Is buoyancy regulation in cyanobacteria an adaptation to exploit separation of light and nutrients?

1999 ◽  
Author(s):  
M. Bormans ◽  
B. S. Sherman ◽  
I. T. Webster
Keyword(s):  
Vertical Distribution ◽  
Field Measurements ◽  
Surface Mixed Layer ◽  
Natural Systems ◽  
Physical Mechanisms ◽  
Algal Abundance ◽  
Lateral Advection ◽  
Australian Freshwater ◽  
The Vertical Distribution

Fogg and Walsby’s (1971) hypothesis that buoyancy regulation in cyanobacteria might be an adaptation to exploit the separation of light and nutrients has since become a paradigm. The evidence of its veracity is examined within observations of algal abundance and chlorophyll distributions in several Australian freshwater systems and is also reviewed from the literature. It is clear from both laboratory experiments and field measurements that filamentous genera such as Anabaena and colony-forming genera such as Microcystis are capable of changing their buoyancy within a diurnal cycle. However, evidence for population migration to exploit separation of light and nutrient availability is tenuous, with most field observations of the vertical distribution of phytoplankton populations showing no evidence of vertical migration to sufficient depth to reach nutrients in stratified systems. Instead, changes in the vertical distribution of phytoplankton suggest a response either to the dynamics of the surface mixed layer or to lateral advection. In natural systems, algal buoyancy appears to be dependent much more on light than on nutrients, this being consistent with the carbohydrate ballast mechanism. Physical mechanisms can provide sufficient replenishment of epilimnetic nutrients to explain the observed net growth rates of phytoplankton populations in situ.

scholarly journals The vertical distribution of biomass burning pollution over tropical South America from aircraft in situ measurements during SAMBBA

2019 ◽  
Vol 19 (9) ◽  
pp. 5771-5790 ◽  
Author(s):  
Eoghan Darbyshire ◽  
William T. Morgan ◽  
James D. Allan ◽  
Dantong Liu ◽  
Michael J. Flynn ◽  
...  
Keyword(s):  
Air Quality ◽  
South America ◽  
Vertical Distribution ◽  
Biomass Burning ◽  
Mixing Layer ◽  
Free Troposphere ◽  
The West ◽  
The Vertical Distribution ◽  
Tropical South America

Abstract. We examine processes driving the vertical distribution of biomass burning pollution following an integrated analysis of over 200 pollutant and meteorological profiles measured in situ during the South AMerican Biomass Burning Analysis (SAMBBA) field experiment. This study will aid future work examining the impact of biomass burning on weather, climate and air quality. During the dry season there were significant contrasts in the composition and vertical distribution of haze between western and eastern regions of tropical South America. Owing to an active or residual convective mixing layer, the aerosol abundance was similar from the surface to ∼1.5 km in the west and ∼3 km in the east. Black carbon mass loadings were double as much in the east (1.7 µg m−3) than the west (0.85 µg m−3), but aerosol scattering coefficients at 550 nm were similar (∼120 Mm−1), as too were CO near-surface concentrations (310–340 ppb). We attribute these contrasts to the more flaming combustion of Cerrado fires in the east and more smouldering combustion of deforestation and pasture fires in the west. Horizontal wind shear was important in inhibiting mixed layer growth and plume rise, in addition to advecting pollutants from the Cerrado regions into the remote tropical forest of central Amazonia. Thin layers above the mixing layer indicate the roles of both plume injection and shallow moist convection in delivering pollution to the lower free troposphere. However, detrainment of large smoke plumes into the upper free troposphere was very infrequently observed. Our results reiterate that thermodynamics control the pollutant vertical distribution and thus point to the need for correct model representation so that the spatial distribution and vertical structure of biomass burning smoke is captured. We observed an increase of aerosol abundance relative to CO with altitude both in the background haze and plume enhancement ratios. It is unlikely associated with thermodynamic partitioning, aerosol deposition or local non-fire sources. We speculate it may be linked to long-range transport from West Africa or fire combustion efficiency coupled to plume injection height. Further enquiry is required to explain the phenomenon and explore impacts on regional climate and air quality.

scholarly journals Vertical Distribution of Arctic Methane in 2009–2018 Using Ground-Based Remote Sensing

2020 ◽  
Vol 12 (6) ◽  
pp. 917
Author(s):  
Tomi Karppinen ◽  
Otto Lamminpää ◽  
Simo Tukiainen ◽  
Rigel Kivi ◽  
Pauli Heikkinen ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Vertical Distribution ◽  
Atmospheric Chemistry ◽  
Polar Vortex ◽  
The Arctic ◽  
Fourier Transform Spectrometer ◽  
Atmospheric Methane ◽  
The Vertical Distribution ◽  
Chemistry Experiment

