Limnology Of The Lake Dept. Conf.

Some Limnological Aspects for the Regulating Lake Of Mosul Dam / Iraq *Basheer Ali Basheer Al-Ni’ma

** Fathi Abdullah Al-Mandeel

*Department of Biology, College of Sciences, University of Mosul e-mail ([email protected]) ** Environmental & Pollution Control Research Center, Mosul University e- mail ([email protected]) ABSTRACT The Regulating Lake of Mosul Dam has a length of (8 km). It is located in the northern part of Iraq about (70 km) north of Mosul city center. This lake was the focus for the present limnological study. Three locations were choosing for water sampling, at the beginning, middle and end of the lake. From each location, five monthly samples were collected at different depths (surface water; 1 meter; 2 meters; 5 meters and near bottom). The sampling period extended for one year, from August 2004 to July 2005. Water samples were analyzed for measuring the following physical properties (water temperature; turbidity and electrical conductivity) and chemical properties (pH; dissolved oxygen concentration; relative saturation with oxygen and chlorophyll a content) in addition to the biological property, the total number of phytoplankton. The results were reviewed and the monthly, Longitudinal and vertical variations within the five different depths were explained. Also, the relationships between the parameters with the total number of phytoplankton were discussed. The results revealed that the monthly variations in water temperature were clear and the values restricted between (10.0-23.8 Cº); Turbidity were less than (3.5 NTU) throughout the year except October and were not correlated with both precipitation and total number of phytoplankton; Electrical conductivity was more than 350 and less than 450 µs/cm and having direct relation with water temperature; The range of pH values was narrow and restricted between (8.2-7.5);The oxygen levels correlated inversely with water temperature and electrical conductivity and the concentrations never fail below (5.4 mg/l) and the total numbers of phytoplankton ranged between (55452 t0 7238320 cells/l), their monthly variations witnessed the occurrence of two peaks. Only water temperature showed variations along the lake’s stretch while the rest parameters showed no variations both along the lake and with the different depths since well mixing process took place continuously in addition to short retention time of the water. Kew words: Regulating lake of Mosul Dam , Iraq , Physical & chemical properties

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Introduction Artificial lakes or reservoirs were established on the river courses for different uses, as flood protection, electrical power generation, fishing, recreational etc. However, the developed lakes will alter the ecological characteristics of the rivers and disturb their ecological balances. Mosul dam lake is one of these lakes which had been formed in (1985) after the construction of Mosul dam on Tigris river, about (70) kilometers north of Mosul city center in Iraq. The general characteristics and ecological balance of this prehistoric river, which have been established for a very long time, started a series of changes during the last decades of the twentieth century due to the construction of dams in Turkey and Iraq. Pre and post period of Mosul dam construction, numerous studies have been conducted on Tigris River, within or near the city. Most of these published works were mentioned in the bibliography of the Tigris River related studies by (Al-Ni’ma 1996) .On Mosul Dam Lake, also, there are numerous published works, but most of them were not in the field of Ecology as Hydrology, Geology, and Engineering etc. As for Ecology there were very few studies. The most extensive one was conducted by AlTayar (1988) who considered the effect of water impoundment on water quality and its effect on water purification plants. He found that water quality of the lake and the river becomes worse despite the short age of the lake. And he classified the lake as mesotrophic and monomictic with a mixing period extended four months (from December 1987 to March 1988). Concerning the aquatic organisms, Al-Tayar (op. cit.) included fecal coli form bacteria and algae in his study. The result revealed that the lake has a positive effect on bacterial count due to low turbidity values and high organic matter concentration. The result revealed, also, that the algal numbers were high but the species number was low. The other contributions on aquatic organism were only two works, the first one carried out by (Rahimo & Ami, 1988) on the zooplankton of the lake. They found that the maximum density of the planktonic Crustacean was in June and the minimum one was in December. The second work by AL-Qado (1989) considered the Chironomus and it’s used as a biological indicator for water quality. In her study Al-Qado found that the genus Stictochironomus was the dominant species in the main lake, it was present on most days of the year and in the different depths. Lakes pollution attracted some researchers as Al-layla et al. (1989) whom tried to find the pollution indicators after (5) years of Mosul dam’s construction. Moreover Al-Rawi, et al. (1994), studied water quality of Dohuk valley, and its potential effect on water of the lake. The present study is a little contribution in this respect and aims to: 1- Determination of the main physical and chemical properties of the regulating lake of Mosul dam and considering their variations along the lake and within different depths. 2- Determination of quantity and quality of the phytoplankton and consider the relationship between phytoplankton and ecological parameters.

