Magnesium:
Magnesium is required universally by chlorophyllus plants as the component of chlorophyll molecule. Magnesium is associated with calcium in all kinds of water but its concentration remains generally lower than the calcium (Venkatsubramani and Meenambal, 2007). It is a main cation causing water hardness. In natural water magnesium comes from natural processes i. e. dissolvent of mineral containing magnesium and from other sources like industrial and agricultural wastes. Magnesium values decreases due to plankton and algal uptake (Rath et. al., 2000). Higher concentration of magnesium reduces the utility of water for domestic use.
The monthly variation in magnesium values are expressed in Table 10.1 to 10.9 whereas seasonal variation is expressed in Figure 10.1 to 10.9.
The level of magnesium at Karambali tank is depicted in Table 10.1. The monthly values of magnesium at this tank fluctuated from 14.67±1.11 mg/l to 29.01±0.24 mg/l, with an average of 21.55±0.97 mg/l. There was decrease in the values of magnesium in the month of July at site I and increased in the month of August at site II. The seasonal variation at Karambali tank is depicted in Figure 10.1. The values ranged from 17.72±0.39 mg/l to 30.33±4.13 mg/l. The least value of magnesium was observed during monsoon at site I while peak value was observed during summer season at site II.

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The monthly values of magnesium at Shendri tank is given in Table 10.2. The level of magnesium ranged from 14.98±0.32 mg/l to 30.38±0.13 mg/l, with an average of 25.32±0.04 mg/l. The lower values of magnesium observed in the month of July at site I and higher in the month of April at site II. The seasonal variation at Shendri tank is given in Figure 10.2. The values fluctuated from 16.83±0.20 mg/l to 29.95±0.27 mg/l. The low value of magnesium was observed during monsoon at site I while high value was observed during summer season at site II. Verma et al. (2011) have obtained the magnesium values form 17 mg/l to 32 mg/l from Kankaria Lake.
The amount of magnesium at Yenechavandi tank is presented in Table 10.3. The values varied from 20.27±0.50 mg/l to 33.08±0.79 mg/l, with an average of 27.01±1.12 mg/l. The fall of magnesium was noted in the month of November at site II while raise in magnesium noted in the month of January at site II. The seasonal variation at Yenechavandi tank is given in Figure 10.3. The values varied from 17.82±0.49 mg/l to 31.49±0.28 mg/l. The fall in value of magnesium was noted during monsoon at site I while raise in the value of magnesium was observed during winter season at site I.
The annual fluctuation in magnesium level at Terani tank is shown in Table 10.4. The values of magnesium ranged from 22.57±0.85 mg/l to 33.37±0.72 mg/l, with an average of 28.85±0.80 mg/l. There was decline in magnesium value in the month of July at site I and incline in the month of May at site I. The seasonal variation at Terani tank is given in Figure 10.4. The values of magnesium ranged from 27.81±0.22 mg/l to 30.92±0.45 mg/l. There was decline in the values of magnesium during winter at site I and incline during summer at site I.
The magnesium values at Narewadi tank is given in Table 10.5. The values of magnesium fluctuated from 17.31±0.32 mg/l to 35.27±0.88 mg/l, with an average of 27.83±1.43 mg/l. The minimum value of magnesium was observed in the month of July at site I and maximum value observed in the month of December at site I. The seasonal variation at Narewadi tank is given in Figure 10.5. The values of magnesium varied from 18.55±0.41 mg/l to 37.57±0.57 mg/l. It was minimum during monsoon at site I and maximum during winter at site II. Mathivanan et al. (2005) have noted the level of magnesium from 6 mg/l to 37 mg/l for fish culture pond. The amount at Pukara dam lies between 16 mg/l to 40 mg/l (Ramesh and Sardhamani, 2009).
The level of magnesium at Vairagwadi tank is expressed in Table 10.6. The level of magnesium varied from 14.06±0.21mg/l to 30.18±0.46 mg/l, with an average of 21.72±0.63 mg/l. There was increase in the value of magnesium in the month of July at site I and maximum in the month of January at site II. The seasonal variation at Narewadi tank is given in Figure 10.6. The values of magnesium fluctuated from 20.27±0.37 mg/l to 30.90±0.40 mg/l. The fall in the value of magnesium was observed during monsoon at site and raise in the magnesium value was noted during winter season at site I.
The monthly variation in magnesium at Kumari tank is expressed in Table 10.7. The magnesium values fluctuated from 8.42±0.40 mg/l to 21.35±1.01 mg/l, with an average of 13.81±0.68 mg/l. There was decline in the value of magnesium in the month of July at site I and incline in the month of February at site II. The seasonal values of magnesium at Narewadi tank is given in Figure 10.7. The values of magnesium ranged from 12.15±0.34 mg/l to 21.10±0.20 mg/l. There was decrease in the value of magnesium during monsoon at site I and increased during summer at site I. v and Sardhamani (2005) have recorded the level of magnesium from 10 mg/l to 20 mg/l for Aliyar reservoir. Hulyal et al. (2011) have noted the values of magnesium from 4.65 mg/l to 21.36 mg/l for Alamatti reservoir. Gaval et al. (2011) have observed the magnesium values from 10.68 mg/l to 19.40 mg/l at Muduganukunte Lake. Magnesium values at Purur Lake ranged from 3 mg/l to 19 mg/l (Usha, 2012).
The variation in magnesium at Kadagaon reservoir is expressed in Table 10.8. The amount of magnesium ranged between 17.65±0.37 mg/l and 32.63±0.13 mg/l, with an average of 26.92±0.28 mg/l. The least value of magnesium was observed in the month of July at site I and peak value was noted in the month of December at site I. The seasonal values of magnesium at Kadagaon reservoir is noted in Figure 10.8. The values of magnesium varied from 22.56±0.99 mg/l to 33.49±0.18 mg/l. There was decline in the value of magnesium during monsoon at site I and inclined during summer at site I. Verma et al. (2012) have given the range of magnesium from 25 mg/l to 34 mg/l for Chandola Lake.
The annual fluctuation in magnesium at Mahagaon reservoir is depicted in Table 10.9. The values of magnesium ranged from 13.65±0.73 mg/l and 26.38±0.12 mg/l, with an average of 21.05±0.04 mg/l. There was decrease in the level of magnesium during the month of July at site I and increased in the month of February at site I. The seasonal fluctuation of magnesium at Mahagaon reservoir is expressed in Figure 10.9. The values of magnesium fluctuated from 18.15±0.41 mg/l to 26.86±0.19 mg/l. There was decrease in the value of magnesium during monsoon at site I and increased during summer at site I. Sathe et al. (2000) have noted the values form 15.59 mg/l to 24.36 mg/l for Lodhe reservoir.
In the present study the decreased value of magnesium during monsoon and increased during summer were observed at Shendri tank, Terani tank, Kumari tank and Mahagaon reservoir. Karambali and Kadagaon reservoir also showed similar trend during seasonal analysis. The lower values of magnesium may be due to high rainfall (Shastri, 2000) while higher values may be due to evaporation of water. According to Rath et al. (2000) planktons utilize magnesium during this season. Similar observations were obtained by Similar trend of magnesium higher in summer and lower in rainy has given by Devi et. al. (2009), Khabade et. al. (2005), Narayana et.al. (2005), Shivanna and Nagendrappa (2012). The maximum magnesium content was observed in summer season by Kataria et. al.(1995) and Naik and Purohit (1996). Magnesium value higher in winter was also noted at Narewadi and Vairagwadi tank for both monthly and seasonally while at Kadagaon it is during monthly. Similar trend of higher in winter was noted by Ramesh and Sardhamani (2009), Verma et al. (2011), Verma et al. (2012)
The permissible limit of magnesium content for drinking purpose is 50 mg/l and maximum limit is 150 mg/l. The magnesium values are found to be below the desirable limit in all tanks and reservoirs water.