Stream metabolism, often referred to as aquatic ecosystem metabolism in both freshwater (lakes, rivers, wetlands, streams, reservoirs) and marine ecosystems, includes gross primary productivity (GPP) and ecosystem respiration (ER) and can be expressed as net ecosystem production (NEP = GPP - ER). Analogous to

metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...

within an individual

organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...

, stream metabolism represents how

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

is created (

primary production In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through ...

) and used ( respiration) within an

aquatic ecosystem An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environ ...

. In

heterotrophic A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

ecosystems, GPP:ER is <1 (ecosystem using more energy than it is creating); in

autotrophic An autotroph is an organism that can convert abiotic sources of energy into energy stored in organic compounds, which can be used by other organisms. Autotrophs produce complex organic compounds (such as carbohydrates, fats, and proteins) us ...

ecosystems it is >1 (ecosystem creating more energy than it is using

Most streams are heterotrophi

A heterotrophic ecosystem often means that allochthonous (coming from outside the ecosystem) inputs of

organic matter Organic matter, organic material or natural organic matter is the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come fro ...

, such as leaves or debris fuel ecosystem respiration rates, resulting in respiration greater than production within the ecosystem. However, autochthonous (coming from within the ecosystem) pathways also remain important to metabolism in heterotrophic ecosystems. In an autotrophic ecosystem, conversely, primary production (by

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

, macrophytes) exceeds respiration, meaning that ecosystem is producing more organic carbon than it is respiring. Stream metabolism can be influenced by a variety of factors, including physical characteristics of the stream (slope, width, depth, and speed/volume of flow), biotic characteristics of the stream (abundance and diversity of organisms ranging from

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

), light and nutrient availability to fuel primary production, organic matter to fuel respiration, water chemistry and temperature, and natural or human-caused disturbance, such as dams, removal of riparian vegetation,

nutrient pollution Nutrient pollution is a form of water pollution caused by too many Nutrient, nutrients entering the water. It is a primary cause of eutrophication of surface waters (lakes, rivers and Coast, coastal waters), in which excess nutrients, usually ni ...

wildfire A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a ...

flooding A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant concern in agriculture, civi ...

. Measuring stream metabolic state is important to understand how disturbance may change the available primary productivity, and whether and how that increase or decrease in NEP influences foodweb dynamics, allochthonous/autochthonous pathways, and trophic interactions. Metabolism (encompassing both ER and GPP) must be measured rather than primary productivity alone, because simply measuring primary productivity does not indicate excess production available for higher trophic levels. One commonly used method for determining metabolic state in an aquatic system is daily changes in oxygen concentration, from which GPP, ER, and net daily metabolism can be estimated. Disturbances can affect trophic relationships in a variety of ways, such as simplifying foodwebs, causing trophic cascades, and shifting carbon sources and major pathways of energy flow (Power et al. 1985, Power et al. 2008). Part of understanding how disturbance will impact trophic dynamics lies in understanding disturbance impacts to stream metabolism (Holtgrieve et al. 2010). For example, in Alaska streams, disturbance of the benthos by spawning

salmon Salmon (; : salmon) are any of several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the genera ''Salmo'' and ''Oncorhynchus'' of the family (biology), family Salmonidae, native ...

caused distinct changes in stream metabolism; autotrophic streams became net heterotrophic during the

spawning Spawn is the Egg cell, eggs and Spermatozoa, sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of freely releasing eggs and sperm into a body of water (fresh or marine); the physical act is ...

run, then reverted to autotrophy after the spawning season (Holtgrieve and Schindler 2011). There is evidence that this seasonal disturbance impacts trophic dynamics of benthic

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s and in turn their

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

predators (Holtgrieve and Schindler 2011, Moore and Schindler 2008). Wildfire disturbance may have similar metabolic and trophic impacts in streams.

References

{{reflist *Odum, Howard T.
"Primary production in flowing waters"
''Limnology and Oceanography'', vol. 1, no. 2, pp. 102–117, April 1956. *Power, M. E.; Matthews, W. J.; Stewart, A. J.
"Grazing minnow, piscivorous bass, and stream algae: dynamics of a strong interaction"
''Ecology'', vol. 66, pp. 1448–1456. *Holtgrieve, Gordon W.; Schindler, Daniel E.; Branch, Trevor A.; A’mar, Z. Teresa
"Simultaneous quantification of aquatic ecosystem metabolism and reaeration using a Bayesian statistical model of oxygen dynamics"
''Limnology and Oceanography'', vol. 55, no. 3, pp. 1047–1063, 2010. *Holtgrieve, Gordon W.; Schindler, Daniel E.
"Marine-derived nutrients, bioturbation, and ecosystem metabolism: reconsidering the role of salmon in streams"
''Ecology'', vol. 92, pp. 373–385. *Moore, Jonathan W.; Schindler, Daniel E.
"Biotic disturbance and benthic community dynamics in salmon-bearing streams"
''Journal of Animal Ecology'', vol. 77, iss. 2, pp. 275–284, March 2008. Aquatic ecology Ecosystems Metabolism Water streams

See also

References