Lake ecosystem

A lake ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions.[1]

Lake ecosystems are a prime example of lentic ecosystems. Lentic refers to stationary or relatively still water, from the Latin lentus, which means sluggish. Lentic waters range from ponds to lakes to wetlands, and much of this article applies to lentic ecosystems in general. Lentic ecosystems can be compared with lotic ecosystems, which involve flowing terrestrial waters such as rivers and streams. Together, these two fields form the more general study area of freshwater or aquatic ecology.

Lentic systems are diverse, ranging from a small, temporary rainwater pool a few inches deep to Lake Baikal, which has a maximum depth of 1642 m.[2] The general distinction between pools/ponds and lakes is vague, but Brown[1] states that ponds and pools have their entire bottom surfaces exposed to light, while lakes do not. In addition, some lakes become seasonally stratified (discussed in more detail below.) Ponds and pools have two regions: the pelagic open water zone, and the benthic zone, which comprises the bottom and shore regions. Since lakes have deep bottom regions not exposed to light, these systems have an additional zone, the profundal.[3] These three areas can have very different abiotic conditions and, hence, host species that are specifically adapted to live there.[1]

Important abiotic factors

Light

Light provides the solar energy required to drive the process of photosynthesis, the major energy source of lentic systems.[2] The amount of light received depends upon a combination of several factors. Small ponds may experience shading by surrounding trees, while cloud cover may affect light availability in all systems, regardless of size. Seasonal and diurnal considerations also play a role in light availability because the shallower the angle at which light strikes water, the more light is lost by reflection. This is known as Beer's law.[4] Once light has penetrated the surface, it may also be scattered by particles suspended in the water column. This scattering decreases the total amount of light as depth increases.[3][5] Lakes are divided into photic and aphotic regions, the prior receiving sunlight and latter being below the depths of light penetration, making it void of photosynthetic capacity.[2] In relation to lake zonation, the pelagic and benthic zones are considered to lie within the photic region, while the profundal zone is in the aphotic region.[1]

Temperature

Temperature is an important abiotic factor in lentic ecosystems because most of the biota are poikilothermic, where internal body temperatures are defined by the surrounding system. Water can be heated or cooled through radiation at the surface and conduction to or from the air and surrounding substrate.[4] Shallow ponds often have a continuous temperature gradient from warmer waters at the surface to cooler waters at the bottom. In addition, temperature fluctuations can vary greatly in these systems, both diurnally and seasonally.[1]

Temperature regimes are very different in large lakes (Fig. 2). In temperate regions, for example, as air temperatures increase, the icy layer formed on the surface of the lake breaks up, leaving the water at approximately 4 °C. This is the temperature at which water has the highest density. As the season progresses, the warmer air temperatures heat the surface waters, making them less dense. The deeper waters remain cool and dense due to reduced light penetration. As the summer begins, two distinct layers become established, with such a large temperature difference between them that they remain stratified. The lowest zone in the lake is the coldest and is called the hypolimnion. The upper warm zone is called the epilimnion. Between these zones is a band of rapid temperature change called the thermocline. During the colder fall season, heat is lost at the surface and the epilimnion cools. When the temperatures of the two zones are close enough, the waters begin to mix again to create a uniform temperature, an event termed lake turnover. In the winter, inverse stratification occurs as water near the surface cools freezes, while warmer, but denser water remains near the bottom. A thermocline is established, and the cycle repeats.[1][2]

LSE Stratification
Fig. 2 Seasonal stratification in temperate lakes

Wind

Foamlines
Fig. 3 Illustration of Langmuir rotations; open circles=positively buoyant particles, closed circles=negatively buoyant particles

In exposed systems, wind can create turbulent, spiral-formed surface currents called Langmuir circulations (Fig. 3). Exactly how these currents become established is still not well understood, but it is evident that it involves some interaction between horizontal surface currents and surface gravity waves. The visible result of these rotations, which can be seen in any lake, are the surface foamlines that run parallel to the wind direction. Positively buoyant particles and small organisms concentrate in the foamline at the surface and negatively buoyant objects are found in the upwelling current between the two rotations. Objects with neutral buoyancy tend to be evenly distributed in the water column.[2][3] This turbulence circulates nutrients in the water column, making it crucial for many pelagic species, however its effect on benthic and profundal organisms is minimal to non-existent, respectively.[3] The degree of nutrient circulation is system specific, as it depends upon such factors as wind strength and duration, as well as lake or pool depth and productivity.

Chemistry

Oxygen is essential for organismal respiration. The amount of oxygen present in standing waters depends upon: 1) the area of transparent water exposed to the air, 2) the circulation of water within the system and 3) the amount of oxygen generated and used by organisms present.[1] In shallow, plant-rich pools there may be great fluctuations of oxygen, with extremely high concentrations occurring during the day due to photosynthesis and very low values at night when respiration is the dominant process of primary producers. Thermal stratification in larger systems can also affect the amount of oxygen present in different zones. The epilimnion is oxygen rich because it circulates quickly, gaining oxygen via contact with the air. The hypolimnion, however, circulates very slowly and has no atmospheric contact. Additionally, fewer green plants exist in the hypolimnion, so there is less oxygen released from photosynthesis. In spring and fall when the epilimnion and hypolimnion mix, oxygen becomes more evenly distributed in the system. Low oxygen levels are characteristic of the profundal zone due to the accumulation of decaying vegetation and animal matter that “rains” down from the pelagic and benthic zones and the inability to support primary producers.[1]

