RESULTS AND DISCUSSION

A. Water quality

Physical and chemical variables analyzed across the sampling sites (lakes) are listed in Table 2. The pH ranged from neutral to alkaline (7.13 – 9.42 as in Fig. 2a), highest being in the Hesaraghatta lake (9.42) due to the increased acid neutralizing capacity.  Ionic concentration was low at Hesarghatta lake (150.7 µS), Hoskere lake (337 µS) and fairly high at Doddabidderakallu lake (3320 µS) owing the industrial pollution. Difference between Hesarghatta and Doddabidderakallu lakes was significant by EC, SAL and TDS (Fig. 2b). Among water chemistry variables, phosphates, chlorides, hardness and alkalinity showed a high value in Doddabidderakallu followed by Varthur akin to conditions in agriculture site while Hesarghatta and Hoskere showed low range reflecting clean water compared to the former sites. Nitrate levels of agricultural field (1.203 mgL^-1) encompassed the low range as observed in Doddabidderakallu (0.84 mgL^-1), Varthur (0.594 mgL^-1), Hoskere (0.246 mgL^-1) and Hesarghatta (0.215 mgL^-1) lakes. High amount of phosphate was sensible in Doddabidderakallu (1.93 mgL^-1) compared to other lakes (Fig. 2c). This high amount of nutrients and ionic concentrations, mainly alkalinity and hardness in Doddabidderakallu can be attributed to the untreated industrial effluents and sewage into the inlet channel. Even though Varthur showed moderate water quality, high amounts of contamination has been reported in the past^[31]. Hoskere and Hesarghatta showed a negligible amount of anthropogenic activities except for few local disturbances. The elevated nitrate and phosphate concentrations in agriculture site were evident from the intrusion of fertilizers.

Table 2: Water quality variables of 5 sampling sites (1-5 as described in study area)

Fig. 2. Variation in water physical and chemical variables [a): pH, b)EC,SAL and TDS, c) N and P, d) chlorophyll composition across sites (mg/l)]

B. Community structure analysis

The community structure of microalgae through microscopic analysis resulted with 27 genus belonging to 4 classes with 2 unidentified filamentous algae (Table 3). The class Bacillariophyta (diatoms) and Chlorophyta dominated at Hoskere and Varthur lake as well as agricultural sample with Achnanthidium Kützing, Gomphonema Ehrenberg, Nitzschia Hassall, Navicula Bory de Saint-Vincent, Chlamydomonas  Ehrenberg, Scenedesmus Meyen and Anabaena  Bory de Saint-Vincent ex Bornet & Flahault accounting more in number (occurrence number in microscopic field). Dodabidarekallu was represented by Nitzschia sp. alone, whose presence justifies high ionic and organic nutrients load. Hoskere was well occupied by diatoms viz., Fragiallria Lyngbye, Sellaphora Mereschowsky, Surirella Turpin along with the former species. Significant relation of ecology of microalgae such as Nitzschia sp., Sellaphora sp., Chlorella M.Beijerinck and Phacus Dujardin (varthur and agricultural field samples) with the extent of pollution load was observed.

Table 3. Community structure of 5 sampling sites (1-5 as described in study area. + indicates presence and – indicates absence of species)

C. Water Quality and Community structure

 Nitzschia sp. was prevalent in Doddabidderakallu with the high quantum of nutrients and ionic concentrations. Compared to this Varthur showed moderate water quality, while, Hoskere and Hesarghatta showed a negligible amount of anthropogenic activities except for few local disturbances. The elevated nitrate and phosphate concentrations is observed in agriculture sites.  The class Bacillariophyta (diatoms) and Chlorophyta dominated at Hoskere and Varthur lake as well as agricultural sample. Occurrence of microalgae such as Nitzschia sp., Sellaphora sp., Chlorella M.Beijerinck and Phacus Dujardin  with the extent of pollution load show significant correlation (p<0.05).

C. Lipid analysis

The neutral lipid profile of the microalgal community revealed characteristic profile of the given community. The neutral lipid profile of each lake which is characteristic feature of the thriving microalgal community is given in Table 4. Agricultural field with Gomphonema sp. and Nitzschia sp. as dominant also reflected more fatty acids as of Doddabidarekallu sample due to inhibition of cell cycle and which causes TAG accumulation. Hoskere and Hesaraghatta (unpolluted water) had relatively less chlorophyll  (Fig. 2d)and fatty acids in lipid profile. This is due to the inability of the diatoms to accumulate more TAG due to lack of any stress. In freshwater, lipid productivity, the mass of lipid that can be produced per day is dependent upon plant biomass production as well as the lipid content of this biomass^[21]. The pattern of fatty acids varies according to the internal and external factors working on the algal cell^{[32, 33]} which concludes that growth rate and the mixed population which competes for the resources, influences on fatty acid composition. Although there are many microalgae as evident from Table 4 that have the ability to accumulate oils under some special cultivation, they have different prospects for biodiesel production in terms of oil yield lipid coefficient and lipid volumetric productivity^[34]. However lipid production varies with variation in algal species with reference to both quantity and quality of lipids^[35].

Table 4. List of polyunsaturated fatty acids

In the current investigation, Doddabidarekallu, Varthur and agriculture field samples were represented by diatoms, which are lipid-rich and have been demonstrated to be an important source for biodiesel^{[36, 37]}. Nitzschia species at Doddabidarekallu site (industrial waste) was prevailing with high organic and ionic content resulted with high lipid profile and chlorophyll content. This supports that environmental condition are decisive variables for lipid in microalgae. However, this has to be explored further through in situ experiments (like axenic culture, synchronous inoculums for bioreactors etc.). For further evidence, role of each keystone micoalgae species in the contribution towards lipid production with its ecological preference has to be studied.