Week 5:Wetlands

Definition and Fundamental Characteristics of Wetlands

• Definition: A wetland is a broad, transitional term used to describe areas that lie between terrestrial (land) and aquatic (water) systems.

• Hydrological Context: These are areas where the water table is usually at or near the surface, or where the land is covered by shallow water.

• The Water Table: This is defined as the specific level at which the ground in a given area becomes saturated with water.

• Soil and Vegetation Interaction: In a wetland, soils are saturated for prolonged periods. This saturation results in specific chemical, physical, and biological characteristics that determine the specific type of vegetation that develops. These soils are referred to as being "hydric in nature."

• Interaction Components: Wetlands allow for the complex interaction between water, soil, vegetation, and light.

• General Parameters: Wetlands can be natural or man-made. They may contain water that is static (still) or flowing. The water chemistry can be fresh, brackish, or salty. This definition includes areas of marine water where the depth at low tide does not exceed $6\,\text{meters}$.

Key Characteristics of Hydric Soils

• Color Patterns: Hydric soils exhibit specific color patterns due to prolonged waterlogging. They often display gray or bluish-gray colors in the upper soil horizons (layers). This coloration is an indicator of reduced iron compounds formed under anaerobic (low-oxygen) conditions.

• Odor: These soils often possess a characteristic "rotten egg" smell. This odor is caused by the absence of oxygen in waterlogged conditions, which leads to the production of compounds such as hydrogen sulfide.

• Texture: While texture varies, hydric soils are frequently clayey or loamy. These textures are effective at retaining water and maintaining saturation for extended durations.

• Chemical Properties: Due to anaerobic conditions, these soils may contain reduced iron and manganese compounds. The pH levels are often lower ($\text{more acidic}$) compared to soils that are well-drained.

• Plant Adaptations: The primary biological indicator of hydric soils is the presence of hydrophytes. These are specialized plants adapted to grow and thrive in waterlogged conditions.

Major Types of Wetlands and Their Features

• Swamps: These are wetlands dominated by trees and shrubs (wooded wetlands).

  • Freshwater Swamps: Typically located in low-lying areas with abundant freshwater, such as floodplains and riverbanks.
  • Saltwater Swamps: Also known as saltwater or tidal marshes, these are found in coastal regions where saltwater from the ocean mixes with freshwater from streams and rivers. They support salt-tolerant vegetation and serve as marine habitats.

• Marshes: These are herbaceous wetlands dominated by non-woody plants like grasses and sedges. Collectively, marshes and swamps are known as "mineral wetlands."

  • Freshwater Marshes: Often found near ponds, lakes, and slow-moving rivers. They are critical feeding and breeding grounds for waterfowl.
  • Saltwater Marshes: Coastal wetlands influenced by tides, serving as nurseries for marine life and providing coastal protection.

• Bogs: Characterized by wet, spongy, poorly drained peaty soil (organic material).

  • Vegetation: Dominated by bog mosses ($\text{Sphagnum}$) and heaths.
  • Hydrology: Bogs are acidic and nutrient-poor. They receive water exclusively from rainfall (precipitation) and discharge water to the groundwater.
  • Ecological Role: They are essential for carbon storage and provide habitats for specialized species.

• Fens: Peat-forming wetlands similar to bogs but with distinct differences. Along with bogs, fens are categorized as "organic wetlands" due to peat accumulation.

  • Hydrology: They are fed by surface water and groundwater that is rich in minerals and nutrients.
  • Characteristics: They are less acidic than bogs and support higher plant diversity, including reeds, grasses, and sedges. They are important for water purification.

• Quaking Bogs (Quaking Fens/Marshes): A type of bog where the surface appears solid but is actually a floating mat of vegetation and organic material.

  • Physical Sensation: Walking on a quaking bog feels solid initially, but the ground quivers or "quakes" with ஒவ்வொரு step because of the buoyancy and compressibility of the waterlogged mat.

• Specialized Wetland Formations:

  • Prairie Potholes: Small, depressional wetlands found in the North American grasslands (the Prairie Pothole Region); essential for waterfowl breeding.
  • Vernal Pools: Seasonal wetlands that fill during the wet season (spring) and dry up during the dry season; crucial for amphibians and invertebrates with unique life cycles.
  • Estuaries: Coastal areas where freshwater rivers meet and mix with saltwater; highly productive nursery sites for fish.
  • Mangrove Swamps: Coastal wetlands dominated by salt-tolerant mangrove trees; they protect coastlines from erosion.

