Lake Qarun is considered to be the oldest natural lake in Egypt and is used as a natural reservoir of drainage water collected from irrigated cultivated lands in El-Fayoum (Fathi & Flower 2005). At present, Lake Qarun is a shrunken remnant of freshwater Lake Moeris (Ball 1939 cited in El-Shabrawy et al. 2015). Due to the impact of human activity, the lake water quality has been deteriorating as a result of increasing salinity (probably in connection with soil salinization) and eutrophication, caused by chemical fertilizer discharge. Water salinity, in particular, changed from slightly brackish to saline condition (35 PSU), with a seasonal fluctuation. The salinity can further increase with global warming (Abdel Wahed et al. 2014). Most freshwater fish originally occurred in the lake (Boraey 1980), but they gradually disappeared except for
The lake was considered an important environment supporting the main fishing grounds and had a rich biological diversity, including birds, plants and fish (Fouda 2012). Since the early 20th century, the lake has been highly modified and gradually become ecologically unstable. For example, the physicochemical parameters documented by Shaaban et al. (1985), Gad (1992), Sabae & Rabeh (2000), Mansour & Sidky (2003), Abdel-Satar et al. (2010) indicated such changes. In biological studies, Abd El-Monem (2001), Mansour & Sidky (2003) and El-Shabrawy et al. (2015) presented considerable changes in plankton communities, and Abdel-Malek & Ishak (1980) and Fishar (2000) reported similar findings for benthic fauna. El-Shabrawy & Taha (1999) reported on the positive effect of zooplankton grazing pressure on phytoplankton assemblages in Lake Qarun.
The autotrophic pathway, including mainly phytoplankton, may be considered one of the food pathways, especially for the aquaculture systems. Most tilapias can feed on phytoplankton or periphyton and their fish-grazing activity can successfully reduce algae (Dempster et al. 1993; Dýkel et al. 2005; Abwao et al. 2014). In natural water bodies, the phytoplankton was found as a food component, e.g. diatoms, chlorophytes, cyanobacteria and dinophytes were identified in Nile tilapia’s guts (Abd El-Karim et al. 2009). Fish may positively, directly or indirectly, affect the phytoplankton (Lacerot et al. 2013) or be closely correlated with chlorophyll
The aim of the present study was to describe the general features of the phytoplankton and fish communities in Lake Qarun and to assess the relationships between selected physicochemical and biological parameters and the variety of fish quality and quantity.
Lake Qarun is the major inland saline and turbid lake in the northern part of El-Fayoum Depression (central Egypt, ~80 km southwest of Cairo, at the margin of the Nile Valley, 29°30’N, 30°40’E). The length of this lake from east to west is about 40 km and the breadth at the widest point is about 6.7 km. The surface area of the lake is about 243 km2, the volume is 924 million m3 and it is located at 43 m below sea level (Anonymous 1995). The deepest point (8.3 m) is located in the northwest. The non-irrigated northern shores of the lake are virtually devoid of vegetation and mark the beginning of the Western Egyptian Desert. The lake has no connection with the sea, being located 320 km south of the Mediterranean coast of Egypt, and is directly supported by the Nile River via the Bahr Yussef canal. Since the early 18th century, the lake has received mainly agricultural wastewater (Anonymous 1995). An increase in the water level can be attributed to the leakage from adjacent groundwater aquifers and from the Wadi El-Rayan Depression (El-Sayed & Guindy 1999; Mansour & Sidky 2003). The total water draining annually into the lake is about 395 million cubic meters (data provided by the Irrigation Department, El-Fayoum). Previously, the lake supported a moderate level of fisheries and caused a decline in water quality (Meininger & Atta 1994).
