Assessing water quality and classifying trophic status for scientifically based managing the water resources of the Lake Timsah, the lake with salinity stratification along the Suez Canal.

Lake Timsah is considered as the biggest water body at Ismailia City with a surface area of 14 km2. It is a saline shallow water basin lies approximately mid-way between the south city of Suez and the north city of Port Said at 30o35'46.55"N and 32o19'30.54″E. Because it receives water with high and low salinities, salinity stratification is producing in the Lake Timsah, with values of 14-40‰ for the surface water and over 40‰ for the bottom water. The temperature of the lake water decreased to below 19 °C in the winter and rose to above 29 °C in the summer; the concentration of dissolved oxygen ranged between 6.5 and 12.2 l-1 and the pH fluctuated between 7.9 in its lower value and 8.2 in its higher value. Water transparency was very low as indicated by Secchi disc readings recorded during this study and varied between 0.3 and 2.7 m. The main chemical nutrient (phosphorus) reached its highest levels of 96 µg l-1 in winter and their lowest values of 24 µg l-1 during summer. This nutrient concentration is high especially by comparing with those of unpolluted marine waters, but is typical of the more eutrophic coastal waters worldwide. The composition and abundance of phytoplankton with dominancy of diatoms and increased population density (20,986 cell l-1) reflect the eutrophic condition of the lake. The intensive growth of phytoplankton was enriched by high concentration of chlorophyll a with annual values ranged between 6.5 and 56 µg l-1. The objective of the present work was quantitative assessment of the quality of the water of the Lake Timsah using different approaches. During the present study, three different approaches were applied for the quantitative assessment of Lake Timsah water quality: the trophic state index (TST); trophic level index (TLI) and water quality index (WQI). Application of the trophic state and trophic level indices (TSI & TLI) revealed that the Lake Timsah has trophic indices of 60 and 5.2 for TSI and TLI, respectively. Both indices reflected the eutrophic condition of the lake waters and confirmed that the eutrophication is a major threat in the Lake Timsah. On the other hand, the WQI calculated for the Lake Timsah during the present study with an average of 49 demonstrated that the water of the Lake Timsah is bad and unsuitable for main and/or several uses. Moreover, WQI allows accounting for several water resource uses and can serve a more robust than TSI and/or TLI and can be used effectively as a comprehensive tool for water quality quantification. In conclusion, the three subjective indices used for the assessment process for the lake water are more suitable and effective for needs of the sustainable water resources protection and management of the Lake Timsah.

Introduction

Water is more critical than energy because we have alternative source of energy, but with n>an class="Chemical">water there is no other choice. Thus, it is necessary to find ecologically sound ways to conserve and protect valuable water resource of the lakes. Actually, the continuous monitoring and the assessment of lake’s water quality are a key issue for the sustainable protection and management. Lakes are often subjected to sudden environmental changes caused by various anthropogenic (industrial, agricultural, water supply, recreational, etc.) and touristic activities along their shores. This is the case in the Lake Timsah, which receives a tremendous amount of untreated waste discharges (domestic, industrial and agricultural), and exhibits rapidly developing touristic activities along its shores. Unfourtunately and for the previously mentioned reasons, the Lake Timsah is suggested to exhibit serious water quality problems.

Water quality (WQ) is a term used to describe the condition, as well as, the suitability of n>an class="Chemical">water for use, and is therefore likely to be subject for perceptions and biases of the observer (Parparov et al., 2006). In other words, the term quality is being subjective rather than absolute term and often reflects the assessment of the user himself for the different uses of the water. For simple explanation, the “oligotrophic lake” which can be considered to have good water quality for swimming on one hand is a lake with poor water quality for fishing on the other.

Different approaches were used for assessing the water quality of lakes worldwide: the n>an class="Chemical">water quality index (WQI) was developed by Horton (1965) in United States, and has been widely applied and accepted in European, African and Asian countries. In 1977 Carlson developed a numerical rather than nomenclature classification for the trophic status of the lakes (TSI). A modification for the trophic state index developed by Carlson into a trophic level index (TLI) has been established by Burns et al. (2005). Actually, the assessment of water quality of lakes is especially relevant when there is a need to balance ecological and socio-economic interests. Because water quality indices characterize and describe forcing factors, such as external nutrients load, consumption of water and climate change in relation to the aquatic ecosystem of the lakes they can be used as a key task for water resources management on scientific bases. (Directive, 2000, Parparov and Hambright, 2007).

Many researchers investigated the water quality of Lake Timsah (AWRC, 1994, SLTDS, 1994, En>an class="Chemical">TPS, 1996, Donia, 2005, Donia, 2011, Ahmad and Kaiser, 2014). All of these studies confirmed that the deterioration of the lake ecosystem & water lake quality has been extended to a serious level, and thus an urgent action is immediately required to restore the Lake Timsah ecosystem and its water resources. Therefore, the present work aims at assessing quantitatively the water quality of the lake through the biologically nomenclature phytoplankton index and through the numerically mathematical indices of Trophic State Index (TSI), Trophic Level Index (TLI), and Water Quality Index (WQI) and to evaluate the suitability of these indices for the needs of sustainable water resources management of the Lake Timsah.

