# River ecosystem

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Type of aquatic ecosystem with flowing freshwater

This stream operating together with its environment can be thought of as forming a river ecosystem.

**River ecosystems** are flowing waters that drain the landscape, and include the [biotic](/source/Biotic_component) (living) interactions amongst plants, animals and micro-organisms, as well as [abiotic](/source/Abiotic) (nonliving) physical and chemical interactions of its many parts.[1][2] River [ecosystems](/source/Ecosystem) are part of larger [watershed](/source/Drainage_basin) networks or catchments, where smaller [headwater](/source/Headwater) streams drain into mid-size streams, which progressively drain into larger river networks. The major zones in river ecosystems are determined by the river bed's gradient or by the velocity of the current. Faster moving turbulent water typically contains greater concentrations of [dissolved oxygen](/source/Oxygen_saturation), which supports greater biodiversity than the slow-moving water of pools. These distinctions form the basis for the division of rivers into [upland and lowland](/source/Upland_and_lowland_(freshwater_ecology)) rivers.

The food base of streams within riparian forests is mostly derived from the trees, but wider streams and those that lack a [canopy](/source/Canopy_(forest)) derive the majority of their food base from [algae](/source/Algae). [Anadromous fish](/source/Fish_migration) are also an important source of [nutrients](/source/Nutrient). Environmental threats to rivers include loss of water, dams, chemical pollution and [introduced species](/source/Introduced_species).[3] A [dam](/source/Dam) produces negative effects that continue down the watershed. The most important negative effects are the reduction of [spring flooding](/source/Flood), which damages [wetlands](/source/Wetland), and the retention of [sediment](/source/Sediment), which leads to the loss of deltaic wetlands.[4]

River ecosystems are prime examples of lotic ecosystems. *Lotic* refers to flowing water, from the [Latin](/source/Latin) *lotus*, meaning washed. Lotic waters range from [springs](/source/Spring_(water)) only a few centimeters wide to major [rivers](/source/River) kilometers in width.[5] Much of this article applies to lotic ecosystems in general, including related lotic systems such as [streams](/source/Stream) and [springs](/source/Spring_(hydrosphere)). Lotic ecosystems can be contrasted with [lentic ecosystems](/source/Lentic_ecosystems), which involve relatively still terrestrial waters such as lakes, ponds, and [wetlands](/source/Wetland). Lentic comes from the Latin *lenis*, meaning calm. Together, these two ecosystems form the more general study area of freshwater or [aquatic ecology](/source/Aquatic_ecology). There is no sharp boundary between the two systems, however.[6]

The following unifying characteristics make the ecology of running waters unique among aquatic habitats: the flow is unidirectional, there is a state of continuous physical change, and there is a high degree of spatial and temporal heterogeneity at all scales ([microhabitats](/source/Microhabitat)), the variability between lotic systems is quite high and the biota is specialized to live with flow conditions.[7]

## Abiotic components (non-living)

The non-living components of an ecosystem are called abiotic components. E.g. stone, air, soil, etc.

### Water flow

A pensive Cooplacurripa River, [NSW](/source/NSW)

Rapids in [Mount Robson Provincial Park](/source/Mount_Robson_Provincial_Park)

Unidirectional water flow is the key factor in lotic (riverine) systems influencing their [ecology](/source/Ecology). Streamflow can be continuous or intermittent. Streamflow is the result of the summative inputs from [groundwater](/source/Groundwater), [precipitation](/source/Precipitation), and [overland flow](/source/Surface_runoff). Water flow can vary between systems, ranging from torrential rapids to slow backwaters that almost seem like [lentic systems](/source/Lake_ecosystem). The speed or velocity of the water flow of the water column can also vary within a system and is subject to chaotic turbulence, though water velocity tends to be highest in the middle part of the stream channel (known as the [thalveg](/source/Thalweg)). This turbulence results in divergences of flow from the mean downslope flow vector as typified by eddy currents. The mean flow rate vector is based on the variability of friction with the bottom or sides of the channel, [sinuosity](/source/Sinuosity), obstructions, and the incline gradient.[5] In addition, the amount of water input into the system from direct precipitation, [snowmelt](/source/Snowmelt), and/or groundwater can affect the flow rate. The amount of water in a stream is measured as [discharge](/source/Discharge_(hydrology)) (volume per unit time). As water flows downstream, streams and rivers most often gain water volume, so at [base flow](/source/Baseflow) (i.e., no storm input), smaller headwater streams have very low discharge, while larger rivers have much higher discharge. The "flow regime" of a river or stream includes the general patterns of discharge over annual or decadal time scales, and may capture seasonal changes in flow.[8][9]

While water flow is strongly determined by slope, flowing waters can alter the general shape or direction of the stream bed, a characteristic also known as [geomorphology](/source/Geomorphology). The profile of the river water column is made up of three primary actions: erosion, transport, and deposition. Rivers have been described as "the gutters down which run the ruins of continents".[10] Rivers are continuously [eroding](/source/Erosion), transporting, and [depositing](/source/Deposition_(geology)) substrate, sediment, and organic material. The continuous movement of water and entrained material creates a variety of habitats, including [riffles](/source/Riffle), [glides](/source/Bacterial_gliding), and [pools](/source/Stream_pool).[11]

### Light

**Light** is important to lotic systems, because it provides the energy necessary to drive [primary production](/source/Primary_production) via [photosynthesis](/source/Photosynthesis), and can also provide refuge for prey species in shadows it casts. The amount of light that a system receives can be related to a combination of internal and external stream variables. The area surrounding a small stream, for example, might be shaded by surrounding forests or by valley walls. Larger river systems tend to be wide so the influence of external variables is minimized, and the sun reaches the surface. These rivers also tend to be more turbulent, however, and particles in the water increasingly attenuate light as depth increases.[11] Seasonal and diurnal factors might also play a role in light availability because the angle of incidence, the angle at which light strikes water can lead to light lost from reflection. Known as [Beer's Law](/source/Beers_law), the shallower the angle, the more light is reflected and the amount of solar radiation received declines logarithmically with depth.[7] Additional influences on light availability include cloud cover, altitude, and geographic position.[12]

### Temperature

[Castle Geyser](/source/Castle_Geyser), [Yellowstone National Park](/source/Yellowstone_National_Park)

A forest stream in the winter near [Erzhausen](/source/Erzhausen), Germany

Cascade in the [Pyrénées](/source/Pyr%C3%A9n%C3%A9es)

Most lotic species are [poikilotherms](/source/Poikilotherm) whose internal temperature varies with their environment, thus temperature is a key abiotic factor for them. Water can be heated or cooled through radiation at the surface and conduction to or from the air and surrounding substrate. Shallow streams are typically well mixed and maintain a relatively uniform temperature within an area. In deeper, slower moving water systems, however, a strong difference between the bottom and surface temperatures may develop. Spring fed systems have little variation as springs are typically from groundwater sources, which are often very close to ambient temperature.[7] Many systems show strong [diurnal](/source/Diurnal_temperature_variation) fluctuations and seasonal variations are most extreme in arctic, desert and temperate systems.[7] The amount of shading, climate and elevation can also influence the temperature of lotic systems.[5]

### Chemistry

Water chemistry in river ecosystems varies depending on which dissolved solutes and gases are present in the [water column](/source/Water_column) of the stream. Specifically river water can include, apart from the water itself,[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

- dissolved inorganic matter and major [ions](/source/Ion) (calcium, sodium, magnesium, potassium, bicarbonate, sulphide, chloride)

- dissolved inorganic nutrients (nitrogen, phosphorus, silica)

- [suspended](/source/Particulate_organic_matter) and [dissolved organic matter](/source/Dissolved_organic_matter)

- gases (nitrogen, nitrous oxide, carbon dioxide, oxygen)

- trace metals and pollutants

#### Dissolved ions and nutrients

Dissolved stream solutes can be considered either *reactive* or *conservative*. Reactive solutes are readily biologically assimilated by the [autotrophic](/source/Autotroph) and [heterotrophic](/source/Heterotrophic) biota of the stream; examples can include inorganic [nitrogen](/source/Nitrogen) species such as [nitrate](/source/Nitrate) or [ammonium](/source/Ammonium), some forms of [phosphorus](/source/Phosphorus) (e.g., soluble reactive phosphorus), and [silica](/source/Silicon_dioxide). Other solutes can be considered conservative, which indicates that the solute is not taken up and used biologically; [chloride](/source/Chloride) is often considered a conservative solute. Conservative solutes are often used as hydrologic tracers for water movement and transport. Both reactive and conservative stream water chemistry is foremost determined by inputs from the geology of its [watershed](/source/Drainage_basin), or catchment area. Stream water chemistry can also be influenced by precipitation, and the addition of pollutants from human sources.[5][11] Large differences in chemistry do not usually exist within small lotic systems due to a high rate of mixing. In larger river systems, however, the concentrations of most nutrients, dissolved salts, and pH decrease as distance increases from the river's source.[7]

