4.3 Principal component analysis – elements
The data on the contents of arsenic, antimony and chromium in water (a – surface water; b – bottom water) and
bottom sediments (c – layer of 0-5cm; d – layer of 15-20cm) also underwent the PCA. For each analyzed
element, the data were collected into matrix X with 11 objects (samples) and 24 parameters (contents of both
forms of a given element in the three examined points; for each sampling point four samples were collected:
surface water, bottom water, bottom sediments from two layers, i.e. 0-5cm and 15-20cm). The data
preprocessing included their centering and standardization.
4.3.1
Arsenic
The obtained PCA results (PC1 and PC2 explained 33.48% and 26.05% of the data variance, respectively) show
that the biggest changes in the As(III) concentrations were observed in the surface water and upper bottom
sediment layer (0-5 cm) in the winter and spring months (January-April). For As(III) and As(V), no major
concentration changes were observed in the water and bottom sediments between May and July. On the other
hand, fluctuations in the arsenic concentrations were seen in the autumn months. When compared to the earlier
period, a significant change in the As(V) content in the surface and bottom water was found in September. The
greatest changes in the As(III) contents in the surface water and upper layer of the bottom sediments were
observed in November (Fig. 10).
(Fig. 10)
In the analyzed points, the As(III) concentrations in the surface water had a strong positive correlation. An
analogous situation was observed for As(V). A positive correlation for As(III) in the bottom water was observed
for sampling point 1 and 2. The As(III) concentration changes in the bottom water for sampling point 3 were not
correlated with the As(III) concentration changes observed for sampling point 1 and 2. The As(V) contents in the
bottom water were positively correlated in all sampling points. In the surface water, no correlation between the
As(III) and As(V) contents was observed. A similar conclusion may be drawn for the bottom water, with the
exception of point 3, in which the As(III) and As(V) contents were positively correlated.
The analysis of data concerning the arsenic contents in the bottom sediments indicated a strong positive
correlation for the As(III) concentration changes in sampling point 1 and 3 (upper layer, 0-5cm). The As(III)
concentration changes observed for sampling point 2 demonstrated a weaker correlation with the As(III)
concentration changes for sampling point 1 and 3. The As(III) contents in the upper sediment layer were not
correlated with the As(III) contents in the lower sediment layer. For point 2, a strong positive correlation
between the As(III) content in the bottom sediment (0-5cm) and the As(III) concentration in the surface water
was observed. For the remaining points, there was also a positive correlation. However, it was weaker. For
sampling point 1, there was a strong negative correlation between the As(III) content in the lower bottom
sediment layer and its concentration in the bottom water. For sampling point 3, the As(III) content in the upper
sediment layer was strongly negatively correlated with the As(III) content in the bottom water. For the remaining
points, such a correlation was not observed. For points 1 and 2, there was a positive correlation for the As(V)
contents in both bottom sediment layers. For point 3, the As(V) content in the lower bottom sediment layer
demonstrated a strong positive correlation with the As(V) content in the surface water in this sampling point. For
point 1, there was a positive correlation between the As(V) contents in the upper bottom sediment layer and
surface water. For point 2, the As(V) contents in the bottom water and lower bottom sediment layer were
correlated. For points 1 and 2, there was a strong negative correlation between the As(V) content in the upper
bottom sediment layer and the As(III) content in the lower bottom sediment layer.
4.3.2
Antimony
The PCA for the data concerning the antimony contents in the samples of the Rybnik Reservoir water and
bottom sediments (PC1 and PC2 explained 43.55% and 18.44% of the data variance, respectively) showed that
the largest fluctuations in the antimony contents occurred in the summer and autumn months. The greatest
variability in the Sb(III) in the bottom and surface water was observed in May, June and July. In the same period,
the Sb(V) contents manifested the largest fluctuations in the bottom sediments. The Sb(V) contents in the surface
and bottom water and the Sb(III) contents in the bottom sediments changed considerably between July and
October (Fig. 11).
(Fig. 11)
For the three analyzed points, the Sb(III) contents in the surface water were positively correlated. A similar
situation was observed for the bottom water. On the other hand, the Sb(III) contents in the surface and bottom
water were strongly negatively correlated in the three points. For sampling point 1 and 3, the Sb(V) contents in
the surface water were strongly positively correlated. For the bottom water, a strong positive correlation was
found for the Sb(V) contents in points 1 and 2. For point 3, a strong positive correlation was observed for the
Sb(III) and Sb(V) contents in the bottom water. A similar correlation was not found for points 1 and 2. For the
surface water, there was a positive correlation between the Sb(III) and Sb(V) contents in sampling points 1 and 3
and no correlation for point 2.
In the upper bottom sediment layer, there was a positive correlation between the Sb(III) contents for points 1 and
2. In the lower bottom sediment layer, a positive correlation was observed for the Sb(III) contents in sampling
points 1 and 2. For points 1, there was a strong negative correlation between the Sb(III) contents in the upper and
lower bottom sediment layers. For point 3, no correlation between the Sb(III) contents in in the upper and lower
bottom sediment layers was observed. The Sb(V) contents in the upper bottom sediment layer were correlated
for sampling points 2 and 3. For all points, there was a strong positive correlation observed for the Sb(V)
contents in the lower bottom sediment layer. For points 2 and 3, there was no correlation between the Sb(V)
contents in both analyzed bottom sediment layers. For sampling points 1 and 2, there was a strong negative
correlation between the Sb(III) and Sb(V) contents in the lower bottom sediment layer.