Phosphorus is important for all organisms because it is a component of DNA and RNA and is involved in cell metabolism as a component of ATP and ADP. Also, phosphorus is not found in large quantities in freshwater systems, limiting photosynthesis in primary producers, making it the main determinant of lentic system production. The phosphorus cycle is complex, but the model outlined below describes the basic pathways. Phosphorus mainly enters a pond or lake through runoff from the watershed or by atmospheric deposition. Upon entering the system, a reactive form of phosphorus is usually taken up by algae and macrophytes, which release a non-reactive phosphorus compound as a byproduct of photosynthesis. This phosphorus can drift downwards and become part of the benthic or profundal sediment, or it can be remineralized to the reactive form by microbes in the water column. Similarly, non-reactive phosphorus in the sediment can be remineralized into the reactive form.[2] Sediments are generally richer in phosphorus than lake water, however, indicating that this nutrient may have a long residency time there before it is remineralized and re-introduced to the system.[3]

Lentic system biota

Bacteria

Bacteria are present in all regions of lentic waters. Free-living forms are associated with decomposing organic material, biofilm on the surfaces of rocks and plants, suspended in the water column, and in the sediments of the benthic and profundal zones. Other forms are also associated with the guts of lentic animals as parasites or in commensal relationships.[3] Bacteria play an important role in system metabolism through nutrient recycling,[2] which is discussed in the Trophic Relationships section.

Primary producers

Nelumbo nucifera LOTUS bud
Nelumbo nucifera, an aquatic plant.

Algae, including both phytoplankton and periphyton are the principle photosynthesizers in ponds and lakes. Phytoplankton are found drifting in the water column of the pelagic zone. Many species have a higher density than water which should make them sink and end up in the benthos. To combat this, phytoplankton have developed density changing mechanisms, by forming vacuoles and gas vesicles or by changing their shapes to induce drag, slowing their descent. A very sophisticated adaptation utilized by a small number of species is a tail-like flagellum that can adjust vertical position and allow movement in any direction.[2] Phytoplankton can also maintain their presence in the water column by being circulated in Langmuir rotations.[3] Periphytic algae, on the other hand, are attached to a substrate. In lakes and ponds, they can cover all benthic surfaces. Both types of plankton are important as food sources and as oxygen providers.[2]

Aquatic plants live in both the benthic and pelagic zones and can be grouped according to their manner of growth: 1) emergent = rooted in the substrate but with leaves and flowers extending into the air, 2) floating-leaved = rooted in the substrate but with floating leaves, 3) submersed = growing beneath the surface and 4) free-floating macrophytes = not rooted in the substrate and floating on the surface.[1] These various forms of macrophytes generally occur in different areas of the benthic zone, with emergent vegetation nearest the shoreline, then floating-leaved macrophytes, followed by submersed vegetation. Free-floating macrophytes can occur anywhere on the system’s surface.[2]

Aquatic plants are more buoyant than their terrestrial counterparts because freshwater has a higher density than air. This makes structural rigidity unimportant in lakes and ponds (except in the aerial stems and leaves). Thus, the leaves and stems of most aquatic plants use less energy to construct and maintain woody tissue, investing that energy into fast growth instead.[1] In order to contend with stresses induced by wind and waves, plants must be both flexible and tough. Light, water depth and substrate types are the most important factors controlling the distribution of submerged aquatic plants.[6] Macrophytes are sources of food, oxygen, and habitat structure in the benthic zone, but cannot penetrate the depths of the euphotic zone and hence are not found there.[1][5]

Invertebrates

Water strider G remigis
Water striders are predatory insects which rely on surface tension to walk on top of water. They live on the surface of ponds, marshes, and other quiet waters. They can move very quickly, up to 1.5 m/s.

Zooplankton are tiny animals suspended in the water column. Like phytoplankton, these species have developed mechanisms that keep them from sinking to deeper waters, including drag-inducing body forms and the active flicking of appendages such as antennae or spines.[1] Remaining in the water column may have its advantages in terms of feeding, but this zone’s lack of refugia leaves zooplankton vulnerable to predation. In response, some species, especially Daphnia sp., make daily vertical migrations in the water column by passively sinking to the darker lower depths during the day and actively moving towards the surface during the night. Also, because conditions in a lentic system can be quite variable across seasons, zooplankton have the ability to switch from laying regular eggs to resting eggs when there is a lack of food, temperatures fall below 2 °C, or if predator abundance is high. These resting eggs have a diapause, or dormancy period that should allow the zooplankton to encounter conditions that are more favorable to survival when they finally hatch.[7] The invertebrates that inhabit the benthic zone are numerically dominated by small species and are species rich compared to the zooplankton of the open water. They include Crustaceans (e.g. crabs, crayfish, and shrimp), molluscs (e.g. clams and snails), and numerous types of insects.[2] These organisms are mostly found in the areas of macrophyte growth, where the richest resources, highly oxygenated water, and warmest portion of the ecosystem are found. The structurally diverse macrophyte beds are important sites for the accumulation of organic matter, and provide an ideal area for colonization. The sediments and plants also offer a great deal of protection from predatory fishes.[3]