Water samples were collected seasonally from the subsurface water layer using a 1.5 dm3 Ruttner sampler from ten sites in Lake Qarun in winter (February), spring (May), summer (August) and in autumn (September) 2012. The lake comprises three main subareas, where water-sampling sites 1, 2 and 3 represent the east, while 4, 5, 6 and 7 represent the middle and 8, 9 and 10 represent the west of the lake (Fig. 1). The fish catch in the lake was carried out at 11 landing sites (Senoris, Abu-Neema, Shakshouk, Abu-Soliman, Abu-Shanab, Kahk, El-Lokanda, El-Rawashdia, El-Saaida, Ayuob and Qarun, from east to west respectively), located in the southern part of the lake. The landing sites 1-3 belong to the east, sites 4-8 to the middle and 9-11 to the west subareas.
During sampling, pH was measured using an Orion Research Ion Analyzer (399A), electrical conductivity – using a conductivity meter (S.C.T.33 YSI), salinity – a portable Hydro Lab equipment, mod. Multi 340I/SET WTW, transparency – a black-white Secchi disk and water temperature – an ordinary thermometer. Water samples were analyzed according to the APHA (1996) procedures. Colorimetric techniques were used for the analysis of nutrients: formation of a reddish purple azo-dye for NO2, Cd reduction for NO3, the phenate method for NH4 and stannous chloride reduction for PO4. Total nitrogen and total phosphorus (after mineralization) were also analyzed colorimetrically.
A defined volume of water was filtered through a glass microfiber filter (GF/F) and the filter with residue was then foiled and refrigerated for pigment analyses. The chlorophyll
The phytoplankton samples were preserved with 4% neutral formalin and Lugol’s iodine solution (Margalef 1974) and then transferred into a glass cylinder. Phytoplankton cells settled for 5 days (APHA 1996). The phytoplankton samples were then siphoned and concentrated to a fixed volume and transferred to plastic vials for microscopic examination. The drop method was applied to count and identify the phytoplankton species. Triplicate samples (5 μl) were taken and examined under an inverted microscope at magnifications of 400× and 1000×. The identification of taxa followed e.g. Huber-Pestalozzi (1961, 1983), Komárek & Anagnostidis (1986, 1989, 1999), Krammer & Lange-Bertalot (1986, 1988, 1991a, 1991b), Anagnostidis & Komárek (1988), Popovský & Pfiester (1990).
Thirteen field trips were conducted in the three subareas in 2012, in December and February (referred to as winter) and in July and September (referred to as summer) and 78 fishermen were interviewed. The fishing season in the lake lasted throughout the year except for 3 months (January, May and June) as a fishery management plan. The fish catch and species composition in each subarea were investigated. Fish from different types of fishing gears and methods were collected and identified to the species level according to Whitehead et al. (1986) and FishBase (2012).
Non-parametric methods (due to lack of normally--distributed data) were applied to test the significant changes of environmental variables in Lake Qarun using the Kruskal-Wallis test. The relationships between physicochemical and biological variables in Lake Qarun were confirmed by calculating the Spearman’s rank correlation coefficient with STATISTICA version 10. The percent similarity of phytoplankton taxa was determined based on a cluster analysis (Multi-Variate Statistical Package, Kov. Comp. Serv. 1985-2009). As predicted, the relationships were statistically significant at the significance level of 0.05.
