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Technogenic Soils From Lead Zinc Mine Wastes
235
Chapter 13. TECHNOGENIC SOILS FROM LEAD AND ZINC MINE WASTES Enzymological research in the United Kingdom Studying the decomposition of vegetation growing on metal mine waste, Williams et al (1977) also carried out enzymological analyses. The waste studied was located around the disused mine at Y Fan (Powys, Wales) and contained high concentrations of lead and zinc. After the abandonment of the mine (1928), the waste was partially colonised naturally by metal-tolerant Agrostis tenuis. An evenly colonised area was selected for study. A similar but uncontaminated area was also selected on a pasture situated about 500 m from the mine. The vegetation on this site consisted primarily of ^. tenuis and Festuca ovina. Urease activity in soil, microbial populations in litter and soil, and microfauna in litter from both sites were compared. Accumulation of litter was greater on the waste, which also contained significantly less humic and fiilvic acids in the soil immediately beneath the litter layer. Urease activity was also significantly lower in the mine soil than in the nearby pasture soil (Table 28). Table 28 Urease activity in a mine soil and a pasture soil at Y Fan, Powys, Wales Reaction mixture Soil + urea solution SoiH-water Urease activity
mg of NH4^-N released from 100 g of soil (on air-dry basis) at 37°C in 3 h Mine soil* Pasture soil* 2.55±0.14 42.62±2.38 1.97±0.25 3.32±0.58 0.58=b0.19 39.31±2.17
Reproduced from: ST. Williams, T. McNeilly and E.M.H. Wellington, Soil Biology & Biochemistry, 1977, Vol. 9, p. 273, with kind permission from Elsevier Science. * Means of two soils significantly different at P = 0.05. Microbial numbers from litter at the two sites were not markedly different, although numbers of fungi were lower on litter from the mine waste, while those of bacteria and actinomycetes were higher. In contrast, numbers of all groups in the mine soil were considerably lower than
236 those in the pasture soil. Similarly, there were fewer animals in the litter on the waste. The low biological activity in the litter and soil of the studied mine waste, caused by the high Pb and Zn concentrations, explains the retarded decomposition of vegetation growing on this site. Clark and Clark (1981) have applied soil enzymological methods, in order to determine the reasons for the differences in the floras of adjacent species-poor and species-rich areas of a limestone terrace in the lead-mining complex on Grassington Moor, in Yorkshire Pennines (England). The northern half of the terrace received drainage water and fme-textured, Pb- and Zncontaining mine waste from abandoned mine workings up slope, and the vegetation there was sparse, floristically impoverished, and composed of species typical of heavy-metal mine areas in the British Isles, i.e. Minuartia vema, Agrostis tenuis, and Festuca ovina. There was no direct input of mine waste on the southern half of the terrace, and there the vegetation was floristically rich and continuous, except where the limestone cropped out. The mean number of species per 0.25 m^ on the species-poor area was 2.4, in contrast to the species-rich area, where it was 10.1. The soils of the species-poor area had lower pH values and contained less humus, NO3"N, NH4^-N, available P, and exchangeable K, compared with those of the species-rich area. The total lead content averaged in the soils of the species-poor and species-rich areas 78,000 and 8,000 |ig g'^ soil, respectively, far above the 350 |ig g'^ threshold value above which lead levels are anomalously high. The soils of both these areas would therefore normally be expected to be toxic to all but tolerant races. The average level of ammonium acetateextractable Pb was 21,800 \ig g'^ soil on the species-poor area and only 311 |Lig g"^ soil on the other area. Zinc levels were mainly lower than those of lead on both areas and the difference in the levels of total and ammonium acetate-extractable Zn between the areas was less marked than for Pb. Acid phosphatase, dehydrogenase, and urease activities and respiration (CO2 evolution) were measured in soil samples taken in the root zone, 2-9 cm below the surface. When expressed on an air-dry soil basis, they were higher in the species-rich soil. However, when expressed on an air-dry organic matter basis, the differences were reduced or eliminated (Table 29). In each half of the terrace there were significant correlations between density of species, amounts of plant nutrients, and enzyme activities, and all were related inversely to the
237
Table 29 Enzyme activities and respiration in soils from a limestone terrace contaminated by Pb- and Zn-containing mine waste on Grassington Moor, Yorkshire Activity or respiration
