**3.1. Geomorphological characterization**

**Phytosociological class Main characteristics**

41. CARDAMINO HIRSUTAE-GERANIETEA PURPUREI (Rivas-Martínez, Fernández-González & Loidi 1999) Rivas-Martínez, Fernández-González & Loidi classis

202 Environmental Risk Assessment of Soil Contamination

50. TUBERARIETEA GUTTATAE (Br.-Bl. in Br.-Bl., Roussine & Nègre 1952) Rivas Goday & Rivas

51. FESTUCO-BROMETEA Br.-Bl. & Tüxen ex Br.-Bl.

54. POETEA BULBOSAE Rivas Goday & Rivas

56. LYGEO-STIPETEA Rivas-Martinez 1978 nom.

57. STIPO GIGANTAE-AGROSTIETEA CASTELLANAE Rivas-Martínez, Fernández-González & Loidi 1999

Martínez in Rivas-Martinez 1978

Conserv. Propos.

Martínez 1963 nom. mut. Propos.

nova, stat. Nov.

1949

40. GALIO-URTICETEA Passarge ex Kopecký Perennial hemycriptophyte and climbing tall herbs of nitrified

43. TRIFOLIO-GERANIETEA Müller 1962 Semi-shaded perennial herb communities of scarce moisture

communities.

rich organic nutrient soils.

wood fringes and other semi-shaded anthropogenic biotope

Annual spring and summer ephemeral internal and external shrub fringes slightly nitrified semi-shaded communities, growing on

external fringe woodlands. Calcareous or mesoeutrophic rich soils in temperate submediterranean central Iberian territories.

Perennial xerophytic and mesophytic grasslands. Anthropogenic grazed baso-neutrophilous or slightly acidophilous mesophytic or slightly xerophytic nutrient rich-pastures largely covered by

Western Mediterranean oceanic thermo- to supramediterranean upper semiarid to humid pastures, grazed and manured, dominated by dwarf perennial grasses and other nutritious

Mediterranean perennial basophilous xerophytic tall bunchy

*rotundifolia* and other *Quercus* natural potential forest

Silicicolous perennial grasslands rich in endemics, serial of *Quercus*

communities on deep and moist soils, widely spread by grazed

Therophytic grasslands. Pioneer spring and early summer ephemeral plant acidophilous or calcifugous communities, dominated by non nitrophilous annual short herbs and grasses,

but localized only in dry or initial soils, mostly in

submediterranean or step territories.

perennial grasses.

communities.

Most of the capped landfills are mixed dumps containing both domestic and industrial waste. Besides mitigating the visual impacts of a landfill, the plant cover prevents its collapse and the

However, in such scenarios the stability of plant communities that become established from the seed bank of the capping soil layer is threatened. Among others, the factors that give rise

and anthropic activities

59. MOLINIO-ARRHENATHERETEA Tüxen 1937 Mesophile to wet often manured meadows and pasture

**Table 1.** Phytosociological classes and mean characteristics of the main species found at the landfills.

pollution of other ecosystems by deposited waste materials.

prostrate chamaephytes…..

dense or short open grasslands.

Here we examine the case of a closed landfill in the Madrid Autonomous Community. This site can be described as one of the most complex scenarios observed among the soil-capped solid waste landfills of the central Iberian Peninsula despite its many features common to all the landfills examined in this region [1]. Located in the municipal district of Getafe (Madrid), this landfill was first described by [9], when it occupied an area of around 70,000 m3 . Fifteen years later (in 2009), the site covered some 95,000 m2 of land.

Continuous waste dumping and subsequent capping with soil from the surroundings has determined the complex morphology of this landfill. In the photo in Figure 2, the landfill appears as a flattened hill rising out of a plain.

**Figure 2.** Picture of the whole landfill in spring of 2009

The landfill site has three main zones: a zone (western) mostly containing solid domestic waste, and two zones (central and eastern) mainly accommodating industrial waste and some inert compounds. We have designated these latter zones "rubble tips" to distinguish them from the landfill proper (Figure 3).

The flatted tops of the landfill correspond to platforms, yet more outstanding are its 12 slopes showing a high variety of exposures (across their 360º). Slope heights are 10-20 m and gradients are 50%. Their profiles are straight and many slopes overlap one another. Many slopes show signs of erosion, especially in troughs, often exposing their waste materials. Leachate surface runoff may be observed in three main discharge areas. The westernmost discharge area occupies a wetland. The other two areas, south of the rubble tips form shallow water sheets in the wettest months and quickly dry when rain ceases at the end of spring. In all these discharge zones and at the foots of the slopes, sheep herds may be found grazing. What is more, these and other animals drink any water that accumulates in these areas in 5 to 6 months of the year.

