(Environment & Ecology) Terrestrial Biomes - Aquatic Biomes, Eutrophication, Ponds, Lakes & Fresh Water Ecosystems


Aquatic Biomes

Water covers about 75% of our planet. From oceans to rivulets, aquatic biomes are host to a wide variety of life-forms, and minerals, from the most common algae to the most mysterious deep-sea creature. In fact, this is where life began billions of years ago, when amino acids first started to come together, Without water, most life forms would be unable to sustain themselves and the Earth would be a barren, desert-like place. Although water temperatures can vary widely, aquatic areas tend to be cooler.

Aquatic biomes (ecosystem) are a group of interacting organisms dependent on one another and their water environment for nutrients (e.g., nitrogen and phosphorus) and shelter, Familiar examples are ponds, lakes and rivers, but aquatic ecosystems also include areas such as floodplains and wetlands, which are flooded with water for all your or only parts of the year, Seemingly inhospitable aquatic ecosystems can sustain life. Thermal springs, for instance, support algae and some insect species at water temperatures near the boiling point; tiny worms live year-round on the ice fields;  and some highly polluted waters can support large populations of bacteria. Even a drop of water is an aquatic ecosystem, since it contains or can support living organisms. In fact, ecologies how these larger aquatic ecosystems work.

These biomes make up about 75% of the total earth’s surface. Life forms in these waters depend on the abiotic factors such as sunlight entering the waters, temperature, Pressure, salt content and so on. Water biomes with lots of light tend to have more flora diversity and the growth of algae and plankton is more. Small water bodies that freeze during the cold seasons, or dry out in the dry and hot seasons tend to have less diversity. Examples of animals found in marine biomes include star fishes, sharks and tuna and sea birds Examples of animals in freshwater biomes are very important include salmon, tilapia worms, water-surface insects and crabs. Aquatic biomes are very important because apart from being home to millions of water animals, they also form the basis of the water cycle and help with atmospheric moisture, cloud formation and precipitation.

Main concepts of terrestrial primary succession can be applied to aquatic ecosystems except for oceans, Over time, most aquatic ecosystem are replaced by terrestrial ecosystems as aquatic ecosystem receive continuous input of soil particles and organic matters. As sediment increases, water depth decreases and types of organisms inhabiting the  ecosystem also change.

Aquatic Biomes are three-dimensional environments that can be divided into district zones based on characteristics such as depth, tidal flow, temperature, and proximity to landmasses. On these parameters, they can be divided into following three parts, which can further be divided in to various sub parts.

1. Fresh Water: Very Small proportion of earth’s area that is only 0.8 percent of the earth’s surface is covered by them. Primary production in a fresh-water ecosystem is controlled by light and nutrients availability. Fresh water can be defined as the water that contains a relatively small amount of dissolved chemical compounds. It includes : Standing Water-lakes and ponds and Moving Water-Rivers & Streams.

2. Transitional Communities: They act as eco tone between terrestrial and aquatic ecosystems, as they lay between the regions of water and landmass hence their inhabitants have to adapt accordingly. They have further been divided as Estuaries and Wetlands.

3. Marine Ecosystem: About 71% of the earth’s surface is covered by marine ecosystem. Marine ecosystem involves: Shorelines, Coral Reefs and Open Ocean.

Fresh Water Ecosystems

Freshwater is defined as having a low salt concentration-usually less than 1%. They are closely linked to soils and biotic components of terrestrial biomes through which they pass. Their characteristics are influenced by patterns and speed of water flow and climate of area in which it is located. Plants and animals in freshwater regions are adjusted to the low salt content and would not be able to survive in areas of high salt concentration (i.e. ocean), The fresh water ecosystem is limited by solar radiation and temperature. Their nutrient limitations are common to that of marine ecosystems, but phosphorus is usually limiting nutrient (rather than nitrogen as in oceans), hence there has been a shift in late 1970’s to phosphate-free detergents.

Freshwater regions have been divided in two categories-standing (lentic) bodies of water, which includes lakes, ponds etc. and moving (lotic) bodies of water, i.e. rivers, streams etc.

Ponds and Lakes

These regions range in size from just a few square meters to thousands of square kilometres. Ponds and lakes may have limited species diversity since they are often isolated from one another and from other water sources like rivers and oceans.

Lakes are large, natural bodies of Standing fresh water, Formed when precipitation, runoff, groundwater seepage fills depressions in earth’s surface. These depressions can be formed by glaciation (Great Lakes, NA), crustal displacement (Lake Nyasa, East Africa) and as big as small seas. Large lakes may have many of same characteristics as oceans.

Lakes and ponds are divided into three different “Zones” which are usually determined by depth and distance from the shoreline. They have been divided in 4 zones as follow:

A. Littoral zone – The topmost zone near the shore of a lake or pond is the Littoral zones This Zone is the warmest since it is shallow, well lit and can absorb more of the sun’s heat. It sustains a fairly diverse community, which can include several species of algae, rooted and floating aquatic plants, grazing snails, claims, insects, crustaceans fishes, and amphibians.

B. Limnetic zone – The near-surface open water surrounded by the littoral zone is this limnetic zone. This zone is well-lit open surface water and farther from the shore, extending to depth penetrated by light. This zone is occupied by phytoplankton, zooplankton, higher animals and produces food and oxygen that supports most of lake’s consumers.

C. Profundal zone – The deepest zone of the lake is the profundal zone. This zone is much colder and denser than the other two. Little light penetrates all the way through the limnetic zone into the profundal zone. It consists of deep, aphotic regions, lacking in oxygen and which are too dark for photosynthesis. This zone is inhabited by fish adapted to cool dark waters.

D. Benthic zone – This zone is actually bottom of lake. Inhabited by organisms that can tolerate cool temperatures and low oxygen levels. Mostly decomposers, detritus feeders and fish that swim from one zone to other inhabit this zone. It is nourished mainly by dead matter that falls from the littoral and limnetic zone and by sediments washing into lakes.

Lakes are often classified according to their production of organic mattered alternatively, Lakes have been classified in following three categories on the basis of the nutrient content or productivity.

A. Oligotrophic – A newly formed lake generally has a small supply of plant nutrients and is called an Oligotrophic lake, i.e., poorly nourished. This type of lake is deep cold having steep banks and small surface area relative to its depth. This lake nutrient-Poor and hence phytoplanktons are sparse. Such a lakes are not very productive and hence do not contain much life. Waters of Oligotrophic Lake are often very clear and have low sediments in decomposable organic matter. Such lakes are generally found in undisturbed regions free from any human interference, for example Lake Baikal in Siberia.

B. Eutrophic – Over time, sediments, organic material and in organic nutrients wash into most oligotrophic lakes giving impetus to the growth of flora and fauna. These when decompose form bottom sediments in benthos. A lake with a large or excessive supply of nutrients (mostly nitrates and phosphates) needed by producers is called a Eutrophic (well nourished) lake. These lakes typically are shallow and have murky brown or green water with poor visibility. Excessive organic matter content in Benthos leads to high decomposition rates and potentially low oxygen, Because of human activity, there  can be large input of nutrients into the lakes resulting into eutrophication (called cultural eutrophication).

C. Mesotrophic – Many lakes fall somewhere between two extremes of nutrients enrichment and therefore are called Mesotrophic lakes. They have moderate nutrient content and moderate amount of Phytoplankton, reasonably productive. Such types of lakes can be considered as a transition phase from Oligotrophic to Eutrophic.


The term ‘eutrophic’ means well-nourished; thus, ‘eutrophication’ refers to natural or artificial addition of nutrients to bodies of water and to the effects of the added nutrient. When the effects are undesirable, eutrophication may be considered a form of pollution. Alternatively, the enrichment of bodies of fresh water by inorganic plant nutrients (e.g. nitrate, phosphate) is called Eutrophication. It may occur naturally but can also be the result of human activity) (cultural eutrophication from fertilizer runoff and sewage discharge) and is particularly evident in slow-moving rivers and shallow lakes, Increased sediment deposition can eventually raise the level of the lake or river bed, allowing land plants to colonize the edges, and eventually converting the area to dry land.

Eutrophication occurs naturally over centuries as lakes age and are filled in with sediments However, human activities have accelerated the rate and extent of eutrophication through both point-source discharges and non-point loadings of limiting nutrients, such as nitrogen and phosphorus, into aquatic ecosystems. Eutrophication was recognized as a pollution problem in European and North American lakes and reservoirs in the mid-20th Century. Runoff from agriculture and development, pollution from septic systems and sewers, and other human-related activities increase the flux of both inorganic nutrients and organic substances into lakes enhancing eutrophication.

