Abstract:
Around 8 km away from the centre of Kolkata city, West Bengal, lies a 12.77 ha (mean depth 1.5 m) freshwater lake, known as the Santragachi Jheel (in this communication stated as Lake-B), in the district of Howrah of West Bengal, India (Lat. 22° 34' 60N Long. 88° 17' 60E; Altitude 8m msl) which has recently attracted the attention of the avian migrant watchers India-wide. About 150 m south-west of Santragachi lake, there is a large (4.0 ha; mean depth 1.5 m) perennial water body (Colony Jheeland in this communication stated as Lake-NB) where no waterfowl colonize during the period of congregation of migratory birds (early October to late March). Limnochemical conditions of these two water bodies were compared during October to March for three consecutive years. Impact of avian colonization was evident from the comparison of limnochemical features of these two adjacent water bodies. Mean data shows much less dissolved 02 (2.00 - 5.00 mg L1) and total hardness (125.31 -
188.53 mg L' CaCO3) while very high phosphate (0.83 - 2.67 mg L1) and nitrate (50.00 -116.67 mg L1) in Lake-B in comparison to Lake-NB (ranges were noted as
4.43 - 6.00 mg L' and 197.58 - 249.20 mg L1 CaCO3 while 1.00 - 1.25 mg Li and
15.00 - 25.00 mg L-' respectively). Gross and net primary productivity were also much different between these two adjacent water bodies. In Lake-B GPP (2066.42 - 3749.67 mg C m-2 d-l) and NPP (1114.99 - 2558.33 mg C rn-2 d-1) were much lower than the mean GPP (4937.50 - 7875.00 mg C m 2 d-1) and NPP (2449.50 - 4250.00 mg C m-2 d-
1) values that were recorded from Lake-NB. Net-Gross ratio, that reflects the rate of respiratory consumption at the primary producer level, was also much higher in LakeB (42.01 - 68.25%) than Lake-NB (45.40 - 57.14%). Lindeman Efficiency, on the contrary, of Lake-B (3.71 - 8.71%) was considerably lower than Lake-NB (7.63 -
13.29%) and such a lower efficiency, even when the nutrients were not in short supply, could be attributed to the thick water hyacinth covering of the Lake-B. Addition of bird guano surely enriched nutrient profile of the Lake-B. Further, the nutrient rich water of Lake-B might have a bottom-up control on the food web, however, very high bird congregation in December-January would surely have a top-down cascading effects on the lake food web. Thereby, mollusk, fish and plankton production supported the large avian congregation during the study period in Lake-B and in sequel a lower total hardness, dissolved oxygen content and primary productivity were recorded.
