Abstract: Lake Qarun, is currently saline, turbid (Secchi disc transparency usually <70 cm) and has no surface outflow. This study was carried out to throw the light on the present status and long term changes of lake water. Surface water and sediment samples were collected and analyzed for nutrient salts, major cations and anions besides some trace metals (Fe, Mn, Zn, Cu, Pb and Cd). Concentrations of nitrite, nitrate and ammonia in the lake sediment (average: 0.89, 9.44 and 156.39 μg g-1, respectively) were obviously higher than those reported for water (average: 0.010, 0.039 and 0.378 mg L-1). The majority of water samples contained >50 μg L-1 Zn, >20 μg L-1 Cu, >50 μg L-1 Pb and >10 μg L-1 Cd. Present study support prior contamination of the sediments with metals, which were deposited during accidental releases from drainage sewage. Long-term changes in Lake Qarun demonstrate a significant increase of nutrient in water, while salinity and major ions were fluctuated depending on the input drains water and the rate of evaporation.
INTRODUCTION
Pollution of the environment is reflected by levels of contamination of rivers, lakes and other reservoirs. There are sites of accumulation of impurities coming from human activity, due to dissolution, precipitation and adsorption (Pertsemli and Voutsa, 2007). Contaminating elements and compounds are transported by water and gather in bottom and allusvial sediments (Ruiz-Fernandez et al., 2009). Eutrophication due to nutrient loading is one of the most extensively studied global environmental concerns (Pereira et al., 2008; Norton et al., 2008). Both N and P are highly particle reactive and most N and P, when discharged into a waterway, are deposited in bottom sediments incorporated into organic matter. Here, bacteria decompose organic matter, through oxygen and sulphate reduction, liberating N and P to pore waters and overlying waters (Amirbahman et al., 2003).
Trace metals are of particular concern as pollutants in aquatic systems as they are not readily removed by natural processes as most organic pollutants (Liu et al., 2008). Recently, the problem of some trace metal concentrations in bottom sediments was widely examined. Sediment-associated metals may be released through either physical disturbance or changes in the water’ physical and chemical variables. Such remobilization enables entry into the various components of the aquatic ecosystem (Singh et al., 2005; Mendil and Uluozlu, 2007). This availability in the entire system that makes integration into the food chain possible and the toxicity of the trace metals can have their greatest effect (Cousins et al., 2002). It is therefore, clear that increased environmental levels have the capability of causing significant effects to biota (Abida et al., 2009).s
Many factors affecting Lake Qarun ecosystem include the climatic conditions, amount of discharged wastewater, seepage from the surrounding cultivated land and geological aspects (Abdel-Satar et al., 2003). As a result of extensive water evaporation from such closed ecosystems, the gradual increase of salts, trace metals, pesticides and other pollutants is expected to change their quality and affect their food web. For this reason, a number of investigations have dealt with the lake water chemistry (Mansour et al., 2000; Ali, 2002; Saad and Hemeda, 2002; Sabae and Ali, 2004). Mansour et al. (2000) found that the salts composing the TDS in lake water were NaCl (61%), MgSO4 (17.9%), Na2SO4 (12.4%), CaSO4 (3.6%), Ca(HCO3)2, CaCO3 (0.2%) and others (1.8%). Saad and Hemeda (2002) stated that the high nutrient concentrations coincided mainly with spreading of the nutrient enriched drainage water over the dense lake bottom water. The distribution of trace elements showed irregular patterns in the lake as a result of interference between several factors such as surrounding environment, closed basin and climatic effects (Abdel-Satar et al., 2003). Sabae and Ali (2004) showed that the distribution of denitrifying bacteria was controlled by the effect of drainage water via El-Bats and El-Wadi Drains, which are loaded with nutrients. Ali and Fishar (2005) mentioned that the eastern part of the lake was generally highly contaminated (concerning trace metals in water, sediment, benthic invertebrate and fishes) in compared with the western one. Flower et al. (2006) concluded that the spheroidal carbonaceous particles were present in the upper 30cm indicating contamination by low pollution level, probably beginning around 1950.
