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Published online 9 January 2007
Published in J Environ Qual 36:254-261 (2007)
DOI: 10.2134/jeq2006.0086
© 2007 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
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TECHNICAL REPORTS

Transformation of a Landfill Covering Amended with Municipal Waste Compost, Perugia, Italy

Mario Businellia,*, Rolando Calandraa, Marcello Pagliaib, Daniela Businellia, Giovanni Gigliottia, Olga Grassellib, Daniel Said-Pullicinoa and Angelo Leccesea

a Dipartimento di Scienze Agrarie e Ambientali, Università di Perugia, Italy
b C.R.A.–Istituto Sperimentale per lo Studio e la Difesa del Suolo, Firenze, Italy

* Corresponding author (mbusinel{at}unipg.it)

Received for publication March 1, 2006.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
This research deals with the transformation of an anthropomorphous landfill covering composed of a fill soil mixed with mechanically separated municipal waste compost. The study site was a municipal landfill near Perugia, Italy. Throughout the years, waste disposal in the landfill was performed by burial in horizontal layers, each one representing a yearly disposal. The external front of the landfill thus represented the yearly disposal over a 10-yr period starting in 1993. Temporal changes in the anthropomorphous soil over this period were studied by examining and describing soil profiles, and by collecting and analyzing soil samples from the 1993, 1994, 1997, and 2001 disposals. The samples were subjected to a series of physical, chemical, and biochemical analyses. The results obtained suggest that over a 10-yr period the top layer gained a pedological structure (subangular blocky and/or crumb) giving rise to an A horizon. Improved soil structure was confirmed by an increase in macroporosity, particularly for pores larger than 50 µm, measured by image analysis of soil thin sections. Total extractable carbon showed an increase in the content of humic substances, evidenced by parameters of humification. Enzymatic activities in the A and C1 horizons were also indicative of soil evolution and may serve as a valid indicator for monitoring the evolution of anthropogenic soils containing municipal waste compost.

Abbreviations: MWC, municipal waste compost • TOC, total organic carbon • TEC, total extractable carbon • HA, humic acids • FA, fulvic acids • NH, nonhumified fraction • HI, humification index • DH%, degree of humification • HR%, humification ratio • SOM, soluble organic matter


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
NUMEROUS human activities lead to changes in natural land conditions. Among these are the scars left by quarries and pits for the excavation of various materials, abandoned industrial zones, embankments along roads and railroad tracks, degraded natural areas, and carelessly planned landfills. In the last decade great importance has been given to engineered landfills due to the ever increasing need to dispose of nonrecyclable waste (Chiampo et al., 1996; Highfill and McAsey, 1997; Read et al., 1997; Morris et al., 2003; Rapti-Caputo et al., 2006).

Engineered landfills, a widespread solid waste management strategy, provide for the disposal of waste at carefully chosen sites. Compaction of waste minimizes the land area involved and daily covering of waste with an adequately thick soil layer maintains sanitation. Controlled landfills are an effective means of resolving terrestrial pollution problems over a short period at a limited cost. Characterized by a modest degree of technology and low energy consumption, landfill management does not normally require specialized staff.

The reclamation of a landfill site is essential to minimize land degradation and is beneficial from both an economical and landscaping point of view. Once a landfill reaches its full capacity and has attained the ultimate planned configuration, it receives a final soil covering (Simon and Muller, 2004). This serves to minimize the infiltration of meteoric water, helps prevent the uncontrolled release of biogas, allows for the proper functioning of percolate and biogas collection systems, compensates for the settling of waste mass over time, and provides for site reclamation and revegetation (Chan et al., 1997). The final cover generally consists of a double layer made up of low-permeability earthen fill or man-made material, which is covered by a loam soil to which compost may be added (Simon and Muller, 2004).

When an earthen material is chosen to serve as the lower layer, clay is frequently used (permeability coefficient K = 10–6 cm s–1) with a thickness between 0.3 and 0.6 m. Clay is generally preferred over sheets of impermeable artificial materials (K = 10–6 cm s–1). The latter are more costly and often subject to rupturing since they are not capable of withstanding the settling of the waste mass or the passage of heavy vehicles over the covering layer. The top layer of loam soil must allow the site to support long-term vegetation once again. To regain the necessary fertility to develop a lasting plant cover, compost can be added to the superficial soil layer or mixed with an inert material such as quarry, excavation, or construction wastes, and subsequently used instead of the loam soil (D'Antonio, 1997).

