from site 1 to 5. These results followed the fly ash-induced changes of the soil pH. The stocks of mobile cations in the mineral topsoil revealed the same trend as those in humus horizons, but on a much lower level. 3.4. Stocks of organic C and total N, C/N ratio of the humus material and mineral soil and organic C pools Stocks of organic C in the humus layer and mineral soil (0–10 cm) increased after several decades of fly

ash deposition in the Du¨ bener Heide area (Table 5). With exception of site 5, the mineral topsoil stored an important portion of the C in forest soils. Within the organic horizons most C was stored in the F horizon followed by the H horizon. Stocks of total N in the organic layer and mineral topsoil decreased from site 1 to 5. The differences in organic C between site 1 (high fly ash loads) and 5 (low fly ash loads) amounted to 26.6 and 9.2 t ha
1 for mineral soil and humus layer, respectively, which is assumed to be caused mainly by alkaline atmospheric depositions. The differences in total N between sites 1 and 5 amounted to 1.278 and 0.465 t ha
1 for mineral soil and humus layer, respectively. The C/N ratio of the humus material increased in the F and H horizons along the fly ash deposition gradient from 20 to 22 at sites 1 and 5, respectively (Table 5). No distinct trends were observed for the mineral topsoil.

120

S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

Table 4 Stocks of salt and water extractable basic and acid cations in organic horizons and mineral soils (0–10 cm) in the Du¨ bener Heide forest area (median of four field reps taken at four occasions in 1999 and 2000) Site

Horizon

Stocks of salt extractable cationsa

Stocks of water extractable cationsb

Ca þ Mg þ Na þ K kmol IE ha
1

H þ Al þ Fe þ Mn kmol IE ha
1

Ca kmol IE ha
1

L F H SHumus layer 0–10 cm

3.49 30.16 12.69 46.33 0.14

0.19 0.96 0.28 1.43 0.01

2.72 27.49 11.75 41.96 0.13

(78)c (91) (93)

2

L F H SHumus layer 0–10 cm

3.73 10.72 5.67 19.72 0.05

0.28 3.18 0.40 3.85 0.01

3.02 7.59 4.90 15.51 0.05

(81) (71) (93)

3

L F H SHumus layer 0–10 cm

2.03 8.88 4.68 15.59 0.06

0.25 2.71 0.41 3.36 0.01

1.64 8.09 4.36 14.09 0.05

(81) (91) (93)

L F H SHumus layer 0–10 cm

2.59 3.08 1.12 6.78 0.02

0.62 4.68 2.90 8.21 0.04

2.11 2.63 0.91 5.65 0.01

L F H SHumus layer 0–10 cm

2.66 3.60 0.65 6.91 0.01

0.53 3.95 1.87 6.36 0.03

2.13 2.96 0.53 5.62 0.01

1

4

5

(92)

(100)

(92) (82) (85) (81) (78) (80) (82) (82) (74)

Ca þ Mg þ Na þ K kmol IE ha
1

H þ Al þ Fe þ Mn kmol IE ha
1

0.39 1.22 0.96 2.57 0.01

0.05 0.28 0.14 0.47 0

0.25 1.09 0.71 2.05 0.01

0.04 0.23 0.20 0.48 0

0.17 0.71 0.72 1.60 0.01

0.03 0.40 0.29 0.73 0

0.30 0.38 0.46 1.14 0

0.10 0.45 0.58 1.13 0.01

0.30 0.39 0.29 0.98 0

0.12 0.54 0.45 1.10 0.01

a

Salt extractable cations (SE): concentrations of cations extractable in 0.5 M NH4Cl solution. Water extractable cations (WE): cations extractable in deionised water. c Figures in parenthesis are the relative contribution of Ca2þ stocks on the sum of SE basic cations in percentage. b

The N eutrophication level of forest soils Nc, i.e. total N expressed in percentage of organic C, decreased in the F and H horizons along the deposition gradient from site 1 to 5 (Table 5). The N level of F and H horizons in all five sites was grouped as n5, regardless the fly ash load. A comparison of different organic C fractions in humic horizons along the fly ash deposition gradient should allow an evaluation of the site-specific availability of the humus material. In the F horizon, concentrations of total organic C (TOC) increased from 20,605 to 33,077 mg C (100 g
1) from site 1 to 5, and correspondingly, fractions of medium- and short-term available soil organic matter fractions, i.e. hot water- and cold water-extractable organic C

(HWC and CWC) increased in the same order (Fig. 3). In contrast, in the H horizon TOC contents decreased from 15,169 to 9967 mg C (100 g
1) from site 1 to 5, whereas contents of HWC and CWC increased. The HWC and CWC as percentages of TOC increased from sites 1 to 5 from 3.6 to 4.7% and 0.7 to 1.1%, respectively, for the F horizon. Corresponding values for the H horizon were 2.8–6.4 and 0.6–1.0%.

