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Bibliographical Research

2.6. Water Quality

2.6.3. Co-occurrence of Keywords

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having the most influential publications, i.e., in terms of average normalized citations re- ceived, the journal of Human and Ecological Risk Assessment had the highest research signifi- cance, with an average normalized citation score of 4.35. Other journals such as Science of the Total Environment (3.91), Ecological Indicators (2.79), Journal of Environmental Management (2.32) and Water Research (2.27) are among journals with a considerable research signifi- cance in the domain of water quality indexing, with average normalized citation scores of more than 2.00. These journals do not possess a higher quantum of articles in this research domain but significantly contribute to the research.

WQI based on LULC and risk assessment

Some of the recent studies have shown the variation of water quality with respect to the changes in the land-use and land-cover patterns of different areas (Zhang et al. 2009; Singh &

Khan 2011; Srivastava et al. 2013; Wilson 2015; de Oliveira et al. 2017; Wang et al. 2018).

Modelling LULC patterns remains one of the major methods of adaptation. Also, some of the most recent literature has associated WQI with health risks, such as (Adimalla 2019; Adimalla

& Qian 2019; He & Wu 2019; Karunanidhi et al. 2020; Ustaoğlu et al. 2020; Wu et al. 2020).

These WQIs have primarily focused on drinking water guidelines and the health risks associ- ated with the consumption of water polluted with majorly heavy metals.

Groundwater quality indexing

Studies involving groundwater quality indexing specifically focused on assessing the hydro- geology of the study area, so that the groundwater can be rendered fit for drinking as well as irrigation purposes (Reza & Singh 2010; Saeedi et al. 2010; Vasanthavigar et al. 2010;

Mohebbi et al. 2013; Adimalla et al. 2018). Areas facing scarcity of surface water were the primary regions of focus, as they are entirely dependent on the local aquifers for meeting their water demands.

Surface water quality indexing

Indexing approaches involving surface waters involved a wider range of areas, compared to the groundwater studies (Varol & Şen 2012; Dede et al. 2013; Chang et al. 2015; Whittaker et al. 2015; Avigliano & Schenone 2016; Gao et al. 2016; Gopal et al. 2018; Wu et al. 2018). The studies involved research areas other than drinking, like assessing the water quality for nu- trients, thereby determining their eutrophication potential. Also, the surface waters included both freshwaters such as rivers, lakes, wetlands, etc. and marine waters such as seas and oceans (Jha et al. 2015).

Mathematical approaches

The development of WQIs based on mathematical approaches is the newest addition to the domain, as these methods did not involve subjective assessments. Instead, they were purely based on mathematical models. Some of the models involved in the research of water quality indexing include relational method or statistics (Srivastava et al. 2011; Yan et al. 2016; Tian et al. 2019), geographically variable (Dunnette 1979; Melloul & Collin 1998; Cude 2001; De Rosemond et al. 2009), multivariate statistics (Melloul & Collin 1998; Howladar et al. 2018;

Rana et al. 2018; Khalid 2019; Kükrer & Mutlu 2019; Patil et al. 2020), probability and fuzzy approach (Nasiri et al. 2007; Lermontov et al. 2009; Song & Kim 2009; Gazzaz et al. 2012;

Yaseen et al. 2018), and finally information entropy (Amiri et al. 2014; Fagbote et al. 2014;

Adimalla et al. 2019; Islam et al. 2020b; Rao et al. 2020; Ukah et al. 2020).

Bibliographical Research Chapter | 2 Indian Institute of Technology Guwahati Page | 29 Fig. 2. 5. Relevant keywords that have appeared in the published literature in the domain of water quality indexing.


Fig. 2. 6. Association of keywords with different clusters.

Areas of research active in various countries

According to Fig. 2. 7, it was observed that India, Malaysia, and Iran have become active in the domain of research on water quality indexing, thus implying that developing countries are now more active in the research involving water quality. Furthermore, it was observed that while India and Iran primarily focused their research on groundwater and its suitability for drinking, Malaysia focused on aquaculture and river pollution and quality involving rejuve- nation of river water.

More quantitative estimations of the author keywords have been presented in Table 2. 2.

It was observed that keywords such as “Water quality index”, “Water quality”, and “Ground- water” have been used predominantly. However, newer approaches for developing WQIs such as using “GIS”, “Principal component analysis”, “Cluster analysis”, “Health risk assessment”,

Multivariate analysis”, and “Factor analysis” are being used lately, which shows a gradual yet effective shift in the adaptation of rational methods rather than employing subjective analysis for developing WQIs.

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(a) (b)


Fig. 2. 7. Research areas and countries active in water quality indexing.

Table 2. 2. Summary of main keywords in water quality index research.

Keyword Occurrences

Water quality index 650

Water quality 340

Groundwater 137

WQI 108

Drinking water 53

GIS 53

Principal component analysis 51

Surface water 47

Eutrophication 44

Physicochemical parameters 42

Heavy metals 37

Hydrogeochemistry 34

Cluster analysis 33

Irrigation 33

Health risk assessment 23


Multivariate analysis 21

River 21

Factor analysis 20

Spatial distribution 20

Nutrients 19

Phytoplankton 19

India 17

Land use 17

Fuzzy logic 16

Quality rating 16

Artificial neural network 15

Statistical analysis 15

Risk assessment 14

Iran 13

Malaysia 13

Surface water quality 13

Aquaculture 12

Groundwater quality index 12

Irrigation water quality 12

Multivariate statistical analysis 12

Trophic state index 12

Correlation analysis 11

Discriminant analysis 11

Macroinvertebrates 11

Major ions 11

River pollution 11

Salinity 11

Sensitivity analysis 11

Urbanization 11



Remote sensing 10

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