Case Study: The Ondiri Swamp, Kenya

• Location: Located near Kikuyu, Kenya, in Kiambu County.
• Significance: It is the source of the Nairobi River.
• Type: It is a protected wetland and peat bog.
• Unique Features: It is the only quaking bog in Kenya and the second deepest wetland in Africa, surpassed only by Duale in Cameroon.

Classification Systems for Wetlands

Cowardin Classification System ($1979$)

Developed for the US government, this system distinguishes between "wetlands" and "deepwater habitats," noting that traditionally, wetlands do not include deep permanent water.

Ramsar Classification System

Adopted in $1990$ (modified in $1996$) to provide a more comprehensive global framework. It identifies three main categories:

1. Marine/Coastal Wetlands: Includes coral reefs, lagoons, estuaries, and brackish water.
2. Inland Wetlands: Includes deltas, rivers, freshwater swamps, and marshes.
3. Man-made Wetlands: Includes ponds, irrigated land, seasonally flooded agricultural land, and salt pans.

Functions, Benefits, and Ecological Value

• Water Quality Improvement: Hydrophytes trap particles from rainfall runoff, acting as natural filters. They remove nutrients, heavy metals, and toxic substances through biodegradation.

• Erosion and Flood Control: Wetlands reduce water flow speed, protecting seashores. They act like sponges, taking up large volumes of water and discharging them slowly, which controls flooding and ensures long-term water availability.

• Groundwater Recharge: They allow water to enter the groundwater system, recharging aquifers and raising the water table for human access.

• Water Cycle and Climate:

  • Evapotranspiration: Wetlands (especially swamps) have a potential evapotranspiration rate $1.5$ to $4.0$ times greater than evaporation from an open pan of water. They lose water more efficiently than tropical rainforests.
  • Rainfall Contribution: Approximately $61\%$ of rainfall comes from evapotranspiration.
  • Microclimate: They influence the local microclimate and mitigate global warming by fixing carbon dioxide ($CO_2$).

• Biodiversity and Habitat: Wetlands provide critical habitats for fish, birds, mammals, and reptiles. They support fisheries, provides pasture/fodder for pastoralists during droughts, and offer products like fuel wood, medicine, honey, and building materials.

• Scientific and Recreational Value:

  • Recreation: Boating, bird viewing, and research. Park fees can fund wetland upkeep.
  • Fossilization: Swamps are extraordinary fossilization environments because they are oxygen-starved, which preserves organic remains.

Threats to Wetland Ecosystems

Human Threats

• Land Conversion: Draining and filling wetlands for rice fields (agriculture), urban development, or highway construction (dredging).
• Health Measures: Draining wetlands to reduce diseases like malaria.
• Resource Extraction: Mining for minerals, oil, and natural gas.
• Pollution: Eutrophication caused by pollution leads to high algal blooms, oxygen depletion, and the subsequent death of flora and fauna.

Natural Threats

• Drought: Can significantly reduce wetland water levels.
• Natural Succession: The gradual change from one wetland state to another (e.g., sediment buildup leads to shallow water and eventually emergent vegetation).
• Sea Level Rise: Threatens coastal wetland balance.

Sustainable Management Strategies

• Legal Protections and Regulation:

  • In the US, a federal permit is required to fill or deposit dredged material.
  • Steering development away from existing wetland areas.
  • Mitigation Banking: Requiring the creation and evaluation of a new wetland before an existing one is destroyed.

• Restoration and Control: Restoring degraded wetlands and controlling the invasion of non-native species. Monitoring waste disposal is also critical.

• The Ramsar Convention (Convention on Wetlands):

  • Origin: Signed in $1971$ in Ramsar, Iran.
  • Mission: "The conservation and wise use of all wetlands through local and national actions and international cooperation, as a contribution towards achieving sustainable development throughout the world."

• Community Involvement:

  • Essential for long-term sustainability.
  • Involves locals in identifying problems, deciding on solutions, and monitoring effectiveness.
  • Utilizing local knowledge reduces enforcement costs and increases responsibility.

• Incentives for Management:

  • Livelihood benefits (fishing, hunting, aquaculture, farming).
  • Income from eco-tourism operations.
  • Improved quality of life (recreation, aesthetic, and cultural values).
  • Indirect benefits from ecosystem functions like flood control and water filtering.