4. Discussion The mass of the organic layer at all five sites along the fly ash deposition gradient in the Du¨ bener Heide forest area was increased up to two-fold when

S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

121

Table 5 Stocks on organic C and total N, C/N ratio, and N eutrophication level in organic horizons and mineral soils (0–10 cm) in the Du¨ bener Heide forest area (median of four field reps taken at four occasions in 1999 and 2000) Site

Horizon

Stocks on Organic C t ha
1

Total N t ha
1

L F H SHumus layer 0–10 cm

3.5 13.8 9.3 26.7 43.5

0.125 0.683 0.449 1.257 2.220

L F H SHumus layer 0–10 cm

4.3 16.3 4.5 25.1 36.3

0.164 0.720 0.204 1.089 1.897

L F H SHumus layer 0–10 cm

3.3 13.2 4.2 20.8 29.3

0.118 0.620 0.246 0.983 1.406

4

L F H SHumus layer 0–10 cm

4.0 8.7 5.6 18.3 37.7

0.136 0.410 0.294 0.840 1.858

5

L F H SHumus layer 0–10 cm

4.2 9.8 3.6 17.5 16.9

0.151 0.483 0.158 0.792 0.942

1

2

3

a b

C/N ratio

Nca

N levelb

31.3 19.7 20.6

3.2 5.1 4.9

n3 n5 n5

20.7

4.8

n5

28.5 20.0 20.4

3.5 4.8 4.9

n4 n5 n5

19.4

5.2

n5

28.2 22.2 22.4

3.5 4.5 4.5

n4 n5 n5

21.0

4.8

n5

28.6 21.4 21.6

3.5 4.7 4.7

n4 n5 n5

20.2

5.0

n5

26.8 22.0 22.2

3.8 4.8 4.5

n4 n5 n5

18.2

5.5

n5

Nc ¼ N eutrophication level, calculated from Nt in percentage of Ct. Groupings in accordance to Konopatzky and Freyer (1996).

compared to results of the German national forest inventory conducted between 1987 and 1993. The mass of the humic layers of the monitored 1650 forest sites ranged between 7 and 73 t ha
1 (10 and 90 percentile) (median ¼ 18 t ha
1) (Deutscher Waldbodenbericht, 1996). The development of ash contents in the H horizon along the deposition gradient reflects different periods of pollutant deposition. These periods range from very high deposition loads of SO2 and fly ash in the early 1970s to periods with less alkaline depositions but still high SO2 emissions in the early 1980s. The results either indicate that the fly ash depositions in the Du¨ bener Heide of the 1970s were remarkably high even at sites that are located about 25 km away from the main emission source at the industrial center Bitterfeld (site 5), or that these sites

were additionally influenced by emissions from the urban-industrial area of Leipzig. The high mass and total ash contents of organic horizons, especially at sites close to the industrial center Bitterfeld, are most likely attributed to the presence of mineral fly ash constituents in the organic horizons that generate organic matter contents as low as 21% (H horizon site 2). Total ash content was significantly negatively correlated with magnetic susceptibility (r ¼
0:384, P < 0:01) in the H horizon. Similar relationships between total ash content of humic layers and magnetic susceptibility were found in 1998 at the same study site, when organic matter contents of the H horizon of only 12% were observed (Klose et al., 2001). The negative relationship between total ash content and magnetic susceptibility may either be a

122 S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

Fig. 3. Organic C pools in the F and H horizons along the fly ash deposition gradient in the Du¨ bener Heide forest area (TOC: total organic C, HWC: hot water extractable organic C, CWC: cold water extractable organic C) (results are median values of four field reps taken at four occasions in 1999 and 2000). Sites were located 8, 16, 14, 18, and 25 km from the Bitterfeld industrial area, respectively.

