Limnology

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Lake Hawea, New Zealand Lake Hawea, New Zealand.jpg
Lake Hāwea, New Zealand

Limnology ( /lɪmˈnɒləi/ lim-NOL-ə-jee; from Greek λίμνη, limne, "lake" and λόγος, logos, "knowledge"), is the study of inland aquatic ecosystems. [1] The study of limnology includes aspects of the biological, chemical, physical, and geological characteristics and functions of inland waters (running and standing waters, fresh and saline, natural and man-made). This includes the study of lakes, reservoirs, ponds, rivers, springs, streams, wetlands, and groundwater. [2] A more recent sub-discipline of limnology, termed landscape limnology, studies, manages, and seeks to conserve these ecosystems using a landscape perspective, by explicitly examining connections between an aquatic ecosystem and its watershed. Recently, the need to understand global inland waters as part of the Earth System created a sub-discipline called global limnology. [3] This approach considers processes in inland waters on a global scale, like the role of inland aquatic ecosystems in global biogeochemical cycles. [4] [5] [6] [7] [8]

Contents

Limnology is closely related to aquatic ecology and hydrobiology, which study aquatic organisms and their interactions with the abiotic (non-living) environment. While limnology has substantial overlap with freshwater-focused disciplines (e.g., freshwater biology), it also includes the study of inland salt lakes.

History

The term limnology was coined by François-Alphonse Forel (1841–1912) who established the field with his studies of Lake Geneva. Interest in the discipline rapidly expanded, and in 1922 August Thienemann (a German zoologist) and Einar Naumann (a Swedish botanist) co-founded the International Society of Limnology (SIL, from Societas Internationalis Limnologiae). Forel's original definition of limnology, "the oceanography of lakes", was expanded to encompass the study of all inland waters, [2] and influenced Benedykt Dybowski's work on Lake Baikal.

Prominent early American limnologists included G. Evelyn Hutchinson and Ed Deevey. [9] At the University of Wisconsin-Madison, Edward A. Birge, Chancey Juday, and Arthur D. Hasler contributed to the development of the Center for Limnology. [10] [11]

General limnology

Physical properties

Physical properties of aquatic ecosystems are determined by a combination of heat, currents, waves and other seasonal distributions of environmental conditions. [12] The morphometry of a body of water depends on the type of feature (such as a lake, river, stream, wetland, estuary etc.) and the structure of the earth surrounding the body of water. Lakes, for instance, are classified by their formation, and zones of lakes are defined by water depth. [13] River and stream system morphometry is driven by underlying geology of the area as well as the general velocity of the water. [12] Another type of aquatic system which falls within the study of limnology are estuaries. Estuaries are bodies of water classified by the interaction of a river and the ocean or sea. [12] Wetlands vary in size, shape, and pattern however the most common types, marshes, bogs and swamps, often fluctuate between containing shallow, freshwater and being dry depending on the time of year. [12]

Light interactions

Light zonation is the concept of how the amount of sunlight penetration into water influences the structure of a body of water. [12] These zones define various levels of productivity within an aquatic ecosystems such as a lake. For instance, the depth of the water column which sunlight is able to penetrate and where most plant life is able to grow is known as the photic or euphotic zone. The rest of the water column which is deeper and does not receive sufficient amounts of sunlight for plant growth is known as the aphotic zone. [12]

Thermal stratification

Similar to light zonation, thermal stratification or thermal zonation is a way of grouping parts of the water body within an aquatic system based on the temperature of different lake layers. The less turbid the water, the more light is able to penetrate, and thus heat is conveyed deeper in the water. [14] Heating declines exponentially with depth in the water column, so the water will be warmest near the surface but progressively cooler as moving downwards. There are three main sections that define thermal stratification in a lake. The epilimnion is closest to the water surface and absorbs long- and shortwave radiation to warm the water surface. During cooler months, wind shear can contribute to cooling of the water surface. The thermocline is an area within the water column where water temperatures rapidly decrease. [14] The bottom layer is the hypolimnion, which tends to have the coldest water because its depth restricts sunlight from reaching it. [14] In temperate lakes, fall-season cooling of surface water results in turnover of the water column, where the thermocline is disrupted, and the lake temperature profile becomes more uniform.

Chemical properties

The chemical composition of water in aquatic ecosystems is influenced by natural characteristics and processes including precipitation, underlying soil and bedrock in the watershed, erosion, evaporation, and sedimentation. [12] All bodies of water have a certain composition of both organic and inorganic elements and compounds. Biological reactions also affect the chemical properties of water. In addition to natural processes, human activities strongly influence the chemical composition of aquatic systems and their water quality. [14]

Oxygen and carbon dioxide

Dissolved oxygen and dissolved carbon dioxide are often discussed together due their coupled role in respiration and photosynthesis. Dissolved oxygen concentrations can be altered by physical, chemical, and biological processes and reaction. Physical processes including wind mixing can increase dissolved oxygen concentrations, particularly in surface waters of aquatic ecosystems. Because dissolved oxygen solubility is linked to water temperatures, changes in temperature affect dissolved oxygen concentrations as warmer water has a lower capacity to "hold" oxygen as colder water. [15] Biologically, both photosynthesis and aerobic respiration affect dissolved oxygen concentrations. [14] Photosynthesis by autotrophic organisms, such as phytoplankton and aquatic algae, increases dissolved oxygen concentrations while simultaneously reducing carbon dioxide concentrations, since carbon dioxide is taken up during photosynthesis. [15] All aerobic organisms in the aquatic environment take up dissolved oxygen during aerobic respiration, while carbon dioxide is released as a byproduct of this reaction. Because photosynthesis is light-limited, both photosynthesis and respiration occur during the daylight hours, while only respiration occurs during dark hours or in dark portions of an ecosystem. The balance between dissolved oxygen production and consumption is calculated as the aquatic metabolism rate. [16]

Vertical changes in the concentrations of dissolved oxygen are affected by both wind mixing of surface waters and the balance between photosynthesis and respiration of organic matter. These vertical changes, known as profiles, are based on similar principles as thermal stratification and light penetration. As light availability decreases deeper in the water column, photosynthesis rates also decrease, and less dissolved oxygen is produced. This means that dissolved oxygen concentrations generally decrease as you move deeper into the body of water because of photosynthesis is not replenishing dissolved oxygen that is being taken up through respiration. [14] During periods of thermal stratification, water density gradients prevent oxygen-rich surface waters from mixing with deeper waters. Prolonged periods of stratification can result in the depletion of bottom-water dissolved oxygen; when dissolved oxygen concentrations are below 2 milligrams per liter, waters are considered hypoxic. [15] When dissolved oxygen concentrations are approximately 0 milligrams per liter, conditions are anoxic. Both hypoxic and anoxic waters reduce available habitat for organisms that respire oxygen, and contribute to changes in other chemical reactions in the water. [15]

Nitrogen and phosphorus

Nitrogen and phosphorus are ecologically significant nutrients in aquatic systems. Nitrogen is generally present as a gas in aquatic ecosystems however most water quality studies tend to focus on nitrate, nitrite and ammonia levels. [12] Most of these dissolved nitrogen compounds follow a seasonal pattern with greater concentrations in the fall and winter months compared to the spring and summer. [12] Phosphorus has a different role in aquatic ecosystems as it is a limiting factor in the growth of phytoplankton because of generally low concentrations in the water. [12] Dissolved phosphorus is also crucial to all living things, is often very limiting to primary productivity in freshwater, and has its own distinctive ecosystem cycling. [14]

Biological properties

Lake George, New York, United States, an oligotrophic lake Lake George from village beach.jpg
Lake George, New York, United States, an oligotrophic lake

Lake trophic classification

One way to classify lakes (or other bodies of water) is with the trophic state index. [2] An oligotrophic lake is characterised by relatively low levels of primary production and low levels of nutrients. A eutrophic lake has high levels of primary productivity due to very high nutrient levels. Eutrophication of a lake can lead to algal blooms. Dystrophic lakes have high levels of humic matter and typically have yellow-brown, tea-coloured waters. [2] These categories do not have rigid specifications; the classification system can be seen as more of a spectrum encompassing the various levels of aquatic productivity.

Professional organizations

People who study limnology are called limnologists. There are many professional organizations related to limnology and other aspects of the aquatic science, including the Association for the Sciences of Limnology and Oceanography, the Asociación Ibérica de Limnología, the International Society of Limnology, the Polish Limnological Society, and the Freshwater Biological Association.

See also

Related Research Articles

Carbon cycle Biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere,

The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major component of many minerals such as limestone. Along with the nitrogen cycle and the water cycle, the carbon cycle comprises a sequence of events that are key to make Earth capable of sustaining life. It describes the movement of carbon as it is recycled and reused throughout the biosphere, as well as long-term processes of carbon sequestration to and release from carbon sinks.

Eutrophication Ecosystem response to the addition of substances

Eutrophication, or hypertrophication, is when a body of water becomes overly enriched with minerals and nutrients which induce excessive growth of algae. This process may result in oxygen depletion of the water body. One example is an "algal bloom" or great increase of phytoplankton in a water body as a response to increased levels of nutrients. Eutrophication is often induced by the discharge of nitrate or phosphate-containing detergents, fertilizers, or sewage into an aquatic system.

Primary production The synthesis of organic compounds from carbon dioxide by biological organisms

In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through chemosynthesis, which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. Almost all life on Earth relies directly or indirectly on primary production. The organisms responsible for primary production are known as primary producers or autotrophs, and form the base of the food chain. In terrestrial ecoregions, these are mainly plants, while in aquatic ecoregions algae predominate in this role. Ecologists distinguish primary production as either net or gross, the former accounting for losses to processes such as cellular respiration, the latter not.