The trophic state of Lake Qarun was determined based on the Trophic Level Index (TLI) (Burns et al. 2005), which includes four partial modules based on the Secchi disk depth (SDD) and the concentrations of chlorophyll
Lake Qarun is a saline inland lake characterized by a significantly differentiated salinity (K-W test, p=0.001) across the lake, which varied between 11.1 PSU and 37.8 PSU during the study period of 2012, with some increasing tendency from the east to west subareas. The electrical conductivity (EC, 16.5-49.1 mS cm-1) and the mineral forms of N and P were statistically significantly differentiated between the sampling sites (Fig. 2). Similar findings with a high EC and large spatial variability in nitrite, nitrate and ammonium concentrations were recorded in August 2011 (El-Shabrawy et al. 2015). The lowest values of EC were related to the highest total nitrogen (max 6.45 mg dm-3), mineral nitrogen (the sum of nitrite, nitrate and ammonium; max 2.34 mg dm-3) and total phosphorus (max 0.63 mg dm-3) concentrations and the lowest salinity at sites 1 and 7, i.e. the east and middle subareas, respectively. The separation of nutrient-rich sites 1 and 7 from the others is connected with the agricultural water discharge from the drainage systems of El-Bats and El-Wadi mentioned by El-Shabrawy et al. (2015). Regarding such a division of areas, the Secchi disk depth (0.3-1.5 m) significantly increased (K-W test, p=0.010), whereas the chlorophyll
The trophic-level based (TLI – Trophic Level Index) assessment of Lake Qarun in 2012 compared to partly available data on SDD, TP and TN from 1995 to 2006 Based on data cited in El-Shabrawy & Dumont (2009), Satar et al. (2010) and El-Shabrawy et al. (2015)
Subareas | Sites The codes of sites’ names are given in Fig. 1, TLI – the trophic level index based on Secchi disc depth – TLISDD, chlorophyll |
TLISDD | TLIChl | TLITP | TLITN | TLI | Trophic state |
---|---|---|---|---|---|---|---|
East | 1 | 6.03 | 5.87 | 8.17 | 8.08 | 7.04 | HYP |
2 | 5.61 | 6.28 | 6.93 | 7.02 | 6.46 | HYP | |
3 | 5.32 | 6.06 | 7.06 | 7.02 | 6.36 | HYP | |
Middle | 4 | 5.22 | 5.95 | 6.86 | 6.49 | 6.13 | HYP |
5 | 5.21 | 5.81 | 6.67 | 7.05 | 6.19 | HYP | |
6 | 4.85 | 4.92 | 6.92 | 7.15 | 5.96 | EUT | |
7 | 5.72 | 5.05 | 7.71 | 7.00 | 6.37 | HYP | |
West | 8 | 4.89 | 4.74 | 7.10 | 7.15 | 5.97 | EUT |
9 | 5.13 | 4.40 | 7.28 | 7.26 | 6.02 | HYP | |
10 | 4.91 | 4.85 | 7.02 | 7.31 | 6.02 | HYP | |
1995 | average for the whole lake | 5.69 | - | 6.29 | 8.05 | 6.68 Average of available partial TLI |
HYP |
1999-2000 | 5.59 | - | 6.82 | - | 6.21 Average of available partial TLI |
HYP | |
2003 | 5.68 | - | 7.71 | - | 6.70 Average of available partial TLI |
HYP | |
2006 | 5.57 | - | 8.30 | - | 6.94 Average of available partial TLI |
HYP | |
2012 Average per lake based on the current data |
5.23 | 5.56 | 7.25 | 7.17 | 6.30 | HYP |
In total, 134 species were recorded in Lake Qarun, including 60 species of Bacillariophyceae, 35 species of Chlorophyceae, 13 species of Cyanophyceae, and less than 10 species each of Dinophyceae, Chrysophyceae, Cryptophyceae and Euglenophyceae. Previous studies suggested that the species richness was much lower, e.g. in 2001 only 49 phytoplankton taxa were recorded (Fathi & Flower 2005).
