Estuaries: Difference between revisions

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==Key Microorganisms==
==Key Microorganisms==


[[Image:overview.jpg|thumb|300px|right|Pelagibacter ubique.]]
Several studies have described estuarine microbial diversity and how freshwater and marine microorganism communities mix along estuarine gradients. Few reports have reported a unique estuarine bacterioplankton community. This is partly due to the dynamic nature of estuaries and the heavy influenced estuarine populations by those that wash in from adjacent environments. Most of the bacterioplankton in typical estuarine was closely related to surrounding freshwater or marine bacterial groups and belongs to the phyla [http://microbewiki.kenyon.edu/index.php/Proteobacteria '' Proteobacteria''], [http://microbewiki.kenyon.edu/index.php/Bacteroides''Bacteroidetes''], and ''Actinobacteria'', with these estuarine phylotypes occurring within a range of salinity are considered as mixed freshwater or marine biota (Hollibaugh,2000). It is therefore reasonable that similar shifts will occur in natural freshwater and marine microbial communities when they encounter estuarine gradients. Study showed that coastal communities were composed of typical marine populations, Proteobacteria phylotypes included members of the common marine bacteria, [http://microbewiki.kenyon.edu/index.php/Roseobacter ''Roseobacter''], and recently cultured [http://microbewiki.kenyon.edu/index.php/Pelagibacter_ubique ''Pelagibacter ubique''] and the [http://microbewiki.kenyon.edu/index.php/Roseobacter ''Roseobacter'' isolate]. Many of these estuarine phylotypes are most found in marine, some of these are typical freshwater-specific genotype, ''Alphaproteobacteria'', ''Betaproteobacteria'', ''Actinobacteria'', and [http://microbewiki.kenyon.edu/index.php/Verrucomicrobium ''Verrucomicrobia''], with relatively little overlap with the marine clades , suggesting that they are marine populations capable of adapting to estuarine conditions, including reduced salinity(Crump, 2004). Freshwater and marine populations contribute a large fraction of the bacteria community in estuaries.
Several studies have described estuarine microbial diversity and how freshwater and marine microorganism communities mix along estuarine gradients. Few reports have reported a unique estuarine bacterioplankton community. This is partly due to the dynamic nature of estuaries and the heavy influenced estuarine populations by those that wash in from adjacent environments. Most of the bacterioplankton in typical estuarine was closely related to surrounding freshwater or marine bacterial groups and belongs to the phyla [http://microbewiki.kenyon.edu/index.php/Proteobacteria '' Proteobacteria''], [http://microbewiki.kenyon.edu/index.php/Bacteroides''Bacteroidetes''], and ''Actinobacteria'', with these estuarine phylotypes occurring within a range of salinity are considered as mixed freshwater or marine biota (Hollibaugh,2000). It is therefore reasonable that similar shifts will occur in natural freshwater and marine microbial communities when they encounter estuarine gradients. Study showed that coastal communities were composed of typical marine populations, Proteobacteria phylotypes included members of the common marine bacteria, [http://microbewiki.kenyon.edu/index.php/Roseobacter ''Roseobacter''], and recently cultured [http://microbewiki.kenyon.edu/index.php/Pelagibacter_ubique ''Pelagibacter ubique''] and the [http://microbewiki.kenyon.edu/index.php/Roseobacter ''Roseobacter'' isolate]. Many of these estuarine phylotypes are most found in marine, some of these are typical freshwater-specific genotype, ''Alphaproteobacteria'', ''Betaproteobacteria'', ''Actinobacteria'', and [http://microbewiki.kenyon.edu/index.php/Verrucomicrobium ''Verrucomicrobia''], with relatively little overlap with the marine clades , suggesting that they are marine populations capable of adapting to estuarine conditions, including reduced salinity(Crump, 2004). Freshwater and marine populations contribute a large fraction of the bacteria community in estuaries.