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Materials and Methods: A-The studied location, general view: Construction works for Mosul Dam (previously known as, Saddam Dam) have been started in (1980) on Tigris River, about (70) km North of Mosul city center (figure 1). The formed lake had been filled, for the first time, in (1985). Mosul Dam project constitutes of two dams, main& regulating dams. They confined two lakes, Main and Regulating Lakes respectively. B- Sampling locations: Along stretch of the regulating lake three locations were chosen, at the beginning, middle and end of the lake (figure 1). Sampling process extended for twelve months, from August (2004) through July (2005).Water samples were collected monthly, using water sampler model Watnabe Keiki,from five depths of each location. The depths were surface water; 1 meter; 2 meters; 5 meters and near the bottom. C- Methods of analysis: The following, physical chemical and biological properties were measured using methods described in (APHA 1975). Analyses were carried out in the same day of sampling. 1-Physical properties: -Water temperature: by mercury thermometer -Turbidity: by turbidity-meter model 2100 A -Electrical conductivity: by Portable conductivity-meter model MC-1, Mark V 2-Chemical properties: -pH: by portable pH-meter model HI 8424 -Dissolved oxygen: by Azide modification of Winkler method. 3-Biological properties: - Chlorophyll a: by Trichromatic method. -Total number of Phytoplankton: following procedure mentioned in (McNabb 1961) and modified by (Hinton and Maulood 1979 ).

Results and Discussion: For the ecological parameters within the studied lake, it is important to mention two main points. First, water in the regulating lake comes from the hypolimnion layer of the main lake (at 30 meters deep).Second, the retention time is short ranging between (24-48) hours (Al-Tayar 1988). Accordingly, longitudinal and vertical variations for all studied parameters were not found in the regulating lake. Temperature: monthly variations for water temperature were evident in the three locations and all depth (table, 1) (Figure, 2). In October (2004) water temperature reached maximum values, above (23 Cº), throughout the year. In the following months temperature decreased gradually reaching minimum values (10 Cº) in January. After that, temperature started to increase until July at the end of the study. The unique feature for this pattern of monthly variation is the rapid decrease in water temperature within one month. From October to November water temperature decreased by (7 Cº).The reason behind this rapid decrease was the dropping of air temperature. The

3

diurnal variations were (17-34 Cº) and (2-13 Cº) in the sampling day of October and November respectively. Thermal stratification was not established in the three locations due to continuous mixing and short retention time. Also, Al-Tayar (1988) did not notice thermal stratification in the same lake. Values of water temperature ranged between (10-25 Cº) which is lower than (9-39 Cº) recorded by Al’Kam et al. (2002) in Sawa Lake due to differences between the geographical locations of the two lakes.

2005

2004

(Table,1) Some chemicophysical and biological properties, for water in the regulating lake of Mosul dam. Each value represents the mean of three locations, each one with five depths

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

Water Temp. Cº

Turb. NTU

E.C µs/cm

19.00 23.01 23.43 16.10 13.03 10.03 10.97 12.60 13.97 14.70 16.33 17.20

5.0 2.1 0.9 1.4 1.3 0.9 0.7 0.7 0.5 1.0 1.7 0.4

405.2 388.4 399.8 369.0 318.7 337.9 363.1 382.4 370.5 388.7 407.6 433.9

pH

D.O mg/l

Rel. Sat. (%)

Chl. a µg/l

Total No. Of Phyto. Cell/l

7.64 7.68 7.75 7.81 7.87 8.11 8.22 8.05 8.05 7.74 7.82 7.69

* * 5.8 7.5 8.0 9.2 10.4 9.5 8.2 8.2 6.1 6.4

* * 69.3 79.2 79.1 86.7 100.6 92.4 83.4 84.8 64.9 69.9

* * 0.35 2.64 2.05 1.48 2.67 1.65 1.92 1.26 1.26 1.58

* 1`27560.0 786609.0 3935194.0 675710.4 437680.7 148627.6 79731.31 199104.6 1792262 1428922 310482.2