#### Dissolved gases

In terms of dissolved gases, [oxygen](/source/Oxygen) is likely the most important chemical constituent of lotic systems, as all aerobic organisms require it for survival. It enters the water mostly via diffusion at the water-air interface. Oxygen's solubility in water decreases as water pH and temperature increases. Fast, turbulent streams expose more of the water's surface area to the air and tend to have low temperatures and thus more oxygen than slow, backwaters.[7] Oxygen is a byproduct of photosynthesis, so systems with a high abundance of aquatic algae and plants may also have high concentrations of oxygen during the day. These levels can decrease significantly during the night when primary producers switch to respiration. Oxygen can be limiting if circulation between the surface and deeper layers is poor, if the activity of lotic animals is very high, or if there is a large amount of organic decay occurring.[11]

#### Suspended matter

Rivers can also transport suspended inorganic and organic matter. These materials can include sediment[13] or terrestrially derived organic matter that falls into the stream channel.[14] Often, organic matter is processed within the stream via mechanical fragmentation, consumption and grazing by invertebrates, and microbial decomposition.[15] Leaves and woody debris recognizable coarse particulate organic matter (CPOM) into particulate organic matter (POM), down to fine particulate organic matter. Woody and non-woody plants have different instream breakdown rates, with leafy plants or plant parts (e.g., flower petals) breaking down faster than woody logs or branches.[16]

### Substrate

The inorganic [substrate](/source/Substrate_(marine_biology)) of lotic systems is composed of the [geologic](/source/Geologic) material present in the catchment that is eroded, transported, sorted, and deposited by the current. Inorganic substrates are classified by size on the [Wentworth scale](/source/Wentworth_scale), which ranges from boulders, to pebbles, to gravel, to sand, and to silt.[7] Typically, substrate [particle size](/source/Particle_size_(grain_size)) decreases downstream with larger boulders and stones in more mountainous areas and sandy bottoms in lowland rivers. This is because the higher gradients of mountain streams facilitate a faster flow, moving smaller substrate materials further downstream for deposition.[11] Substrate can also be organic and may include fine particles, autumn shed leaves, [large woody debris](/source/Large_woody_debris) such as submerged tree logs, moss, and semi-aquatic plants.[5] Substrate deposition is not necessarily a permanent event, as it can be subject to large modifications during flooding events.[11]

## Biotic components (living)

The living components of an ecosystem are called the biotic components. Streams have numerous types of biotic organisms that live in them, including bacteria, primary producers, insects and other invertebrates, as well as fish and other vertebrates.

[Co-occurrence network](/source/Co-occurrence_network) of a bacterial community in a stream[17]

### Microorganisms

[Bacteria](/source/Bacteria) are present in large numbers in lotic waters. Free-living forms are associated with decomposing organic material, [biofilm](/source/Biofilm) on the surfaces of rocks and vegetation, in between particles that compose the substrate, and suspended in the [water column](/source/Water_column). Other forms are also associated with the guts of lotic organisms as [parasites](/source/Parasitism) or in [commensal](/source/Commensal) relationships.[7] Bacteria play a large role in energy recycling (see [below](#Trophic_relationships)).[5]

[Diatoms](/source/Diatom) are one of the main dominant groups of [periphytic](https://en.wiktionary.org/wiki/periphytic) algae in lotic systems and have been widely used as efficient indicators of water quality, because they respond quickly to environmental changes, especially organic pollution and eutrophication, with a broad spectrum of tolerances to conditions ranging, from oligotrophic to eutrophic.[18][19][20]

[Fungi](/source/Fungus) are also very frequently present in lotic environments. These are mostly miscroscopic, and found for the most as asexual ([anamorph](/source/Teleomorph%2C_anamorph_and_holomorph)) [aquatic hyphomycete](https://en.wikipedia.org/w/index.php?title=Aquatic_hyphomycete&action=edit&redlink=1) [spores](/source/Spore), or less frequently as sexual ([teleomorph](/source/Teleomorph%2C_anamorph_and_holomorph)) spores freely floating in waters. However, the main body of the fungi, the [mycelium](/source/Mycelium), live freely in [sediments](/source/Sediment), on decaying organic material,[21] as parasites on or in other organisms (such as on [animals](/source/Animal), or [algae](/source/Algae)),[22][23] as [endophytes](/source/Endophyte),[24] in plants, or as [mutualists](/source/Mutualism_(biology)) in the guts of [insects](/source/Insect).[25]

### Biofilm

Different biofilm components in streams.[26] Principal components are algae and bacteria.

A [biofilm](/source/Biofilm) is a combination of algae (diatoms etc.), fungi, bacteria, and other small [microorganisms](/source/Microorganism) that exist in a film along the [streambed](/source/Streambed) or the [benthos](/source/Benthos).[27] Biofilm assemblages themselves are complex,[28] and add to the complexity of a streambed.

The different biofilm components (algae and bacteria are the principal components) are embedded in an [exopolysaccharide](/source/Exopolysaccharide) matrix (EPS), and are net receptors of inorganic and organic elements and remain submitted to the influences of the different environmental factors.[26]

[Epilithic](/source/Epilithic) [diatoms](/source/Diatom) from a river bed
[18] (size bars are 30 μm)

This slime on streambed [cobbles](/source/Cobble_(geology)) is a biofilm

Biofilms are one of the main [biological interphases](/source/Interphase) in river ecosystems, and probably the most important in [intermittent rivers](/source/Intermittent_river), where the importance of the [water column](/source/Water_column) is reduced during extended low-activity periods of the [hydrological cycle](/source/Hydrological_cycle).[26] Biofilms can be understood as [microbial consortia](/source/Microbial_consortia) of [autotrophs](/source/Autotroph) and [heterotrophs](/source/Heterotroph), coexisting in a matrix of hydrated [extracellular polymeric substances](/source/Extracellular_polymeric_substance) (EPS). These two main biological components are respectively mainly [algae](/source/Algae) and [cyanobacteria](/source/Cyanobacteria) on one side, and [bacteria](/source/Bacteria) and [fungi](/source/Fungi) on the other.[26] [Micro](/source/Microfauna)- and [meiofauna](/source/Meiofauna) also inhabit the biofilm, predating on the organisms and organic particles and contributing to its evolution and dispersal.[29] Biofilms therefore form a highly active biological consortium, ready to use organic and inorganic materials from the water phase, and also ready to use light or chemical energy sources. The EPS immobilize the cells and keep them in close proximity allowing for intense interactions including cell-cell communication and the formation of synergistic consortia.[30] The EPS is able to retain [extracellular enzymes](/source/Extracellular_enzyme) and therefore allows the utilization of materials from the environment and the transformation of these materials into dissolved nutrients for the use by algae and bacteria. At the same time, the EPS contributes to protect the cells from desiccation as well from other hazards (e.g., [biocides](/source/Biocide), [UV radiation](/source/UV_radiation), etc.) from the outer world.[26] On the other hand, the packing and the EPS protection layer limits the diffusion of gases and nutrients, especially for the cells far from the biofilm surface, and this limits their survival and creates strong gradients within the biofilm. Both the biofilm physical structure, and the plasticity of the organisms that live within it, ensure and support their survival in harsh environments or under changing environmental conditions.[26]

### Primary producers

Periphyton

Common water hyacinth in flower

Algae, consisting of [phytoplankton](/source/Phytoplankton) and [periphyton](/source/Periphyton), are the most significant sources of primary production in most streams and rivers.[7] Phytoplankton float freely in the water column and thus are unable to maintain populations in fast flowing streams. They can, however, develop sizeable populations in slow moving rivers and backwaters.[5] Periphyton are typically filamentous and tufted algae that can attach themselves to objects to avoid being washed away by fast currents. In places where flow rates are negligible or absent, periphyton may form a gelatinous, unanchored floating mat.[11]

