Rethinking urban ecology for sustainable development
Ecology always deals with the nexus between nature and living organism. Ecology of urban settlement is the scientific study of the relation between nature and living organisms and their surroundings in the context of an urban environment. The urban environment refers to environment dominated by high-density residential and commercial buildings, paved surfaces, and other urban-related factors that create a unique landscape dissimilar to the previous studies in the field of ecology.
Urbanization is one of the 21st century's most transformative trends. Cities are the dominant force in sustainable economic growth; development and prosperity in both developed and developing countries. In developing countries, urbanization is taking place at a rapid pace. Currently 54 per cent of the world's population (4 billion people) resides in urban areas. By 2030, 2 billion people will move to cities, placing unprecedented pressure on infrastructure and resources, particularly those related to water, soil etc.
Both local shipping and long-distance trade are required to meet the resource demands important in maintaining urban areas. Carbon dioxide (CO2) emissions from the transport of goods also contribute to accumulating greenhouse gases and nutrient deposits in the soil and air of urban environments. In addition, shipping facilitates the unintentional spread of living organisms, and introduces them to environments that they would not naturally inhabit.
In Dhaka city, Around 250 industries are discharging chemical pollutants into Buriganga and Sitalakka River. Every day 4,000 tons solid waste and 22,000 tons tannery waste mix with water in Buriganga River. Different industries and their contribution to the pollution in Dhaka are: pulp and paper 47.4 per cent; pharmaceuticals 15.9 per cent; metals 14 per cent; food industry 12.1 per cent; fertilizers/pesticides 6.6 per cent. In urban areas, sewages are connected directly with the rivers and low-lying part around the urban areas.
Wetlands around our city are being shattered through land development and dumping of toxic effluents and untreated sewage. In Bangladesh, cities have sprung up alone the banks of different rivers. Industrial effluents have totally destroyed the biota in the rivers near these large urban areas. In Dhaka, 20 canals have lost her lives out of 42. Liquid, solid wastes and heavy metals - copper (CU), iron (Fe), lead (Pb) and nickel (Ni) are exacerbating the level of Biological Oxygen Demand(BOD), Chemical Oxygen Demand(COD), (Dissolved Oxygen)DO, (Total Dissolved solids)TDS, (Acidity or Alkalinity)PH of water.
According to World Health Organization (WHO), the estimated number of death as of pollution is 37,000 per year in Bangladesh. A fourth of the death in Bangladesh and a sixth in the world's total death result from environmental contamination, mostly caused by air pollution. Particulate matter 2.5 and 10, which is responsible for causing many lung diseases -- such as asthma, asphyxia, Pneumonia, obstructive lung disease, bronchitis, lower respiratory infection, lung cancer, etc -- is found on an average 7 to 8 times higher in public areas where the permissible limit of PM (particulate matter) 10 is 65 micrograms per cubic metre and for PM(particulate matter)-2.5, it is 150 micrograms per cubic metre. Major air pollutants in Dhaka city are suspended particulate matter, hydrocarbons, carbon monoxide, nitrogen oxides, lead, carbon dioxide, methane, etc emitted from the motorised vehicle.
Alien species often have no natural predators and pose a substantial threat to the dynamics of existing ecological populations in the new environment where they are introduced. Alien species are populations of organisms living in a range in which they did not naturally evolve due to intentional or inadvertent human activity. The Urban Planning Act (1919) specified that the city should have a green belt, and it prescribed the number of trees that should be planted within the belt. But we are cutting down a huge number of trees without planting them according to the law. In addition, planting or cultivation of non-native/ invasive alien species has become a widespread culture in Bangladesh. There are more than 300 exotic plant species in Bangladesh which are assumed to be cultivated as economic crops -- Mahogony (swietenia mahagoni), Eucalyptus (eucalyptus globulus), Minzium (acacia mangium) and Akashmoni (acacia auricoliformis). Basically, if we plant these trees in urban areas, these trees create environmental insurgencies.
Increased transportation between urban centres furthers the incidental movement of animal and plant species. Increase in urban population has created a tremendous pressure on the existing network of intra-urban and inter-urban roads and highways as both the number and the volume of vehicular of traffic increases within the city or in its outskirts at specific time of the day, especially during rush hours. The number of motorized vehicles plying in streets of Dhaka was around 140,000 in 1995, 185,000 in 2000 and 290,000 in 2007. Now it is around 3, 85,000. Apart from that, there is a question of registration and non-registration. Bangladesh Road and Transport Authority mentions, there are almost 29.48 lakh registered vehicles in the country.
At this moment high-rise buildings dominate many regions of Dhaka city. These buildings have enormous dissident reservoirs to hold water. The pressure of water in the distribution pipes of WASA is not enough to fill these huge reservoirs -- water is tired from these pipes by illegally connecting water pumps straight on WASA lines. As a result, other houses in the neighbourhood undergo from water shortage.
Dhaka city is merely served by a sewerage system, which is not able of accommodating huge loads of sewage at specific points. The high-rise apartment buildings are creating extra load of sewage at specific points at specific times of the day. This teeming may debilitate the whole system. Where there is no sewerage line, huge septic tanks need to be erected to clutch the sewage. If constructed in dangerous revitalize areas, this may contaminate the groundwater, pollute the land and lake ecology.
Every year, 8th November has been celebrated as world urbanism or world town planning day. This special day recognizes and promotes the role of planning in creating liveable communities. World Urbanism Day presents an excellent opportunity to look at planning from a global perspective, an event which appeals to the conscience of citizens and public authorities in order to draw attention to the environmental impact resulting from the development of cities and territories.
We have to be committed to diminishing environmental pollution, address unplanned construction of high-rise buildings all over the city and setting buildings codes, ensure proper solid waste disposal system. It is imperative of proper planning and maintenance of urban open spaces -- parks and green belts around large cities where areas in the outskirts of the city are reserved for vegetation. Context demands for the better management of existing road networks and effective traffic management system, urban governance, resource efficiency and coordination among urban security agencies, disaster preparedness for common development goal for all.
Shishir Reza is an environmental analyst and Associate Member, Bangladesh Economic Association