Very few invertebrates are able to inhabit the cold, dark, and oxygen poor profundal zone. Those that can are often red in color due to the presence of large amounts of hemoglobin, which greatly increases the amount of oxygen carried to cells.[1] Because the concentration of oxygen within this zone is low, most species construct tunnels or borrows in which they can hide and make the minimum movements necessary to circulate water through, drawing oxygen to them without expending much energy.[1]

Fish and other vertebrates

Fish have a range of physiological tolerances that are dependent upon which species they belong to. They have different lethal temperatures, dissolved oxygen requirements, and spawning needs that are based on their activity levels and behaviors. Because fish are highly mobile, they are able to deal with unsuitable abiotic factors in one zone by simply moving to another. A detrital feeder in the profundal zone, for example, that finds the oxygen concentration has dropped too low may feed closer to the benthic zone. A fish might also alter its residence during different parts of its life history: hatching in a sediment nest, then moving to the weedy benthic zone to develop in a protected environment with food resources, and finally into the pelagic zone as an adult.

Other vertebrate taxa inhabit lentic systems as well. These include amphibians (e.g. salamanders and frogs), reptiles (e.g. snakes, turtles, and alligators), and a large number of waterfowl species.[5] Most of these vertebrates spend part of their time in terrestrial habitats and thus are not directly affected by abiotic factors in the lake or pond. Many fish species are important as consumers and as prey species to the larger vertebrates mentioned above.

Trophic relationships

Primary producers

Lentic systems gain most of their energy from photosynthesis performed by aquatic plants and algae. This autochthonous process involves the combination of carbon dioxide, water, and solar energy to produce carbohydrates and dissolved oxygen. Within a lake or pond, the potential rate of photosynthesis generally decreases with depth due to light attenuation. Photosynthesis, however, is often low at the top few millimeters of the surface, likely due to inhibition by ultraviolet light. The exact depth and photosynthetic rate measurements of this curve are system specific and depend upon: 1) the total biomass of photosynthesizing cells, 2) the amount of light attenuating materials and 3) the abundance and frequency range of light absorbing pigments (i.e. chlorophylls) inside of photosynthesizing cells.[5] The energy created by these primary producers is important for the community because it is transferred to higher trophic levels via consumption.

Bacteria

The vast majority of bacteria in lakes and ponds obtain their energy by decomposing vegetation and animal matter. In the pelagic zone, dead fish and the occasional allochthonous input of litterfall are examples of coarse particulate organic matter (CPOM>1 mm). Bacteria degrade these into fine particulate organic matter (FPOM<1 mm) and then further into usable nutrients. Small organisms such as plankton are also characterized as FPOM. Very low concentrations of nutrients are released during decomposition because the bacteria are utilizing them to build their own biomass. Bacteria, however, are consumed by protozoa, which are in turn consumed by zooplankton, and then further up the trophic levels. Nutrients, including those that contain carbon and phosphorus, are reintroduced into the water column at any number of points along this food chain via excretion or organism death, making them available again for bacteria. This regeneration cycle is known as the microbial loop and is a key component of lentic food webs.[2]

The decomposition of organic materials can continue in the benthic and profundal zones if the matter falls through the water column before being completely digested by the pelagic bacteria. Bacteria are found in the greatest abundance here in sediments, where they are typically 2-1000 times more prevalent than in the water column.[7]

Benthic Invertebrates

Benthic invertebrates, due to their high level of species richness, have many methods of prey capture. Filter feeders create currents via siphons or beating cilia, to pull water and its nutritional contents, towards themselves for straining. Grazers use scraping, rasping, and shredding adaptations to feed on periphytic algae and macrophytes. Members of the collector guild browse the sediments, picking out specific particles with raptorial appendages. Deposit feeding invertebrates indiscriminately consume sediment, digesting any organic material it contains. Finally, some invertebrates belong to the predator guild, capturing and consuming living animals.[2][8] The profundal zone is home to a unique group of filter feeders that use small body movements to draw a current through burrows that they have created in the sediment. This mode of feeding requires the least amount of motion, allowing these species to conserve energy.[1] A small number of invertebrate taxa are predators in the profundal zone. These species are likely from other regions and only come to these depths to feed. The vast majority of invertebrates in this zone are deposit feeders, getting their energy from the surrounding sediments.[8]

Fish

Fish size, mobility, and sensory capabilities allow them to exploit a broad prey base, covering multiple zonation regions. Like invertebrates, fish feeding habits can be categorized into guilds. In the pelagic zone, herbivores graze on periphyton and macrophytes or pick phytoplankton out of the water column. Carnivores include fishes that feed on zooplankton in the water column (zooplanktivores), insects at the water’s surface, on benthic structures, or in the sediment (insectivores), and those that feed on other fish (piscivores). Fish that consume detritus and gain energy by processing its organic material are called detritivores. Omnivores ingest a wide variety of prey, encompassing floral, faunal, and detrital material. Finally, members of the parasitic guild acquire nutrition from a host species, usually another fish or large vertebrate.[2] Fish taxa are flexible in their feeding roles, varying their diets with environmental conditions and prey availability. Many species also undergo a diet shift as they develop. Therefore, it is likely that any single fish occupies multiple feeding guilds within its lifetime.[9]