Acid phosphatase (\ig of/?-nitrophenol) Dehydrogenase ()Lig of triphenylformazan) Urease (mg of urea) Respiration at current moisture content (mgofC) Respiration at field capacity (mg of C)
Species-]poor(SP) S' OM" 9.9 67.4 (2.7)*** 38.3 260.4 (21.5) 1.5 10.0 (0.4) 0.085 *** * 0.578
0.067
0.456
Area Species-rich (SR) OM S 79.5 18.1 (2.2) 11026.4 2503.0 30.4 6.9 (2.7) 0.093 0.409
0.090
0.396
Ratio (SR/SP) OM S 1.8 1.2 65.4
42.3
4.6
3.0
1.1
0.7
1.3
0.9
Reproduced from: R.K. Clark and S.C. Clark, The New Phytologist, 1981, Vol. 87, p. 808. Activity or respiration registered in 1 g of air-dry soil in 24 h. Activity or respiration reported for 1 g of air-dry organic matter in 24 h. ^^^ For activity values, standard deviations are given in parentheses. * For respiration values, the least significant difference is 0.016 at /^ < 0.05. ***** . Considerably less than field capacity. levels of extractable lead. The conclusion has been drawn that nutrient enrichment is involved in the formation of the species-rich area on Grassington Moor; the higher enzyme activities in the species-rich area indicated that metal detoxification was taking place there, and the higher organic matter content of this area is related to the enzyme activities. Enzymological research in Romania The raw and the revegetated wastes at the Sasar mine (Baia Mare, Maramure§ county), the ores of which contain Pb and Zn as well as Cu, Cd, and some other heavy metals, were studied enzymologically by Soreanu (1983). An adjacent native meadow soil served for comparison. The revegetation experiment started in 1975 and comprised unfertilised and NPK-fertilised mine waste plots seeded with a mixture of perennial grasses and legumes or with individual grass and legume species or sunflower. In 1980, samples were taken from the 0-20-cm depth of each plot and native soil for determining invertase, dehydrogenase, phosphatase, and urease activities in wastes and soil, respectively. It was found that revegetation caused an increase in each activity as compared with those measured in the raw waste, but
238 except for urease activity, the other activities did not reach the values recorded in the native soil. The fertilised plots revegetated with the grass-legume mixture gave the best results in respect of plant cover percentage, herbage yield, and enzyme activities of wastes. Biological recultivation experiments involving enzymological analyses were also carried out at the Rodna mine (Bistrita-Nasaud county) (Kiss et al, 1989b, 1990). The spoils submitted to recultivation had resulted from underground mining of lead and zinc ores, their concentration by flotation, and decantation in a pond. In June 1987, small recultivation plots (7 m^ = 2 x 3.5 m) were installed on three terraces (VIII, V, and III) from the nine terraces of the spoil dump. Terrace VIII was 2 years old, whereas terraces V and in were 7 and 10 years old, respectively. The level difference between terraces was approximately 3.5 m. On each terrace there were both plots with southwestern aspect and plots with south-eastern aspect. In all, 14 spoil plots were installed in the following variants: 1. covering with soil plus fertilising with farmyard manure (FYM) plus NPK plus seeding with Italian ryegrass and meadow clover (RC); 2. FYM plus NPK plus RC; 3. NPK plus RC; and 4 NPK The soil used was a loamy sand of low fertility. The thickness of soil cover on spoil plots was 10 cm. The farmyard manure was applied at a rate of 40 t ha'V The mineral fertilisers used were NH4NO3, single superphosphate, and potash salt (KCl), applied at rates of 150 kg of N, 200 kg of P2O5, and 250 kg of K2O ha'V Italian ryegrass {Lolium multiflorum) and meadow clover {Trifolium pratense) were sown at rates of 25 and 60 kg of seeds ha'\ respectively. On each terrace, untreated places in the vicinity of the experimental plots served as controls (in all, six places). All treatments were performed on the same day (June 24, 1987). Then, each plot was moistened with water from the Some§ul Mare River which flows at a 25-m distance from the foot of the spoil dump. Systematic watering of the plots was assured from the same source. The plots were supplementarily fertilised with NH4NO3 (150 kg of N ha'^) in October 1987. Two large plots (50 m^ = 20 x 2.5 m) were installed on terrace VI. Plot I was covered with 10 cm of soil, fertilised with NPK, and sown with Italian ryegrass and meadow clover. Plot II was also covered with 10 cm of soil and fertilised with NPK, but it was not sown with