Turbidity: Water turbidity in the regulating lake revealed two main characters. First, turbidity was generally low. The values were below (3.5) NTU throughout the year except in August. Second, the monthly variations were not clear and showed no direct relation with the precipitation and snow melt (Table 1) & (Figure 3).These two characters are consequences of water impoundment in the main lake where suspended matters of Tigris River are settled. Al-Ni’ma (1982), before the dam construction, mentioned that the maximum turbidity values in Tigris river at T3 location (which is submerged by water lake later on) reached (125) NTU while the absolute maximum value, in the present study, was only (6.5) NTU. Turbidity values ranged between (6.0 - 0.3) NTU which were considered low comparing to (4 – 12) and (7.7 – 26.0) NTU recorded by Al-Tayar (1988) and Al-Qado (1989) in the main lake respectively. This significant difference is due to wide variations between the amounts of rains that had been fallen. In (1988) it was (576.1) mm and (280) mm in (2005). The study revealed no relationship between turbidity and total number of phytoplankton, which means that the main reason for the regulating lake turbidity was

4

the silt particles. Similar condition is prevalent in all Iraqi surface water. Al-Hamed (1966) concluded that the turbidity of Tigris and Euphrates Rivers is formed mainly from silt particles since the two rivers are considered poor in phytoplankton and decayed organic matters. Electrical conductivity: The absolute electrical conductivity values throughout the studied period were more than (315) and less than (450) μs/cm, and the mean annual value was (318) μs/cm. The monthly variations were evident (Figure 4).During summer months the values were high, exceeding (370) μs/cm .From November-February they decreased with the decline in air temperature. And from March, values have begun to increase up to the end of sampling in July. Monthly variations for electrical conductivity were parallel with water temperature. The salt content of Iraqi standing water bodies is widely different. Low values were noticed in the northern reservoirs as Dokan and Darbandi-Khan, and high values were noticed in the Middle plain as Al-Habbaniyah and Al-Tharthar (Talling 1980). pH: In the regulating lake, pH values ranged between (7.5-8.2 ).The results agree with Talling (1980).He noticed that the pH values for Iraqi inland water were around (8.0).This narrow range may be due to buffer capacity, which is not measured in the present work. However, according to Al-Tayar (1988), alkalinity values ranged between (121-127) mg/l and the pH range was (8.07-8.40) .From the previously published papers, it seems that the narrow range for pH values is a characteristic feature of Iraqi lakes. The range was (7.4-8.5) in Dohuk lake Al-Nakshabandi (2002); (7.1-8.3) in Dokan lake (Shaban 1980); (8.0-8.4) in Sawa lake (Al’kam et al. 2002) and (7.6-8.6) in Southern marshes (Al-Lami 1986). Monthly variations were clear, the mean values for the three locations and all depths was in August (7.6) .The values tend to increase gradually in the following months reaching maximum in February, where the mean was (8.2). After that, values decreased gradually reaching minimum in July, at the end of the present study (figure 5). During variations an abrupt increase was occurred between December and January and also a sudden decrease between April and May. The mean values for these rapid changes were (0.23 and 0.24) respectively. Monthly pH variations showed direct relationship with water temperature (figure 5). Similar relation was also observed in the regulating lake by Al-Tayar (1988) and (Al-Qado 1989).In other Iraqi lakes the variations were completely different (i.e.) the high values recorded in summer and the low one in winter, as in Dokan lake Shaban (1980) and in Dohuk lake by (AlNakshabandi 2002). During the present study, no direct relationship was found, neither between pH and total number of phytoplankton nor with chlorophyll (a). This confirmed that water temperature is the major factor which affects pH values in the lake. Dissolved oxygen: Dissolved oxygen levels showed clear monthly variations through the period of study (figure 4). The minimum concentrations in October increased gradually during the following months up to February when maximum concentrations (above 10.0 mg/l) were recorded. The period February–June witnessed gradual decline in concentrations. According to Al-Tayar (1988), the minimum levels in October were expected. He mentioned that the main lake, in this month, reach later stages of

