tailieunhanh - Wetland - An introduction

Wetland can be understood as an ecological system lie on a continuum between uplands, where excessive water is not a factor for plant growth, and deeply flooded lands, or aquatic systems, where flooding excludes rooted emergent vegetation. Figure 1 shows how to describe this wetland concept | WETLAND - AN INTRODUCTION Le Anh Tuan Catholic University of Leuven, Belgium December, 2003 --- oOo --- I. WHAT IS WETLAND ? Wetland can be understood as an ecological system lie on a continuum between uplands, where excessive water is not a factor for plant growth, and deeply flooded lands, or aquatic systems, where flooding excludes rooted emergent vegetation. Figure 1 shows how to describe this wetland concept. Arbitrary Arbitrary Upland Wetland Aquatic High water table High water Low water table Low water Seasonally saturated Seasonally flooded soils Figure 1. Wetland in general meaning (Kadlec & Knight, 1996) More than 100 years before, in many cities, towns and villages around the whole world, natural wetlands have been used as convenient wastewater discharge sites as long as sewage has not been collected (Kadlec and Knight, 1996). There is over 6 percent of land surface of the world, or million km2, is wetland (Bazilevich et al, 1971, Maltby & Turner, 1983). In natural wetlands, the 5-day Biochemical oxygen demand (BOD5) from wastewater can be removed by the support of a large and diverse population of bacteria which grow on the submerged roots and stems of aquatic plants. These plants have also the ion exchange or adsorption capacity in wastewater. In addition, the wastewater solids will be accumulate in the wetland bed by their quiescent water conditions. Other aspects of wetlands are considered as determining factors on climatic stable and balance. Wetlands are residence places for many kinds of wildlife as birds, retiles, amphibians, and so on. Over the past 20 years, the application of constructed wetlands (CW) for domestic and municipal pollution control has been rediscovered and has gradually developed in many European countries and many parts of the world today. The most advantage of CW is their simple construction, low energy process requiring minimal operational cost. However, constructed wetland treatment may be economical relative to other