The main objectives of this study were to evaluate the temporal transformation of a surface landfill soil, and to identify physical, chemical, and biochemical indicators that can adequately characterize the renaturalization process. The landfill soil was initially obtained by mixing an excavated soil with mechanically separated municipal waste compost (MWC) which is of limited use as a soil fertilizer due to high content of inert materials and heavy metals.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Site Description and Soil Sampling
The site under study was a controlled landfill located in the municipality of Perugia (Umbria region, Italy) and managed by Gesenu S.p.A (Fig. 1). Due to its hillside location the landfill was constructed by excavating the downhill side, forming a basin for the disposal of waste. The excavation was sealed at the bottom by an impermeable barrier made of a material with a high clay content, and includes two superimposed drainage networks. The first, lying below this impermeable layer allows for the drainage of ground water and at the same time serves to monitor the impermeability of this layer, while the second, lying above, is designed for the systematic collection of landfill percolation and its subsequent treatment.


Figure 1
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  		Fig. 1. Map of the site where the landfill is located. (a) Italy; (b) Umbria Region; (c) Perugia landfill.

 
Since 1993, waste disposal was performed in horizontal overlapping layers starting from the downhill side and rising to the upper-most level, year after year, up to the maximum level planned. Each depositional layer represents a yearly accumulation of waste materials with its respective covering layer and the external front constitutes a step at the landfill surface. To study the effects of municipal waste compost on the temporal transformation mechanisms of the anthropomorphous soil, samples were collected (in 2003) from the depositional layers corresponding to the years 1993, 1994, 1997, and 2001, thus representing a time series of soils 10, 9, 6, and 2 yr from compost amendment, respectively.

Excavations were made in the external fronts of the selected layers to expose the soil profiles. Field pedological examination identified three major horizons. The uppermost layer was an A horizon composed of fill material amended with compost. The second layer was a C1 horizon composed of unamended fill soil. Beneath this was a C2 horizon consisting of low permeability substrate. The main characteristics of the excavation soil, low permeability material, and the MWC are given in Table 1. Soil samples were collected directly from each horizon of each soil profile. Replicate soil samples were sampled with an auger since further excavation of profiles was deemed to be hazardous for landfill stability. A total of 9 samples was collected for each horizon, corresponding to 27 samples for each depositional year, for a total of 108 samples for the 4 depositions chosen. A portion of each sample was stored at –20°C and utilized for the biochemical analyses. The remaining sample portions were dried in air at 20°C, passed through a 2-mm sieve, and used for the physical and chemical analyses.


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  		Table 1. Average chemical properties of the substrates used over a 10-yr period.{dagger}

 
Physical Analyses
The soil profiles, including the presence and the type of soil structure, were described according to the Soil Survey Manual (USDA, 1993). Soil classification was made using Keys to Soil Taxonomy (USDA, 2006).

Soil texture was determined using the pipet method (Gee and Or, 2002). Water retention was determined using the Richard's membrane apparatus as described by Romano and Santini (2002). Soil porosity measurements were made by image analysis of thin sections of undisturbed soil samples (Pagliai et al., 1984; Murphy, 1986). In brief, three replicate undisturbed soil samples were collected in correspondence with the A (0 to 10 cm) and C1 horizons from each of the four years selected for the study. The samples were dried by acetone replacement of water, impregnated with a polyester resin and made into 60 x 70 mm, vertically oriented thin sections having a thickness of 30 µm (Murphy, 1986). Image Pro-Plus software (Media Cybernetics, Silver Spring, MD) was used to characterize pore morphology from the digital images of the thin sections using the approach described by Pagliai et al. (1984). The analyzed images of each thin section covered an area of 45 x 55 mm, avoiding the edges where disruption can occur. Total porosity and morphological distributions were measured according to pore shape and size, the instrument being set to measure pores >50 µm. Pore shape was expressed by a shape factor (calculated as perimeter2/[4{pi} x area]) that was subsequently divided into regular (more or less rounded) pores (shape factor 1–2), irregular (shape factor 2–5), and elongated (shape factor >5). These classes approximately correspond to those used by Bouma et al. (1977). Pores of each shape class were further subdivided into size classes according to their equivalent pore diameter for regular or irregular pores, or their width for elongated pores (Pagliai et al., 1983, 1984; Pagliai, 1988). Thin sections were also examined using a Zeiss R POL microscope at 25x magnification to observe the soil structure, i.e., to gain a qualitative assessment of the structure.

