The results of physico-chemical analysis are presented in Table 1. The Tigris River water temperature varied among the 12 months period. But, the values of temperature degrees for the four sampling locations ranged between 11.1 and 30.7. The temperature of the ambient air influenced the variance in water temperature during the 12 months period. The mean values showed that they are within the acceptable range of water temperature of surface river water. Under natural conditions, the temperature of rivers' water varies between 0°C and 30°C (Chapman, 2003).
Table 1
Mean values of physico-chemical characteristics of the Tigris River in Baghdad during a period of 12 months
Parameter | WHO Standards | Station 1 Min-Max | Station 2 Min-Max | Station 3 Min-Max | Station 4 Min-Max |
Temperature ◦C) | - | 11.1-30.2 | 11.6-30.2 | 11.2-30.2 | 11.2-30.7 |
pH | 6.5-8.5 | 7.1-8.2 | 7.1-8.2 | 7.1-8.2 | 7.2-8.2 |
EC (microsemens) | 1000 | 620-1210.5 | 589.2-1220 | 890-1289 | 934-1295 |
TH (mg/L) TDS (mg/L) TSS (mg/L) | <500 500 25 | 240.3-520.5 569-804 35.5-99.2 | 280.6-530.4 550.5-804 40.2-140.8 | 288.6-531.7 755-1219 44.2-141.9 | 360.6-546.9 855-1303 55.6-141.9 |
DO (mg/L) BOD (mg/L) COD (mg/L) Turbidity(mg/L) No3 (mg/L) SO42− (mg/L) PO43− (mg/L) | 4 <5 20-200 <5 ≤ 10 200 5.5 | 6.8-8.5 3.5-5.9 71.3-562.4 15.3- 30.4 3.6-11.3 130.5-420 0.12-0.55 | 6.9-8.5 5.5-6.9 70.8-620.5 17.5- 34.8 3.2-11.3 209.9-70.50.13-0.55 | 6.9-8.5 5.5-6.9 99.4-612.9 17.5- 35.6 6.9-11.4 189.9-470.9 0.8-0.98 | 6.9-8.6 5.5-6.9 70.1-502.6 17.5- 35.6 8.7-11.9 188.3-470.8 0.41-0.99 |
pH is a key parameter to establish the suitability of river water for different purposes (Venkatesharaju et al, 2010). pH values ranged between 7.1 to 8.2 for the four stations. These values were also within the permissible WHO standards and these results were similar to previous studies confirming a slight alkalinity of the Tigris River water (Ali, 2018; Al-Abdrabba et al, 2015). This alkalinity of the Tigris River surface water could be attributed to the increased disposal of domestic wastes into the river water at different sites along the Tigris river in Baghdad.
Electrical conductivity (EC) of river water represents a function of the concentration of ions in a solution, the nature of dissolved substance, and the temperature (Tolgyessy, 1993). Results of the current study showed that the values of EC for sampling station 1 ranged between (620-1210.5 µS/cm−1) and (589.2-1220 µS/cm−1) for sampling station 2. While sampling station 3 had EC values ranging from (890) to (1289) and station 4 had EC values ranging between (934-1295 µS/cm−1). Variance of EC values in the Tigris River is correlated with season and river water
temperature. In winter, lower EC values were detected in all sampling stations. On the other hand, higher EC values were registered during summer and during high temperature season. The reason for the decrease of EC values in winter season is due to the increase of rainfall, which may cause the accumulation of ions in river water. Yearly precipitation in Baghdad ranges from 100 to 400 mm/year (Al-Quraishi, & Negm, 2019). The increased values in summer could be caused by the increased agricultural, industrial, and other anthropogenic activities at the sampling stations. The results of the current study confirm results obtained by previous studies regarding the increased EC values in the Tigris River water in Baghdad (Flayyh and Rasheed, 2016; Mustafa, 2012). But, the registered values of EC in the current study especially in the fourth station were higher than the results obtained by some more recent studies (Atta, 2020; Al-Ani et al, 2019).