239 ryegrass and clover, instead, it was treated with about 50 kg of spoil taken from the surface layer of terrace I (the lowest and oldest, 15-year-old, terrace). This spoil contained seeds of plants and microorganisms from the spontaneous flora and microflora, respectively. For covering plots I and II the same soil was used as in the case of the small plots. The NPK fertilisers and their rates and the seed rates were also the same. All treatments and the first watering were carried out on July 5, 1988. The large plots, like the small ones, were moistened systematically with water from the Some§ul Mare River. A supplementary NH4NO3 dosage (150 kg of N ha'^) was administered in October, 1988. Controls of the large plots were also untreated places in their vicinity. For enzymological analyses, six series of samples were collected from the 0-10-cm depth of the small plots and their controls in the June 1987-October 1989 period, and four series of samples from the same depth of the large plots in the July 1988-October 1989 period. Phosphatase, catalase, and actual and potential dehydrogenase activities were determined. The so-called nonenzymatic catalytic activity (i.e. nonenzymatic H202-splitting capacity) was also assayed. Based on the activity values, the enzymatic indicator was calculated for each plot and control. This indicator is considered as an index of the biological quality of soil (and spoil). The results have shown that the enzymatic activities (but not the nonenzymatic catalytic activity), the enzymatic indicators calculated for the whole period of experiments (19871989), and the herbage yields in 1989 gave the highest values in the spoil plots covered with soil, treated with organic and mineral fertilisers and sown with ryegrass and clover or with plants from the spontaneous flora. Complex treatment of the small plots was more efficient in creating an enzymatic and herbage production potential in spoils than was mineral fertilisation alone or mineral fertilisation plus seeding of ryegrass and clover. Covering of spoils with soil proved to be a more important recultivation measure even in comparison with organic fertilisation. The enzymatic indicators of control places showed a tendency to increase with the age of terraces. Nevertheless, the control places even on the 10-year-old terrace III were much less enzyme-active than the soil-covered small and large plots aged only -2.5 and -1.5 years, respectively. It has also been found that the south-western or south-eastern aspect of the plots subjected to the same treatment had no significant effect on the enzymatic indicators and
240
herbage yields. In conclusion, for the recultivation of raw and young spoils at lead and zinc mines, covering with soil, fertilisation with NPK, and sowing a grass-legume mixture were recommended, and for the recultivation of old spoils NPK fertilisation was recommended as the minimum treatment. This conclusion was confirmed by enzymological analyses of spoils and native soil carried out in the next years. Thus, in 1992 (May 25 and August 28) samples were taken from three depths: 0-10, 10-20, and 20-30 cm. The enzymatic indicator showed again the highest values in the soil-covered small and large spoil plots and in the native soil and, as expected, the lowest values were recorded in the youngest (untreated control and only NPK-fertilised) spoils (Kiss £?/a/., 1992, 1994). Evolution of the enzymatic potential in the 0-10-cm layer of spoil plots at the Rodna mine during the 1987 (1988)-1994 period was also evaluated (Pa§ca et al, 1994; Cristea et al, 1995). Figure 15 was selected to illustrate the evolution of enzymatic potential in soilcovered spoil plots (plots 1, I, and II) as compared to plots 2 and 3 (not covered with soil), untreated spoils (controls 1-3, I, and II), and native soil. It is evident from this figure that the favourable effect of a soil cover on the enzymatic potential of spoils is long-lasting. Results of the analyses carried out during 1996 (i.e. 9 and 8 years after the installation of small and large plots, respectively, at the Rodna mine) have confirmed the long-lasting effect of soil cover on the enzymatic potential of spoils (0-30-cm layer), as the enzymatic indicators of soil (spoil) quality could be ranked in the order: plot I > plot II > native soil > plot 4 > plot 1 » untreated spoils (control 1-3). The humus content showed the same order. But due to the fertilisation of plots, their total N, available P, and exchangeable K contents were higher and much higher than those of the native soil and untreated spoils, respectively. pH and carbonate content decreased in the soil-covered plots (Pa§ca et al 1997a, b, 1998). The soil cover also resulted in increased nematode abundance, diversity, and maturity index (Popovici, 1993, 1995; Popovici et al, 1995; Pa§ca^/a/., 1997b, 1998). Development of the mites and collembolans was also favoured in the soil-covered plots (Pa§ca et al, 1997b).