Chemical Analyses
Soil pH was measured with a glass electrode using a 1:2.5 sample/water ratio (Thomas, 1999), and electrical conductivity (EC) was measured on the saturation extract (Rhoades, 1999). Calcium carbonate content was determined by the modified Van Slyke manometric method (Loeppert and Suarez, 1996), total organic carbon (TOC) by the Walkley and Black wet dichromate oxidation method (Nelson and Sommers, 1996), total N by Kjeldahl digestion (Bremner, 1996), and available P by the Olsen method (Kuo, 1996). Cation exchange capacity was determined in BaCl2 by the Gilman method (Sumner and Miller, 1996).

Humic substances were extracted and purified as described by Ciavatta et al. (1990). Briefly this method involved extraction of humic substances with a 0.1 M NaOH and 0.1 M Na4P2O7 solution (1:10 w/v soil to solution ratio) under N2 at 65°C for 24 h. The suspensions were centrifuged at 12 000 x g for 20 min, and the supernatants were filtered through a 0.45-µm membrane filter. An aliquot of the extracts was acidified to pH 2 with H2SO4 to separate humic from fulvic acids. Coagulated humic acids (HA) were collected, while the supernatants containing the fulvic acids (FA) were further purified on 10 to 12 cm3 of insoluble polyvinylpyrrolidone (Aldrich, Germany) previously equilibrated in 0.005 M H2SO4 (Petrussi et al., 1988). The eluate contained the nonhumified fraction (NH) that is characterized by the presence of organic compounds such as carbohydrates, free aminoacids, and peptides which are co-extracted in alkaline solutions (Cheshire, 1979). The NH fraction was discarded while the retained fraction was eluted with 0.5 M NaOH and represented the purified FA. The organic C concentration of the filtered alkaline extract (total extractable C, TEC), as well as that of the FA and HA fractions, was determined by the Walkley-Black method (Nelson and Sommers, 1996), and the following humification parameters were calculated:

(i)Humification index (HI): the ratio NH/(HA+FA), where NH = TEC–(HA+FA). This index is normally 0.5 or higher and may even reach 1 for slightly humified soils. However, when soil organic C is highly humified this index approaches zero.
(ii)Degree of humification (DH%): the ratio [(HA+FA)/TEC] x 100. The DH% approaches 100% when the alkaline extract organic C is completely humified (i.e., NH = 0) and 50% when HI = 1.
(iii)Humification ratio (HR%): the ratio [(HA+FA)/TOC] x 100. The HR% parameter is proportional to the state of humification of the soil organic matter.

Soluble organic matter (SOM) was extracted from all soil samples by shaking 20 g of sample with 100 mL of deionized and degassed water for 24 h at room temperature. After centrifugation at 12 000 x g for 20 min the supernatant was collected. The extraction was repeated and the supernatants were joined. The water extracts were filtered through 0.7-µm GF/F glass microfiber filters and 0.45-µm Supor 450 polysulphone membrane filters. Dissolved organic C was then determined by the wet dichromate method (Nelson and Sommers, 1996).

Biochemical Analyses
The amount of microbial biomass C was measured with the chloroform fumigation/extraction method (Vance et al., 1987). An extraction efficiency coefficient of 0.38 was used to convert soluble C in biomass C (Vance et al., 1987). Enzyme activities were determined using the following procedures: dehydrogenase (Von Mersi and Schinner, 1991); phosphodiesterase (Browman and Tabatabai, 1978); protease (Ladd and Buttler, 1972); arylsulphatase (Tabatabai and Bremner, 1970); o-diphenoloxidase (Perucci et al., 2000).