5

stratification. And one has to keep in mind that the hypolimnion layer of the main lake (with low dissolved content) is the source of water for the regulating lake. Solubility of oxygen is inversely related with water temperature, salinity and directly with air pressure (Cole 1979).This statement is applied to the regulating lake under study. The range of dissolved oxygen concentrations ranged between (5.1-11.4 mg/l) which is almost similar to (6.0 – 11.0) and (5.5- 10.6) mg/l in the same lake and Dokan lake recorded by Al-Tayar (1988) and (Shaban 1980). In Dohuk Lake and marshes the ranges were wider. They are (2.4-11.8) and (3.0-11.9) as mentioned by AlNakshabandi (2002) and (Al-lami 1986). Stratification in oxygen concentrations was not observed in the lake due to short retention time and the continuous mixing takes place in the lake. Relative saturation for oxygen: The pattern of monthly variations for relative saturation of oxygen was parallel with that of dissolved oxygen concentrations. The lowest ratios were recorded in November and the highest ratios in February. The mean minimum and maximum values for all samples were (69.34 & 100.65 %), In November and February respectively. Generally, relative saturation values were more than (75%) for a period of six months. In the rest months values never fall below (85%). In Dokan Lake relative saturation values ranged between (63-121 %) (Toma 2000), which is very close to the range of the lake under study. In Iraqi marshes the range was wider (39.9-136.7) Al-Lami (1986), because the effective factors on dissolved oxygen content have a wider range. Chlorophyll (a): concentrations of Chlorophyll (a) throughout the studied period (one Year) were less than (5.0) μg/l. And monthly variations were not evident (figure, 8), however there were three distinct peaks with values exceeded (2.5) μg/l, in October; November & February. The minimum values were noticed in June where the mean was (1.3) μg/l .The peak of October coincident with the maximum peak for total number of phytoplankton, when the numbers were more than (4) million cell/l. in all locations and depths. In the rest months chlorophyll (a) showed no relationship with the number of the phytoplankton. The absence of direct relation between chlorophyll (a) content and phytoplankton number (figure 8) indicated that chlorophyll content is affected by volume of Phytoplankton more than their number. The Green algae, as Lund (1969) said, contains chlorophyll more than Diatoms. Same Phenomenon was observed by Shaban (1980) in Dokan Lake. Chlorophyll content in our lake ranged between (0.05-4.75) ug /l, and in Al-Qadisiyah mesotrophic lake was (0.28- 68.5) ug/l. (Kassim et al. 1999). Total number of phytoplankton: Throughout different month of the year, total number of phytoplankton witnesses occurrence of two peaks (figure 8).The first one in November, it was very distinct, since the numbers were very high comparing with the rest months. As an example the surface water of the first location contains more than (7) millions cell/l. In months, just before and after November the number were only (8%) & (3%) of the peak’s value .Second peak occurred in May (late spring and early (summer) .It was less distinct than the first one, where the mean number for the three locations and the five depths was (1792262) cell/l.

6

Determination of parameters which were responsible for the excessive increment of algae in November is not precise, according to Reynold (1984) the responses of phytoplankton for different ecological parameters are well known, but the interactions of their effects obstruct the correct explanation. The regulating lake is classified, according to Reynolds (op. cit.), as Diacmic Lake. This type of lake is suitable for a number of lakes in the temperate region which are mesotrophic and shallow, less than (30) meter deep (Hutchinson, 1967). Phytoplankton diversity: Identification of the phytoplankton taxa revealed that they were (42) species belong to four major groups. They are, in descending order, Diatoms (76.19 %); Green algae 16.66 %); Dinoflagellate (4.76 %) and blue green algae (2.38 %).It seems, obviously, that the diatoms are the most dominant phytoplankton in the regulating lake. This case is very common in Iraqi surface water as Tigris & Euphrates rivers Al-Ni’ma (1982); Abdul jabber (1979) In lesser Zab ; Shaban (1980) in Dokan Lake;Al-Nakshabandi (2002) in Dohuk Lake and Al-Lami (1986) in southern marshes of Iraq. However, detailed information about the phytoplankton of the regulating lake and their nutrients can be finding in Al-Ni'ma and Al-Mandeel (2007).