Materials and methods

Description of the study Lake

Lake Timsah which has a surface area of 14 km2 can be considered as the biggest water body at Ismailia City, and is a n>an class="Chemical">saline shallow water basin with salinity stratification along the Suez Canal. It lies approximately mid-way between the south city of Suez and the north city of Port Said at 30o35′46.55“N and 32o19′30.54″E (Fig. 1). It has an irregular shoreline giving it approximately a triangular shape with elongated sides extending roughly 5 km from east to west, excluding peripheral lagoons; and 4.5 km from north to south with a maximum depth of more than 25 m in the vicinity of the navigational pass way of the Suez Canal. Most of the floor of the Lake Timsah is muddy; with an apparently anaerobic black mud in the deeper areas and aerobic grey mud in shallower areas (El-serehy and Sleigh, 1992). Its shores, shallow water and some dredged areas are more sandy but with few rocky outcrops. The Lake Timsah receives saltwater mainly from the Suez Canal; and freshwater from different sources (including: Ismailia canal; rare seasonal streams; and from sewage outlets) creating salinity stratification in the lake water. Chemical analysis and nutrient concentrations in the water of the Lake Timsah were given by many investigators (for example Fox, 1926, Morcos, 1967, Morcos, 1968, El-Serehy and Sleigh, 1992). The sea-grasses (Halophila stipulacea & Ceratophyllum demersum) and the green algae (Enteromorpha intestinalis & Ulva sp.), as well as, the red algae (Nitophyllum punctatum, Acanthophora delilei and Spyridia claoata) grow in the Lake Timsah and contribute with phytoplankton in the oxigination of its water (El-Serehy and Sleigh, 1992). Different limnological variables and characteristics of the Lake Timsah are presented in Table 1.

Fig. 1

A map of the Lake Timsah showing the location of the four sampling stations in the Lake Timsah. The inset shows the position of the Lake Timsah on the Suez Canal.

Table 1

Limnological variables for the Lake Timsah.

Parameters	Lake Timsah
Location	Ismailia City on the Suez Canal
Origin	Natural
Latitude	30o35′46.55′'N
Longitude	32o19′30.54′'E
Surface area (km2)	14
Water volume (m3)	80 × 106
Average depth (m)	2–28
Catchment area (km)	4.5

Lake monitoring

A total of 144 pan class="Chemical">water samples were collected from four stations selected in the Lake Timsah. The four sampling stations were chosen to repn>resent different ecological conditions prevailing in the lake. Each station was visited monthly, through complete year, from January to December 2016. The locations of the sampling stations are shown in Fig. 1, while coordinates and descriptive features of anthropn>ogenic activities of the four sampling stations are shown in Table 2.

Table 2

Locations and descriptive features of anthropogenic activities of the four sampling stations of the Lake Timsah.

Sampling sites	Coordinates of sampling sites	General features of anthropogenic activities
(Station I)	30°33′18″N-32°17′69″E	-Recreational beach along the lake shore-Sediments have grey colour
		-Sediment texture are dominated by median sand
		-Vegetation:
		Few seaweeds
		-Macrofaunal abundance:
		High abundance
(Station II)	30°34′45′'N-32°16′87″E	-Freshwater intrusion-Agricultural discharge
		-Wastewater discharge
		-The floor of the lake is covered with sand and rocks
		-Vegetation:
		Filamentous and thalloid algae
		Blue green algal mats
		-Macrofaunal abundance:
		High abundance of copepod and amphipod crustaceans
(Station III)	30° 35′ 46″N-32° 18′ 25″E	-Recreational beach along the lake shore-Industrial workshop for shipyards
		-Domestic outfall areas
		-Oil contamination-Concrete platform floor covered with mud
		-Vegetation:
		Filamentous and thalloid algae
		Blue green algal mats
		-Macrofaunal abundance:
		High abundance of polycheate, acidians and barnacles
(Station IV)	30°35′64″N-32°19′30″E	-Recreational beach along the Suez Canal shore-Sediment texture are dominated by median sand-Vegetation: Rich growth of brown, red and blue-green algae-Macrofaunal abundance: High abundance

The salinity and temperature of the near-surface water (50–75 cm) were recorded monthly using a portable electronic salinometer (MC Salinity/Temperature Bridge). The pH values were recorded using pH meter (model 201/digital pH meter). The transpn>arency of the Lake Timsah n>an class="Chemical">water was measured using Secchi disc (SD) with 30 cm in diameter and painted with two contrasting black and white colours.

In the field, the collected water samples were subdivided into glass and plastic bottles. The parts of n>an class="Chemical">water sample being stored in glass bottles usually contained 1 ml chloroform as preservative for analysis of N and P; while the water sample parts stored in plastic bottles were kept with few drops of hydrochloric acid as preservative for analysis of silicates (APHA, 2005). In the laboratory, colorimetric methods for nutrients analysis were used and the resulting colour intensity was being measured using a Pye SP 500 spectrophotometer (Parsons et al., 1984). For determination of chlorophyll a concentration, the acetone extraction method (Golterman, 1969) was applied.

Samples of phytoplankton were collected by horizontal hauls with a net of a mesh size of 33 µm, and fixed with acetic Lugol’s iodine solution with final concentration of 1% (Throndsen, 1978). Phytopn>lankton taxa were identified using an inverted microscopn>e (Nikon TMS, magnification: 200×, 400× and 600×). The most commonly used literatures were consulted to ascertain the taxonomy of the phytopn>lankton spn>ecies (Krammer and Lange-Bertalot, 1986, Krammer and Lange-Bertalot, 1988, Sournia, 1986, Popovski and Pfiester, 1990, Cox, 1996, Komarek and Anagnostidis, 1999, John et al., 2002). Taxa and author names were confirmed following standardized databases for phytoplankton taxonomy (Guiry and Guiry, 2013).

