**1. Introduction**

162 Current Issues of Water Management

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exchange in hyporheic zones on longitudinal transport of solutes in streams and

Wetlands are defined as water systems with marsh or fen and with water that is static or flowing, fresh or brackish, the depth of which at low tide is below 6m [5]. Natural wetlands are characterized by emergent aquatic vegetation such as cattails (typha), rushes (Scirpus) and reeds (Phragmites), and by submerged and floating plant species. Wetlands are categorized into three main categories: (1) fresh water coastal wetlands, (2) flood – plain wetlands and (3) constructed wetlands. These are valuable ecosystems as they support services which contribute significantly to human well - being. Some of these services are fish and fiber, water supply, water purification, flood regulation, recreational opportunities and tourism.

In this chapter, we focus our attention to potential of wetlands as water purifiers. This is important because harmful substances enter into wetland systems through animal waste from farms, toxic chemicals from factories and pesticides present in rain water. The large and diverse population of bacteria which grow on the submerged roots and stems of aquatic plants play an important role in removing BOD5 from waste water. Wetland plants take up harmful substances into their roots and change the harmful substances into the less harmful ones before they are released into the water body. Harmful substances partly get buried in the wetland soil. The soil bacteria convert these into substances, which are not harmful. Soil microbes (*Bacillus subtilis* and *Pseudomonas fluorescens*) convert pesticides into simpler nontoxic compounds. This process of degradation of pesticides and subsequent conversion into non-toxic compounds is known as "biodegradation". The biodegradation is influenced by factors such as moisture, temperature, pH and organic matter content.

The chapter is organized as follows. In the next section, we present a study of a natural wetland of flood – plain type. This section summarizes a previous study of this natural wetland by the author and presents some new results. Section 3 discusses the design and construction of constructed wetlands.

Wetlands for Water Quality Management – The Science and Technology 165

herons, storks and cormorants, and an important wintering ground for large numbers of

It is known that the population persistence boundaries in water column depth–turbulence space are set by sinking losses and light limitation [1]. In shallow waters, the most strongly limiting process is nutrient influx to the bottom of the water column (e.g., from sediments). In deep waters, the most strongly limiting process is turbulent upward transport of nutrients to the photic zone. Consequently, the highest total biomasses are attained in turbulent waters at intermediate water column depths and in deep waters at intermediate turbulences. These patterns have been found insensitive to the assumption of *fixed versus flexible algal carbon -to – nutrient stoichiometry*. They arise irrespective of whether the water column is a surface layer above a deep water compartment or has direct contact with sediments. This helps us understand the relevant dynamical processes in the physical

KNP is a natural wetland which can be categorized as a flood – plain type. The economic value of the park is dependent on tourist activities. The tourists are mainly attracted by Siberian Crane, the migratory bird which adds aesthetic value to KNP. It provides a large habitat for migratory birds; Siberian crane being the flagship species. With reference to migratory birds, the biomass is divided into two categories: "Good" and "Bad". The excess

Boundary wall Bund Canal Hard top road Motorable road Aquatic area Footpath

migrant ducks.

Additional stations formerly sampled Stations presently sampled

Fig. 2. Situational map of Keoladeo National Park

systems in natural as well constructed wetlands.

**Biotic part of Keoladeo National Park** 

**Light vs nutrient supplies** 
