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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
01 Jul 1991-Botany
TL;DR: There was either too little or too much disturbance from water-level fluctuations in the regulated lakes, both resulting in reduced structural diversity, and the natural hydrologic regime at the unregulated lake resulted in intermediate disturbance and high diversity.
Abstract: WILCOX, D. A., and MEEKER, J. E. 1991. Disturbance effects on aquatic vegetation in regulated and unregulated lakes in northern Minnesota. Can. J. Bot. 69: 1542-1551. The effects of water-level regulation on aquatic macrophyte communities were investigated by comparing two regulated lakes in northern Minnesota with a nearby unregQlated lake. Natural annual fluctuations of about 1.8 m were replaced with fluctuations of 1.1 m and 2. 7 m in the regulated lakes, and the timing of water-level changes was also altered. Quadrats were sampled along transects that followed depth contours representing different plant habitats in the unregulated lake. Ordinations showed that the macrophyte communities at all sampled depths of the regulated lakes differed from those in the unregulated lake. The unregulated lake supported structurally diverse plant communities at all depths. In the lake with reduced fluctuations, only four taxa were present along transects that were never dewatered; all were erect aquatics that extended through the entire water column. In the lake with increased fluctuations, rosette and mat-forming species dominated transects where drawdown occurred in early winter and disturbance resulted from ice formation in the sediments. The natural hydrologic regime at the unregulated lake resulted in intermediate disturbance and high diversity. There was either too little or too much disturbance from water-level fluctuations in the regulated lakes, both resulting in reduced structural diversity.

149 citations

Journal ArticleDOI
TL;DR: The tight relationship between the rates of βGlcA and glucose uptake indicated the existence of a specific, coupled hydrolysis-uptake system in lacustrine bacteria.
Abstract: Kinetics of β-glucosidase activity (βGlcA) and bacterial activity (glucose uptake, thymidine incorporation) and cell numbers were measured in the euphotic zone and in the water column of Pluβsee during spring phytoplankton bloom development and after its breakdown. Heterotrophic bacteria were the major producers of the enzyme. Activity of free β-glucosidase, unassociated with microbial cells, was negligible. βGlcA displayed a distinct temporal and spatial distribution pattern in lake water. βGlcA was low when algal populations grew actively, but during the algal bloom breakdown βGlcA increased rapidly. The increase in βGlcA was proportional to the abundance of bacteria and to their heterotrophic uptake of glucose, as well as to bacterial production, measured by the thymidine incorporation method. In contrast with its response to pH, β-glucosidase exhibited no obvious adaptation to ambient temperature of lake water. βGlcA produced by aquatic bacteria was under control of a repression-induction mechanism, and synthesis was derepressed when the level of directly assimilable hexoses (glucose or galactose) fell below a critical level. The tight relationship between the rates of βGlcA and glucose uptake indicated the existence of a specific, coupled hydrolysis-uptake system in lacustrine bacteria.

149 citations

Journal ArticleDOI
Abstract: We report results collected year-round since 1998 in northern Marguerite Bay, just inside the Antarctic Circle. The magnitude of the spring phytoplankton bloom is much reduced following winters with reduced sea-ice cover. In years with little winter sea-ice the exposed sea surface leads to deep mixed layers in winter, and reduced water-column stratification the following spring. Summer mixed-layer depths are similar, however, so the change is not in overall light availability but toward a less stable water column with greater vertical mixing and increased variability in the light conditions experienced by phytoplankton. Macronutrient concentrations are replete at all times, but the increased vertical mixing likely reduces iron availability. The timing of bloom initiation is similar between heavy and light ice years, occurring soon after light returns in early spring, at a mixed-layer averaged light level of < 1 mol photon m−2 d−1. Ongoing regional climate change in the WAP area, and notably the ongoing loss of winter sea-ice, is likely to drive a downward trend in the magnitude of phytoplankton blooms in this region of the Antarctic Peninsula.

149 citations

Journal ArticleDOI
TL;DR: In this article, an intensive sampling program was carried out at a coastal station in the Northwestern Mediterranean Sea to study the relationship between phytoplankton distributions, as evaluated by taxonomic pigments, and the hydrographic structures of the water column.
Abstract: Between March 1992 and April 1993, an intensive sampling program was carried out al a coastal station in the Northwestern Mediterranean Sea to study the relationship between phytoplankton distributions, as evaluated by taxonomic pigments, and the hydrographic structures of the water column. The study period covered the range of hydrographic conditions which prevail in the Mediterranean Sea. The 0 to 75 m integrated chlorophyll a concentration averaged 23.3 mg m(-2), with the highest values (above 45 mg m(-2)) restricted to semi-mixed periods. The major phytoplankton signature and water column structure relationships were: (1) phytoplanktonic prokaryotes (cyanobacteria and prochlorophytes) appear sensitive to water column mixing with prochlorophytes being the most sensitive group as strong stratification is associated with the highest biomass found mainly in deeper waters; (2) prymnesiophytes and chrysophytes (19'-BF and 19'-HF) appear the most abundant under a variety of conditions and therefore seem able to adapt to various water column structures; (3) diatoms bloom in semi-mixed conditions, but while these conditions are necessary, they are not sufficient for bloom formation; and (4) green chlorophyll b-containing flagellates appear to require strong mixing. During the stratification period, 2 noticeable wind-induced mixing events occurred, and while the first did not have any marked influence on the phytoplankton community, the second was followed by a subsurface development of green flagellates and diatoms. This second wind-mixing event also altered the vertical prokaryote distribution, but 1 wk alter this perturbation vertical segregation of prochlorophytes and cyanobacteria was reestablished. The results suggest that, while different phytoplankton taxa are generally adapted to specific water column structures, this is not always the case, especially at small scales where specific light/nutrient requirements may have to be met.

149 citations

Journal ArticleDOI
TL;DR: Sediments play a crucial role as a source (to the water column) of bio-degrading bacteria and as a carbon-rich environment for bacteria to proliferate and metabolize microcystin and other biogenic toxins produced by cyanobacteria, suggesting that sedimentsplay a critical role in microcyStin degradation in aquatic systems.

149 citations


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