Field and Laboratory Studies on Nile Phytoplankton in Egypt III. Some Physical and Chemical Characteristics of Aswan High Dam Lake (Lake Nasser)

I In t . Revue ges . Hydrobiol . 1 74 1 1989 1 3 I 329-348 I

AHMED M . AHMED. AHMED A . MOHAMMED. SPRINWEL I., and AHMED M . EL-OTIFY

Botany Department. Faculty of Science. Assiut University. Assiut. Egypt

Field and Laboratory Studies on Nile Phytoplankton in Egypt I11 . Some Physical and Chemical Characteristics of Aswan High Dam

Lake (Lake Nasser)

key words: Aswan High Dam Lake (AHDL). seasonal variations. vertical variations. stratification . temperature. oxygen concentration

Abstract

Seasonal. local and monthly vertical variations in physical and chemical characteristics of Aswan High Dam Lake (AHDL) were followed during the period from March 1982 to February 1984 . The results show that there were distinct seasonal thermal variations . Similarly. thermal stratification was evident from late spring through early autumn . Oxygen content appeared t o vary with the changes in pH value . Water transparency in the southern part was greatly reduced by the in- coming silt laden flood especially in summer months . consequently. nitrate-nitrogen and total residue increased considerably in this part during summer . The recorded minimum N-concentration ( 2 . 3 5 ~ 8 1-1) was certainly limiting the growth of phytoplankton . Suspended and organic matter exhibited somewhat irregular variations a t least during the period of this study .

Contents

1 . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 . Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 . Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.1.1. Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2. pH value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.3. Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.4. Transparency . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.5. Alkalinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.6. Total dissolvcd solids . . . . . . . . . . . . . . . . . . . . . . . . 3.1.7. Nitrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.8. Organic matter . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.9. Total residue . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.10. Total suspended matter . . . . . . . . . . . . . . . . . . . . . . . 3.2.1. Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2. pHvalues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3. Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.4. Transparency . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.5. Alkalinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.6. Total dissolved solids . . . . . . . . . . . . . . . . . . . . . . . . 3.2.7. Nitrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.8. Organic matter . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.9. Total residue . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.1. Seasonal and local fluctuations . . . . . . . . . . . . . . . . . . . . . . .

3.2. Monthly and vertical fluctuations . . . . . . . . . . . . . . . . . . . . . .

3.2.10. Total suspended matter . . . . . . . . . . . . . . . . . . . . . . . 2 2 Int . Revue ges . Hydrobiol . 74 (1989) 3

330 330 333 333 333 333 333 333 333 333 335 335 336 336 337 337 339 340 341 341 341 342 342 342 3 u

330 A. M. AHMED e t al.

4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346

I. Introduction

Almost 20 years have passed since the const,ruction of Aswan High Dain (AHD) and the creation of Aswan High Dain Lake (AHDL). Throughout this period, no systematic and intensive work has been conducted to follow the changes that might take place in the physical, chemical and hiological characteristics of the lake. However, sporadic work has been done concerning its physical and chemical Characteristics (ENTZ 1970; ENTZ & RAMZY 1971; NESSIM 1972; ENTZ and LATIF 1974; ELEWA 1976; LATIF 1977;

During the last ten years, AHDL was certainly subject to considerable c!hangea in water characteristics as a result of the remarkable reduction in the amount of water flowing into it. Accordingly, E ~ T Z (1980) mentioned that suspended material in lake water does not exceed a few rnilligrains per litre. This means that the main bulk of suspended clay is sediinent’ed in Lake Nubia (the southern part of AHDL). ELEWA (1976) found that the organic matter contents were higher in spring and summer than in autumn and winter. The same author reported that surface water contained more organic niat,ter than deep layem This increase in spring and summer seasons agrees well with the development of tJhe plankton community as the lake water temperature increases (LATIF 1974a). In addition, ENTZ and LATIF (1974) obtained results indicating a decline in nitra,te concentrations from south to north along Lake Nubia-Nasser. Due to these variations in niixogen contents, GOLTERMAN (1975) could not predict qualitative or quantitative effects of nitrate levels on the phytoplankton in the Nile system in Egypt.

From the preceding literature it is evident that iiiost of these studies were of a sporadic nature and some of ihem dealt with aspects other than biology. Thus, the aim of the present two works (part I11 and IV) was to provide a coiiipreherisive study dealing with seasonal, local and monthly vertical variations in the physical and chemical characteristics of the wa8ter and, consequently, qualitative and quantitative changes in the phytoplankton of AHDL. This study was performed seasonally froiti March 1982 to February 1984 at, seven (I-VII) successive sites spread aloiig the niaiii body of the lake and situated 10,45, 105, 143, 210, 245 and 300 kiloinet,ers respectively south of AHD. In addkion, niontjhly samples were collected vertically from various depths (0, 3, 5, 8, 10, 15 and 20 m) at site I (10 km south of AHI)) during the same period of study and subjected to the same analyses..