Assessment of Lake Timsah water quality

Trophic State Index (TSI) was calculated using a logarithmic transformation (Ln) of the chlorophyll a concentration (n>an class="Chemical">Chl. a) in microgram per liter, Secchi disc depth (SD) in meters and the total phosphorus (TP) in microgram per liter according the following equation (Carlson, 1977):where,

Burns et al. (2005) modified TSI developed by Carlson (1977) into TLI (trophic level index). Both indices (TSI & TLI) use values of chlorophyll a concentration (n>an class="Chemical">Chl), the depth of Secchi disc (SD) and the concentration of total phosphorus (TP), while the TLI index also includes total nitrogen (TN). The numerical values of the trophic level index (TLI) for the Lake Timsah water were calculated using the following equation (Burns et al., 2005):Where,

Vollenweider’s method for assessing a pan class="Chemical">water body’s tropn>hic state (1989), accepn>ted by the Organization for Economic Co-Operation and Developn>ment (OECD, 1982); Canada, 2004, MDDEn>an class="Chemical">P, 2007 was also applied to classify the trophic status of the lake.

To develop an overall status of the Lake Timsah water, the values recorded for the physico-chemical parameters of pH, dissolved n>an class="Chemical">oxygen, phosphate, silicate, nitrate, nitrite and ammonia, were mathematically transformed into a single number that represents the water quality level according to (Sánchez, et al., 2007). A range extended from 0 to 100 was assigned to give the quality value to each parameter. Each Q value was multiplied by a weighting factor based on the importance of the parameter, and summation of the weighted Q value yielded the water quality index (WQI) characterizing the water as very bad (0–25), bad (25–50), intermediate or medium (51–70), good (71–90), or excellent (91–100). The (WQI) was determined using the equation given by Pesce and Wunderlin (2000), as following:Where,

K is a subjective constant with a value of (0.25) for bad water; and a value of (1) for good quality n>an class="Chemical">water. C is the normalized value of the parameter while P is the relative weight assigned to each parameter (Smith, 1990).

Results

Physico-chemical conditions of the Lake Timsah

The minimum and maximum values of different physical and chemical parameters measured at the four sampling sites chosen at the Lake Timsah are shown in Table 3. The surface water temperature varied between 16 °C in winter months at station IV and 30 °C in summer months at station I. Salinity levels ranged between 17‰ (During Winter, at station II) and 40‰ (During Summer at station I) and with an average of 36‰. The dissolved n>an class="Chemical">oxygen values in the Lake Timsah water ranged between 6.5 mg l−1 during summer and 12.2 mg l−1 during winter for minimum and maximum values, respectively; while the nutrient concentration (P) remained extremely high, fluctuating between 24 and 96 µg l−1 at the four sampling stations with no apparent differences. The present study recorded slightly alkaline mean values for pH and with 7.8 for minimum and 8.4 for maximum values, respectively. The high concentration of chlorophyll a showed pronounced temporal and spatial variations with minimum values of 6.5 µg l−1 during summer at station IV, and maximum values of 56 µg l−1 during spring at station II. Total nitrogen concentration ranged between 430 and 780 µg l−1 for the minimum and the maximum values, respectively. The dissolved nitrate in the lake water fluctuated between 6.7 µM and 17.8 µM for its minimum and maximum values, respectively. During the present study, the reactive silicate showed its maximum concentration during summer and with being values of 4.1 µM. The maximum values of 1.2 µM were recorded for the dissolved ammonium during summer and the minimum values of 0.2 µM during autumn.

Table 3

Minimum (Min), Maximum (Max), average, and standard deviation (SD) of physico- chemical parameters measured during the present study and used to evaluate: trophic state index (TSI); trophic level index (TLI) and water quality index (WQI) of the Lake Timsah.

Parameter	Min	Max	Average	SD
Secchi disc transparency (m)a, b	0.5	2	1	±0.30
Temperature (°C)	16	30	22	±2.40
Salinity (‰)	17	40	36	±4.80
pHc	7.8	8.4	8.2	±0.01
Total Phosphorusa, b (µg l−1)	24	96	48	±7.00
Total Nitrogenb (µg l−1)	430	780	720	±76.8
Chlorophyll aa, b (µg l−1)	6.5	56	20	±5.70
TN/TP ratio	15.5	16.7	16	±4.30
Phosphatec (µM)	63.6	85.2	81.4	±6.20
Nitratec (µM)	6.7	17.8	9.75	±5.40
Silicatec (µM)	1.4	4.1	3.4	±0.70
Ammoniac (µM)	0.2	1.2	0.8	±0.10
Dissolved oxygenc (mg l−1)	6.5	12.2	9.4	±3.00
Nitritec (µM)	0.08	0.8	0.6	±0.03
TSI	50	70	60	±9.30
TLI	4.1	6.3	5.2	±0.87
WQI	27	67	49	±8.83

Measured parameters used for calculating TSI.

Measured parameters used for calculating TLI.

Measured parameters used for calculating WQI.

Minimum (Min), Maximum (Max), average, and standard deviation (pan class="Disease">SD) of physico- chemical parameters measured during the present study and used to evaluate: tropn>hic state index (TSI); tropn>hic level index (TLI) and n>an class="Chemical">water quality index (WQI) of the Lake Timsah.

