Anoxic apele

Anoxic waters are areas of sea water or fresh water that are depleted of dissolved oxygen Apele anoxice sunt zone de apa de mare sau apa dulce, care sunt epuizate de oxigen dizolvat . This condition is generally found in areas that have restricted water exchange. Aceasta conditie este, in general, gasit in zone care au restrictionat schimbului de apa.

In most cases, oxygen is prevented from reaching the deeper levels by a physical barrier (silt) as well as by a pronounced density stratification, in which, for instance, heavier hypersaline waters rest at the bottom of a basin. In majoritatea cazurilor, oxigenul este impiedicat de a ajunge la niveluri mai profunde de o bariera fizica (namol), precum si printr-o stratificare densitate pronuntat, in care, de exemplu, mai grele hypersaline restul apele in partea de jos a unui bazin. Anoxic conditions will occur if the rate of oxidation of organic matter by bacteria is greater than the supply of dissolved oxygen conditii anoxice va avea loc in cazul in care rata de oxidare a materiei organice de catre bacterii este mai mare decat oferta de oxigen dizolvat

Anoxic waters are a natural phenomenon, and have occurred throughout geological history. Apele anoxice sunt un fenomen natural, si s-au produs-a lungul istoriei geologice. Anoxic basins exist at present, for example, in the Baltic Sea and elsewhere (see below). bazinele anoxice exista in prezent, de exemplu, in Marea Baltica si in alta parte (vezi mai jos). Recently, there have been some indications that eutrophication has increased the extent of the anoxic areas in areas including the Baltic Sea, and the Gulf of Mexico. ^{[ citation needed} Recent, au existat unele indicii ca eutrofizarea a crescut gradul de zone anoxice in domenii, inclusiv Marea Baltica, si Golful Mexic ^{[. necesita citare ]}

[ edit ] Causes and effectsCauze si efecte

Anoxic conditions result from several factors; for example, stagnation conditions, density stratification , inputs of organic material, and strong thermoclines . Anoxic rezulta din conditiile de mai multi factori, de exemplu, stagnare conditii, stratificare densitate , intrari de materii organice, si puternic thermoclines . The bacterial production of sulfide starts in the sediments, where the bacteria find suitable substrates, and then expands into the water column. Productia bacteriene de sulfura incepe in sedimente, in cazul in care bacteriile gasi substraturi potrivite, iar apoi se extinde in coloana de apa.

When oxygen is depleted in a basin, bacteria first turn to the second-best electron acceptor, which in sea water is nitrate . Denitrification occurs, and the nitrate will be consumed rather rapidly. Cand oxigenul este saracit intr-un bazin, bacterii randul sau, primul la cele mai bune acceptor de electron-al doilea, care, in apa de mare este nitrat . Denitrificare are loc, si nitrat vor fi consumate destul de rapid. After reducing some other minor elements, the bacteria will turn to reducing sulfate . Dupa reducerea unor alte elemente minore, bacteriile se va intoarce la reducerea sulfat . If anoxic sea water becomes reoxygenized, sulfides will be oxidized to sulfate according to the chemical equation: In cazul in care apa de mare anoxic devine reoxygenized, sulfuri va fi oxidat pentru sulfat, conform ecuatiei chimice:

HS ⁻ + 2 O ₂ → HSO ₄ ⁻ HS ^- + ₂ O 2 → HSO ₄ ^-

In the Baltic Sea the slowed rate of decomposition under anoxic conditions has left remarkably preserved fossils retaining impressions of soft body parts, in Lagerstätten . ^{[ citation needed ]} In Marea Baltica a incetinit rata de descompunere in conditii anoxice a parasit remarcabil conservate fosile de retinere impresii de parti ale corpului moale, in Lagerstätten . ^{necesita citare ]}

[ edit ] Anoxic basins bazine anoxice

• Bannock Basin , eastern Mediterranean Sea Bannock bazinul , estul Marii Mediterane
• Black Sea Basin, off eastern Europe, below 50 metres (150 feet); Marii Negre, bazinul, de pe Europa de Est, sub 50 de metri (150 picioare);
• Caspian Sea Basin, below 100 metres (300 feet); Marii Caspice bazinul, sub 100 de metri (300 picioare);
• Cariaco Basin , off north central Venezuela Cariaco bazinul , de pe la nord central Venezuela ;
• Gotland Deep , in the Baltic off Sweden ; Gotland Deep , in Marea Baltica off Suedia ;
• L'Atalante basin , eastern Mediterranean Sea L'Atalante bazinul , in estul Marii Mediterane
• Mariager Fjord , off Denmark Mariager Fjord , off Danemarca ;
• Orca Basin , northeast Gulf of Mexico Bazinul Orca , nord-est de Golful Mexic
• Saanich Inlet , off Vancouver Island Canada Saanich Inlet , de pe Insula Vancouver Canada