SAAD 1980).

i!. Materials and Methods

[Site d e s c r i p t i o n : Aswan High Dam Lake (previously referred to as Lake Nasser), with a length of about 300 km in south Elgypt, and Lake Nubia (180 km in north Sudan) form the huge reservoir created after the construction of Aswan High Dam (see Fig. 1). This rrwrvoir is one of the largest man-made lakes in Africa and is second in terms of area to Lake Volta in Ghana. It extends from Aswan High Dam (AHD) in Egypt to the Dal Catsrect in Sudan between 23’58’ and 2O027‘ north latitude and between 30°35’ and 33‘15’ east longitudc (ENTZ 1974).

The mean width of the lake a t a water level of 160 m is 8.9 km, and increases t o 18 km when the water level reaches 180 m. The mean depth of the lake a t a water level of 160 m is 20.6 m and 24.8 m at a level of 180 m (ENTZ 1973). The lake is long and narrow, and has many dendritic side areas known as “Khors”. The number of important Khors on the eastern shore is 158, but on the western shore i t is only 42. The following are some hydraulic data concerning the storage basin:

Studies on Nile Phytoplankton in Egypt TIT. 33 1

High Dam

l- a > (3 W

G C A L E

051ols?o25

Figure 1. Map showing sample collection sites in Aswan High Dam Lake.

Area of storage lake . . . . . . . . . . . . . . . . . . . . . . 5000 km2

Total capacity of the reservoir . . . . . . . . . . . . . . . . . 164000. 106 m3

Storage capacity for silt . . . . . . . . . . . . . . . . . . . . 30000. 106 m3 Quantity of water guaranteed by resen oir per year

Highest level of stored water . . . . . . . . . . . . . . . . . . 183 m

. . . . . . . . 84000. loG m3

Tho water level at AHDL still fluctuates from year to year. Data concerning the minimum and maximum water levels in the lake from 1964 to 1984 were obtained from the Aswan High Dam Authority and are given in Table 1. 30*


Table 1. Minimum and maximum water levels in AHDL from 1964 to 1984

Years Minimum Date Maximum Date (m.a.s.1) (m.a.s.1)

1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984

105.94 115.75 119.02 133.48 145.29 150.85 153.81 159.65 162.49 158.20 161.00 165.60 172.42 171.60 172.40 173.03 171.18 171.13 170.18 165.64 162.97

- 7.1964 23. 7.1965 29. 7.1966 26. 7.1967 21. 7. 1968 22. 7. 1969 20. 8.1970 25. 7. 1971 28. 7. 1972 27. 7. 1973 16. 7. 1974 30. 7. 1975 27. 7. 1976 30. 7. 1977 20. 8. 1978 1. 8. 1979

24. 7.1980 31. 7.1981 11. 8. 1982 8. 8. 1983

31.12.1984

126.80 132.86 141.32 151.08 156.55 161.29 164.88 167.64 165.30 166.12 170.64 176.71 177.55 177.20 177.47 175.95 176.22 175.96 172.63 169.86 164.65

31.12.1964 4.11.1965

31. 12. 1966 31.12.1967 15.11. 1968 23.10.1969 26.11.1970 16.12.1971 28.10. 1972 2. 11. 1973

10.11. 1974 10.12. 1975 22.10. 1976 27.11.1977 7. 11.1978 1.11.1979

31.10.1980 3. 11. 1981 8.11.1982

19.10. 1983 13. -21. 9.1984

* Ministry of Information, State Information Service, Egypt

P r o c e d u r e s : Sampling was carried out seasonally from March 1982 to February 1984 at seven successive sites (I-VII) along the main body of the lake, situated 10,45, 105, 143,210, 245 and 300 km south of AHD, respectively. I n addition monthly samples were collected from different depths (0,3,5,8,10,15 and 20 m) a t site I (10 km south of AHD) during the same period of study.

T e m p e r a t u r e : The water temperature was always measured in situ. pH v a l u e : The p H value was determined using a Thymol blue p H tester (Hach, model 17-j). O x y g e n : The dissolved oxygen content of the water was determined according to Winkler’s

method (1962). The percentage oxygen saturation was calculated using the table of TRUESDALE et al. (1955).

T r a n s p a r e n c y : Water transparency was measured with a Secchi disc. A l k a l i n i t y : Total alkalinity was determined as carbonates. Disso lved so l ids : A known volume of water sample was filtered and the filtrate was left

overnight a t 105 O C to evaporate. After weighing the dissolved solids content was calculated per litre.

N i t r a t e : The nitrate-nitrogen content was determined by the sodium salixylate method (Deutsche Einheitsverfahren zur Wasser-, Abwasser, und Schlammuntersuchung 1960).

O r g a n i c m a t t e r : The organic matter was determined according t o the method described by STOCKDALE and DEXTER (1938) and recommended by KLEIN (1973).

T o t a l r e s i d u e : A known volume of water sample was evaporated a t 105 O C . After weighing, the dry residue was calculated per litre.