Plants exhibit limited adaptations to fast flow and are most successful in reduced currents. More primitive plants, such as [mosses](/source/Moss) and [liverworts](/source/Marchantiophyta) attach themselves to solid objects. This typically occurs in colder headwaters where the mostly rocky substrate offers attachment sites. Some plants are free floating at the water's surface in dense mats like [duckweed](/source/Duckweed) or [water hyacinth](/source/Water_hyacinth). Others are rooted and may be classified as submerged or emergent. Rooted plants usually occur in areas of slackened current where fine-grained soils are found.[12][11] These rooted plants are flexible, with elongated leaves that offer minimal resistance to current.[1]

Living in flowing water can be beneficial to plants and algae because the current is usually well aerated and it provides a continuous supply of nutrients.[11] These organisms are limited by flow, light, water chemistry, substrate, and grazing pressure.[7] Algae and plants are important to lotic systems as sources of energy, for forming microhabitats that shelter other fauna from predators and the current, and as a food resource.[12]

### Insects and other invertebrates

Up to 90% of [invertebrates](/source/Invertebrate) in some lotic systems are [insects](/source/Insect). These species exhibit tremendous diversity and can be found occupying almost every available habitat, including the surfaces of stones, deep below the substratum in the [hyporheic zone](/source/Hyporheic_zone), adrift in the current, and in the surface film.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

Insects have developed several strategies for living in the diverse flows of lotic systems. Some avoid high current areas, inhabiting the substratum or the sheltered side of rocks. Others have flat bodies to reduce the drag forces they experience from living in running water.[31] Some insects, like the giant water bug ([Belostomatidae](/source/Belostomatidae)), avoid flood events by leaving the stream when they sense rainfall.[32] In addition to these behaviors and body shapes, insects have different life history [adaptations](/source/Adaptation) to cope with the naturally occurring physical harshness of stream environments.[33] Some insects time their life events based on when floods and droughts occur. For example, some mayflies synchronize when they emerge as flying adults with when snowmelt flooding usually occurs in Colorado streams. Other insects do not have a flying stage and spend their entire life cycle in the river.

Like most of the primary consumers, lotic invertebrates often rely heavily on the current to bring them food and oxygen.[34] Invertebrates are important as both consumers and prey items in lotic systems.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

The common orders of insects that are found in river ecosystems include [Ephemeroptera](/source/Ephemeroptera) (also known as a [mayfly](/source/Mayfly)), [Trichoptera](/source/Trichoptera) (also known as a [caddisfly](/source/Caddisfly)), [Plecoptera](/source/Plecoptera) (also known as a [stonefly](/source/Stonefly), [Diptera](/source/Diptera) (also known as a true [fly](/source/Fly)), some types of [Coleoptera](/source/Coleoptera) (also known as a [beetle](/source/Beetle)), [Odonata](/source/Odonata) (the group that includes the [dragonfly](/source/Dragonfly) and the [damselfly](/source/Damselfly)), and some types of [Hemiptera](/source/Hemiptera) (also known as true bugs).[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

Additional invertebrate [taxa](/source/Taxa) common to flowing waters include [mollusks](/source/Mollusk) such as [snails](/source/Snail), [limpets](/source/Limpet), [clams](/source/Clam), [mussels](/source/Mussel), as well as [crustaceans](/source/Crustacean) like [crayfish](/source/Crayfish), [amphipoda](/source/Amphipoda) and [crabs](/source/Crab).[11]

### Fish and other vertebrates

[New Zealand longfin eels](/source/New_Zealand_longfin_eel) can weigh over 50 kilograms.

The [brook trout](/source/Brook_trout) is native to small streams, creeks, lakes, and spring ponds.

Fish are probably the best-known inhabitants of lotic systems. The ability of a fish species to live in flowing waters depends upon the speed at which it can swim and the duration that its speed can be maintained. This ability can vary greatly between species and is tied to the habitat in which it can survive. Continuous swimming expends a tremendous amount of energy and, therefore, fishes spend only short periods in full current. Instead, individuals remain close to the bottom or the banks, behind obstacles, and sheltered from the current, swimming in the current only to feed or change locations.[1] Some species have adapted to living only on the system bottom, never venturing into the open water flow. These fishes are [dorso-ventrally](/source/Anatomical_terms_of_location#Dorsal_and_ventral) flattened to reduce flow resistance and often have eyes on top of their heads to observe what is happening above them. Some also have sensory barrels positioned under the head to assist in the testing of substratum.[12]

Lotic systems typically connect to each other, forming a path to the ocean (spring → stream → river → ocean), and many fishes have life cycles that require stages in both fresh and salt water. [Salmon](/source/Salmon), for example, are [anadromous](/source/Anadromous) species that are born in freshwater but spend most of their adult life in the ocean, returning to fresh water only to spawn. [Eels](/source/Eel) are [catadromous](/source/Catadromous) species that [do the opposite](/source/Eel_life_history), living in freshwater as adults but migrating to the ocean to spawn.[7]

Other vertebrate taxa that inhabit lotic systems include [amphibians](/source/Amphibian), such as [salamanders](/source/Salamander), [reptiles](/source/Reptile) (e.g. snakes, turtles, crocodiles and alligators) various bird species, and mammals (e.g., [otters](/source/Otter), [beavers](/source/Beaver), [hippos](/source/Hippopotamus), and [river dolphins](/source/River_dolphin)). With the exception of a few species, these vertebrates are not tied to water as fishes are, and spend part of their time in terrestrial habitats.[7] Many fish species are important as consumers and as prey species to the larger vertebrates mentioned above.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

## Trophic level dynamics

The concept of [trophic levels](/source/Trophic_level) are used in [food webs](/source/Food_web) to visualise the manner in which energy is transferred from one part of an ecosystem to another.[35] Trophic levels can be assigned numbers determining how far an organism is along the [food chain](/source/Food_chain).

1. Level one: [Producers](/source/Autotroph), plant-like organisms that generate their own food using solar radiation, including [algae](/source/Algae), [phytoplankton](/source/Phytoplankton), [mosses](/source/Moss) and [lichens](/source/Lichen).

1. Level two: [Consumers](/source/Consumer), animal-like organism that get their energy from eating producers, such as [zooplankton](/source/Zooplankton), small fish, and [crustaceans](/source/Crustacean).

1. Level three: [Decomposers](/source/Decomposer), organisms that break down the dead matter of consumers and producers and return the nutrients back to the system. Example are [bacteria](/source/Bacteria) and [fungi](/source/Fungi).

All energy transactions within an [ecosystem](/source/Ecosystem) derive from a single external source of energy, the sun.[35] Some of this solar radiation is used by producers (plants) to turn inorganic substances into organic substances which can be used as food by consumers (animals).[35] Plants release portions of this energy back into the ecosystem through a [catabolic](/source/Catabolic) process. Animals then consume the potential energy that is being released from the producers. This system is followed by the death of the consumer organism which then returns nutrients back into the ecosystem. This allow further growth for the plants, and the cycle continues. Breaking cycles down into levels makes it easier for ecologists to understand [ecological succession](/source/Ecological_succession) when observing the transfer of energy within a system.[35]

### Top-down and bottom-up affect

Flowing rivers can act as [dispersal vectors](/source/Dispersal_vector) for plant matter and invertebrates.

