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Freshwater Ecosystems

By: Tabitha Mishra
| Last updated: January 12, 2017

What Does Freshwater Ecosystems Mean?

A freshwater ecosystem is a region with bodies of water that have salt concentrations lower than those found in ecosystems, typically below one percent. These include lakes, ponds, rivers, streams, and wetlands.

Safeopedia Explains Freshwater Ecosystems

Freshwater ecosystems are vital to all life. Only 3% of the world’s water is freshwater, and 99% of that freshwater is locked in glaciers or underground. Most of the water used by humans comes from the more accessible sources found in these ecosystems.

Unfortunately, these important sources of freshwater are threatened by acidification, eutrophication (mineral enrichment), and contamination from chemicals and pollutants.

Types of Freshwater Ecosystems

Freshwater ecosystems are classified as one of three types, based on the region in which they are located:

  • Lotic freshwater ecosystems have bodies of water that move in one direction, like rivers and streams. The three zones in these systems are:
    • Source zone (also known as the headwaters zone), a narrow, fast-moving zone where the temperature is very cold and which contains a large amount of dissolved oxygen.
    • Transition zone, the middle part of the stream or river, where the flow is deeper and gentler and the temperature is warmer. It has less oxygen than the source zone.
    • Floodplain zone, the mouth of the stream or river and has a slower flow, warm temperature and very low levels of dissolved oxygen, with poor diversity of flora and fauna.
  • Lentic freshwater ecosystems exist within stagnant water bodies like ponds and lakes, and vary greatly in size. Seasonal or sessile pools last for a few months, while others last for many years. These ecosystems support a limited number of species and have three zones:
    • Littoral zone, near the shoreline. It is shallow, warm, and hosts various algae, aquatic plants, crustaceans, clams, insects, amphibians, and other species.
    • Limnetic/photic zone, the open water zone where sunlight supports photosynthesis. It is dominated by planktons.
    • Profundal/aphotic zone, where sunlight hardly penetrates and photosynthesis is not possible. This zone is cold and it supports heterotroph aquatic animals that feed on dead organisms.
  • Wetland freshwater ecosystems are still bodies of water like marshes, swamps, and bogs. Plant species like hydrophytes and animal species like amphibians, reptiles, birds, and shellfish are supported by this ecosystem.

The Decline of Freshwater Ecosystems

Freshwater ecosystems are facing a crisis as pollutants degrade habitats and water quality, affecting the species that depend on these ecosystems for survival. According to research, the population of monitored freshwater species has declined by 84% and about one third of wetland ecosystems have been lost.

The United Nations Environment Programme (UNEP) has initiatives like The Economics of Ecosystems and Biodiversity (TEEB) that aims to mainstream the values of biodiversity and ecosystem services into decision making at various levels. The Global Peatlands Initiative is a combined effort by leading experts and institutions aimed at saving peatlands.


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