The Effect of Tharthar-Tigris Canal on the Environmental Properties of the Tigris River Northern Baghdad, Iraq

: The present study is considered the first on this sector of the Tigris River after 2003. It is designed for two aims, the first is to demonstrate the seasonal variations in physicochemical parameters of Tharthar-Tigris Canal and Tigris River; the second is to explain the possible effects of canal on some environmental properties in the Tigris River. Water samples were being collected monthly. Six sampling sites were selected, two on Tharthar Canal and four along the Tigris River, one before the confluence as a control site and the others downstream the confluence with the canal. For a period from January to December 2020, nineteen physicochemical parameters were investigated including air and water temperature, turbidity, electrical conductivity, salinity dissolved oxygen, percent oxygen saturation, biological oxygen demand, pH, total hardness, calcium, magnesium, sulphate, total dissolved solids, total suspended solids, total alkalinity, bicarbonate, nitrate and phosphate. The results showed that air and water temperatures were close in both Tigris and canal. The waters were well aerated, slightly alkaline and over saturation was recorded several times, while biological oxygen demand values did not exceed 5 mg/L along study period. The high values of conductivity, salinity, total dissolved solids, total hardness, calcium and sulphate ions in Tharthar water increased in the Tigris River below the confluence. Whereas, the low values of turbidity, TSS, total alkalinity and bicarbonate in the arm diluted in the main river. It has been concluded that Tharthar Canal affected the Tigris River by either increasing or diluting of the Tigris chemical components.


Introduction:
Rivers are a major source of water. Although they involve just 0.006 percent of Earth's freshwater, rivers supply drinking water for numerous communities around the world. Water withdrawal from rivers is also used in industrial operations and for irrigation of farmland. Rivers afford opportunities for recreational activities and aesthetic enjoyment 1 . Physicochemical parameters of rivers have been greatly deteriorated due to anthropogenic and industrial activities 2 . Tharthar-Tigris Canal or "Dhira'a Dijla" is human-mediated river that obtains its characteristics from Tharthar Lake 3 .
River channel confluences are sites of significant hydraulic and morphological change within fluvial networks. The local and downstream effects of confluences can have profound effects on the physical water parameters and aquatic animal structures 4,5 .The portion of the river system affected by merging of flows at a junction is defined as Confluence Hydrodynamic Zone (CHZ). Also, confluences play a crucial role in the health of lotic water system and regulate the dynamic of sediment downstream the joining point 6 . So, the present study is considered the first on this sector of the Tigris River after 2003. It is designed for two aims, to demonstrate the seasonal variations in physicochemical parameters of Tharthar-Tigris Canal and the Tigris River and to explain the possible effects of canal on some environmental properties in Tigris River.

Sample measurements
All samples were taken near stream bank about 8-10 m from the shore line at depth 30-50 cm, taking into account not to take samples of stagnant water 8 . It was kept in a well stopped polyethylene bottle 1000 ml at 4°C in a refrigerator for the next day for analysis to minimize the changes in the 1179 composition due to bacteria. Some properties were conducted in the study site directly, such as air and water temperature, electrical conductivity, pH and total dissolved solids. Air temperature was measured in the shade by using digital air thermometer while, water temperature, electrical conductivity, salinity, total dissolved solid sand pH were measured by HANA (HI9811). Turbidity was measured by the turbidity meter Jenwaw company Model-6035. Dissolved oxygen and biological oxygen demand were measured by using Azide modification of Winkler titration method 8 . The percentage of oxygen saturation was calculated as reported in EPA 9 . Total suspended solids were measured according to the procedure stated by Spellman 8 . Total hardness, calcium and magnesium were measured according to standard methods 10 . Sulphate ion was made according to the procedure described by Brands and Tripke 11 . Reactive phosphate was measured by using the ascorbic acid method 8 . UV-Spectrophotometric Screening Method was used for the determination of nitrate as described in standard methods by Baird et al. 10 .
Finally, sulfuric acid titration method were used for determining total alkalinity as described by Spellman 8 .

