Sustainable Water Resources Management https://doi.org/10.1007/s40899-018-0230-z
ORIGINAL ARTICLE
Impact of landuse on groundwater quality of Bangladesh Saleem A. Salman1 · Shamsuddin Shahid1 · Morteza Mohsenipour1 · Hamid Asgari1 Received: 20 September 2016 / Accepted: 30 January 2018 © Springer International Publishing AG, part of Springer Nature 2018
Abstract Groundwater pollution is a major concern in water resources management across the world. The objective of this study is to characterize groundwater quality and identify the impact of landuse on groundwater quality of Bangladesh. Total of 113 groundwater samples, collected from shallow aquifers at different locations of Bangladesh were analysed to estimate eight standard groundwater quality indices namely, sodium absorption ratio (SAR), soluble sodium percentage (SSP), residual sodium bi-carbonate (RSBC), permeability index (PI), total hardness (TH), magnesium adsorption ratio (MAR), Kelly’s ratio (KR) and total dissolved solids (TDS). The results showed that the SAR in groundwater of Bangladesh varies between 1 and 818, SSP between 9 and 99%, RSBC between − 13 and 719 meq/L, PI between 21 and 112%, TH between 233 and 19400 meq/L, MAR between 5 and 74%, KR between 0.06 and 135 meq/L, and TDS in the range of 51–15200 mg/L. Significant differences in groundwater quality indices between agricultural and forest lands were observed. The study revealed that higher amount of total dissolved salt in groundwater was due to sea water intrusion into the coastal aquifer. Relation between agriculture and groundwater quality suggests that though the nitrate concentration in groundwater was less than permissible level, it might increase in future due to extensive use of nitrogen-based chemical fertilizers in agriculture. Keywords Groundwater quality · Landuse · Statistical analysis · Water quality indices · Geographical information system · Bangladesh
Introduction Groundwater sources provide 43% of total water used for irrigation and 40% of the total drinking water globally (Siebert et al. 2010; Shahid et al. 2017). In many countries of the world, it is the only source of potable water (Margat and Van der Gun 2013). In some North African and Middle Eastern countries, groundwater is sole source of all kinds of water supply (NGWA 2013). The present trend in groundwater use indicates that it will continue to play a crucial role in global water security, agro-economy and people’s livelihood (Shahid et al. 2014; Singh et al. 2015). However, there is a growing concern in the recent years on groundwater contamination due to anthropogenic activities. Rapid population growth, economic development and urbanization have directly or indirectly affected groundwater quality in many countries of the world (Lutz et al. 2010). Sea water intrusion * Morteza Mohsenipour
[email protected] 1
to coastal aquifers due to unsustainable management of groundwater resources is another major factor of groundwater contamination (Comte et al. 2016). As groundwater is the major the source of clean water supply, identification of the causes of groundwater pollution is very important for protection of this precious resource. Groundwater quality includes the physical, chemical, and biological qualities of groundwater (Todd and Mays 2005). Temperature, turbidity, colour, taste, and odour are the physical parameters of groundwater quality. Since groundwater is usually colourless, odourless, and without specific taste, the main concern with groundwater is its chemical and biological qualities. The pollutants responsible for degradation of groundwater quality can be classified into two groups based on their source namely, natural pollutants and anthropogenic pollutants. Groundwater may be contaminated by numerous anthropogenic activities (Thamer and Bujang 2004). Pollutants generated by human activities on the land surface seep into the earth and contaminate groundwater resources. Therefore, landuse has a direct link to groundwater contamination.
Faculty of Civil Engineering, Universiti Teknologi Malaysia, Skudai, 81310 Johor Bahru, Malaysia
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Number of studies has been conducted to assess the impacts of landuse on groundwater quality (Healey 1999; Chen et al. 2003; Gupta et al. 2005; Kristin and Richard 2005; Zampella et al. 2007; Joarder et al. 2008; Chenini and Khemiri 2009). Healey (1999) used correlation analysis to measure the inter-relationship between surface and groundwater quality. Kristin and Richard (2005) predicted groundwater nitrate concentration from landuse in Nantucket Island using samples from 69 wells. They used Tobit and logistic regressions to estimate the effect of agricultural landuse on nitrate concentrations in groundwater. Zampella et al. (2007) assessed the relationships between the chemical properties of groundwater and landuse patterns in the Mullica river basin to estimate the thresholds at which significant changes in water quality occurred. The major objective of the present study is to assess the impact of landuse on groundwater quality in Bangladesh. Agriculture shares a major portion of gross domestic product (GDP) and plays an important role in economy and livelihood of Bangladesh. The growth of agriculture in recent decades has helped the country to achieve food security. However, excessive use of nitrogen based fertilizes has increased the risk of groundwater pollution at the same time (Mohsenipour et al. 2015). It is expected that characterization of groundwater quality and assessment of the impacts of landuse on groundwater quality would help in mitigating planning towards protection of groundwater resources from contamination.