Lentic food webs

As noted in the previous sections, the lentic biota are linked in complex web of trophic relationships. These organisms can be considered to loosely be associated with specific trophic groups (e.g. primary producers, herbivores, primary carnivores, secondary carnivores, etc.). Scientists have developed several theories in order to understand the mechanisms that control the abundance and diversity within these groups. Very generally, top-down processes dictate that the abundance of prey taxa is dependent upon the actions of consumers from higher trophic levels. Typically, these processes operate only between two trophic levels, with no effect on the others. In some cases, however, aquatic systems experience a trophic cascade; for example, this might occur if primary producers experience less grazing by herbivores because these herbivores are suppressed by carnivores. Bottom-up processes are functioning when the abundance or diversity of members of higher trophic levels is dependent upon the availability or quality of resources from lower levels. Finally, a combined regulating theory, bottom-up:top-down, combines the predicted influences of consumers and resource availability. It predicts that trophic levels close to the lowest trophic levels will be most influenced by bottom-up forces, while top-down effects should be strongest at top levels.[2]

Community patterns and diversity

Local species richness

The biodiversity of a lentic system increases with the surface area of the lake or pond. This is attributable to the higher likelihood of partly terrestrial species of finding a larger system. Also, because larger systems typically have larger populations, the chance of extinction is decreased.[10] Additional factors, including temperature regime, pH, nutrient availability, habitat complexity, speciation rates, competition, and predation, have been linked to the number of species present within systems.[2][6]

Succession patterns in plankton communities – the PEG model

Phytoplankton and zooplankton communities in lake systems undergo seasonal succession in relation to nutrient availability, predation, and competition. Sommer et al.[11] described these patterns as part of the Plankton Ecology Group (PEG) model, with 24 statements constructed from the analysis of numerous systems. The following includes a subset of these statements, as explained by Brönmark and Hansson[2] illustrating succession through a single seasonal cycle:

Winter
1. Increased nutrient and light availability result in rapid phytoplankton growth towards the end of winter. The dominant species, such as diatoms, are small and have quick growth capabilities. 2. These plankton are consumed by zooplankton, which become the dominant plankton taxa.

Spring
3. A clear water phase occurs, as phytoplankton populations become depleted due to increased predation by growing numbers of zooplankton.

Summer
4. Zooplankton abundance declines as a result of decreased phytoplankton prey and increased predation by juvenile fishes.
5. With increased nutrient availability and decreased predation from zooplankton, a diverse phytoplankton community develops.
6. As the summer continues, nutrients become depleted in a predictable order: phosphorus, silica, and then nitrogen. The abundance of various phytoplankton species varies in relation to their biological need for these nutrients.
7. Small-sized zooplankton become the dominant type of zooplankton because they are less vulnerable to fish predation.

Fall
8. Predation by fishes is reduced due to lower temperatures and zooplankton of all sizes increase in number.

Winter
9. Cold temperatures and decreased light availability result in lower rates of primary production and decreased phytoplankton populations. 10. Reproduction in zooplankton decreases due to lower temperatures and less prey.

The PEG model presents an idealized version of this succession pattern, while natural systems are known for their variation.[2]

Latitudinal patterns

There is a well-documented global pattern that correlates decreasing plant and animal diversity with increasing latitude, that is to say, there are fewer species as one moves towards the poles. The cause of this pattern is one of the greatest puzzles for ecologists today. Theories for its explanation include energy availability, climatic variability, disturbance, competition, etc.[2] Despite this global diversity gradient, this pattern can be weak for freshwater systems compared to global marine and terrestrial systems.[12] This may be related to size, as Hillebrand and Azovsky[13] found that smaller organisms (protozoa and plankton) did not follow the expected trend strongly, while larger species (vertebrates) did. They attributed this to better dispersal ability by smaller organisms, which may result in high distributions globally.[2]

Natural lake lifecycles

Lake creation

Lakes can be formed in a variety of ways, but the most common are discussed briefly below. The oldest and largest systems are the result of tectonic activities. The rift lakes in Africa, for example are the result of seismic activity along the site of separation of two tectonic plates. Ice-formed lakes are created when glaciers recede, leaving behind abnormalities in the landscape shape that are then filled with water. Finally, oxbow lakes are fluvial in origin, resulting when a meandering river bend is pinched off from the main channel.[2]

Natural extinction

All lakes and ponds receive sediment inputs. Since these systems are not really expanding, it is logical to assume that they will become increasingly shallower in depth, eventually becoming wetlands or terrestrial vegetation. The length of this process should depend upon a combination of depth and sedimentation rate. Moss[5] gives the example of Lake Tanganyika, which reaches a depth of 1500 m and has a sedimentation rate of 0.5 mm/yr. Assuming that sedimentation is not influenced by anthropogenic factors, this system should go extinct in approximately 3 million years. Shallow lentic systems might also fill in as swamps encroach inward from the edges. These processes operate on a much shorter timescale, taking hundreds to thousands of years to complete the extinction process.[5]