Statistical analysis
The data were analysed by using one-way ANOVA, SPSS V. 16. Duncan's multiple range tests were used to compare the means of the studied sites parameters to detect differences.

Results and Discussion:
The results showed that air temperatures fluctuated seasonally. The highest values were in summer, whereas, the lowest values were in winter (Fig. 3). This may be related to the Iraqi climate characterized by hot, dry in summers and cold, rainy in winters 12 .
The statistical analysis for air temperature showed significant differences (P≤ 0.05) among the sites of the river and the canal. Whereas, no significant differences were manifested (P˃ 0.05) between site 2 and site 3 in Tharthar Canal (Table  1).
Moreover, the values of water temperatures increased in summer especially in July and decreased in winter as shown in Fig. 4.
The statistical analysis showed no significant differences (P˃ 0.05) in water temperatures between sites on Tigris River and that on the canal ( Table 1).
The data of electrical conductivity and salinity content in Tharthar Canal and the Tigris River are represented in Table 1 and Figs. 5 and 6. At site 1 upstream CHZ, electrical conductivity and salinity ranged from 530-1110 μS/cm with salinity unite from 0.33-0.71‰ in August and March, respectively. Whereas in Tharthar Canal, they ranged from 660-2070 μS/cm with salinity unite from 0.42-1.3‰ in January and May, respectively. By contrast, the highest and lowest readings of electrical conductivity and salinity were recorded at site 4, they ranged from 660-1110 μS/cm with salinity unite from 0.42-070‰ in January and June, respectively. In addition, the values ranged from 620-970 μS/cm with salinity unite from 0.39-0.62‰ in August and July, respectively downstream CHZ. Furthermore, the highest average values of electrical conductivity and salinity in the canal increased their values in the Tigris from 788.33 μS/cm, 0.504‰ in site 1 upstream CHZ to 942.5 μS/cm, 0.603‰ in site 4 at immediately downstream CHZ, respectively as shown in Table 1. High value of salinity in Tharthar Canal was related to the source of water, it receives water from Tharthar Lake characterized as brackish water, this fact was mentioned by Al-Ansari et al. 13 .
For temporal variation, the highest values of electrical conductivity and salinity were recorded in spring season especially in May, in sites 2 and 3 on the canal (Figs. 5 and 6). This increase may be related to the decreasing of discharge rate, the  average rate was 13 m 3 /s recoded in May 2020 as shown in Fig. 2.
Our results are compatible with other previous confluences studies conducted on the Tigris River. Al-Saadi et al. 14 showed that the high values of conductivity in Al-Adaim River increased the conductivity of the Tigris River from 427 μS/cm before the confluence to 498 μS/cm after the confluence. Ramadhan et al. 15 found that high values of conductivity in Tharthar canal increased the conductivity of Tigris River downstream the confluence zone. Also, Nashaat et al. 16 showed that high values of conductivity and salinity in Diyala River increased their values in the Tigris River below the confluence of two rivers.
According to Hanrahan 17 Tharthar Canal is considered as oligohaline water, whereas, the Tigris River is considered as freshwater, then turned to oligohaline water in site 4 at immediately downstream CHZ. Table 1 and Fig. 7 show that turbidity values at site 1 upstream CHZ ranged from 8.16 to 131 NTU recorded in March and May, respectively. In the Tharthar Canal, they varied from 3.68 NTU in April to 22.33 NTU in July. Whereas, the minimum value was 10.9 NTU in November and the maximum values was 114 NTU in May in site 4 at immediately downstream CHZ. Also, it ranged from 11.73 -137 NTU in February and May, respectively downstream CHZ. The statistical analysis indicates significant differences (P≤ 0.05) between the Tigris River and Tharthar Canal and no significant differences were found out (P> 0.05) between sites 2 and 3 on Tharthar Canal (Table1).
Seasonally, the values of turbidity in the Tigris River increased in spring season especially during May. While, they never changed in the two sites of the canal, during the four seasons of the year (Fig. 7). This case may be related to the differences in the amounts of discharged water of both rivers particularly in May (Fig. 2).
