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Environmental Study on a Coastal River of Bangladesh with Reference to Irrigation Water Quality Assessment: a Case Study on Shailmari River, Khulna

Md. Muhyminul Islam*
Tropical Hydrogeology and Environmental Engineering (TropHEE), Technische Universitaet Darmstadt, Darmstadt, Germany

Israth Rabeya
Environmental Science Discipline, Khulna University, Khulna, Bangladesh

Nazia Hassan
Environmental Science Discipline, Khulna University, Khulna, Bangladesh

Sadhon Chandra Swarnokar
Environmental Science Discipline, Khulna University, Khulna, Bangladesh

Masudur Rahman
Environmental Science Discipline, Khulna University, Khulna, Bangladesh

Mosummath Hosna Ara
Chemistry Discipline, Khulna University, Khulna, Bangladesh

Abul Kalam Azad
Environmental Science Discipline, Khulna University, Khulna, Bangladesh

Abstract/ Executive Summary:

Water quality is the critical environmental determinant that influences agricultural production and therefore, the economy that solely depends on its agricultural productions. Batiaghata Upazilla is one of the major crop productive areas of Khulna region and the agricultural production here largely depends on the natural water of the Shailmari River system around it. The present study was conducted to assess the suitability of this coastal river water for irrigational use. 66 water samples were collected during this study in three consecutive agricultural seasons, viz., pre-monsoon (22), monsoon (22) and post-monsoon (22) from 11 sampling stations within the river system considering the high (11) and ebb (11) tides for each station. Standard methods were followed throughout the study period for the collection of the samples and analysis of major physicochemical parameters (pH, EC, TDS, salinity, Na, K, Ca, Mg, Cl, HCO3, SO4, NO3 and PO4). Hydrochemical characterization using Piper trilinear diagram shows that the water of the river system is Na-Cl dominated saline water type in pre-monsoon, whilst most of the samples of the river and the connected channel are characterized as freshwater of Ca-Mg-Na-HCO3 and Ca-Na-MgHCO3 types in monsoon and post-monsoon respectively. The calculated values of chemical indices like SAR, %Na, KI, PI and MH using the results of the analysed parameters indicate that the river water is chemically unsuitable for use in irrigation during pre-monsoon, while in the monsoon and post-monsoon the river water is within good to the permissible limit for the use in the agricultural fields. However, high %Na, KI and MH values with high salinity of the channel water limit its use in agricultural applications in monsoon and post-monsoon. The USSL (United States Salinity Laboratory) diagram depicts that the river water is C4-S4 type with very high salinity and sodium content in pre-monsoon, while in other seasons the water is mostly C1-S1, C2-S1 or C2-S2 types (low to moderate salinity and sodium) in the river. Wilcox diagram shows that the river water is “suitable” for irrigation during monsoon and post-monsoon as most of the samples range within “Excellent to Good” and “Good to permissible” categories, while it is “unsuitable” for crop irrigation during pre-monsoon when SAR (Sodium Adsorption Ratio) and EC (Electrical Conductivity) values of the water reach to their peaks.

Keywords: Coastal River, Irrigation, Suitability, Salinity, SAR, % Na, FAO, Piper, USSL, Shailmari, Khulna

Location: Shailmari River, Khulna, Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Water quality

Objectives:

Therefore, appointing a befitting irrigation water source which could guarantee the safe and required amount of crop production throughout the year is of prime concern in this locality. Studies on the water quality of the groundwater and Rupsha-Kazibacha River systems around Batiaghata have already been done, but information regarding the irrigation water quality of the Shailmari River system, which passes through this upazilla and supports the irrigation-based agriculture of the area, is vague.

Methodology:

2.2. Sampling, Preservation, and Preparation Prior selecting the water sampling sites from a well-studied reconnaissance survey, samples were collected from 11 sampling stations based on the characterizing features of the locations along the river. Coordinates of the sampling stations were extracted in the field by using a GARMIN Geographic Positioning System (GPS) device. Samples were collected from the midstream of the river by using an engine boat and following the guidelines of standard methods [20]. Samples for cationic and anionic analyses were collected in separate 500 ml PET bottles and cationic samples were preserved by adding HCl (to pH ~ 2). Then samples were carried to the laboratory and preserved at 4⁰C prior to laboratory analysis. Following the aforesaid procedures, samples were collected for three agricultural seasons namely Pre-monsoon (May, 2014), Monsoon (August, 2014) and Post-monsoon (October, 2014) from the similar stations throughout the study period. Tidal cycles were considered carefully and therefore, 22 samples were collected during each sampling seasons considering both of high and low tides for each station. The number of samples in total was 66.

2.3. In-Situ and Laboratory Measurements Physical parameters- pH, Dissolved Oxygen (DO), Total Dissolved Solid (TDS), and Electrical Conductivity (EC) were measured in-situ using portable pH meter, DO meter (HACH sensION156 portable) and EC/TDS meter (HANNA H1-9635) after calibration [20]. All other major ions (Na+, K+, Ca2+, Mg2+, HCO3 −, Cl−, NO3 −, 2 SO4 − and 3 PO4 − ) were analysed following the standard procedures. HCO3 − was determined tritimetrically with HCl at the sampling sites using methyl orange indicator.Sodium (Na+ ) and potassium (K+ ) were measured using GENWAY flame photometer (Model No. PEP 7 and PEP 7/C). Tritimetric methods were used for determining calcium (Ca2+), magnesium (Mg2+) and chloride (Cl−). UV-visible spectrophotometer was used to detect sulphate ( 2 SO4 −), ortho-phosphate ( 3 PO4 − ) and nitrate ( NO3 −) in the water samples [20]. Replicate analysis of blank, standards and water samples were performed during the study to achieve the precision and accuracy and kept within ±5% by repeatative anlysis after calculating the ionic balance errors.