The phytoplankton density in Lake Qarun ranged from 75 to 140 × 104 cells dm-3 in the spring (Fig. 3A). A similar density was noted in autumn. The most abundant phytoplankton was observed in summer and winter – its density reached 935 × 104 cells dm-3 and 815 × 104 cells dm-3, respectively. The annual phytoplankton growth in Lake Qarun indicated the enhanced density in its east subarea and a decreasing tendency toward the west subarea with the minimum at site 8. The spatial variation of the phytoplankton density could refer to local trophic conditions, especially inflows of contaminants (Abdel-Satar et al. 2010). Such findings are reported for large lakes situated within urban or agricultural catchments (e.g. Dembowska et al. 2015). Comparing the annual variation in phytoplankton taxonomic composition at the class level, Bacillariophyceae and Dinophyceae co-dominated in phytoplankton assemblages (Fig. 3B), with a similar decreasing tendency toward the west as it was observed in the total density. The highest contribution of Dinophyte was recorded at the first site, and diatoms dominated in assemblages at the other sites in the Bacilariophyceae:Dinophyceae ratio of up to 3:1 (site 9). Furthermore, such a large difference between sites 1-5 and 6-10 was confirmed by the cluster analysis based on the percentage similarity in the taxonomic structure (Fig. 4).
The seasonal variation of phytoplankton structure indicated that diatoms predominated in spring and winter, whereas dinophytes predominated in summer assemblages (Fig. 5). In autumn, both groups co-dominated. The contribution of other groups was much smaller, with a distinct and seasonally similar presence of Chlorophyceae and Cyanophyceae. Bacillariophyceae were dominated by
Dominant species in phytoplankton assemblages in Lake Qarun in 2012
Species the currently accepted taxonomical names of species according to Guiry & Guiry (2016) |
Sampling sites the codes of 10 sampling sites were given in Fig. 1, |
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The main fishing gear used in the lake were trammel nets, beach seines, handlines and traps. There were four types of trammel nets which differed in their design, characters, dimensions and mesh sizes according to their target species. The first trammel net (Ghazl Bolti) targeted mainly tilapias, particularly
The total catch of fish and seafood was estimated using the yearbook statistics of GAFRD (2013). A significant increase in the Lake Qarun catch was recorded from 2003 to 2012 (excluding 2006) (Fig. 6). By analogy, an increasing trend of the total national production was also recorded in Egypt (Samy-Kamal 2015). According to El-Serafy et al. (2014), the fish production level in Lake Qarun is rather low compared to other Egyptian lakes. During the 2012 fishing season, the total catch in Lake Qarun was estimated at 4410 tons according to GAFRD (2013). In winter, the catch was 1731 tons (ca. 39.35%), and 2679 tons (ca. 60.7%) in summer. The catch in the lake was composed mainly of tilapias (dominant
The fish and seafood catches in Lake Qarun according to subareas are presented in Table 3. The production of the east subarea was about 27.2% (1199 tons) of the annual lake catch (11.3% in winter and 15.9% in summer). The middle subarea produced about 35.7% (1573.7 tons), most of which (26.0%) was caught in winter and the rest in summer. The catch of the west subarea accounted for about 37.1% (1637.3 tons) of the lake catch (about 30.0% in summer and about 7.1% in winter).
Seasonal variation in fish and seafood catches in subareas of Lake Qarun in 2012
Subarea | East | Middle | West | Total | |||
---|---|---|---|---|---|---|---|
Season | winter | summer | winter | summer | winter | summer | |
Catch, ton | 500.0 | 699.0 | 1146.7 | 427.0 | 314.7 | 1322.6 | 4410.0 |
Catch, % | 11.34 | 15.85 | 26.00 | 9.68 | 7.14 | 29.99 | 100.0 |
Subarea, % | 27.19 | 35.68 | 37.13 |