For spatial variation, the low mean values of turbidity in Thathar Canal (site 2 and 3) decreased the value of turbidity in the Tigris River from 34.75 NTU upstream the confluence to 28.65 NTU at immediately downstream CHZ. Then they increased gradually downstream away from the confluence ( Table 1). This result corresponded with Kassim et al. 18 and Abdul Jabar et al. 19 who reported that low values of turbidity in Lower Zab Tributary reduced the turbidity of Tigris River downstream the confluence of two rivers. Nashaat et al. 16 showed that the low values of turbidity in Diyala River reduced the mean value of turbidity in the Tigris River from 45.44 NTU before the confluence to 43.18 NTU after the confluence. Also, Nashaat and Al-Bahathy 20 found that turbidity in the Euphrates River increased downstream Hindiya Dam relating that to the frequent fluxes from opening dam spillways which led to release sediments which were settled in the bottom layer of the dam.  The values of pH in Tharthar Canal and Tigris River were slightly alkaline (Fig. 8), and no significant differences (P˃ 0.05) were found among all studied sites ( Table 1). The results of this study are parallel with the most previous studies conducted on the Tigris River such as Ramadhan et al. 15 and Alazawii 21 . Additionally, Hassan et al. 22 showed that pH values of Tharthar Canal and Tigris River within narrow range were slightly alkaline.
Our results showed that waters in both Tharthar Canal and Tigris River was well aerated and the values of DO didn't fall below 6.5 mg/L and oxygen saturation level above 100% was recorded many times in all study sites over the year ( Table  1). The statistical analysis revealed no significant differences (P˃ 0.05) among all sites for DO and POS (Table 1).
Seasonal variations in DO and POS values are recorded in Figs. 9 and 10. The minimum values of DO were recorded in summer season and the maximum were in winter season. In addition, the minimum values of POS were recorded during summer at all sites on Tigris River, conversely associated with the two sites on the Canal. This is mainly due to the inverse relationship that exists between dissolved oxygen and temperature. Cold water holds more dissolved oxygen than warm water because colder water molecules are less active. This inhibits dissolved oxygen ions. These results are supported by other previous local studies 23,24 . Based on Pennington and Cech 25 DO level in the present study was within the permissible limit as mentioned above. Fig. 11 and Table 1 shows the results of BOD 5 at site 1 upstream CHZ ranged from 1.4 mg/L in August to 3.6 mg/L in December. On the Canal, the lowest value was 0.9 mg/L in November and the highest value was 3.5 mg/L in February. Whereas, the minimum amount was 1.5 mg/L in August and the maximum was 3.6 mg/L in February at site 4 immediately downstream CHZ. While, the minimum amount was 0.9 mg/L in August and the maximum was 4.3 mg/L in February downstream CHZ.  The statistical analysis of BOD 5 showed no significant difference among all studied sites (P˃ 0.05) and the mean values for all sites were equal which was recorded 2 mg/L (Table 1).
According to Li and Liu 26 the values of BOD 5 were doubtful in its cleanliness and did not exceed 5 mg/L along study period.
Seasonally, in the Tigris River the maximum and minimum values of BOD 5 were in winter and summer. Whereas, on the Canal, the maximum and minimum values were in spring and autumn seasons, respectively. This may be associated with the raising of water temperature in spring leading to increased biodegradable of organic matter. These results agree with other previous studies conducted on the same river 16, 27, 28

Figure 11. Variations of the biological oxygen demand value during the study period
The values of total hardness and calcium hardness in both Tharthar Canal and Tigris River are represented in Table 1 and Figs. 12 and 13. At site1 upstream CHZ they ranged from 284 and 68.13 mg/L to 440 and 124.25 mg/L, respectively. On the Canal, they ranged from 288 and 93.12 mg/L to 960 and 228.45 mg/L, respectively. Whereas, in site 4 at immediately downstream CHZ they ranged from 300 and 72.144 to 556 and 176.35 mg/L, respectively while, they ranged from 288 and 60.12 mg/L to 460 and 148.296 mg/L downstream CHZ.
