PHYTODIVERSITY AND THEIR SEASONAL VARIATIONS IN WETLANDS OF LALMAI HILL AREAS OF COMILLA

Abstract

A hydrobiological study on three different water bodies of Lalmai Hill areas of Cumilla was carried out from October 2017-September 2019. In the study, relationships among several water quality parameters, the diversity of phytoplankton and composition of aquatic macrophytes were seen. The seasonal variations of the above mentioned hydrobiological components of the wetland ecosystems were also elaborated. In the seven studied stations, namely, station 1 to station 7, the total species of phytoplankton recorded were 352. The recorded genera of this investigation which were reported previously were 65. The division wise distribution of the recorded species showed following distributional pattern: Cyanophyta 39, Chlorophyta 123, Euglenophyta 81, Chrysophyta 54, Cryptophyta 13 and Pyrrhophyta 2. Algal division wise percentage distribution of phytoplankton in the wetlands of Lalmai Hill areas of Cumilla was: Cyanophyta, 12.50%; Chlorophyta, 39.42%; Euglenophyta, 25.96%; Chrysophyta 17.31%; Pyrrhophyta, 0.64% and Cryptophyta, 4.17%. Members of Chlorophyta were found to dominate in all the studied stations which contributed more than 39% of the total phytoplankton community. Out of 352 recorded species of phytoplankton, 312 species were previously recorded in different studies in Bangladesh. Preliminary data on the rest 40 species of phytoplankton cast hope that this will be new algal reports for Bangladesh. The unreported 40 species, dominated division was Euglenophyta (15 taxa) followed by Chlorophyta (14 taxa) and Cyanophyta (11 taxa). A total of 42 species of aquatic macrophytes was recorded where Ludwigia adscendens (L.) Hara and Lemna minor Roxb. were found to be the most dominant species. The monthly ranges of recorded physical parameters were air temperature 16.4-35.5ºC for all the stations, water temperature 16.2-35.4ºC and Secchi depth 52-112 cm. During the period of investigation, the ranges of chemical parameters were alkalinity 0.03-4.4 meq/l, conductivity 31.0- 640 μS/cm, DO 6.4-14.9 mg/l, pH 5.8-8.5, TDS 12.0-753.0 mg/l, SRP 2.31- 613.52 μg/l l, SRS 0.17-265.82 mg/l and NO3-N 0.01-1.58 mg/l for all seven stations. The range of recorded biological parameters where total phytoplankton density was 0.06×106 ind/l - 30.40×106 ind/l, chl-a was 4.00-249.82 μg/l and phaeopigment was 0.19-92.06 μg/l for all seven studied stations.

Pearson correlation of phytoplankton density showed positive correlation with alkalinity, soluble reactive silicate, chlorophyll a and phaeopigment in station 1. All these, alkalinity showed 1% level significant. In station 2, phytoplankton density showed positive correlation with only nitrate nitrogen. It showed 1% level significant with nitrate nitrogen. In station 3, phytoplankton density showed positive correlation pH and chlorophyll-a. Among these phytoplankton density showed 5% level significant with pH and 1% level significant with chlorophyll-a. In station 4, phytoplankton density showed positive chlorophyll-a. Here phytoplankton density showed 5% level significant with chlorophyll-a. In station 5, phytoplankton density showed positive correlation with dissolved oxygen. In this station phytoplankton density showed 1% level significant with dissolve oxygen. In station 6, phytoplankton density showed positive correlation with alkalinity, conductivity, soluble reactive phosphate, chlorophyll-a and phaeopigment. Among these phytoplankton density showed 5% level significant with conductivity and soluble reactive phosphate and 1% level significant with alkalinity, chlorophyll-a and phaeopigment. In station 7, phytoplankton density showed positive correlation with pH, alkalinity, conductivity, soluble reactive silicate, chlorophyll-a and phaeopigment. Among these phytoplankton density showed 1% level significant with conductivity, chlorophyll-a and phaeopigment and 5% level significant with pH, alkalinity and soluble reactive silicate. According to Shannon-Winner diversity index, station 7 is more diverse than all other stations and in Jaccard Index shows all the stations are highest 9.45% similar in September 2018 and their intersecting members were 19. In this research work, diversity of phytoplankton and macrophytes were studied according to four different seasons. Winter and pre-monsoon was dominated by a diverse group of phytoplankton in both study year whereas monsoon was dominated by the abundance of different species of macrophytes. The present investigation has revealed that the studied stations have a diverse variety of phytoplankton and macrophytes according to the four distinct seasons. Total diatom index showed that the studied wetlands are free from significant organic pollution. The investigation generated some important baseline data on the pollution status and phytoplankton community structure of wetlands of Hill areas. These data would be helpful in planning for future policy decisions on using these wetlands as an ecotourist center as well as in the better conservation and management of the precious wildlife in the world-famous sanctuary. Analysis and interpretation of the data on phytoplankton and water quality parameters provided the necessary information to assess the impact of tourism related activities on the hydrobiology of the wetlands.