Human impacts

Acidification

Sulfur dioxide and nitrogen oxides are naturally released from volcanoes, organic compounds in the soil, wetlands, and marine systems, but the majority of these compounds come from the combustion of coal, oil, gasoline, and the smelting of ores containing sulfur.[3] These substances dissolve in atmospheric moisture and enter lentic systems as acid rain.[1] Lakes and ponds that contain bedrock that is rich in carbonates have a natural buffer, resulting in no alteration of pH. Systems without this bedrock, however, are very sensitive to acid inputs because they have a low neutralizing capacity, resulting in pH declines even with only small inputs of acid.[3] At a pH of 5–6 algal species diversity and biomass decrease considerably, leading to an increase in water transparency – a characteristic feature of acidified lakes. As the pH continues lower, all fauna becomes less diverse. The most significant feature is the disruption of fish reproduction. Thus, the population is eventually composed of few, old individuals that eventually die and leave the systems without fishes.[2][3] Acid rain has been especially harmful to lakes in Scandinavia, western Scotland, west Wales and the north eastern United States.

Eutrophication

Eutrophic systems contain a high concentration of phosphorus (~30 µg/L), nitrogen (~1500 µg/L), or both.[2] Phosphorus enters lentic waters from sewage treatment effluents, discharge from raw sewage, or from runoff of farmland. Nitrogen mostly comes from agricultural fertilizers from runoff or leaching and subsequent groundwater flow. This increase in nutrients required for primary producers results in a massive increase of phytoplankton growth, termed a plankton bloom. This bloom decreases water transparency, leading to the loss of submerged plants. The resultant reduction in habitat structure has negative impacts on the species’ that utilize it for spawning, maturation and general survival. Additionally, the large number of short-lived phytoplankton result in a massive amount of dead biomass settling into the sediment.[5] Bacteria need large amounts of oxygen to decompose this material, reducing the oxygen concentration of the water. This is especially pronounced in stratified lakes when the thermocline prevents oxygen rich water from the surface to mix with lower levels. Low or anoxic conditions preclude the existence of many taxa that are not physiologically tolerant of these conditions.[2]

Invasive species

Invasive species have been introduced to lentic systems through both purposeful events (e.g. stocking game and food species) as well as unintentional events (e.g. in ballast water). These organisms can affect natives via competition for prey or habitat, predation, habitat alteration, hybridization, or the introduction of harmful diseases and parasites.[4] With regard to native species, invaders may cause changes in size and age structure, distribution, density, population growth, and may even drive populations to extinction.[2] Examples of prominent invaders of lentic systems include the zebra mussel and sea lamprey in the Great Lakes.

See also

References

  1. ^ a b c d e f g h i j k l m n o p Brown, A. L. (1987). Freshwater Ecology. Heinimann Educational Books, London. p. 163. ISBN 0435606220.
  2. ^ a b c d e f g h i j k l m n o p q r s t u v w x y Brönmark, C.; L. A. Hansson (2005). The Biology of Lakes and Ponds. Oxford University Press, Oxford. p. 285. ISBN 0198516134.
  3. ^ a b c d e f g h i j k Kalff, J. (2002). Limnology. Prentice Hall, Upper Saddle, NJ. p. 592. ISBN 0130337757.
  4. ^ a b c Giller, S.; B. Malmqvist (1998). The Biology of Streams and Rivers. Oxford University Press, Oxford. p. 296. ISBN 0198549776.
  5. ^ a b c d e f g Moss, B. (1998). Ecology of Freshwaters: man and medium, past to future. Blackwell Science, London. p. 557. ISBN 0632035129.
  6. ^ a b Keddy, P.A. (2010). Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. ISBN 0521739675.
  7. ^ a b Gliwicz, Z. M. "Zooplankton", pp. 461–516 in O'Sullivan (2005)
  8. ^ a b Jónasson, P. M. "Benthic Invertebrates", pp. 341–416 in O'Sullivan (2005)
  9. ^ Winfield, I. J. "Fish Population Ecology", pp. 517–537 in O'Sullivan (2005)
  10. ^ Browne, R. A. (1981). "Lakes as islands: biogeographic distribution, turnover rates, and species composition in the lakes of central New York". Journal of Biogeography. 8 1: 75–83. doi:10.2307/2844594. JSTOR 2844594.
  11. ^ Sommer, U.; Z. M. Gliwicz; W. Lampert; A. Duncan (1986). "The PEG-model of seasonal succession of planktonic events in freshwaters". Archiv für Hydrobiologie. 106: 433–471.
  12. ^ Hillebrand, H. (2004). "On the generality of the latitudinal diversity gradient" (PDF). American Naturalist. 163 (2): 192–211. doi:10.1086/381004. PMID 14970922.
  13. ^ Hillebrand, H.; A. I. Azovsky (2001). "Body size determines the strength of the latitudinal diversity gradient". Ecography. 24 (3): 251–256. doi:10.1034/j.1600-0587.2001.240302.x.

Bibliography

Bugdasheni Managed Reserve

Bugdasheni Managed Reserve (Georgian: ბუღდაშენის ტბის აღკვეთილი) is a protected area in Ninotsminda Municipality in Samtskhe-Javakheti region of Georgia. It protects Bugdasheni Lake on the south-eastern part of the volcanic Javakheti Plateau, at an altitude of 2042 m above sea level.

Bugdasheni Lake ecosystem is undergoing restoration. It has been considered to be included into Ramsar Convention list of Wetlands of international importance.Bugdasheni Managed Reserve is part of Javakheti Protected Areas which also includes Javakheti National Park, Kartsakhi Managed Reserve, Sulda Managed Reserve, Khanchali Managed Reserve, Madatapa Managed Reserve.