The statistical analysis for total hardness and calcium hardness indicates significant differences (P≤ 0.05) between the two rivers and no significant differences (P> 0.05) between the two sites on Tharthar Canal (Table 1).
Also, the results showed that the high mean values of total hardness and calcium hardness in Tharthar Canal increased their values in Tigris River from 354 and 86.52 mg/L before the confluence to 431, 123.91 mg/L in site 4 at immediately downstream CHZ, then returned to the first state downstream away from the confluence zone as we recorded in sites 5 and 6 ( Table 1).The highest levels of total hardness and calcium ion in Tharthar Canal water comes from chemical weathering of sedimentary rocks in Tharthar Lake containing this ion such as marl, limestone and gypsum 3 .
According to Spellman 8 Tharthar Canal water is considered very hard water above 300 mg/L. While, the Tigris River water ranged from hard to very hard water. The real cause of hardness in the Tigris River is the nature of catchments area through which the Tigris River flows 29 .
These results are in line with several previous confluences studies conducted on the Tigris River. Al-Saadi et al. 14 observed that high values of total hardness in Al-Adaim River increased the hardness of Tigris River from 345 mg/L before confluence to 384 mg/L after confluence. Also, Al-Lami et al. 30 showed that the high value of hardness in the Tharthar Canal raised the hardness of the Tigris River. Furthermore, Nashaat et al. 16 Table 1 show the values of magnesium hardness. In site 1 upstream CHZ, the values of magnesium hardness ranged from 12.01in December to 56.39 mg/L in November. In the Canal, the lowest value was 9.45 mg/L in December and the highest value was 129.18 mg/L in November. Whereas, the minimum and maximum values ranged from 12.04 to 50.45 mg/L in March and November, respectively in site 4 immediately downstream CHZ. While, it was ranged from 9.12 mg/L in March to 46.24 mg/L in February downstream CHZ.
The statistical analysis indicates significant differences (P≤ 0.05) between the river and the canal and no significant differences (P> 0.05) between the two sites in Tharthar Canal (Table 1).
For spatial variations, thehighest average value is recorded 40.34 mg/L in Tharhar Canal. While, the lowest average value recorded 26.68 mg/L at site 5 in Tigris River ( Table 1). The highest level of Mg 2+ in canal water can be attributed to the weathering of rocks, particularly magnesiumsilicate 3 .
For temporal variation, magnesium ion values in both river and canal decreased in summer. Whereas, increased in spring and autumn in the canal (Fig.  14). This may be related to differences in rate of discharge, volume of water and geological and structure 30 .Similar results were also obtained in other Iraqi inland water 16,23 . Fig. 15 and Table 1 show sulphate values during the study period. At site 1 upstream CHZ, the values ranged from 10 mg/L in October to 50 mg/L in February. In the canal, the lowest value was 20 mg/L in March and July to 90 mg/L in August. Whereas, the minimum and maximum value of sulphate ranged from 30 in March and December to 60 mg/L in April, May and November in site 4 immediately downstream CHZ. While, it was ranged from 20 mg/L in January, March, July, August and October to 60 mg/L in November downstream CHZ.
The statistical analysis indicates significant differences (P≤ 0.05) between the two rivers and no significant difference (P˃ 0.05) between sites 5 and 6.
For spatial variations, the highest average value was in site 2 on the arm reached 59.16 mg/L. While, the lowest average value recorded 13.48 mg/L in site 1 on Tigris River before the confluence. This leads to increase the concentration of sulphate ions in site 4 downstream CHZ reached 45 mg/L (Table 1).