Meromictic lake Lake with layers of water that do not intermix

A meromictic lake has layers of water that do not intermix. In ordinary, "holomictic" lakes, at least once each year, there is a physical mixing of the surface and the deep waters.

Solubility pump A physico-chemical process that transports dissolved inorganic carbon from the oceans surface to its interior

In oceanic biogeochemistry, the solubility pump is a physico-chemical process that transports carbon from the ocean's surface to its interior.

Lake stratification

Lake stratification is the separation of lakes into three layers:

  1. Epilimnion: the top of the lake.
  2. Metalimnion : the middle layer, which may change depth throughout the day.
  3. Hypolimnion: the bottom layer.
Aquatic ecosystem An ecosystem in a body of water

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 freshwater ecosystems.

Water aeration process of increasing or maintaining the oxygen saturation of a body of water

Water aeration is the process of increasing or maintaining the oxygen saturation of water in both natural and artificial environments.

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

Trophic state index A measure of how much nutrient are in a body of water.

Trophic State Index (TSI) is a classification system designed to rate water bodies based on the amount of biological activity they sustain. Although the term "trophic index" is commonly applied to lakes, any surface water body may be indexed.

Ocean deoxygenation is the expansion of oxygen minimum zones in the world's oceans as a consequence of anthropogenic emissions of carbon dioxide. The change has been fairly rapid and poses a threat to fish and other types of marine life, as well as to people who depend on marine life for nutrition or livelihood.

Freshwater environmental quality parameters are the natural and man-made chemical, biological and microbiological characteristics of rivers, lakes and ground-waters, the ways they are measured and the ways that they change. The values or concentrations attributed to such parameters can be used to describe the pollution status of an environment, its biotic status or to predict the likelihood or otherwise of a particular organisms being present. Monitoring of environmental quality parameters is a key activity in managing the environment, restoring polluted environments and anticipating the effects of man-made changes on the environment.

Facultative lagoon waste treatment pond

Facultative lagoons are a type of waste stabilization pond used for biological treatment of industrial and domestic wastewater. Sewage or organic waste from food or fiber processing may be catabolized in a system of constructed ponds where adequate space is available to provide an average waste retention time exceeding a month. A series of ponds prevents mixing of untreated waste with treated wastewater and allows better control of waste residence time for uniform treatment efficiency.

A thermal bar is a hydrodynamic feature that forms around the edges of holomictic lakes during the seasonal transition to stratified conditions, due to the shorter amount of time required for shallow areas of the lake to stratify.

Soda lake Lake that is strongly alkaline

A soda lake or alkaline lake is a lake on the strongly alkaline side of neutrality, typically with a pH value between 9 and 12. They are characterized by high concentrations of carbonate salts, typically sodium carbonate, giving rise to their alkalinity. In addition, many soda lakes also contain high concentrations of sodium chloride and other dissolved salts, making them saline or hypersaline lakes as well. High pH and salinity often coincide, because of how soda lakes develop. The resulting hypersaline and highly alkalic soda lakes are considered some of the most extreme aquatic environments on Earth.

Stephen R. Carpenter Limnologist, ecologist, environmentalist

Stephen Russell Carpenter is an American lake ecologist who focuses on lake Eutrophication which is the over-enrichment of lake ecosystems leading to toxic blooms of micro-organisms and fish kills.

Hypoxia refers to low oxygen conditions. Normally, 20.9% of the gas in the atmosphere is oxygen. The partial pressure of oxygen in the atmosphere is 20.9% of the total barometric pressure. In water, oxygen levels are much lower, approximately 1%, and fluctuate locally depending on the presence of photosynthetic organisms and relative distance to the surface.

Carlos M. Duarte Spanish marine biologist

Carlos Manuel Duarte is a marine ecologist conducting research on marine ecosystems globally, from polar to the tropical ocean and from near-shore to deep-sea ecosystems. His research addresses biodiversity in the oceans, the impacts of human activity on marine ecosystems, and the capacity of marine ecosystems to recover from these impacts. He is also interested in transdisciplinary research, collaborating with scientists and engineers across a broad range of fields to solve problems in the marine ecosystem and society. He is currently a professor at the King Abdullah University of Science and Technology.

Lake metabolism

Lake metabolism represents a lake ecosystem's balance between carbon fixation and biological carbon oxidation. Lake metabolism includes the carbon fixation and oxidation from all organism within the lake, from bacteria to fishes.

Benthic-pelagic coupling are processes that connect the benthic zone and the pelagic zone through the exchange of energy, mass, or nutrients. These processes play a prominent role in both freshwater and marine ecosystems and are influenced by a number of chemical, biological, and physical forces that are crucial to functions from nutrient cycling to energy transfer in food webs.

References

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  3. Global limnology: up-scaling aquatic services and processes to planet Earth: https://www.tandfonline.com/doi/pdf/10.1080/03680770.2009.11923903?needAccess=true
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Further reading