Water column

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

Persistent organic pollutants at the base of the Antarctic marine food web.

Abstract: Various organochlorine pesticides and brominated diphenyl ethers (BDE-47, -99, and -100) were measured in sea ice algae, water column plankton, and juvenile and adult krill collected in the Palmer Long-Term Ecological Research (LTER) region west of the Antarctic Peninsula during late austral winter and midsummer, 2001-2002. BDEs were 100-1000 times higher in ice algae and 2-10 times higher in phytoplankton than the most abundant organochlorine pesticide, hexachlorobenzene (HCB), reflecting the current production and use of BDEs versus organochlorine pesticides. However, concentrations of HCB and BDEs were significantly lower in summer plankton than in ice algae indicating lower atmospheric inputs, removal from the water column, and/or biodilution of persistent organic pollutants at the base of the food web during summer. Concentrations of HCB (juvenile and adult krill) and BDEs (juvenile krill) were not significantly different from their primary food source (ice algae, phytoplankton), and BDEs were significantly lower in adult krill versus phytoplankton, indicating no biomagnification of HCB or BDEs during transfer from plankton to krill. The high concentrations of BDEs and HCB in ice algae and associated juvenile krill illustrate the importance of sea ice as a vector for entry of POPs into the Antarctic marine ecosystem.

Annual cycle of benthic nutrient fluxes in Tomales Bay, California, and contribution of the benthos to total ecosystem metabolism*

Abstract: Benthic fluxes of dissolved nutrients, oxygen, dissolved inorganic carbon, and total alkalinity were measured over a 2 yr period in Tomales Bay, California, USA, using in situ incubation chambers. Release of dissolved nutrients from the sediment peaked in late summer and was lowest in winter. The difference between C:N: P flux ratios and composition of suspended particulates indicated the existence of a sink for regenerated N, relative to C and P. Total alkalinity flux revealed that carbon metabolism by net sulfate reduction represented ca one-third of total benthic metabohsm Partitioning net system fluxes into component fluxes suggested that the equivalent of ca 70 to 80 % of the available particulate C, N and P was respired within the water column, while about 20 to 30 O/O was respired by the benthos. During spring, increasing light resulted in higher water column productivity, followed closely by rising water column respiration. With low delivery of the new organic material to the benthos, and low residual organics in the sediment, benthic respiration remained low. Fallout of particulate material, coinciding with peak water temperature in late summer, resulted in a 'crossover' with benthic respiration temporarily exceeding water column respiration.

Diagenetic behavior of methylmercury in organic-rich coastal sediments

Abstract: Conditions regulating the formation and diagenetic behavior of methylmercury, CH,Hg(II), in marine sediments are poorly characterized, although understanding these condiions is essential to understanding the modes of transfer of this contaminant to the water column and biota. We report the first high-resolution profiles of CH,Hg(II) concentrations in pore waters extracted under rigorous oxygen-free and trace metal clean conditions from organic-rich contaminated marine sediments. Methylmercury was present at concentrations reaching 10 ng liter-l as Hg (50 PM) in pore waters extracted from the anoxic sediment layers but was below our detection limit in pore waters recovered from the surficia: oxic layers. Dissolved CHjHg(II) in the anoxic layers accounts for up to 30% of the total dissolved Hg but < 1% of the CH,Hg(II) adsorbed onto particles. Our data suggest that the surficial oxic sediment layer senres as a geochemical barrier to the diffusion of dissolved CH,Hg(II) accumulated in anoxic sediments to the overlying waters. Burrowing organisms, however, likely assimilate CH,Hg(II) directly from the underlying anoxic sediments and become active vectors of methylmercury to benthic predators, such as nordic shrimp and cod.

Factors controlling methane oxidation in shield lakes: The role of nitrogen fixation and oxygen concentration1

Abstract: During summer stratification methane-oxidizing bacteria in Lake 227 are confined to a narrow zone within the thcrmoclinc because of their sensitivity to high epilimnctic oxygen concentrations. This oxygen sensitivity is based on the dependence of the oxi- dizers on an oxygen-sensitive nitrogen fixation process. Thus epilimnetic methane oxi- dation is absent during periods of nitrogen limitation, since high epilimnetic oxygen concentrations prevent nitrogen fixation. During periods of overturn and throughout the winter, the methane oxidizers become oxygen insensitive and oxidation occurs rapidly throughout the water column. This oxygen insensitivity likely occurs as a result of high in situ concentrations of dissolved inorganic nitrogen, which replaces nitrogen fixation as a source for fixed nitrogen, Under ice-cover, rapid mcthanc oxidation throughout the water column can be a major cause of total anoxia.