241 -o- PLOT 1 -iHPL0T2 -A- PLOT 3 - • - CONTROL 1-3 -X- NATIVE SOIL
700 T
1987 1988 1989 1990 1991 1992 1993 199^ YEAR -o-PLOT I • PLOT II -A-CONTROL I -•- CONTROL II -X- NATIVE SOIL
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1988 1989 1990 1991 1992 YEAR
1993 199^
Figure 15. Evolution of the enzymatic potential in some spoil plots installed at the lead and zinc mine in Rodna. Redrawn from: D. Pa§ca, S. Kiss, M. Dragan-Bularda, R. Cri§aii and V. Muntean, Studia Universitatis Babe§Bolyai, Biologia, 1994, Vol. 39 (1), pp. 97 and 101; V. Cristea, S. Kiss, D. Pa§ca, M. Dragan-Bularda, R. Cri§an and V. Muntean, CoUoques Phytosociologiques, 1995, Vol. 24, pp. 174 and 176.
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The spoils and native soil at the Rodna mine were subjected to microbiological analyses, too. Some of the results obtained were briefly described by Pa§ca et al (1998). Global numbers of the aerobic heterotrophic, ammonifying, sulphate-reducing, and ironreducing bacteria determined in the 0-10-cm layer of spoils and native soil in summers of 4 years (1993-1996) were of the same level in the soil-covered plots I and 1 and in the native soil and always exceeded the numbers recorded in the untreated spoils. At the Rodna mine, an experiment using ligneous plants for revegetation of spoils was also carried out (Cristea et al, 1995; Pa§ca et al, 1996). Young trees and bushes were planted on the 4-year-old terrace VIII (on its both parts having south-western and south-eastern aspect, respectively), in October 1989. Hippophae rhamnoides, Colutea arborescens, Salix gracilis, Robinia pseudacacia, and Pinus nigra succeeded in surviving. Growth of Hippophae rhamnoides (sea buckthorn) was especially luxuriant. In the May 1994-September 1995 period, six series of spoil samples were taken from the root zone of 7/. rhamnoides and from the control (unplanted) places. The native soil was also sampled. Sampling depths were 0-10, 10-20, and 20-30 cm. The same enzymatic and nonenzymatic catalytic activities were determined in all samples as those specified above for the small and large experimental plots, and the enzymatic indicators of soil (spoil) quality were calculated. Figure 16 shows that the enzymatic indicators of the 0-10- and 10-20-cm layers present the order: control spoil < spoil from the root zone of H. rhamnoides < native soil. In the 2030-cm layer the enzymatic potential is similar in both spoils, and lower than in the native soil. The aspect-dependent variation of this potential is very low. The finding that H. rhamnoides increased the enzymatic potential of spoils supports the opinion, according to which fixation of spoils by ligneous species supplements the coverage by herbaceous plants and contributes to a better and faster ecological and economic reintegration of spoil dumps. In 1996, the spoil from the root zone of//, rhamnoides was again found to be more enzyme-active than that from the control places, but it did not reach the activity level of the soil-covered plots or native soil (Pa§ca et al, 1997a).