This study was conducted to infer the present chemical status of the lake water and sediment and long-term changes in lake nutrient, salinity and major ions. The seasonal and regional distribution of heavy metals and the quality of the input water through two main drains (El-Wadi and El-Bats) were also assessed.
MATERIALS AND METHODS
Site Description
Lake Qarun, is a remnant of a much bigger one and was originally a freshwater
lake. It is located in the Western desert in the deepest part of Fayoum depression
and lies 83 km South West of Cairo (Fig. 1). It is a closed
basin that collects the agricultural wastewater drainage of Fayoum Province.
Most of this discharge is brought to the lake via two large Drains, El-Batts
(at the Northeastern corner) and El-Wadi (near mid point of the Southern shore).
| Fig. 1: | Map of Lake Qarun showing sampling locations (original) |
Lake Qarun is currently saline and turbid (Secchi disc transparency usually <70 cm) and has no surface outflow. The drain water is less saline than that the lake (Fathi and Flower, 2005) but is undoubtedly contaminated by agro-chemicals. The lake supports a moderate fishery and is frequented by water birds, however, the water quality is declining and the bird numbers are diminishing (Meininger and Atta, 1994). The Egyptian Company of Salts and Minerals (EMISAL) was created on its coast to extract salts and minerals. This project was started in 1986 (EMISAL, 1996). The discharge of agricultural drainage water (about 400 million meter3 year-1) in Lake Qarun is considered one of the greatest causes of water quality impairment in the lake (Ali, 2002).
Sampling and Analysis
Surface water and sediment samples were collected from the Lake during four
sampling campaigns at six sites in the period from February to November 2006.
Sites 1 and 2 represent the Eastern area, while sites 3 and 4 represent the
middle area and sites 5 and 6 represent the Western area of the lake (Fig.
1). The water samples were collected by a polyvinyl chloride Van Dorn water
sampler and kept cool in ice on the spot. Sediment samples were collected using
an Eckman dredge. For water and sediment, triplicate samples were taken and
mixed at each site to be representative. The sediments were put in air-sealed
plastic bags and kept cool in ice on the spot. Two additional water samples,
one in El-Wadi Drain and one in El-Batts Drain were collected.
Field Measurements
The electrical conductivity of the water samples (mS cm-1) was
measured by using a conductivity meter (S.C.T.33 YSI), transparency (cm) by
Secchi disc, pH by Orion Research Ion Analyzer 399A pH meter and water temperature
by an ordinary thermometer. CO32– and
HCO3– were measured titrimetrically on the spot,
where samples were titrated against standard H2SO4 (0.02
N) using phenolphthalein and methyl orange indicators. Also, Dissolved Oxygen
(DO) content was determined by azide modification method as specified in APHA
(2005).
Water Analysis
Water samples were analyzed for all selected variables, according to procedures
specified in American Public Health Association (2005). Total Solids (TS) were
measured by evaporating a known volume of well mixed sample, TDS were determined
by filtrating a volume of sample with glass micro fiber filter (GF/C) and a
known volume of filtrate was evaporated at 105°C. Chemical Oxygen Demand
(COD) was performed by potassium dichromate oxidation and Biochemical Oxygen
Demand (BOD) by 5 days incubation methods. Chloride was determined by argentometric
and sulphate by gravimetric methods. Sodium and potassium were measured directly
using the flame photometer model Jenway PFP, UK. Calcium and magnesium were
determined by EDTA titrimetric method. Concentrations of nitrite, nitrate, ammonia,
orthophosphate (ortho-P) and reactive silicate in water were determined using
the calorimetric techniques with formation of reddish purple azo-dye, Cd reduction,
phenate, stannous chloride reduction and molybdosilicate methods, respectively.
Total phosphorus (total-P) was measured as reactive phosphate after persulphate
digestion. Total Fe, Mn, Zn, Cu, Pb and Cd in water were measured after digestion
using an atomic absorption reader (Perkin Elmer 3110 USA) with graphite atomizer
HGA-600.