Area of the study Geographically, Bangladesh is located between latitude: 20°34′N–26°38′N and longitude: 88°01′E–92°41′E. Rainfall in Bangladesh varies from 1600 mm in the northwest to more than 4400 mm in the northeast. About 75% of rainfall occurs during monsoon (Shahid 2010). Groundwater is mainly recharged by rainwater during monsoon. Therefore, groundwater table comes very near to surface in the end of monsoon and makes it highly vulnerable to pollution.
Data and methodology Groundwater quality data, collected by British Geological Survey (BGS) at 113 locations distributed over the country were downloaded from BGS website. Location of data points in the map of Bangladesh is shown in Fig. 1. The data were re-arranged for necessary statistical analysis using statistical software. Data were compiled in such a way that they could also be used for producing map of different groundwater quality indices using geographical information system (GIS). The
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Sustainable Water Resources Management
Fig. 1 Location of groundwater sample collection points
methods used in the proposed research are described briefly in the following section. Empirical rule was used to assess the quality of groundwater sample data. The empirical rule states that approximately 95% of the measurements are within the interval of mean ± two standard deviation. In the present study, all the groundwater data were found within this limit. A total of eight standard water quality indices namely, sodium absorption ratio (SAR), soluble sodium percentage (SSP), residual sodium bi-carbonate (RSBC), permeability index (PI), total hardness (TH), magnesium adsorption ratio (MAR), Kelly’s ratio (KR) and total dissolved solids (TDS) were calculated from groundwater quality data. Following equations were used to calculate various groundwater quality indices:
SAR = (
SSP =
Na+ Ca2+ +Mg2+ 2
(1)
)1
2
( − ) Na + K+ × 100
Ca+2 + Mg+2 + Na+ + K+
(3)
RSBC = HCO−3 − Ca+2 PI =
( + ) Na + HCO−3
Ca+2 + Mg+2 + Na+
( ) TH = Ca+2 + Mg+2 × 50
(2)
× 100
(4) (5)
Sustainable Water Resources Management Table 1 Summary of groundwater quality indices at 113 locations of Bangladesh Parameter SAR SSP RSBC PI TH MAR KR TDS
Max (mg/L) 818 99 719 112 19,400 73 134 15,200
Min (mg/L) 1 9 − 13 21 233 5 0.06 51
Mean (mg/L) 19.4 45.2 214.5 59.4 3785.1 31.1 2.9 764.8
MAR =
Std. dev (mg/L)
KR =
81.7 23.2 151.6 23.6 3306.1 13.5 13.1 1824.7
Mg+2 × 100 Ca+2 + Mg+2
(6)
Na+ Ca+2 + Mg+2
(7) (8)
[ ] TDS = 0.64 × EC × 106 (mmohs/cm)
The inverse distance interpolation method was used for the mapping of groundwater quality indices. Geostatistical analysis tool of ArcMap 9.1 (ESRI 2004) was used for this purpose. Inverse distance method is a standard approach
TDS
SAR
RSBC
PI
MAR
SSP
TH
KR
Fig. 2 Box plots of different groundwater quality indices in Bangladesh
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which is widely used for preparation of surface map from point measurements. Multiple-regression and non-parametric correlation analyses were conducted among various quality parameters to identify the influence of different factors on groundwater quality. The aim of those analyses was also to identify the causes of groundwater quality hazards. Furthermore, non-parametric Mann–Whitney test was conducted among the sets of groundwater quality data collected from different landuse zones to decipher if there are any differences in groundwater quality due to landuse.
Impacts of landuse on groundwater quality Groundwater samples were divided into three classes namely, urban, agriculture and forest according to their location. The Mann–Whitney test was conducted among two sets of data individually at a time to distinguish if there are any differences in groundwater quality indices among different zones. Obtained results are summarized in Table 2. The values in the table indicate the confidence level of rejection of null hypothesis of similar mean. The results show significant difference in groundwater quality indices at 90% level of confidence only between agriculture and forest lands. No significant difference between urban and agriculture lands was observed. Therefore, it can be remarked that agricultural activities have changed groundwater quality indices in Bangladesh.