Cooperative Institute for Limnology and Ecosystems Research

The Cooperative Institute for Limnology and Ecosystems Research (CILER) fosters research collaborations between the National Oceanic and Atmospheric Administration (NOAA) Office of Oceanic and Atmospheric Research (OAR) Great Lakes Environmental Research Laboratory (GLERL), Michigan State University (MSU), and the University of Michigan (UM). It is one of 16 NOAA Cooperative Institutes (CIs).The CILER research themes are:

Climate and Large Lake Dynamics

Coastal and Nearshore Processes

Large Lake Ecosystem Structure and Function

Remote Sensing of Large Lake and Coastal Ocean Dynamics

Marine Environmental Engineering

Dystrophic lake

Dystrophic lakes, also known as humic lakes, are lakes that contain high amounts of humic substances and organic acids. The presence of these substances causes the water to be brown in colour and have a generally low pH of around 4.0-6.0. Due to these acidic conditions, there is little biodiversity able to survive, consisting mostly of algae, phytoplankton, picoplankton, and bacteria. Ample research has been performed on the many dystrophic lakes located in Eastern Poland, but dystrophic lakes can be found in many areas of the world.

Experimental Lakes Area

IISD Experimental Lakes Area (IISD-ELA, known as ELA before 2014) is an internationally unique research station encompassing 58 formerly pristine freshwater lakes in Kenora District Ontario, Canada. Previously run by Fisheries and Oceans Canada, after being de-funded by the Canadian Federal Government, the facility is now managed and operated by the International Institute for Sustainable Development (IISD) and has a mandate to investigate the aquatic effects of a wide variety of stresses on lakes and their catchments. IISD-ELA uses the whole ecosystem approach and makes long-term, whole-lake investigations of freshwater focusing on eutrophication.In an article published in AAAS's well-known scientific journal Science, Eric Stokstad described ELA's "extreme science" as the manipulation of whole lake ecosystem with ELA researchers collecting long-term records for climatology, hydrology, and limnology that address key issues in water management. The site has influenced public policy in water management in Canada, the USA, and around the world.Minister of State for Science and Technology, Gary Goodyear, argued that "our government has been working hard to ensure that the Experimental Lakes Area facility is transferred to a non-governmental operator better suited to conducting the type of world-class research that can be undertaken at this facility" and that "[t]he federal government has been leading negotiations in order to secure an operator with an international track record." On April 1, 2014, the International Institute for Sustainable Development announced that it had signed three agreements to ensure that it will be the long-term operator of the research facility and that the facility would henceforth be called IISD Experimental Lakes Area. Since taking over the facility, IISD has expanded the function of the site to include educational and outreach opportunities and a broader research portfolio.

Fish pond

A fish pond, or fishpond, is a controlled pond, artificial lake, or reservoir that is stocked with fish and is used in aquaculture for fish farming, or is used for recreational fishing or for ornamental purposes. In the medieval European era it was typical for monasteries and castles (small, partly self-sufficient communities) to have a fish pond.

Geography of Cambodia

Cambodia is a country in mainland Southeast Asia, bordering Thailand, Laos, Vietnam, the Gulf of Thailand and covers a total area of 181,035 km2 (69,898 sq mi). The country is situated in its entirety inside the tropical Indomalayan ecozone and the Indochina Time zone (ICT).Cambodia's main geographical features are the low lying Central Plain that includes the Tonlé Sap basin, the lower Mekong River flood-plains and the Bassac River plain surrounded by mountain ranges to the north, east, in the south-west and south. The central lowlands extend into Vietnam to the south-east. The south and south-west of the country constitute a 443 km (275 mi) long coast at the Gulf of Thailand, characterized by sizable mangrove marshes, peninsulas, sandy beaches and headlands and bays. Cambodia's territorial waters account for over 50 islands. The highest peak is Phnom Aural, sitting 1,810 metres (5,938 ft) above sea level.The landmass is bisected by the Mekong river, which at 486 km (302 mi) is the longest river in Cambodia. After extensive rapids, turbulent sections and cataracts in Laos, the river enters the country at Stung Treng province, is predominantly calm and navigable during the entire year as it widens considerably in the lowlands. The Mekong's waters disperse into the surrounding wetlands of central Cambodia and strongly affect the seasonal nature of the Tonlé Sap lake.Two third of the country's population live in the lowlands, where the rich sediment deposited during the Mekong's annual flooding makes the agricultural lands highly fertile. As deforestation and over-exploitation affected Cambodia only in recent decades, forests, low mountain ranges and local eco-regions still retain much of their natural potential and although still home to the largest areas of contiguous and intact forests in mainland Southeast Asia, multiple serious environmental issues persist and accumulate, which are closely related to rapid population growth, uncontrolled globalization and inconsequential administration.The majority of the country lies within the Tropical savanna climate zone, as the coastal areas in the South and West receive noticeably more and steady rain before and during the wet season. These areas constitute the easternmost fringes of the south-west monsoon, determined to be inside the Tropical monsoon climate. Countrywide there are two seasons of relatively equal length, defined by varying precipitation as temperatures and humidity are generally high and steady throughout the entire year.

