Bibliographical Research
2.6. Water Quality
2.6.3. Co-occurrence of Keywords
Bibliographical Research Chapter | 2
Indian Institute of Technology Guwahati Page | 27
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.
TH-2896_176104004
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.
Bibliographical Research Chapter | 2
Indian Institute of Technology Guwahati Page | 31
(a) (b)
(c)
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
TH-2896_176104004
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
CCME WQI 10
NSFWQI 10
Remote sensing 10
Bibliographical Research Chapter | 2
Indian Institute of Technology Guwahati Page | 33