Revision as of 04:22, 9 April 2010

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"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."[[2]].The estuarine environmental is characterized by a constant mixing of freshwater, salt and sediment, which is carried into the estuarine from sea and water. Wave energy along the ocean beach is perodic and high.The mixture and fluctuation of salt and freshwater impose challenges to the physical and chemical environment, the animals and microbes. Estuaries are transition zones between rivers and the sea, which differ from both in abiotic and biotic factors(McLusky,2004).Thus estuaries are among the most highly productive ecosystems on the earth. The gradient of conditions from the open sea into the sheltered estuary changes the salinity ranging from full strength seawater to freshwater. Associated change is sedimentary conditions from coarse sediment to fine sediments. Other changes include nutrient input, pollutant and chemical concentration along with estuarine flows.

The activities of microorganisms dominate the functions and structures of estuarine ecosystems, and thus are critical in controlling the function and structure of estuarine ecosystems. Various flows process in an estuary and those flows that may be dominated by microbial activities. large number of bacteria, fungi and protozoa have been found in estuaries and benthic sediment, their distribution, species abundant food references interact with their physical and chemical environment.

The importance of estuary

The productivity and variety of estuarine habitats support a wonderful abundance and diversity of species. Thousands of species of fish, shore birds, marine mammals, clams, shellfish and other widelife survival in and around estuarine habitats.Many fish and shellfish species, including most commercially and recreationally important species, depend on the sheltered waters of estuaries as home to spawn and for their offspring to grow and live. Because the high productivity of living organism, migratory birds also take estuaries as ideal places for resting and reproducing.

In addition to serving as important habitat for wildlife, estuaries also provide valuable environmental services. The water flowing to ocean carries sediments, organic and inorganic nutrients and pollutants. Much of the sediments and pollutants are filtered out when they flows through wetlands, swamps and salt marshes. This filtration process deposits harmful pollutants and then creates an environment for microbes biodegrade these sediments. Estuaries plants also can absorb tide and storm surges, providing peaceful and stable habitats for widelife.This natural buffer also help prevent erosion and stabilize the coast. The transition character of estuaries provide important research value for scientists.Wide range of problems in biology, geology, chemistry, physics, sociology are studied in and around estuaries. Estuaries also provide a great deal of aesthetic enjoyment for the people who live, work, or recreate in and around them.[[3]]

Physical environment

Conceptual diagrams of estuarine vegetation.

Physical characteristics

Water movements and hydrodynimc aspects are dominant controlling factors in estuarine ecosystem. The changes of physical factors occur quickly relative to biological and chemincal transformation.

Circulation

Circulation is defined as the residual water movement, which is calculated based on different time scales. Circulation stimulates fluxes of dissolved constituents and particulate materials such as sediments, detritus matter, bacteria and plankton. The energy drives estuarine circulation is from solar heating , gravitational attraction between the moon and the sun and wind wave. A given estuary usually is dominated by one circulation type, but it is possible to change one circulation model to another temporarily. The circulation cause water flow to a certain direction, but the dissolved and particulate constituents will not necessarily move to certain direction too(John W. Day,1989).

Mixing event

Estuaries regions experience salt water mixes with water derived from land drainage. Mixing is the process whereby a water is diluted ir redistributed with other water body. Mixing event can be divided by long or short time scale. The estuatine circulation movements are the primary mechanism of mixing. Mixing changes the distribution in time and scale of dissolved material in fresh and ocean water. The estuarine salinity alone beach is the most important indicator of mixing, that is, salinity can be used to track water source and mixing frequence.

Chemical environment

Salinity

Substantial river discharges and relatively shallow nearshore waters often result in large fluctuations and strong spatial gradients in salinity, In most estuaries reduced salinity associate with finer substrates, the finer substrate, the easier reduce salinity from estuaries.Salinity of estuaries usually increases away from a freshwater source such as a river, although evaporation sometimes causes the salinity at the head of the estuary to exceed seawater. The vertical salinity structure and the nature of salinity variation along the estuary are the features of the salinity structure of coastal waterways[4].

Oxidation

Much of the organic matter carried to an estuary by rivers, and produced by phytoplankton, marshes, comes to the sediment surface. Oxygen is the most important electron acceptor in organic matter respiration, but at the anerobic estuarine water column or saturated sediment sulfate become more significant electron acceptors. The major product of sulfate reduction is hydrogen sulfide, which give salt marsh soils pungent smell. In general, reactions are more oxidized near the sediment – water interface and more reduced deeper in the sediment.