Guelta

A guelta (Arabic: قلتة‎, also transliterated qalta or galta; Berber: agelmam) is a pocket of water that forms in drainage canals or wadis in the Sahara. The size and duration will depend on the location and conditions. It may last year-round through the dry season if fed by a source such as a spring. When a river (wadi) dries up, there may be pockets of water remaining along its course (c.f. oxbow lake). In Western Sahara, gueltas correspond with oases.Some examples include Guelta d'Archei in Chad and Timia in Niger.

Lake Nabugabo

Lake Nabugabo is a small freshwater lake in Uganda.

Lake Ngaroto

Lake Ngaroto is a peat lake in Waipa District of New Zealand.

Located 19 km south of Hamilton and 8 km north-west of Te Awamutu, it has a surface area of 108 ha, making it the largest of the Waipa peat lakes. The lake is hypertrophic, leading to eutrophication with corresponding poor water quality.

Lake Suesca

Lake Suesca is a natural water body situated on the Altiplano Cundiboyacense, belonging to the municipalities of Suesca and Cucunubá in the department of Cundinamarca, Colombia. The basin has a semi-elliptical shape that extends on a north–south axis, with roughly 6 kilometres (3.7 mi) length and 2 kilometres (1.2 mi) width. The average depth is 8 metres (26 ft). It is located in the Eastern Ranges, on the anticlinal of Nemocón, in the northeast of the department, at an altitude of 2,800 metres (9,200 ft).

Lake Waikare

Lake Waikare is the largest of several shallow lakes in the upper floodplain of the Waikato River in New Zealand's North Island. It is a riverine lake, located to the east of Te Kauwhata and 40 kilometres north of Hamilton. It covers 34 km².

Due to its shallow nature (its depth is never more than two metres) and the heavy use of fertiliser in the surrounding farming district, the waters of the lake are in poor condition. A 2010 report showed that of all the measured lakes it had the highest trophic level index, a measurement of the amount of pollutants.

Lakes of New Zealand

There are 3,820 lakes in New Zealand that have a surface area larger than one hectare. Many of the lakes in the central North Island are volcanic crater lakes. The majority of the lakes near the Southern Alps were carved by glaciers. Artificial lakes created as hydroelectric reservoirs are common in South Canterbury, Central Otago and along the Waikato River.

Loktak Lake

Loktak Lake (Meitei: ꯂꯣꯛꯇꯥꯛ) is the largest freshwater lake in Northeast India and is famous for the phumdis (heterogeneous mass of vegetation, soil and organic matter at various stages of decomposition) floating over it. The lake is located near Moirang in Manipur state, India. The etymology of Loktak is Lok = "stream" and tak = "the end". The largest of all the phumdis covers an area of 40 km2 (15 sq mi) and is situated on the southeastern shore of the lake. Located on this phumdi, Keibul Lamjao National Park is the only floating national park in the world. The park is the last natural refuge of the endangered Sangai (state animal), Rucervus eldii eldii or Manipur brown-antlered deer (Cervus eldi eldi), one of three subspecies of Eld's deer.This ancient lake plays an important role in the economy of Manipur. It serves as a source of water for hydropower generation, irrigation and drinking water supply. The lake is also a source of livelihood for the rural fishermen who live in the surrounding areas and on phumdis, also known as "phumshongs". Human activity has led to severe pressure on the lake ecosystem. 55 rural and urban hamlets around the lake have a population of about 100,000 people.

Considering the ecological status and its biodiversity values, the lake was initially designated as a wetland of international importance under the Ramsar Convention on 23 March 1990. It was also listed under the Montreux Record on 16 June 1993, "a record of Ramsar sites where changes in ecological character have occurred, are occurring or are likely to occur".

Lonar Lake

Lonar Lake, also known as Lonar crater, is a notified National Geo-heritage Monument, saline, soda lake, located at Lonar in Buldhana district, Maharashtra, India. Lonar Lake was created by a meteor impact during the Pleistocene Epoch. It is one of the four known, hyper-velocity, impact craters in basaltic rock anywhere on Earth. The other three basaltic impact structures are in southern Brazil. Lonar Lake has a mean diameter of 1.2 kilometres (3,900 ft) and is about 137 metres (449 ft) below the crater rim. The meteor crater rim is about 1.8 kilometres (5,900 ft) in diameter.It was identified in 1823 by a British officer named C.J.E. Alexander. Lonar Crater sits inside the Deccan Plateau—a massive plain of volcanic basalt rock created by eruptions some 65 million years ago. Its location in this basalt field suggested to some geologists that it was a volcanic crater. Today, however, Lonar Crater is understood to be the result of a meteorite impact that occurred between 35,000 and 50,000 years ago. The water in the lake is both saline and alkaline.

Geologists, ecologists, archaeologists, naturalists. and astronomers have published studies of various aspects of this crater lake ecosystem. Lonar

The crater's age is usually estimated to be 52,000 ± 6,000 years (Pleistocene), although a study published in 2010 gives an age of 570,000 ± 47,000 years.The Smithsonian Institution, the United States Geological Survey, Geological Society of India, the University of Sagar and the Physical Research Laboratory have conducted extensive studies of the site. Biological nitrogen fixation was discovered in this lake in 2007.