T o t a l s u s p e n d e d m a t t e r : After shaking, a defined volume of water sample was filtered through a weighed glass fiber filtre. The filtre was dried over night a t 105 OC. The amount of suspended matter per litre was then calculated.

Studies on Nile Phytoplankton in Egypt 111. 333

3. Results

3.1. Seasonal and local fluctuations

3.1.1. Temperature

The seasonal variations in the mean temperature of water samples collected from different, sites along the main body of AHDL are shown in Table 2. The results show that water temperature fluctuated between a minimum of 17.7 "C in winter 198211983 and a rnaxirnum of 27.2 "C in summer 1982.

3.1.2. pH value

Generally, there were no considerable looal variations in pH value during the different seasons. The recorded pH values were always on the alkaline side (Table 2). The lowest pH value (7.8) was observed in autumn 1982 a t site I1 and the highest (8.9) in summer 1982 and 1983 a t site V.

3.1.3. Oxygen

The absolute values for dissolved oxygen in the water along the main body of AHDL are given in Figure 2. It can be clearly seen that there were irregular local variations in oxygen contents during a given season. However, wide seasonal differences were recorded. The minimum value was 4.27 mgl-1 (49.8 0,'") in autumn 1982 at site I and the maximum was 8.98 mg 1-1 (97.2 in winter 1982/83 a t site I. The results for site V I (245km south from AHD) gave a different picture: the highest values, 8.14 mgl-1 (103.8 O i 0 ) and 8.07 mgl-1 (101.9 O/o), were recorded in the summer of 1982 and 1983 respectively.

3.1.4. Transparency

From the results presented in Figure 3, it can be seen that the Secchi disc transparency ranged froin a minimum of 28 cm in summer 1983 a t site VII to a maximum of 380 cm in autumn 1982 at site I. A gradual increase from south to north along the main body of AHDL was observed in the summer and autumn seasons. The decrease in transparency in late summer could be due to the increased silt load carried by the water entering the lake. However, irregular local variations were also recorded in the winter and spring seasons. The marked increase in transparency in the north part of the lake might be due to the sedimentation of silt and other suspended matter.

3.1.5. Alkalinity

The total alkalinity showed mostly irregular local or seasonal variations during the period of this study and ranged between 68 mgl-1 in summer 1982 st site V and 120 nigl-1 in winter 1983/84 at site IV (Table 2).

3.1.6. Total dissolved solids

The total dissolved solids content ranged between 110 mgl-1 in spring 1982 at site 11 and 180 mgl-1 in the same season a t site I (Table 2). Only a slight increase in total

334 A. M. AHD.IED e t al.

Table 2. Physical arid chemical characteristics of water samples collected seasonally at different sites along the main body of AHDL from spring 1982 to winter 1983/1984

Sites 1982/1983 1983/1984 Spring Summer Autumn Winter Spring Summer Autumn Winter

Temp. 18.9 27.2 21.7 17.7 - 26.5 - 17.8 oc

pH value I - 8.4 8.0

I1 - 8.5 7.8 111 - 8.8 7.9 IV - 8.8 8.2 V - 8.9 8.0

VI - 8.8 7.9 VII - 8.8 7.9 Total alkalinity (mgl-1)

I 116 110 104 I1 116 108 106

I11 116 102 108 TV 106 104 102 V 100 068 104

VI 104 098 104 VII 100 108 098 Total dissolved solids (mgl-1)

I 180 165 164 I1 110 155 163

111 140 134 151 IV 120 150 151 V 150 141 162

VI 120 120 161 VII 120 120 132 Total suspended matter (mgl-1)

I 10 10 I1 70 10

I11 50 28 IV 50 21 V 25 11

V I 10 40 VII 10 60 Total residue (mgl-1)

I 190 175 I1 180 165

JJI 190 162 IV 170 171 V 175 152

VI 130 160 VI1 130 170 Organic matter (mgl-1)

I - 2.50 I1 - 2.33

I11 - 3.33 IV - 4.17 V - 3.33

VI - 3.33 VII - 3.33

68 60 13 71 78 80

132

232 223 164 222 240 241 264

1.67 4.17 2.50 2.50 1.77 3.33 4.17

8.4 8.3 8.5 8.0 8.2 8.5 8.0

106 108 110 108 108 106 100

174 173 172 172 172 171 172

49 69 73 71 83 69 78

223 242 245 243 255 240 250

5.80 3.19 3.19 5.88 2.24 0.25 1.37

8.3 8.4 8.45 8.5 8.9 8.8 8.0

110 108 106 106 106 116 110

141 151 140 150 850 150 152

71 71 72 83 73 92

128

212 222 212 233 223 242 280

2.50 3.33 2.50 3.33 3.33 1.67 2.50

8.1 8.4 8.4 8.5 8.5 8.5 8.4

112 112 112 120 110 108 098

150 162 152 150 150 134 130

72 78 71 83 83 79 82

222 240 223 233 233 213 212

1.67 5.00 3.33 5.83 2.50 2.50 3.33


9

9

8

7

6

8

7

6

5

m 7 E

- 7 -

6 - & 5 2 4

2 9

g 7

x

Z 8

6

8 7

6

5

9

8

7

6

Spring 1982

Summer 1982

i' Autumn 1982

Winter 1983 119% ? r II 111 N Y YI VII c

- - 300 km

Pigura 2. Seasonal local variations in dissolved oxygen concentration along the main body of AHDL from spring 1982 to winter 1983/1984.

dissolved solids was recorded in winter 1982/83, when there were no major differences between the different sites along the main body of AHDL.