A common issue with trophic level dynamics is how resources and production are regulated.[36] The usage and interaction between resources have a large impact on the structure of food webs as a whole. Temperature plays a role in food web interactions including top-down and bottom-up forces within ecological communities. Bottom-up regulations within a food web occur when a resource available at the base or bottom of the food web increases productivity, which then climbs the chain and influence the [biomass](/source/Biomass_(ecology)) availability to higher trophic organism.[36] Top-down regulations occur when a predator population increases. This limits the available prey population, which limits the availability of energy for lower trophic levels within the food chain. Many biotic and abiotic factors can influence top-down and bottom-up interactions.[37]

### Trophic cascade

Another example of food web interactions are [trophic cascades](/source/Trophic_cascade). Understanding trophic cascades has allowed ecologists to better understand the structure and dynamics of food webs within an ecosystem.[37] The phenomenon of trophic cascades allows [keystone predators](/source/Keystone_predator) to structure entire food web in terms of how they interact with their prey. Trophic cascades can cause drastic changes in the energy flow within a food web.[37] For example, when a top or keystone predator consumes organisms below them in the food web, the density and behavior of the prey will change. This, in turn, affects the abundance of organisms consumed further down the chain, resulting in a cascade down the trophic levels. However, empirical evidence shows trophic cascades are much more prevalent in terrestrial food webs than aquatic food webs.[37]

## Food chain

 Example of a river food web. [Fungi](/source/Fungus) ([aquatic hyphomycetes](/source/Aquatic_hyphomycetes)) and [Bacteria](/source/Bacteria) can be seen in the red box at the bottom. Fungi and bacteria (and other decomposers, like worms) decompose and recycle nutrients back to the habitat, which is shown by the light blue arrows. Without fungi and bacteria, the rest of the food web would starve, because there would not be enough nutrients for the animals higher up in the food web. The dark orange arrows show how some animals consume others in the food web. For example, [lobsters](/source/Lobster) may be eaten by humans. The dark blue arrows represent one complete [food chain](/source/Food_chain), beginning with the consumption of [algae](/source/Algae) by the water flea, *[Daphnia](/source/Daphnia)*, which is consumed by a small fish, which is consumed by a larger fish, which is at the end consumed by the [great blue heron](/source/Great_blue_heron).[38]

A [food chain](/source/Food_chain) is a linear system of links that is part of a food web, and represents the order in which [organisms](/source/Organism) are consumed from one trophic level to the next. Each link in a food chain is associated with a trophic level in the ecosystem. The numbered steps it takes for the initial source of energy starting from the bottom to reach the top of the food web is called the food chain length.[39] While food chain lengths can fluctuate, aquatic ecosystems start with primary producers that are consumed by primary consumers which are consumed by secondary consumers, and those in turn can be consumed by tertiary consumers so on and so forth until the top of the food chain has been reached.[40] When the top has been reached, or even before then, there are [decomposers](/source/Decomposer) that utilize dead organic material, and are releasing nutrients into the environment, or are then again eaten by other organisms.[41]

### Primary producers

[Primary producers](/source/Primary_producer) start every food chain. Their production of energy and nutrients comes from the sun through [photosynthesis](/source/Photosynthesis). Algae contributes to a lot of the energy and nutrients at the base of the food chain along with terrestrial [litter-fall](/source/Litter-fall) that enters the [stream](/source/Stream) or [river](/source/River).[42] Production of organic compounds like carbon is what gets transferred up the food chain. Primary producers are consumed by herbivorous [invertebrates](/source/Invertebrate) that act as the [primary consumers](/source/Primary_consumer). Productivity of these producers and the function of the ecosystem as a whole are influenced by the organism above it in the food chain.[43]

### Primary consumers

[Primary consumers](/source/Primary_consumer) are the invertebrates and macro-invertebrates that feed upon the primary producers. They play an important role in initiating the transfer of energy from the base trophic level to the next. They are regulatory organisms which facilitate and control rates of [nutrient cycling](/source/Nutrient_cycle) and the mixing of aquatic and terrestrial plant materials.[44] They also transport and retain some of those nutrients and materials.[44] There are many different functional groups of these invertebrate, including grazers, organisms that feed on algal [biofilm](/source/Biofilm) that collects on submerged objects, shredders that feed on large leaves and detritus and help break down large material. Also [filter feeders](/source/Filter_feeder), macro-invertebrates that rely on stream flow to deliver them fine [particulate organic matter](/source/Particulate_organic_matter) (FPOM) suspended in the [water column](/source/Water_column), and gatherers who feed on FPOM found on the substrate of the river or stream.[44]

### Secondary consumers

The [secondary consumers](/source/Secondary_consumer) in a river ecosystem are the [predators](/source/Predation) of the primary consumers. This includes mainly [insectivorous](/source/Insectivore) fish.[45] Consumption by invertebrate insects and macro-invertebrates is another step of energy flow up the food chain. Depending on their abundance, these predatory consumers can shape an ecosystem by the manner in which they affect the trophic levels below them. When fish are at high abundance and eat lots of invertebrates, then algal biomass and primary production in the stream is greater, and when secondary consumers are not present, then algal biomass may decrease due to the high abundance of primary consumers.[45] Energy and nutrients that starts with primary producers continues to make its way up the food chain and depending on the ecosystem, may end with these predatory fish.

### Decomposers

The [decomposers](/source/Decomposer) in a river system are composed of [bacteria](/source/Bacteria), [fungi](/source/Fungus), [protists](/source/Protist), and many [invertebrates](/source/Invertebrate) like [insects](/source/Insect) and [snails](/source/Snail). They are crucial to benthic food webs and in the river ecosystem as a whole.[46] The fungi and bacteria in river ecosystems live mostly on decaying [organic matter](/source/Organic_matter) from [animals](/source/Animal) and [plants](/source/Plant). The decomposing fungi in river ecosystems include [saprotrophs](/source/Saprotrophic_nutrition), living on [leaf litter](/source/Plant_litter) and submerged wood, and other dead organic matierials.[21] The protists include [pseudofungi](/source/Pseudofungi) like [oomycetes](/source/Oomycete) that also are found on leaves and submerged plant material. The invertebrates include [arthropods](/source/Arthropod) and [molluscs](/source/Mollusca). Most [benthic](/source/Benthic_zone) insects and certain snails are functionally classified as "*shredders*" that break down plant material.[47]

## Food web complexity

[Diversity](/source/Species_diversity), [productivity](/source/Productivity_(ecology)), [species richness](/source/Species_richness), [composition](/source/Species_composition) and [stability](/source/Ecological_stability) are all interconnected by a series of feedback loops. Communities can have a series of complex, direct and/or indirect, responses to major changes in [biodiversity](/source/Biodiversity).[43] Food webs can include a wide array of variables, the three main variables ecologists look at regarding ecosystems include species richness, [biomass of productivity](/source/Productivity_(ecology)) and [stability](/source/Ecological_stability)/resistant to change.[43] When a species is added or removed from an ecosystem it will have an effect on the remaining food web, the intensity of this effect is related to species connectedness and food web robustness.[48] When a new species is added to a river ecosystem the intensity of the effect is related to the robustness or resistance to change of the current food web.[48] When a species is removed from a river ecosystem the intensity of the effect is related to the connectedness of the species to the food web.[48] An [invasive species](/source/Invasive_species) could be removed with little to no effect, but if important and native primary producers, prey or predatory fish are removed you could have a negative [trophic cascade](/source/Trophic_cascade).[48] One highly variable component to river ecosystems is food supply ([biomass](/source/Biomass_(ecology)) of [primary producers](/source/Primary_producer)).[49] Food supply or type of producers is ever changing with the seasons and differing habitats within the river ecosystem.[49] Another highly variable component to river ecosystems is nutrient input from wetland and terrestrial [detritus](/source/Detritus).[49] Food and nutrient supply variability is important for the [succession](/source/Ecological_succession), [robustness](/source/Ecological_robustness) and connectedness of river ecosystem organisms.[49]

## Trophic relationships

### Energy inputs

[Pondweed](/source/Elodea_canadensis) is an autochthonous energy source.

Energy sources can be [autochthonous](/source/Indigenous_(ecology)) or allochthonous.

- **Autochthonous** (from the Latin "auto" = "self) energy sources are those derived from within the lotic system. During [photosynthesis](/source/Photosynthesis), for example, [primary producers](/source/Primary_producer) form organic carbon compounds out of carbon dioxide and inorganic matter. The energy they produce is important for the community because it may be transferred to higher [trophic levels](/source/Trophic_level) via consumption. Additionally, high rates of [primary production](/source/Primary_production) can introduce [dissolved organic matter](/source/Dissolved_organic_matter) (DOM) to the waters.[11] Another form of autochthonous energy comes from the decomposition of dead organisms and feces that originate within the lotic system. In this case, bacteria decompose the [detritus](/source/Detritus) or coarse [particulate](/source/Particulate) organic material (CPOM; >1 mm pieces) into fine particulate organic matter (FPOM; <1 mm pieces) and then further into inorganic compounds that are required for photosynthesis.[5][11][50] This process is discussed in more detail below.

Leaf litter is an allochthonous energy source.

