Document Type : Research articles.
Author
Soil Sci. Dept., Fac. of Agric., Cairo Univ., Egypt
Abstract
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 neighbouring 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 waterlogging, 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
Keywords
)
View on SCiNiTO