Sediment Analysis
For total trace metals, sediment samples were allowed to defrost, then were
air-dried in a circulating oven at 60°C. A total digestion for one gram
sediment was carried out according to the method of Kouadia
and Trefry (1987) to insure complete dissolution of all present elements.
The elements determined were Na+, K+, Ca2+,
Ba2+, Fe, Mn, Zn, Cu, Pb and Cd. The solutions were directly analyzed
for total Na+, K+, Ca2+, Ba2+, Fe,
Mn and Zn by atomic absorption spectrophotometry (Perkin Elmer 3110 USA), while
total Cu, Pb and Cd were analyzed by atomic absorption with a graphite atomizer
(HGA-600). The sediment samples were also analyzed for some chemical variables:
organic matter and carbonate content. The organic matter content was determined
by oxidation with K2Cr2O7 in acidic media (Jackson
et al., 1984). The carbonate content was determined by the method
described in American Society of Agronomy (1982). The
dried sample was treated by hydrochloric acid and the carbon dioxide developed
was collected in standard sodium hydroxide and then back titrated for the excess
hydroxide using phenolphthalein as indicator. The concentrations of exchangeable
ammonia, nitrite and nitrate were measured using the KCl extraction and quantified
directly by indophenol blue, modified Griess-Hosvay and hydrazine-CuSO4
reduction methods, respectively according to American Society
of Agronomy (1982).
Statistical Analysis
Results of water samples were tested for significant differences for all
variables among different seasons, while the sediment variables were tested
for different sites by means of one-way ANOVA. In addition, the variables studied
in drain's water samples were tested among the two drains. The relationship
between the different studied variables in water and sediment were assigned
by computing the correlation coefficients (r) to indicate the nature and the
sources of the polluting substances.
RESULTS
Water Analysis
The ranges, means and Standard Deviation (SD) of the studied physical and
chemical variables in water samples are given in Table 1.
In addition, the water level in Lake Qarun during the study period is presented
in Fig. 2. The Secchi disk reading showed significant seasonal
difference (p<0.05). Sites 4, 5 and 6 exhibited the lowest values (50 cm)
during summer. Electrical conductivity showed high significant differences among
seasons (p<0.01) and was positively correlated (n = 6, p<0.05) with many
variables like, TDS (r = 0.9), Cl- (r = 0.84), SO42–
(r = 0.60), Na+ (r = 0.62) and K+ (r = 0.82), which constitute
the major anions and cations in the water.
| Fig. 2: | Water level of Lake Qarun during the study period (Cited from Dr. Radwan Abd-Ellah (NIOF)) |
| Table 1: | Ranges, means and SD results of the physical and chemical variables in Lake Qarun water |
| Original | |
The TS and TDS values showed significant differences among seasons (p<0.05). They increased during summer, while spring sustained the lowest values at most sites. TDS maintained positive relationships (n = 6, p<0.05) with HCO3– (r = 0.76), Cl- (r = 0.63), SO42– (r = 0.53) and K+ (r = 0.81). The water showed moderately an alkaline character with pH values ranging from 8.1 to 8.73, it showed high significant difference (p<0.01) among different seasons. DO varied from ~5 mg L-1 to more than twofold with high significant differences within seasons. The dominant anions (Cl– and SO42–) and major cations (Na+, K+, Ca2+ and Mg2+) showed higher concentrations in summer. By evaluating the results obtained on a mass basis, it seems that the concentrations of major cations showed proportions of Na+ > Mg2+ > Ca2+ > K+ and major anions of Cl–> SO42–> HCO3–> CO32–. Inorganic nitrogen forms and ortho-Phosphate exhibited local variations with irregular seasonal trends. While the total-P values exhibited regional variations with significant seasonal trends (Table 1, Fig. 3a-f). Silicate showed a gradual decrease from winter up to autumn at different sites. Fe, Mn, Zn and Cu showed irregular distribution patterns, while Pb and Cd values were characterized by remarkable seasonal variations (p<0.01) and highly correlated with each other (r = 0.99, n = 24, p<0.05).