- **Allochthonous** energy sources are those derived from outside the lotic system, that is, from the terrestrial environment. Leaves, twigs, fruits, etc. are typical forms of terrestrial CPOM that have entered the water by direct litter fall or lateral leaf blow.[7] In addition, terrestrial animal-derived materials, such as feces or carcasses that have been added to the system are examples of allochthonous CPOM. The CPOM undergoes a specific process of degradation. Allan gives the example of a leaf fallen into a stream.[5] First, the soluble chemicals are dissolved and [leached](/source/Leaching_(chemical_science)) from the leaf upon its saturation with water. This adds to the DOM load in the system. Next [microbes](/source/Microbe) such as [bacteria](/source/Bacteria) and [fungi](/source/Fungi) [colonize](/source/Colonize) the leaf, softening it as the [mycelium](/source/Mycelium) of the fungus grows into it. The composition of the microbial community is influenced by the species of tree from which the leaves are shed (Rubbo and Kiesecker 2004). This combination of bacteria, fungi, and leaf are a food source for [shredding invertebrates](/source/Invertebrate),[51] which leave only FPOM after consumption. These fine particles may be colonized by microbes again or serve as a food source for animals that consume FPOM. Organic matter can also enter the lotic system already in the FPOM stage by wind, [surface runoff](/source/Surface_runoff), [bank](/source/Bank_(geography)) [erosion](/source/Erosion), or [groundwater](/source/Groundwater). Similarly, DOM can be introduced through [canopy](/source/Canopy_(biology)) drip from rain or from surface flows.[7]

### Invertebrates

[Invertebrates](/source/Invertebrate) can be organized into many [feeding guilds](/source/Guild_(ecology)) in lotic systems. Some species are shredders, which use large and powerful mouth parts to feed on non-woody CPOM and their associated microorganisms. Others are [suspension feeders](/source/Filter_feeder), which use their [setae](/source/Setae), filtering aparati, nets, or even secretions to collect FPOM and microbes from the water. These species may be passive collectors, utilizing the natural flow of the system, or they may generate their own current to draw water, and also, FPOM in Allan.[5] Members of the gatherer-collector guild actively search for FPOM under rocks and in other places where the stream flow has slackened enough to allow deposition.[11] Grazing invertebrates utilize scraping, rasping, and browsing adaptations to feed on [periphyton](/source/Periphyton) and [detritus](/source/Detritus). Finally, several families are predatory, capturing and consuming animal prey. Both the number of species and the abundance of individuals within each guild is largely dependent upon food availability. Thus, these values may vary across both seasons and systems.[5]

### Fish

Fish can also be placed into [feeding guilds](/source/Guild_(ecology)). Planktivores pick [plankton](/source/Plankton) out of the [water column](/source/Water_column). [Herbivore](/source/Herbivore)-[detritivores](/source/Detritivore) are [bottom-feeding](/source/Bottom_feeder) species that ingest both [periphyton](/source/Periphyton) and [detritus](/source/Detritus) indiscriminately. Surface and water column feeders capture surface prey (mainly terrestrial and emerging insects) and drift ([benthic](/source/Benthic) invertebrates floating downstream). Benthic invertebrate feeders prey primarily on immature insects, but will also consume other benthic invertebrates. [Top predators](/source/Apex_predator) consume fishes and/or large invertebrates. [Omnivores](/source/Omnivore) ingest a wide range of prey. These can be [floral](/source/Floral), [faunal](/source/Fauna), and/or detrital in nature. Finally, [parasites](/source/Parasite) live off of host species, typically other fishes.[5] Fish are flexible in their feeding roles, capturing different prey with regard to seasonal availability and their own developmental stage. Thus, they may occupy multiple feeding guilds in their lifetime. The number of species in each guild can vary greatly between systems, with temperate warm water streams having the most benthic invertebrate feeders, and tropical systems having large numbers of detritus feeders due to high rates of allochthonous input.[11]

## Community patterns and diversity

[Iguazu Falls](/source/Iguazu_Falls) –  an extreme lotic environment

[Beaver Run](/source/Beaver_Run_(Bowman_Creek)) –  a placid lotic environment

### Local species richness

Large rivers have comparatively more species than small streams. Many relate this pattern to the greater area and volume of larger systems, as well as an increase in habitat diversity. Some systems, however, show a poor fit between system size and [species richness](/source/Species_richness). In these cases, a combination of factors such as historical rates of [speciation](/source/Speciation) and [extinction](/source/Extinction), type of [substrate](/source/Substrate_(marine_biology)), [microhabitat](/source/Microhabitat) availability, water chemistry, temperature, and disturbance such as flooding seem to be important.[7]

### Resource partitioning

Although many alternate theories have been postulated for the ability of [guild-mates](/source/Guild_(ecology)) to coexist (see Morin 1999), [resource partitioning](/source/Resource_partitioning) has been well documented in lotic systems as a means of reducing competition. The three main types of resource partitioning include habitat, dietary, and temporal segregation.[7]

[Habitat segregation](/source/Niche_differentiation#Spatial_partitioning) was found to be the most common type of resource partitioning in natural systems (Schoener, 1974). In lotic systems, microhabitats provide a level of physical complexity that can support a diverse array of organisms (Vincin and Hawknis, 1998). The separation of species by substrate preferences has been well documented for invertebrates. Ward (1992) was able to divide substrate dwellers into six broad assemblages, including those that live in: coarse substrate, gravel, sand, mud, woody debris, and those associated with plants, showing one layer of segregation. On a smaller scale, further habitat partitioning can occur on or around a single substrate, such as a piece of gravel. Some invertebrates prefer the high flow areas on the exposed top of the gravel, while others reside in the crevices between one piece of gravel and the next, while still others live on the bottom of this gravel piece.[7]

Dietary segregation is the second-most common type of resource partitioning.[7] High degrees of [morphological specializations](/source/Niche_differentiation#Morphological_differentiation) or behavioral differences allow organisms to use specific resources. The size of nets built by some species of invertebrate [suspension feeders](/source/Filter_feeder), for example, can filter varying particle size of FPOM from the water (Edington et al. 1984). Similarly, members in the grazing guild can specialize in the harvesting of algae or detritus depending upon the morphology of their scraping apparatus. In addition, certain species seem to show a preference for specific algal species.[7]

[Temporal segregation](/source/Niche_differentiation#Temporal_partitioning) is a less common form of resource partitioning, but it is nonetheless an observed phenomenon.[7] Typically, it accounts for coexistence by relating it to differences in life history patterns and the timing of maximum growth among guild mates. Tropical fishes in [Borneo](/source/Borneo), for example, have shifted to shorter life spans in response to the [ecological niche](/source/Ecological_niche) reduction felt with increasing levels of species richness in their ecosystem (Watson and Balon 1984).

### Persistence and succession

Over long time scales, there is a tendency for species composition in pristine systems to remain in a stable state.[52] This has been found for both invertebrate and fish species.[7] On shorter time scales, however, flow variability and unusual precipitation patterns decrease habitat stability and can all lead to declines in persistence levels. The ability to maintain this persistence over long time scales is related to the ability of lotic systems to return to the original community configuration relatively quickly after a disturbance (Townsend et al. 1987). This is one example of temporal succession, a site-specific change in a community involving changes in species composition over time. Another form of temporal succession might occur when a new habitat is opened up for [colonization](/source/Colonization). In these cases, an entirely new community that is well adapted to the conditions found in this new area can establish itself.[7]

### River continuum concept

Meandering stream in [Waitomo](/source/Waitomo), New Zealand

[River Gryffe](/source/River_Gryffe) in Scotland

Rocky stream in [Hawaii](/source/Hawaii)

The [River continuum concept](/source/River_continuum_concept) (RCC) was an attempt to construct a single framework to describe the function of temperate lotic ecosystems from the headwaters to larger rivers and relate key characteristics to changes in the biotic community.[53] The physical basis for RCC is size and location along the gradient from a small stream eventually linked to a large river. Stream order (see [characteristics of streams](/source/Stream#Characteristics_of_streams)) is used as the physical measure of the position along the RCC.

According to the RCC, low ordered sites are small shaded streams where allochthonous inputs of CPOM are a necessary resource for consumers. As the river widens at mid-ordered sites, energy inputs should change. Ample sunlight should reach the bottom in these systems to support significant periphyton production. Additionally, the biological processing of CPOM (coarse particulate organic matter – larger than 1 mm) inputs at upstream sites is expected to result in the transport of large amounts of FPOM (fine particulate organic matter – smaller than 1 mm) to these downstream ecosystems. Plants should become more abundant at edges of the river with increasing river size, especially in lowland rivers where finer sediments have been deposited and facilitate rooting. The main channels likely have too much current and turbidity and a lack of substrate to support plants or periphyton. Phytoplankton should produce the only autochthonous inputs here, but photosynthetic rates will be limited due to turbidity and mixing. Thus, allochthonous inputs are expected to be the primary energy source for large rivers. This FPOM will come from both upstream sites via the decomposition process and through lateral inputs from floodplains.