3.1.7. Nitrate

The results illustrated in Figure 4 show pronounced local variations during the same season and seasonal variations a t the same site. The lowest value (8.2 pg N 1-1) was recorded in summer 1982 at site V and the highest (1058.8 pg N1-1) in summer 1983 at site VII.

3.1.8. Organic matter

Generally, i t can be seen that the values for organic matter fluctuated from a minimum of 0.25 mgl-1 in winter 1982/1983 a t site V I to a maximum of 5.88 mgl-1

336

a 0 0

2 + 300

A. M. AHMED et a].

' 1

Summer 1983 -

10

Spring 1982

200

100

t

*" % 2oo 100 t > c

Autumn 1982

2 100

: 0 0 V

200

100

0 0

300

2 00

loo 0 0 b I I1 III IY Y YI Y1I

300 km

Seasonal local variations in water transparency along the main body of AHDL from

o__- - -- . - L

Figure 3. apring 1982 to winter 1983/1984.

recorded in the same season a t site IV. However, local variations during the different smsons did not exhibit any regular trend (Table 2).

3.1.9. Total residue

The total residue (total dissolved solids +suspended matter) fluctuated between 130 mgl-1 in spring 1982 a t sites VI and VII and 280 mgl-1 in summer 1983 a t s i h VII (Table 2). In general, it can bs seen that there were no regular local or seasonal variations in total residue levels.

3.1.10. Total suspended matter

The total suspended matter fluctuated between a minimum of 10 mgl-i in spring 1982 at site I and summer 1982 a t Bite I and I1 and a maximum of 132 mgl-1 in autumn 1982 at site VII. In autumn 1982 and summer 1983, a gradual increase in totalsuspend- ed matter was recorded along the main body of AHDL from site I to site VII (Table 2).


12

200 ::: i Spring 1982

100

00

400

200

100 00

500 350

- 250

m 150 x z 50 ' 450 0"

350

- - I

Summer 1982 Summer 1982

1

300 k m -. ~

--- Figure 4. Seasonal local variations in nitrate-nitrogen concentration along the main body of

AHDL from spring 1982 to winter 1983/1984.

3.2. Monthly and vertical fluctuations

3.2.1. Temperature

Figure 5 shows the monthly temperature fluctuations a t site I of AHDL. The temperatures of water samples collected during spring and summer were rat her high. The highest (28.0 "C) was recorded in the surface-to-3 m layer in July 1982. During autumn and winter, the temperature decreased to a minimum of 15.5 "C in January 1983.

The onset of epilimnion* formation was not recorded a t the same time in the two years of study (March 1982 and June 1983). The epilimnion extended to a depth of more than 20 m in November 1982 and December 1983. It is worth pointin gout that the epilimnion was more stable in the summer and autumn of 1983 than in 1982 (Fig. 6).

* ELSTER and EINSELE'B (1937) definition of the epilimnion was used: The upper water layer is considered to be an epilimnion when it has a maximum temperature difference of 0.2" C from the water surface to the lower boundary of this layer.

338 A. M. AHNED et al.

1982 1983 1984

0

3

5

E - a

g 10 c +

0

15

20

Figure 5.

[I I I!

I I'l, I .

, 1 8 8 l8 . . 17

1.1 . Temperature distribution in AHDL at site I (10 km south of AHD) ("C).

"C r

30 -

18

14 -

-

- E 1

f 10 - n W 0

Ill IV v VI VII VllI IX x XI XI1 I I I 111 IV Y Vl VII Ylll IX x XI XII 1 I[

1982 1983 1984

Figure 6. A surface water temperature ("C) in AHDL at site I (10 km south of AHD); B formation of the epilimnion in AHDL at site I.

Studies on Nilc Phytoplankton in Egypt 111. 339

3.2.2. yH values

The depth-time diagram showing the monthly pH variations is given in Figure 7. I n general, the distributions of the pH values and oxygen concentrations are similar, as has been shown by tjhe isopleths.

1982 1983 1984

3 -

- 5 - - f + a 2 8

10

15

I L

20 L Figure 7.

0

3

5 - E - 2z + aJ n 8 n

10

15

2c

Vertical distributiop of p H in AHDL at site I (10 km south of AHD).

1982 1983 1984

111 1Y Y YI YII Ylll IX x XI XI1 I I1 111 IY Y YI YU YIII Ix x XI xt I I1 1

Figure 8. Vertical distribution of oxygen concentration (yo saturation) in AHDL a t site I (10 km south of AHD).