For seasonal variation, sulphate ions in Tharthar Arm water were more than this in the Tigris River during all the seasons of the year as explain in Fig. 15.The high values of sulphate in the canal water were attributed to gypsum nature of Tharthar Lake from which the canal takes its water 3 . Our results are parallel with Kassim et al. 18 who showed that high values of sulphate in Lower Zab increased the concentration of sulphate ions in Tigris River after the confluence of two rivers. Alao, Lamare and Singh 31 found that high value of sulphate ions in Lunar River increased their value in Lukha River from 163.25 mg/L before confluences to 1512.50 mg/L after the confluences of two rivers. The data of total dissolved solids are represented in Table 1 and Fig. 16. In site 1 upstream CHZ, the values of TDS ranged from 260 mg/L in August to 560 mg/L in March. On the Canal, the lowest value was 330 mg/L in January to 1400 mg/L in May. Whereas, the minimum and maximum value of TDS ranged from 330 to 560 mg/L in January and June, respectively in siet4 immediately downstream CHZ. While, it was ranged from 310 mg/L in August to 480 mg/L in July downstream CHZ. In addition, statistical analysis showed that no significant differences (P˃ 0.05) among all studied sites (Table 1).
For spatial variations, the highest mean value was in the canal. While, the lowest mean value was in site1. This lead to elevate the concentration of TDS in Tigris River from 395 mg/L upstream CHZ to 471mg/L in site 4 immediately downstream CHZ. This may be related to variations in topography, hydrology, geology, precipitation and local climate between the river and the canal 7,29 .
For temporal variation, the highest values of TDS recorded in spring season especially in May on Tharthar Canal. This may be attributed to the decreasing in the rate of discharge (Fig. 2). These results are compatible with other previous confluences studies conducted on the same river 15, 16,21 .
As for TSS, in site 1 upstream CHZ, the values of TSS varied from 1 mg/L in February to 118 mg/L in May. On the Canal, the lowest value was 4 mg/L in April and the highest value was 29 mg/L in July. Whereas, the minimum and maximum value of TSS ranged from 2 to 102 mg/L in March and May, respectively in site 4 immediately downstream CHZ. While, it was ranged from 1 mg/L in February to 125 mg/L in May downstream CHZ (Fig. 17).
The statistical analysis indicates significant differences (P≤ 0.05) between both rivers. While, no significant differences were recorded (P> 0.05) between the two sites on the canal and among all sites on the Tigris River (Table 1).
For spatial variations, the highest mean value of TSS recorded in Tigris River upstream and downstream the confluence compared with sites 2 and 3 on the Canal. For this the mean value of TSS in Tigris River decreased from 34.25 mg/L in site 1 to 25.91 mg/L in site 4 at immediately downstream CHZ, due to the mixing of Tharthar water with Tigris (Table 1).
Seasonally, TSS concentration in Tigris River increased during spring season particularly in May. While, it never changed in the two sites of the Canal, during the four seasons of the year as shown in Fig. 17. This may be related to the differences in discharged water amounts for both rivers especially in May (Fig. 2).   Our result is parallel with Payne et al. 32 who observed that the value of TSS in Lower Mississippi River declined after the confluence with Ohio River. Furthermore, low TSS value of Illinois River reduced its values in Mississippi River from 69.2 to 60.2 mg/L downstream the confluence.
The values of total alkalinity and bicarbonates in Tigris River and Tharthar Canal are shown in Table 1 and Figs. 18 and 19. In site 1 upstream CHZ, the values of total alkalinity and bicarbonates ranged from 152.5, 145 to 231.8, 212 mg/L, respectively. On the Canal, the lowest values were 67.1, 75 and highest values were 176.9,177 mg/L, respectively. Whereas, in site 4 ranged from 73.2, 80 to 183, 191 mg/L, respectively. While, they ranged from 109.8,128 to 186, 205 mg/L downstream CHZ, respectively.
The statistical analysis of both total alkalinity and bicarbonate revealed significant differences (P≤ 0.05) between Tharthar Canal and Tigris River and no significant differences (P˃ 0.05) between sites 2 and 3 on Tharthar Canal (Table 1).