Chapter 13. TECHNOGENIC SOILS FROM LEAD AND ZINC MINE WASTES Enzymological research in the United Kingdom Studying the decomposition of vegetation growing on metal mine waste, Williams et al (1977) also carried out enzymological analyses. The waste studied was located around the disused mine at Y Fan (Powys, Wales) and contained high concentrations of lead and zinc. After the abandonment of the mine (1928), the waste was partially colonised naturally by metal-tolerant Agrostis tenuis. An evenly colonised area was selected for study. A similar but uncontaminated area was also selected on a pasture situated about 500 m from the mine. The vegetation on this site consisted primarily of ^. tenuis and Festuca ovina. Urease activity in soil, microbial populations in litter and soil, and microfauna in litter from both sites were compared. Accumulation of litter was greater on the waste, which also contained significantly less humic and fiilvic acids in the soil immediately beneath the litter layer. Urease activity was also significantly lower in the mine soil than in the nearby pasture soil (Table 28). Table 28 Urease activity in a mine soil and a pasture soil at Y Fan, Powys, Wales Reaction mixture Soil + urea solution SoiH-water Urease activity
mg of NH4^-N released from 100 g of soil (on air-dry basis) at 37°C in 3 h Mine soil* Pasture soil* 2.55±0.14 42.62±2.38 1.97±0.25 3.32±0.58 0.58=b0.19 39.31±2.17
Reproduced from: ST. Williams, T. McNeilly and E.M.H. Wellington, Soil Biology & Biochemistry, 1977, Vol. 9, p. 273, with kind permission from Elsevier Science. * Means of two soils significantly different at P = 0.05. Microbial numbers from litter at the two sites were not markedly different, although numbers of fungi were lower on litter from the mine waste, while those of bacteria and actinomycetes were higher. In contrast, numbers of all groups in the mine soil were considerably lower than
236 those in the pasture soil. Similarly, there were fewer animals in the litter on the waste. The low biological activity in the litter and soil of the studied mine waste, caused by the high Pb and Zn concentrations, explains the retarded decomposition of vegetation growing on this site. Clark and Clark (1981) have applied soil enzymological methods, in order to determine the reasons for the differences in the floras of adjacent species-poor and species-rich areas of a limestone terrace in the lead-mining complex on Grassington Moor, in Yorkshire Pennines (England). The northern half of the terrace received drainage water and fme-textured, Pb- and Zncontaining mine waste from abandoned mine workings up slope, and the vegetation there was sparse, floristically impoverished, and composed of species typical of heavy-metal mine areas in the British Isles, i.e. Minuartia vema, Agrostis tenuis, and Festuca ovina. There was no direct input of mine waste on the southern half of the terrace, and there the vegetation was floristically rich and continuous, except where the limestone cropped out. The mean number of species per 0.25 m^ on the species-poor area was 2.4, in contrast to the species-rich area, where it was 10.1. The soils of the species-poor area had lower pH values and contained less humus, NO3"N, NH4^-N, available P, and exchangeable K, compared with those of the species-rich area. The total lead content averaged in the soils of the species-poor and species-rich areas 78,000 and 8,000 |ig g'^ soil, respectively, far above the 350 |ig g'^ threshold value above which lead levels are anomalously high. The soils of both these areas would therefore normally be expected to be toxic to all but tolerant races. The average level of ammonium acetateextractable Pb was 21,800 \ig g'^ soil on the species-poor area and only 311 |Lig g"^ soil on the other area. Zinc levels were mainly lower than those of lead on both areas and the difference in the levels of total and ammonium acetate-extractable Zn between the areas was less marked than for Pb. Acid phosphatase, dehydrogenase, and urease activities and respiration (CO2 evolution) were measured in soil samples taken in the root zone, 2-9 cm below the surface. When expressed on an air-dry soil basis, they were higher in the species-rich soil. However, when expressed on an air-dry organic matter basis, the differences were reduced or eliminated (Table 29). In each half of the terrace there were significant correlations between density of species, amounts of plant nutrients, and enzyme activities, and all were related inversely to the
237
Table 29 Enzyme activities and respiration in soils from a limestone terrace contaminated by Pb- and Zn-containing mine waste on Grassington Moor, Yorkshire Activity or respiration