Turbidity generally indicates the quantity of non-dissolved materials and substances in water. Turbidity can be seen as a measure of water clarity and it’s usually expressed in Nephelometric Turbidity Unit (NTU) (Berthouex and Brown, 2018). Turbidity values for sampling station 1 ranged between (15.3- 30.4 NTU) and (17.5- 34.8 NTU) for sampling stations 2. Sampling station 3 and 4 had turbidity values between (17.5- 35.6 NTU). These values were significantly higher than the WHO permissible limits of turbidity in freshwaters (<5 NTU). The current results show increased levels of turbidity in the Tigris river water passing through Baghdad and turbidity values registered in this research are higher than the results obtained by previous studies, which indicated the noticeable increase in turbidity in the Tigris River water in Iraq (Alwan, Muhammed, and Jassem, 2013; Al-Suhili, Khudair, and Abdulrazzak, 2016). Reasons for such increased turbidity values in the Tigris River could be attributed to the domestic sewage discharge, industrial wastewater discharge, and agricultural activities at the four sampling stations.
Water hardness is resulted from the presence of calcium (Ca) and magnesium (Mg) compounds, and by different other metals. Hard water does not pose a danger to the public health, but economically it represents one of the most critical water quality parameters (Berthouex and Brown, 2018). In fact, hard water helps teeth and bones grow; and lowers toxicity to lead poisoning from lead pipelines. On the other hand, soft waters are believed to be associated with cardiovascular diseases (Spellman, 2003). The total hardness values of the Tigris River in this study were high. Sampling station 1 showed values ranging between (240.3-520.5) and the values of the sampling station 2 were (280.6-530.4). Sampling station 3 and 4 had total hardness values ranging between (288.6 to 546.9). These values were higher than results obtained by previous studies (Al-Marsoumi, Al-Bayati, Al-Mallah, 2006). The current study indicated that the Tigris River has hard water within the city of Baghdad. This result confirms other previous literature that showed the Tigris River was characterized with high total hardness (Hashim, 2017; Al-Obaidi, 2009). However, the current study showed higher results of water hardness than any other former study.
Values of total dissolved solids (TDS) for sampling station 1 ranged from 569 to 804 mg\L and for the second sampling station were (550.5-804 mg/L). While sampling station 3 and 4 had values ranging between (755 to 1303 mg/L). These values were within the WHO acceptable limits of total dissolved solids in river waters (1000 mg\L). However, the increased values could be attributed to higher concentrations of discharged effluents nearby the sampling stations since the four sampling locations are considered heavily populated and industrialized areas. These results are higher than the results obtained by some previous studies that indicated the Tigris River is characterized with increased values of TDS and that the river water is more saline in the central and southern areas of Iraq (Al-Shujairi, Sulaiman, and Najemaldin, 2015; Ali and Shaban, 2014). Moreover, high concentrations of TDS are common in freshwaters in arid climates, as the case in Iraq, which is considered an arid region (Boyd, 2015). Al-Saady and Abdullah (2014) indicated that the registered increased TDS values along the Tigris river in Baghdad and the southern areas resulted from several factors such as: the agricultural lands along the Tigris river that are characterized with high salt content. In addition, there is a noticeable reduction in levels of the Tigris river water in Baghdad. Moreover, the high evaporation of river water that lead to increasing salt in river water. It’s noteworthy that the increase of TDS downstream the Tigris River is resulted from the extensive agricultural activities in the area between Baghdad and Umara city. However, runoff and return flow from agricultural land that contain fertilizers can also lead to high TDS value (Saady and Abdullah, 2014).
Total suspended solids (TSS) represent a measure of the weight of relatively insoluble materials in the ambient water. Suspended solids can include both organic (detritus and biosolids) and inorganic (sand or finer colloids) constituents (Spellman, 2003). The WHO does not have a limit for TSS, but the European Union set (25 mg/L) as a limit for fisheries and aquatic life in rivers (Chapman, 2003). TSS values for the 1st sampling station ranged between (35.5-99.2 mg/L). TSS values for the 2nd station were (40.2-140.8 mg/L). While TSS values for the third and fourth sampling stations ranged between (44.2 to 141.9 mg/L). The current high TSS results shown in this study come in consistence with the ones obtained by (Al-hassany & Al- Bayyati, 2017; Matti, 2014). Though, the current study had much higher results than the previous studies.
Dissolved oxygen is a very important water characteristic. DO is necessary to preserve most forms of aquatic life and to allow the decomposition of organic matter, including organic wastes (Nesaratnam, 2014). The current study showed the average value of dissolved oxygen (DO) in the Tigris river water was ranging from (6.8 mg/L to 6.8 mg/L) at all the four sampled stations. These values are acceptable according to the Iraqi and international standards where DO values must not be less than 4 mg/L. The current results agree with previous studies confirming that the dissolved oxygen levels in the Tigris River water are within the acceptable international standards (Matti, 2014; Al-Bayatti, Al-Arajy, and Al-Nuaemy, 2012).