Effects of Eutrophication

Algal Blooms – An algal bloom or marine bloom or water bloom is a rapid increase in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically only one or a few phytoplankton species are involved and some blooms may be recognized by discoloration of the water resulting from the high density of pigmented cells. Although there is a no officially recognized threshold level, algae can be considered to be blooming at concentrations of hundreds to thousands of cells per milliliter, depending on the causative species. Algal bloom concentration may reach millions of cells per milliliter. Colours observed are green, yellowish-brown, or red. Bright green blooms may also occur. These are a result of blue-green algae, which are actually bacteria (cyanobacteria).

Some algal blooms are the result of an excess of nutrients (particularly phosphorus and nitrogen) into waters and higher concentrations of these nutrients in water cause increased growth of algae and green plants. As more algae and plants grow, others die. This dead organic matter becomes food for bacteria that decompose it. With more food available, the bacteria increase in number and use up the dissolved oxygen in the water. When the dissolved oxygen content decreases, many fish and aquatic insects cannot survive. This results in a dead area. Algal blooms may also be of concern as some species of algae produce neurotoxins.

At the high cell concentrations reached during some blooms, these toxins may have severe, biological impacts on wildlife. Algal blooms composed of phytoplankton known to naturally produce bio-toxins are often called Harmful Algal Blooms, or HABs.

Harmful Algal Blooms (HABs) – while single species blooms can turn the water surface red, brown, yellow, green or white, they are often generically referred to as “red tides” and are often associated with harmful or toxic effects. When the blooming microalgae have properties that are deemed harmful to humans or other life, the blooms are called Harmful Algal Blooms, or HABs. In recent years, there has been growing alarm over what appears to occurring over larger areas and lasting longer, HABs are also being recorded in areas where previously they were not known. In other cases, algal species previously benign, or even unknown, have suddenly emerged to become problematic. HABs can kill marine life and cause losses to aquaculture operations. A number of species release powerful toxins that can make their way through the food web to affect seabirds, marine mammals and humans sometimes fatally.

Some toxic species can cause a variety of human ailments, contracted either through inhaling airborne toxins, skin contact or , more commonly, eating contaminated shellfish, These toxins may cause amnesia, stomach cramps, nausea, memory loss, paralysis and even death. Not all HABs are toxic. Only forty or so species are believed to produce such potent toxins. Some species are merely unpalatable to other marine life because of gelatinous envelopes or other characteristics and they exact their harmful effects by essentially starving the food chain. Other species can cause physical damage, as the blooms of species which contain barbs that lodge among gill tissues of fish, causing death. Such blooms can cause a great deal to financial damage by killing farmed fish, which are grown in crowded aquaculture pens. Some blooms of algae are not inherently harmful but may result in severe environment impacts. For instance, low oxygen conditions may result from the decay of excessive amounts of algal growth caused by nutrient pollution.

Although there are some scientists who believe the increase in reports of HABs is a function of increased awareness and monitoring, others have provided compelling evidence that, for some regions, human activities play an important role. The primary human contribution to HABs is thought to be nutrient pollution – from, amongst other things, agriculture, sewage outfalls and mining – creating a more favorable, nutrient – rich environment in coastal waters in which certain groups of phytoplankton can thrive. Climate change may also be making some coastal environments more hospitable to harmful phytoplankton species, Many species of phytoplankton are also transported around the world in ships’ ballast water and discharged in areas where they did not previously occur. Others are distributed accidentally through the transfer of shellfish for aquaculture.

Hypoxia – Hypoxia is reduced dissolved oxygen content of a body of water. The algae may keep out the light and when they eventually die. they are decomposed by bacteria which consume oxygen in this process so that the water may become temporarily anoxic (hypoxia) which may be toxic to aquatic life.

Other effects of Eutrophication

  • Fishes and various aquatic organisms die on large scale.
  • The water can have a bad taste, color and odor which have a negative impact on the environment and surroundings.
  • It also reduces the biodiversity caused by loss of species.
  • Some phytoplankton species produce toxins that cause severe symptoms such as diarrhea, memory loss, paralysis and in severe cases death.