Statistical Analysis
The results reported are the average values of determinations made on nine replicates. All data were subjected to an analysis of variance using the least significant difference test and comparing the differences among or within the appropriate soil horizons.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Physical Soil Properties
The pedological inspection of the profiles made it possible to identify the absence of pedogenetic features and structure in any of the four C1 and C2 horizons. The C1 horizon was composed of a silt loam material having a yellow (2.5Y 7/6) color when dry and light olive brown (2.5Y 5/4) when moist. The C2 horizon was a clay loam, calcareous material having a light gray (5Y 7/2) color when dry and dark gray (5Y 4/1) when moist. At all four sites, the C1 and C2 horizons did not vary in their composition but only in their thickness (30 to 60 cm and 40 to 70 cm, respectively). The uppermost horizon at each site, made from the mixing of MWC with the same material of the C1 horizon, had varying thickness (10 to 50 cm) and organic matter content, together with additional characteristics that allowed it to be classified as a pedogenetic A horizon. The characteristics of the A horizons are reported in Table 2. Over the time series studied the A horizon became more and more gray-brown in color. Its hydrological characteristics improved, in particular with respect to the available water capacity (Table 3). Similarly, the field capacity and permanent wilting point increased (Table 3). The soil structure, initially polyhedric subangular blocky, tended to be crumb in the oldest fill deposits.


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  		Table 2. Description of the profile of the A horizon in the samples from the deposition having different age.

 

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  		Table 3. Hydrological parameters of the A horizon.{dagger}

 
The anthropomorphous soils described above can be classified as a Typic Ustorthents (USDA, 2006) or Anthropic Regosol (FAO, 1998) for the most recent soil (2 yr old), an Anthraquic Ustorthents (USDA, 2006) or Anthropic Regosol (FAO, 1998) for the 6-yr-old soil, and a Typic Haplanthrepts (USDA, 2006) or Terric Anthrosol (FAO, 1998) for the oldest soil (10 yr old). The 9-yr-old soil was a moderately eroded phase of the latter.

Table 4 shows the percentage of total thin section area occupied by pores >50 µm (macroporosity). In the surface layer (0 to 10 cm) of the A horizons the macroporosity significantly increased with time, particularly 9 yr after compost addition. This is in accordance with the decrease in the mean values obtained for bulk density (from 1.28 Mg m–3 for the most recent soil to 1.15 Mg m–3 for the oldest soil) for this horizon. This increase in macroporosity was probably related to the addition of organic matter to soil through compost application as well as the effect of the amendment on biological activity. The strong relationship between organic matter and soil porosity and structure has been widely demonstrated (Giusquiani et al., 1995; Pagliai and Vignozzi, 1998). Although a similar trend occurred for the C1 horizon, the increase in macroporosity was not statistically significant.


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  		Table 4. Variation in soil macroporosity over the 10-yr time series after amendment with compost.{dagger}

 
Pore size distribution is a property that should be considered for a thorough characterization of soil macropores, especially for elongated, continuous pores. Many of these pores directly influence plant growth by facilitating root penetration as well as by increasing the storage and transmission of water and gases through the soil (Pagliai et al., 2004). Moreover, Russell (1978), Tippkötter (1983), Pagliai and De Nobili (1993), and Pagliai and Vignozzi (1998, 2002) reported that feeding roots require pores ranging from 100 to 200 µm to grow into. According to Greenland (1977), pores of an equivalent pore diameter ranging from 0.5 to 50 µm are storage pores that serve as a water reservoir for plants and microorganisms. Transmission pores are elongated and continuous, with dimensions ranging from 50 to 500 µm and are important in soil–water–plant relationships, as well as in maintaining a good soil structure. In fact, damage to soil structure can be recognized by a decrease in the proportion of transmission pores. Pores larger than 500 µm are important for soil drainage and aeration.

Results also show an increase in total macroporosity and a modification in the soil pore system with time from compost incorporation (Table 4 and Fig. 2 and 3). Pore shape and size distribution in the A and C1 horizons of soils 9 and 10 yr after compost addition showed large differences compared with soils after 2 and 6 yr (Fig. 2 and 3). The increase in macroporosity over time reflected an increase in the proportion of elongated pores. In the A horizon, this increase was mainly due to the proportion of elongated pores in the large size classes (>500 µm); however, an increase was also observed in the elongated transmission pores (50 to 500 µm). A similar trend was observed in C1 horizons (Fig. 3). The size distribution of macropores showed that soil physical qualities improved with soil age.


