Materials and Methods

Study Area

For this study, the area of interest was subbasin of Metaponto agricultural site, located in southern Basilicata, Italy, across the municipalities of Policoro, Scanzano Jonico, Montalbano Jonico and Pisticci, approximately 11,698 ha in size and crossed by two main rivers, Sinni and Agri, and from many secondary water bodies. Figure 1 shows the location of the study area.

Topographically, the area is characterised by fairly distinct variations in elevation in the western part of the basin, away from the coast, and extremely flat terrain in the nearshore portions of the basin, to the south and east. The main soils in the area are the “soils of the alluvial plains” and the “soils of the Ionian coastal plain”. The soils of the alluvial plains are those formed along the fluvial channels of the

Fig. 1 Study area overview (circles indicate soil profile sites)

rivers crossing the area. Therefore, they are soils on alluvial and lake deposits, with variable grain size from clayey to stony. The soils of the Ionian coastal plain consist of marine deposits of different ages, from Pleistocene to Holocene, and of alluvial deposits of variable grain size. The soils of the internal areas, less extensive than those described above, are those that formed on a substrate of sandstones with alternations of marl and clay.

Much of the basin is used for agricultural purposes. Major crops and land uses receiving applications of nutrients and chemicals include cereals, vegetables and fruit orchards. Soils that support these land uses range from the loam to clay loam, in the northern portions of the basin, to the fine silty loams in the southern basin.

Geo Database Implementation

A spatial digital database for the study area was established through the assembly of various publicly available physiographic data sets (land use, soils, climate, depth to groundwater, elevation).

Such datasets characterised features considered to be directly or indirectly involved in the leaching process, thus characterising boundary conditions. Data was structured into feature datasets and raster datasets, in that both discrete and continuous data types were implemented in this study (Table 1).

Table 1 Summary of the GIS datasets

Feature

Data format

Spatial resolution

Data source

Land use

Vector

Digitised form 1:10,000 scale

INEA-Progetto SIGRIA

Soil texture

Vector

Cell size 20 m

Basilicata region Senise

Soil profile depth

Vector

Cell size 20 m

Basilicata region Senise

Precipitation (years)

Raster

Cell size 20 m

AdB

Temperature (year mean)

Raster

Cell size 20 m

AdB

Elevation

Raster

Cell size 20 m

SAFE-Univ. Basilicata

Freatimetry

Raster

Cell size 20 m

AdB

Table 2 Land use classes from the original map are summarised into 10 main categories

Data manipulation and spatial analysis were performed to finally produce output datasets as described in the previous table.

2.2.1 Land Use

Land use dataset, published within Progetto Sigria, INEA 2000, was used to describe cropped species at parcel level and furthermore to define the spatial extent of the whole GIS project in this work. Table 2 shows cropped surfaces in hectares summarised by aggregated land use classes.

Fruit orchards land use dataset, published within Progetto Sigria, INEA 2000, was used to describe cropped species at parcel level and furthermore to define the spatial extent of the whole GIS project in this work. Fruit orchards cover almost 44 % of total study area, followed by ploughed areas covering 15 %, vegetables 10 % and cereals 10 %. Non-vegetated areas, such as urban or water bodies, make up for 15 %.

Soil data were originally acquired from regional geology agency in tabular format for 52 soil profiles sampled across the study area (see circles in Fig. 1. For each profile, a fictitious soil system was adopted, assuming the soil to be composed of only two layers, A and B, the first being superficial and 40 cm thick (this was the average depth of the first horizon for all the soil profiles and the latter reaching the water table). A fictitious soil profile was obtained for each real soil profile by averaging textural data with a weighted procedure using horizon depths as weights. Data were then imported into GIS and spatial structure of sand, clay and silt contents, and depth measures were analysed with Exploratory Spatial Data Analysis (ESDA) tools, by means of classic statistical and geostatistical analyses. After interpolation, continuous surfaces for sand, clay, silt and soil profile depth were produced in raster format for both A and B soil layers (maps not shown).

Sand, silt and clay raster datasets were concurrently queried with a map calculator using a set of SQL statements, each defining a texture constraint for each soil class according to USDA classification system, in order to produce two final texture maps (Fig. 2), one for each fictitious soil layer.

Fig. 2 Texture map for layers (a) and (b)

2.2.2 Precipitation, Temperature and Evapotranspiration

Climate data on a daily basis for the 1999–2009 period for all the climatic stations localised in the area of interest were provided by Regional Agriculture Services. The Voronoi algorithm was used for spatial partitioning of the study area according to the subarea of influence of each rainfall station. The Voronoi cells for the area under study are shown in Fig. 3.

Fig. 3 Positions of meteorological stations and Voronoi polygons of the study area. Alphanumeric codes identify the soil profiles used for this study

2.2.3 Elevation

Contour lines on IGM 1:5,000 base maps were digitised, and a triangulated irregular network was created from them and finally converted into a raster dataset. From elevation grid, slope grid was derived as well.

2.2.4 Depth to Groundwater

The laboratory of Soil and Contaminant Hydrology of the University of Basilicata provided tabular data for 192 measuring wells, 51 of which were located within the study area. Once imported into GIS as a point feature dataset, groundwater depth at measuring stations was interpolated using Kriging, thus resulting in a continuous surface (map not shown).

 
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