2.4. Water Quality Indices and Classification Methods Different water quality parameters like Total Hardness (TH), TDS classes were used in the study to assess the quality of the water. In agriculture, water quality is an important criterion for the development of a successful and sustainable irrigation scheme. In order to assess the suitability of the river water for irrigation use, various parameters like percentage of sodium (Na%), sodium absorption ratio (SAR), residual sodium carbonate (RSC), permeability index (P.I.), Kelly’s index (KI), Magnesium Hazard (MH) were used in the study using the mentioned equations. Na% is a measure of salinity hazard in water and together with EC is useful in classifying the irrigation water. SAR expresses the sodium or alkali hazard in irrigation water and quantifies the relative proportions of sodium to calcium and magnesium. The amount of bicarbonate and carbonate in excess of alkaline earth metals (Ca and Mg) also affects the irrigation water quality and is quantified by calculating the residual sodium carbonate (RSC) content of the water. Permeability of the soil depends also on the quality of the irrigation water and permeability index (PI) classifies the water-based on concentrations of sodium, calcium, magnesium and bicarbonate in the water to assess its suitability for irrigation use. KI is a measure of classification of the water for irrigation and sodium is measured against calcium and magnesium to calculate this parameter. The excess of magnesium concentration in water is harmful for soil and affects plant growth. MH is used to evaluate the quality of the water-based on the quantity of magnesium in the irrigation water. Graphical methods related to water quality classifications were used in this study to further evaluate the irrigation water quality of the river system. A Piper diagram was applied to find the water classes and its dominating ions in different seasons and stations. Wilcox diagram and U.S Salinity Laboratory (USSL) classifications diagram were also applied to find the seasonal variability and suitability of the river water for irrigation.

Source of Information: Journal of Geoscience and Environment Protection, 2016, 4, 41-64 ISSN Online: 2327-4344 ISSN Print: 2327-4336

Article Link (Online Journal): http://dx.doi.org/10.4236/gep.2016.410003 R

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The results of the study on the irrigation water quality of the Shailmari River and its adjacent channel clearly demonstrate that the hydrochemistry of the river system is highly variable to the seasonal changes and therefore, the water quality also. In premonsoon, the river water is highly concentrated with major ions that exhibit high salinity (high EC). Na+ and Cl− dominate the major cationic and anionic chemistry in premonsoon, showing an order of Na+ > Mg2+ > Ca2+ > K+ and Cl− > 2 SO4 − > HCO3 − > NO3 − > 3 PO4 − accordingly. Higher load of the ions may be attributed to the seawater mixing coupled with limited freshwater inflow, wreathing inputs and anthropogenic discharges into the water bodies. Monsoon and post-monsoon precipitation impose a freshening effect (dilution) on the river water chemistry that leads to reorder the ionic pattern of the river water in these seasons. The cationic order of Ca2+ > Na+ > Mg2+ > K+ and Na+ > Ca2+ > Mg2+ > K+ was found in monsoon and post-monsoon respectively, while the anions showed an order of HCO3 − > Cl− > 2 SO4 − > NO3 − > 3 PO4 − and HCO3 − > 2 SO4 − > Cl− > NO3 − > 3 PO4 − in the consecutive sampling seasons. During pre-monsoon, the river water is Na-Cl type, while in monsoon and post-monsoon the water becomes Ca-Mg-Na-HCO3 and Ca-Na-Mg-HCO3 type, respectively, showing temporary hardness. Irrigational suitability of the river water in terms of calculated values of SAR, %Na, RSC, PI, KI and MH together with TDS, NO3-N and pH classes was assessed for the three sampling seasons which restricted the use of the river water for irrigation in pre-monsoon. The values were found within the limits of suitability for irrigating the crops during rest of the two agricultural seasons. However, higher KI and MH values with high salinity make it doubtful to use the channel water even in the monsoon and post-monsoon seasons. USSL and Wilcox diagrams were applied to verify the results and found the river water unsuitable for use in pre-monsoon, complying with the results extracted from the calculated parameters for this and also other studied seasons. This river system supports the regional agricultural production of this area and plays a pivotal role in the livelihood of a large number of people dependent on agricultural production. The use of high saline and sodic water in the early monsoon might deteriorate soil fertility and agricultural production in the long run. Besides, domestic and industrial waste and wastewater discharge adversely affect the water chemistry of the river system that in turn degrading the irrigation water quality, posing a potential menace to the agricultural communities. Therefore, from the study, it could be concluded that proper water management strategies with the inclusion of long-term river water quality monitoring, awareness building against waste dumping, finding alternative sources and efficient methods for irrigation would ensure the sustainable agricultural production of this locality and this study would be the basis of future studies for such purposes.

Knowledge Management: Journal