references: Abdul-Jabbar, R. A. 1981. Ecological Study on lower Zab. - M.Sc.Thesis, College of Sciences, University of Sulaimaniyah. (In Arabic) Al- Hamed, M. I., 1966. Limnological studies on the inland water of Iraq. - Bull. Iraqi, Nat. Hist. Mus. 3 (5): 1-22. Al’kam, F. M.; Hassan, F. M. And Al-Saadi H. A. 2002. Seasonal Variations for Physico-Chemical Properties of Sawa lake-Iraq. - Ecological Research, 5 (2):55-65. (In Arabic) Al-Lami, A. A. 1986. Ecological study on phytoplankton of some marshes south of Iraq.- M Sc Thesis ,College of Sciences ,University of Basra. (In Arabic) Al-Layla, M. A., Al- Rawi, S. M. and Al- Tayar T. A. 1989. Pollution of Saddam Lake. –Saddam research center. (Confidential): 30 pages. Al-Nakshabandi, I. Y. 2002. A phyco-limnological Study on Dohuk Impoundment and its main watershed. Ph. D. Thesis, Coll. of Agriculture – Univ. of Dohuk. Al-Ni’ma, B.A.B. 1982. A study on the limnology of the Tigris and Euphrates River. M. Sc. Thesis Univ. of Salahaddin: 250 pages Al-Ni’ma, B.A.B. 1996. Restricted Bibliography on Tigris River related publications up to 1994. - Journal of Al-Rafidain Engineering No. 4 Vol. 3 (In Arabic). Al-Ni'ma and Al-Mandeel 2007. Phytoplankton and Their Nutrients in the regulating lake of Mosul Dam in Nineveh Province-Iraq. Proceeding of the First Conference of the Environmental & Pollution Control Research Center Mosul University , (56) June 2007:Pages 11-23(In Arabic) Al-Qado, S. M. A. 1989. Limnologocal and cytological study for Chironomus in Nineveh province and use it as an indicator for water quality. M. Sc. Thesis, College of Sciences, University of Mosul. (In Arabic).

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Al-Rawi, S. M., Mustafa, M. H. and Al-Kawaz, H.A. 1994. Study of Pollution in Dohuk Valley and Impact upon Saddam Lake Water Quality. - Saddam Dam Res. Cent. (Confidential) Al-Tayar, Taha A. 1988. Effect of Saddam Dam on water Quality and it’s reflecting on adequacy on water purification plants. M. Sc. Thesis, College of Civil engineering, University of Mosul. (In Arabic) APHA, AWWA and WPCF. 1976. Standard methods for the examination of water & wastewater.- 14th ed. A.P.H.A., 1015 Eighteenth street NW, Washington, DC 20036 – U S A.: 1193p . Cole, G. A. 1979. Text book of limnology. - 2nd Ed. The C. V. Mosby Co. St. Louis, U.S.A. Hinton, G. C. F. & Maulood, B. K. 1979. Modified method for the enumeration of either marine or fresh water phytoplankton concentrated on a membrane filter. - Tropical Ecol. 20 (2):192-194. Lund, J. W. G.1969. Phytoplankton in eutrophication, causes, consequences and correctives. - Proc. of a Symposium National Academy of Science, Washington: 661p. McNabb, C.D. 1961. Enumeration of fresh water phytoplankton concentration on the membrane filters. - Limnol. And Oceanogr. 15: 57 – 61. Rahemo, Z. I. F. and Ami S.N. 1988. Zooplankton of Saddam Dam Lake. Agriculture & Forces, Basic Sciences, (confidential): 30. Reynolds, C.S. 1984. The ecology of freshwater phytoplankton. - Cambridge Univ. Press Cambridge. 365p. Shaban, Ali G. A. 1980 Ecological Study on Phytoplankton of Dokan Lake. - M. Sc. Thesis, College of Sciences, University of Sulaimaniyah. (In Arabic) Talling, J. F. 1980. Phytoplankton in Euphrates and Tigris Mesopotamia Ecology and Destiny.- by Julian Rzoska, Monographia Biologicae, Volume 38: 109 p. Toma, J. J. 2000.Limnology study of Dokan Lake. M. Sc. Thesis Univ. of Sulaimaniyah, Iraq.