Figure 2
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  		Fig. 2. Macropore size distribution according to equivalent pore diameter for regular and irregular pores and width for elongated pores, in the A horizon (0 to 10 cm) 2, 6, 9, and 10 yr after compost amendment. All data represent the mean of three determinations. Values, expressed as a percentage of the total area occupied by pores belonging to each size class per thin section, represent the mean (n = 9).

 

Figure 3
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  		Fig. 3. Macropore size distribution according to equivalent pore diameter for regular and irregular pores and width for elongated pores, in the C1 horizon 2, 6, 9, and 10 yr after compost amendment. All data represent the mean of three determination. Values, expressed as a percentage of the total area occupied by pores belonging to each size class per thin section, represent the mean (n = 9).

 
Macroporosity, pore shape, and size distribution variations with soil age were also reflected in the nature of the soil structure. Figure 4 presents photomicrographs of thin sections of the A horizon that show that recent samples (after 2 yr) exhibit a very compact soil structure in which separate aggregates are absent (Bullock et al., 1985). With time, soil structure became more open, and soil aggregates separated by elongated, continuous, planar pores of different sizes became evident. According to Bullock et al. (1985) such aggregates can be rather porous inside. The variations in macroporosity among samples from different periods of deposition suggest that the initially massive structure was transformed to subangular blocky structure over time.


Figure 4
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  		Fig. 4. Microphotographs of vertically oriented thin sections of the A horizon (0 to 10 cm) 2, 6, 9, and 10 yr after compost amendment, showing the transformation from a compact, massive structure (after 2 yr) to a more open subangular blocky structure (after 9 and 10 yr). Plane-polarized light; pores appear white; frame length 3 cm.

 
In the C1 horizons lower macroporosity values indicated a more compact structure with respect to the A horizons (Fig. 5). However, as for the A horizons, the increase in elongated transmission pores (50 to 500 µm) over time reflected a better development of subangular blocky structure that should have improved water movement (Pagliai et al., 2004).


Figure 5
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  		Fig. 5. Microphotographs of vertically oriented thin sections of the C1 horizon 2, 6, 9, and 10 yr after compost amendment, showing an increase of elongated and continuous pores along the time series (from 2 to 10 yr). Plane-polarized light; pores appear white; frame length 3 cm.

 
Chemical Soil Properties
Table 5 shows some chemical characteristics of the horizons over the 10-yr period studied. Only the A horizon showed significant differences with soil age subsequent to compost application. These changes include a greater TOC content of the A horizon compared with that of the C1 and C2 horizons. This difference was a direct consequence of compost application. Moreover, in A horizons the TOC content increased with soil age, with the highest organic C content occurring in the oldest deposit (i.e., 1993). Compost OM added to the soil is normally subject to oxidation processes that result in the loss of C as CO2 with time (Bohn et al., 1985). The increase in TOC with time in these A horizons can probably be attributed either to different quantities of compost applied to the surface horizon (considering that this experiment was not performed in the laboratory but in the field) or to organic residues derived from the natural vegetation growing at the soil surface. The latter hypothesis is however less likely because the OC contribution from the herbaceous species present (Amaranthus spp. and Festuca arundinacea) was expected to be very limited. These species only grow in spring and in autumn while dry conditions in summer prevent their growth. Consequently, the primary influence of vegetation on soil properties is the favorable effect on soil structure exerted by roots.


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  		Table 5. Chemical characteristics of the landfill covering soils relative to the samples from the 2001, 1997, 1994, and 1993 depositions.{dagger}

 
Although the A horizon TEC values, when normalized to TOC content, did not show significant differences with soil age, the organic matter fractions expressed as a percentage of the TEC showed significant variations. In fact, the relative content of FA and NH decreased while HA content increased with time. This behavior is indicative of an ongoing humification process in the A horizon and can be further appreciated by the increase in the values of DH and HR (Table 6). These parameters are widely used to evaluate the humification status of soil organic matter (Gigliotti et al., 1999). In fact, over the 10-yr experimental period, the DH and HR double while the HI decreases by more than half, suggesting that these humification parameters are useful indicators for monitoring the renaturalization process. Moreover, the increase in available P and total N (Table 5) showed that even these soil fertility parameters exhibit a positive trend and can be suitable as additional indicators of soil evolution.