Biota should change with this change in energy from the headwaters to the mouth of these systems. Namely, shredders should prosper in low-ordered systems and grazers in mid-ordered sites. Microbial decomposition should play the largest role in energy production for low-ordered sites and large rivers, while photosynthesis, in addition to degraded allochthonous inputs from upstream will be essential in mid-ordered systems. As mid-ordered sites will theoretically receive the largest variety of energy inputs, they might be expected to host the most biological diversity.[53][5][7]

Just how well the RCC actually reflects patterns in natural systems is uncertain and its generality can be a handicap when applied to diverse and specific situations.[5] The most noted criticisms of the RCC are: 1. It focuses mostly on [macroinvertebrates](/source/Macroinvertebrates), disregarding that plankton and fish diversity is highest in high orders; 2. It relies heavily on the fact that low ordered sites have high CPOM inputs, even though many streams lack [riparian](/source/Riparian) habitats; 3. It is based on pristine systems, which rarely exist today; and 4. It is centered around the functioning of temperate streams. Despite its shortcomings, the RCC remains a useful idea for describing how the patterns of ecological functions in a lotic system can vary from the source to the mouth.[5]

Disturbances such as congestion by dams or natural events such as shore flooding are not included in the RCC model.[54] Various researchers have since expanded the model to account for such irregularities. For example, J.V. Ward and J.A. Stanford came up with the Serial Discontinuity Concept in 1983, which addresses the impact of [geomorphologic](/source/Geomorphology) disorders such as congestion and integrated inflows. The same authors presented the Hyporheic Corridor concept in 1993, in which the vertical (in depth) and lateral (from shore to shore) structural complexity of the river were connected.[55] The [flood pulse concept](/source/Flood_pulse_concept), developed by W. J. Junk in 1989, further modified by P. B. Bayley in 1990 and K. Tockner in 2000, takes into account the large amount of nutrients and organic material that makes its way into a river from the sediment of surrounding flooded land.[54]

## Human impacts

 Anthropogenic influences on river systems.[56] Examples are mainly from settings with a modest technological influence, especially in the period of about 10,000 to 4000 cal yr BP.

Humans exert a [geomorphic](/source/Geomorphic) force that now rivals that of the natural Earth.[57][58] The period of human dominance has been termed the [Anthropocene](/source/Anthropocene), and several dates have been proposed for its onset. Many researchers have emphasised the dramatic changes associated with the [Industrial Revolution](/source/Industrial_Revolution) in Europe after about 1750 CE (Common Era) and the [Great Acceleration](/source/Great_Acceleration) in technology at about 1950 CE.[59][60][61][62][63]

However, a detectable human imprint on the environment extends back for thousands of years,[64][65][66][67] and an emphasis on recent changes minimises the enormous landscape transformation caused by humans in antiquity.[68] Important earlier human effects with significant environmental consequences include [megafaunal extinctions](/source/Megafaunal_extinctions) between 14,000 and 10,500 cal yr BP;[69] [domestication of plants](/source/Domestication_of_plants) and [animals](/source/Domestication_of_animals) close to the start of the [Holocene](/source/Holocene) at 11,700 cal yr BP; agricultural practices and deforestation at 10,000 to 5000 cal yr BP; and widespread generation of anthropogenic soils at about 2000 cal yr BP.[62][70][71][72][73] Key evidence of early anthropogenic activity is encoded in early [fluvial successions](/source/Fluvial_processes),[74][75] long predating [anthropogenic effects](/source/Human_impact_on_the_environment) that have intensified over the past centuries and led to the modern worldwide river crisis.[76][77][63]

### Pollution

River pollution can include but is not limited to: increasing sediment export, excess nutrients from fertilizer or urban runoff,[78] sewage and septic inputs,[79] [plastic pollution](/source/Plastic_pollution),[80] nano-particles, pharmaceuticals and personal care products,[81] synthetic chemicals,[82] road salt,[83] inorganic contaminants (e.g., heavy metals), and even heat via thermal pollutions.[84] The effects of pollution often depend on the context and material, but can reduce [ecosystem functioning](/source/Ecosystem_function), limit [ecosystem services](/source/Ecosystem_services), reduce stream biodiversity, and impact human health.[85]

Pollutant sources of lotic systems are hard to control because they can derive, often in small amounts, over a very wide area and enter the system at many locations along its length. While direct pollution of lotic systems has been greatly reduced in the United States under the government's [Clean Water Act](/source/Clean_Water_Act), contaminants from diffuse non-point sources remain a large problem.[11] Agricultural fields often deliver large quantities of sediments, nutrients, and chemicals to nearby streams and rivers. Urban and residential areas can also add to this pollution when contaminants are accumulated on impervious surfaces such as roads and parking lots that then drain into the system. Elevated nutrient concentrations, especially nitrogen and phosphorus which are key components of fertilizers, can increase periphyton growth, which can be particularly dangerous in slow-moving streams.[11] Another pollutant, [acid rain](/source/Acid_rain), forms from sulfur dioxide and nitrous oxide emitted from factories and power stations. These substances readily dissolve in atmospheric moisture and enter lotic systems through precipitation. This can lower the pH of these sites, affecting all trophic levels from algae to vertebrates.[12] Mean species richness and total species numbers within a system decrease with decreasing pH.[7]

### Flow modification

A [weir](/source/Weir) on the [River Calder, West Yorkshire](/source/River_Calder%2C_West_Yorkshire)

Flow modification can occur as a result of [dams](/source/Dam), water regulation and extraction, channel modification, and the destruction of the river floodplain and adjacent riparian zones.[86]

[Dams](/source/Dam) alter the flow, temperature, and sediment regime of lotic systems.[7] Additionally, many rivers are dammed at multiple locations, amplifying the impact. Dams can cause enhanced clarity and reduced variability in stream flow, which in turn cause an increase in [periphyton](/source/Periphyton) abundance. Invertebrates immediately below a dam can show reductions in species richness due to an overall reduction in habitat heterogeneity.[11] Also, thermal changes can affect insect development, with abnormally warm winter temperatures obscuring cues to break egg [diapause](/source/Diapause) and overly cool summer temperatures leaving too few acceptable days to complete growth.[5] Finally, dams fragment river systems, isolating previously continuous populations, and preventing the migrations of [anadromous](/source/Anadromous) and [catadromous](/source/Catadromous) species.[11]

### Invasive species

[Invasive species](/source/Invasive_species) have been introduced to lotic systems through both purposeful events (e.g. stocking game and food species) as well as unintentional events (e.g. hitchhikers on boats or fishing waders). These organisms can affect natives via competition for prey or habitat, predation, habitat alteration, hybridization, or the introduction of harmful diseases and parasites.[7] Once established, these species can be difficult to control or eradicate, particularly because of the connectivity of lotic systems. Invasive species can be especially harmful in areas that have [endangered](/source/Endangered) biota, such as mussels in the Southeast United States, or those that have localized [endemic](/source/Endemic_(ecology)) species, like lotic systems west of the Rocky Mountains, where many species evolved in isolation.

## See also

- [Ecology portal](https://en.wikipedia.org/wiki/Portal:Ecology)

- [Betty's Brain](/source/Betty's_Brain) – software that "learns" about river ecosystems

- [Flood pulse concept](/source/Flood_pulse_concept)

- [Lake ecosystem](/source/Lake_ecosystem)

- [Rheophile](/source/Rheophile)

- [Riparian zone](/source/Riparian_zone)

- [River continuum concept](/source/River_continuum_concept)

- [River drainage system](/source/Drainage_system_(geomorphology))

- [RIVPACS](/source/RIVPACS)

- *[The Riverkeepers](/source/The_Riverkeepers)*

- [Upland and lowland rivers](/source/Upland_and_lowland_(freshwater_ecology))

## References

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1. **[^](#cite_ref-BiologyConcepts&Connections_2-0)** "Biology Concepts & Connections Sixth Edition", Campbell, Neil A. (2009), page 2, 3 and G-9. Retrieved 2010-06-14.