A recent study, conducted by IIT Bombay found that the minerals, in the lake soil, are very similar to the minerals found in moon rock brought back during Apollo Program.

Pond

A pond is an area filled with water, either natural or artificial, that is smaller than a lake. It may arise naturally in floodplains as part of a river system, or be a somewhat isolated depression (such as a kettle, vernal pool, or prairie pothole). It may contain shallow water with marsh and aquatic plants and animals.Factors impacting the type of life found in a pond include depth and duration of water level, nutrient level, shade, presence or absence of inlets and outlets, effects of grazing animals, and salinity.Ponds are frequently man-made, or expanded beyond their original depth and bounds. Among their many uses, ponds provide water for agriculture and livestock, aid in habitat restoration, serve as fish hatcheries, are components of landscape architecture, may store thermal energy as solar ponds, and treat wastewater as treatment ponds.

Ponds may be fresh, saltwater, or brackish.

Tonlé Sap

Tonlé Sap (Khmer: ទន្លេសាប IPA: [tunleː saːp], literally large river (tonle); fresh, not salty (sap), commonly translated to 'great lake') is a seasonally inundated freshwater lake, the Tonlé Sap Lake and an attached river, the 120 km (75 mi) long Tonlé Sap River, that connects the lake to the Mekong River. They form the central part of a complex hydrological system, in the 12,876 km2 (4,971 sq mi) Cambodian floodplain covered with a mosaic of natural and agricultural habitats that the Mekong replenishes with water and sediments annually. The central plain formation is the result of millions of years of Mekong alluvial deposition and discharge. From a geological perspective, the Tonlé Sap Lake and Tonlé Sap River are a current freeze-frame representation of the slowly but continuously shifting lower Mekong basin. Annual fluctuation of the Mekong's water volume, supplemented by the Asian monsoon regime, causes a unique flow reversal of the Tonle Sap River.The Tonlé Sap Lake occupies a geological depression (the lowest lying area) of the vast alluvial and lacustrine floodplain in the lower Mekong basin, which has been induced by the collision of the Indian Plate with the Eurasian Plate. The lake's size, length and water volume varies considerably over the course of a year from an area of around 2,500 km2 (965 sq mi), a volume of 1 km3 (0.24 cu mi) and a length of 160 km (99 mi) at the end of the dry season in late-April to an area of up to 16,000 km2 (6,178 sq mi), a volume of 80 km3 (19 cu mi) and a length of 250 km (160 mi) as the Mekong maximum and the peak of the southwest monsoon's precipitation culminate in September and early-October.As one of the world's most varied and productive ecosystems the region has always been of central importance for Cambodia's food supply. It proved capable of largely maintaining the Angkorean civilization, the largest pre-industrial settlement complex in world history. Directly and indirectly it affects the livelihood of large numbers of a predominantly rural population. Due to ineffective administration and widespread indifference towards environmental issues, the lake and its surrounding ecosystem are coming under increasing pressure from over-exploitation and habitat degradation, fragmentation, and loss. All Mekong riparian states have either announced or already implemented plans to increasingly exploit the river's hydroelectric potential. A succession of international facilities that dam the river's mainstream is likely to be the gravest danger yet for the entire Tonle Sap eco-region.The largest freshwater lake in Southeast Asia, it contains an exceptional large variety of interconnected eco-regions with a high degree of biodiversity and is therefore a biodiversity hotspot. It was designated a UNESCO biosphere reserve in 1997.

Varthur

Varthur is a suburb situated in the Eastern periphery of Bangalore City and part of the internationally famous Whitefield township. Varthur is a Hobli and part of Bruhat Bangalore Mahanagara Palike. Varthur was a Legislative Assembly in the state of Karnataka but was split into three legislative assemblies C.V.Raman Nagar, Mahadevapura and Krishnarajapura in the year 2008. It is also one of the wards of BBMP. It is located in South-Eastern Bangalore between old Airport road and Sarjapur road. Varthur is very close to ITPB.

There are many IT companies in Varthur Hobli. The head office of one of the largest IT companies, Wipro Technologies is situated at Doddakannelli, Varthur Hobli. Some other companies such as Cisco Systems, ARM, and Aricent Group, are situated in Varthur Hobli

At Varthur, people celebrate Brahmarathotsava of Sri Chennaraya Swamy, which happens on the day of Ratha Saptami. It is one of the famous events that happen in this area. Two days later is Karaga of Sri Draupathamma (Draupadi) at Sri Dharmaraya Swamy (Yudhishthira) temple, which happens at night and is visited by thousands of people from Varthur, Gunjur, Madhuranagara, Whitefield, Ramagondannahalli, Balagere, Sorahunase, Immadihalli, Harohalli, Muthsandra, Kotur.

Zigetangcuo Lake

Zigetangcuo Lake (Chinese: 兹格塘错) is a crenogenic meromictic lake in the North Tibetan Plateau. It is located in Nagqu Prefecture, north of Dongqiao. It has an area of 18,700 ha at an altitude of 4560 meters. It is the meromictic lake with the highest known altitude.

Aquatic ecosystems
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Consumers
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Microorganisms
Food webs
Example webs
Processes
Defense,
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Ecology: Modelling ecosystems: Other components
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ecology
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interaction
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ecology
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Ponds, Pools, and Puddles
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