**4. Results**

### **4.1 Hydrogeochemical analysis of the crater lake**

### *4.1.1 Physico-chemical parameters*

The physico-chemical analyses of the lake water are presented in **Table 1**. The physico-chemical characteristics show slight variability over the 2 to 3 year monitoring period. The pH values for the lake water range from 6.20 to 7.7. The pH is more acidic (< 7) during the dry season (March–June) and becomes more alkaline (rises to >7) during October–December period. Temperatures are highest during the month of March–April (270 -30°C) and correlates well with highest EC (340- 390 μs/cm) and TDS (150-170 mg/l) values. In general, there is a gradual decrease in temperature from 30°C in March to 20°C in December each year.

#### *4.1.2 Major cations*

The major cations (Mg, Ca, Na and K) concentrations are in the order of-Mg > Ca > K > Na. The highest concentration of Mg range from 30 mg/l to 40 mg/l, Ca from 21 mg/l to 25 mg/l, Na from 8 to 11 mg/l and K from 5.38 to 15 mg/l and are observed during the dry season (January to April) while the lowest concentration of Mg (16 to ≥25 mg/l), Ca (10 to 15 mg/l), Na (3 to 5.25 mg/l) were observed during the rainy season (August to October) (**Table 2**). Comparative analysis of Fe concentration with Patterson 1986 [9] show that the Fe concentration have increased from 0.27 to 0.612 mg/l over the last 29 yrs. It is observed that Fe concentration progressively increased from 0.332 mg/l in October, 2014 to 3.249 mg/l within the period of lake color change activities from November 2014 to February 2015. From the physico-chemical concentrations of the lake over the study period shows that it is seasonally dependent. However, a comparison of the pH values in the present study with that reported by Patterson [9] showed a decrease in pH from 9.35 to ≤7 with corresponding decrease in alkalinity (CaCO3) from 335 mg/l to 187 mg/l.



**Table 1.** *Physico-chemical parameters of the Pidong volcanic crater Lake (may 2013–April 2015).*

#### *Hydrogeochemistry of the Pidong Crater Lake, Jos Plateau Volcanic Province, Nigeria… DOI: http://dx.doi.org/10.5772/intechopen.99720*


**Table 2.** *Comparative hydrogeochemical data of 1986 and present study (after Lar [12]).*

*Hydrogeochemistry of the Pidong Crater Lake, Jos Plateau Volcanic Province, Nigeria… DOI: http://dx.doi.org/10.5772/intechopen.99720*