Biochemical Oxygen Demand (BOD) is the amount of oxygen microorganisms use to decompose organic wastes that are present in water (Carmen, 2009). BOD is a very commonly used environmental test and considered as the most important marker of river water organic pollution (Nesaratnam, 2014). BOD values ranged between (3.5-5.9 mg/L) at sampling station 1 and (5.5-6.9 mg/L) at the second sampling station. While sampling station 3 and 4 registered BOD values ranging between (5.5-6.9 mg/L). The increased BOD range detected at the four sampling stations exceeds the international standards for BOD levels in river waters (<5 mg/L). The current results are much higher than the ones obtained by (Al-Zoubaidy, Sulaymon, & Razzak, 2009; Ismail and Abed, 2013) indicating an increase in the BOD concentrations in the Tigris River water in Baghdad. High BOD concentrations in the Tigris River water indicate an increase in pollution caused by organic sources.
Chemical Oxygen Demand (COD) is the mass of oxygen needed for the complete oxidation of an organic compound present in water (Wiesmann, Choi, and Dombrowski, 2007). For this reason, COD is an important indicator of organic contamination in surface water. COD values for the 1st sampling station ranged between (71.3-562.4 mg/L) while the 2nd sampling station had values ranging from (70.8-620.5 mg/L). Sampling stations 3 and 4 had COD values ranging between (70.1 to 612.9 mg/L). These results show the Tigris river water is heavily polluted with organic matter coming from the sewage discharged directly into the river without any treatment. Previous studies had similar results showing an increase in the COD values of the Tigris River water in Baghdad (Ma’alah, 2013; Alobaidy et al, 2010).
Nitrogen is present in the river water in the form of nitrate (NO3). Presence of Nitrate in the water indicates that the river is polluted with sewage. Nitrate in river water can be a serious public health danger to both human and animal infants. High concentrations of nitrate in drinking water can even cause death (Drinan & Spellman, 2001). Agricultural activities are considered the main source of nitrate pollution (Singh, & Tripathi, 2007). Values of nitrate detected at the 1st sampling station ranged from (3.6-11.3 mg/L) and (3.2-11.3 mg/L) for the 2nd sampling station. Sampling station 3 had nitrate (NO3) values ranging from (6.9-11.4 mg/L) and (8.7-11.9 mg/L) for sampling station 4. The high concentrations of nitrate in the four sampling locations are caused by the continuous wastes discharge, agricultural fertilizers, and domestic garbage dumps. Similar previous results obtained by (Al-Shemari & Abdulhussain, 2013; Rabee, Abdul-Kareem, & Al-Dhamin, 2011) indicated the presence of high nitrate levels in the Tigris River water in Baghdad. However, the current study showed higher nitrate (NO3) values at the fourth sampling station. Previous studies did not register such higher values in that location. This shows that the sampling station 4 is being polluted heavily over the past few years.
There are two forms of sulfur (S) common in water and wastewater: sulfate (SO42−) and hydrogen sulfide (H2S). Sulphate (SO42−) in high concentrations can cause a laxative effect and a bitter taste and is considered a nuisance in drinking water (Berthouex and Brown, 2018). The 1st sampling station had mean values ranging from (130.5-420mg/L) and the 2nd sampling station had values ranged from (209.9-470.5 mg/L). Sampling station 3 had values ranged from (189.9-470.9 mg/L) and (188.3-470.8 mg/L) for the fourth sampling station. Previous studies (Hashim, 2018; Al-Fatlawy, Rabee & Abdul-Kareem, 2011) showed similar high Sulphate concentrations indicating that the Tigris River water in Baghdad had increased levels of Sulphate and that those concentrations had exceeded the permissible international limits for Sulphate in freshwaters.
Phosphate (PO43−) is the ideal form of phosphorus (P) for plant growth. It is a major cause of excessive algae growth and degraded water quality especially in lakes (Berthouex and Brown, 2018). Phosphate values at the four sampling stations ranged between (0.8-0.99 mg/L). The detected concentrations are within the acceptable WHO for phosphate in freshwaters.