The fish species structure was differentiated in subsequent subareas. In the east subarea,
The highest phytoplankton density and chlorophyll
The correlations between the physicochemical and biological variables in Lake Qarun were tested with Spearman’s rank correlation coefficient and are presented in Table 4. The large catch of
Statistical relationships (R-Spearman correlation coefficient) between physicochemical and biological variables in Lake Qarun
Variables | Total catch | Others | ||||
---|---|---|---|---|---|---|
Total catch | - | 0.829 | n.s. | n.s. | n.s. | n.s. |
0.829 | - | n.s. | n.s. | n.s. | n.s. | |
n.s. | n.s. | - | n.s. | n.s. | n.s. | |
n.s. | n.s. | n.s. | - | n.s. | n.s. | |
n.s. | n.s. | n.s. | n.s. | - | n.s. | |
Other fish species | n.s. | n.s. | n.s. | n.s. | n.s. | - |
Phytoplankton density | n.s. | n.s. | n.s. | -0.943 | n.s. | n.s. |
Bacillariophyceae | n.s. | n.s. | n.s. | n.s. | n.s. | n.s. |
Dinophyceae | n.s. | n.s. | 0.943 | -0.829 | n.s. | n.s. |
Chlorophyll |
n.s. | n.s. | n.s. | -0.943 | n.s. | n.s. |
Total nitrogen | n.s. | n.s. | n.s. | n.s. | n.s. | n.s. |
Total phosphorus | n.s. | n.s. | 0.943 | n.s. | n.s. | n.s. |
Secchi disk depth | n.s. | n.s. | n.s. | n.s. | n.s. | n.s. |
Trophic Level Index | n.s. | n.s. | 0.943 | n.s. | n.s. | n.s. |
Ammonium | n.s. | n.s. | 0.829 | n.s. | n.s. | n.s. |
Nitrite | n.s. | n.s. | n.s. | -0.829 | n.s. | n.s. |
Nitrate | n.s. | n.s. | n.s. | -0.812 | n.s. | n.s. |
Orthophosphate | n.s. | n.s. | n.s. | n.s. | n.s. | -0.943 |
Temperature | n.s. | n.s. | n.s. | n.s. | n.s. | n.s. |
Salinity | n.s. | n.s. | n.s. | 0.829 | n.s. | n.s. |
pH | n.s. | n.s. | 0.829 | n.s. | n.s. | n.s. |
Electrical conductivity | n.s. | n.s. | n.s. | 0.829 | n.s. | n.s. |
*statistically significant correlation, p<0.05, n = 40, n.s. – not significant
In Lake Qarun, four major groups: mullets, soles, tilapias and shrimps (with different diet preferences and direct/indirect pressure on phytoplankton) have been recorded in the total catch for many years. Mullets can be detritivorous (Porter et al. 1996), benthivorous (Cardona & Castelló 1989) and planktivorous (Cardona et al. 1996; Torras et al. 2000; El-Shabrawy & Khalifa 2007). Abdel-Malek (1980) found that the lake mullet (
Variables Total catch
Strong or slight physicochemistry-phytoplankton--fish correlations were previously mentioned e.g. by Reid et al. (2000) or James et al. (2003) in seawaters and by Hansen & Carey (2015) in temperate waters, where fishery (through top-down control) can be an important contributor to environmental changes. However, some reckless actions (e.g. overstocking or excessive feeding of fish in aquaculture systems) can lead to enhanced water degradation (Legaspi et al. 2015). In Lake Qarun, the complexity of biological and chemical interactions (e.g. food availability, competition, predation) and the additional input of pollutants (e.g. heavy metals, pesticides) affect the abundance and structure of aquatic organisms (e.g. Abou El-Geit et al. 2013; El-Shabrawy et al. 2015). The earliest response to the variability of this lake ecosystem is shown by phytoplankton, especially its spatial heterogeneity.
More than 130 species belonging to Bacillariophyceae, Chlorophyceae, Chrysophyceae, Cryptophyceae, Cyanophyceae, Dinophyceae and Euglenophyceae were recorded in phytoplankton assemblages of Lake Qarun. The highest annual phytoplankton density was recorded in the east subarea, and its decreasing tendency was recorded along the sampling sites, i.e. toward the west subarea. Bacillariophyceae and Dinophyceae co-dominated the phytoplankton, with a similar decreasing tendency in their density toward the west. The concentration of chlorophyll
The results of this study suggest that short-term relationships between the water quality indices and the fish structure in Lake Qarun were reflected and, to a large extent, determined by some significant correlations, e.g. between the dominant species: