Ecosystems

The term ecosystem refers to the combination of different components (physical and biological) of the environment. Aspects that define an ecosystem are physical factors (such as soil or rocks) together with biotic organisms (plants and animals). When these develop in the same environment a steady state develops and a stable system is created.

Freshwater ecosystems include:

• Permanent and temporary rivers and streams;
• Permanent lakes and reservoirs;
• Seasonal lakes, marshes and swamps, including floodplains;
• Forested, alpine and tundra wetlands;
• Springs and oases; and
• Groundwater systems and geothermal wetlands.

Ecosystem Services

Fresh water is fundamental to life and contributes to all the major benefits provided to people, both directly and indirectly, from ecosystems.

Ecosystem Services Provided by Freshwater and the Hydrologic Cycle

Provisioning Services	Regulatory Services	Cultural Services
Water quantity and quality for consumptive use (drinking, domestic use, agricultural and industrial use) Water for non-consumptive use (generating power and transport/navigation) Aquatic organisms for food and medicines	Maintenance of water quality (natural filtration and water treatment) Buffering of flood flows, erosion control through water-land interactions and flood control infrastructure Climate regulation (source and sink for greenhouse gases, and influence on temperature and precipitation)	Recreation (river rafting, sport fishing etc.) Tourism (river viewing) Existence values (aesthetic functions of freely flowing rivers)
Supporting Services Nutrient cycling (role in maintenance of floodplain fertility Ecosystem resilience Mitigation of climate change (mangroves and floodplains providing physical buffering)

Further information is provided in the Functions of Wetlands section.

Biomes and Ecoregions

Biomes are globally similar areas, like ecological communities of plants and animals, soil organisms and climatic conditions. Characteristics that define biomes include plant spacing (forest, woodlands, savanna) or plant types (trees, shrubs, and grasses). Climatic factors that determine the distribution of biomes are latitude (arctic, boreal, temperate, subtropical, and tropical) and humidity (from humid to arid). A fundamental classification of biomes is Terrestrial (land) biomes, Freshwater biomes, and Marine biomes

Many different classification systems are available and exist in parallel, for example:

• Holdridge Scheme;
• Whittaker's Biome-type Classification Scheme;
• Walter System;
• Bailey System; and
• WWF.

The system developed by the World Wide Fund for Nature (WWF) is an ecological classification system of the world that has identified

• 14 biomes, called major habitat types;
• 867 terrestrial ecoregions;
• 426 Freshwater Ecoregions; and
• 229 coast and shelf Marine Ecoregions.

More information on ecoregions in the basin is provided in the section Ecoregions and Biodiversity Hotspots.

Ecosystems in the basin

The Kunene River basin includes the following ecosystems:

• Aquatic Ecosystems;
• Desert Ecosystems;
• Forest Ecosystems; and
• Savanna Ecosystem.

Aquatic Ecosystems

An Aquatic ecosystem is an ecosystem located in a body of water with communities of organisms that depend on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems.

Marine ecosystems are among the largest of Earth's aquatic ecosystems. They include oceans, salt marsh and intertidal ecology, estuaries and lagoons, mangroves and coral reefs, the deep sea and the sea floor.

Freshwater ecosystems can be divided into three general types, characterized by the speed of water movement: slow moving water such as in pools, ponds and lakes; rapidly moving water like streams and rivers and wetlands without water movement.

Desert Ecosystems

Deserts are defined as areas with an average annual precipitation of less than 250 millimeters per year, or as areas where more water is lost by evapotranspiration than falls as precipitation. Deserts have the reputation of being unable to support life. In reality however deserts often have high biodiversity.

Forest Ecosystems

A forest or woodland is an area with a high density of trees. There are many definitions of a forest, based on various criteria.

Savanna Ecosystems

A savanna is a grassland ecosystem characterised by vegetation and seasonal water availability. One main factor that defines savanna is the open canopy. The open canopy consists of small and widely spaced trees and allows sufficient sunlight to reach the ground to support grass growth. Savannas are normally found in transition zones between forest and desert. Large parts of Africa are covered with savannas.

For information on ecoregions in the basin refer to the Ecoregions and Biodiversity Hotspots section.