Aquatic Ecosystem
By
Dr. Ashok Kumar
Preface
An aquatic ecosystem is an ecosystem located in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems.
Marine ecosystems cover approximately 71 per cent of the earth′s surface and contain approximately 97 per cent of the plant′s water. They generate 32 per cent of the world′s net primary production. They are distinguished from freshwater ecosystems by the presence of dissolved compounds, especially salts, in the water. Approximately 85 per cent of the dissolved materials in seawater are sodium and chlorine. Seawater has an average salinity of 35 parts per thousand (ppt) of water. Actual salinity varies among different marine ecosystems.
Marine ecosystems can be divided into the following zones: oceanic (the relatively shallow part of the ocean that lies over the continental shelf); Profundal (bottom or deep water) ; Benthic (bottom substrates); Intertidal (the area between high and low tides) ; estuaries; Salt marshes; Coral reefs; and hydrothermal vents (where chemosynthetic sulfur bacteria from the food base).
Classas of organisms found in marine ecosystems include brown algae, dinoflagellates, corals, cephalopods, echinoderms and sharks. Fish caught in marine ecosystems are the biggest source of commercial foods obtained from wild populations.
Environmental problems concerning marine ecosystems include unsustainable exploitation of marine resources (for example overfishing of certain species), marine pollution, climate change, and building on coastal areas.
Lake ecosystems can be divided into zones: pelagic (open offshore waters) ; profundal; littoral (nearshore shallow waters) ; and riparian (the area of land bordering a body of water). Two important subclasses of lakes are ponds, which typically are small lakes that intergrade with wetlands, and water reservoirs. Many lakes, or bays within them, gradually become enriched by nutrients and fill in with organic sediments, a process called eutrophication. Eutrophication is accelerated by human activity within the water catchment area of the lake.
The major zones in river ecosystems are determined by the river bed′s gradient or by the velocity of the current. Faster moving turbulent water typically contains greater concentrations of dissolved oxygen, which supports greater biodiversity than the slow moving water of pools. These distinctions forms the basis for thedivision of rivers into upland and lowland rivers. The food base of streams within riparian forests is mostly derived from the trees, but wider streams and those that lack a canopy derive the majority of their food base from algae. Anadromous fish are also an important source of nutrients. Environmental threats to rivers include loss of water, dams, chemical pollution and introduced species.
Aquatic ecosystems perform many important environmental functions. For example, they recycle nutrients, purify water, attenuate floods, recharge ground water and provide habitats for wildlife. Aquatic ecosystems are also used for human recreation, and are very important to the tourism industry, especially in coastal regions.
The health of an aquatic ecosystem is degraded when the ecosystem′s ability to absorb a stress has been exceeded. A stress on an aquatic ecosystem can be a result of physical, chemical or biological alterations of the environment. Physical alterations include change in water temperature, water flow and light availability. Chemical alterations include changes in the loading rates of biostimulatory nutrients, oxygen consuming materials, and toxins. Biological alterations include the introduction of exotic species. Human populations can impose excessive stresses on aquatic ecosystems.
Contents
1 – Introduction
2 – Acoustic Ecology
3 – Algal Bloom
4 – Aquatic Adaptation
5 – Freshwater Ecology
6 – Aquatic Biodiversity
7 – Plankton
8 – Aquatic Predation
9 – Benthos
10 – Deep-sea Exploration
11 – Ecohydrology
12 – GIS and Aquatic Science
13 – Freshwater Fish
14 – Lentic Ecosystem
15 –Lotic Ecosystem
16 – Coral Reef
17 – Life in Water
18 – Marine Ecology
19 – The Aquatic Environment
20 – Instream Water Issues
ساحة النقاش