Abstract:
Land use change can have adverse impacts on aquatic habitats and biodiversity leading to change
in socio-economic activities of a country. This study aims to analyze the impact of land use
change on eco-hydrology of Arial beel - a depression spanning about 723 km2 between the
Ganges and the Dhaleshwari rivers south of Dhaka, the capital of Bangladesh. The changes of
land use were detected by studying six classified and two unclassified Landsat TM Satellite
images of Arial Beel area. Analysis of the classified images from 1984 to 1999 revealed that the
areas under crop production (consists of Boro and other rabi crops) remained relatively
unchanged at 32% of the study area during this period. Grass production increased from 5% to
11% over the years when livestock farming become popular in the locality. The analysis of
Landsat TM image of the study area for 1989 and 2010 together with data from BBS and ground
truthing showed that alteration in cropping pattern (from traditional varieties to high yielding
varieties) and reduction of net cultivable area are the most possible pathways of land use change
in the study area between 1984 and 2010. As gradual shift of high yielding varieties of crops
could lead to more intensive use of chemical fertilizers and pesticides thus degrading the quality
of water, water quality was considered as the indicator for ecosystem function of Arial Beel in
the current study. Chemical analysis of the water samples taken at two times, one set in premonsoon
and another set in early monsoon, revealed most of the parameters, including dissolved
oxygen, pH, ammonia and nitrogen were within the tolerable limits. Nitrogen concentration
varied from 0.15 mg/l to 0.25 mg/l, which is within the acceptable limit (<0.3 mg/l) but
phosphorus concentration ranged from 0.2 mg/l to 0.45 mg/l, which is significantly above the
acceptable limit (<0.015 mg/l). The high level of phosphorous contribution is mainly attributed
to extensive use of fertilizer and popularity of livestock farming in the locality. However, the
concentration is likely to decrease with increased mixing of accumulated rainwater in depression
areas and floodwater from the surrounding rivers. Nevertheless, the very high level of
phosphorous concentration in the month of June is a concern for beel fisheries and other aquatic
lives of the beel. Findings from the participatory field research and secondary literature review
revealed that the fish availability of the beel has been affected and some native fish species are
now endangered- substantially impacting the livelihood activities of the fishermen. Future
studies need to be carried out to explore to what extent the high level of phosphorous
proliferation will continue, and the likelihood of plankton or algal blooms in Arial Beel.
