A water-based ecosystem encompassing the biological communities and physical-chemical environment of freshwater, estuarine, or marine habitats. Aquatic ecosystems provide critical services including water purification, flood attenuation, and biodiversity support.
An aquatic ecosystem is an ecological system in which water is the primary medium, encompassing the living organisms (biotic component) and the physical and chemical environment (abiotic component) that interact within freshwater, estuarine, and marine habitats. Freshwater aquatic ecosystems include rivers and streams (lotic systems), lakes and ponds (lentic systems), and wetlands, each with distinct physical characteristics, nutrient dynamics, and biological communities. Key abiotic factors governing aquatic ecosystem health include water temperature, dissolved oxygen, pH, nutrient concentrations (nitrogen and phosphorus), flow regime, substrate composition, and light availability. Aquatic ecosystems provide essential services including water purification through nutrient uptake and sediment retention, flood water storage and attenuation, carbon sequestration, fisheries production, recreation, and biodiversity support. The health of aquatic ecosystems is assessed through biological indicators (macroinvertebrate indices, fish assemblages, algal communities), water chemistry, and physical habitat metrics. Freshwater ecosystems are among the most threatened on Earth, with extinction rates for freshwater species estimated to be 3-5 times higher than those for terrestrial species. Major threats include habitat degradation, water pollution, flow alteration by dams, invasive species, and climate change.