340 A. M. AHMED et nl.

Table 3. Monthly variations in physical and chemical characteristics of water samples collected and 20 ni) from March

1982 Depth Mar. Apr. May Jun. Jul. Aug. Scp. Oct. Nov. Dec. Jan.

Transparency (Secchi-disk 314 220 300 225 130 185 266 474 380 336 320 readings [em])

Om 3 m 5 m 8 m

10 m 15 m 20 m Om 3 m 6 m 8 m

10 m 15 m 20 m

Om 3 m 5 m 8 m

10 m 15 m 20 m

Om 3 m 5 m 8 m

10 m 15 m 20 m

116 100 116 102 120 108 120 - - - - - - - 10 45 25 80 70 50 40

190 205 180 190 180 170 180

114 114 108 108 102 116 124 104 110 112 106 112 138 104 - - - - - - - - - - - - - -

10 10 9 '10

12 10 12 20 11 15 13 10 11 10

165 165 155 155 154 155 154 160 152 160 153 160 151 155

110 110 116 114 116 104 116 110 118 112 114 118 116 108 112 110 108 114 118 110 112 112 112 110 104 116 112 114 114 108 112 108 100 112 118 114 118 112 110 112 106 118 120 118 116 106 110 114 118 118 120 122 116 106 110 114

2.50 3.33 2.50 2.50 1.67 1.67 2.50 1.67 3.33 4.17 3.33 3.33 2.50 3.33 2.50 4.17 3.33 3.33 1.67 1.67 3.33 4.17 1.67 4.17 1.67 1.67 1.67 6.67 1.67 4.17 3.33 3.33 2.50 2.50 2.50 2.50 0.83 4.17 2.50 0.83 3.33 2.50 2.50 2.50 0.83 3.33 0.83 3.33 0.83 2.50 2.50 2.50 2.50 2.50 1.67 1.67

10 12 20 11 11 68 10 10 11 10 11 11 11 81 10 11 30 12 17 11 13 80 12 14 11 12 11 11 11 79 21 10 30 31 16 11 24 30 11 14 29 11 20 10 20 81 7 10 29 28 17 10 13 49 14 11

175 163 172 162 162 232 140 151 161 174 172 162 162 2&2 153 152 171 162 181 165 154 242 152 154 171 164 172 153 162 221 1.52 151 181 162 180 165 174 212 151 154 180 161 190 150 170 202 150 1.50 193 182 170 150 163 210 154 151

During 1982 and 1983, bhe pH valoes in the epilimnion often fluctuated between 8 and 9. As a result of the higher algal production in the trophogenir layer during spring and summer, the pH value rose to 8.9, which was the highest value recorded (April 1982, from 0 to 3 m depth). The lowest pH values were recorded in November/ Deceinber 1982, December 1983 and ,January 1984.

3.2.3. Oxygen

The data for t,he vertical distribution of oxygen concentrations a t site I are given in Figure 8. It is worth pointing out rhat the oxygen concentrations exceeded the saturation level only in April and July 1982 and in May 1983. I n May 1983, the oxygen saturation was 100.4 "/,, a t 3 m depth. This was the annual rnaxinium recorded a t the time of Intensive phytoplankton development. Oxygen concentrations above saturation level are generally caused by the relatively high assimilation activity of the phytoplanktonic algae. Thorefore, the measured values give a clue as to the magnitude of the photosynthetic activity of the algae.

Stndics on Nile Phytoplankton in Egypt 111. 341

from AHDL at site I (10 kin south of AHD) a t various depths (0 m, 8 ni, 6 in, 8 in, 10 ni, 15 m 1982 to February 1984

__ ~ ~ _ _ _

1983 1984 Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Jan. Feb.

220 285 240 146 220 132 164 245 420 353 412 390 320

106 110 106 112 118 114 128

5.80 1.99 1.99 1.04 0.33 2.24 1.20

49 50 41 39 50 38 52

223 223 213 211 222 218 234

116 114 112 114 110 110 110 110 110 108 114 112 116 114 112 114 112 108 108 106 112 108 110 112 114 110 108 110 112 114 110 106 108 108 110 110 114 110 114 110 110 114 108 108 110 106 110 112 116 114 116 112 114 112 114 106 106 108 110 112 112 112 118 112 116 114 112 104 108 108 110 118 114 112 116 114 112 114 116 106 108 106 110 116

2.05 2.05 2.88 5.00 5.00 2.50 4.17 3.33 1.67 1.67 2.50 1.67 3.71 3.71 2.05 2.50 3.33 3.33 3.33 3.33 3.33 2.50 2.50 3.33

10.15 1.21 2.88 4.17 2.50 3.33 4.17 1.67 1.67 2.50 3.33 2.50 8.41 3.11 1.21 3.33 2.50 2.50 1.67 3.33 3.33 2.50 0.83 4.17 1.97 2.80 2.96 2.50 2.50 3.33 1.67 1.67 0.83 2.50 0.83 3.33 2.80 2.88 2.05 3.33 2.50 5.00 3.33 3.33 1.67 2.50 2.50 3.33 0.46 1.97 1.21 1.67 2.50 2.50 2.50 3.33 1.67 1.67 1.67 3.33