Phytoplankton species composition and community structure of the Lake Timsah

The present study recorded and identified a total of 164 species of phytoplankton in the Lake Timsah belonging to 5 families: Bacillariophyceae (95 species); Dinophyceae (31 species); Chloropn>hyceae (11 spn>ecies); Cyanopn>hyceae (13 spn>ecies); Euglenopn>hyceae (14 spn>ecies) (Table 4) .The percentage contribution of 58, 18.9, 6.7, 8 and 8.5 % to the phytopn>lankton community was recorded for Bacillariopn>hyceae, Dinopn>hyceae, n>an class="Chemical">Chlorophyceae, Cyanophyceae and Euglenophyceae, respectively. Characteristic phytoplankton groups and algal indicator species for the trophic status classification of the Lake Timsah are shown in Table 5. The standing crop of species was generally high reaching a highest density of 20,986 cell l−1 at station II, and a visible decreasing in the algal density reaching 11,115 cell l−1 at station (IV). Overall, the Bacillariophyceae was the most abundant group of phytoplankton, followed by the Dinophyceae rank and the Euglenophyceae and the Cyanophyceae. While the Bacillariophyceae formed the largest group in almost every month, the Dinophyceae group represented a large part of the phytoplankton community during the study period, although the population varied during the sampling seasons. The members of the family Euglenophyceae were recorded largely around the year. On the other hand, members of Cyanophyceae were present in the samples received in some seasons and the numbers tend to remain high, a fact contrary to the other groups of phytoplankton. For example, presence of the members of blue-green algae was recorded in summer and autumn months only. Algal blooms were noticed frequently in summer and autumn during the sampling period.

Table 4

List of phytoplankton taxa and species collected from the coastal water of the Lake Timsah during the present study.

Bacillariophyceae	70. Plagiogramma vanheurchii Grun
1. Achnanthes brevipes Agardh	71. Pleurosigma angulatum (Quekett) Smith
2. Amphiprora alata Kützing	72. Rhabdonema adriaticum Kütz
3. A. paludosa Smith	73. Rhizosolenia alata Brightwell
4. Amphora marina Smith	74. R. alata f. gracillima (Cleve) Grunow
5. Asterionella japonica Cleve	75. R. alata f. indica Nothig
6. Bacillaria paradoxa (Müller) Grunow	76. R. calcar-avis Schultze
7. Bacteriastrum delicatulum Cleve	77. R. imbricata Brightwell
8. B. hyalinum Lauder	78. R. fragillissima Bergon
9. Bellerochea malleus Brigh	79. R. robusta Ralfs
10. Biddulphia aurita (Lyng.) Breb.	80. R. stolterfothii Peragallo
11. Biddulphia favus (Ehrenberg) Van Heurck	81. R. styliformis Brightwell
12. B. longicruris Greville	82. Schroederella delicatula (Peragallo) Pavillard
13. B. mobiliensis (Bailey) Grunow	83. Skeletonema costatum (Greville) Cleve
14. B. obtusa (Kützing) Ralfs	84. Stephanopyxis nipponica Gran & Yendo
15. B. smithii Van Heurch	85. Striatella unipunctata Lyngb
16. Campylodiscus noricus var. hibernicus (Ehrenberg) Grunow	86. Surirella capronii Breb
17. Cerataulina bergonii (Peragallo) Schütt	87. S. ovata Kützing
18. Chaetoceros affinis Lauder	88. S. robusta Ehrenberg
19. C. anastomosans Grunow	89. Synedra crystallina (Agardh) Kützing
20. C. compressus Lauder	90. S. ulna (Nitzsch) Ehrenberg
21. C. curvisetus Cleve	91. Synedra undulate Bail
22. C. decipiens Cleve	92. Thalassionema nitzschioides (Grunow) Mereschkowsky
23. C. densus Cleve	93. Thalassiosira ngustelineata (Schmidt) Fryxell & Hsle
24. C. lorenzianus Grunow	94. Thalassiothrix frauenfeldii (Grunow) Grunow
25. C. peruvianus Brightwell	95. T. longissima Cleve & Grunow
26. C. radicans Schütt	Dinophyceae
27. C. tetrastichon Cleve	1. Ceratium breve (Ostenfeld & Schmidt)
28. C. tortissimus Gran	2. C. egyptiacum Halim
29. Climacodium biconcavum Cleve	3. C. extensum (Gorret) Cleve
30. C. frauenfeldianum Grun	4. Ceratium falcatum (Kofoid) Jørgensen
31. Climacosphenia moniligera Ehrenberg	5. C. furca Claparède & Lachmann
32. Cocconeis placentula Ehrenberg	6. C. fusus (Ehrenberg) Dujardin
33. Coscinodiscus excentricus Ehrenberg	7. C. karasteni Pavillard
34. C. granii Gough	8. C. kofoid Jörgensen
35. C. marginatus Ehrenberg	9. C. longirostrum Gourret
36. C. radiatus Ehrenberg	10. C. macroceros var. gallicum Kofoid
37. Cyclotella meneghiniana Kützing	11. C. massiliense (Gourret) Jörgensen
38. Cymbella ventricosa Kützing	12. C. puchellum Schröder
39. Diploneis interrupta (Kützing) Cleve	13.C. symmetricum Pavillard
40. Fragilaria capucina Desmazières	14. C. trichoceros (Ehrenberg) Kofoid
41. Guinardia flaccida (Castracane) Peragallo	15. C. tripos (Muller) Nitzsch
42. Gyrosigma attenuatum (Kützing) Rabenhorst	16. Dinophysis caudate Savielle-Kent
43. G. balticum (Ehrenberg) Rabenhorst	17. D. fortii Pavillard
44. Hemiaulus heibergii Cleve	18. D. rotundata Claparède & Lachmann
45. Lauderia borealis Gran	19. Diplopsalis rotunda (Lebour) Wood
46. Leptocylindrus danicus Cleve	20. Exuviaella compressa Ostenfeld
47. Licmophora abbreviata Agardh	21. E. marina Cienkowski
48. L. flabellata (Greville) Agardh	22. Goniaulax minuta Kofoid & Mich
49. L. gracilis (Ehrenberg) Grunow	23. Noctiluca miliaris Suriray
50. Lithodesmium undulatum Ehrenberg	24. Oxytoxum scolopax Stein
51. Melosira granulata (Ehrenberg) Ralfs	25. Phalacroma rapa Jörgensen
52. M. sulcata (Ehrenberg) Kützing	26. Prorocentrum marinum (Cienkowski) Loeblich
53. M. varians Agardh	27. P. micans Ehrenberg
54. Navicula cancellata Donkin	28. Protoperidinium cerasus (Paulsen) Balech
55. Navicula cryptocephala Kützing	29. P. depressum (Bailey) Balech
56. N. cuspidate Kützing	30. P. divergens (Ehrenberg) Balech
57. N. dicephala Ehrenberg	31. Pyrophacus horologium Stein
58. N. gracilis Cleve	Chlorophyceae
59. N. placentula Ehrenberg	1. Actinastrum hantzschii Lagerheim
60. Nitzschia closterium (Ehrenberg) Smith	2. Chlamydomonas sp
61. N. kützingiana Hilse	3. Chlorella vulgaris Beijerinck
62. N. longissima (Brébisson) Ralfs	4. Closterium gracile Brébisson ex Ralfs
63. N. obtuse Smith	5. Pediastrum clathratum (Schröder) Lemmermann
64. N. pacifica Cupp	6. Scenedesmus bijuga (Turpin) Lagerheim
65. N. palea (Kütz) Smith	7. S. dimorphus (Turpin) Kützing
66. N. pungens var. atlantica Cleve	8. S. obliquus (Turpin) Kützing
67. N. seriata Cleve	9. S. quadricauda (Turpin) Brébisson
68. N. sicula (Castracane) Hustedt	10. Staurastrum gracile Ralfs ex Ralfs
69. N. sigma (Kützing) Smith	11.Stigoclonium sp.
Cyanophyceae	Euglenophyceae
1. Chroococcus turgidus (Kützing) Nägeli	1. Astasi klebsi Lemmermann
2. Gomphospheria aponina Kützing	2. Euglena acus Ehrenberg
3. Lyngbya major Meneghini ex Gomont	3. Euglena baltica Schüler
4. Merismopedia punctata Meyen	4. E. ehrenbergi Klebs
5. Oscillatoria constricta Szafer	5. E. klebsi Mainx
6. O. erythraea (Ehrenberg) Geitler	6. E. oxyuris Schmarda
7. O. limnetica Lemmermann	7. E. rubra Mainx
8. O. limosa (Roth) Agardh	8. E. sanguinae Ehrenberg
9. O. simplicissima Gomont	9. Phacus acuminate Stokes
10. O. tenuis Agardh ex Gomont	10. P. caudatus Hübner
11. Phormidium ambiguum Gomont	11. P. longicauda (Ehrenberg) Dujardin
12. Spirulina major Kützing & Gomont	12. P. pleuronectes Müller
13. S. platensis (Gomont) Geitler	13. Trachelomonas hispida (Perty) Stein
	14. T. volvocina Ehrenberg