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‫بعض الصفات اللمنولوجية للبحيرة التنظيمية لسد الموصل‪/‬العراق‬

‫** فتحـي عبـد اللـه المنـديل‬

‫*بشـير علـي بشـير النعمــة‬

‫*قسم علوم الحياة ‪ ،‬كلية‪ ،‬العلوم ‪ ،‬جامعة الموصل‬

‫‪))[email protected]‬‬

‫**مركـز بحوث البيئة والسيطرة على التلوث‪،‬جامعة الموصل )‪([email protected]‬‬

‫الخلصة‬ ‫يبلغ طول البحيرة التنظيمية لسد الموصل (‪ )8‬كيلومترات وتقع في الجزء الشمالي من العراق حيث‬ ‫تبعد بحدود (‪ )70‬كيلومترا عن مركز مدينة الموصل‪.‬هذه البحيرة كانت هدفا للدراالعينات‪.‬لوجية الحالية‪.‬‬ ‫تم اختيار ثلثة مواقع لجمع العينات ‪ .‬الموقع الول في بداية البحيرة والثاني في منتصفها والثالث في‬ ‫نهايتها‪.‬وفي كل شهر من أشهر السنة كان يتم جمع خمسة عينات من كل موقع من هذه المواقع الخمسة‬ ‫(عينة من سطح البحيرة ومن على عمق متر واحد و ‪ 2‬متر و ‪ 5‬أمتار وقرب القعر) ‪ .‬استمرت عملية‬ ‫جمع النماذج سنة واحدة امتدت من شهر آب (‪ )2004‬ولغاية تموز (‪.)2005‬‬ ‫تم تحليل عينات المياه لغرض قياس الصفات الفيزياوية (درجة حرارة المياه والعكورة وقابلية التوصيل‬ ‫الكهربائي) وال صفات الكيمياو ية ( قي مة الس الهيدروجي ني وترك يز الوك سجين المذاب والتش بع الن سبي‬ ‫وتركيز كلوروفيل (أ) فضل عن الصفة البايولوجية المتمثلة بالعدد الكلي للهائمات النباتية‪.‬‬ ‫تم عرض النتائج وتفسير التغيرات الشهرية والطولية وضمن العماق الخمسة المختلفة كما تم مناقشة‬ ‫العلقات الموجودة بين العوامل المختلفة مع العدد الكلي للهائمات النباتية‪.‬‬ ‫أظهرت النتائج أن التغيرات الشهر ية فـي در جة حرارة الماء كا نت واض حة وتراو حت ب ين (‪ 10,0‬و‬ ‫‪23,8‬م ‪ .)º‬وعكورة الماء كانت أقل من ( ‪ ) NTU 3.5‬خلل أشهر السنة المختلفة ما عدا شهر تشرين‬ ‫الول وأن قيمها لم تظهر ارتباطا مع كمية المطار الهاطلة أو مع عدد الهائمات الطحلبية‪ .‬قيم التوصيل‬ ‫الكهربائي كا نت أك ثر من (‪ )350‬وأ قل من (‪ )450‬مايكرو سيمنز‪ /‬سم ‪،‬و قد أظهرت ارتبا طا مباشرا مع‬ ‫درجـة حرارة الماء‪ .‬قيـم الس الهيدروجينـي كان مداهـا ضيقـا حيـث تراوح بيـن (‪ .)8.2-7.5‬مسـتويات‬ ‫الوكسـجين كانـت مرتبطـة بعلقـة عكسـية مـع كـل مـن درجـة حرارة الماء والتوصـيل الكهربائي‪ ،‬ولم‬ ‫تنخ فض قي مه عن (‪ 5.4‬مل غم‪/‬ل تر)‪ .‬وأن العدد الكلي للهائمات النبات ية تراوح العدد الكلي للهائمات النبات ية‬ ‫بيـن (‪ 7238320-55452‬خليـة‪/‬لتـر)‪ ،‬وقـد شهدت تغيراتهـا الشهريـة حصـول قمتان خلل السـنة‪ .‬أبدت‬ ‫درجة حرارة الماء فقط تغيرات واضحة على طول البحيرة أما باقي العوامل أخرى فلم تظهر أية تغيرات‬ ‫تذكـر سواء على طول البحيرة أو ض من العماق المختل فة لن عمل ية المزج في البحيرة كا نت تح صل‬ ‫باستمرار وبشكل جيد فضل عن أن مدة مكوث الماء كانت قصيرة‪.‬‬ ‫الكلمات الدالة‪ :‬البحيرة التنظيمية لسد الموصل ‪ ،‬العراق ‪ ،‬الصفات الفيزيائية والكيميائية لمياه البحيرة‬ ‫‪9‬‬