10 11 12 10 15 7

23

161 172 162 161 165 1 60 173

10 9 9

10 9

13 7

171 171 170 172 170 173 170

31 30 20 11 9

13 16

162 161 161 162 160 1 63 160

21 19 8 8

18 13 6

162 161 160 160 160 173 160

10 10 8 9 8

13 8

161 162 160 161 160 173 170

71 71 72 71 72 82 59

212 212 213 213 223 232 213

21 11 11 12 21 72 11 10 * 12 12 11 42 0 11 9 9 9 60

18 31 19 9 19 40 8 12 8 8 9 41

10 13 10 10 13 62 10 15 10 9 9 50

162 171 181 142 141 222 152 161 182 142 142 192 150 161 180 140 140 202 160 181 180 150 150 192 150 172 180 150 150 192 160 160 180 150 153 213 162 165 175 153 164 192

3.2.4. Transparency

The monthly Secchi-disc transparency a t site I ranged from a minimum of 130 cm in July 1982 and 1983 to a maxiinuni of 474 cm in October 1982 (Table 3).

3.2.5. Alkalinity

Table 3 shows the vertical variations in total alkalinity a t site I of AHDL. No major variations were observed from the surface to a depth of 20 ni during the whole period of study. Two minima of 100 mgl-1 were recorded in March (3 in deep) and June (10m deep) respectively in 1982. The highest value (138nigl-1) was recorded a t a depth of 20 m in April 1982.

3.2.6. Total dissolved solids

At the beginning of this study in March 1982, the concentrations of total dissolved solids at site I were particularly low a t depths greater than 5 m and were lowest

342 A. M. AHMXII et al.

1902 1903 190L

0

3

- 5 E I

c c a 2 10

15

20

IV Y YI Yli Ylll IX x XI XI1 I 11

Figurc 9. Vertical distribution of total dissolved solids concentrations in AHDL a t site I (10 km south of AHD).

(110 mgl-1) in the 8 t o 10 111 layer. A similarly low value (120 mgl-1) Isas also recorded a t the surface in .January 198-1. It should also be mentioned that a moderate rediiction in total dissolved solids level (130 nigl-1) wits recorded at a depth of 8 111 in the early winter of 1983/84. The highest value (182 mgl-1) was found at depths of 10 and 20 i n

in Noveinher 1982 arid February 1983 (Fig. 9).

3.2.5. Nit’rate

From Figure 10 i t can he seen that the lowest nitrogen concentrations were often recorded in early spring and late suinrner, the lowest value of 2.35 pgN1-1 being observed in September 1982 a t a dept,h of 8 meter. Otherwise, the nitrogen concentrations were higher, and the maximum level was recorded in June 1985, when the concentration n-as 301.2 pgN1-1 in the 15 to 20 in layer.

It, should he noted that, the N conceiitjrations a t depths down to 8 111 decreased markedly in August anti Septeinher 1982. This reduction in the trophogenic zone was attrihut,aMe mainly to higher ratos of phytoplankton growth (see part, 1 V : MOHAMMED et al. 1989).

3.2.8. Organic matter

The vertical distril)ution of organic matter at, site I of AHDL showed a marked increase in organic matter in the suinrner and early autumn of 1983. The highest value for organic matter was recorded at a depth of 5 m, where the concentration was 10.15 mgl-1 in March 1983. A lowest value, 0.33 mgl-1, was observed in February 1983 a t a depth of 10 ni (Table 3).

3.2.9. Total residue

Table 3 shows that the total residue in the surface-to-20 m layer increased considerably in certain months of the study (November 1982, Fehruary and August 1983, and

Studies on Nile Phytoplankton in Egypt 111.

1982 1983 1984

313

Figure 10. Vertical distribution of nitrate-nitrogen concentration in AHDL at site I (10 km south of AHD).

February 1984), but there were no obvious differences in the concentrations of the total residue a t different depths. However, a considerable decrease was recorded i n December 1983 and January 1984, especially in the 0-to-5 m layer. Gcnerally, total residue concentrations in spring 1982 and autumn 1983, were slightly higher a t the surface than a t other water depths. Otherwise, the higher values were found a t depths of 10 m or more during the whole period of study. A ininiiniim value of 1-10 mgl-1 was recorded in both December 1983 and January 1984 at a depth of 5 m, and a. maximum of 242 mgl-1 was found in Noveinher 1982 a.t depths of 3 and 5 In.

3.2.10. Total suspended matter,

The vertical distribution of total suspended matter was very similar to that of total residue : the highest total suspended matter values were recorded in almost thc same periods of study (March, Noveinher 1982, February and August 1983 and Febru- ary 1984 (Table 3). In addition, there were no regular monthly or vertical variations in total suspended matter levels during the whole period of study. I t can be clearly seen that they ranged between a minimum of 6 mgl-1 in June 1983 at a depth of 20 m and a maximuin of 82 mgl-1 in August 1983 a t a depth of 15 m.

