Brackish marshes develop from salt marshes where a significant freshwater influx dilutes the seawater to brackish levels of salinity. This commonly happens upstream from salt marshes by estuaries of coastal rivers or near the mouths of coastal rivers with heavy freshwater discharges in the conditions of low tidal ranges. [1]
The salinity levels in brackish marshes can range from 0.5 ppt to 35 ppt. [2] Marshes are also characterised by low-growing vegetation and bare mud or sand flats. [3] Due to the variations in salinity, brackish marshes create a distinctive ecosystem where plants from either freshwater or saltwater marshes can co-inhabit. [4] The salinity levels also change with the tides, decreasing at low tide and increasing at high tide as ocean water feeds farther upriver. [5]
In terms of biodiversity, a brackish marsh serves a unique ecological niche. [8] Its vegetation is a byproduct of its salinity levels. High salinity serves as an evolutionary barrier for most plants, creating a less diverse number of plant species as an ecosystem moves from fresh to saltwater. Thus, there are only a few colonies of saltwater native plants in freshwater and almost no freshwater plants in saltwater ecosystems. [4] However, in brackish marshes both types of plants are prevalent and are in fact high in plant productivity. [4] Examples include, arrow arum ( Peltandra virginica ), soft rush (Juncus effusus), cattail ( Typha ), and sawgrass ( Cladium ). [2]
These plants are usually halophytic in order to survive these conditions. [9] For example brackish sites in Georgia, U.S., are dominated by species such as smooth cord grass (Sporobolusalterniflora), big cordgrass ( Spartina cynosuroides), and black rush ( Juncus roemerianus). [4] Other communities are cabbage palm ( Sabal palmetto ), sand cordgrass ( Spartina bakeri ), black rush ( Juncus roemerianus ), saltgrass ( Distichlis spicata , Paspalum distichum ), and mixed halophytes ( Batis maritima , Salicomia virginica). [10] Along with salinity, brackish marshes face high physical stress due to flooding and wave currents creating adaptive traits within the plant community. [11]
These plant communities also create an environment that provides a nursery for juvenile fish, crustaceans, [12] and birds. [13] Fauna use the shallow habitat and the turbidity of the water to protect themselves from predators. Similarly the surface of the marsh is covered with vegetation which is used by the nekton species for shelter, leaving enough space to move underneath between the stems. [14]
The trophic levels within a brackish marsh has been shown to depend on the amount of macro organic matter in the upper level of soil. This macro organic matter is believed to be the food source of detritivore benthic animals that support higher trophic levels. These materials build up as the marsh matures, making age another factor in the biodiversity of a brackish marsh. [14]
Algae also make up a large part of the biodiversity in brackish marshes. The most common algae, diatoms, make up a large portion of the algal community in brackish marshes. [15] Diatoms are eukaryotic microorganisms that have a cell wall that is composed of silica and can exists in freshwater or marine environments making them good candidates for brackish marshes. [15] These diatoms can be either planktic, which float freely in the water column, or benthic, which attach to a substrate. [15] Some examples of diatoms that can be found in brackish marshes are from the genera (Navicula), (Nitzschia), (Diploneis), (Cyclotella), (Cymbella), (Fragilaria), (Gyrosigma), (Tabularia), (Amphora), (Cocconeis), and many more. [16] Many different organisms in these brackish marshes depend on diatoms as a food source so they are ecologically important. Some examples of organisms that feed on diatoms are bivalves, [17] mollusks, [18] fish, [18] copepods, [18] decapod larvae, [18] and ducks, [19] as well as many others. Many organisms in these brackish marshes consume diatoms so they are very valuable to maintaining balance in these types of ecosystems.
Another group of algae that is present in brackish marshes are fucoid algae. [20] This is a type of brown macroalgae in the class Phaeophyceae. [20] Brown algae are eukaryotic stramenopiles which means that they are at one point flagellated and most people know them as seaweeds in coastal areas. [21] Examples of brown algae that have been found in brackish marshes are Fucus vesiculosus , Ascophyllum nodosum, [20] the genus Sphacelaria, [22] and many others.