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  		Table 6. Humification parameters.{dagger}

 
Biochemical Soil Properties
A general increase in biomass C content and enzyme activities in the A horizon can be observed at 10 and 6 yr from compost addition, respectively (Table 7). This increase with soil age may be surprising since various authors report an initial enhancement of microbial populations (Behera and Wagner, 1974; Griffiths et al., 1998) that feed on fresh organic matter followed by a subsequent decrease in the population sizes and rate of enzyme production due to the decay of fresh organic matter (Jans-Hammermeister et al., 1997). In our study, this first enhancement is surely not evident, because the first sampling of the soil was made 2 yr after compost addition when this process was probably already concluded. According to the theory of Fontaine et al. (2003), microbial activity that promotes the evolution of organic matter in the soil is highly specific. Microorganisms that selectively mineralize fresh organic matter are called "r-strategists," and when such labile material is exhausted, they die or become dormant because of their inability to utilize the remaining soil organic matter. This latter organic matter may serve as a C source for the so-called "k-strategists" that succeed the "r-strategists" in the last stages of fresh organic matter decomposition, when most labile compounds have been exhausted and only polymerized compounds remain. "K-strategists" remain continuously active because they utilize the residual soil organic matter that is almost inexhaustible due to the small fraction of total organic matter that undergoes mineralization. The microbial activity of the "k-strategists" could explain the observed general tendency of the enzymatic activities to level out in the A horizons of the older soils.


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  		Table 7. Soil microbial biomass and enzyme activities of samples from the landfill-covering soils.{dagger}

 
Moreover, the results obtained for the C1 horizon show a similar increase in biomass C and enzymatic activities with soil age, particularly at 9 y from compost addition (Table 7). Considering that the mineral C1 horizon was composed of the original excavation soil without compost amendment, one would expect it to have a constant microbial biomass and enzymatic activity over time. Nonetheless, the observed increase in enzymatic activities as well as the temporal delay with respect to the A horizon seem to suggest that this enhancement was probably due to the migration of microorganisms from the overlying A horizon. Microorganisms have the capability to move through the soil both by random mobility (taxis in the absence of a chemical gradient) and in response to a chemical gradient (chemotaxis) (Ginn et al., 2002; Singh et al., 2002). Both motility processes are proportional to the water flux. The first, which is also influenced by the biomass content, could have been responsible for the biomass enhancement in the C1 horizon as a consequence of the increase in biomass in the A horizon. The second mobility process might be due to nutrient percolation from the A horizon towards the C1 horizon, resulting in a flux of microorganisms associated with the gradient in nutrient supply.

These considerations suggest that variations in biochemical parameters of the A and C1 horizons can serve as good indicators to evaluate soil quality in anthropogenic soils renaturalized through the application of compost. Due to the variety of biochemical processes involved in transformation of compost organic matter, such an indicator cannot be linked to the activity of a single enzyme. In fact, the results obtained show that a positive trend in soil quality may involve dehydrogenase, phosphodiesterase, protease, and diphenoloxidase but not arylsulphatase. More important than the particular enzyme activities enhanced is the number of enzyme tests that express an increasing trend with soil age. The more enzyme activities are enhanced, the higher the positive response of the test will be. In our study the increases in four of the five enzyme activities tested in A and C1 horizons enables us to infer that 10 yr after the addition of compost the landfill-covering soil showed a measurable improvement of soil fertility.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Physical, chemical, and biochemical analyses of the MWC-amended cover soils of landfill deposits from different years have enabled us to evaluate variations in the soil over 10 yr. We found that the capping soil developed a well-structured A horizon with a significant increase in soil porosity, especially with respect to elongated continuous pores. Chemical characterization of the A horizon also showed that over the 10-yr period humification processes clearly influenced the chemical nature of the organic matter originally applied to the soil with the compost. The variations in microbial biomass and major enzyme activities (dehydrogenase, phosphodiesterase, protease, and o-diphenoloxidase) in the A and C1 horizons could serve as indicators of soil quality and were capable of describing the evolution of these anthropogenic soils in which compost amendment was adopted to promote their fertility.


   ACKNOWLEDGMENTS
 
This research was financially supported by the Italian Ministry of Education, University and Research (PRIN). The authors would like to thank Gesenu S.p.A. for rendering their landfill to complete disposition for the purposes of this research.


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





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