4. Discussion

Aswan High Dam Lake (AHDL), which can he regarded as a newly created head- water of the Nile in Egypt, has not yet reached tJhe steady state, and its development in relation to the factors present in its surrounding areas should be a subject of continuous study.


Temperature, which represents onc of the main factors influencing the periodicity and distribution of phytoplankton in water masses (VIVES and BENITO 1958; EL- NAGGAR 1977; SAGE-WILLIAM et al. 1978; AIIMED et al. 1986:;'and MOHAMMED et al. 1986), was ineasurcd during this investigation. Water temperatures at the different sites along the main body of AHDL naturally exhibited seasonal variations. In addition, some vertical differences were recorded indicating that thermal stratification is present a t least for part of the year, but breaks down in winter. NESSIM (1972) and ELEWA (1976) correspondingly reported that thermal stratification in AHDL is absent in winter, the water being complctely mixed and the water column showing a very slight difference in temperature. SAAD (1980) studied the thermal stratification only in February 1970 and found that the difference between the minimum and the maximum temperabures was 0.6 "C.

The wat,er transparency of AHDL presents a complex picture as i t is affected by many factors, including the inflowing turbid water from the River Nile, the development of phytoplankton and vertical water movement (windaction). Watertransperency varied considerably during the present study, ranging from 28 cm in the southern part t o 474 crn in the northern part,, depending on season. This agrees well with the results obtained by ELEWA (1976), who found that water transparency in AHDL ranged from 25 cm to 370 cni, depending on seasons and region in 1974. According to ENTZ (1970), the transparency of AHDL varied between 20 and 350 cm, as compared with a range of 20 to 450 cm for Lake Volta. This wide range of variation is apparently not typical of the natural lakes, where the transparency may be even greater. In Lake Edku (Egypt) it ranged from 45 cm to 125 cm (SAWN 1974), while 550 cni have been reported for Lake Ontario (RYDER 1973). The decrease in transparency at the southern sites of AHDL in late summer (August 1983) and in aut,umn (November 1982) is due to the turbidity caused by the silt laden flood. This decrease in transparency was always associat,ed with the decIine of the phytoplankton population. ENTZ (1974) pointed out that a certain amount of silt reaches only the southern part of AHDL, and the flood water loaded with silt lowers the water transparency in the part affected. The changes in transparency in the northern part of AHDL may be due to changes in algal populations. This is also suggested by the findings of ALMAZAN and BOYED (1978)'; MISRA and YADAV (1978); SCHWARZKOPF and HERGENRADER (1978) ; ANTOINE and AL-SAADI (1982); SAAD and ANTOINE (1982), who studied various water areas.

The relatively alkaline pH values recorded in AHDL could be principally due to the increased photosynthetic activity (ALEEM and SAMAAN 1969 ; EL-WAKEEL and WAHBY 1970) and diversity (RAO 1955; PROWSE and TALLING 1958; PRESCOTT 19635 DURREL 1964; REYNOLDS and Z I L E N ~ ~ ~ ~ ~ ; KOMAFCENKO and VACILEVA 1975; ROLAND 1976; RAMADAN and SHEHATA 1976; EL-AYOUTY and IBRAIIIM 1980) of phyt'oplank- tonic algae. The alkaline water habitat was always found to be dominated by diatoms or blue-green algae, Similarly, the local variations in the pH value recorded in this investigation are in accordance with results reported for the Nile system in Egypt (SAAD 1980; AHMED etal. 1986; MOHAMMED etal. 1986) and AHDL (NESSIM 1972; ELEWA 1976).

The dissolved oxygen concentrations showed remarkable local variations in the different seasons. According t o some authors (SAAD 1978; SAAD and ANTOINE 1978; SAAD and ANTOINE 1982), these local variations can be attributed to the activity of biological processes that release or consume oxygen at different localities. As regards the vertical distribution, it was found that O2 st,ratification was quite distinct in summer. ELEWA (1976) stated that the cooling down in autumn was always accompanied by the destruction of oxygen stratification in AHDL. It seems worth pointing out that, during the present study, the relatively high concentrations of dissolved oxygen were mostly associated with increased phytoplankton populations. This means that


they may have been due to the photosynthetic activity of phytoplankton organisms. In this respect MANGY (1971), stated that the surface water obtains its oxygen supply mainly from the atmosphere and from the photosynthetic activity of green aquatic flora. Similarly, TALLING (1976) observed that oxygen supersaturation due to photosynthetic activity is often encountered in regions with abundant phytoplankton.