Table 5

Characteristic phytoplankton groups and algal indicator species for the trophic status classification of the Lake Timsah.

Criteria	Lake Timsah
Population Density	Rich (20986 cell l−1)
Variety	Considerable number (164 species)
Distribution	To little depth (<3 m)
Algal blooms	Frequent
Diatom quotient (Centrales/Pennales)	1.2
Characteristic groups and algal indicator species	Bacillariophyceae
	Asterionella japonica Cleve
	Chaetoceros lorenzianus Grunow
	Nitzschi pungens var. atlantica Cleve
	Rhizosolenia alata Brightwell
	R. alata f. gracillima (Cleve) Grunow
	Schroederella delicatula (Peragallo) Pavillard
	Skeletonema costatum (Greville) Cleve
	Thalassionema nitzschioides (Grunow) Mereschkowsky
	Dinophyceae
	Ceratium egyptiacum Halim
	C. furca (Ehrenberg) Claparède & Lachmann
	Noctiluca miliaris Suriray
	Protoperidinium cerasus Paulsen
	Protoperidinium depressum (Bailey) Balech
	Cyanophyceae
	Lyngbya major Meneghini ex Gomont
	Oscillatoria constricta Szafer
	O. erythraea (Ehrenberg) Geitler
	Phormidium ambiguum Gomont
	Spirulina major Kützing & Gomont
	Euglenophyceae
	Euglena Baltica J. Schüler
	E. oxyuris Schmarda
	Phacus acuminate Stokes
	P. longicauda (Ehrenberg) Dujardin
	Trachelomonas hispida (Perty) Stein

List of phytoplankton taxa and species collected from the coastal pan class="Chemical">water of the Lake Timsah during the present study.

Lake Timsah water quality

The numerical trophic state index (TSI), trophic level index (TLI) and water quality index (WQI) for the Lake Timsah were given in Table 3. The average numerical values calculated for TSI, TLI in the n>an class="Chemical">water of the Lake Timsah with 60 and 5.2 for each assessment scale, respectively show clearly the eutrophic conditions of the lake water. The internationally accepted criteria of the OECD, 1982, Canada, 2004, MDDEP, 2007, Nürnberg, 2001, and University of Florida (1983) for the trophic status classification of lakes were applies for the current assessment and also confirmed the eutrophication conditions in the Lake Timsah water (Table 6). On the other hand, the numerical WQI in the water of the Lake Timsah with an average rank of 49 classify the Lake Timsah water with characteristics of bad water for use by humans. Descriptions corresponding to use with ranks and descriptors of water quality index (WQI), trophic level index (TLI) and trophic state index (TSI) applied for the Lake Timsah and its water during the present study are shown in Table 7.