Acid phosphatase (\ig of/?-nitrophenol) Dehydrogenase ()Lig of triphenylformazan) Urease (mg of urea) Respiration at current moisture content (mgofC) Respiration at field capacity (mg of C)
Species-]poor(SP) S' OM" 9.9 67.4 (2.7)*** 38.3 260.4 (21.5) 1.5 10.0 (0.4) 0.085 *** * 0.578
0.067
0.456
Area Species-rich (SR) OM S 79.5 18.1 (2.2) 11026.4 2503.0 30.4 6.9 (2.7) 0.093 0.409
0.090
0.396
Ratio (SR/SP) OM S 1.8 1.2 65.4
42.3
4.6
3.0
1.1
0.7
1.3
0.9
Reproduced from: R.K. Clark and S.C. Clark, The New Phytologist, 1981, Vol. 87, p. 808. Activity or respiration registered in 1 g of air-dry soil in 24 h. Activity or respiration reported for 1 g of air-dry organic matter in 24 h. ^^^ For activity values, standard deviations are given in parentheses. * For respiration values, the least significant difference is 0.016 at /^ < 0.05. ***** . Considerably less than field capacity. levels of extractable lead. The conclusion has been drawn that nutrient enrichment is involved in the formation of the species-rich area on Grassington Moor; the higher enzyme activities in the species-rich area indicated that metal detoxification was taking place there, and the higher organic matter content of this area is related to the enzyme activities. Enzymological research in Romania The raw and the revegetated wastes at the Sasar mine (Baia Mare, Maramure§ county), the ores of which contain Pb and Zn as well as Cu, Cd, and some other heavy metals, were studied enzymologically by Soreanu (1983). An adjacent native meadow soil served for comparison. The revegetation experiment started in 1975 and comprised unfertilised and NPK-fertilised mine waste plots seeded with a mixture of perennial grasses and legumes or with individual grass and legume species or sunflower. In 1980, samples were taken from the 0-20-cm depth of each plot and native soil for determining invertase, dehydrogenase, phosphatase, and urease activities in wastes and soil, respectively. It was found that revegetation caused an increase in each activity as compared with those measured in the raw waste, but
238 except for urease activity, the other activities did not reach the values recorded in the native soil. The fertilised plots revegetated with the grass-legume mixture gave the best results in respect of plant cover percentage, herbage yield, and enzyme activities of wastes. Biological recultivation experiments involving enzymological analyses were also carried out at the Rodna mine (Bistrita-Nasaud county) (Kiss et al, 1989b, 1990). The spoils submitted to recultivation had resulted from underground mining of lead and zinc ores, their concentration by flotation, and decantation in a pond. In June 1987, small recultivation plots (7 m^ = 2 x 3.5 m) were installed on three terraces (VIII, V, and III) from the nine terraces of the spoil dump. Terrace VIII was 2 years old, whereas terraces V and in were 7 and 10 years old, respectively. The level difference between terraces was approximately 3.5 m. On each terrace there were both plots with southwestern aspect and plots with south-eastern aspect. In all, 14 spoil plots were installed in the following variants: 1. covering with soil plus fertilising with farmyard manure (FYM) plus NPK plus seeding with Italian ryegrass and meadow clover (RC); 2. FYM plus NPK plus RC; 3. NPK plus RC; and 4 NPK The soil used was a loamy sand of low fertility. The thickness of soil cover on spoil plots was 10 cm. The farmyard manure was applied at a rate of 40 t ha'V The mineral fertilisers used were NH4NO3, single superphosphate, and potash salt (KCl), applied at rates of 150 kg of N, 200 kg of P2O5, and 250 kg of K2O ha'V Italian ryegrass {Lolium multiflorum) and meadow clover {Trifolium pratense) were sown at rates of 25 and 60 kg of seeds ha'\ respectively. On each terrace, untreated places in the vicinity of the experimental plots served as controls (in all, six places). All treatments were performed on the same day (June 24, 1987). Then, each plot was moistened with water from the Some§ul Mare River which flows at a 25-m distance from the foot of the spoil dump. Systematic watering of the plots was assured from the same source. The plots were supplementarily fertilised with NH4NO3 (150 kg of N ha'^) in October 1987. Two large plots (50 m^ = 20 x 2.5 m) were installed on terrace VI. Plot I was covered with 10 cm of soil, fertilised with NPK, and sown with Italian ryegrass and meadow clover. Plot II was also covered with 10 cm of soil and fertilised with NPK, but it was not sown with