The relation between nitrate-nitrogen and total counts of phytoplakton (part IV: MOHAMMED et al. 1989) indicates the importance of these ions for phytoplankton growth. Generally, it was found that in AHDL the phytoplankton was relatively low, regardless of site or sampling depth, when nitrate-nitrogen was accumulating (not being actively consumed). The decrease in nitrate concentrations could be principally due to its utilization by phytoplankton (HUTCHINSON 1957) as well as its reduotion by denitrifying bacteria (MUNAWAR 1970; ELWAKEELand WAHBY 1970; SEENAYYA 1971), which consequently limit the growth of some algae that are unable to fix atmospheric nitrogen (TALLINO 1976). RZOSKA and TALLING (1966), working on the Blue Nile, found that nitrate-nitrogen concentrations fell below 20 pg1-i during the maximum growth of MeEosira. EGBORGE (1974), working on the river Oshun (Nigeria), found that nitrate acc:umular~ion occiirred aL Lhe heginning and end of phytoplankton growth. PROWSE and TALLTNG (1958) obtained similar results during their work on the White Nile. It must be pointed out that the rapid increase in the N03-N content of samples taken from site VII (about 300 km south of AHD) in summer 1983 was mainly due to the inflow of flood water loaded wich clay silt.

Finally, i t can be said that these changes in the physical and chemical characteristics usually allow some plankton organisms to bloom or flourish while others disappear or are a t least suppressed. The corresponding changes in the density and diversity of the phytoplankton in AHDL will be dealt with in part IV (MOHAMMED et al. 1989).

5r Summary

This paper represents an attempt to follow the variations in the physical and chemical characteristics of AHDL water after about two decades of impoundment. The studies were performed seasonally from spring 1982 to winter 1983184 by collect- ing surface water samples at) seven sites (El-Berba, Kalabsha, Allaqui, El-Madic, Amada, Tushka and Adendan) along the main body of AHDL some 10,45, 105, 143, 210, 245 and 300 km south of AHD, respectively. In addition, water samples were collected monthly (March 1982 to February 1984) from the surface and a t depths of 3, 5, 8, 10, 15 and 20 m at site I (El-Berba, 10 km south of AHD). The results can be summarized as follows:

Water temperature showed considerable seasonal variations and ranged from 17.7 "C in winter 1982/83 to 27.2 "C in summer 1982. The pH values lied in the vicinity of 8.0, Water transparency ranged from a minimum of 28 cm a t Adendan (site VII, 300 km south of AHD) in summer 1983 to a maximum of 380 cm a t El-Berba (site I) in autumn 1982. Dissolved oxygen, generally, ranged from 4.27 mgl-1 (49.8 O/,-,) in autumn 1982 to 8.98 mgl-1 (97.2 O/,,) in winter. The oxygen saturation reached its maximum value (103.8 O i O ) in summer. Total alkalinity ranged from 68 to 120 mgl-1. Total dissolved solids concentrations ranged from I10 to 180 mgl-1. Suspended matter, total residue and organic matter generally varied somewhat irregularly during the period of study. The nitrate-nitrogen content ranged from 8.24 pg1-1 (site V summer, 1982) to 1058.8 pgl-1 (site VII, summer 1983).

Both monthly and vertical variations in some physical and chemical characteristics were also followed. Water temperature rangod from a minimum of 15 "C (20 m deep) in March 1983 to a maximum of 28 "C (0 and 3 m deep) in July 1982. The pH values 23 Inti Revue ges. Hydrobiol. 74 (1989) 3

m PI tt around 8.0. Water transparency hhowed pronounc ctl inontlily var1:Lt ior is ant1 ranged froin R miniiiiuin of 1 3 0 cztii in July 1982 to a i i i a ~ ~ i n u i i i of 174 cm i n C)c tober 1982. l h ~ s o l v ~ r t oxygen levels ranged from 1 .3 rngl-1 (15.6 ",,) at :t clepth of 20 111

(July 1982) to 8.98 mgl-1 (97.8 ( I ,,) at the watctt hurface (Febiuaq 19S3). Total a l l d - 1111ty ranged from I00 nigl-1 (June 1982 at a depth of 1 0 i n ) to 158 ingl-1 ( . 4 p i l 1982 a t a depth of 20 in), the total dissolved solids concentration from 110 itigl-1 (Mwch 1982 at dryths of S and 10in) t o 182 nigl-1 (February 1983 at 20 111 r l c p t h ) . The NO?-N concwitrat ion showctl czorisiderable variationq i r i monthly ver t iL*al (list ri- bution. I t rmgetl froin 2.35 [pgl-j (Septemhcr 1982 at a depth of 8 m ) to 301.2 pg1-l (Junch 1983 at a depth of 15 and 20 m). Siiy)er~ded matter, total residue and organic' matter exhihitcd generally somewlint i r i egiilar Iariations.

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Prof. Dr. ED M. AHDfEn Botany Department Faculty of Science Assiut University Assiut, Egypt

Manuscript accepted: July 31st, 1988

Documents

Field and Laboratory Studies on Nile Phytoplankton in Egypt III. Some Physical and Chemical Characteristics of Aswan High Dam Lake (Lake Nasser)