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## Further reading

- Brown, A. L. 1987. Freshwater Ecology. Heinimann Educational Books, London. P. 163.

- Carlisle, D. M. and M. D. Woodside. 2013. [Ecological health in the nation's streams](https://purl.fdlp.gov/GPO/gpo41741), [United States Geological Survey](/source/United_States_Geological_Survey). P. 6.

- Edington, J. M., Edington, M. A., and J. A. Dorman. 1984. Habitat partitioning amongst hydrophyschid larvae of a Malaysian stream. Entomologica 30: 123–129.

- Hynes, H. B. N. 1970. Ecology of Running Waters. Originally published in Toronto by University of Toronto Press, 555 p.

- Morin, P. J. 1999. Community Ecology. Blackwell Science, Oxford. P. 424.

- Power, M. E. (1990). ["Effects of fish in river food webs"](https://web.archive.org/web/20130524034630/http://myclasses.naperville203.org/staff/NNHSWeather/KraftsonAPES/Shared%20Documents/UNIT%202%20DEVELOPING%20ECOSYSTEMS/Effects%20of%20Fish%20on%20River%20Food%20Webs.pdf) (PDF). *Science*. **250** (4982): 811–814. [Bibcode](/source/Bibcode_(identifier)):[1990Sci...250..811P](https://ui.adsabs.harvard.edu/abs/1990Sci...250..811P). [doi](/source/Doi_(identifier)):[10.1126/science.250.4982.811](https://doi.org/10.1126%2Fscience.250.4982.811). [PMID](/source/PMID_(identifier)) [17759974](https://pubmed.ncbi.nlm.nih.gov/17759974). [S2CID](/source/S2CID_(identifier)) [24780727](https://api.semanticscholar.org/CorpusID:24780727). Archived from [the original](http://myclasses.naperville203.org/staff/NNHSWeather/KraftsonAPES/Shared%20Documents/UNIT%202%20DEVELOPING%20ECOSYSTEMS/Effects%20of%20Fish%20on%20River%20Food%20Webs.pdf) (PDF) on 2013-05-24.

- Rubbo, M. J.; Kiesecker, J. M. (2004). ["Leaf litter composition and community structure: translating regional species changes into local dynamics"](https://doi.org/10.1890%2F03-0653). *Ecology*. **85** (9): 2519–2525. [Bibcode](/source/Bibcode_(identifier)):[2004Ecol...85.2519R](https://ui.adsabs.harvard.edu/abs/2004Ecol...85.2519R). [doi](/source/Doi_(identifier)):[10.1890/03-0653](https://doi.org/10.1890%2F03-0653).

- [Schoener, T. W.](/source/Thomas_W._Schoener) (1974). "Resource partitioning in ecological communities". *Science*. **2** (4145): 369–404. [Bibcode](/source/Bibcode_(identifier)):[1974Sci...185...27S](https://ui.adsabs.harvard.edu/abs/1974Sci...185...27S). [doi](/source/Doi_(identifier)):[10.1126/science.185.4145.27](https://doi.org/10.1126%2Fscience.185.4145.27). [PMID](/source/PMID_(identifier)) [17779277](https://pubmed.ncbi.nlm.nih.gov/17779277). [S2CID](/source/S2CID_(identifier)) [43846597](https://api.semanticscholar.org/CorpusID:43846597).

- Townsend, C. R.; Hildrew, A. G.; Schofield, K. (1987). "Persistence of stream invertebrate communities in relation to environmental variability". *Animal Ecology*. **56** (2): 597–613. [Bibcode](/source/Bibcode_(identifier)):[1987JAnEc..56..597T](https://ui.adsabs.harvard.edu/abs/1987JAnEc..56..597T). [doi](/source/Doi_(identifier)):[10.2307/5071](https://doi.org/10.2307%2F5071). [JSTOR](/source/JSTOR_(identifier)) [5071](https://www.jstor.org/stable/5071).

- Vannote, R. L.; Minshall, G. W.; Cummins, K. W.; Sedell, J. R.; Cushing, C. E. (1980). "The river continuum concept". *Canadian Journal of Fisheries and Aquatic Sciences*. **37**: 130–137. [Bibcode](/source/Bibcode_(identifier)):[1980CJFAS..37..130V](https://ui.adsabs.harvard.edu/abs/1980CJFAS..37..130V). [doi](/source/Doi_(identifier)):[10.1139/f80-017](https://doi.org/10.1139%2Ff80-017). [S2CID](/source/S2CID_(identifier)) [40373623](https://api.semanticscholar.org/CorpusID:40373623).

- Vinson, M. R.; Hawkins, C. P. (1998). "Biodiversity of stream insects: variation at local, basin, and regional scales". *Annual Review of Entomology*. **43**: 271–293. [doi](/source/Doi_(identifier)):[10.1146/annurev.ento.43.1.271](https://doi.org/10.1146%2Fannurev.ento.43.1.271). [PMID](/source/PMID_(identifier)) [15012391](https://pubmed.ncbi.nlm.nih.gov/15012391).

- Ward, J. V. 1992. Aquatic Insect Ecology: biology and habitat. Wiley, New York. P. 456.

- Watson, D. J.; Balon, E. K. (1984). "Ecomorphological analysis of fish taxocenes in rainforest streams of northern Borneo". *Journal of Fish Biology*. **25** (3): 371–384. [Bibcode](/source/Bibcode_(identifier)):[1984JFBio..25..371W](https://ui.adsabs.harvard.edu/abs/1984JFBio..25..371W). [doi](/source/Doi_(identifier)):[10.1111/j.1095-8649.1984.tb04885.x](https://doi.org/10.1111%2Fj.1095-8649.1984.tb04885.x).

## External links

Wikimedia Commons has media related to [Rivers](https://commons.wikimedia.org/wiki/Category:Rivers).

Wikimedia Commons has media related to [Streams](https://commons.wikimedia.org/wiki/Category:Streams).

Wikimedia Commons has media related to [Springs](https://commons.wikimedia.org/wiki/Category:Springs).

Look up ***[lotic](https://en.wiktionary.org/wiki/lotic)*** in Wiktionary, the free dictionary.

- [USGS real time stream flow data for gauged systems nationwide](https://waterdata.usgs.gov/nwis/rt)

v t e Rivers, streams and springs Rivers (lists) Alluvial river Braided river Blackwater river Channel Channel pattern Channel types Confluence Distributary Drainage basin Mountain river Subterranean river River bifurcation River ecosystem River source Tributary Streams Arroyo Beck Bourne Burn Chalk stream Coulee Current Stream bed Stream channel Streamflow Stream gradient Stream pool Perennial stream Winterbourne Springs (list) Estavelle/Inversac Geyser Holy well Hot spring list list in the US Karst spring list Mineral spring Ponor Rhythmic spring Spring horizon Sedimentary processes and erosion Abrasion Anabranch Aggradation Armor Bed load Bed material load Granular flow Debris flow Deposition Dissolved load Downcutting Erosion Headward erosion Knickpoint Palaeochannel Progradation Retrogradation Saltation Secondary flow Sediment transport Suspended load Wash load Water gap Fluvial landforms Ait Alluvial fan Antecedent drainage stream Avulsion Bank Bar Bayou Billabong Canyon Chine Cut bank Estuary Floating island Fluvial terrace Gill Gulch Gully Glen Meander scar Mouth bar Oxbow lake Riffle-pool sequence Point bar Ravine Rill River island Rock-cut basin Sedimentary basin Sedimentary structures Strath Thalweg River valley Wadi Fluvial flow Helicoidal flow International scale of river difficulty Log jam Meander Plunge pool Rapids Riffle Shoal Stream capture Waterfall list of waterfalls Whitewater Surface runoff Agricultural wastewater First flush Urban runoff Floods and stormwater 100-year flood Crevasse splay Flash flood Flood Urban flooding Non-water flood Flood barrier Flood control Flood forecasting Flood-meadow Floodplain Flood pulse concept Flooded grasslands and savannas Inundation Storm Water Management Model Return period Point source pollution Effluent Industrial wastewater Sewage River measurement and modelling Baer's law Baseflow Bradshaw model Discharge (hydrology) Drainage density Exner equation Groundwater model Hack's law Hjulström curve Hydrograph Hydrological model Hydrological transport model Infiltration (hydrology) Main stem Playfair's law Relief ratio River Continuum Concept Rouse number Runoff curve number Runoff model (reservoir) Stream gauge WAFLEX Wetted perimeter Volumetric flow rate River engineering Aqueduct Balancing lake Canal Check dam Dam Drop structure Daylighting Detention basin Erosion control Fish ladder Floodplain restoration Flume Infiltration basin Leat Levee River morphology Retention basin Revetment Riparian-zone restoration Stream restoration Weir River sports Canyoning Fly fishing Rafting River surfing Riverboarding Stone skipping Triathlon Whitewater canoeing Whitewater kayaking Whitewater slalom Related Aquifer Aquatic toxicology Body of water Hydraulic civilization Limnology Riparian zone River valley civilization River cruise Sacred waters Surface water Wild river Rivers by length Rivers by discharge rate Drainage basins Whitewater rivers Flash floods River name etymologies Countries without rivers

