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.