Table 6

Internationally accepted criteria for trophic status classification of the water bodies with comparison applied to the Lake Timsah.

		Chlorophyll a	(µg l−1)	Transparencya	(m)
Trophic status	TP (µg l−1)	Mean	Maximum	Mean	Maximum
OECD criteriab
Ultra-oligotrophic	<4	<1	<2.5	>6	>12
Oligotrophic	<10	<2.5	<8	>3	>6
Mesotrophic	10–35	2.5–8	8–25	1.5–3	3–6
Eutrophic	35–100	8–25	25–75	0.7–1.5	1.5–3
Hypereutrophic	>100	>25	>75	<0.7	<1.5
Canadian criteriac
Ultra-oligotrophic	<4	<1	<2.5	>6	>12
Oligotrophic	4–10	<2.5	<8	>3	>6
Mesotrophic	10–20	2.5–8	8–25	1.5–3	3–6
Meso-eutrophic	20–35	–	–	–	–
Eutrophic	35–100	8–25	25–75	0.7–1.5	1.5–3
Hypereutrophic	>100	>25	>75	<0.7	<1.5
Quebec criteriad
Oligotrophic	4–10	1–3	–	5–12	–
Mesotrophic	10–30	3–8	–	2.5–5	–
Eutrophic	30–100	8–25	–	1–2.5	–
Hypereutrophic	–	–	–	–	–
Nürnberg criteriae
Oligotrophic	<10	<3.5	–	–	–
Mesotrophic	10–30	3.5–9	–	–	–
Eutrophic	31–100	9.1–25	–	–	–
Hypereutrophic	–	–	–	–	–
Swedish criteriaf
Oligotrophic	<15	<3	–	>3.96	–
Mesotrophic	15–25	3–7	–	2.43–3.96	–
Eutrophic	25–100	7–40	–	0.91–2.43	–
Hypereutrophic	>100	>40	–	<0.91	–
Lake Timsah resultsg
Ultra-oligotrophic	–	–	–	–	–
Oligotrophic	–	–	–	–	–
Mesotrophic	–	–	–	–	–
Eutrophic	24–96	20	56	1	2
Hypereutrophic	–	–	–	–	–

Transparency by Secchi disk depth.

Ryding and Rast (1994).

Environment Canada (2004).

MDDEP (2007).

Nürnberg (2001).

University of Florida (1983).

Present study.

Table 7

Descriptions corresponding to the use of water quality index (WQI) [modified from Smith, 1990], trophic level index (TLI) [modified from Burns et al., 2005] and trophic state index (TSI) [modified from Carlson, 1977] applied for the Lake Timsah.

Water quality	WQI		TLI			TSI
	Rank	Descriptor	Rank	Descriptor		Rank Descriptor
Excellent	91–100	Eminently usable for all purposes	2–3	Oligotrophic		<40 Oligotrophic
Good	71–90	Suitable for all uses	3–4	Mesotrophic		40–50 Mesotrophic
Intermediate	51–70	Main use and/or some uses may be jeopardized	4–5	Meso-eutrophic		50–60 Eutrophic
Bad	25–50	Unsuitable for main and/or several uses	5–6	Eutrophic		60–80 Eutrophic
Very Bad	0–25	Totally unsuitable for main and/or many uses	6–7	Hyper-eutrophic		>80 Eutrophic

Internationally accepted criteria for trophic status classification of the pan class="Chemical">water bodies with comparison apn>plied to the Lake Timsah.

Descriptions corresponding to the use of pan class="Chemical">water quality index (WQI) [modified from Smith, 1990], tropn>hic level index (TLI) [modified from Burns et al., 2005] and tropn>hic state index (TSI) [modified from Carlson, 1977] apn>plied for the Lake Timsah.

Discussion

The need for the present study aroused because of the significance of the fragile ecosystem of the lakes of the Suez Canal (Bitter Lakes & Lake Timsah) and the proposed development activities in the canal area (El-Serehy et al., 2014, El-Serehy et al., 2018). The lake Timsah is under an increasing human popn>ulation density pressure, and the increase in n>an class="Species">human population is associated with decreasing water resources and increasing organic pollution in the Lake Timsah water. The human population of the area increased to one million and five hundred populations by 2017 (Central Agency for Public Mobilization and Statistics, CAPMAS, 2017). The study of the flora and fauna of the Lake Timsah is very valuable to understand the composition of its biota for purposes of exploitation and conservation, and also because it is one of the lakes of the Suez Canal which is the main link between the Red Sea and the Mediterranean. Moreover, quantitative assessment of the water of the Lake Timsah using different approaches as an integral part of water resources management is very important to characterize the water quality problems in the biggest water body along the Suez Canal at Ismailia City for sustainable water resources management.