239 ryegrass and clover, instead, it was treated with about 50 kg of spoil taken from the surface layer of terrace I (the lowest and oldest, 15-year-old, terrace). This spoil contained seeds of plants and microorganisms from the spontaneous flora and microflora, respectively. For covering plots I and II the same soil was used as in the case of the small plots. The NPK fertilisers and their rates and the seed rates were also the same. All treatments and the first watering were carried out on July 5, 1988. The large plots, like the small ones, were moistened systematically with water from the Some§ul Mare River. A supplementary NH4NO3 dosage (150 kg of N ha'^) was administered in October, 1988. Controls of the large plots were also untreated places in their vicinity. For enzymological analyses, six series of samples were collected from the 0-10-cm depth of the small plots and their controls in the June 1987-October 1989 period, and four series of samples from the same depth of the large plots in the July 1988-October 1989 period. Phosphatase, catalase, and actual and potential dehydrogenase activities were determined. The so-called nonenzymatic catalytic activity (i.e. nonenzymatic H202-splitting capacity) was also assayed. Based on the activity values, the enzymatic indicator was calculated for each plot and control. This indicator is considered as an index of the biological quality of soil (and spoil). The results have shown that the enzymatic activities (but not the nonenzymatic catalytic activity), the enzymatic indicators calculated for the whole period of experiments (19871989), and the herbage yields in 1989 gave the highest values in the spoil plots covered with soil, treated with organic and mineral fertilisers and sown with ryegrass and clover or with plants from the spontaneous flora. Complex treatment of the small plots was more efficient in creating an enzymatic and herbage production potential in spoils than was mineral fertilisation alone or mineral fertilisation plus seeding of ryegrass and clover. Covering of spoils with soil proved to be a more important recultivation measure even in comparison with organic fertilisation. The enzymatic indicators of control places showed a tendency to increase with the age of terraces. Nevertheless, the control places even on the 10-year-old terrace III were much less enzyme-active than the soil-covered small and large plots aged only -2.5 and -1.5 years, respectively. It has also been found that the south-western or south-eastern aspect of the plots subjected to the same treatment had no significant effect on the enzymatic indicators and
240
herbage yields. In conclusion, for the recultivation of raw and young spoils at lead and zinc mines, covering with soil, fertilisation with NPK, and sowing a grass-legume mixture were recommended, and for the recultivation of old spoils NPK fertilisation was recommended as the minimum treatment. This conclusion was confirmed by enzymological analyses of spoils and native soil carried out in the next years. Thus, in 1992 (May 25 and August 28) samples were taken from three depths: 0-10, 10-20, and 20-30 cm. The enzymatic indicator showed again the highest values in the soil-covered small and large spoil plots and in the native soil and, as expected, the lowest values were recorded in the youngest (untreated control and only NPK-fertilised) spoils (Kiss £?/a/., 1992, 1994). Evolution of the enzymatic potential in the 0-10-cm layer of spoil plots at the Rodna mine during the 1987 (1988)-1994 period was also evaluated (Pa§ca et al, 1994; Cristea et al, 1995). Figure 15 was selected to illustrate the evolution of enzymatic potential in soilcovered spoil plots (plots 1, I, and II) as compared to plots 2 and 3 (not covered with soil), untreated spoils (controls 1-3, I, and II), and native soil. It is evident from this figure that the favourable effect of a soil cover on the enzymatic potential of spoils is long-lasting. Results of the analyses carried out during 1996 (i.e. 9 and 8 years after the installation of small and large plots, respectively, at the Rodna mine) have confirmed the long-lasting effect of soil cover on the enzymatic potential of spoils (0-30-cm layer), as the enzymatic indicators of soil (spoil) quality could be ranked in the order: plot I > plot II > native soil > plot 4 > plot 1 » untreated spoils (control 1-3). The humus content showed the same order. But due to the fertilisation of plots, their total N, available P, and exchangeable K contents were higher and much higher than those of the native soil and untreated spoils, respectively. pH and carbonate content decreased in the soil-covered plots (Pa§ca et al 1997a, b, 1998). The soil cover also resulted in increased nematode abundance, diversity, and maturity index (Popovici, 1993, 1995; Popovici et al, 1995; Pa§ca^/a/., 1997b, 1998). Development of the mites and collembolans was also favoured in the soil-covered plots (Pa§ca et al, 1997b).
