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Monsoon Rainwater Chemistry and Its Potable Status: a Case Study Monsoon Ainwater Chemistry and Its Potable Status: a Case Study from South-east Coastal Belt of Bangladesh from South-east Coastal Belt of Bangladesh

S.K.Saha
Environmental Science Discipline, Khulna University, Khulna 9208, Bangladesh

A.J.M.Saleh
Institute of Water Resource and Flood control, Bangladesh University of Engineering and Technology, Dhaka 1000

M.A. Jahid
Institute of Water Resource and Flood control, Bangladesh University of Engineering and Technology, Dhaka 1000

M.A.Rahman
Institute of Water Resource and Flood control, Bangladesh University of Engineering and Technology, Dhaka 1000

S. Naznin
Institute of Water Resource and Flood control, Bangladesh University of Engineering and Technology, Dhaka 1000

Uthpal Kumar
Environmental Science Discipline, Khulna University, Khulna 9208, Bangladesh

Abstract/ Executive Summary:

Major ion chemistry of rain water from a selected area has been determined. The rainwater is slightly acidic as in the case with rain waters globally. All major cations and anions are present in delectable amount. HCO3 - is the dominant anion in the study area and its concentration generally decreases subsequent showers. Such decrease in concentration also is noticed in case of other cations and anions. The influence of seawater in the chemistry of rain water is quite significant in the present study. Although at the beginning of the first rainfall event, bicarbonate ion predominates, its concentration gradually diminishes with the passage of time, but sometimes erratic values are noticed and even in the last fraction of a continuous rainfall. Most of the other cations and anions behave similarly to that of bicarbonate ion. Concentrations of various chemical constituents are not constant in local rainwater and it varies from rainfall event to event. It is also dependent on the various local meteorological parameters. Different calculated weight ratios such as SO42-/Na+ etc. are compared with seawater. The results indicate the influence of southern seawater to a great extent. Moreover, non-marine origin from the onshore such as dust particles, automobile exhaust, smoke etc. also contribute significant amount of the dissolved constituents in the rainwater. A household survey was conducted to know about the water using pattern of the study area. However the calculated major cations and anions are below the potability status of DoE standard which is not viable for human health.

Keywords: Monsoon, Rainwater, Rainwater chemistry, Bengal basin, Bangladesh.

Location: Pathargata Sadar, Badurtala, Char Lathimara, Kathaltali, Taluk Kathaltali and Kalipur villages

Start Date: 00-06-2003

End Date: 00-09-2003

Program Area: Crop-Soil-Water Management

Commodity: Rain water

Objectives:

In the Bengal basin due to the temperature effect, rain water expected to be near neutral. Very little information towards chemical composition of rainwater is available in Bangladesh part. In the present study, the rainwater chemistry were analyzed to highlights its potability status.

Methodology:

Patharghata and Kathaltali unions in Patharghata Upazila of Barguna District are studied for their monsoon rainwater chemistry. The samples have collected from Pathargata Sadar, Badurtala, Char Lathimara, Kathaltali, Taluk Kathaltali and Kalipur villages during June-September, 2003.

Prior to data collection, a reconnaissance survey has been conducted in different regions of the study area. A household survey was conducted through personal interview during June-September, 2003 to know the water using pattern of the study area.

A wide mouthed stainless steel pot was used to collect the rainwater sample which was filtered through Whatman paper (no. 42) immediately after collection to remove any particulate matter if any. The sample was transferred to clean and dried plastic bottles. The pH, EC, and TDS were measured at the field. The bottle was rinsed with sampled water during the collection of samples and then securely sealed with proper leveling and preserved for chemical analysis.

The laboratory analyses were done in Environmental Science Discipline laboratory of Khulna University.

Source of Information: Khulna University Studies, 7(2): 1-6, 2006

Article Link (Online Journal): KUS -05/36-211105

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The South Asian summer monsoon has a purely maritime origin and traverse with respect to India. In addition to bring an important source of moisture the monsoon winds also provide vast amount of sea salts which are well known cloud condensation nuclei. Admittedly, the present work is somewhat speculative in the context of Bangladesh. Much more research is needed to completely understand the complex nature of precipitation chemistry involved during the monsoon. From the chemical analysis of monsoon rainwater from the study area, the following conclusions can be drawn (i)Most of the rainwater has a tendency towards slightly acidic character (Av. pH 5.95) (ii) All major cations and anions are present in detectable amount. HCO3, SO-2 4 and Na+ are the predominant anion and cations in the studied sample (iii) Although in the beginning of the first shower, bicarbonate ion predominates, its concentration gradually diminishes with passage of time but sometimes erratic values are also noticed and ever in the fraction of a continuous shower, high bicarbonate concentration is noticed (iv) Most of the other cations and anions behave similarly as bicarbonate ion (v) Weight ratios of Na+ /SO-2 4 points out the unusual marine conditions (vi) The rainwater chemistry of the study area is below the range of a DoE standard. A concern over chemical point of view that acidic water as well as less natural quality is not suitable for human consumption. So it is an argent need to enrich the mineral constituents and alkali nature before advocating for drinking purpose.

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