Principal Component Analysis - The applicability of a Water Quality Index (WQI) as an assessmen

CHAPTER 4 RESULTS

4.3 Principal Component Analysis

Figure 4-12: PCA showing the water quality data from 1979 to 2018 for site 90194. The biplot explains the 83% variance in water quality data with a total of 66% variance explained in the first axis and 17% in the second axis

4.3.2. Calculation of PCA plots for site 90167

The PCA biplot in figure 4-13 explains a 72% variation between the water quality variables and time in site 90194. The first axis of the PCA explains the 44% variation for the differences in water quality variables and the second axis explained the 28% temporal variation of water variables.

We have observed that Ca²⁺, Mg²⁺, EC, SO42-, Cl^- were grouped and characterised by positive high PC values in 1983, 1985, 1986, 1990-1994, and 2003-2007 (Figure 4-13). There was a presence of a high concentration of Ca²⁺, Mg²⁺, EC, SO42-, Cl^- at site 90167 in the mid-1980s, mid-1990s, and mid-2000s (Figure 4-13). Potassium has positive PC values but is independent of Ca²⁺, Mg²⁺, EC, SO42-, Cl^- in its contribution to the water quality status of site 90167. High K⁺ concentration was present between 2005 to 2007 at site 90167. Nitrate/nitrite reflected a positive PC value but a negative PC loading to Ca²⁺, Mg²⁺, EC, SO42-, Cl^-, and K⁺ (Figure 4-13).

Nitrate/nitrite has a high concentration in 2006 and 2010-2018 and could be problematic to the water quality status if it is not monitored. pH reflected a negative PC loading to Ca²⁺, Mg²⁺, EC, SO42-, Cl^-, K⁺, and NO2-/NO3-. pH levels on site 90167 were high in 1996-1997, 2000-2002, 2008,

2009 and 2010-2018. The PCA indicated that the Crocodile-West River at site 90167 was impacted less by land-use activities in 1976 -1979 and 1980-1987 (Figure 4-13).

Figure 4-13: PCA showing the water quality data from 1976 to 2018 for site 90167. The PCA explains the 72% variance in water quality data with a total of 44% variance explained in the first axis and 28% in the second axis

4.3.3. Calculation of PCA plots for site 90203

The PCA biplot in figure 4-14 explains an 86% variation between the water quality variables and time in site 90203. The first axis of the PCA explains the 47% variation for the differences in water quality variables and the second axis explained the 38% temporal variation of water variables (Figure 4-14). The Ca²⁺, Mg²⁺, EC, SO42-, Cl^-, and K⁺ are grouped and characterised by positive high PC 1 values and pH has a strong loading in the positive PC 1 plane (Figure 4-14).

Nitrate/nitrite and phosphate reflected negative loading to pH, Ca²⁺, Mg²⁺, EC, SO42-, Cl^-, and K⁺ (Figure 4-14). The PCA analysis indicated that the concentration of Ca²⁺, Mg²⁺, EC, SO42-, Cl^-, and K⁺ were highest in 1991-1995 and 2003 while the concentration of pH and NO3-/NO2- and

PO43- were highest in 1996, 1999, 2002, 2009, and 2013- 2018. Site 90203 was impacted minimally by natural and land-use activities in 1985-1989, 1990, 2004-2008, and 2010-2012 (Figure 4-14).

Figure 4-14: PCA biplot showing the water quality data from 1985 to 2018 for site 90203.

The PCA biplot explains the 86% variance in water quality data with a total of 47% variance explained in the first axis and 38% in the second axis

4.3.4. Calculation of PCA plots for site 90204

The PCA biplot in figure 4-15 shows an 87% variation between the water quality variables and time in site 90203. The first axis of the PCA biplot explains the 71% variation for the differences in water quality variables and the second axis explained the 16% temporal variation of water variables in site 90204 (Figure 4-15). The water variables Ca²⁺, Mg²⁺, EC, SO42-, Cl^-, and K⁺ are grouped and characterised by positive high PC 1 values. Nitrate/nitrite, ammonia, and phosphate reflected negative loading to Ca²⁺, Mg²⁺, EC, SO42-, Cl^-, and K⁺ (Figure 4-15). The PCA biplot explains a high concentration of Ca²⁺, Mg²⁺, EC, SO42-, Cl^- and K⁺ in 1991-1995, 2002, 2003, 2007 and 2015 and high concentration of pH, NO3-/NO2- and PO43-in 1994, 1996, 1997, 1999, 2000, 2001, 2009 and 2012-2018. Site 90204 was impacted the least by natural and land-use activities in 1984, 1986-1988, 2004, 2006, 2008 and 2010-2011 (Figure 4-15).

