G. M. Tarekul Islam

Implications of agricultural land use change to ecosystem services in the Ganges delta

Ecosystems provide the basis for human civilization and natural capital for green economy and sustainable development. Ecosystem services may range from crops, fish, freshwater to those that are harder to see such as erosion regulation, carbon sequestration, and pest control. Land use changes have been identified as the main sources of coastal and marine pollution in Bangladesh. This paper explores the temporal variation of agricultural land use change and its implications with ecosystem services in the Ganges delta. With time agricultural lands have been decreased and wetlands have been increased at a very high rate mainly due to the growing popularity of saltwater shrimp farming. In a span of 28 years, the agricultural lands have been reduced by approximately 50%, while the wetlands have been increased by over 500%. A large portion (nearly 40%) of the study area is covered by the Sundarbans which remained almost constant which can be attributed to the strict regulatory intervention to preserve the Sundarbans. The settlement & others land use type has also been increased to nearly 5%. There is a gradual uptrend of shrimp and fish production in the study area. The findings suggest that there are significant linkages between agricultural land use change and ecosystem services in the Ganges delta in Bangladesh. The continuous decline of agricultural land (due to salinization) and an increase of wetland have been attributed to the conversion of agricultural land into shrimp farming in the study area. Such land use change requires significant capital, therefore, only investors and wealthier land owners can get the higher profit from the land conversion while the poor people is left with the environmental consequences that affect their long-term lives and livelihood. An environmental management plan is proposed for sustainable land use in the Ganges delta in Bangladesh.

On the Distribution of Sediments at Channel Bifurcation

Experiments were conducted to study the distribution of sediments at a channel bifurcation. The test rig consisted of a straight main channel, which bifurcated into two branch channels of different widths. The test rig was a mobile bed with fixed bank. Four different types of noses were used to study the phenomenon. For each nose, three upstream discharges viz.: 20 1/s, 30 1/s and 40 1/s were used. The evolution of bed level and the variation of discharges in the downstream branches were discussed. The ratio of the downstream discharges per unit width (q 1 /q 2 ) and the ratio of the sediment transports per unit width (s 1 /S 2 ) were estimated and set to the general nodal point relations which described the distribution of sediments to the downstream branches.