S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

result of a direct input of tertiary sands or an indirect effect of alkaline fly ash on soil biota (Klose et al., 2001). Liming in the Ho¨ glwald experiment did increase the activity of earthworms that mixed mineral material from below into the humic horizons. Thus the mineral content increased from 23 to about 41% (Kreutzer, 1995). The pH values for the H horizon of all five sites in the Du¨ bener Heide were well above the median pH (H2O) of 4.1 (3.4 and 5.6 for the 10 and 90 percentile) estimated during the German national forest inventory (Deutscher Waldbodenbericht, 1996). In the mineral soil (0–10 cm) the pH ranged between 3.7 and 5.5 (10 and 90 percentile) (median: pH 4.1). The comparison of pH values at the five forest sites with those of a ‘‘background’’ site located in northern Brandenburg revealed that the soil pH at all sites in the Du¨ bener Heide is elevated by fly ash. Background pH (H2O) values at Neuglobsow varied between 3.8 and 3.9 for the H horizon and the mineral soil (0–3 cm), respectively (Weisdorfer et al., 1998). Lower pH values in the L horizon compared to the F and H horizons indicate that a re-acidification of the uppermost layer of forest floor caused by recent litter and a marked decrease in deposition of basic cations since the mid 1980s (i.e. in acid neutralisation capacity) began to take place. These results are in agreement with findings by Bellmann and Grote (1998). The soil acidification potential indicates a higher re-acidification potential of forest sites that received high fly ash loads relative to less affected sites. Site 5 is an exception to this trend, most likely due to additional emissions from the urban-industrial region Leipzig. Forest sites with a fly ash-induced elevated soil pH also expressed higher ECEC. Differences in the clay content between the five sites were low, ranging from 3.0 mass% at site 1 to 2.3 mass% at site 5. Because of the low clay contents, organic colloids with pHdependent (variable) exchange sites play the most important role for ECEC of the soil. One drastic effect of liming is the deprotonation of functional groups, mainly carboxyl groups, of the humus matrix. Thus, the ECEC increased as well as base saturation (BS). Similar results were reported for limed forest soils (Kreutzer, 1995). The higher BS of the humic horizon at site 1 relative to those at site 5 would indicate better humus types than moder to raw humus-type moder classified

123

for this site. However, humus types were classified according to macro-morphological characteristics rather than to their chemical properties. The imbalance between morphology and chemistry (i.e. pH value, C/N ratio, base saturation) of humic horizons in fly ash affected forest soils were described by several authors (Konopatzky et al., 1998; Nebe et al., 2001; Koch et al., 2002). Base saturations near 100%, as found in the mineral topsoil at site 1 in the Du¨ bener Heide, would suggest sites on carbonate-rich parent material, whereas silicatic substrates, as found in the study area, naturally reveal a base saturation <30%. Thus, the base saturation at sites 4 and 5 represents semi-natural conditions for this sandy texture, whereas those at sites 1 to 3 are markedly increased by fly ash depositions. Base saturations of surface soils at the background site in a ‘‘clean air’’ area in northern Brandenburg, Germany, ranged between 16 and 6% for 0–3 and 3–19 cm soil depth, respectively, and was about 48% for the H horizon (Weisdorfer et al., 1998). These results indicate that a large part of the buffer capacity of the accumulated fly ash was transformed into exchange buffer, as suggested by Kreutzer (1995). A comparison of concentrations of salt and water extractable cations suggested that monovalent cations are more mobile in fly ash influenced soils than bivalent cations, supporting the general model of ion sorption in soils according to their concentration in the soil solution and valency. Further, stocks of basic cations in the forest floor were enhanced by fly ash depositions mainly due to Ca2þ accumulations in the F and H horizons. Studies by Kreutzer (1995) on the dynamics of the retention of Ca2þ and Mg2þ, deriving from lime, showed that Ca2þ was more strongly retained by exchange reactions than Mg2þ. After complete dissolution of lime, about 70% of the Ca and 30% of the Mg were still present in the humus layer, representing about 50% of the acid neutralization capacity of the applied lime. Stocks of C and N in the forest floor along the five study sites indicate an increase in carbon storage and/ or that a great part of the N from deposition and fertilization has accumulated in the surface soil of forests in the Du¨ bener Heide. A number of authors have shown that liming has stimulated the mineralization of organic matter and thus a reduction in the storage of humus (Hetsch and Ulrich, 1979; Marschner

