How Urban Ecosystems may enhance the overall efficiency of the Urban Settlements?

Urban Ecosystem : -Business District, Cairo, Egypt
Source :- http://www.britannica.com/EBchecked/media/149336/Urban-ecosystems-such-as-the-one-seen-from-Cairo-Tower

Stockholm has a large and varied ecological structure. In the City of Stockholm, parks and green space occupy 56 km2 (26%), and water area cover 28 km2 (13%) of the total area of 215 km2. This is considerably more water and green space than possessed by most other cities, and gives Stockholm its unique character. The city is situated on a number of islands between the fresh water lake Mc’laren and the brackish Baltic Sea. Stockholm also has a special feature with a number of green wedges pointing towards the city centre. This allows the ecosystems close to the city centre to be linked with larger ecosystems outside of the city.

An ecosystem can be defined as ‘‘a set of interacting species and their local, non-biological environment functioning together to sustain life’’ (Moll and Petit, 1994). However, the borders between different ecosystems are often diffuse. In the case of the urban environment, it is both possible to define the city as one single ecosystem or to see the city as composed of several individual ecosystems, e.g. parks and lakes (Rebele,1994). The urban ecosystem hence forms after human interventions and interferences takes place for more complex economic and institutional activities. These can be divided into seven further sub-categories to give a general outlook of its broad types. However, the urban ecosystem can be perceived to as a single system performing all the activities and also as a combination of different systems which are inter-related and inter-dependent for their efficient functioning. Following seven types of urban ecosystem has been identified and it may vary according to the view as the system as a whole or in various systems in isolation to form an efficient functional system.

Street trees are stand-alone trees, often surrounded by paved ground.  Lawns/parks are managed green areas with a mixture of grass, larger trees, and other plants. Areas such as playgrounds and golf courses are also included in this group.  Urban forests are less managed areas with a denser tree stand than parks. Cultivated land and gardens are used for growing various food items. Wetlands consist of various types of marshes and swamps. Lakes/sea includes the open water areas. Streams refer to flowing water. Other areas within the city, such as dumps and abandoned backyards, may also contain significant populations of plants and animals. It should be possible, however, to place most urban ecosystems or elements in one of the above mentioned categories.

Source : -http://www.thehighpoint.com/expo/S_Natural.html

Air – Filtration and Reduction in the Impact of Air Pollution - Vegetation reduces air pollution, but to what level seems to depend on the local situation (Svensson and Eliasson, 1997). The reduction is primarily caused by vegetation filtering pollution and particulates from the air. Filtering capacity increases with more leaf area, and is thus higher for trees than bushes or grassland (Givoni, 1991). Due to the larger total surface area of needles, coniferous trees have a larger filtering capacity than trees with deciduous leaves (Stolt, 1982). This capacity is also greater because the needles are not shed during the winter, when the air quality is usually worst. However, coniferous trees are sensitive to air pollution and deciduous trees are better at absorbing gases (Stolt, 1982). A mix of species therefore seems to be the best alternative. In general, vegetation is much better than water or open spaces for filtering the air. The method or the subsequent approach to maximize the self-sustenance of the urban ecosystem may vary from region to region with the change in the complexity of them with topography, climatic conditions, soil conditions, hydrology, etc, to name a few. A thick vegetation planted in accordance with the soil condition and the hydrology of the area generally helps in the reduction of the Carbon footprints.

Micro-climate regulation, at street and city level - These urban ecosystems may regulate the micro-climatic conditions. The urban heat island effect is caused by the large area of heat absorbing surfaces, in combination with high amounts of energy use in cities. All natural ecosystems in urban areas will help to reduce these differences. Water areas in the city will help even out temperature deviations both during summer and winter. Vegetation is also important. A single large tree can transpire 450 l of water per day. It is very important for the planners to understand the concept and functioning of these urban ecosystems. If used constructively, they can be a great support for maintaining, enhancing and improving the conditions of the natural system as a whole.

Noise reduction - Noise from traffic and other sources creates health problems for people in urban areas. One source states that a dense shrubbery, at least 5 m wide can reduce noise levels by 2 dB(A) and that a 50-m wide plantation can lower noise levels by 3–6 dB(A). Increasing the areas with soft ground and vegetation may decrease these noise levels. Vegetation may also contribute by shielding the visual intrusion of traffic and thus making it less disturbing: Evergreen trees are preferred in this case.

Rainwater drainage - The built-up infrastructure, with concrete and tarmac covering the ground, results in alterations of water flow compared to an equivalent rural catchment. A higher proportion of rainfall becomes surface-water run-off which results in increased peak flood discharges and degraded water quality through the pick-up of e.g. urban street pollutants (Haughton and Hunter, 1994). The impervious surfaces and high extraction of water cause the groundwater level of many cities to decrease. Vegetated areas contribute to solving this problem in several ways. The soft ground of vegetated areas allows water to seep through and the vegetation takes up water and releases it into the air through evapotranspiration.

Sewage Treatment - In many cities, large scale experiments are taking place where natural systems, mainly wetlands, are being used to treat sewage water. The wetland plants and animals can assimilate large amounts of the nutrients and slow down the flow of the sewage water, allowing particles to settle out on the bottom. Up to 96% of the nitrogen and 97% of the phosphorous can be retained in wetlands, and so far wetland restorations have largely been successful, increasing biodiversity and substantially lowering costs of sewage treatment (Ewel, 1997). The cost of nitrogen reduction through wetland restoration has been calculated to 20–60 SEK while the cost in a sewage treatment plant is 33–350 SEK (Gren, 1995). Other benefits of wetlands, e.g. biomass production and biodiversity, have not been included in these figures.

A city is a stressful environment for its citizens. The overall speed and number of impressions cause hectic lifestyles with little room for rest and contemplation. The recreational aspects of all urban ecosystems, with possibilities to play and rest, are perhaps the highest valued ecosystem service in cities. All ecosystems also provide aesthetic and cultural values to the city and lend structure to the landscape. Botkin and Beveridge (1997) argue that ‘‘Vegetation is essential to achieving the quality of life that creates a great city and that makes it possible for people to live a reasonable life within an urban environment’’.

These are just a few examples, natural systems if studied intensively holds the questions of many of the urban settlements and the concept of self-sustenance of them can be further implemented in the further era of development. The ecologists inclusion in the planning activities and the role played by them should be strengthened and appropriateness of the document of 'environment impact assessment' should be put at the serious examination. The complexity of the modern urban settlements should include the intensity of the significance of the various natural systems involved in it's formation.

These urban ecosystems have to be understood more intensively and they have to be wisely used to make and improve the efficiency of the urban ecosystem which at large affects the lives of the inhabitants. The integration of the land use and transportation planning to build the sustainable cities of the future may look a myth, if the consideration of the urban settlements as a system is not considered while preparing the plans. I wonder sometimes how the planners may after studying the complexity of the urban settlements generally ignores and side-lines this fact of the city as a system. You may build wider roads, may increase the infrastructural developments, may provide green spaces as per standards, but if you fails in understanding the concept of system, I doubt for the real sustainable future of our cities.

Sources : Different.