Ecological Studies on Lake Al-Asfar (Al-Hassa, Saudi Arabia) with Special References to the Sediment

MATERIALS AND METHODS

Site Description
Lake Al-Asfar is one of the important shallow wetland lakes. It is located on Al-Hassa, Eastern region of Saudi Arabia. Al-Hassa Province is one of the largest oases in the world and located (25° 05' and 25° 40') in the Southern part of the Eastern region of Saudi Arabia. The main salient morphologic features of Lake Al-Asfar are wetlands, sabkhas and sand dunes. There are salt tolerant vegetation (halophyte) found in some of the less salt affected sabkha areas.

Sampling and Analysis
Samples were collected from lake Al-Asfar from May, 2008 to April, 2009. Subsurface water samples (2 L) were taken from the lake on each visit. A liter was not filtered and is used for pH, conductivity, alkalinity and chlorophyll. Other liter one was filtered through a Whatman GF C^-1 filter apparatus equipped with suction pump for analysis. This sample was used for analysis of the major ions for which preservation is not essential. After tightly capping, samples were returned to laboratory and kept in the dark at 4°C until analysis.

Sediment Studies
The sediment samples were taken from the uppermost 1 cm sediment collected during the April, 2008 by a spade box core device (GKG). One sediment core was retrieved from the lake using a technique of Berglund and Ralska-Jasiewiczsowa (1986). The core was sectioned as 2 cm interval and each 2 cm section sample was placed in a Whirlpak bag for temporary storage in a cold at 4°C. Sub-sampling for fungal spore occurrence was taken place during initial core sectioning avoiding contamination.

After dissolution of sediment samples, the metal concentrations were measured by a Varian Atomic Absorption Spectrophotometer (AA-6800F, Shimadzu, Japan).

Sediment core was dissected and side surfaces placed under aseptic conditions in sterilized plastic bags. Fungal spores were isolated by the dilution plate method as described by Abdel-Hafez et al. (1990). Glucose-Czapek’s agar medium supplemented by chloromphinicol (0.5 mg L^-1) and rose bengal (30 μg L^-1) and incubated at 28°C for 7 days. Five replications were performed for each sample and the developing fungi were identified and counted and the numbers were calculated per gram dry soil. Pythium sp., which were expected to be in the sediment were isolated using VP3 (Ali-Shtayeh et al., 1986) selective medium: sucrose 20 g L^-1, corn meal agar 17 g L^-1, agar 23 g L^-1, CaCl₂ 0.01 g L^-1, MgSO₄.7H₂O 0.01 g L^-1, ZnCl₂ 0.001 g L^-1, micro-elements: CuSO₄.5H₂O 0.02 mg L^-1, MoO₃ 0.02 mg L^-1, MnCl₂ 0.02 mg L^-1, FeSO₄.7H₂O 0.02 mg l L^-1, antibiotics: pimarcin, 5 mg L^-1, vancomycin, 75 mg L^-1, penicillin, 50 mg L^-1, pentachloronitrobenzene, 130 mg L^-1 and thiamine-HCl 100 μg L^-1. Soil from the sediment soil was putted on VP3 media and fungi isolated identified using the Key of Pythium species (Plaates-Niterink and Van-der, 1981) and others (Abdelzaher, 1999). Hyphal tips of colonies appeared in VP3 medium were transferred to Water Agar (WA) 2.5-3% and incubated at 20°C to obtain a colony c. 1 cm diameter. The agar medium was inverted and incubated until the colony reached the edge of Petri dish. Slivers of agar containing single hyphal tips were removed from the margin of the colony and transferred to Corn Meal Agar (CMA) (Plaats-Niterink and Van-der, 1981) slants for storage. Hyphal tips were also transferred to CMA+500 μg mL^-1 wheat germ oil to stimulate the formation of sexual structures. Pieces from 7-day-old colonies incubated at 25°C were transferred to Nutrient Broth (NB) to confirm the absence of bacteria. The developing fungi were identified according to (Booth, 1977; Domsch and Gams, 1972; Domsch et al., 1980; Raper and Fennell, 1965; Samson et al., 2004).

Physico-Chemical Characteristics
Temperature and pH values of lake water were measured in the field by a digital pH-meter (Lutron, pH 204), respectively. The Secchi disc depth was measured also in the filed. Conductivity was measured using calibrated conductivity meter (CM 25 conductivity meter). Dissolved oxygen was measured according to Winkler method (Strickland and Parsons, 1972). The calculated values are the mean of triplicates; the standard deviation was less than 5% of these mean values. Chlorophyll-a content of water was determined according to the method described by Strickland and Parsons (1972).