241 -o- PLOT 1 -iHPL0T2 -A- PLOT 3 - • - CONTROL 1-3 -X- NATIVE SOIL
700 T
1987 1988 1989 1990 1991 1992 1993 199^ YEAR -o-PLOT I • PLOT II -A-CONTROL I -•- CONTROL II -X- NATIVE SOIL
o Q
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Figure 15. Evolution of the enzymatic potential in some spoil plots installed at the lead and zinc mine in Rodna. Redrawn from: D. Pa§ca, S. Kiss, M. Dragan-Bularda, R. Cri§aii and V. Muntean, Studia Universitatis Babe§Bolyai, Biologia, 1994, Vol. 39 (1), pp. 97 and 101; V. Cristea, S. Kiss, D. Pa§ca, M. Dragan-Bularda, R. Cri§an and V. Muntean, CoUoques Phytosociologiques, 1995, Vol. 24, pp. 174 and 176.
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The spoils and native soil at the Rodna mine were subjected to microbiological analyses, too. Some of the results obtained were briefly described by Pa§ca et al (1998). Global numbers of the aerobic heterotrophic, ammonifying, sulphate-reducing, and ironreducing bacteria determined in the 0-10-cm layer of spoils and native soil in summers of 4 years (1993-1996) were of the same level in the soil-covered plots I and 1 and in the native soil and always exceeded the numbers recorded in the untreated spoils. At the Rodna mine, an experiment using ligneous plants for revegetation of spoils was also carried out (Cristea et al, 1995; Pa§ca et al, 1996). Young trees and bushes were planted on the 4-year-old terrace VIII (on its both parts having south-western and south-eastern aspect, respectively), in October 1989. Hippophae rhamnoides, Colutea arborescens, Salix gracilis, Robinia pseudacacia, and Pinus nigra succeeded in surviving. Growth of Hippophae rhamnoides (sea buckthorn) was especially luxuriant. In the May 1994-September 1995 period, six series of spoil samples were taken from the root zone of 7/. rhamnoides and from the control (unplanted) places. The native soil was also sampled. Sampling depths were 0-10, 10-20, and 20-30 cm. The same enzymatic and nonenzymatic catalytic activities were determined in all samples as those specified above for the small and large experimental plots, and the enzymatic indicators of soil (spoil) quality were calculated. Figure 16 shows that the enzymatic indicators of the 0-10- and 10-20-cm layers present the order: control spoil < spoil from the root zone of H. rhamnoides < native soil. In the 2030-cm layer the enzymatic potential is similar in both spoils, and lower than in the native soil. The aspect-dependent variation of this potential is very low. The finding that H. rhamnoides increased the enzymatic potential of spoils supports the opinion, according to which fixation of spoils by ligneous species supplements the coverage by herbaceous plants and contributes to a better and faster ecological and economic reintegration of spoil dumps. In 1996, the spoil from the root zone of//, rhamnoides was again found to be more enzyme-active than that from the control places, but it did not reach the activity level of the soil-covered plots or native soil (Pa§ca et al, 1997a).