Results and discussion Statistical analysis of groundwater quality indices The groundwater quality indices were calculated at all the 113 sampling locations. Obtained results are summarized in Table 1. It was found that the average TDS in the groundwater of Bangladesh is very high. Some of other indices like SAR and TH were also comparatively high in Bangladesh. The box plots of different groundwater quality indices are shown in Fig. 2. The box plots in the figure show that number of outliers in the positive direction for indices like TDS, SAR, RSBC, MAR and KR. This means extreme values of these indices in some locations. As the higher value of an index represents corresponding quality hazard, extreme values of these indices mean presence of corresponding groundwater quality hazards in some locations of Bangladesh.
Multiple regression and correlation analysis From the box plots, it can be observed that TDS is a major hazard in groundwater quality of Bangladesh. Therefore, multiple regression and correlation analysis among the constituents of TDS were carried out to find the major constituents of TDS and the cause of TDS hazard in groundwater quality of Bangladesh. All the constituents of TDS were used to find the best regression equation that describes the TDS. The obtained equation is given below:
TDS = 0.131 + 1.168 Cl− + 1.085 HCO3 − + 1.107 SO4 2− + 0.753 Na+ + 0.9687 Ca2+
(9)
+ 1.661 K+ Table 2 Confidence level (%) in the differences of groundwater quality indices among the landuse zones
Table 3 Correlation coefficients between various constituents of TDS
Landuse types
Groundwater quality indices
Agriculture and urban Agriculture and forest
TDS Ca2+ Mg2+ Na+ K+ HCO3− Cl− NO3−–N SO42−
TDS
SAR
SSP
PI
MAR
KR
91.6 –
– 99.4
– 99.3
– 98.2
– 92.8
– 99.3
TDS
Ca2+
Mg2+
Na+
K+
HCO3−
Cl−
NO3−–N
SO42−
1 0.17 0.68 0.99 0.73 0.07 0.99 0.01 0.08
1 0.46 0.06 0.17 0.57 0.09 0.09 0.13
1 0.59 0.75 0.28 0.65 0.07 0.21
1 0.69 − 0.03 0.99 − 0.02 0.05
1 0.09 0.71 0.32 0.12
1 − 0.05 0.13 − 0.03
1 − 0.02 0.11
1 0.11
1
Bold indicates significant at 95% confidence level
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Fig. 3 Spatial distribution of eight groundwater quality indices in Bangladesh
The regression Eq. (9) revealed that though nitrate is a major constituent of TDS, it is not a major cause of high TDS values in the groundwater of Bangladesh. Nitrate pollution of groundwater in agricultural land is a major concern in all over the world (Mohsenipour et al. 2014). However, agricultural activities have still not changed the
TDS in groundwater of Bangladesh. The correlation coefficients between different constituents of TDS are given l− are the main in Table 3. The table shows that N a− and C constituents of TDS in the groundwater of Bangladesh. As origin of NaCl is marine, it can be remarked that sea water
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intrusion in the coastal aquifer is the main cause of TDS or salinity hazard in Bangladesh.
Spatial distribution of groundwater quality indices Spatial distributions of groundwater quality indices in Bangladesh are shown in Fig. 3. The maps show that most of the groundwater quality index are very high in the southern coastal region of Bangladesh. Therefore, it can be remarked that groundwater quality hazards mostly occur in the coastal region of Bangladesh. This may be due to sea water intrusion into the coastal aquifers or may be due to intensive agriculture or other anthropogenic activities in the region.
Conclusion Groundwater quality data, collected from different locations of Bangladesh were used to map the spatial distribution of eight standard groundwater quality indices. The index values were analyzed using various statistical methods to assess the impacts of landuse on groundwater quality. The box plots of groundwater quality indices reveal outliers for some of the indices which indicate groundwater quality hazards in some locations. Spatial distributions of groundwater quality indices show that extreme values are mostly located in the southern coastal areas. Correlation analysis among the constituents of TDS revealed that sea water intrusion into the coastal aquifers is the cause of major quality hazards in the groundwater of Bangladesh (extreme values TDS). The differences in groundwater quality indices between agriculture and forest lands indicates that agricultural activity has changed the groundwater quality of Bangladesh. Although the results showed that nitrate is not responsible for high TDS, the differences in groundwater quality indices between agriculture and forest lands indicates that nitrogenbased chemical fertilizer used in agriculture can change the groundwater quality in Bangladesh in future.
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