3.2 Physico-chemical factors in relation to freshwater snail
distribution and abundance
The physico-chemical factors analyzed included temperature, pH, Total
Dissolved Solid (TDS), color, current/velocity, calcium, magnesium,
nitrate, phosphate, dissolved oxygen, turbidity and depth. The water
temperature ranged between 26.4 °C and 29.7 °C, with highest water
temperature recorded at site with lentic water and the lowest at site
with human activity. pH was lowest at sites with vegetation cover (7.0),
and highest at lotic water site (8.1). Concentration of magnesium, and
water velocity was lowest at lotic water site and highest at lentic
water site, with a range of 1.10 mg/L to 6.02 mg/L and 2.12m/s to
3.77m/s respectively. Sites with human activity and lentic water
recorded consistently lower values for turbidity, while higher values
were associated with sites with vegetation cover and lotic water.
However, total dissolved solids, dissolved oxygen levels, color, depth
and concentration of calcium, nitrates and phosphate, did not show any
remarkable variation between all the sampling sites.
Among the physico-chemical factors measured, pH (p = <
0.01), current velocity (p = < 0.01) and magnesium ion
content (p = < 0.01) varied significantly across the
four sampling sites along Warwade dam from April to October 2019 (Table
3). Regarding water pH, the actual difference occurred between areas
with vegetation cover (pH = 7.4) and lotic water (pH = 7.9). Also,
current velocity at sites with vegetation cover (2.94 m/s) and lotic
water (2.72 m/s) was significantly lower compared to lentic water (3.51
m/s). However, sites with human activities did not have a mean velocity
that was significantly different from either site with vegetation cover
or from lentic water or lotic water. The concentration of magnesium ion
was significantly different among all pair wise comparison: lentic water
had a concentration of 4.38mg/L, vegetation cover 3.36mg/L, human
activity 3.14mg/L and lotic water 1.24mg/L.
Of all the physico-chemical factors measured during the study period,
only calcium ion concentration was significantly associated with snail
abundance (P = 0.04). The relationship between snail abundance
and concentration of calcium was found to be strongly negative (r =
-0.8). This implies that increase in relative snail abundance was
associated with a corresponding decrease in the mean concentration of
calcium ion in the dam. Though not statistically significant, snail
abundance showed a positive relationship with water temperature, color,
turbidity and concentration of magnesium ion. Physico-chemical factors
found to be negatively associated with snail abundance but not
statistically significant include pH, velocity, depth, dissolved oxygen
levels, and concentration of nitrate and phosphate ions. Total dissolved
solids did not show any relationship with freshwater snail abundance in
Warwade dam (r = -0.02), is shown in Table 4.