The negative PC loading of pH and NO3-/NO2-is greater than the PC loading of PO43-and NH3

which was indicative that the pollution from irrigation return flow from fertilisers from agricultural activities contributed more than the pollution from untreated effluent from informal settlements and treated wastewater treatment works (Figure 4-15).

Figure 4-15: PCA biplot showing the water quality data from 1980 to 2018 for site 90204. The PCA biplot explains the 87% variance in water quality data with a total of 71% variance explained in the first axis and 16% in the second axis

4.3.5. Calculation of PCA plots for site 90233

The PCA biplot in figure 4-16 explains an 87% variation between the water quality variables and time. The first axis of the PCA biplot explains the 71% variation for the differences in water quality variables and the second axis explained the 16% temporal variation of water variables of Crocodile-West River at site 90233 over time. Calcium (Ca²⁺), electrical conductivity (EC), sulphate (SO42-), phosphate (PO43-), chloride (Cl^-), nitrate/nitrite (NO3-/NO2-), magnesium (Mg²⁺), pH, and potassium (K⁺) are grouped and characterised by positive high PC 1 and PC 2 values.

on site 90233 of the Crocodile-West River but are not influenced by each other. The water quality at site 90233 was equally influenced by a combination of natural and anthropogenic activities.

The PCA analysis showed that NO3-/NO2-, PO43-, Mg²⁺, and Ca²⁺ were dominant pollutant in 2009 and 2012-2018. EC, Cl^-, SO42-, pH, and K⁺ were dominant elements in 1992, 1993, 1998, 1999, and 2007 while NH3 was the dominant element in 1997, 2000, 2006, 2008, and 2010-2011. Site 90233 was impacted the least by the natural and anthropogenic activities in 1991, 1994-1996, and 2002-2005.

Figure 4-16: PCA biplot showing the water quality data from 1990 to 2018 for site 90233. The biplot explains the 74% variance in water quality data with a total of 43% variance explained in the first axis and 31% in the second axis

4.3.6. Calculation of spatial and temporal trends in PCA biplot for all sites

The PCA biplot figure 4-17 explains the variation between the water quality variables and different sites. The first axis of the PCA indicated 75% variation and second axis indicated 14% variation of water quality variables in all the different sites during the years surveyed. The analysis of PCA biplot figure 4-17 explains a high concentration of NO3-/NO2- and K⁺ in site 90194 in the 1980s, 1990s, 2000s and 2010s and only high concentrations of PO43- and NH3 in the 1980s. Site 90167

had high concentration of Cl^- and pH in the 1970s, 1980s, 2000s and 2010s which was like site 90204 and 90233.The PCA biplot showed that site 90204 had high concentration of PO43- and NH3 in the 1980s and high concentration of EC, Ca²⁺, Mg²⁺ and SO42- in the 1980s and 2010s (Figure 4-17). Site 90203 and site 90233 also had high concentration of EC, Ca²⁺, Mg²⁺ and SO42-

in the 1980s similarly to site 90204 but also had high concentration of EC, Ca²⁺, Mg²⁺ and SO42-

in the 1990s, 2000s and 2010s (Figure 4-17).

Figure 4-17: PCA biplot showing the water quality data from 1976 to 2018 for all sites. The PCA biplot explains the 89% variance in water quality data with a total of 75% variance explained in the first axis and 14% in the second axis

Dalam dokumen The applicability of a Water Quality Index (WQI) as an assessment tool for urban rivers : a case study in the Crocodile River (Halaman 78-85)