We analyzed the vertical distribution of atmospheric methane (CH 4 ) retrieved from measurements by ground-based Fourier Transform Spectrometer (FTS) instrument in Sodankylä, Northern Finland. The retrieved dataset covers 2009–2018. We used a dimension reduction retrieval method to extract the profile information, since each measurement contains around three pieces of information about the profile shape between 0 and 40 km. We compared the retrieved profiles against Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) satellite measurements and AirCore balloon-borne profile measurements. Additional comparison at the lowest tropospheric layer was done against in-situ measurements from a 50-m-high mast. In general, the ground-based FTS and ACE-FTS profiles agreed within 10% below 20 km and within 30% in the stratosphere between 20 and 40 km. Our method was able to accurately capture reduced methane concentrations inside the polar vortex in the Arctic stratosphere. The method produced similar trend characteristics as the reference instruments even when a static prior profile was used. Finally, we analyzed the time series of the CH 4 profile datasets and estimated the trend using the dynamic linear model (DLM).

Patterns of bubble desorption during the solidification of a multicomponent melt

2000 ◽  
Vol 419 ◽  
pp. 263-282 ◽  
Author(s):  
M. A. ROGERSON ◽  
S. S. S. CARDOSO
Keyword(s):  
Field Measurements ◽  
Metal Casting ◽  
Physical Parameters ◽  
Dissolved Gas ◽  
Layer Spacing ◽  
Physical Mechanisms ◽  
Geological Formation ◽  
Bubble Layers ◽  
Geological Context

The desorption of bubbles during solidification of a melt occurs in processes as diverse as the making of ice cubes, the formation of igneous rocks and the casting of metals. In both the metal casting and rock formation processes, careful observation of the final solid suggests that the desorbed bubbles often form regular spatial patterns. Understanding and quantifying the mechanisms by which such patterns arise is important. In the geological context, comparison between field measurements and the predictions of a model will allow geologists to estimate in-situ magma properties. In the metal casting context, engineers would like to be able to specify mould geometries and cooling conditions to ensure that the distribution of bubbles will not compromise the strength of critical sections of the casting.In the present study, we develop a detailed mathematical model to predict the distribution of desorbed bubbles in a solidified melt. Our new model builds upon previous knowledge on this phenomenon in the geological context (Toramaru et al. 1996, 1997). We describe desorption of a dissolved gas in a semi-infinite melt, solidified by a one-dimensional heat flux. In the absence of convection, the transfer of heat and solute occurs mainly by a diffusive mechanism and the crystallization proceeds most rapidly near the cooled boundary. The crystals formed contain almost no dissolved gas and hence the concentration of gas dissolved in the melt increases progressively towards the cooled boundary. Diffusion of dissolved gas from the crystallizing zone is slow and, as a result, the local melt becomes supersaturated and gas bubbles desorb. The full equations for this coupled solidification and desorption processes are solved numerically.We find that bubbles desorb forming a sequence of layers parallel to the cooled boundary. The spacing between these bubble layers increases geometrically from the cooled boundary. We give a physical interpretation for this geometric pattern and analyse the effect of physical parameters on the layer spacing. We show that our theoretical model captures the important physical mechanisms involved in the solidification and desorption processes by comparing its predictions with available measurements from a geological formation.

IN SITU MEASUREMENT OF DISSOLVED MATERIALS AS AN INDICATOR OF ORGANIC TERRAIN TYPE

1973 ◽  
Vol 53 (2) ◽  
pp. 231-236 ◽  
Author(s):  
M. E. WALMSLEY ◽  
L. M. LAVKULICH
Keyword(s):  
Ph Value ◽  
Environmental Parameters ◽  
Field Measurements ◽  
Oxygen Electrode ◽  
Natural Systems ◽  
Terrain Type ◽  
Ion Activity ◽  
Different Types ◽  
Dissolved Load

Portable equipment has been used to measure selected environmental parameters in situ. A battery-operated potentiometer used in conjunction with several specific ion electrodes, a platinum redox electrode, and a combination pH electrode were used to obtain ion activity, pH, and Eh measurements of natural systems. In addition, dissolved oxygen concentration was measured using an oxygen electrode and battery-operated meter. Results from the analysis of several streams are presented to illustrate the application of the technique to field measurements of streams as an indicator of environmental disturbance. Information collected also allowed for the differentiation of different types of organic terrain based on the dissolved load of the saturated organic materials. The terrain type referred to as fen had a higher activity of Na, Cl, and Ca, a higher pH value, and a lower concentration of oxygen than the bog terrain type. These results are explained with reference to organic terrain morphology and the distribution of permafrost in the study area.

scholarly journals In situ constraints on the vertical distribution of global aerosol

2019 ◽  
Vol 19 (18) ◽  
pp. 11765-11790 ◽  
Author(s):  
Duncan Watson-Parris ◽  
Nick Schutgens ◽  
Carly Reddington ◽  
Kirsty J. Pringle ◽  
Dantong Liu ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
Climate Model ◽  
Cloud Condensation Nuclei ◽  
Upper Troposphere ◽  
Aerosol Forcing ◽  
Wide Range ◽  
Vertical Distributions ◽  
The Vertical Distribution ◽  
Unique Dataset