124

S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

and Wilcynski, 1991). The latter authors reported a humus loss of 15% 3 years after application of 6100 kg lime ha
1 in the Grunewald forest near Berlin, Germany. However, short-time changes in the C storage due to liming may be impaired by the spatial heterogeneity of the organic C content (Kreutzer, 1995). Matzner (1985) reported that both increases and decreases had occurred some decades after liming in the Solling area, Germany. These contradictory effects may be partly explained by an increased litter production of leaves and roots, which compensate for the increased decomposition (Kreutzer, 1995). Humus accumulation is largely governed by organic matter input and its chemical composition. As documented by Bergmann et al. (1998), annual pine needle litter input in the study area was about 2.3 Mg ha
1 per year and did not vary significantly between two sites with high and low fly ash loads. In contrast, the annual input of understory litter differed significantly between the sites, ranging from 2.29 Mg ha
1 per year at the high-input site to 1.41 Mg ha
1 per year at the low-input site. Corresponding values for pine root litter input were 0.35 and 0.07 Mg ha
1 per year, also reflecting significant differences between both sites. The decomposition of the needle litter did not differ significantly between the sites. In contrast, the type, amount and chemical composition of the understory litter varied between heavy and less fly ash-affected sites, reflecting the historical deposition situation in the Du¨ bener Heide. The decomposition of the understory litter was largely governed by the nitrogen dynamics, which may differ considerably among sites although the C chemistry is similar (Bergmann et al., 1998). Fly ash deposition decreased C/N ratios of the H and F horizon along the five forest sites in the Du¨ bener Heide. A decrease in C/N ratios of the humus layer from 31 to 24 due to alkaline depositions and N fertilization in the study area between 1967 and 1989 was described by Konopatzky and Freyer (1996) and Bellmann and Grote (1998). As a consequence, humus types changed from raw humus forms to raw humus-type moder. Similar results were reported by Kreutzer (1995) from the Ho¨ glwald experiment in southern Bavaria, where C/N ratios of the H horizon decreased from 24 to about 21 within 7 years after liming. The decrease of C/N ratio in humic horizons upon alkaline depositions may

indicate that N, mineralized in concomitance with the decomposition of organic materials, was refixed in the remaining or newly formed organic matter as suggested by Tamm (1991). The N eutrophication level of the forest floor decreased along the deposition gradient in the Du¨ bener Heide. These results can be explained by higher atmospheric NOx deposition and N fertilization to mitigate forest damage due to past air pollution at sites 1 to 3 compared to sites 4 and 5. The N concentration in the F and H horizons and mineral topsoil exceeded the critical loads for this element in pine stands with the raw humus-type moder (n4) as proposed by Kopp and Kirschner (1992) in all five forest sites. Relative contributions of medium (HWC) and short-term (CWC) available C on TOC in the humic horizons indicated a reduced availability of organic C compounds in soils with high historical fly ash deposition loads and/or an enhanced initial C decomposition under a more alkaline soil environment. Further, results suggest that considerable amounts of lignitederived ‘black’ C (or geogenic C) were accumulated in particular in the H horizon at sites 1 and 2, leading to high TOC measurements. Atmospheric fly ash contains substantial amounts of black C. Despite the fact that coals are a very diverse set of materials, lignite material mainly consists of aromatic and aliphatic C (Rumpel et al., 1998). Compared to lignite, recent (or pedogenic) soil organic matter contains large amounts of polysaccharides and lignin structures (Rumpel et al., 1998). Combusted organic substances, such as charcoal and ash, however, are characterized by highly aromatic structures. Subsequently, lignite-derived carbonaceous particles are extremely stabile against microbial degradation or chemical extraction (Goldberg, 1985). This would explain the results obtained for the H horizon along this fly ash deposition gradient, and suggest an accumulation of lignite C in this horizon. The contrary development of TOC and medium and short-term available C fractions (i.e. HWC and CWC) in the F horizon may be attributed to a higher availability of F material relative to H material due to the formation of recalcitrant compounds during the decomposition process. Rumpel et al. (1998) documented a decrease of recent, readily decomposable organic C compounds from the surface to the subsoil.

