Impact of the environmental conditions and physiographic position on degradation of soil and water resources at north fayoum depression, Egypt

الملخص EN

This study aims to throw light on the environmental impact as related to soil degradation at north Fayoum depression, with special interest to the heavy metals pollution of some water supplied by a number of drainage canals.

This trail was achieved through studying seven sites were carefully selected adjacent to the southern shoreline of Lake Qarun.

By nature, these sites are fragile because of constraints imposed by the unique hydrological setting as well as parent material of calcareous in nature, gypsiferous and / or saline and climatic conditions.

The obtained results showed wide variations in soil characteristics of these sites, i.e., topographic-sequence (-43 to -28 m), ground-water table depth (65 to > 135 cm), soil texture grades (loamy sand to clay), CaCO3 content (8.1 to 53.3%), gypsum content (2.83-15.65%), organic matter (0.79-3.74 %), soil salinity (EC = 3.8-87.9 dS / m) and sodicity levels (ESP = 7.5-47.3), consequently they differ in their soil taxonomic units and the suitability classes for agricultural purposes.

However, wetness, soil texture, CaCO3, gypsum and salinity/alkalinity are the most effective limitations for soil productivity, with an intensity degree ranged between slight and very severe (rating > 90 and <40).

Also, the suitability classes of the studied soils could be ranged between unsuitable (N1ws1s3n) and moderately suitable (S2ws1s3n) for the current condition as well as moderately suitable (S2s1) and highly suitable (S1s3).

As a general view, soil macro-morphology showed an extremely salinity for some of the studied soils, which is one additional stressor affects the soil characteristics and the nature and distribution of vegetation.

In addition, pounded Aquisalids either developed on the soil surface as brittle salt crusts or fluffy almost snow like crust.

The oxidation-reduction chemical reactions (redoximorphic) in subsoil layers can cause changes in the soil pH.

The micro-morphological features show that the redox concentrations (mottling) are yellowish brown (Jarosite) in the upper stratum, pale yellow (Limonite) in the mid-profile, reddish brown (Hematite) for the upper fringe of water table and yellowish (Goethite) in the deepest portion.

The oxidized zone is characterized by dark grayish brown and slight hard due to the dominance of ferric oxides, while the reduced one shows a dark gray and hard, due to the dominance of ferrous oxides.

Also, the SO42- enriched deposits encouraging the microbial transformed H2S under the reduction conditions, this medium represents a better environment for transforming amorphous ferric oxides (Fe2O3) to be appeared black in the form of pyrite (FeS2).

The prevailing environmental conditions are mostly affected the features of CaCO3 and gypsum, which are found in either biorelicts of shell fragments or orthic lime nodules and intercalary clusters of gypsum crystals.

Soil chemical degradation emphasized by salinity and sodicity levels of the studied soil sites, which are coupled with salinity and sodicity levels of both groundwater table and the neighboring drains.

However, the drainage water will be accumulated and resulting in high more saline groundwater table (within 1.5 m of soil surface), and subsequently water logging, high salinization and alkalinization conditions as well as the gleization process, which leads to aquic phase.

These conditions led to internal physical, biological and chemical deteriorations as well as led to a reduction in a soil’s ability to inactive toxic compounds.

Heavy metal concentrations of either major nutritive (Fe, Mn, Zn and Cu) or non-nutritive (Pb, Cd, Ni and Co) showed a regular distribution pattern in the groundwater table, drainage water in drains and Lake Qarun.

Also, their concentrations at the eastern and middle parts of the studied area, generally, contained higher values, and tended to decrease westwards.

This may be attributed to the environmental impact of pollution sources which coming from El Batts and El Wadi drains and many anthropogenic activities.

Whereas, heavy metals concentrations in soil were mostly related to soil texture, where the clayey soils exhibited higher available contents of all studied heavy metals as compared to both medium and relatively coarse textured ones.

This may be due to the former soils had a larger capacity, high CEC, to adsorb these metals from soil solution