Shatt Al-Arab river is the main source of fresh water to Basrah city , it plays a vital role in various sectors of economy such as agriculture , livestock production , industrial activities , hydropower generation , fisheries and other creative activities . The water of Shatt Al-Arab was deteriorated due to some important sources like increasing urbanization, industrialization , and agriculture activities .
Different models of Water Quality Indices (WQIs) and Water Pollution Indices (WPIs) were considered as effective tools to assess the water quality and suitability for different purposes .
Five stations were selected at the middle part of Shatt Al-Arab river , the first station (Al-Mohamadiyat) ,the second station (Al-Sindibad ) , the third station (Al-Maqal ) , the fourth station (Al-Bradhiya ), and the fifth station (Abuflowse). Water and sediments samples were collected monthly from December , 2012 to November , 2013 during the low tide period . Thirty-one water variables ( Air and water temperature, DO, BOD5, TDS , Salinity , EC , pH, TA, CO2 , TH, Ca+2 , Mg+2 , Turbidity ,SD ,TSS, NO2-,NO3- , NH3+, TN, PO4 -3 , TP , B+3,SO4-2 ,Cl- , Na+ , K+,SAR, FC ,Chlorophyll a(Chl.a) ,Phaeophytine a ( Phaeo.a) , and Algal Biomass ) were measured to assess the water quality and degree of pollution . Also , the grain size and TOC% contents of sediments were detected as required for the study of heavy metals and hydrocarbons pollution.
The water quality for general use (GWQI) , drinking use (DWQI) and irrigation use(IWQI) was assessed according to CCMEWQI , and NSFWQI indices . The water quality for aquaculture use was assessed according to MOCWQI index , while the Eutrophication status was assessed according to TSI and TRIX indices and organic pollution according to OPI index.
Results showed that the variables of the river were ranged as below: Air temperatures ( 11.5- 44.0 )ᵒC ,while the water temperatures (13.0-33.4) ᵒC , DO ( 3.1-10.4) mg/l , BOD5 ( ND -3.6 ) mg/l , TDS( 1012-7741 ) mg/l , Salinity(0.8-6.1 ) PSU , EC( 1.57-10.85 ) mS/cm , pH ( 7.40-8.52 ) , TA( 93.0-152.5)mg/l, CO2( ND -15.48) mg/l , TH ( 435-2440 )mg/l, Ca+2 ( 21.6-293.4)mg/l , Mg+2 (75.7-521.6 ) mg/l, Turbidity(8.13-140 ) NTU , SD( 0.3-1.5) m , TSS( 2.3-50.1) mg/l , NO2- (0.515-11.256 ) mg/m3, NO3-( 60-3330) mg/m3 , NH3+(280-3080 )
mg/m3, TN(1281-6228 ) mg/m3, PO4 -3 ( 0.328-8.045) mg/m3, TP(3.238-52.164 ) mg/m3 , B+3(0.067-1.957 ) mg/l ,SO4-2 ( 830.4-1569.6) mg/l, Cl- (199.9-2999.1) mg/l, Na+(42.2-1464)mg/l , K+(2.1-120 ) mg/l, SAR( 3.27-75.62), FC(ND-17300 ) CFU/100 ml , Chl.a (ND-48.06 ) mg/m3 ,Phaeo. a ( 0.053-11.841) mg/m3 , and Algal Biomass ( ND - 3220.02) mg/m3 , while in sediments : sand ( 1-10.33 )% , silt ( 43.67 – 78.00)% , clay ( 17.33- 55.33 ) % , and TOC( 5.48-12.69 )% .
According to GWQI range( 32.09-55.89) , DWQI range(14.97-32.70) and IWQI range(20.14-50.33) , the water of the middle part of Shatt Al-Arab river can be classified as poor - marginal for general and for irrigation use (except station 4 which was poor for general use, and station 5 which was poor for irrigation use ), whereas it can be classified as poor for drinking use . According to NSFWQI range (113.82-607.46) , the water of Shatt Al-Arab can be classified as poor-unsuitable for drinking use . On the other hand , the water can be considered as medium – Excellent water for aquaculture use according to MOCWQI range .
TSI range (45.40-56.09) referred to mesotrophy- eutrophy water , whereas water can be classified as very high trophic level according to TRIX range (6.73-7.54) . OPI range (4.5-4.75) referred to weak organic –non organic pollution status .
Seven heavy metals ions : Cd+2 , Cu+2 , Fe+2 , Mn+2 , Ni+2 , Pb+2 and Zn+2 were selected to determine their concentrations in dissolved , particulate (exchangeable and residual) phases ,and sediments (exchangeable and residual) . HPI and Igeo indices were used as heavy metals pollution indices for water and sediment, respectively .
Results showed that the concentrations of the previous metals in dissolved phase were (3.01 , 2.35 , 89.45 , 4.48 , 9.51 , 43.67, 7.58 )µg/l, respectively , whereas in the exchangeable phase of particulate were(48.56 , 53.22 , 8968.76 , 1748.58 , 120.14 , 271.52 , 243.16 )µg/g dry weight respectively , and in the residual phase of particulate were (57.59, 88.68 , 21571.74 , 365.90 ,163.39 , 388.44 , 219.42 ) µg/g dry weight . HPI range (130.41-196.97)referred to polluted water according to impermissible values of dissolved Pb , Fe and Cd .
In sediments , the concentrations of the metals in the exchangeable phase were (7.96 , 20.27 , 4104.61 , 663.18 , 75.70 , 74.97 , 46.33 ) µg/g-dry weight, respectively ,while in the residual phase were (5.12 , 23.84 , 16381.18 , 328.91 , 158.94 , 30.00 , 59.88 ) µg/g-dry weight, respectively . According to Igeo values ,
the sediments of middle part of Shatt Al-Arab river can be classified as unpolluted with Fe and Zn , while unpolluted-moderately polluted with Cu , Mn and Pb , and moderate-strongly polluted with Cd and Ni .
Total Petroleum Hydrocarbons (TPHs) were determined in water and sediments samples using spectrofluorometery. Aliphatic (n-alkanes) and polynucleic Aromatic Hydrocarbons(PAHs) compounds have been identified using capillary Gas Chromatography (GC).
Results showed that the range of TPHs concentrations in water was (5.18 - 37.59) µg/l ,while in the sediments, it was ( 4.76-45.24 ) µg/g dry weight . Total aliphatic ( n-alkanes ) concentrations in water ranged (8.81-35.58) µg/l , while in sediments they were ( 4.76-10.09) µg/g dry weight . The carbon chain length of n-alkanes in water and sediments samples were recorded from C7-C31 dominated by C22-C25 .
The range of PAHs compounds in water was ( 5.81 – 47.96) ng/l ,dominated by carbazol and anthracene ( as light PAHs) and chrysene and floranthene (as heavy PAHs) . Whereas in sediments the PAHs ranged from (4.318) to (28.48) ng/g dry weight dominated by carbazol and anthracene ( as light PAHs) and indeno (1,2,3,c,d) pyrene and benzo(g,h,i)perylene (as heavy PAHs).
The LMW/HMW ,CPI index and Pristine/Phytane values indicated that the source of n-alkanes hydrocarbons in the water and sediments of Shatt Al-Arab river was mainly biogenic and pyrogenic and at least petrogenic .Whereas the LMW/HMW , Phenanthrene /Anthracene , and Flouranthene / Pyrene ratios indicated that the source of PAHs compounds in the water of Shatt Al-Arab river was mainly pyrogenic and petrogenic , while in the sediments, it was pyrogenic only.