Importance of Wetlands and role of Landscape Architects in their conservation
Wednesday, April 08, 2015
Wetlands form the transitional zone or ecotone between land and water both spatially (edges where land meets water) and over time (land and water at the same place in different seasons), where saturation with water is the dominant factor determining the nature of soil development and the types of plant and animal communities living in and on it (Cowardian et al., 1979). They are usually formed in the depressions (subjected to flooding) and groundwater seeps. However, contrary to the popular misconception, wetlands are not constantly wet. Understanding this shifting, transitional character is essential to working with wetlands. Wetland type is determined primarily by local hydrology and the unique pattern of water flow through an area. In general, there are two broad categories of wetlands: coastal and inland. Enhanced appreciation of wetlands in the recent past has led to the signing of many international agreements for protecting them, among which the Ramsar convention is the most important.
The Ramsar Convention on Wetland in 1971, in Iran (http://www.ramsar.org) characterised wetlands as : “... areas of marsh, fen, peatland, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six meters.”
Water is usually, but not always, flowing in the Riverine System. Upland islands or Palustrine wetlands may occur in the channel, but they are not included in the Riverine System. Palustrine Moss-Lichen Wetlands, Emergent Wetlands, Scrub-Shrub Wetlands, and Forested Wetlands may occur adjacent to the Riverine System, often on a floodplain (Fig 1).
Wetlands are probably the earth’s most important freshwater resource and are also the most threatened. They perform manifold functions in the maintenance of the ecological balance of the region. Some of the important functions include water storage, protection from storms and floods, recharge of ground water aquifers, water filtration and purification, fisheries, agriculture, wildlife resource, transport, recreation, etc. In traditional landscapes these wetlands have specific features: wet grasslands, rushes, willows, etc. but in some regions the systematic drainage of this water-logged soil has resulted in the disappearance of these buffer zones.
India is richly endowed with wetlands evident from the high-altitude lakes of the Himalayas; floodplain wetlands of major river systems and their extensive network of tributaries draining from the Indian landmass in all directions. They are fragile ecosystems that are susceptible to damage even with a little change in the composition of biotic and abiotic factors. They are threatened due to inadequate water holding capacity, excessive withdrawal, pollution due to raw sewage and sullage, industrial effluents, eutrophication, leached fertilizers and insecticides . Refer Fig 2
Wetlands near urban centres are under increasing developmental pressure for residential, industrial and commercial facilities. Urban and industrial development increases the amount of surface water run-off from the land after rainfall. This raises flood heights and increases the flow rate of rivers, increasing the risks of flood damage. Increased run-off brings with it various substances that degrade water quality. Effluents from some sewage treatment plants built to handle the needs of growing communities also reduce water quality. But, passing through wetlands, cleansing action takes place as many pollutants are removed, retained or utilised by the wetlands. Urban wetlands in certain instances function as recharge areas. This is especially true in communities where ground water withdrawals are heavy. Thus, urban wetlands are essential for preserving public water supplies.
Wetlands consist of multiple linked paths (waterways, habitat types, biodiversity on the site –Refer figure 3) that interact through energy flows, moving biota, and water flows. Watershed conditions and downstream wetlands are linked as they influence the soil and hydrologic regime of the downstream areas. India’s entire land surface has been altered through long-term human use and manipulations (e.g., intensive cropping, deforestation, intensive grazing and alteration of water flows). Anthropogenic alteration of the hydrological regime has further led to the alterations in natural drainage (Gopal, 1982). Ground water can flow in shallow local aquifer systems where water is near the land surface or in deeper intermediate and regional aquifer systems (Refer fig. 4). Differences in hydraulic head cause ground water to move back to the land surface or into surface-water bodies; this process is called ground-water discharge. In wetlands that are common discharge areas for different flow systems, waters from different sources can mix. Ground-water discharge will influence the water chemistry of the receiving wetland whereas ground-water recharge will influence the chemistry of water in the adjacent aquifer. Lack of any comprehensive wetland protection policy measures for inland wetlands in most states is the primary cause of urban wetland degradation and loss.
Wetland loss may be defined as “the loss of wetland area, due to conversion of wetland to non-wetland areas as a result of human activity” and wetland degradation is “the impairment of wetland functions as a result of human activity”. About 50 % of the world’s wetlands have been lost in the last century, primarily through drainage for agriculture, urban development and water system regulations. It has been estimated that nearly one hectare degraded at the tick of every minute of the clock. (Narayanan, 2008) This alarming scenario calls for Landscape professionals to intervene with ecological approaches of Design in wetland areas.
Landscape design in areas of such fragile resources is best done by aggregating land uses, and maintaining small patches and corridors of “nature” throughout developed areas, as well as some human activity spatially scattered in the broader matrix. Ideally, all such design should incorporate wetlands. Landscape ecology approaches mean sustainable management and manipulation of ecosystems. This requires understanding the spatial scales at which wetland processes operate, including hydrological elements, surface as well as ground. As Landscape Architects, our homework of understanding the wetlands is especially critical before intervening in sites with such fragile ecosystems because they are a resource from which sustainable development, design and construction benefit.
Diversity of species and habitat, and varied fractal physical forms are functional essentials. Several points are critical to wetland protection and restoration:
Wetland plants are essentially hydrophytes (fig 5) that tolerate flooding which would normally kill dry land plants. Like all plants, wetland species require air and sunlight, most have at least their leaves above water. Species that grow underwater require clear water to get sunlight. Many wetland plants require alternating flooding and drier conditions.
Too deep or too long inundation can kill wetland species. In natural wetlands, this alternating wet and dry states control nutrient availability, set up conditions for germination, influence wildlife behavior, and keep weedy invaders out –especially important in newly planted wetlands. Built or restored wetlands require precise water-level control and a seasonal draining of the basin. Use a “stop-log” or “flash board”, an adjustable spillway formed by boards or logs set into a vertical channel in a dam. Valves only control flow volume, but stop log spillways regulate water level directly and simply. There are many such sustainable Landscape construction ideas which can be talked about at length.
However, to restore or create a wetland, observation of natural wetlands in the region along with their edge conditions is the key. This is no place for aesthetic theories that condemn mimicking nature. Wetlands consultant Hammer emphasizes that “the created wetland must closely imitate natural systems adapted to that region if it to succeed without excessive operational and maintenance cost.” The principles of energy and nutrient flows, common to all ecosystems when applied to the design of human environment, provide the only ethical and pragmatic alternative to the future health of the emerging regional landscape. Landscape architects can play a leading role in establishing a genuinely new theory of sustainable landscape development in a profound departure from all past design theory, which was primarily based upon aesthetics. By laying out this new framework with an ecological basis for design, they can establish a foundation for practice of landscape architecture that has no counterpart in the field of architecture or city planning. In fact, both of these allied professionals need to better integrate into their own worldviews the principles of sustainable development to bolster their own less developed – and more static philosophy of land planning. ...
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