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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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TL;DR: In this paper, rates of phytoplankton growth and production were measured with 14C techniques at stations near the Hawaiian Islands and at about 28°N, 155°W in the North Pacific subtropical gyre during August and September 1985.
Abstract: Rates of phytoplankton growth and production were measured with 14C techniques at stations near the Hawaiian Islands and at about 28°N, 155°W in the North Pacific subtropical gyre during August and September 1985. Ratios of light-saturated assimilation averaged 9.5 ± 1.4 g C (g Chl a)−1 h−1 during the photoperiod. Doubling times in the upper 30 m of the water column averaged 14±3 h. Relative growth rates were estimated to be 85–90% of nutrient-saturated values. Over the upper 200 m of the water column photosynthetic rates uncorrected and corrected for grazing and phytoplankton respiration losses were 315 ± 26 and 450±37 mg C m−2 d−1, respectively. The former figure is comparable to the highest daily photosynthetic rates inferred from 14C studies at this station during 1968–1980 and is about twice the mean of those historical productivity numbers. These results contradict the paradigm of subtropical gyres as vast biological deserts characterized by constantly low biomass and low turnover rates limited by the supply of nutrients. However, further studies will be needed to determine whether these high growth and production rates are typical or atypical of the central regions of the oceans.
147 citations
147 citations
TL;DR: In this article, the role of different transfer mechanisms in the elimination of radionuclides from the water column is discussed, and the results were compared with simultaneous observations of the water and seston.
Abstract: The rates of sedimentation of fallout nuclides were determined by means of sediment traps during 28 months after the Chernobyl accident in southern Lake Paijanne, Finland. The spatial distribution of the radionuclide content of the lake bottom was studied on 35 sediment cores in winters 1987/88 and 1988/89. The results were compared with simultaneous observations of the radionuclide content of the water and seston. The role of different transfer mechanisms in the elimination of radionuclides from the water column is discussed. The values recorded for the flux to the lake sediments were on average of the same order of magnitude as the initial deposition on the lake surface (Cs-137 65 kBqm−2). The radionuclide flux to the sediments was rapid during the first months after the accident. After that the elimination of dissolved nuclides from the water mass became significantly slower. The highest flux rate was that of Ce-144 and the lowest that of Rh-106 (Ru-106). Of the radiocesium, about half of the initial inventory was transferred to the sediments after the first observation year. The content of radionuclides showed considerable spatial variation on the lake bottom (Cs-137 7–280 kBqm−2). Direct adsorption of radiocesium explains unexpectedly high concentrations on shallow erosion bottoms. There was a clear tendency for the concentrations to increase with depth, as a result of the focusing effect. Sediment resuspension had a significant impact on the total flux of radionuclides to deepwater sediments. Estimates were made of the resuspended flux of radionuclides.
147 citations
TL;DR: In this article, the rates of uncoupled and coupled denitrification in the River Colne at 4 sites were measured monthly by 15 N isotope-pairing technique from October 1996 to March 1998.
Abstract: The River Colne is a muddy macrotidal estuary on the east coast of England, with strong decreasing gradients of NO3 - and NH4 + down the estuary due to inputs from the river and upstream sewage treatment works. The rates of uncoupled (Dw) and coupled (Dn) denitrification in the sedi- ments at 4 sites were measured monthly by 15 N isotope-pairing technique from October 1996 to March 1998. There was a significant spatial and temporal variation in the rates of Dw and Dn. The highest rates were observed at Site 1 and the lowest at Site 4, corresponding to the highest NO3 - con- centrations in the water column and highest organic contents in the sediments at Site 1 and the lowest at Site 4. Short-term kinetic experiments showed that rates of Dw increased with increasing NO3 - con- centration in the water column, up to 500 µM NO3 - at Site 2 (the middle site along the estuary), and were not saturated up to 600 µM NO3 - at Site 1 or 180 µM NO3 - at Site 4. Field observations and kinetics experiments indicated a large sediment potential for Dw at all sites. Nitrate availability lim- ited the rates of Dw and was the main factor regulating the rates of Dw in this estuary. It was calcu- lated that 32 to 44% of total oxidised nitrogen inputs or 20 to 25% of the total inorganic nitrogen inputs (total oxidised nitrogen + ammonium) into the estuary by the River Colne and the sewage treatment works were removed from the estuary by uncoupled denitrification (Dw) and total denitri- fication (Dw + Dn) respectively, in the sediments before they were transported into the North Sea. Microphytobenthos, mainly diatoms, assimilated 4.1% of the ammonium inputs or 2.3% of total inor- ganic nitrogen inputs into the estuary and temporarily retained the assimilated nitrogen in the estu- ary. They also affected the rates of denitrification in a complex manner, by regulating the depth of oxygen penetration by photosynthetic oxygen production and respiratory oxygen uptake. Photosyn- thesis inhibited the rates of Dw but stimulated Dn. The overall effect of microphytobenthos on denitri- fication was to increase the percentages of Dn in the total denitrification. The loads of nitrogen through the River Colne estuary to the North Sea was significantly attenuated by the removal of nitrate from the water column by Dw and of nitrate produced from ammonium via nitrification in the sediment by Dn.
147 citations
TL;DR: Five red water dinoflagellate blooms took place in La Jolla Bay, California, between May 1964 and December 1966 and even in the densest patches the cells appeared to be physiologically active based upon measurements of photosynthetic rate, nitrate reductase activity, and observed motility.
Abstract: Five red water dinoflagellate blooms took place in La Jolla Bay, California, between May 1964 and December 1966. Predominant organisms were Gymnodinium spp. and Cochlodinium spp. (May 1964), Prorocentrum micnns (April 1965) and Gonyaulux po2yedra (June-July 1964, J unc-July 1965, and Dccembcr 1966). Ccl1 concentration and chlorophyll a content were measured during each bloom with values up to 20 X 10’ cells/ liter and approximately 500 pug chlorophyll a/liter. During the day, the organisms appeared in discrete patches that apparently dispersed at night. Cell carbon and nitrogen content of the organisms often excecdcd that available in surface waters or in the water column. Cells must be concentrated both vertically and horizontally to account for the numbers observed in patches during the day. Even in the densest patches the cells appeared to be physiologically active based upon measurements of photosynthetic rate, nitrate reductase activity, and observed motility. Decline of blooms was associated with increases in dissolved organic carbon, orthophosphate and monophosphate esters. The May 1964 bloom was decimated by grazing of
146 citations