4.3.3
Chromium
The PCA results (PC1 and PC2 explained 42.45% and 22.43% of the data variance, respectively) point to the
considerable fluctuations in the Cr(III) and Cr(VI) contents in water and bottom sediments within the analyzed
period. High variability in the Cr(III) contents in the surface and bottom water and the upper bottom sediment
layer was observed in the winter and spring months (January-April). In the same period, the greatest changes in
the Cr(VI) content were found in the bottom water. The Cr(III) content in the bottom water and the Cr(VI)
content in the lower bottom sediment layer fluctuated between May and July. In the autumn season (similarly to
spring), the highest variability in the Cr(III) contents was discerned for the surface and bottom water and the
upper bottom sediment layer. The biggest changes in the Cr(VI) concentrations were observed in the bottom
water (Fig. 12).
(Fig. 12)
The Cr(III) contents in the surface water were strongly positively correlated for all sampling points. An
analogous situation was observed for the bottom water. On the other hand, there was a strong negative
correlation between the Cr(III) contents in the surface and bottom water. For the three analyzed points, a strong
positive correlation was found for the Cr(III) contents in the surface water and upper bottom sediment layer. For
point 2, there was a correlation observed for the Cr(VI) contents in the surface and bottom water. The Cr(III)
contents in the upper bottom sediment layer demonstrated a strong positive correlation for all points. For the
bottom sediments, the correlation for the Cr(III) contents was only observed for points 2 and 3. For point 1, the
Cr(III) contents in the upper and lower bottom sediment layers were negatively correlated. An analogous
situation was not observed for sampling points 2 and 3. The Cr(VI) contents in the lower bottom sediment layer
demonstrated a strong positive correlation for all sampling points. Such a situation was not observed for the
upper bottom sediment layer. The Cr(III) and Cr(VI) contents in the lower bottom sediment layer revealed a
strong negative correlation.
100
Cumulative percentage of explained variance
90
80
70
60
50
40
30
20
10
0
1
2
3
4
5
6
7
8
Principal component number
9
10
11
Fig. 6 Cumulative percentage of explained variance by the subsequent principal components
b
a
6
0.5
5
November
0.4
4
2a
0.3
2
1
0
-1
October
Loadings on PC 2
PC 2 26.05%
3
January
February
2b
1b
1a
3a
2a
3c
0.1
3d
1c
3d
2d
2b
August
1d
3b
-0.1
-2
July
Fig. 10.
3c
0
April
-3
-4
1a
2c
1c
0.2
September
March
As(III)-water
As(III)-sediment
As(V)-water
As(V)-sediment
3a
June
-2
0
1d
May
2
PC 1 33.48%
2c
2d
1b
3b
4
6
8
-0.2
-0.3
-0.2
-0.1
As(III) and As(V) contents in water and bottom sediments: A)
0
0.1
Loadings on PC 1
0.2
0.3
Projection
0.4
of
objects onto the plane PC1, PC2; B) Projection of loadings onto the plane PC1, PC2. Symbols: a – surface water;
b – bottom water; c – bottom sediment (0-5cm); d – bottom sediment (15-20cm). The digits in the figure B
correspond to the sampling points
a
b
4
0.4
3
2b
0.3
September
2a
October
3a
Loadings on PC 2
PC 2 18.44%
August
1
0
-1
3b
3b
1d
2a
0
2b
2c
-0.1
2d
3d
Sb(III)-water
Sb(III)-sediment
Sb(V)-water
Sb(V)-sediment
1c
February
-0.3
May
3c
January
-3
-6
-4
-2
0
PC 1 43.55%
2
4
-0.4
-0.4
6
1c
1b
-0.2
November
-2
2d
3a
1d
April
1b
1a
0.1
June
March
1a
0.2
July
2
-0.3
-0.2
-0.1
0
Loadings on PC 1
3d
2c
3c
0.1
0.2
0.3
Fig. 11. Contents of Sb(III) and Sb(V) in water and bottom sediments: A) Projection of objects onto the plane
PC1, PC2; B) Projection of loadings onto the plane PC1, PC2. Symbols: a – surface water; b – bottom water; c –
bottom sediment (0-5cm); d – bottom sediment (15-20cm). The digits in the figure B correspond to the sampling
points
a
b
4
0.3
3
Cr(III)-water
Cr(III)-sediment
Cr(VI)-water
Cr(VI)-sediment
0.2
July
September
1
August
June
October
0
May
2a
3d
2b
1d
-3
2d
2c
-0.3
March
April
-4
-2
-1
0
PC 1 42.45%
1
2
3b
1b
3
3c
3c
-0.1
January
February
2c
4
1a
0
-2
-3
1c
1c
1a
-0.2
-4
-5
1d 2a
1b
3a
November
-1
2d
0.1
Loadings on PC 2
PC 2 23.44%
2
3d
-0.4
-0,3
-0,2
3a
3b
2b
-0,1
0
Loadings on PC 1
0,1
Fig. 12. Contents of Cr(III) and Cr(VI) in water and bottom sediments: A) Projection of objects onto the plane
PC1, PC2; B) Projection of loadings onto the plane PC1, PC2. Symbols: a – surface water; b – bottom water; c –
bottom sediment (0-5cm); d – bottom sediment (15-20cm). The digits in the figure B correspond to the sampling
points
0,2