Variation In Chlorophyll Content Research Articles

Temporal and vertical variations of chlorophyll concentrations in high mountain lakes of the Adamello-Brenta Regional Park (Trentino, Italy)

Temporal and vertical variations of chlorophyll concentrations in high mountain lakes of the Adamello-Brenta Regional Park (Trentino, Italy)

Effects of elevated atmospheric CO 2 and temperature on leaf optical properties in Acersaccharum

Elevated partial pressures of atmospheric carbon dioxide, similar to numerous causes of plant stress, may alter leaf pigmentation and structure and thus would be expected to alter leaf optical properties. Hypotheses that elevated CO 2 pressure and air temperature would alter leaf optical properties were tested for sugar maple ( Acer saccharum) in the middle of its fourth growing season under treatment. The saplings had been growing since 1994 in open-top chambers and partial shade at Oak Ridge, Tennessee under the following treatments: (1) ambient CO 2 pressure and air temperature (control); (2) CO 2 pressure approximately 30 Pa above ambient; (3) air temperatures 3°C above ambient; and (4) elevated CO 2 and air temperature. Under elevated CO 2 or temperature, spectral reflectance, transmittance and absorptance in the visible spectrum (400–720 nm) tended to change in patterns that generally are associated with chlorosis, with maximum differences from the control near 700 nm. However, these changes were not significant at P=0.05. Although reflectance, transmittance and absorptance at 700 nm correlated strongly with leaf chlorophyll concentration, variability in chlorophyll concentration was greater within than among treatments. The lack of treatment effects on pigmentation explained the non-significant change in optical properties in the visible spectrum. Optical properties in the near-infrared (721–850 nm) were similarly unresponsive to treatment with the exception of an increased absorptance throughout the 739–850 nm range in leaves that developed under elevated air temperature alone. This response might have resulted from effects of air temperature on leaf internal structure.

Management of lakes and reservoirs during global climate change

Preface. Changes in Atmospheric Circulation and Climate over the North Atlantic and Europe T.D. Davies, et al. Linkages Between Atmospheric Weather and the Dynamics of Limnetic Phytoplankton C.S. Reynolds. The Influence of Weather Conditions on the Seasonal Plankton Development in a Large and Deep Lake (L. Constance): I. The Impact of Irradiance, Air Temperature and Wind on the Algal Spring Development - An Analysis Based on Long-Term Measurements U. Gaedke, et al. II. Water Column Stability Derived from One-Dimensional Hydrodynamical Models D. Ollinger, E. Bauerle. III. The Impact of Water Column Stability on Spring Algal Development U. Gaedke, et al. IV. The Response of Crustacean Zooplankton to Variations in Water Temperature and Algal Growth in Spring and Early Summer D. Straile, W. Geller. Fluctuations of Phytoplankton Production and Chlorophyll Concentrations in a Small Humic Lake During Six Years (1990-1995) J. Keskitalo, K. Salonen. Sudden and Gradual Responses of Phytoplankton to Global Climate Change: Case Studies from Two Large, Shallow Lakes (Balaton, Hungary, and the Neusiedlersee, Austria/Hungary) J. Padisak. Impact of Climate-Affected Flowrates on Phytoplankton Dynamics in Dam Reservoirs B. Desortova, P. Puncochar. Managing Reservoir Water Quality in the Vltava River Board Area J. Duras. The Mass Invasion of Several Blue-Green Algae in Two Drinking-Water Supply Reservoirs in Southern Poland H. Bucka. Water Quality in the Lakes and Reservoirs of Romania T.L. Constantinescu. Long-Term Variation of Chlorophyll Content in Rybinsk Reservoir (Russia) in Relation to its Hydrological Regime N.M. Mineeva, A.S. Litvinov. Long-Term Hydrobiological Investigations on Lakes in Northwest Russia V.G.Drabkova, et al. The Timing of Warming -- An Important Regulator of Change in Lake Plankton Communities R. Adrian. The Influence of Year-to-Year Changes in Position of the Atlantic Gulf Stream on the Biomass of Zooplankton in Windermere North Basin, UK D.G. George, D.P. Hewitt. Environmental Factors Influencing the Recruitment and Growth of Underyearling Perch (Perca fluviatilis) in Windermere North Basin, UK, from 1966 to 1990 I.J. Winfield, et al. Fluctuations in Lake Fisheries and Global Warming D. Gerdeaux. Interannual Synchronous Dynamics in North Temperate Lakes in Wisconsin, USA T.K. Kratz, et al. Working Group Topic 1: Modelling the Responses of Lakes to Day-to-Day Changes in Weather C.S. Reynolds, et al. Working Group Topic 2: Detecting and Predicting the Responses of Lakes to Global Climate Change U. Gaedke, et al. Working Group Topic 3: Managing Water Quality in a Changing World D.G. George, et al. Working Group Topic 4: International Networks of Lake Sites T.K. Kratz, et al. Index.

