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Three irrigation water resources were chosen at district Kafr-Saqr, El-Sharkia Governorate to assess their quality and their impact on the heavy metals content in the soil.
The chemical parameters, biological and chemical oxygen demand, and heavy metals concentrations of three different water irrigation resources are mainly highly significantly different and affected the soil characteristics as following.
The continuous irrigation of soil by using wastewater resulted in continuous increase in the electrical conductivity. The distribution of soluble cations and anions appear to have a similar trend to those obtained for EC values. They mostly decrease with increasing soil depth in the soil irrigated with fresh and mixed water. In contrast, the distribution of soluble cations and anions in the soil irrigated with drainage water show the opposite trend as they increase with depth. Increasing concentrations of heavy metals in the surface soil layer (0 – 20cm) of the investigated soil locations
The enzymatic activity is an important factor in soil and in this study urease and phosphatase evaluated as a function of soil EC. The correlation between soil EC and urease and phosphatase activity was performed by statistical analysis.
The chosen irrigation waters were the Nile water from Bahr Muways Canal (location I, represented by the Abu- Hammudah village), mixed water (1:1 ratio) from Bahr Muways Canal and Bahr Hadus drain, (location II, represented by Ahmed Abd-Allah Village), and the drainage water from Bahr Hadus drain (location III, represented by Izbet el-Kobre). Irrigation waters were sampled during two years for two successive seasons winter and summer (2013/14 and 2014/15). Soil samples were collected from each location from four depths (0-20, 20-40, 40-60 and 60-100 cm) to determine some soil properties and their content of heavy metals. Also to determine some enzymes activity ( Urease-Phosphatase ) to determine the effect of EC on their activity.
Another surface soil samples from four depths (0-20, 20-40) were collected from the first location only (location I, represented by the Abu- Hammudah village) to determine the effect of different concentrations of Cd2+ and Pb2+, and incubation time on urease – phosphatase activity .The obtained results indicated that:
a. Assessment of water resources used for irrigation.
Mean pH values of the collected irrigation water samples were within the permissible limits (6.5 to 8.4). On the other hand, the small increase of pH values of the drainage water (III) may be attributed to the temporal increase in the Na+ ions in the drainage water.
EC values of mixed and drainage water were above the normal range which should be < 0.7 dS.m-1. Also, the mixed and drainage irrigation waters had approximately 3.5 and 5.6 folds the salinity of the fresh water (location I) indicating possible salinity hazards when using such water in irrigation purposes for a long time.
TDS (Total dissolved salts) values of fresh water were within the normal range (< 450 mg.L-1). Meanwhile, mixed and drainage water were classified as of slightly and moderatly salinity hazards.
Values of turbidity were mainly differed according to the resource of irrigation water. The highest values of the suspended materials were found in the drainage water, then mixed and fresh water.
Results indicated that in the Nile water the soluble ions were found in the following sequence: Ca++ > Mg++ > Na+. > K+ In the mixed and drainage water soluble Na+ ions were dominant followed by Ca++ or Mg++ ions. On the other hand, the obtained results showed that the chloride ion was the dominant anion followed by sulphate then bicarbonate in all used irrigation water resources. Also, the results show that all collected samples of irrigation water were contaminated with NO3– N ions. This contamination was lower than the permissible limit (5 mg.L-1).
SAR values of fresh water were < 1.0. The SAR values for mixed and drainage waters ranged from 2.62 to 2.69 and 3.68 to 3.76, respectively. This means that the fresh and mixed water are safe for irrigation, as the SAR values must be < 3.
BOD and COD values violated the standard limits of law 48/1982 (10 mg.L-1 for drainage water and 6 mg.L-1 for fresh water) except for the BOD values of fresh water. On the other hand, the COD/BOD ratios ranged from 1 to 1.5 meaning that the organic matter was soluble and may be useful for soil fertility.
The present study indicated that all the studied heavy metals in the irrigation water did not violate the allowable limits and were within the permissible limits 0.01 mg.L-1 for Cd; 0.2 mg.L-1 for Cu; 5.0 mg.L-1 for Pb; 2.0 mg.L-1 for Zn; and 5 mg.L-1 for Fe.
Statistical, analyses LSD for the relationships between the different parameters, used in assessing the quality of the different irrigation water resources, were mainly highly significant different.
b. Impact of the irrigation water resources on some physical characteristics of the investigated soil at different locations.
The obtained results indicated that there were small differences in the texture classes of the three locations. Whereas, the clay content changed from 37% and 41%; the clay + silt fractions increased in all locations with increasing soil profile depth.
c. The impact of using different irrigation water resources on some chemical characteristics of the soil.
The increase in the pH values for the soil irrigated with the mixed and drainage water may be attributed to the dominance of the basic forming cations, especially Na+.
The continuous irrigation of soil by wastewater resulted in continuous increases in EC values. At the same time, the amount of total soluble salts in all layers of the studied locations were generally < 4 dS.m-1.
The application of the different irrigation waters led to an increase in soluble Na+, Ca++ and Mg ++ in the soil. The concentration of soluble cations were found in the order of Na+ > Ca++ > or = Mg ++ > K+. Meanwhile, the soluble anions were found in the following order: Cl- > SO4= > HCO3-.
The total concentrations of heavy metals were different in soil profile layers according to irrigation water resource; and generally, the concentration of heavy metals increased in the two upper surface layers (0 - 20 and 20 - 40 cm).
The enzymatic activity is an important factor in soil and in this study urease and phosphatase evaluated as a function of soil EC. The correlation between soil EC and urease and phosphatase activity was performed by statistical analysis. It was found that soil EC has a significant effect on urease and phosphatase activity and were also found to be different among soil depth. from results of present study, it is concluded that the soil EC must be taken into account while evaluating the enzymatic activities of soil .
d- Effect of EC on urease and phosphatase activity.
Data shows that the EC affected the urease and phosphatase activity significantly, statistical analysis shows that EC correlated negatively with urease and phosphatase activity
e- Effects of pollution of Pb2+and Cd2+ on soil urease and phosphatase activity
The data clear that the different concentration of Pb2+ and Cd2+ effect (inhibit) the urease and phosphatase activity with the increase of Pb2+ and Cd2+ concentrations and also with the time incubation .
Effect of cadmium on urease
Cadmium inhibits enzyme activity in all metal concentrations compared with control. The metal when applied in soil by 10,15 and 20 ppm dose decreased the activity of urease.
Effect of cadmium on phosphatase
Cadmium inhibit enzyme activity in all metal concentrations compared with control. The metal when applied in soil by 10, 15 and 20 ppm dose decreased the activity of urease.
Effect of lead on tested enzymes
Lead is toxic and inhibit all enzymes under all treatments.
The different concentrations of Cd2+ and Pb2+ also the difference of incubation time affected negatively on urease and phosphatase Activity.
Km and Vmax were changed for each enzyme as type of used heavy metal where the kinetic result match with activity results as the state of inhibition the values of Km and Vmax affected in same trend and decreased in the same ordered where the case of activation the values of Km and Vmax increase in the same trend.
Heavy metals in soil affect enzymes activity and enzymes kinetics in various way effect depends on metal type where some metals consider toxic to all microorganisms which is the major source of soil enzyme or interact with enzyme in irreversible change to alter the structure of enzyme so inactive enzymes that like in apply of cadmium and lead. Time of incubation play role in affecting enzymes activity. Environmental pollution with metal when reach soil inactive soil enzymes at high concentration of metal led to decrease soil quality and fertility.