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Spatio-seasonal Variations of Salinity and Associated Chemical Properties in the Middle Section of Karnaphuli River Water, Chittagong, Bangladesh Using Laboratory Analysis and GIS Technique

Sajal Roy
Department of Soil Science, Faculty of Biological Sciences, University of Chittagong, Chittagong-4331, Bangladesh

Md. Akhtaruzzaman
Department of Soil Science, Faculty of Biological Sciences, University of Chittagong, Chittagong-4331, Bangladesh

Biswajit Nath
Department of Geography and Environmental Studies, Faculty of Biological Sciences, University of Chittagong, Chittagong-4331, Bangladesh

Abstract/ Executive Summary:

This research was performed to assess the concentration of cations and anions associated with salinity of different sampling locations (SL) in the middle section of Karnaphuli river (KR) water in two seasons. The mean values of pH and electrical conductivity (EC) of all the SL were found to be 7.23 and 3.74 mS/cm in pre-monsoon while 6.87 and 1.04 mS/cm in monsoon. The average values of chloride, bicarbonate, sulfate and phosphate were found to be 3.50, 1.31, 3.85 and 1.08 folds higher in pre-monsoon compared to monsoon as confirmed through the laboratory analysis. In contrast, the mean contents of calcium, magnesium, potassium and sodium in pre-monsoon were found to be 2.16, 3.13, 2.54 and 2.84 times higher compared to the monsoon period. The values of all parameters among the SL differed significantly (p<0.05) in the two seasons. In the ArcGIS Spatial analyst tool, Surface interpolation technique of Inverse Distance Weighted (IDW) method was further utilized to get the variations of KR water. Moreover, the results of this study will be helpful for river management planners to take early protection from further deterioration of the quality of KR water to certain extent.

Keywords: Anion, Cation, Karnaphuli river, Monsoon, Pre-monsoon, Salinity, Sampling location

Location: Karnaphuli River Water, Chittagong, Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Water salinity, Water management

Objectives:

Therefore, the objectives of this study are to determine the pH, EC, concentrations of cations (e.g., Na⁺ , K⁺ , Ca²⁺ and Mg²⁺) and anions (e.g., Cl⁻ , SO₄ ²⁻, CO₃ ²⁻, HCO₃ ⁻ and PO₄ 3- ) from the MSKR water collected from different SL in two different seasons (pre-monsoon and monsoon) of the year 2018.

Methodology:

Study Area: The KR is strongly influenced by the tidal action in its estuary part which meets with the BOB in the south. The KR is recognized as the most important and largest river in Chittagong. The total length of KR is 270 km, where its mouth meets with the Bay of Bengal and its source location is in Saitah, Mizoram, India. Karnaphuli or Khawthlangtuipui (in Mizo, meaning “western river”), is the largest and considered as the most important river in Chittagong and the Chittagong Hill Tracts. The KR divides the Chittagong district into two parts, one is confined with the city and port in the meandering section of the KR and another is the heavy industrial area. The Chittagong city is mostly concentrated with urban areas located in the western bank of KR with a population estimated over 5.02 million and predominantly they depend on the KR water. The maximum and minimum temperature is above 35⁰ and 24.5⁰ from February to November. The Chittagong division is situated in the eastern parts of Bangladesh which is covered by hills with north-south trending folded mountain range. The surface geology of the area consists of beach and dune sand formation and valley alluvium and colluvium type. In the present study, very specific area is considered which is middle section of KR and is referred to MSKR, because of its being directly influenced by the several heavy industrial wastes and nearby agricultural runoff into the water. The aquatic life of the KR is under threat due to the pollution and oil spill leakage by the tankers in different times that caused several environmental degradations. The MSKR extents from 22º15'45" N to 22º20'20" N latitude and 91º47'35" E to 91º52'15" E longitude approximately with area of only 9.53 km² . Shows location of MSKR along with locations of WS used in this study. Water Sample Collection, Measurement Process and Laboratory Analysis: The present study was carried out in the MSKR where a total of 60 WS were collected from ten SL. From each station, three samples were collected by simple random sampling method and considered to get the mean values. All the SL are represented. The first SL was started from the locality called Avoymitra ghat and continued toward the confluence of sea which ended beside Super Petro Chemical Private Ltd. industry at SL 10. The WS were collected in plastic bottles in two different seasons of the year including GPS measurements of the same points, one in pre-monsoon (April) and another in monsoon (July). Statistical Data Analysis, Interpretation and GIS Mapping: To determine the specific differences between pairs of means of the obtained results, the Duncan’s Multiple Range Test (DMRT) method was performed by using statistical packages for social sciences (SPSS version 16). The standard deviation and correlation analyses were then performed in the same software.

Source of Information: International Journal of Environmental Science and Development, Vol. 11, No. 8, August 2020

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

It was evident from the present study that the salinity level, as well as the concentration of cations and anions except phosphate in MSKR water, increased with the progressing of distance towards the confluence of the river where it meets with the sea (BOB). The two different season-based major parameters maps including other associated cations and anions result clearly represent the spatio-seasonal variation of MSKR water. The concentrations of major cations and anions varied significantly and it was observed in the descending order of concentration: Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ and Cl⁻ > HCO₃ ²⁻ > SO₄ ²⁻ > PO₄ ³⁻ in both pre-monsoon and monsoon seasons. The higher concentration of these parameters in pre-monsoon compared to monsoon season was also clearly evident which may be due to the dilution effect of the river water in the monsoon period. Moreover, statistical analyses also support the salinity and its associated cations and anions which were found strongly correlated (1-tailed 0.05 level and 0.01 level significant) each other. The present study further suggests more SL points consideration, multi-seasonal and multi-year investigation as well as the study of entire KR channel in future to know the KR water variability in detail with the aid of GIS and remote sensing techniques.

Knowledge Management: Journal