An aquatic ecosystem is an ecosystem 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 fresh water ecosystem (Alexander, 1999).

Autotrophic organisms are producers that generate organic compound from inorganic material. Algae use solar energy to generate biomass from carbon dioxide and are possibly the most important autotrophic organism in aquatic environments. (Alexander 1999) Euryhaline organisms are salt tolerant and can survive in marine ecosystems, while stenohaline or salt intolerant species can only live in fresh water environment. Other mammals and many animals act as reservoirs of oocysts which can infect humans.

Hepatitis A is an enteric virus that is very small; it   can be transferred through contaminated water causing outbreaks. The virus is excreted by a person carrying it, and if the sewage contaminates the water supply, then the virus is carried in the water until it is consumed by a host.
            Helminths are parasitic worms that grow and multiply in sewage and wet soil. They enter the body by burrowing through the skin, or by ingestion of the worm in one of its many lifecycle phases.
            The microorganisms, or microbes, that constitutes the foundation of the aquatic abundance include bacteria, bacteria – like organism called archaea, viruses, protozoa, helminths, and protists. Microbes are natural and vital members of all aquatic communities, and are the foundation of lake and stream ecology. Without them; the natural water worlds would not be possible (Madigan et.al, 2000). Certain microbes, however, when present in excessive numbers, pose a threat to human health (www.freedrinkingwater). Leaves and branches that fall into lake and streams are an important source of organic matter. Bacteria and other microbes break down these materials, making their nutrients available for other aquatic creatures.

Water microbiology is concern with the microorganisms that live in water, or can be transported from one habitat to another by water; water can support the growth of many types of microorganism. This can be advantageous. For example, the chemical strains of yeast provide us with bear and bread. As well, the growth of some bacteria in contaminated water can help digest the poisons from water.
            However presence of other disease causing microbes in water is unhealthy and even life threatening. For example bacterial that live in the intestinal tract of humans and other warm blooded animal such as Eschericha Coli, Salmonella Shigella, and vibrio, can contaminated water if feaces enters the water. Contaminated of drinking water with a type of Escherichia coli known as 0157:H7 can be fatal. The intestinal tract of warm blooded animals also contains viruses that can contaminate water and cause disease examples include rotavirus and entero viruses and the coxsackie virus. Another group of microbes of concern in water microbiology are protozoa; the two protozoa of the most concern are the giardia and the cryptosporidium. They live normally in the intestinal treat of animals such as beaver and dear. Giardia and cryptosporidium form dormant and hardy forms called cysts during their life cycles. The cysts forms are resistant to chlorine, which is the most popular form of drinking water disinfection, and can pass through the filters used in many water treatment plants (WHO, 1996). If ingested in drinking water they can cause debilitating and prolonged diarrhea in humans and can be life threatening to those people with impaired immune systems.
            Many microorganisms are found naturally in fresh and salt water. These include bacteria, cyanobacteria, protozoa, algae, and tiny animals such as rotifers. These can be important in the food chain that forms the basis of life in the water. For example, the microbes called cyanobacteria can convert the energy of the sun into the energy it needs to live. The plentiful numbers of these organisms in turn are used as food for other life. The algae that thrive in water are also an important food source for other forms of life.
            A variety of microorganisms live in fresh water. The region of a water body near the shoreline (the littoral zone) is well lighted, shallow, and warmer than other regions of the water. Photosynthetic algae and bacteria that use light as energy thrive in this zone. Further away from the shore is the limnitic zone. Photosynthetic microbes also line here. As the water deepens, temperatures become colder and the oxygen concentration and light in the water decrease. Now microbes that require oxygen do not thrive. Instead, purple and green sulfur bacteria, which can grow without oxygen, dominate (Madigan et. al 2000). Finally,    at the bottom of fresh waters (the benthic zone), few microbes survives. Bacteria that can survive in the absence of oxygen and sunlight, such as methane producing bacteria, thrive. Saltwater presents a different environment to microorganism. The higher salt concentration, higher pH, and lower nutrients, relative to freshwater, are lethal to many microorganisms.   But, salt loving (halophilic) bacteria abound near the surface, and same bacteria that also live in freshwater are plentiful (i.e; pseudomonas and vibrio). Also, in 2001 researchers demonstrated that the ancient’s form of microbial life known as archaebacteria is one of the dominant forms of life in the ocean. The role of archaebacteria in the ocean food chain is not yet known, but must of vital importance.
            Another microorganism found in saltwater is a type of algae known as dinoflagellelates. The rapid growth and multiplication of dinoflagellelates can turn the water red. This “red tide” depletes the water of nutrients and oxygen which can cause many fish to die. As well, humans can become ill by eating contaminated fish.
            Water can also be an ideal means of transporting microorganism form one place to another. For example, the water that is carried in the hulls of ships to stabilize the vessels during their ocean voyages is now known to be a means of transporting microorganism, around the globe (Ruiz e.t al. 2000). One of these organisms, a bacterium called vibrio cholerae, causes life threatening diarrhea in humans. Drinking water is usually treated to minimize the risk of microbial contamination. The importance of drinking water treatments has been known for centuries. For example in pre-Christmas times, the storage of drinking water in jugs made of metal was practiced. Now, the anti-bacterial effect of some metal is known.  

            Like all ecosystems, fresh water ecosystems require energy inputs to sustain the organisms within. In lakes and streams, plants and also certain microbes conduct photosynthesis to harvest the sun’s energy.
            Microbial photosynthesizers include protists (Known as algae) and cyanobacteria. Other protists and animals feed on these organisms, forming the next link in the food chain. (www.lenntech)
            Decomposers form an especially important part of fresh-water ecosystems because they consume dead bodies of plants animals and other microbes. These microbial agents of decay are can important part of the ecosystem because they convert detritus (dead and decaying matter) and organic materials into needed nutrients, such as nitrate, phosphate, and sulfate. Decomposers and other microbe are thus essential to the major biogeochemical cycles by various part of the ecosystem, both living and non-living. Without decomposers, minerals and nutrients critical to plant and animal growth would not be made available to support other levels of the fresh-water food chain (www.primewater).

            Aerobic decomposers in water need oxygen to survive and do their work. The lapping waves and babbling brook help increase the level of dissolved oxygen that is crucial to so many creatures in lake and stream ecosystem, none more so than the bacteria. If there is not enough oxygen in the water, many parts of the system suffer; the aerobic decomposers cannot digest plant matter, insects cannot develop and mature, and fish cannot play their part, whether browsing for small food particles or eating other fish.
            The bacterium vibrio cholerae, while rare in the United States, remains a significant source of disease and death in countries without advanced sewage treatment and with no potable water supplies. For example, a cholerae epidemic in 1991 killed more than a thousand people in Peru (South America) where more than 150,000 case of the illness were confirmed.

Alexander, David E (1999) Encyclopedia of environmental  science Springer.
Madigan, M.M., J. Martinko, and J. Parker (2000) Brock Biology of Microorganisms. 8th edition pg 2-5.
Ruiz, G.M., T.K. Rawlings, F.C. Dobbs, et al. (2000) “Global spread of microorganisms by ships, volume 1.
WHO, (1996) Guideline for drinking water quality. 2:2
www.freedrinkingwater.com / microorganism.
www.lenntech.com/water microbiology 


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