Long Term Changes in Water Quality of Lake from 1953 till 2006
Long-term studies in lakes have provided direct clues to the effect of increased major nutrients with the increase of water discharge from drains and their effect on abiotic and biotic characters. The mean concentration of the major nutrients (nitrite, ammonia, ortho and total phosphorus) had been gradually increased from 1953 till 2006 (Table 2), corresponding to the enhanced nutrient loading from agriculture and sewage drains.
| Fig. 3: | Multiple box and whisker plots of nutrient salts in lake water. The central box covers the middle 50% of the data values, between the lower and upper quartiles, while the central point represents the median (original). (a) Nitrate (μg L-1), (b) Nitrite (μg L-1), (c) ammonia (μg L-1), (d) orthophosphate (μg L-1), (e) total phosphate (mg L-1) and (f) silicate (mg L-1) |
| Table 2: | Physical and chemical Features of Lake Qaurn during different time periods |
*Not available, 1953-55 after Naguib (1958); 1995 after Anonymous (1997); 1999-2000 after Ali (2002) |
|
Salinity was reported to be 21.94 ‰ in 1953, showed an increase to 42.86 ‰ in 1999/2000, followed by a re-decreased to 35.31 ‰ in 2006 (Table 2). The concentrations of major cations followed salinity in their feature, where their changes depending on the rate of evaporation and the amount of freshwater discharged from drains.
| Table 3: | Ranges, means and SD results of the studied variables in Lake Qarun sediment |
Sediment Analysis
The ranges, means and SD of the studied variables in the collected sediment
samples are given in Table 3. The present results indicated
that there was no significant difference (p>0.05) between the levels of organic
matter and carbonate within sites. The OM exhibited positive correlations (n
= 24, p<0.05) with each of Mn (r = 0.72), Zn (r = 0.62), Cd (r = 0.75)
and Cu (r = 0.84). The dominant species of nitrogen in the lake sediment is
ammonia (Fig. 4a-c). Ammonia-nitrogen showed
insignificant spatial variation and high significant temporal variations (p<0.01).
Ammonia exhibited positive correlation (r = 0.81, n = 6, p<0.05) with mud
percent. Sodium showed higher levels than potassium and the two elements fulfilled
positive relationship (r = 0.76, n = 24 p<0.05). Calcium concentrations showed
wide range. The levels of barium decreased Westward far from drainage water
sources. By evaluating the results obtained on a mass basis, it seems that the
concentrations of studied elements in Lake Qarun sediment showed proportions
of Ca2+ > Na+ > Ba2+ > K+.
The collected lake sediments are mainly composed of very fine sand and mud along
with minor fraction of medium and coarse sand besides some mollusca shell fragments
(Table 4). As expected, trace metals concentrations in the
lake sediments displayed a wide range with insignificant variations within sites.
The highest levels of zinc were situated at site 3 (419 μg g-1)
and copper at sites 3 and 4 (195, 169 μg g-1). The highest concentration
of lead found with the current study was at site 5 (147 μg g-1),
whereas the lowest was at site 1 (8 μg g-1). The highest Cd
concentration (27 μg g-1) was found at site 3 close to effluent
discharges from El-Wadi Drain. Positive correlations (n = 24, p<0.05) between
concentrations of Zn/Cd, Cu/Zn and Cu/Cd (r = 0.81, 0.72 and 0.67, respectively)
were registered.
| Fig. 4: | Multiple box and whisker plots of exchangeable nutrient salts in lake sediment. Details as in Fig. 3 (original). (a) Exchangeable nitrite (μg g-1), (b) exchangeable nitrate (μg g-1) and (c) exchangeable ammonia (μg g-1) |
| Table 4: | Summary of sieve test results for sediment samples collected from the Lake Qarun during the study period |
| *Personal communication with Mr. Hassan Farahat (NIOF) | |
Physical and Chemical Characteristics of El-Wadi and El-Bats Drains Water
The results revealed that the effluent of El-Wadi Drain contained low total
solid values, compared with El-Bats Drain (Table 5). The
COD values of the two drains showed lower values than those recorded in Lake
Qarun, it showed high significant difference among drains (p<0.01), where,
El-Wadi Drain had lower value than El-Bats Drain (Table 5).