Qualitative and Quantitative Analysis of Phytoplankton Composition
The technique developed by Uttermohl (1936) was adopted for quantitative investigation of the phytoplankton. One and half liter water sample was collected in a cylinder on each sampling occasion and treated with Lugols iodine solution (Iodine in potassium iodide). Each sample was then allowed to settle at least 36 h, where upon the supernatant was siphoned off and the volume was adjusted to 100 mL and kept at 4°C until analysis. Besides, Sedjwick-Rafter cell was repeatedly used for cell counting. The simplified methods described by Willen (1976) and Hobro and Willen (1977) were followed for counting phytoplankton. The average numbers of phytoplankton (unicellular, colonial and filamentous) were performed for every species. The results were then, expressed as number of cells per liter. Qualitative analysis was carried out using the preserved as well as fresh samples. These were examined microscopically for the identification of the present genera and species. Diatoms frustules with and without chloroplast was included. The algal taxa were identified according to standard references, including Smith (1950), Fott (1972), Bourrelly (1981) and Prescott (1987). The calculated values are the mean of triplicates; the standard deviation was less than 5% of these mean values.

RESULTS AND DISCUSSION

The biotic variables used to describe different freshwater areas are often related to environmental factors such as climate, chemistry and pollution. A consideration of these factors leads to a better understanding the biology of aquatic habitats. The present study was carried out in a shallow Lake Al-Asfar.

The results of heavy metals from Lake Al-Asfar are shown in Fig. 1. The data revealed that the maximum content of Zn (5.2 ppm) and Cu (2.5 ppm) were recorded at 5.0 and 25.0 cm depth, respectively. The highest value of Pb was 9.02 ppm at 1.0 cm depth. Establishment of metal levels in sediments could play an important role in detecting sources of pollution in aquatic systems (El-Sammak and El-Sabrouti, 1995; Peters et al., 2001; Fathi and Abdelzaher, 2003). Accordingly, the highest value of Pb in the sediment at 0.5 cm depth is a clear indicator of lake pollution in agreement with Fathi et al. (2001). Shakweer et al. (1993) reported that Cu and Zn concentration in the fish flesh were found to be lower than the levels allowable for the human consumption. However, values of Pb were higher than the tolerable concentration for man. This pollution could was thought to be associated with the input from different drains (Fathi and Abdelzaher, 2003).

Eight fungal species belonging to 4 genera were collected from the sediment soil of Lake Al-Asfar. Penicillium oxalicum Currie and Thom was the most common fungus recovered from all sections of the core up to the 10 cm deep section of the core (Table 1). Penicillium oxalicum could be tolerating anoxic condition. Pythium sp., was present in the most upper section of the sediment and disappeared thereafter.

Fig. 1:	Heavy metals stratigraphy from Lake Al-Asfar sediment

Table 1:	Fungi presented in Al-Asfar Lake sediment

Pythium catenulatum Matthews, P. flevoense Van der Plaats-Niterink, P. papillatum Matthews, Pythium group F and Pythium group P were found to be occurred only in the upper 2 cm of the sediment. This indicates that Pythium sp., could not to be tolerate the absence of oxygen. Trichoderma koningii Oudem and Trichoderma sp., were only found in the upper 4 cm of the sediment. In Japan, many isolates of Trichoderma sp. were isolated from the sediment of Sagami Bay of Off-Izu Islands (Imada et al., 2001; Fathi and Abdelzaher, 2003). This result was the harmony with the present study which indicated that Trichoderma sp., prefers that condition. Aspergillus niger Van Tieghem was detected up to 6 cm deep while Penicillium oxalicum was detected up to 10 cm depth and no fungi were found after that. Noteworthy that no active fungal spores were detected below 10 cm sediment depth (Table 1).

The average water temperature of Lake Al-Asfar was subjected to seasonal variations. The lowest values were recorded during winter (12.5°C), while the highest value was found at the summer (33.2°C).

