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Water column

About: Water column is a research topic. Over the lifetime, 13706 publications have been published within this topic receiving 496626 citations.


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Journal ArticleDOI
TL;DR: Linking the small‐scale functional role of periphyton to ecosystem‐level P retention will require more detailed studies in a variety of ecosystems or large mesocosms.
Abstract: Eutrophication caused by phosphorus (P) leads to water quality problems in aquatic systems, particularly freshwaters, worldwide. Processing of nutrients in shallow habitats removes P from water naturally and periphyton influences P removal from the water column in flowing waters and wetlands. Periphyton plays several roles in removing P from the water column, including P uptake and deposition, filtering particulate P from the water, and attenuating flow, which decreases advective transport of particulate and dissolved P from sediments. Furthermore, periphyton photosynthesis locally increases pH by up to 1 unit, which can lead to increased precipitation of calcium phosphate, concurrent deposition of carbonate-phosphate complexes, and long-term burial of P. Actively photosynthesizing periphyton can cause super-saturated O 2 concentrations near the sediment surface encouraging deposition of metal phosphates. However, anoxia associated with periphyton respiration at night may offset this effect. Linking the small-scale functional role of periphyton to ecosystem-level P retention will require more detailed studies in a variety of ecosystems or large mesocosms. A case study from the Everglades illustrates the importance of considering the role of periphyton in P removal from wetlands. In general, periphyton tends to increase P retention and deposition. In pilot-scale constructed periphyton-dominated wetlands in South Florida, about half of the inflowing total P was removed.

282 citations

Journal ArticleDOI
TL;DR: In this article, the role of water column methanotrophy (microbial methane oxidation) as a control on methane release was quantified by measuring water column methane profiles (concentration and δ13C) and oxidation rates at eight stations in an area of active methane venting in the Eel River Basin, off the coast of northern California.

282 citations

Journal ArticleDOI
TL;DR: A 38-year record of bottom water dissolved oxygen concentrations in coastal marine ecosystems around Denmark (1965-2003) and a longer partially reconstructed record of total nitrogen (TN) inputs (1900- 2003) were assembled to describe long-term patterns in hypoxia and anoxia.
Abstract: A 38-year record of bottom water dissolved oxygen concentrations in coastal marine ecosystems around Denmark (1965-2003) and a longer partially reconstructed record of total nitrogen (TN) inputs (1900-2003) were assembled to describe long-term patterns in hypoxia and anoxia Interannual variations in bottom water oxygen concentrations were analyzed in relation to various explanatory variables (bottom temperature, wind speed, advective transport, TN loading) Reconstructed TN loads peaked in the 1980s with a gradual decline to the present, commensurate with a legislated nutrient reduction strategy Mean bottom water oxygen concentrations during summer have significantly declined in coastal marine ecosystems, decreasing substantially during the 1980s and were extremely variable thereafter Despite decreasing TN loads, the worst hypoxic event ever recorded in open waters occurred in 2002 For estuaries and coastal areas, bottom water oxygen concentrations were best described by TN input from land and wind speed in July-September, explaining 52% of the interannual variation in concentrations For open sea areas, bottom water oxygen concentrations were also modulated by TN input from land, however, additional significant variables included advective transport of water and Skagerrak surface water temperature and explained 49% of interannual variations in concentrations Reductions in benthic species number and alpha diversity were significantly related to the duration of the 2002 hypoxic event Gradual decreases in diversity measures (species number and alpha diversity) over the first 2-4 weeks show that the benthic community undergoes significant changes before the duration of hypoxia is severe enough to cause the community to collapse Enhanced sediment-water fluxes of NH4+ and PO43- occur with hypoxia, increasing nutrient concentrations in the water column, and stimulating additional phytoplankton production Repeated hypoxic events have changed the character of benthic communities and how organic matter is processed in sediments Our data suggest that repeated hypoxic events lead to an increase in susceptibility of Danish waters to eutrophication and further hypoxia (Less)

280 citations

Journal ArticleDOI
01 Oct 1993
TL;DR: In this paper, the vertical profiles of dissolved organic carbon (DOC) content were obtained monthly, in the North-Western Mediterranean at the DYFAMED-1 site (43°25′N, 07°52′E).
Abstract: During 1991 and 1992, detailed vertical profiles of dissolved organic carbon (DOC) content were obtained monthly, in the North-Western Mediterranean at the DYFAMED-1 site (43°25′N, 07°52′E). DOC was measured using a high temperature catalytic oxidation method. In the 150–2000 m layer, DOC distribution was quite uniform, with a content of about 0.6–0.7 mg C l−1. In surface waters, DOC concentration changed according to hydrological situation and primary production cycle. During February, waters were DOC-homogeneous through the whole water column; then surface concentrations increased until autumn with maxima of about 1.1–1.2 mg C l−1 between 0 and 50 m depths. Assuming that the DOC is continuously removed from surface waters by diffusive processes during the stratified period and that the DOC accumulated in surface waters until the end of autumn is removed by advection during the short period of winter deep water formation, we find that an amount of 18.4 g Cm−2y−1 is transferred to the deep layer. This value is more than twice the particulate organic carbon flux measured on sediment traps (4–7 g Cm−2 y−1), but agrees with published new production values.

279 citations

Book ChapterDOI
TL;DR: In this paper, a steady-state model, calibrated to different observed summer conditions, was used to assess the response of the system to reductions in nutrient inputs, with the response being greater for nitrogen reductions.
Abstract: Nutrient over-enrichment in many areas around the world is having pervasive ecological effects on coastal ecosystems. These effects include reduced dissolved oxygen in aquatic systems and subsequent impacts on living resources. The largest zone of oxygen-depleted coastal waters in the United States, and the entire western Atlantic Ocean, is found in the northern Gulf of Mexico on the Louisiana/Texas continental shelf influenced by the freshwater discharge and nutrient load of the Mississippi River system. The mid-summer bottom areal extent of hypoxic waters (<2 mg 1−1 02) in 1985–1992 averaged 8000 to 9000 km2 but increased to up to 16000 to 20 700 km2 in 1993–2001. The Mississippi River system is the dominant source of fresh water and nutrients to the northern Gulf of Mexico. Mississippi River nutrient concentrations and loading to the adjacent continental shelf have changed in the last half of the 20th century. The average annual nitrate concentration doubled, and the mean silicate concentration was reduced by 50%. There is no doubt that the average concentration and flux of nitrogen (per unit volume discharge) increased from the 1950s to 1980s, especially in the spring. There is considerable evidence that nutrient-enhanced primary production in the northern Gulf of Mexico is causally related to the oxygen depletion in the lower water column. Evidence from long-term data sets and the sedimentary record demonstrate that historic increases in riverine dissolved inorganic nitrogen concentration and loads over the last 50 years are highly correlated with indicators of increased productivity in the overlying water column, i.e. eutrophication of the continental shelf waters, and subsequent worsening of oxygen stress in the bottom waters. Evidence associates increased coastal ocean productivity and worsening oxygen depletion with changes in landscape use and nutrient management that resulted in nutrient enrichment of receiving waters. A steady-state model, calibrated to different observed summer conditions, was used to assess the response of the system to reductions in nutrient inputs. A reduction in surface layer chlorophyll and an increase in lower layer dissolved oxygen resulted from a reduction of either nitrogen or phosphorus loading, with the response being greater for nitrogen reductions.

277 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023458
2022969
2021497
2020502
2019502
2018466