Autotrophic nutrients

Autotrophic nutrients are important for the functional estuarine ecosystems, because they are raw materials for the primary producers. The nutrients include various chemical elements, vitamins thiamin, biotin and cyanocobalamin. Concentrations of these nutrients in estuaries are changing due to the mixing of river and ocean water. Generally increasing concentrations of ammonium and phosphate ion with depth because of relatively slow upward diffusion of these ions toward the sediment – water interface. Other organic compounds occur at the same oxidation state in cellular material and dissolved in the external environment(John W.DAY,1989).

Biological interactions

Distribution of estuarine organisms

The life of the plants and animals living in estuaries are mostly organisms with marine affinities that live in the central parts of estuaries. They either enter estuaries as part of a movement or migrate during their lifetimes with water flows, or their ancestor move into estuaries and the offspring become residents in estuaries. True estuarine organisms could live in sea but are sometimes absent from the sea probably due to competition from other animals. Migrants organisms spend part of their life in estuaries for feeding or reproducing. Others are purely migrants that use estuaries as routes to move, such as salmon and eel.

Many studies of the distribution and abundance of animals and plants in estuaries have shown that the number of species within estuaries is less than the number of species within either the sea or the freshwater, but these species may be very abundant (McLusky, 2004).

Food web

Within the estuaries, the plants and other primary producers (algae) convert energy into living biological materials. Detritus feeders, plant grazers and zooplankton are first consumers, the second consumers are tertiary consumers, such as estuarine birds, ducks, invertebrate predator and fish. Excreta and detritus pass to the decomposer tropic level where microorganisms break down the material. At each stage in this trophic sequence energy is consumed, and some of it is excrete as waste, or converted into body growth, and heat after respiration (McLusky, 2004). Food web accompany with organic and inorganic matter transportation. Chemical elements passing through food webs in these estuarine ecosystems have multiple alternatives to transfer. Study has shown that the primary producers and seston showed significant variations between dry and rainy season. Compositions of C and N in mixed zooplankton, copepods, filter-feeders bivalves and juvenile mullet were directly related with the seston signals (Jara, 2009).

Microbial communities

Bacteria

Bacteria are the most numerous organisms in the es, averaging between 10^6 to 10^7/ml organisms in water and 10^8 to 10^10 per dry weight of sediment. Sediments and salt marsh soil generally harbor more bacteria per unit volume than does the water column. Within the water column, high densities may be found in the surface layer than subsurface layer, aerobic and facultative anaerobic bacteria are most common, pseudomonads and Vibrio are most often isolated species. Sediment and waterlogged soils show very high densities of bacteria, which decrease in abundant with depth of soils. Higher bacteria densities have been found in most estuaries than the nearby coast and river water (John W.DAY,1989).

Fungi

The number of fungi living in estuaries is extremely large. Some of fungi are unique in estuaries, while others have a broader range of habitats. Aquatic fungi and yeast dominate species in aquatic environment, few of fungi associate with particles or solid matters in the water. In sediments, the active species of fungi primarily are found in surface aerobic zones. The densities of fungi are decrease rapidly with soil depth, but the spores of fungi are found throughout sediments (John W.DAY,1989).

Processes associated with microorganisms

Every process of energy and matter are closely related with microbes in estuaries. It has been estimated that half of the aerobic and anaerobic transformations of organic matter in salt marsh are the result of microbial metabolism.

Carbon cycling

Bacteria show a variety of metabolic pathways in which carbon flow and cycling. As many of the sediment and water-logged soils of estuaries are anoxic, the anaerobic decomposition is important. These processes are associated with a functional bacterial group. The complex organic matters are used by the fermenters and dissimilatory nitrogenous oxide reducers. The sulfate reducers and methane producers were once thought to have more restrictedly distributed (John W.DAY, 1989). Studies have shown seasonal and interannual dynamics of free-living bacterioplankton and microbially labile organic carbon along the salinity gradient of estuary. Bacterioplankton abundance may be an important indicator of ecosystem health in this and other eutrophied estuaries, because of the positive relationships between Bacterioplankton abundance, dissolved MLOC, and dissolved oxygen (Leila J. Hamdan,2007).

