Limnology of Lake Ashura, Dinajpur, Bangladesh Md Almujaddade Alfasane, Md Ataul Gani, Md Shafiqul Islam

Results of limnological investigation of lake Ashura showed that air and water temperatures were 31.5 ± 0.25oC and 30.0 ± 0.45oC, respectively in the month of April, 2011. pH, alkalinity, conductivity, dissolved oxygen and TDS of water were 7.11 ± 0.02, 2.96 ± 0.58 meq/l, 760.67 ± 8.08 μS/cm, 7.72 ± 0.41 mg/l and 104.67 ± 1.53 mg/l, respectively. The concentration of NO3-N, SRP and SRS were 63.33 ± 25.16 μg/l, 11.60 ± 1.60 μg/l and 14.36 ± 0.25 mg/l, respectively. Phytoplankton biomass as chl a and concentration of phaeopigment were 5.33 and 3.41 μg/l, respectively. The density of phytoplankton was 552.84 × 10 ind/l. A total of 35 species of phytoplankton were recorded of which 15 belonged to Euglenophyceae, followed by Chlorophyceae (8), Bacillariophyceae (7), Cyanophyceae (4) and Cryptophyceae (1). Macrophyte flora was represented by 31 species. The dominant species were Eichhornia crassipes (Mart.) Solms, Ludwigia adscendens (L.) Hara. and Oryza sativa L. Introduction Occurrence of natural lakes or true lakes in Bangladesh is scarce. There are only three true lakes namely, Rainkhyongkine, Bogakain and Ashuhila Beel or Ahshula Beel (Khan et al. 1994, Rashid 1991, Khondker et al. 2010). Islam and Uddin (1969) published an algological report on Lake Rainkyhongkine and recently, limnology of Lake Bogakain has been carried out by Khondker et al. (2010). The exact location of the above mentioned two natural lakes of Bangladesh was known (Khan et al. 1994, Rashid 1991). But the location of the third natural lake of Bangladesh i.e., Ashuhila Beel or Ahshula Beel was not clearly mentioned in either of the two literature (Khan et al. 1994, Rashid 1991). In both the literature, it is mentioned that the lake is situated in the northern fringe of eastern Barind. Since Barind tract (part of the Rajshahi division) is a vast area it was difficult to find the exact location of the lake. However, Alam and Begum (2005) studied the community based participatory fisheries management in a wetland named Ashurar Beel. It is situated in a remote area of Nawabganj Upazila of Dinajpur district and at an altitude of 27 m from the mean sea level. Ashurar Beel lies closer to the river Karotoa (Alam and Begum 2005) and it is aligned along the north-west-south-east direction of the Karotoa fault (Rashid 1991), Ashurar Beel could be the third natural lake of Bangladesh, hereinafter called Lake Ashura. The present attempt was made to investigate the water quality along with phytoplankton and macrophyte flora of Lake Ashura. Materials and Methods Water sample was collected from the south eastern fringe of the lake in April, 2011. A one liter capacity plastic bottle was dipped manually under the surface to collect water sample for physicochemical analyses. A total of two liter water sample was collected and from it, one liter was fixed by using Lugol’s Iodine and sedimented for concentrating plankton. The second one liter sample was transported in a Cool Box to the Laboratory for analyses. The time necessary to *Author for Correspondence: