Climate change
Climate change occurs when changes in Earth's climate system result in new weather patterns that last for at least a few decades, maybe for millions of years. The climate system is comprised of five interacting parts, the atmosphere, cryosphere and lithosphere; the climate system receives nearly all of its energy from the sun, with a tiny amount from earth's interior. The climate system gives off energy to outer space; the balance of incoming and outgoing energy, the passage of the energy through the climate system, determines Earth's energy budget. When the incoming energy is greater than the outgoing energy, earth's energy budget is positive and the climate system is warming. If more energy goes out, the energy budget is negative and earth experiences cooling; as this energy moves through Earth's climate system, it creates Earth's weather and long-term averages of weather are called "climate". Changes in the long term average are called "climate change"; such changes can be the result of "internal variability", when natural processes inherent to the various parts of the climate system alter Earth's energy budget.
Examples include cyclical ocean patterns such as the well-known El Nino Southern Oscillation and less familiar Pacific decadal oscillation and Atlantic multidecadal oscillation. Climate change can result from "external forcing", when events outside of the climate system's five parts nonetheless produce changes within the system. Examples include changes in solar volcanism. Human activities can change earth's climate, are presently driving climate change through global warming. There is no general agreement in scientific, media or policy documents as to the precise term to be used to refer to anthropogenic forced change; the field of climatology incorporates many disparate fields of research. For ancient periods of climate change, researchers rely on evidence preserved in climate proxies, such as ice cores, ancient tree rings, geologic records of changes in sea level, glacial geology. Physical evidence of current climate change covers many independent lines of evidence, a few of which are temperature records, the disappearance of ice, extreme weather events.
The most general definition of climate change is a change in the statistical properties of the climate system when considered over long periods of time, regardless of cause. Accordingly, fluctuations over periods shorter than a few decades, such as El Niño, do not represent climate change; the term "climate change" is used to refer to anthropogenic climate change. Anthropogenic climate change is caused by human activity, as opposed to changes in climate that may have resulted as part of Earth's natural processes. In this sense in the context of environmental policy, the term climate change has become synonymous with anthropogenic global warming. Within scientific journals, global warming refers to surface temperature increases while climate change includes global warming and everything else that increasing greenhouse gas levels affect. A related term, "climatic change", was proposed by the World Meteorological Organization in 1966 to encompass all forms of climatic variability on time-scales longer than 10 years, but regardless of cause.
During the 1970s, the term climate change replaced climatic change to focus on anthropogenic causes, as it became clear that human activities had a potential to drastically alter the climate. Climate change was incorporated in the title of the Intergovernmental Panel on Climate Change and the UN Framework Convention on Climate Change. Climate change is now used as both a technical description of the process, as well as a noun used to describe the problem. Prior to the 18th century, scientists had not suspected that prehistoric climates were different from the modern period. By the late 18th century, geologists found evidence of a succession of geological ages with changes in climate. In the years since, a great deal of scientific progress has been made understanding the workings of the climate system. On the broadest scale, the rate at which energy is received from the Sun and the rate at which it is lost to space determine the equilibrium temperature and climate of Earth; this energy is distributed around the globe by winds, ocean currents, other mechanisms to affect the climates of different regions.
Factors that can shape climate are called climate forcings or "forcing mechanisms". These include processes such as variations in solar radiation, variations in the Earth's orbit, variations in the albedo or reflectivity of the continents and oceans, mountain-building and continental drift and changes in greenhouse gas concentrations. There are a variety of climate change feedbacks that can either amplify or diminish the initial forcing; some parts of the climate system, such as the oceans and ice caps, respond more in reaction to climate forcings, while others respond more quickly. There are key threshold factors which when exceeded can produce rapid change. Forcing mechanisms can be either "internal" or "external". Internal forcing mechanisms are natural processes within the climate system itself. External forcing mechanisms can be either natural. Whether the initial forcing mechanism is internal or external, the response of the climate system might be fast, slow (e.g. thermal exp
Coral
Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They live in compact colonies of many identical individual polyps. Corals species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton. A coral "group" is a colony of myriad genetically identical polyps; each polyp is a sac-like animal only a few millimeters in diameter and a few centimeters in length. A set of tentacles surround a central mouth opening. An exoskeleton is excreted near the base. Over many generations, the colony thus creates a large skeleton characteristic of the species. Individual heads grow by asexual reproduction of polyps. Corals breed sexually by spawning: polyps of the same species release gametes over a period of one to several nights around a full moon. Although some corals are able to catch small fish and plankton using stinging cells on their tentacles, most corals obtain the majority of their energy and nutrients from photosynthetic unicellular dinoflagellates in the genus Symbiodinium that live within their tissues.
These are known as zooxanthellae. Such corals require sunlight and grow in clear, shallow water at depths less than 60 metres. Corals are major contributors to the physical structure of the coral reefs that develop in tropical and subtropical waters, such as the enormous Great Barrier Reef off the coast of Queensland, Australia. Other corals do not rely on zooxanthellae and can live in much deeper water, with the cold-water genus Lophelia surviving as deep as 3,300 metres; some have been found on the Darwin Mounds, northwest of Cape Wrath and others as far north as off the coast of Washington State and the Aleutian Islands. Aristotle's pupil Theophrastus described the red coral, korallion, in his book on stones, implying it was a mineral, but he described it as a deep-sea plant in his Enquiries on Plants, where he mentions large stony plants that reveal bright flowers when under water in the Gulf of Heroes. Pliny the Elder stated boldly that several sea creatures including sea nettles and sponges "are neither animals nor plants, but are possessed of a third nature".
Petrus Gyllius copied Pliny, introducing the term zoophyta for this third group in his 1535 book On the French and Latin Names of the Fishes of the Marseilles Region. Gyllius further noted, following Aristotle, how hard it was to define what was a plant and what was an animal; the Persian polymath Al-Biruni classified sponges and corals as animals, arguing that they respond to touch. People believed corals to be plants until the eighteenth century, when William Herschel used a microscope to establish that coral had the characteristic thin cell membranes of an animal. Presently, corals are classified as certain species of animals within the sub-classes Hexacorallia and Octocorallia of the class Anthozoa in the phylum Cnidaria. Hexacorallia includes the stony corals and these groups have polyps that have a 6-fold symmetry. Octocorallia includes blue coral and soft corals and species of Octocorallia have polyps with an eightfold symmetry, each polyp having eight tentacles and eight mesenteries.
Fire corals are not true corals. Corals are sessile animals and differ from most other cnidarians in not having a medusa stage in their life cycle; the body unit of the animal is a polyp. Most corals are colonial, the initial polyp budding to produce another and the colony developing from this small start. In stony corals known as hard corals, the polyps produce a skeleton composed of calcium carbonate to strengthen and protect the organism; this is deposited by the coenosarc, the living tissue that connects them. The polyps sit in cup-shaped depressions in the skeleton known as corallites. Colonies of stony coral are variable in appearance. In soft corals, there is no stony skeleton but the tissues are toughened by the presence of tiny skeletal elements known as sclerites, which are made from calcium carbonate. Soft corals are variable in form and most are colonial. A few soft corals are stolonate. In some species this is thick and the polyps are embedded; some soft corals are form lobes. Others have a central axial skeleton embedded in the tissue matrix.
This is composed either of a fibrous protein called gorgonin or of a calcified material. In both stony and soft corals, the polyps can be retracted, with stony corals relying on their hard skeleton and cnidocytes for defence against predators, soft corals relying on chemical defences in the form of toxic substances present in the tissues known as terpenoids; the polyps of stony corals have six-fold symmetry. The mouth of each polyp is surrounded by a ring of tentacles. In stony corals these are cylindrical and taper to a point, but in soft corals they are pinnate with side branches known as pinnules. In some tropical species these are reduced to mere stubs and in some they are fused to give a paddle-like appearance. In most corals, the tentacles are retracted by day and spread out at night to catch plankton and other small organisms. Shallow water species of both stony and soft corals can be zooxanthellate, the corals supplementing their plankton diet with t
Soil erosion
Soil erosion is the displacement of the upper layer of soil, one form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, ice, air, plants and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind erosion, zoogenic erosion, anthropogenic erosion. Soil erosion may be a slow process that continues unnoticed, or it may occur at an alarming rate causing a serious loss of topsoil; the loss of soil from farmland may be reflected in reduced crop production potential, lower surface water quality and damaged drainage networks. Human activities have increased by 10 -- 40 times the rate. Excessive erosion causes both "on-site" and "off-site" problems. On-site impacts include decreases in agricultural productivity and ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the eventual end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses.
Water and wind erosion are the two primary causes of land degradation. Intensive agriculture, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion. However, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils. Rainfall, the surface runoff which may result from rainfall, produces four main types of soil erosion: splash erosion, sheet erosion, rill erosion, gully erosion. Splash erosion is seen as the first and least severe stage in the soil erosion process, followed by sheet erosion rill erosion and gully erosion. In splash erosion, the impact of a falling raindrop creates a small crater in the soil, ejecting soil particles; the distance these soil particles travel can be as much as 0.6 m vertically and 1.5 m horizontally on level ground. If the soil is saturated, or if the rainfall rate is greater than the rate at which water can infiltrate into the soil, surface runoff occurs.
If the runoff has sufficient flow energy, it will transport loosened soil particles down the slope. Sheet erosion is the transport of loosened soil particles by overland flow. Rill erosion refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes. Where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are of the order of a few centimeters or less and along-channel slopes may be quite steep; this means that rills exhibit hydraulic physics different from water flowing through the deeper, wider channels of streams and rivers. Gully erosion occurs when runoff water accumulates and flows in narrow channels during or after heavy rains or melting snow, removing soil to a considerable depth. Valley or stream erosion occurs with continued water flow along a linear feature; the erosion is both downward, deepening the valley, headward, extending the valley into the hillside, creating head cuts and steep banks.
In the earliest stage of stream erosion, the erosive activity is dominantly vertical, the valleys have a typical V cross-section and the stream gradient is steep. When some base level is reached, the erosive activity switches to lateral erosion, which widens the valley floor and creates a narrow floodplain; the stream gradient becomes nearly flat, lateral deposition of sediments becomes important as the stream meanders across the valley floor. In all stages of stream erosion, by far the most erosion occurs during times of flood, when more and faster-moving water is available to carry a larger sediment load. In such processes, it is not the water alone that erodes: suspended abrasive particles and boulders can act erosively as they traverse a surface, in a process known as traction. Bank erosion is the wearing away of the banks of a river; this is distinguished from changes on the bed of the watercourse, referred to as scour. Erosion and changes in the form of river banks may be measured by inserting metal rods into the bank and marking the position of the bank surface along the rods at different times.
Thermal erosion is the result of weakening permafrost due to moving water. It can occur both at the coast. Rapid river channel migration observed in the Lena River of Siberia is due to thermal erosion, as these portions of the banks are composed of permafrost-cemented non-cohesive materials. Much of this erosion occurs. Thermal erosion affects the Arctic coast, where wave action and near-shore temperatures combine to undercut permafrost bluffs along the shoreline and cause them to fail. Annual erosion rates along a 100-kilometre segment of the Beaufort Sea shoreline averaged 5.6 metres per year from 1955 to 2002. At high flows, kolks, or vortices are formed by large volumes of rushing water. Kolks cause extreme local erosion, plucking bedrock and creating pothole-type geographical features called Rock-cut basins. Examples can be seen in the flood regions result from glacial Lake Missoula, which created the channeled scablands in the Columbia Basin region of eastern W
Bathymetry
Bathymetry is the study of underwater depth of lake or ocean floors. In other words, bathymetry is the underwater equivalent to topography; the name comes from Greek βαθύς, "deep", μέτρον, "measure". Bathymetric charts are produced to support safety of surface or sub-surface navigation, show seafloor relief or terrain as contour lines and selected depths, also provide surface navigational information. Bathymetric maps may use a Digital Terrain Model and artificial illumination techniques to illustrate the depths being portrayed; the global bathymetry is sometimes combined with topography data to yield a Global Relief Model. Paleobathymetry is the study of past underwater depths. Bathymetry involved the measurement of ocean depth through depth sounding. Early techniques used cable lowered over a ship's side; this technique measures the depth only a singular point at a time, is therefore inefficient. It is subject to movements of the ship and currents moving the line out of true and therefore is not accurate.
The data used to make bathymetric maps today comes from an echosounder mounted beneath or over the side of a boat, "pinging" a beam of sound downward at the seafloor or from remote sensing LIDAR or LADAR systems. The amount of time it takes for the sound or light to travel through the water, bounce off the seafloor, return to the sounder informs the equipment of the distance to the seafloor. LIDAR/LADAR surveys are conducted by airborne systems. Starting in the early 1930s, single-beam sounders were used to make bathymetry maps. Today, multibeam echosounders are used, which use hundreds of narrow adjacent beams arranged in a fan-like swath of 90 to 170 degrees across; the packed array of narrow individual beams provides high angular resolution and accuracy. In general, a wide swath, depth dependent, allows a boat to map more seafloor in less time than a single-beam echosounder by making fewer passes; the beams update many times per second, allowing faster boat speed while maintaining 100% coverage of the seafloor.
Attitude sensors allow for the correction of the boat's roll and pitch on the ocean surface, a gyrocompass provides accurate heading information to correct for vessel yaw. A boat-mounted Global Positioning System positions the soundings with respect to the surface of the earth. Sound speed profiles of the water column correct for refraction or "ray-bending" of the sound waves owing to non-uniform water column characteristics such as temperature and pressure. A computer system processes all the data, correcting for all of the above factors as well as for the angle of each individual beam; the resulting sounding measurements are processed either manually, semi-automatically or automatically to produce a map of the area. As of 2010 a number of different outputs are generated, including a sub-set of the original measurements that satisfy some conditions or integrated Digital Terrain Models. Selection of measurements was more common in hydrographic applications while DTM construction was used for engineering surveys, flow modeling, etc.
Since ca. 2003–2005, DTMs have become more accepted in hydrographic practice. Satellites are used to measure bathymetry. Satellite radar maps deep-sea topography by detecting the subtle variations in sea level caused by the gravitational pull of undersea mountains and other masses. On average, sea level is higher over ridges than over abyssal plains and trenches. In the United States the United States Army Corps of Engineers performs or commissions most surveys of navigable inland waterways, while the National Oceanic and Atmospheric Administration performs the same role for ocean waterways. Coastal bathymetry data is available from NOAA's National Geophysical Data Center, now merged into National Centers for Environmental Information. Bathymetric data is referenced to tidal vertical datums. For deep-water bathymetry, this is Mean Sea Level, but most data used for nautical charting is referenced to Mean Lower Low Water in American surveys, Lowest Astronomical Tide in other countries. Many other datums are used depending on the locality and tidal regime.
Occupations or careers related to bathymetry include the study of oceans and rocks and minerals on the ocean floor, the study of underwater earthquakes or volcanoes. The taking and analysis of bathymetric measurements is one of the core areas of modern hydrography, a fundamental component in ensuring the safe transport of goods worldwide. Bathometer Bathymetric chart Depth gauge General Bathymetric Chart of the Oceans Global Relief Model Hydrographic survey Ocean surface topography Terrain Overview for underwater terrain, data formats, etc. High resolution bathymetry for the Great Barrier Reef and Coral Sea A. PO. MA. B.-Academy of Positioning Marine and Bathymetry Bathymetric Data Viewer from NOAA's NCEI
Sediment
Sediment is a occurring material, broken down by processes of weathering and erosion, is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation and if buried, may become sandstone and siltstone. Sediments are most transported by water, but wind and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian deposition. Glacial moraine deposits and till are ice-transported sediments. Sediment can be classified based on its grain composition. Sediment size is measured on a log base 2 scale, called the "Phi" scale, which classifies particles by size from "colloid" to "boulder". Composition of sediment can be measured in terms of: parent rock lithology mineral composition chemical make-up.