Nitrogen cycling

Nitrogen is a major limited nutrient for primary production in estuaries. The processes that are dominated by active microbes include decertification, dissimilatory nitrogenous oxide reduction, and nitrogen fixation. Nitrogen cycling in estuaries corresponds to the water mixture and microbial community shifting. Nitrogen cycling across steep gradients in salinity, oxygen and dissolved inorganic nitrogen in sandy 'subterranean estuaries', it controls both the amount and form of nitrogen discharged to the coastal ocean. The abundance of betaproteobacterial ammonia-oxidizing bacteria (beta-AOB) was dramatically lower in the freshwater compared with saline stations, while ammonia-oxidizing archaea (AOA) abundance almost remained constant across estuarine sites. This differing response to salinity altered the ratio of beta-AOB to AOA. Analysis of ammonia-oxidizing enrichment cultures at a range of salinities revealed that AOA persisted solely in the freshwater enrichments(Santoro,2008).

Key Microorganisms

Pelagibacter ubique.

Several studies have described estuarine microbial diversity and how freshwater and marine microorganism communities mix along estuarine gradients. Few reports have reported a unique estuarine bacterioplankton community. This is partly due to the dynamic nature of estuaries and the heavy influenced estuarine populations by those that wash in from adjacent environments. Most of the bacterioplankton in typical estuarine was closely related to surrounding freshwater or marine bacterial groups and belongs to the phyla Proteobacteria, Bacteroidetes, and Actinobacteria, with these estuarine phylotypes occurring within a range of salinity are considered as mixed freshwater or marine biota (Hollibaugh,2000). It is therefore reasonable that similar shifts will occur in natural freshwater and marine microbial communities when they encounter estuarine gradients. Study showed that coastal communities were composed of typical marine populations, Proteobacteria phylotypes included members of the common marine bacteria, Roseobacter, and recently cultured Pelagibacter ubique and the Roseobacter isolate. Many of these estuarine phylotypes are most found in marine, some of these are typical freshwater-specific genotype, Alphaproteobacteria, Betaproteobacteria, Actinobacteria, and Verrucomicrobia, with relatively little overlap with the marine clades , suggesting that they are marine populations capable of adapting to estuarine conditions, including reduced salinity(Crump, 2004). Freshwater and marine populations contribute a large fraction of the bacteria community in estuaries.

Current Research

1. Ammonia-oxidizing archaea (AOA) are ubiquitous and abundant in marine waters and sediments, they contributes to the N cycle in estuarine and coastal environments through coupled nitrification–denitrification or nitrification–anammox (anaerobic oxidation of ammonium) processes. Dang studies the sedimentary AOA diversity, amoA genotype communities and spatial distribution in the Changjiang Estuary and the adjacent East China Sea. Results indicated the gradients of surface-water salinity and sediment sorting coefficient are significantly correlated with the distribution of AOA communities.The archaeal amoA sequences had quite high similarity with known sequences from various soil environments or coastal and estuarine environments of the East Pacific Ocean, suggesting that similar archaeal AOA communities might exist in similar estuarine environments across the geographical distance(Dang HY,2008). Caffrey studied the abundance of ammonia-oxidizing bacteria (AOB) and AOA amoA genes in six different estuaries at multiple sites.AOA rather than AOB are responsible for much of the nitrification in estuarine sediments.The potential nitrification rates increased as abundance of AOA amoA increased, suggesting that AOA are more significant than AOB in estuarine nitrogen cycling(Jane M Caffrey,2007).


2.In bottom waters of stratified estuaries,oxygen consumed primarily by bacteria exceed atmospheric and photosynthetic reoxygenation.This anoxic environmental inhibit most living marine species, but large number of bacteria and protists are still active by changing their metabolism to anaerobic respirations.The activity and phylogenetic composition of bacterioplankton communities across hypoxia/anoxia estuaries were studied. Bacterioplankton communities in anoxic estuaries of the Chesapeake Bay were very similar to those in oxic surface waters in summer even when oxygen respiration shifted to nitrate respiration, suggesting functional redundancy appearance.The forms of respiration used by bacterioplankton control redox conditions, which generate feedback to the phylogenetic composition of bacterioplankton communities ultimately. Estuaries are periodically refreshed with oxygen and chemical sediments from ocean, thus bacterioplankton community shift their respiratory processes and phylogenetic composition as chemical conditions change seasonally(B C. Crump, 2007).


