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The research work titled “Spatio-temporal analysis of groundwater quality in
central Kerala” was carried out at the College of Agriculture, Vellayani during the period
2019 to 2021. The objectives set for the study were to analyze the inter-regional variation
in groundwater quality parameters over ten years using various multivariate and
geostatistical techniques in Alappuzha and Kottayam districts. Also to analyze the
interrelationship between the water quality parameters and groundwater levels and to map
the locations using the GIS package. 26 location in the Alappuzha district and 22 locations
in the Kottayam district was selected for the study. Secondary data on fourteen
groundwater quality parameters (Electrical conductivity (EC), pH, Total Hardness (TH),
Total alkalinity (TA), anions; CO3, HCO3, SO4, NO3, Cl, F, and cations; Na, K, Ca, and
Mg) and groundwater levels were collected from Central Ground Water Board for ten years
(2010-2019).
On the secondary data of fourteen quality parameters, descriptive statistics such as
mean, standard deviation, and coefficient of variation were investigated. The parameters
were compared with drinking and agricultural irrigation guidelines defined by the Bureau
of Indian Standards (BIS) and the World Health Organization (WHO). All parameters in
the Alappuzha district, with the exception of fluoride (F-) in the location Thaikkattusseri
(F-: 2.86 mg/L), were confirmed to be within BIS and WHO limits. Two parameters, total
alkalinity (TA) and potassium (K+) were found to be over the standard limits in the
Kottayam District. In Vaikkom, the TA was higher than the norm (BIS: 300 mg/L), while
in three locations, Changanasserry, Ezhinjillam, and Thiruvarpu, the K+ was higher than
the limit (WHO: 10 mg/L). All of the other parameters were determined to be within the
BIS and WHO guidelines.
Principal component analysis (PCA) was carried out for the construction of the
Principal component weighted Water Quality Index (WQI). In the Alappuzha district, four
principal components contributed 82.71 percent of the total variation. In the Kottayam
district, three principal components accounted for 86.06 percent of the total variation.
Based on the WQI, the locales in Alappuzha districts are grouped into five: very low, low,
medium, high, and very high. The Index is found to be increasing with the parameters EC,
TH, HCO3, and TA, and the ‘very low’ category had mean value for the parameters 58.8
μS/cm, 15.64 mg/L, 11.28 mg/L, and 7.39 mg/L respectively, the ‘low’ category recorded
the mean values 159.95 μS/cm, 44.5 mg/L, 45.52 mg/L, and 35.95 mg/L respectively. The
‘medium category had the mean values 200.17 μS/cm, 69.45 mg/L, 78.52 mg/L, and 55.56
mg/L parameter levels respectively. For the category, ‘high’, mean values were 252.65
μS/cm, 110 mg/L, 164.11 mg/L, and 182.23 mg/L respectively for the parameters. In the
category ‘very high’, recorded mean values for these parameters were 297.39 μS/cm, 98.21
mg/L, 116.82 mg/L, and 89.36 mg/L respectively.
In the Kottayam district with a CV of 41.38 percent and a mean of 95.09, the
estimated WQI ranged from 17.88 in Kattanam to 161.14 in Cherthalai. WQI was found to
be below the mean value in 16 of the 26 locations. In the Kottayam district, the estimated
WQI varied from 22.04 in Narianganam to 300.48 in Vaikom, with a CV of 83.65 percent
and a mean of 94.78. WQI was found to be below the mean value in 15 of the 22 locations.
The Index is found to be increasing with the parameters EC, TH, HCO3, and TA, and the
‘very low’ category had mean value for the parameters 94.09 μS/cm, 21.21 mg/L, 17.73
mg/L, and 13.57 mg/L respectively, the ‘low’ category recorded the mean values 241.21
μS/cm, 55.27 mg/L, 36.28 mg/L, and 31.53 mg/L respectively. The ‘medium category had
the mean values of 374.02 μS/cm, 106.62 mg/L, 125.79 mg/L, and 89.99 mg/L parameter
levels respectively. For the category, ‘high’, mean values were 594.89 μS/cm, 109.34
mg/L, 41.6 mg/L, and 31.61 mg/L respectively for parameters. In the category ‘very high’,
recorded mean values for these parameters were 592.78 μS/cm, 211.88 mg/L, 297.5 mg/L,
and 201.39 mg/L respectively.
The interrelationship between water quality parameters and groundwater level was
studied using Pearson's correlation coefficient. In the Alappuzha district, the parameters
EC (-0.45), pH (-0.65), TH (-0.5), TA (-0.42), HCO3 (-0.42), and Ca (-0.51) had a
significant negative correlation with groundwater level. NO3 (0.33, p-value=0.1) was the
only parameter with a positive correlation but was found to be non-significant. In the
Kottayam district, a positive-significant correlation was present in parameters pH (0.75),
TA (0.22), SO4 (0.59), and Mg (0.6), and a negative significant correlation was present in
EC (-0.61), TH (-0.52), HCO3 (-0.48), Na (-0.54) and Ca (-0.46). The remaining parameters
were found to have a non-significant correlation.
The temporal change was analyzed employing the relative change in the level of
each parameter for ten years in selected districts. In the Alappuzha district, a positive
temporal increase was observed in all the parameters except pH over ten years. In the
Kottayam district, a considerable increase was observed in parameters TH, TA, HCO3,
SO4, F, and Mg and a decline in the levels of EC, pH, NO3, Na, K, and Ca.
Thematic map based on WQI and groundwater level (GWL) was prepared using
ArcGIS software version 10.4 for Alappuzha and Kottayam districts. Based on the thematic
maps, spatial distribution and variation of groundwater quality parameters and
groundwater level were drawn. In the Alappuzha district, both WQI and GWL maps were
categorized into ten classes. Nearing the various water bodies, WQI was recorded higher.
The locations bordered by the Pathanamthitta district had comparatively lower WQI. From
the GWL map, it was inferred that as the elevation of the district increased, the depth to
the water table was increasing. The change observed was according to the topography of
the district. In the Kottayam district, locations bordered by Alappuzha showed high WQI
value and the locations bordered by the Idukki district had comparatively less WQI. In
Kottayam also, depth to the water table showed an increasing trend with the elevation.
Spatial and temporal variations in the Alappuzha and Kottayam districts were
studied with the help of multivariate and geostatistical techniques. Both methods confirmed
the inter-regional and timely disparity of fourteen groundwater quality parameters and
groundwater level.

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