During the present study, a total of 164 phytoplankton species were identified, corresponding to diatoms, dinoflagellates, green microalgae, cyanobacteria and euglenoids. The phytopn>lankton community of the Lake Timsah was characterized by higher popn>ulation density with maximum values (20,986 cell l−1) during summer and lower density (11,115 cell l−1) during winter, and the dominancy of the diatom groupn>. n>an class="Chemical">Phytoplankton structure and abundance are result of spatial and temporal changes in physical, chemical and biological variables (Roy and Chattopadhyay, 2007, Pacheco et al., 2010, Zhang et al., 2011, Demir et al., 2014, Napiórkowska-Krzebietke and Hutorowicz, 2014). Among the algal communities, diatom taxa are considered as a group sensitive to water chemistry and specific ecological conditions, and thus are used as an indicator for water-quality in many aquatic systems (Stevenson and Smol, 2003, Zhang et al., 2011). The diatom species are also useful parameters to monitor changes temporally and spatially. Moreover, diatoms can be used as one of the tools for assessing water quality (Mariacristina and Antonio, 2006). During the present study, Diatoms formed the dominant component of phytoplankton in the Lake Timsah with population density of 17,838 cell l−1 and representing 85 % of the total phytoplankton counts. Owing to the relatively short life cycle, the diatoms respond rapidly to the physico-chemical changes and eutrophication thus indicating information on nutrient changes (Rahmati et al., 2011, Darling, 2015). They can indicate rapidly a change in water quality and can be used successfully in biomonitoring programs (Stevenson and Pan, 1999). Moreover, diatoms are strongly correlated to total phosphorus (TP) concentrations (Wang et al., 2014). In the Lake Timsah water with higher concentration of phosphorus (TP: 24–96 µg l−1), diatom species such as Asterionella japonica Cleve, Chaetoceros lorenzianus Grunow, Nitzschia. pungens var. atlantica Cleve, Rhizosolenia alata Brightwell, R. alata f. gracillima (Cleve) Grunow, Schroederella delicatula (Peragallo) Pavillard, Skeletonema costatum (Greville) Cleve, Thalassionema nitzschioides (Grunow) Mereschkowsky were the dominant diatom species. These dominant diatom species can be suggested as indicators to eutrophic status of the Lake Timsah ecosystem, a phenomenon used as potent indicator of trophic status in the water of many lakes (Demir et al., 2014). Morover, the utility of phytoplankton quotients with particular reference to diatom quotient, which can be derived from dividing the number of species of Centrales over that of Pennales can indicate the trophic status of the aquatic ecosystem, with being 0.0 to 0.2 for oligotrophy, and 0.2 to 3.0 for eutrophy (Nygaard, 1970). The data provided in Table 5, with diatom quotient of 1.2 can support the presence of eutrophic diatom algal indicators and confirm the eutrophy of the Lake Timsah.

On the other hand, the phytoplankton euglenoid forms, represented by fourteen species and constituting 8.5% of the total algal community, are rightly represented in this manner owing to the increasing of organic matters contamination in the Lake Timsah pan class="Chemical">water. The amount of the discharging effluents to the Lake Timsah as recorded by the International Center for environmental and developn>ment (ICDE, 1998) were 1.3 × 106 m3/day. Euglenoids are the more dominant protists in aquatic habitats usually rich in organic matter (Sleigh, 1989).

Pattern of the spn>atial and temporal distribution and taxonomic composition of phytopn>lankton in the study area was generally uniform, a phenomenon reflecting more homogenous hydrograpn>hic characteristics of the four sites. The amount of the standing cropn> of planktonic n>an class="Species">algae attained a higher population density of between 11,115 cell l−1 and 20,986 cell l−1 (Table 5), a fact attributed to the high nutrients availability (24–96 µg l−1), environmental factors and the ongoing eutrophication process caused by anthropogenic activities in the lake area (Table 2) . The phytoplankton community in the Lake Timsah, therefore, is characterized by high population density, higher number of algal species diversity (164 species), a combination that can be associated with high levels of nutrients, high values of chlorophyll a, high productivity, thus suggesting the eutrophication nature of the Lake Timsah.

Many efforts have been made to establish an accepted criteria and levels to classify lakes based on trophic status, nutrients, total phosphorus as well as on certain other physical (e.g., n>an class="Chemical">water transparency, oxygen dissolved in the water) and biological (e.g., algal pigments) characteristics (OECD, 1982, Vollenweider, 1989, Galvez-Cloutier and Sánchez, 2007, Zębek, 2009, Ferreira et al., 2011). A nutrient ratio (N/P) has been used to explain phytoplankton populations, or identify a nutrient limiting factor (Redfield, 1958, Hecky and Kilham, 1988). Redfield Ratio (Nitrogen to Phosphorus in molecular weights: 224/30 = 7.46) is considered as an established baseline for nutrient availability (Wetzel, 1983) and it has been suggested that Phosphorus becomes limiting nutrient in water bodies containing TN/TP value greater than 7, whereas a ratio below 7 is a reflection of nitrogen as limiting factor for algal growth (Meybeck et al., 1989, Chapman, 1996). For practical purposes, TN/TP value less than 10 indicates a nitrogen shortage, and value higher than 20 as phosphorus shortage. Lower TN/TP ratios are observed in eutrophic lakes and high in mesotrophic and oligotrophic lakes. The present study reports TN/TP ranging between 8.13 and 17.9, while the average ratio is 15, a fact indicating that in the Lake Timsah, nitrogen remains the limiting nutrient (Table 3).

The blooming of blue green algae (cyanobacteria) is frequently associated with eutropn>hic conditions; a situation had been encountered during the present study where n>an class="Disease">algal blooms were detected in the study area. The blue green algae dominate at low TN/TP ratios, and become rare when the TN/TP ratio is greater than 29 (Smith 1983). Based on the results of the present investigation, Lake Timsah can be considered as eutrophic and presented TN/TP as more lower than 29. Apart from the TN/TP ratios, the individual concentrations of TP and TN can also be correlated with the flourishing and dominancy of cyanobacteria in the aquatic ecosystem. The probability of cyanobacteria blooming is 40% for TP concentration of 30–70 μg l−1, but this probability rises to reach 80% when the TN concentration in the water is 100 μg l−1 (Downing et al., 2001). Thus, using of various protocols is largely determined by the scope of the work and the objectives of such analyses to interpret the summer algal blooming detected in the lake during the present work.