The drain's effluent are slightly enriched in Na+, K+,
Ca2+ and Mg2+, where the order of abundance on a mass
basis was Na+ > Ca2+ >Mg2+ > K+.
| Table 5: | The physical and chemical variables for water samples in the drain's effluents |
| Original | |
DISCUSSION
Lakes provide a historical record of the conditions of the environments that surrounds them (Nesbeda, 2004). The increase in DO concentration in winter and spring may be due to the fall in water temperature and phytoplankton blooming (Konsowa, 2007). The distribution of major anions and cations in lake water were governed mainly by the rate of evaporation, the intrusion of drainage water and consumption of lake salts by EMISAL Company. Anthropogenic sources of nutrients coupled with modifications to the environment and climate are now so pervasive that no aquatic system can be considered as truly pristine (Edwards and Withers, 2008). Natural water have small concentrations of nitrates and phosphorus. But these nutrients increase with runoff from agricultural lands (especially intensively cultivated lands with large inputs of synthetic fertilizers) and urban wastewater, creating eutrophication (Yang et al., 2003; Liu et al., 2009). The obtained results revealed that ammonia accounted for the major proportion of total soluble inorganic nitrogen. Nitrite showed low levels than the corresponding values of nitrate due to the fast conversion of NO2– to NO3– ions by nitrifying bacteria (Sabae and Ali, 2004). Water level showed positive correlation (n = 4, p<0.05) with nitrite (r = 0.98) and nitrate (r = 0.84) and a negative correlation with ammonia (r = -0.94). This explains the dependence of nutrient levels on the intrusion of drainage water. Phosphorus that enters the system through anthropogenic sources, such as fertilizer-runoff, potentially could be incorporated into either inorganic or organic fractions. Once phosphorus accumulates within a lake, it can cycle through the water column and promote algal blooms indefinitely (Christophoridis and Fytianos, 2006; Mainstone et al., 2008; Edwards and Withers, 2008). The Ortho-Phosphate at sites 4, 5 and 6 showed high significant seasonal variations (p<0.01), while sites 1, 2 and 3 showed irregular variation (p = 0.36). This reflecting the effect of drainage water, where agriculture is a major contributor of phosphorus to receiving waters (Dougherty et al., 2004). The gradual decrease in silicate from winter up to autumn can explain the abundance of diatoms (75% of total phytoplankton density) from July to the end of autumn and their sharp decline in February and during the spring (Konsowa, 2007). Regionally, silicate showed higher values in the Western side than the eastern and middle area (Fig. 3), this was concurrently with diatoms abundance (Konsowa, 2007). The interference between several factors such as surrounding environment, closed basin and climatic effects may be suggest the irregular distribution patterns of metals in Qarun Lake. The concentration of Fe in water was within the values previously reported by Mansour and Sidky (2003) (average: 460 μg L-1). However, Pb and Zn exhibited higher concentrations (average: 209.4 and 74.5 μg L-1) than previously reporteds (average: 20 μg L-1), reflecting a recent pollution events. Site 1 (infront of El-Batts Drain) showed the highest value of Fe concentration (1810 μg L-1), suggesting an anthropogenic source of iron input (e.g., fertilizers) (Ali, 2002). Also, the sharp increase in Cu concentration at site 3 in spring (193 μg L-1) is mainly due to agricultural sewage discharge from El-Wadi Drain, where copper can be derived from a number of sources including agricultural materials, atmospheric deposition and sewage sludge (Cousins et al., 2002). The trace metals concentrations exceed the marine water guidelines established by Environmental Protection Agency (1994) for Zn, Cu, Pb and Cd. However, many samples contained concentrations of Zn, Pb, Cu and Cd exceeding the chronic criteria (86, 8.5 2.9 and 9.3 μg L-1, respectively). Anthropogenic influences, rather than natural enrichment of the water by metals may be the main reasons (Wasim Aktar et al., 2008), where, Cd is present as an impurity in several products, including phosphate fertilizers and detergents (Greaney, 2005).
