Table 3.
Characteristics of physico-chemical water parameters and altitude.
| Physico-chemical parameters | Median | Min – Max | Seasonal differences, mean (SD) | Regional differences in rainy season, mean (SD) | Corr. ratio | Bravais-Pearson correlations | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dry season | Rainy season | North | South | B. p. | Tur | Temp | pH | EC | DO | ORP | |||
| Altitude (m.a.s.l.) | 175 | 74–513 | 322 (106) | 140 (38)* | 0.15* | 0.01 | −0.39* | 0.02 | 0.52* | −0.47* | 0.33 | ||
| Turbidity (NTU) | 18 | 2–730 | 12 (11) | 227 (218)* | 257 (242) | 206 (206) | 0.13* | 0.35* | −0.21 | −0.12 | −0.07 | −0.10 | |
| Temperature (°C) | 26.5 | 19.5–30.0 | 25 (1.9) | 27.6 (1.5)* | 26.8 (1.8) | 28.2 (1.1)* | 0.29* | −0.17 | −0.10 | −0.04 | −0.23 | ||
| Acidity (pH) | 7.6 | 6.5–9.0 | 7.8 (0.5) | 7.3 (0.4)* | 7.4 (0.4) | 7.3 (0.4) | 0.09* | 0.40* | 0.34* | 0.14 | |||
| Electrical conductivity (µS/cm) | 152 | 10–623 | 194 (139) | 152 (92)* | 231 (80) | 101 (58)* | 0.15* | −0.08 | 0.43* | ||||
| Dissolved oxygen (%) | 85 | 25–138 | 92 (18) | 73 (16)* | 72 (17) | 73 (16) | 0.06 | −0.05 | |||||
| Redox potential (mV) | 86 | −39–275 | 118 (79) | 85 (28) | 75 (11) | 92 (34) | 0.00 | ||||||
Abbreviations: m.a.s.l. = meters above mean sea level, NTU = nephelometric turbidity units, mean = arithmetic mean, SD = standard deviation, Corr. ratio = correlation ratio, B. p. = B. pseudomallei, Tur = turbidity, Temp = temperature, pH = acidity, EC = electrical conductivity (proxy for salinity), DO = dissolved oxygen, ORP = redox potential. N = 67; exceptions: turbidity (n = 66), median, minimum and maximum of altitude in the rainy season (n = 31). The Bravais-Pearson correlation coefficient (r) is given for directional correlations between physico-chemical parameters, the correlation ratio (η2) for undirectional correlations between the presence of B. pseudomallei and physico-chemical parameters, range from 0 (no correlation) to 1 (perfect correlation). Statistical tests: seasonal comparison: paired t-test (n = 31 pairs, for turbidity n = 30 pairs), regional comparison: t-test, correlation ratio: t-test, Bravais-Pearson correlations: Pearson test; *statistically significant correlations or differences between groups, p < 0.01.