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Marta Sebastin Javier Arístegui María F. Montero Jose Escanez F. Xavier Niell 《Progress in Oceanography》2004,62(2-4):131
The enzymatic activity of alkaline phosphatase (APA) was studied in the transition zone between the African upwelling system and the open ocean waters of the Canary Islands region. This region is recurrently dominated by the presence of upwelling filaments that may transport nutrient-enriched waters out into the open ocean before nutrients become exhausted by plankton. Turnover rates by APA were generally low in the whole region, but detectable in all the measurements carried out. On average, turnover rates were higher in the upwelling stations, and APA in those waters seemed to be mainly generated by heterotrophic bacteria to supply easily assimilable organic C. APA outside the upwelling area showed an inverse hyperbolic relationship with increasing phosphate, suggesting the presence of both constitutive and Pi-inducible APA. In these offshore waters, a threshold of 0.1 μM of phosphate could be defined for the regulatory function of Pi on APA. Thus, APA in nutrient-poor waters seemed to be induced to compensate for Pi-deficiency. Turnover rates in the filaments showed basal (probably constitutive) levels, whereas they increased in the surrounding waters, where phosphate concentration presumably did not satisfy plankton P-demands. The fertilising effect of the filaments and associated cyclonic eddies extended to at least 175 km offshore, where basal alkaline phosphatase activities were still found. The magnitude of this effect depends probably on the intensity of upwelling events and the degree of recirculation of filament water back to the coastal jet. 相似文献
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Carlos Jiménez Jesus Mercado José Aguilera J. M. rodriguez-Maroto F. X. Niell 《International Journal of Salt Lake Research》1995,4(3):223-232
Turbulence is known to enhance growth in microalgae. We studied the possible effects of the extra inorganic carbon supplied to the cultures when air bubbling is the source of turbulence. A set of experiments was carried out to separate the effects of the subsidiary action of agitation on growth from those due to possible carbon enrichment from air CO2 when air bubbling was the source of mixing. It was found that air bubbling does not induce an increase of the concentration of inorganic carbon in HCO
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-enriched growth media, and that no differences appear between air-bubbled and CO2-free air-bubbled cultures. On the other hand, photosynthetic O2 was accumulated in the medium in non-mixed cultures, which showed higher respiration and lower photosynthetic rates, probably due to photoinhibition induced by oversaturation of O2. Growth rate, maximal cell density and photosynthetic efficiency were higher in aerated cultures than in non-aerated ones. 相似文献
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Adsorption-desorption of phosphate and its availability in the sediment of a saline lake (Fuente de Piedra,southern Spain) 总被引：1，自引：0，他引：1
V. Clavero M. García J. A. Fernández F. X. Niell 《International Journal of Salt Lake Research》1993,2(2):153-163
Seasonal changes of soluble reactive phosphorus concentrations in sediments of Fuente de Piedra, a saline lake, have been
observed and linked to salinity changes. Phosphate availability in sediments was studied in the laboratory under different
salinities, from 10 to 70 g L−1. Changes in adsorption of dissolved phosphate appear to be controlled by salinity variations. The adsorption coefficient
increases with salinity and the amount of phosphorus adsorbed ranged between 10 and 30 per cent of the total. Salinity-modulated
adsorption is proposed as the primary mechanism explaining the seasonal dynamics of phosphorus in this saline lake and its
effects on progressive eutrophication. 相似文献
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Pattern of phosphorus forms in a Mediterranean shallow estuary: Effects of flooding events 总被引：4，自引：0，他引：4
Floods are responsible for the variation in the concentration of different phosphorus forms contained in the sediment of a small shallow estuary (Palmones River). The maximum differences were observed in the middle estuary, while other stations, placed in the inner and outer parts, showed a less sensitive response. The apatite forms (AIP) are the major ones. Noticeable changes in the concentration of different phosphorus forms are related with fine grain size sediment. In spite of different responses obtained along the estuary, the results reveal the possibility of using phosphorus concentration as a flood event index, discarding the use of phosphorus speciation for the same purpose. 相似文献
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