Outwelling
Encyclopedia
Outwelling is a hypothesized process by which coastal salt marsh
es and mangroves, “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
, thus increasing the productivity of local fisheries
or other coastal plants. Outwelling also nourishes plankton
communities and causes a spike in activity.
The majority of outwelling is dissolved organic carbon (DOC) and some particulate organic carbon (POC) Outwelling expels salt
(90 g salt/m2), silicate
(1.0 mmol/m2), orthophosphate (0.03 mmol/m2), and nitrate
(0.04 mmol/m2) during each tidal cycle
.
Outwelling is affected by a number of different factors. For one, the amount of outwelling is dependent upon the primary production of an estuary
, thus, highly productive salt marshes result in increased outwelling. It is also dependent on tidal amplitude and geomorphology
of the estuary. Outwelling is not a steady process, and is affected by large rain
falls or inundation events (the larger the inundation, the greater the outwelling).
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; however, another study done in Louisiana
near the extensive salt marshes where tidal amplitude is larger found that outwelling contributed a significant amount of organic carbon to the nearby waters.
Outwelling occurs as pulses that correlate to inundation and precipitation
events, productivity and tidal fluctuations. In some cases, it is macrofauna and algae
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.
Salt marsh
A salt marsh is an environment in the upper coastal intertidal zone between land and salt water or brackish water, it is dominated by dense stands of halophytic plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh...
es and mangroves, “hot spots” of production, produce an excess amount of carbon each year and “outwell” these organic nutrients and detritus into the surrounding coastal embayment
Headlands and bays
Headlands and bays are two related features of the coastal environment.- Geology and geography :Headlands and bays are often found on the same coastline. A bay is surrounded by land on three sides, whereas a headland is surrounded by water on three sides. Headlands are characterized by high,...
or ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
, thus increasing the productivity of local fisheries
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
or other coastal plants. Outwelling also nourishes plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
communities and causes a spike in activity.
The majority of outwelling is dissolved organic carbon (DOC) and some particulate organic carbon (POC) Outwelling expels salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
(90 g salt/m2), silicate
Silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...
(1.0 mmol/m2), orthophosphate (0.03 mmol/m2), and nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
(0.04 mmol/m2) during each tidal cycle
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
.
Outwelling is affected by a number of different factors. For one, the amount of outwelling is dependent upon the primary production of an estuary
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
, thus, highly productive salt marshes result in increased outwelling. It is also dependent on tidal amplitude and geomorphology
Geomorphology
Geomorphology is the scientific study of landforms and the processes that shape them...
of the estuary. Outwelling is not a steady process, and is affected by large rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
falls or inundation events (the larger the inundation, the greater the outwelling).
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; however, another study done in Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...
near the extensive salt marshes where tidal amplitude is larger found that outwelling contributed a significant amount of organic carbon to the nearby waters.
Outwelling occurs as pulses that correlate to inundation and precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
events, productivity and tidal fluctuations. In some cases, it is macrofauna and algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
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.