For spatial variation, the highest average value of total alkalinity and bicarbonate recorded upstream CHZ were 176.14 and 185.33 mg/L, respectively. While, the lowest average values recorded on Tharthar Canal were 105.51 and 120.5 mg/L, respectively (Table 1). This leads to a decrease in their values in site 4 at immediately downstream CHZ, then, quickly after, they came back to the first state.
High values of total alkalinity in Tigris River water are mainly due to bicarbonate ions which are abundant in Iraqi inland waters. This was pointed out in many previous studies 19,22,29 .
For temporal variation, the highest values of total alkalinity and bicarbonate were recorded in the winter season especially in January. While the lowest values recorded summer and autumn. A similar result on the same river were obtained by 16,33,34 .   respectively. While, they ranged from 0.49, 0.00025 to 0.998, 0.023 mg/L downstream CHZ, respectively. Statistical analysis of nitrate and phosphate showed that no significant difference among all studied sites (P˃ 0.05) ( Table 1).
For spatial variation, the highest mean values of nitrate and phosphate were at site 1 upstream CHZ. Whereas, the lowest mean values were on the Tharthar Canal. This, in turn, decreased the mean values in site 4 at immediately downstream CHZ (Table 1).
These results are compatible with Al-Dhamin et al. 35 pointed out the low values of nitrate and phosphate in Al-Tharthar-Euphrates Canal, which lowered their values in the Euphrates River from 3.4 and 0.4 mg/L before the confluence to 2.7 and 0.3 mg/L after the confluence, respectively.
For temporal variation, the maximum values of nitrate were recorded during the spring season, especially in April. Whereas, the minimum values were during summer especially in June for both rivers (Fig. 20). The high values in spring could be attributed to the rainfall, higher rainfall washes out nitrate from the land into the river 36 . The same finding was also obtained by Hassan et al. 22 related that to the increasing of nutrient plant in the spring season and decreasing in the summer season.
For phosphate ions, the lowest values were in the spring season, while the highest values were during summer, especially in sites 5 and 6 ( Fig. 21). This increase can be attributed to the decomposition of organic materials containing phosphate compounds in addition to the presence of urban waste such as sewage.
Our findings are supported by several previous confluences studies implemented on the Tigris River, Al-Lami 30 observed that phosphate ions in Tharthar Canal lower than in Tigris River. Therefore, Tharthar water reduced phosphate concentration of Tigris River from 0.0102 mg/L before confluence to 0.00726 mg/L after the confluence. Furthermore, Al-Lami et al. 29 showed that the concentrations of phosphate ions along Tigris River, ranged from undetected concentrations to 0.124 mg/L. Also, Al-Azzawe 27 found that phosphate values in Tigris River within allowable limit and fluctuated between 0.003 mg and 0.12 mg. Hassan et al. 22 reported a higher mean value of phosphate ions downstream the confluence of Tharthar Canal with Tigris River. They recorded 0.42 mg/L compared with the present study, which was 0.0064 mg/L. This could be attributed to the differences in methods was applied to assess the phosphate ions In short, nitrate concentrations in all sites were within an acceptable level of nitrate in stream ecosystems, less than 1 mg/L 8 . Additionally, phosphate concentrations in Tharthar Canal and Tigris River northern Baghdad City remained within low values. Furthermore, they were slightly higher than the standard value (0.01 mg/L) in pristine streams as stated by EPA 37 and Allan et al. 38 . This may be returned to unaffected by human activities.

Conclusion:
It can be concluded that the water properties of the Tharthr Canal and Tigris River are different in terms of many parameters such as flow rate, conductivity, salinity, TDS, TSS, turbidity, total hardness, calcium, magnesium, sulphate, total alkalinity, bicarbonate, nitrate and phosphate. Thus, Tharthar water impact Tigris water within and downstream the confluence zone, changes its properties from fresh to oligohaline, hard to very hard water, increased TDS, calcium and sulphate ions. Whereas, the values of turbidity, TSS, total alkalinity and bicarbonate have been reduced. Finally, pH values of both rivers tend to be alkaline, and the levels of DO and nitrate fall within the permissible limits.