### **3.2. Composition of the capping soil layer: Factors linked to fertility, salinity, metal toxicity, organic compounds and erosion**

To identify the soil factors that mainly determine the landfill's vegetation, mostly arising from the seed bank of the capping soil, we used a stratified sampling procedure (platforms, adjacent rubble tips and main surface leachate discharge zones). At each site, samples were collected using a hoe from the top soil layer (0-10 cm) to give an average soil sample. 57 of such samples were transported to the laboratory, where they were air-dried and sieved (< 2 mm). These samples were then subjected to each of the techniques mentioned in the following sections. Sampling sites 27 to 31 correspond to piles of waste deposited directly in the easternmost discharge zone with no type of cover at all. Although these samples do not correspond to the capping soil, they were collected to assess the possible effect of these waste materials on the soils of the discharge zone in future studies. Corresponding results do not appear in the tables provided below.

**Figure 3.** Main areas of the landfill and sites where capping soil samples were collected. 03/08/2009 Google Earth Image. UTM coordinates: X=442599 Y=4459459, 30T.

#### **a. Soil fertility indicators**

In the 57 soil samples, we examined several variables related to soil fertility with consequent impacts on the vegetation. The procedures described in [10] were used to determine: pH in water and in a saturated soil paste, percentage organic matter by potassium dichromate reduction, Kjedahl total nitrogen, pseudototal (by extraction with nitric and perchloric acids at 4:1) and exchangeable (by extraction with ammonium acetate, pH 7) concentrations of Ca, K, Na and Mg, and pseudototal and bioavailable P and P2O5 concentrations, analyzed by plasma emission spectroscopy (ICP-OES).

The Complex Nature of Pollution in the Capping Soils of Closed Landfills: Case Study in a Mediterranean Setting http://dx.doi.org/10.5772/57223 205

**3.2. Composition of the capping soil layer: Factors linked to fertility, salinity, metal toxicity,**

To identify the soil factors that mainly determine the landfill's vegetation, mostly arising from the seed bank of the capping soil, we used a stratified sampling procedure (platforms, adjacent rubble tips and main surface leachate discharge zones). At each site, samples were collected using a hoe from the top soil layer (0-10 cm) to give an average soil sample. 57 of such samples were transported to the laboratory, where they were air-dried and sieved (< 2 mm). These samples were then subjected to each of the techniques mentioned in the following sections. Sampling sites 27 to 31 correspond to piles of waste deposited directly in the easternmost discharge zone with no type of cover at all. Although these samples do not correspond to the capping soil, they were collected to assess the possible effect of these waste materials on the soils of the discharge zone in future studies. Corresponding results do not appear in the tables

**Figure 3.** Main areas of the landfill and sites where capping soil samples were collected. 03/08/2009 Google Earth

In the 57 soil samples, we examined several variables related to soil fertility with consequent impacts on the vegetation. The procedures described in [10] were used to determine: pH in water and in a saturated soil paste, percentage organic matter by potassium dichromate reduction, Kjedahl total nitrogen, pseudototal (by extraction with nitric and perchloric acids at 4:1) and exchangeable (by extraction with ammonium acetate, pH 7) concentrations of Ca, K, Na and Mg, and pseudototal and bioavailable P and P2O5 concentrations, analyzed by

**organic compounds and erosion**

204 Environmental Risk Assessment of Soil Contamination

Image. UTM coordinates: X=442599 Y=4459459, 30T.

plasma emission spectroscopy (ICP-OES).

**a. Soil fertility indicators**

provided below.


**Table 2.** pH, organic matter (OM, %), nitrogen (N, %), pseudo-total concentration (T) of nutrient elements (mg kg-1) and percentage of exchangeable fraction (E) in soil samples collected from landfill proper.

The results of these determinations in each soil sample are provided in Tables 2 and 3. All results are provided to highlight the huge variation existing for each factor. pH varied from 7.0 to 8.5, given the alkaline nature of the surrounding soils used to cap the landfill. The distributions of all variables failed to vary significantly between the landfill proper and rubble tips.