v t e Aquatic ecosystems General components and freshwater ecosystems General Acoustic ecology Algal bloom Anoxic waters Aquatic adaptation Aquatic animal Insect Mammal Water bird Aquatic biomonitoring Aquatic plant Aquatic population dynamics Aquatic predation Aquatic respiration Aquatic science Aquatic toxicology Benthos Bioluminescence Biomass Cascade effect Colored dissolved organic matter Dead zone Ecohydrology Eutrophication Fisheries science Food chain Food web GIS and aquatic science Hydrobiology Hypoxia Macrobenthos Meiobenthos Microbial ecology Microbial food web Microbial loop Mycoloop Nekton Neuston Particle Pelagic zone Photic zone Phytoplankton Plankton Pleuston Productivity Ramsar Convention Sediment trap Semiaquatic Shoaling and schooling Siltation Spawn Stable isotope analysis in aquatic ecosystems Stream metabolism Substrate Thermal pollution Trophic level Underwater camouflage Water column Zooplankton Freshwater Freshwater biology Freshwater biome Freshwater environmental quality parameters Freshwater fish Hyporheic zone Limnology Lake ecosystem Lake stratification Macrophyte Pond Fish pond Rheotaxis River Ecosystem Stream bed Stream pool Trophic state index Upland and lowland Water garden Wetland Bog Brackish marsh Fen Freshwater marsh Freshwater swamp forest Ecoregions List of freshwater ecoregions (WWF) Africa and Madagascar Latin America and the Caribbean List of marine ecoregions Specific examples Everglades Maharashtra North Pacific Subtropical Gyre San Francisco Estuary Marine ecosystems (components) General Deep scattering layer Diel vertical migration f-ratio Iron fertilization Large marine ecosystem Marine biology Marine chemistry Marine food web Marine primary production Marine snow Ocean fertilization Oceanic physical-biological process Ocean turbidity Photophore Thorson's rule Upwelling Viral shunt Whale fall Marine life Census of Marine Life Deep-sea community Deep-water coral Marine fungi Marine invertebrates Marine larval ecology Seagrass Seashore wildlife Wild fisheries Microorganisms Marine bacteriophage Marine prokaryotes Marine protists Marine viruses Paradox of the plankton Vertebrates Marine mammal Marine reptile list Saltwater fish Coastal fish Coral reef fish Deep-sea fish Demersal fish Pelagic fish Seabird Marine habitats Bay mud Marine coastal ecosystem Coastal biogeomorphology Cold seep Coral reef Davidson Seamount § Ecology Estuary Intertidal ecology Intertidal wetland Kelp forest Hydrothermal vent Lagoon Mangrove Marine biomes Mudflat Oyster reef Rocky shore Salt marsh Salt pannes and pools Seagrass meadow Sponge ground Sponge reef Tide pool Conservation Coral bleaching Ecological values of mangroves Fisheries and climate change HERMIONE Human impact on marine life Marine conservation activism Marine pollution Marine protected area Lakes portal Oceans portal Category

v t e Ecology: Modelling ecosystems: Trophic components General Abiotic component Abiotic stress Behaviour Biogeochemical cycle Biomass Biotic component Biotic stress Carrying capacity Competition Ecosystem Ecosystem ecology Ecosystem model Green world hypothesis Keystone species List of feeding behaviours Metabolic theory of ecology Productivity Resource Restoration Producers Autotrophs Chemosynthesis Chemotrophs Foundation species Kinetotrophs Mixotrophs Myco-heterotrophy Mycotroph Organotrophs Photoheterotrophs Photosynthesis Photosynthetic efficiency Phototrophs Primary nutritional groups Primary production Consumers Apex predator Bacterivore Carnivores Chemoorganotroph Foraging Generalist and specialist species Intraguild predation Herbivores Heterotroph Heterotrophic nutrition Insectivore Mesopredators Mesopredator release hypothesis Omnivores Optimal foraging theory Planktivore Predation Prey switching Decomposers Chemoorganoheterotrophy Decomposition Detritivores Detritus Microorganisms Archaea Bacteriophage Lithoautotroph Lithotrophy Marine Microbial cooperation Microbial ecology Microbial food web Microbial intelligence Microbial loop Mycoloop Microbial mat Microbial metabolism Phage ecology Food webs Biomagnification Ecological efficiency Ecological pyramid Energy flow Food chain Trophic level Example webs Lakes Rivers Soil Tritrophic interactions in plant defense Marine food webs cold seeps hydrothermal vents intertidal kelp forests North Pacific Gyre San Francisco Estuary tide pool Processes Ascendency Bioaccumulation Cascade effect Climax community Competitive exclusion principle Consumer–resource interactions Copiotrophs Dominance Ecological network Ecological succession Energy quality Energy systems language f-ratio Feed conversion ratio Feeding frenzy Mesotrophic soil Nutrient cycle Oligotroph Paradox of the plankton Trophic cascade Trophic mutualism Trophic state index Defense, counter Animal coloration Anti-predator adaptations Camouflage Deimatic behaviour Herbivore adaptations to plant defense Mimicry Plant defense against herbivory Predator avoidance in schooling fish

v t e Ecology: Modelling ecosystems: Other components Population ecology Abundance Allee effect Consumer-resource model Depensation Ecological yield Effective population size Intraspecific competition Logistic function Malthusian growth model Maximum sustainable yield Overpopulation Overexploitation Population cycle Population dynamics Population modeling Population size Predator–prey (Lotka–Volterra) equations Recruitment Small population size Stability Resilience Resistance Random generalized Lotka–Volterra model Species Biodiversity Density-dependent inhibition Ecological effects of biodiversity Ecological extinction Endemic species Flagship species Gradient analysis Indicator species Introduced species Invasive species / Native species Latitudinal gradients in species diversity Minimum viable population Neutral theory Occupancy–abundance relationship Population viability analysis Priority effect Rapoport's rule Relative abundance distribution Relative species abundance Species diversity Species homogeneity Species richness Species distribution Species–area curve Umbrella species Species interaction Antibiosis Biological interaction Commensalism Community ecology Ecological facilitation Interspecific competition Mutualism Parasitism Storage effect Symbiosis Spatial ecology Biogeography Cross-boundary subsidy Ecocline Ecotone Ecotype Disturbance Edge effects Foster's rule Habitat fragmentation Ideal free distribution Intermediate disturbance hypothesis Insular biogeography Land change modeling Landscape ecology Landscape epidemiology Landscape limnology Metapopulation Patch dynamics r/K selection theory Resource selection function Source–sink dynamics Niche Ecological trap Ecosystem engineer Environmental niche modelling Guild Habitat Marine Semiaquatic Terrestrial Limiting similarity Niche apportionment models Niche construction Niche differentiation Ontogenetic niche shift Other networks Assembly rules Bateman's principle Bioluminescence Ecological collapse Ecological debt Ecological deficit Ecological energetics Ecological indicator Ecological threshold Ecosystem diversity Emergence Extinction debt Kleiber's law Liebig's law of the minimum Marginal value theorem Thorson's rule Xerosere Other Allometry Alternative stable state Balance of nature Biological data visualization Ecological economics Ecological footprint Ecological forecasting Ecological humanities Ecological stoichiometry Ecopath Ecosystem based fisheries Endolith Evolutionary ecology Functional ecology Industrial ecology Macroecology Microecosystem Natural environment Regime shift Sexecology Systems ecology Urban ecology Theoretical ecology Outline of ecology

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Adapted from the Wikipedia article [River ecosystem](https://en.wikipedia.org/wiki/River_ecosystem) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/River_ecosystem?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.