Scientific Studies have been carried out to establish a quality criteria and thresholds for classification of lakes according to their trophic status on the basis of nutrient concentrations, and certain physical and biological characteristics (OECD, 1982, Galvez-Cloutier and Sánchez, 2007, Hutorowicz et al., 2011, Hutorowicz and Pasztaleniec, 2014, n>an class="Chemical">Phillips et al., 2013). Moreover, estimation of trophic level using protocols largely based on the phytoplankton biomass and measurement of chemical constituents and/or combination of both seems effective, especially over the past decades these protocols were refined, standardized and modified. But the results are hard to compare especially when the information originates through the use of different methods and sampling gear (Kasprzak et al., 2008). In the present study, the applying of the internationally accepted criteria of OECD (1982), Environment Canada, 2004, MDDEP, 2007 for classifying the trophic status indicated that the eutrophic condition for the Lake Timsah. The classification –in respect to the trophic conditions reported through the present study is given in Table 6, these data indicate that the Lake Timsah can be considered as eutrophic. The microscopic evaluation of phytoplankton samples and calculation of algal biomass remain significant in studies focusing on biological parameters but are, however, labour-intensive as well as demanding taxonomic skills of the investigators. An alternate is chlorophyll a concentration, though with limitations, has gained interest of the researchers as a quick and easy-to-measure index of phytoplankton biomass.

The present study employs Carlson’s Trophic State Index (TSI) and Burns et al.’s Trophic Level Index (TLI) with the understanding that both indices are a well-tested robust quantitative method and repn>licable methodology considering biological and physical parameters and the findings are presented in Table 3. A TSI value between 40 and 50 is usually associated with mesotropn>hic (moderate productivity); values greater than 50 are associated with eutropn>hic (high productivity), and values less than 40 are associated with oligotropn>hic nature (lower productivity) of the n>an class="Chemical">water body (Murthy and Shivalingaiah, 2008). A TLI values between 3 and 4 is usually associated with mesotrophic (moderate productivity); values greater than 5 are associated with eutrophic (higher productivity), and values less than 4 are associated with oligotrophic nature (lower productivity) of the water body (Burns et al., 2005). If the TSI and TLI are calculated using Carlson’s method and Burns et al’s method, measuring Secchi disk depth, chlorophyll a and total phosphorous and nitrogen values, the present study reveals that the Lake Timsah of the Suez Canal has an average Index of 60 and 5.2 for the two trophic indices of TSI and TLI, respectively and confirming the eutrophication problem as a serious threat in the Lake Timsah. Water quality assessed with the TSI and TLI is more suitable for needs of natural water resources management if eutrophication is a major threat (Parparov et al., 2010).

Moreover, different physical and chemical factors can be used to assess water quality of the aquatic ecosystems (Sargaonkar and Deshpn>ande, 2003). The mathematical rating reflecting the composite effects of these factors on the overall n>an class="Chemical">water quality of the lake water can suggest the valuable approach for quantitative assessment in the form of WQI. During the present study, seven parameters vise: pH, dissolved oxygen, nitrate, nitrite, ammonia, phosphate and silicate were selected to calculate the WQI of the Lake Timsah. The results indicated that the water quality of the lake ranged between intermediate (67%) and bad (27%) waters with being average of 49% (Table 3) on one hand, and report the unsuitability of the Lake Timsah waters for main and/or several human uses on the other (Table 7). The water quality index (WQI) allows the reduction of big amounts of physical, chemical, and biological data to a single number in a simple reproducible manner. So, the WQI is suggested to be the most helpful tool to enable waterbody managers, policy makers, and even public to evaluate the water quality. Many researchers adopted the use of The WQI as one of the simplest effective methods used in assessing the overall water quality of the lakes worldwide (Hamilton and Parparov, 2010, Parparov et al., 2010, Tyagi et al., 2013).

Conclusions

Lake Timsah can be classified as eutrophic lake in respect to greater species diversity and higher population density of its phytoplankton community. The eutrophication status of the Lake Timsah water has been confirmed by other numerical indices rather than nomenclature phytopn>lankton index. Away from the eutropn>hication conditions, the Lake Timsah suffering from n>an class="Chemical">water quality problems due to different anthropogenic activities as it receives a tremendous amount of untreated domestic and industrial waste discharges and agricultural drainage. The water quality problems of the Lake Timsah are suggested to affect the health and the different components of the aquatic ecosystem, and also affect the people living around the lake, as well as, the health of the highly increased inhabitants in the area. During the present study, three different approaches were applied for the quantitative assessment of Lake Timsah water quality: the trophic state index (TST); trophic level index (TLI) and water quality index (WQI). Application of the trophic state and trophic level indices (TSI & TLI) revealed that Lake Timsah has indices of 60 and 5.2, respectively and confirm eutrophic status of the lake waters. Water quality assessed with both indices is more suitable for lake management needs if eutrophication is a major threat. The WQI calculated for the Lake Timsah with an average of 49 demonstrated that the water of the Lake Timsah is bad and unsuitable for main and/or several uses. In conclusion, WQI allows using of several parameters for measuring water quality and can serve a more robust than TSI and/or TLI and can be used effectively as a comprehensive tool for water quality quantification and thence, improve the efficiency of scientifically based management required for protection and sustainable development of the water resources of Lake Timsah.