This leads to an ambiguity in which clay can be used as a composition. Sediment is transported based on the strength of the flow that carries it and its own size, volume and shape. Stronger flows will increase the lift and drag on the particle, causing it to rise, while larger or denser particles will be more to fall through the flow. Rivers and streams carry sediment in their flows; this sediment can be in a variety of locations within the flow, depending on the balance between the upwards velocity on the particle, the settling velocity of the particle. These relationships are shown in the following table for the Rouse number, a ratio of sediment fall velocity to upwards velocity. Rouse = Settling velocity Upwards velocity from lift and drag = w s κ u ∗ where w s is the fall velocity κ is the von Kármán constant u ∗ is the shear velocity If the upwards velocity is equal to the settling velocity, sediment will be transported downstream as suspended load. If the upwards velocity is much less than the settling velocity, but still high enough for the sediment to move, it will move along the bed as bed load by rolling and saltating.
If the upwards velocity is higher than the settling velocity, the sediment will be transported high in the flow as wash load. As there are a range of different particle sizes in the flow, it is common for material of different sizes to move through all areas of the flow for given stream conditions. Sediment motion can create self-organized structures such as ripples, dunes, or antidunes on the river or stream bed; these bedforms are preserved in sedimentary rocks and can be used to estimate the direction and magnitude of the flow that deposited the sediment. Overland flow can transport them downslope; the erosion associated with overland flow may occur through different methods depending on meteorological and flow conditions. If the initial impact of rain droplets dislodges soil, the phenomenon is called rainsplash erosion. If overland flow is directly responsible for sediment entrainment but does not form gullies, it is called "sheet erosion". If the flow and the substrate permit channelization, gullies may form.
The major fluvial environments for deposition of sediments include: Deltas Point bars Alluvial fans Braided rivers Oxbow lakes Levees Waterfalls Wind results in the transportation of fine sediment and the formation of sand dune fields and soils from airborne dust. Glaciers carry a wide range of sediment sizes, deposit it in moraines; the overall balance between sediment in transport and sediment being deposited on the bed is given by the Exner equation. This expression states that the rate of increase in bed elevation due to deposition is proportional to the amount of sediment that falls out of the flow; this equation is important in that changes in the power of the flow change the ability of the flow to carry sediment, this is reflected in the patterns of erosion and deposition observed throughout a stream. This can be localized, due to small obstacles. Erosion and deposition can be regional. Deposition can occur due to dam emplacement that causes the river to pool and deposit its entire load, or due to base level rise.
Seas and lakes accumulate sediment over time. The sediment can consist of terrigenous material, which originates on land, but may be deposited in either terrestrial, marine, or lacustrine environments, or of sediments originating in the body of water. Terrigenous material is supplied by nearby rivers and streams or reworked marine sediment. In the mid-ocean, the exoskeletons of dead organisms are responsible for sediment accumulation. Deposited sediments are the source of sedimentary rocks, which can contain fossils of
Sewage sludge
Sewage sludge is the residual, semi-solid material, produced as a by-product during sewage treatment of industrial or municipal wastewater. The term "septage" refers to sludge from simple wastewater treatment but is connected to simple on-site sanitation systems, such as septic tanks; when fresh sewage or wastewater enters a primary settling tank 50% of the suspended solid matter will settle out in an hour and a half. This collection of solids is known as raw sludge or primary solids and is said to be "fresh" before anaerobic processes become active; the sludge will become putrescent in a short time once anaerobic bacteria take over, must be removed from the sedimentation tank before this happens. This is accomplished in one of two ways. In an Imhoff tank, fresh sludge is passed through a slot to the lower story or digestion chamber where it is decomposed by anaerobic bacteria, resulting in liquefaction and reduced volume of the sludge. After digesting for an extended period, the result is called "digested" sludge and may be disposed of by drying and landfilling.
More with domestic sewage, the fresh sludge is continuously extracted from the tank mechanically and passed to separate sludge digestion tanks that operate at higher temperatures than the lower story of the Imhoff tank and, as a result, digest much more and efficiently. "Biosolids" is a term used in conjunction with reuse of sewage solids after sewage sludge treatment. Biosolids can be defined as organic wastewater solids that can be reused after stabilization processes such as anaerobic digestion and composting. Opponents of sewage sludge reuse reject this term as a public relations term. Class A sludge is dried and pasteurized, is known as "exceptional" quality. Class B includes all sludge not classified as Class A. Class B sludge is "undigested" and is volatile. Both classes of sludge may still contain pharmaceutical wastes; the amount of sewage sludge produced is proportional to the amount and concentration of wastewater treated, it depends on the type of wastewater treatment process used.
It can be expressed as kg dry solids per cubic metre of wastewater treated. The total sludge production from a wastewater treatment process is the sum of sludge from primary settling tanks plus excess sludge from the biological treatment step. For example, primary sedimentation produces about 110–170 kg/ML of so-called primary sludge, with a value of 150 kg/ML regarded as being typical for municipal wastewater in the U. S. or Europe. The sludge production is expressed as kg of dry solids produced per ML of wastewater treated. Of the biological treatment processes, the activated sludge process produces about 70–100 kg/ML of waste activated sludge, a trickling filter process produces less sludge from the biological part of the process: 60–100 kg/ML; this means that the total sludge production of an activated sludge process that uses primary sedimentation tanks is in the range of 180–270 kg/ML, being the sum of primary sludge and waste activated sludge. United States municipal wastewater treatment plants in 1997 produced about 7.7 million dry tons of sewage sludge, about 6.8 million dry tons in 1998 according to EPA estimates.
As of 2004, about 60% of all sewage sludge was applied to land as a soil amendment and fertilizer for growing crops. Production of sewage sludge can be reduced by conversion from flush toilets to dry toilets such urine-diverting dry toilets and composting toilets. Bacteria in Class A sludge products can regrow under certain environmental conditions. Pathogens could remain undetected in untreated sewage sludge. Pathogens are not a significant health issue if sewage sludge is properly treated and site-specific management practices are followed. Micro-pollutants can become concentrated in sewage sludge; each of these disposal options comes with myriad potential — and in some cases proven — human health and environment impacts. Sterols and other hormones have been detected. One of the main concerns in the treated sludge is the concentrated metals content. Leaching methods can be used to meet the regulatory limit. In 2009 the EPA released the Targeted National Sewage Sludge Study, which reports on the level of metals, chemicals and other materials present in a statistical sample of sewage sludges.
Some highlights include: Silver is present to the degree of 20 mg/kg of sludge, on average, a near economically recoverable level, while some sludges of exceptionally high quality have up to 200 milligrams of silver per kilogram of sludge. Barium is present at the rate of 500 mg/kg. Lead, arsenic and cadmium are estimated by the EPA to be present in detectable quantities in 100% of national sewage sludges in the US, while thallium is only estimated to be present in 94.1% of sludges. Sewage treatment plants receive various forms of hazardous waste from hospitals, nursing homes and households. Low levels of constituents such as PCBs, brominated flame retardants, may remain in treated sludge. There are thousands other components of sludge that remain untested/undetected disposed of from modern society that end up in sludge which have been proven to be hazardous to both human and ecological health. In 2013 in South Carolina PCBs were discovered in high levels in wastewater sludge; the problem was not discovered until thou
Benthic zone
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos and include microorganisms as well as larger invertebrates, such as crustaceans and polychaetes. Organisms here live in close relationship with the substrate and many are permanently attached to the bottom; the benthic boundary layer, which includes the bottom layer of water and the uppermost layer of sediment directly influenced by the overlying water, is an integral part of the benthic zone, as it influences the biological activity that takes place there. Examples of contact soil layers include sand bottoms, rocky outcrops and bay mud; the benthic region of the ocean begins at the shore line and extends downward along the surface of the continental shelf out to sea. The continental shelf is a sloping benthic region that extends away from the land mass. At the continental shelf edge about 200 meters deep, the gradient increases and is known as the continental slope.
The continental slope drops down to the deep sea floor. The deep-sea floor is called the abyssal plain and is about 4,000 meters deep; the ocean floor is not all flat but has submarine ridges and deep ocean trenches known as the hadal zone. For comparison, the pelagic zone is the descriptive term for the ecological region above the benthos, including the water-column up to the surface. Depending on the water-body, the benthic zone may include areas that are only a few inches below water, such as a stream or shallow pond. For information on animals that live in the deeper areas of the oceans see aphotic zone; these include life forms that tolerate cool temperatures and low oxygen levels, but this depends on the depth of the water. Benthos are the organisms that live in the benthic zone, are different from those elsewhere in the water column. Many have adapted to live on the substrate. In their habitats they can be considered as dominant creatures, but they are a source of prey for Carcharhinidae such as the lemon shark.
Many organisms adapted to deep-water pressure cannot survive in the upper parts of the water column. The pressure difference can be significant; because light does not penetrate deep into ocean-water, the energy source for the benthic ecosystem is organic matter from higher up in the water column that drifts down to the depths. This dead and decaying matter sustains the benthic food chain; some microorganisms use chemosynthesis to produce biomass. Benthic organisms can be divided into two categories based on whether they make their home on the ocean floor or a few centimeters into the ocean floor; those living on the surface of the ocean floor are known as epifauna. Those who live burrowed into the ocean floor are known as infauna. Extremophiles, including piezophiles, which thrive in high pressures, may live there. Sources of food for benthic communities can derive from the water column above these habitats in the form of aggregations of detritus, inorganic matter, living organisms; these aggregations are referred to as marine snow, are important for the deposition of organic matter, bacterial communities.
The amount of material sinking to the ocean floor can average 307,000 aggregates per m2 per day. This amount will vary on the depth of the benthos, the degree of benthic-pelagic coupling; the benthos in a shallow region will have more available food than the benthos in the deep sea. Because of their reliance on it, microbes may become spatially dependent on detritus in the benthic zone; the microbes found in the benthic zone dinoflagellates and foraminifera, colonize quite on detritus matter while forming a symbiotic relationship with each other. Modern seafloor mapping technologies have revealed linkages between seafloor geomorphology and benthic habitats, in which suites of benthic communities are associated with specific geomorphic settings. Examples include cold-water coral communities associated with seamounts and submarine canyons, kelp forests associated with inner shelf rocky reefs and rockfish associated with rocky escarpments on continental slopes. In oceanic environments, benthic habitats can be zoned by depth.
From the shallowest to the deepest are: the epipelagic, the mesopelagic, the bathyal, the abyssal and the deepest, the hadal. The lower zones are in pressurized areas of the ocean. Human impacts have occurred at all ocean depths, but are most significant on shallow continental shelf and slope habitats. Many benthic organisms have retained their historic evolutionary characteristics; some organisms are larger than their relatives living in shallower zones because of higher oxygen concentration in deep water. It is not easy to map or observe these organisms and their habitats, most modern observations are made using remotely operated underwater vehicles, submarines. Benthic macroinvertebrates have many important ecological functions, such as regulating the flow of materials and energy in river ecosystems through their food web linkages; because of this correlation between flow of energy and nutrients, benthic macroinvertebrates have the ability to influence food resources on fish and other organisms in aquatic ecosystems.
For example, the addition of a modera
