{{Short description, Excess nutrients produced by salt marshes Outwelling is a hypothesized process by which coastal

salt marsh A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated ...

es and

mangrove A mangrove is a shrub or tree that grows in coastal saline water, saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evoluti ...

s, “hot spots” of production, produce an excess amount of carbon each year and “outwell” these organic nutrients and detritus into the surrounding coastal embayment or

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

, thus increasing the productivity of local

fisheries Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life; or more commonly, the site where such enterprise takes place ( a.k.a. fishing ground). Commercial fisheries include wild fisheries and fish farms, both ...

or other coastal plants. Outwelling also nourishes

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

communities and causes a spike in activity. The majority of outwelling is

dissolved organic carbon Dissolved organic carbon (DOC) is the fraction of organic carbon operationally defined as that which can pass through a filter with a pore size typically between 0.22 and 0.7 micrometers. The fraction remaining on the filter is called particu ...

(DOC) and some particulate organic carbon (POC) Outwelling expels

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...

(90 g salt/m2),

silicate In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...

(1.0 mmol/m2),

orthophosphate A phosphoric acid, in the general sense, is a phosphorus oxoacid in which each phosphorus (P) atom is in the oxidation state +5, and is bonded to four oxygen (O) atoms, one of them through a double bond, arranged as the corners of a tetrahedron. ...

(0.03 mmol/m2), and

nitrate Nitrate is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...

(0.04 mmol/m2) during each

tidal cycle Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can ...

. Outwelling is affected by a number of different factors. For one, the amount of outwelling is dependent upon the primary production of an

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

, thus, highly productive salt marshes result in increased outwelling. It is also dependent on tidal amplitude and

geomorphology Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or n ...

of the estuary. Outwelling is not a steady process, and is affected by large

rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...

falls or inundation events (the larger the inundation, the greater the outwelling). Outwelling occurs as pulses that correlate to inundation and

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

events, productivity and tidal fluctuations. In some cases, it is

macrofauna Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is ''flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. Zoo ...

and

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

that are pulsed out of the salt marsh into the water column rather than nutrients, but this has a similar effect of attracting small fish and nourishing the marine environment. Outwelling does not occur in every estuary. It is more evident and occurs more in estuaries bordering extensive coastal marshes. For example, a study done in a New England salt marsh found no evidence of outwelling, and in fact found that the salt marshes import carbon;Nixon, S.W. 1980. Between coastal marshes and coastal water—a review of twenty years of speculation and research in the role of salt marshes in estuarine productivity and water chemistry. pp. 437-525 in P. Hamilton and K.B. MacDonald, eds. Wetland processes with emphasis on modeling. Plenum Press, New York, NY. USA. however, another study done in

Louisiana Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-smallest by area and the 25th most populous of the 50 U.S. states. Louisiana is borde ...

near the extensive salt marshes where tidal amplitude is larger found that outwelling contributed a significant amount of organic carbon to the nearby waters.

Ramifications

Because of this hypothesis, many states have passed laws protecting

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

based on the rationale that protecting estuaries will protect the food source of local fish populations.

Controversy

The Outwelling hypothesis has been hotly debated for decades. There are many studies examining this hypothesis, but there has not yet been a firm conclusion. It appears that it may occur in some estuaries at some times, but there is a body of evidence contesting the claimed amount of organic carbon export, and even whether marshes export carbon at all.

References

Ecological processes