S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

5. Conclusions Forest soils of the Du¨ bener Heide region were altered in humus morphology and physico-chemical properties by past fly ash emissions. Effective cation exchange capacity and base saturation of fly ash affected soils are not necessarily comparable with those parameters in natural ecosystems, because the dynamics of Ca and Mg from emissions in these soils remains unknown. Long-term fly ash depositions in the Du¨ bener Heide forest area did not result in the formation of a mull type humus, as expected from soil chemical properties and vegetation structure (i.e. promotion of ground vegetation and broad-leaved tree species). Therefore, characterisation of soil reaction and base status as well as humus morphology at forest sites subjected to alkaline depositions requires a new classification system. Element stocks of the forest sites along the deposition gradient indicate an accumulation of emissionderived compounds such as CaO, MgO, inert C sources and N in the humic layer. In spite of the general reduction of alkaline air pollution, a continuing re-acidification of forest soils from the top- to the subsoil, a reduction of exchange sites and thus, a drastical loss of basic cations, a continued high N eutrophication and an accumulation of organic matter in the forest floor may be expected for the future development of pine stands on sandy soils in Northeastern Germany.

Acknowledgements The senior author thanks the State Ministry of Sciences and Arts of Saxony, Germany, for fellowship support while at Dresden University of Technology.

References Baronius, G., 1992. Zur Ausbildung und Dynamik von Erna¨ hrungsund Chlorosezusta¨ nden der Kiefer (Pinus sylvestris L.) im Immissionsgebiet Du¨ bener Heide. Dresden University of Technology, Tharandt, Germany. Bellmann, K., Grote, R., 1998. Introduction to the SANA-project (SANA: regeneration of the atmosphere above the new state of Germany—effects on forest ecosystems). In: Hu¨ ttl, R.F., Bellmann, K. (Eds.), Changes of Atmospheric Chemistry and

125

Effects on Forest Ecosystems: A Roof Experiment Without a Roof, Nutrients in Ecosystems, vol. 3. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 1–15. Bergmann, C., Fischer, T., Hu¨ ttl, R.F., 1998. Decomposition of needle-, herb-, root-litter and Of-layer humus in three Scots pine stands. In: Hu¨ ttl, R.F., Bellmann, K. (Eds.), Changes of Atmospheric Chemistry and Effects on Forest Ecosystems: a Roof Experiment Without a Roof. Nutrients in Ecosystems, vol. 3. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 177–186. Bronner, H., Bachler, W., 1979. Der hydrolisierbare Stickstoff als Hilfsmittel fu¨ r die Scha¨ tzung des Stickstoffnachlieferungsvermo¨ gens von Zuckerru¨ ben. Landwirtsch. Forsch 32, 255–261. Deutscher Waldbodenbericht, 1996. Ergebnisse der bundesweiten Bodenzustandserhebung im Wald von 1987–1993 (BZE), vol. 1, Bundesministerium fu¨ r Erna¨ hrung, Landwirtschaft und Forsten, Bonn, Germany. Erhard, M., Flechsig, M., 1998. A landscape model for the investigation of atmogenic pollution effects on the dynamics of Scots pine ecosystems. In: Hu¨ ttl, R.F., Bellmann, K. (Eds.), Changes of Atmospheric Chemistry and Effects on Forest Ecosystems: A Roof Experiment Without a Roof, Nutrients in Ecosystems, vol. 3. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 283–311. Finkbeiner, A., Friedrich, R., Grimm, O., 1993. Modellierung der Emissionen ausgewa¨ hlter umweltrelevanter Schadstoffe und Bestimmung ihres zeitlichen Trends. University of Stuttgart, Stuttgart, Germany. Goldberg, E.D., 1985. Black carbon in the environment: properties and distribution. Wiley, New York. Hetsch, W., Ulrich, B., 1979. Die langfristige Auswirkung von Kalkung, Bodenbearbeitung und Lupinenanbau auf die Bioelementvorra¨ te zweier Flottsandstandorte. German J. For. Sci. 98, 236–244. Hildebrand, E.E., 1986. Zustand und Entwicklung der Austauschereigenschaften von Mineralbo¨ den aus Standorten mit erkrankten Waldbesta¨ nden. German J. For. Sci. 105, 60–76. Klose, S., Koch, J., Ba¨ ucker, E., Makeschin, F., 2001. Indicative properties of fly-ash affected forest soils in Northeastern Germany. J. Plant Nutr. Soil Sci. 164, 561–568. Klose, S., To¨ lle, R., Ba¨ ucker, E., Makeschin, F., 2003. Stratigraphic distribution of atmospheric deposits in forest soils in the Lusatian mining district, Eastern Germany. Water Air Soil Pollut. 142, 3–25. Koch, J., Klose, S., Makeschin, F., 2002. Stratigraphic and spatial differentiation of chemical properties in long-term fly ash influenced forest soils in the Du¨ bener Heide region, Northeast Germany. Forstw. Cbl. 121, 157–170. Konopatzky, A., Freyer, C., 1996. Erfassung und Analyse des ¨ kosystemen des Wandels der Oberbo¨ denzusta¨ nde von Kiefern-O Eintragsmodellgebietes Du¨ bener Heide. Final report of the multidisciplinary research project SANA (project E 1.2), vol. 4, GSF Mu¨ nchen, Germany. Konopatzky, A., Kirschner, G., Kallweit, R., 1998. Bodenzustandswandel in den Wa¨ ldern des Nordostdeutschen Tieflandes. AFZ/ Der Wald 9, 479–482.