Fig. 2:	Seasonal variations of (a) temperature, (b) pH, (c) total dissolved salts, (d) visibility, (e) oxygen content and (f) Chl-a content in Lake Al-Asfar during the investigation period. Vertical bars indicate SE, n = 3

The differences in temperature represent one of the main factors responsible for the differences in the phytoplankton quantity and quality (Fathi and Flower, 2005; Fathi et al. (2009)). Like all inland waters (Flower, 2001) the pH values of Lake Al-Asfar ranged between 7.65 and 8.86 at winter spring and spring, respectively. The lowest values of pH recorded in the Al-Asfar lake may be due to the great amount of agricultural water discharged into the lake (Fig. 2), as well as, to the decomposition of plankton and organic matter (Gharib and Soliman, 1998; Fathi et al., 2009). Figure 2 showed that the total dissolved salts in the Lake water was higher in summer (8.02 g L^¯1), whereas it dropped to a minimum level in winter (3.32 g L^-1). The lake water showed low transparency in summer (18 cm) and the highest in winter (25.0 cm) (Fig. 2a-f). Water transparency was greatly affected by phytoplankton and zooplankton blooms (Gharib and Soliman, 1998; Fathi and Flower, 2005) and disturbance (circulation) of the sediment by wind. Dissolved oxygen is an important variable for identification of different water masses (Fathi et al., 2001). Various aquatic animals including fishes require high levels of oxygen. Figure 2 showed that the maximum oxygen concentration (15.21 mg L^-1) was recorded in spring, while the minimum (5.29 mg L^-1) was recorded in the winter (Fig. 2). The relatively high concentrations of dissolved oxygen recorded in this study could be due to the increased photosynthetic activity of phytoplankton populations.

Table 2:	Relative occurrence of the phytoplankton on Lake Al-Asfar during the study period
(High = 4; Moderate = 3; Frequent = 2; Rare = 1)

In this respect, Talling (1976) stated that oxygen super saturation due to photosynthetic activity is often encountered in regions with abundant phytoplankton. On the other hand Chlorophyll-a content in spring exceeded that recorded in other samples (Fig. 2), which could be attributed to vigorous phytoplankton growth (Fathi and Kobbia, 2000; Fathi and Abdelzaher, 2003).

It is evident from the data in Table 2 and Fig. 3-5 that there are is a seasonal differences in quantitative and qualitative composition of the phytoplankton. According to phytoplankton abundance the data of Fig. 4 shows that the highest count was found to be in spring (21.30x10⁵ cell L^-1), followed by summer (18.40x10⁵ cell L^-1) and the lowest crop was harvested in autumn (9.40x10⁵ cell L^-1).

Fig. 3:	Percentage composition of the main algal groups recorded at Lake Al-Asfar during the investigation period

Fig. 4:	Phytoplankton abundance for Lake Al-Asfar during the investigation period. Vertical bars indicate SE, n = 3

It could be clearly seen that Chlorophyceae was the most dominant group, Bacillariophyceae ranked second, Cyanophyceae the third, Euglenophyceae the fourth and Dianophycae come the fifth group in the order of dominance during studied period (Fig. 3). Bacillariophyceae reached maximum in winter (38.32%) which was associated with increased numbers of Cyclotella meneginiana, while the minimum (21.21%) was recorded in summer.

Fig. 5:	Seasonal variations of the species richness (total number of phytoplankton taxa encounted per standard sample count) of Lake Al-Asfar phytoplankton, during the investigation period. Vertical bars indicate SE, n = 3

In contrast, the blue green algae reached its maximum level in the summer (34.22%), while the minimum (18.21%) was found to be in winter. Euglenophyceae was appeared in all seasons except winter. However, Dinophyceae was recorded in summer, autumn and winter (Fig. 3).

Total of forty three genera were mainly identified during the whole period of study (Table 2). Out of these, 15 genera belong to Chlorophyceae, 17 to Bacillariophyceae, 7 to Cyanophyceae, 3 to Euglenophyceae and 1 to Chrysophyceae. On the other hand, the maximum species richness (38 species) was found in the spring, while the minimum (15 species) was in the winter (Fig. 5). Generally, the phytoplankton showed a remarkable increase as compared with the previous records (Fathi et al. (2009)) and this indicated high level of eutrophication in Lake Sector. Furthermore, Fathi et al. (2009) reported that Lake Al-Asfar is indicates heavy polluted in autumn and winter and moderate pollution in spring and summer.

In conclusion, the investigated lake is contaminated with discharge waters containing chemical fertilizers in addition to domestic and industrial effluents. Pollution and climate greatly affected the hydrography and the physico-chemical properties of water as manifested by the high amounts of organic matter, high concentrations of nutrient salts which caused some increase in levels of eutrophication.

ACKNOWLEDGMENT

The author would like to acknowledge the assistance provided by different laboratories of the Biology Department, College of science, King Faisal University for both, allowing using some of their equipments and/or providing some basic materials for performing the experiments needed for the study.