3. The bioremediation potentials of microbes in different environments are hot topics for microbiologists. Some estuaries near urban and industrial areas received high inputs of a large variety of micro-pollutants including polycyclic aromatic hydrocarbons (PAHs).PAHs are toxic, mutagenic and carcinogenic for human health and the environment. Examination of the ecology of PAH degrading microorganisms is thus essential to prevent ecological damage caused by organic pollutants in estuary ecosystem. Research have found that a large number of bacterial species are able to bio-degrade PAHs,but the diversity of the bacterial community are also dramatically reduced due to special carbon source availability in PAHs pollutants. Analysis of the 16S rRNA gene sequences confirmed that Cycloclasticus spp., play an universal key role in degradation of low-molecular-weight PAHs in marine environments. Additionally, Pseudomonas spp., considered as a good PAH-degrading bacterial group in soil or in sediment, also increased their competition and adaptation in PAHs degradation in the seawater macrocosm(Niepceron,2010).

References

Hongyue Dang, Xiaoxia Zhang, Jin Sun et al. (2008)Diversity and spatial distribution of sediment ammonia-oxidizing crenarchaeota in response to estuarine and environmental gradients in the Changjiang Estuary and East China Sea. Microbiology 154, 2084-2095.

Crump BC, Peranteau C, Beckingham B , Cornwell JC.(2007).Respiratory succession and community succession of bacterioplankton in seasonally anoxic estuarine waters.APPLIED AND ENVIRONMENTAL MICROBIOLOGY. 73(21): 6802-6810.

Caffrey, J. M., Bano, N., Kalanetra, K. & Hollibaugh, J. T. (2007). Ammonia oxidation and ammonia-oxidizing bacteria and archaea from estuaries with differing histories of hypoxia. ISME J 1, 660–662.

Maïté Niepceron , Florence Portet-Koltalo , Chloé Merlin , Anne Motelay-Massei , Sylvie Barray & Josselin Bodilis (2010). Both Cycloclasticus spp. and Pseudomonas spp. as PAH-degrading bacteria in the Seine estuary (France). FEMS Microbiology Ecology. 71 (1): 137-147.

McLusky, D.S. and Elliott, M. (2004) "The Estuarine Ecosystem: ecology, threats and management." New York: Oxford University Press Inc. ISBN 0-19-852508-7

John W.DAY, Charles A.S, W.Michael K, Alejandro Y.A.(1989) "Estuarine Ecology." Wiley-Interscience; 1 edition. ISBN-10-0471062634.

Jara-Marini ME, Soto-Jimenez MF, Paez-Osuna F(2009). Trophic relationships and transference of cadmium, copper, lead and zinc in a subtropical coastal lagoon food web from SE Gulf of California. CHEMOSPHERE. 77(10): 1366-1373.

Leila J. Hamdan, and Robert B. Jonas(2007). Seasonal and interannual dynamics of free-living bacterioplankton and microbially labile organic carbon along the salinity gradient of the Potomac River. Estuaries and Coasts.29(1):40-53.


Santoro, A. E. ;Francis, C. A. ;de Sieyes, N. R. ;Boehm, A. B(2008). Shifts in the relative abundance of ammonia-oxidizing bacteria and archaea across physicochemical gradients in a subterranean estuary. Environmental Microbiology. 10(4): 1068-1079.

Hollibaugh, J. T., P. S. Wong, and M. C. Murrell. 2000. Similarity of particle-associated and free-living bacterial communities in northern San Francisco Bay, California. Aquat. Microb. Ecol. 21:103-114

Crump, B. C., C. S. Hopkinson, M. L. Sogin, and J. E. Hobbie. 2004. Microbial biogeography along an estuarine salinity gradient: combined influences of bacterial growth and residence time. Appl. Environ. Microbiol. 70:1494-1505.

Edited by student of Angela Kent at the University of Illinois at Urbana-Champaign.