The sediments with high amounts of organic matter act as traps and reservoirs for metals of anthropogenic origin (Camusso et al., 2002) this achieved by the positive correlations recorded between OM and each of Mn, Zn, Cu and Cd. Sites 4, 5 and 6 showed high carbonate content, suggesting an enrichment of sediments by mollusca and partly by calcareous fragments (Goher, 2002; Flower et al., 2006).
Nutrient cycling throughout lakes is directly linked to processes operating within the lake and surrounding environs (Amirbahman et al., 2003). Excess nutrient supplies from atmospheric deposition, agricultural fertilizer runoff and other anthropogenic sources, can have adverse effects on aquatic ecosystems and also influence the N and P distributions and concentrations in overlying waters and sediments (Murray et al., 2005). The decrease in ammonia levels in sediment during winter and spring coincided with the increase of dissolved oxygen concentrations in the overlying water during the same seasons. The present study showed higher increase (about 413 times) of exchangeable ammonia levels than that recorded in lake water. Ammonia itself is a non-persistent and non-cumulative toxic substance, thus the high levels of ammonia released by the sediment do not cause a problem especially when the DO % is high (Johnston and Minnaard, 2003). The levels of exchangeable nitrite and nitrate in lake sediment increased Westward far from the discharging drainage sources (Fig. 4). The exchangeable NO3–-N concentrations are mostly higher than NO2–-N values suggesting the oxidized conditions of lake sediment and the two showed high increased in their levels compared with that recorded in lake water (about 243 and 88 times, respectively). These reflect the importance of internal nutrient loading when determining the trophic condition of the water body (Liikanen et al., 2002).
The insignificant spatial variations of trace metals in the lake sediments reflecting the differential behavior of trace metals rich agricultural and domestic effluents draining into lake ecosystem. While there are no guidelines recommended for Fe and Mn, the present results (average: 2671.4 and 775.7 μg g-1, respectively) are higher than (about 3 times) the levels detected by Mansour and Sidky (2003) (814.5, 288.0 μg g-1). This dramatic increase, which is too large to be solely caused by the weathering of sandstone, suwsggesting an anthropogenic source of metals input (e.g., fertilizers; pesticides) (Abdel-Satar et al., 2003). The increase of the studied metals especially at sites 1 and 3 may be related to the amount of sewage entering the lake through El-Bats and El-Wadi Drains.
Lake sediments provide an archive of environmental change both within the lake ecosystem and region and therefore, have been used across the world in order to study natural environmental change or human impacts (Yang et al., 2003; Sayed and Abdel-Satar, 2009). Present data support prior contamination of the sediments with metals, which were likely deposited during accidental releases from drain's sewage. Zn and Cd levels at the majority of sites were more than acute guidelines (112 and 4.2 μg g-1, respectively) cited by US Environmental Protection Agency (1997). This can attributed to anthropogenic influences, rather than natural enrichment of the sediment by metal (Vest et al., 2009). In addition, the levels of Cu and Pb in most samples were below the acute guidelines (108 and 112 μg g-1, respectively), but exceeded the chronic criteria (18.7 and 30.2 μg g-1, respectively), which have a small but negative effect on the surrounding.
The data from the drain's effluents compared with the in-lake data suggest a massive input of nutrients into the lake. The high nutrient salts concentrations in the two drains can be explained on the basis of the high amount of agricultural runoff and domestic sewage inflow from the adjacent cultivated land and neighboring villages to the drains (Sayed and Abdel-Satar, 2009). Except for COD, bicarbonate and ortho-P, the studied variables showed no significant differences (p<0.05) among the two drains. This indicated that the two drains receive the same inputs from agricultural and domestic wastes.
We can conclude that municipal and agricultural sewage input into Lake Qarun causes serious pollution of its water and bottom sediments mainly by increasing the amount of nutrient and trace metals (Cu, Zn, Pb and Cd). Sediment-associated trace metals also represent a potential hazard to the aquatic environment and may be released to the water column upon disturbance. If accidental releases from drain`s sewage continue, chronic accumulation of trace metals in the lake will persist, providing a continuing hazard to the lake water.