## 4 Results and Discussion
### Correlation Matrix Evaluation and Seasonal Variation
In the wet season, the NO\({}_{3}-\)N concentration was 0.7, 1.9, and 1.9 for rivers, Lake Hawassa, and point sources, respectively. The value of NO\({}_{3}-\)N increases in the rainy season due to the contribution of agricultural runoff and use of fertilizers. The PO\({}_{4}-\)P concentration of rivers was 6.5 mg/L, PO\({}_{4}-\)P of Lake Hawassa was 3.3 mg/L, and that of point sources was 43.8 mg/L in dry season. In the wet season, the PO\({}_{4}-\)P concentration was 7.4, 2.9, and 25.7 for rivers, Lake Hawassa, and point sources, respectively (Table 6). Similarly, [PERSON] [58] reported that Ethiopian Rift Valley lakes generally have lower EC values in the rainy season than in the dry season, due to dilution by rain coupled with minimal evaporation rates during the rainy season. \begin{table}
\begin{tabular}{l c c c c c c c c c c c c c c c c} \hline
**Codes** & **SS** & **TDS** & **EC** & **pH** & **NH\({}_{3}-\)N** & **NO\({}_{3}-\)N** & **PO\({}_{4}-\)P** & **DO** & **BOD** & **COD** & **TN** & **TP** & **Mg\({}^{2*}\)** & **Ca\({}^{2*}\)** & **Na\({}^{*}\)** & **K+** & **Temperature** \\ \hline MS1 & 17.3 & 89 & 178 & 7.1 & 0.04 & 0.6 & 3.6 & 4.1 & 13.8 & 88.3 & 5.8 & 0.001 & 7.2 & 20 & 32.5 & 6.7 & 19.2 \\  &  
The TN (TP) of rivers was 8 (0.12) mg/L in dry seasons and 5(0.26) mg/L in wet season, and TN (TP) of lakes was 5.3 (0.2) mg/L in dry season and 5.2 (0.6) mg/L in wet season. Hence, there is an obvious increase of TN in rivers and Lake Hawassa when temperature increases due to lower dilution and greater agricultural contribution from the upper stream by irrigation, whereas TP in rivers and Lake Hawassa increases in wet seasons due to greater agricultural, rural, and urban runoff. The TN (TP) from point sources was 31.8 (7.2) mg/L in dry season and 13.9 (5.4) mg/L in wet season. This shows that TN (TP) of point sources increases significantly with increasing temperature due to lower dilution. The NH\({}_{3}-\)N of rivers was 0.2 mg/L, NH\({}_{3}-\)N of Lake Hawassa was 0.83 mg/L, and that of point sources was 4.72 mg/L in dry season. In the wet season, the NH\({}_{3}-\)N values were 0.03, 0.71, and 3.6 for rivers, Lake Hawassa, and point sources, respectively. The decreases in NH\({}_{3}-\)N level in the rainy season might be due to dilution effect (Table 6). The positive correlation between temperature and TN, TP, EC, TDS, NH\({}_{3}-\)N, and PO\({}_{4}-\)P indicates the increase in the concentration of nutrients as the temperature increases (dry period). It also confirms the major contributors of nutrients were the point sources that are releasing a relatively higher amount of pollutants than the agricultural and other sources, as this value lowers during the wet season due to dilution effect. However, the increase in nutrient (NO\({}_{3}-\)N) concentration in rivers and Lake Hawassa in the wet season might be due to the increased contribution of agricultural runoff and use of fertilizers. Sodium, calcium, magnesium, and potassium concentrations of the rivers were 49.1, 13.06, 55.1, and 7.74 mg/L in dry season and 28.9, 32.7, 10.1, and 5.7 mg/L in wet seasons. Sodium, calcium, magnesium and potassium concentrations of the lake were 214, 23.8, 8.7, and 19.7 mg/L in dry season and 178.9, 25.1, 7.3, and 17.2 mg/L in wet season. The sodium, calcium, magnesium, and potassium concentrations of the point sources were 575.2, 38.2, 11.5, and 26.2 mg/L, respectively, in the dry season and 375.2, 38.2, 9.5, and 50.1 mg/L. respectively in the wet season (Table 6). There was an observed decrease in ions when the temperature decreased in the study area. This can be ascribed to the discharge of industrial and domestic effluents, which contribute large amounts of alkaline ions to the river system, as the conductivity depends mainly on the ion concentration in surface water [52]. The natural range of sodium ions in water and soil is so low that their existence can show river pollution caused by human activities. Calcium is added to water from soil, industrial wastes, and natural resources.