Yellow-green algae can also be found in brackish marshes. Yellow-green algae are eukaryotic algae in the class Xanthophyceae. [23] An example of this is Vaucheria. [22]
Green algae can also be found in brackish marshes. Some examples of the different genera of green algae that can be found in brackish marshes are Enteromorpha, Ulothrix, Rhizoclonium, Blidingia, Percursaria, and many others. [22]
Typically, sedges and grasses dominate the vegetation in brackish marshes. Plants in brackish marshes are salinity tolerant and they tolerate frequent flooding. [24] They also have frequent tidal waves disturbing the area as well as seasonal hurricanes and tropical storms. (Julia bass) According to (Makenzie) plants in coastal marshes resist salinity by refraining from the uptake of salt via their root system. Some examples of plants that grow in brackish marshes are Panicum hemitomon, Spartina patens, Zostera japonica, Haloxylon recurvum, Juncus roemerianus, Borrichia frutescens, [24] Schoenoplectus americanus, Distichlis spicata and many others. [25]
Brackish marshes are very important for flood control. [11] However, they are often subject to heavy pollution and habitat degradation from land reclamation. [12] For example, the Indian River Lagoon has suffered significant man-made changes since the 1940s. Marshes were often dredged or impounded to prevent mosquitoes, however this led to the disruption of connectivity by replacing marshes with open water. These changes prevented fires that allowed invasive species to move into the remaining marshes. [10]
Brackish marsh environments are especially susceptible to human degradation; they are ideal areas for land conversion and development because they aren’t rocky and tend to be located in temperate coastal regions. Brackish marshes are areas that can provide connections for both land and water access. [6]
There are many ways humans have disrupted and degraded brackish marshes. When humans divert water from these marshes it leads to land sinking, also known as subsidence. Humans have also modified the vegetation of brackish marshes to change water and sediment flow. Brackish marshes have been subjected to an overabundance of nutrients and pollutants from industrial and urban sources. Environmental stressors from human impact have changed brackish marsh biodiversity to mainly stress-tolerant invasive grasses. Additionally, negative consequences of climate change, such as sea level rise, will likely begin to harm brackish marsh ecosystems. [6] [7]
Brackish marshes can be restored by human intervention. Studies have found that given that restoration is properly carried out, fish do not discriminate between restored or natural marshes. [14]
As in most habitats, the greatest threat towards brackish marshes are humans. Traditionally, direct human activities such as dredging and development are the main cause of destruction. Pollution has also been a threat to brackish marshes through chemical run-off. [5] Once degraded, it could take at least 30 to 90 years for restored marsh soil to become equivalent to a natural marsh in terms of nitrogen and organic carbon profile. In some cases, these process could take over 200 years to achieve the wetland soil characteristics of certain communities. [26]
For conservation, the key is to restrict human activities. Installing a passive management system could help restore certain species using brackish marshes' role as an ecological nursery. [27] For some areas, periodic livestock grazing could help create a better habitat for certain species of birds. [13] Brackish marshes are a unique type of wetland and the local circumstances are paramount to consider for either conservation, biodiversity, or restoration.
Brackish marshes are also great in reducing nutrient pollution such as nitrogen. [28] There are many sources of nitrogen entering the water systems especially in Texas. In Texas there are many dairy farms as well as ranch land and farm land. All these are sources of nitrogen in the Texas water systems. Having large amounts of nitrogen in a water system can cause eutrophication, harmful algal blooms, and fish kills. [28] In wetlands, nitrogen is used by the vascular and non-vascular vegetation to grow, therefore removing the nitrogen naturally and preventing a large amount of nitrogen from entering the coastal region creating anoxic habitats in the ocean. [28] Conservation of the brackish marsh wetlands can be a last resort to help prevent these potential problems.
Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater and fresh water together, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root brak. Certain human activities can produce brackish water, in particular civil engineering projects such as dikes and the flooding of coastal marshland to produce brackish water pools for freshwater prawn farming. Brackish water is also the primary waste product of the salinity gradient power process. Because brackish water is hostile to the growth of most terrestrial plant species, without appropriate management it is damaging to the environment.
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 environments and are an example of an ecotone. Estuaries are subject both to marine influences such as tides, waves, and the influx of saline water, and to fluvial influences such as flows of freshwater and sediment. The mixing of seawater and freshwater provides high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world.
Wetlands, or simply a wetland, is a distinct ecosystem that is flooded or saturated by water, either permanently or seasonally. Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The primary factor that distinguishes wetlands from terrestrial land forms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique anoxic hydric soils. Wetlands are considered among the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal species. Methods for assessing wetland functions, wetland ecological health, and general wetland condition have been developed for many regions of the world. These methods have contributed to wetland conservation partly by raising public awareness of the functions some wetlands provide. Constructed wetlands are designed and built to treat municipal and industrial wastewater as well as to divert stormwater runoff. Constructed wetlands may also play a role in water-sensitive urban design.
A marsh is - according to ecological definitions - a wetland that is dominated by herbaceous rather than woody plant species. More in general, the word can be used for any low-lying and seasonally waterlogged terrain. In Europe and in agricultural literature low-lying meadows that require draining and embanked polderlands are also referred to as marshes or marshland.
A salt marsh, saltmarsh or salting, 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 by dense stands of salt-tolerant plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh in trapping and binding sediments. Salt marshes play a large role in the aquatic food web and the delivery of nutrients to coastal waters. They also support terrestrial animals and provide coastal protection.
Coos Bay is an estuary where the Coos River enters the Pacific Ocean, the estuary is approximately 12 miles long and up to two miles wide. It is the largest estuary completely within Oregon state lines. The Coos Bay watershed covers an area of about 600 square miles and is located in northern Coos County, Oregon, in the United States. The Coos River, which begins in the Oregon Coast Range, enters the bay from the east. From Coos River, the bay forms a sharp loop northward before arching back to the south and out to the Pacific Ocean. Haynes Inlet enters the top of this loop. South Slough branches off from the bay directly before its entrance into the Pacific Ocean. The bay was formed when sea levels rose over 20,000 years ago at the end of the Last Glacial Maximum, flooding the mouth of the Coos River. Coos Bay is Oregon's most important coastal industrial center and international shipping port, with close ties to San Francisco, the Columbia River, Puget Sound and other major ports of the Pacific rim.
Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes, ponds, rivers, streams, springs, bogs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats can be classified by different factors, including temperature, light penetration, nutrients, and vegetation. There are three basic types of freshwater ecosystems: Lentic, lotic and wetlands. Freshwater ecosystems contain 41% of the world's known fish species.
A Ramsar site is a wetland site designated to be of international importance under the Ramsar Convention, also known as "The Convention on Wetlands", an international
A tidal marsh is a marsh found along rivers, coasts and estuaries which floods and drains by the tidal movement of the adjacent estuary, sea or ocean. Tidal marshes experience many overlapping persistent cycles, including diurnal and semi-diurnal tides, day-night temperature fluctuations, spring-neap tides, seasonal vegetation growth and decay, upland runoff, decadal climate variations, and centennial to millennial trends in sea level and climate.
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 environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems. Freshwater ecosystems may be lentic ; lotic ; and wetlands.
Marine ecosystems are the largest of Earth's aquatic ecosystems and exist in waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the surface of the Earth and account for more than 97% of Earth's water supply and 90% of habitable space on Earth. Seawater has an average salinity of 35 parts per thousand of water. Actual salinity varies among different marine ecosystems. Marine ecosystems can be divided into many zones depending upon water depth and shoreline features. The oceanic zone is the vast open part of the ocean where animals such as whales, sharks, and tuna live. The benthic zone consists of substrates below water where many invertebrates live. The intertidal zone is the area between high and low tides. Other near-shore (neritic) zones can include mudflats, seagrass meadows, mangroves, rocky intertidal systems, salt marshes, coral reefs, lagoons. In the deep water, hydrothermal vents may occur where chemosynthetic sulfur bacteria form the base of the food web.
Classification of wetlands has been a problematical task, with the commonly accepted definition of what constitutes a wetland being among the major difficulties. A number of national wetland classifications exist. In the 1970s, the Ramsar Convention on Wetlands of International Importance introduced a first attempt to establish an internationally acceptable wetland classification scheme.
A freshwater marsh is a non-tidal, non-forested marsh wetland that contains fresh water, and is continuously or frequently flooded. Freshwater marshes primarily consist of sedges, grasses, and emergent plants. Freshwater marshes are usually found near the mouths of rivers, along lakes, and are present in areas with low drainage like abandoned oxbow lakes. It is the counterpart to the salt marsh, an upper coastal intertidal zone of bio-habitat, which is regularly flushed with sea water.
Low marsh is a tidal marsh zone located below the Mean Highwater Mark (MHM). Based on elevation, frequency of submersion, soil characteristics, vegetation, microbial community, and other metrics, salt marshes can be divided to into three distinct areas: low marsh, middle marsh/high marsh, and the upland zone. Low marsh is characterized as being flooded daily with each high tide, while remaining exposed during low tides.
Sporobolus pumilus, the saltmeadow cordgrass, also known as salt hay, is a species of cordgrass native to the Atlantic coast of the Americas, from Newfoundland south along the eastern United States to the Caribbean and north-eastern Mexico. It was reclassified after a taxonomic revision in 2014, but the older name, Spartina patens, may still be found in use. It can be found in marshlands in other areas of the world as an introduced species and often a harmful noxious weed or invasive species.
Juncus roemerianus is a species of flowering plant in the rush family known by the common names black rush, needlerush, and black needlerush. It is native to North America, where its main distribution lies along the coastline of the southeastern United States, including the Gulf Coast. It occurs from New Jersey to Texas, with outlying populations in Connecticut, New York, Mexico, and certain Caribbean islands.
An inland salt marsh is a saltwater marsh located away from the coast. It is formed and maintained in areas when evapotranspiration exceeds precipitation and/or when sodium- and chloride-laden groundwater is released from natural brine aquifers. Its vegetation is dominated by halophytic plant communities.
Estuary freshwater inflow is the freshwater that flows into an estuary. Other types of environmental flows include instream flow, the freshwater water flowing in rivers or streams, and estuary outflow, the outflow from an estuary to the ocean.
Freshwater salinization is the process of salty runoff contaminating freshwater ecosystems, which can harm aquatic species in certain quantities and contaminate drinking water. It is often measured by the increased amount of dissolved minerals than what is considered usual for the area being observed. Naturally occurring salinization is referred to as primary salinization; this includes rainfall, rock weathering, seawater intrusion, and aerosol deposits. Human-induced salinization is termed as secondary salinization, with the use of de-icing road salts as the most common form of runoff. Approximately 37% of the drainage in the United States has been effected by salinization in the past century. The EPA has defined two thresholds for healthy salinity levels in freshwater ecosystems: 230 mg/L Cl− for average salinity levels and 860 mg/L Cl− for acute inputs.
The marsh organ is a collection of plastic pipes attached to a wooden framework that is placed in marshes to measure the effects of inundation time and flood frequency on the productivity of marsh vegetation. The information is used for scientific research purposes.
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