Abstract. Despite ongoing efforts, the vertical distribution of aerosols globally is poorly understood. This in turn leads to large uncertainties in the contributions of the direct and indirect aerosol forcing on climate. Using the Global Aerosol Synthesis and Science Project (GASSP) database – the largest synthesised collection of in situ aircraft measurements currently available, with more than 1000 flights from 37 campaigns from around the world – we investigate the vertical structure of submicron aerosols across a wide range of regions and environments. The application of this unique dataset to assess the vertical distributions of number size distribution and cloud condensation nuclei (CCN) in the global aerosol–climate model ECHAM-HAM reveals that the model underestimates accumulation-mode particles in the upper troposphere, especially in remote regions. The processes underlying this discrepancy are explored using different aerosol microphysical schemes and a process sensitivity analysis. These show that the biases are predominantly related to aerosol ageing and removal rather than emissions.

scholarly journals Reverse engineering field-derived vertical distribution profiles to infer larval swimming behaviors

2019 ◽  
pp. 201900238 ◽  
Author(s):  
M. K. James ◽  
J. A. Polton ◽  
A. R. Brereton ◽  
K. L. Howell ◽  
W. A. M. Nimmo-Smith ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
State Of The Art ◽  
Distribution Patterns ◽  
Environmental Cues ◽  
Biophysical Models ◽  
Marine Larvae ◽  
In Situ Observations ◽  
The Vertical Distribution ◽  
Larval Swimming

Biophysical models are well-used tools for predicting the dispersal of marine larvae. Larval behavior has been shown to influence dispersal, but how to incorporate behavior effectively within dispersal models remains a challenge. Mechanisms of behavior are often derived from laboratory-based studies and therefore, may not reflect behavior in situ. Here, using state-of-the-art models, we explore the movements that larvae must undertake to achieve the vertical distribution patterns observed in nature. Results suggest that behaviors are not consistent with those described under the tidally synchronized vertical migration (TVM) hypothesis. Instead, we show (i) a need for swimming speed and direction to vary over the tidal cycle and (ii) that, in some instances, larval swimming cannot explain observed vertical patterns. We argue that current methods of behavioral parameterization are limited in their capacity to replicate in situ observations of vertical distribution, which may cause dispersal error to propagate over time, due to advective differences over depth and demonstrate an alternative to laboratory-based behavioral parameterization that encompasses the range of environmental cues that may be acting on planktic organisms.

scholarly journals Analyses of Spatial Distributions of Sulfate-Reducing Bacteria and Their Activity in Aerobic Wastewater Biofilms

1999 ◽  
Vol 65 (11) ◽  
pp. 5107-5116 ◽  
Author(s):  
Satoshi Okabe ◽  
Tsukasa Itoh ◽  
Hisashi Satoh ◽  
Yoshimasa Watanabe
Keyword(s):  
In Situ Hybridization ◽  
Vertical Distribution ◽  
Reduction Rate ◽  
Sulfate Reducing Bacteria ◽  
Sulfur Cycle ◽  
Sulfate Reducing ◽  
High Sulfate ◽  
Reducing Bacteria ◽  
The Vertical Distribution

ABSTRACT The vertical distribution of sulfate-reducing bacteria (SRB) in aerobic wastewater biofilms grown on rotating disk reactors was investigated by fluorescent in situ hybridization (FISH) with 16S rRNA-targeted oligonucleotide probes. To correlate the vertical distribution of SRB populations with their activity, the microprofiles of O2, H2S, NO2 −, NO3 −, NH4 +, and pH were measured with microelectrodes. In addition, a cross-evaluation of the FISH and microelectrode analyses was performed by comparing them with culture-based approaches and biogeochemical measurements. In situ hybridization revealed that a relatively high abundance of the probe SRB385-stained cells (approximately 109 to 1010cells per cm3 of biofilm) were evenly distributed throughout the biofilm, even in the oxic surface. The probe SRB660-stained Desulfobulbus spp. were found to be numerically important members of SRB populations (approximately 108 to 109 cells per cm3). The result of microelectrode measurements showed that a high sulfate-reducing activity was found in a narrow anaerobic zone located about 150 to 300 μm below the biofilm surface and above which an intensive sulfide oxidation zone was found. The biogeochemical measurements showed that elemental sulfur (S0) was an important intermediate of the sulfide reoxidation in such thin wastewater biofilms (approximately 1,500 μm), which accounted for about 75% of the total S pool in the biofilm. The contribution of an internal Fe-sulfur cycle to the overall sulfur cycle in aerobic wastewater biofilms was insignificant (less than 1%) due to the relatively high sulfate reduction rate.

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