126

S. Klose, F. Makeschin / Forest Ecology and Management 183 (2003) 113–126

Kopp, D., Kirschner, G., 1992. Fremdstoffbedingter Standortswandel aus periodischer Kartierung des Standortzustandes in den Wa¨ ldern des nordostdeutschen Tieflandes nach Ergebnissen der Standortserkundung. Beitra¨ ge fu¨ r Forstwirtschaft und Landschaftso¨ kologie 26 (2/4), 62–71. Kreutzer, K., 1995. Effects of forest liming on soil processes. Plant Soil 168/169, 447–470. Marschner, B., Wilcynski, A., 1991. The effect of liming on quantity and chemical composition of soil organic matter in a pine forest in Berlin, Germany. Plant Soil 137, 229–236. Matzner, E., 1985. Auswirkung von Du¨ ngung und Kalkung auf den Elementumsatz in zwei Waldo¨ kosystemen in Sollingen. Allg. Forstz. 41, 1143–1147. Matzner, B., 1987. Der Stoffumsatz zweier Waldo¨ kosysteme im So¨ llingen, Forschungszentrum Waldo¨ kosysteme Waldsterben. University of Go¨ ttingen, Germany. Nebe, W., Pommnitz, M., Jeschke, J., 2001. Aktueller Standortszustand und Waldumbau im nordwestsa¨ chsischen Tiefland. Forst Holz 56, 3–6. Neumeister, H., Peklo, P., Niehus, B., 1997. Umweltbelastungen in der Region Leipzig–Halle–Bitterfeld und deren Bewertung: Immissionsbedingte Stoffeintra¨ ge. In: Feldmann, R., Auge, H., Flachowsky, J., Klotz, S., Kro¨ nert, R. (Eds.), Regeneration und

nachhaltige Landnutzung- Konzepte fu¨ r belastete Regionen. Springer, Berlin, New York, pp. 35–41. Rumpel, C., Knicker, H., Ko¨ gel-Knabner, I., Skjiemstad, J.O., 1998. Types and chemical composition of organic matter in reforested lignite-rich mine soils. Geoderma 86, 123–142. Tamm, C.O., 1991. Nitrogen in Terrestrial Ecosystems, Ecological Studies, vol. 81. Springer, Berlin, Heidelberg, New York. To¨ lle, R., Raasch, H., 1989. Zur Anwendung eines hochfrequenten Messverfahrens fu¨ r den Nachweis von ferromagnetischem Eisen in der Umwelt. Wiss. Zeitschr. Humboldt University Berlin 1, 45–47. Ulrich, B., Mayer, R., Khanna, P.K., 1979. Deposition von Luftverunreinigungen und ihre Auswirkungen in Waldo¨ kosystemen im Solling. Monogr. Faculty of Forestry, University of Go¨ ttingen, vol. 58, Go¨ ttingen, Germany. Weisdorfer, M., Schaaf, W., Blechschmidt, R., Schu¨ tze, J., Hu¨ ttl, R.F., 1998. Soil chemical response to drastic reductions in deposition and its effects on element budgets of three Scots pine ecosystems. In: Hu¨ ttl, R.F., Bellmann, K. (Eds.), Changes of Atmospheric Chemistry and Effects on Forest Ecosystems: A Roof Experiment Without a Roof, Nutrients in Ecosystems, vol. 3. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 187–225.