Intraspecific variation in photosynthetic responses of trebouxioid lichens with reference to the activity of a carbon-concentrating mechanism.

The photosynthetic responses of a range of trebouxioid lichens were investigated to determine whether variations in net assimilation rates shown by populations of the same species collected from different habitats could be correlated with adjustments in carbon-concentrating mechanism (CCM) activity. The activity of a CCM was inferred from the high affinity for CO2 [i.e. low CO2 compensation point (Γ); low external CO2 concentration at which half-maximal assimilation rates are reached (K 0.5 CO2)], the release of a pool of accumulated dissolved inorganic carbon (Ci) during light/dark transient measurements of CO2 exchange and values for carbon isotope discrimination intermediate between those characteristic of C3 and C4 terrestrial plants. Higher net and gross assimilation rates were expressed by lichens collected from shaded woodland habitats. The higher rates were not accounted for by variations in chlorophyll content. Lichens with high assimilation rates also showed an increased affinity for CO2 as demonstrated by low CO2 compensation points and K 0.5 values and the magnitude of the Ci pool accumulated upon illumination and released after darkening of the thalli. However, there was no correlation between assimilation rates and organic matter or instantaneous carbon isotope discrimination measurements, with the latter remaining roughly consistent whatever the provenance or species of the lichen material. The data are discussed with reference to significant environmental factors which are likely to control photosynthesis in the habitats studied.

Observed trends of chlorophyll concentration in the surface layer of the Northern and Central Atlantic (1979–1983)

To preserve and utilize the biosphere it is imperative that we understand the long-term dynamics of the primary production process on our planet. Variability of chlorophyll concentration in the ocean is one of the most important components of this process. However, size and access make its investigation labour-intensive. Dependence of primary production on high variability of hydrophysical phenomena in the ocean (fluctuations of currents, frontal zones, etc.) makes it difficult to locate points to measure chlorophyll concentration dynamics. To locate such quasistationary zones with respect to seasonal dynamics of chlorophyll concentration by satellite data the Institute of Biophysics (Russian Academy of Sciences, Siberian Branch) has developed a geoinformation system. Its use made it possible to locate such zones over the entire ocean. The work shows zones on the Central and Northern Atlantic. They form the ground to analyse perennial dynamics of chlorophyll concentration. The quasistationary zones are proposed for systematic monitoring of phytopigment concentration by space-borne and marine craft.

Sources of variability in the column photosynthetic cross section for Antarctic coastal waters

Using a highly resolved Long Term Ecological Research (LTER) database collected near Palmer Station, Antarctica, from 1991 to 1994, the variability in the column photosynthetic cross section (Ψ*, m2 g Chl α−1) was analyzed. The relationship between the daily integrated primary production rates versus the product of surface irradiance (QPAR(0+)) and the integrated chlorophyll content (down to 0.1% QPAR(0+)) gave a Ψ* value of 0.0695 m2 g Chl α−1 (r2=0.85, p<0.001, n=151) which is similar to those determined for temperate and tropical seas. However, the average value of single Ψ* estimates is higher (0.109±0.075 m2 g Chl α−1) with extreme values extending over a fiftyfold range (0.009–0.488 m2 g Chl α−1). The possible drivers of this variability are analyzed in detail, considering variables which are presently used in biooptical models (e.g., surface irradiance and chlorophyll content) and those which are not (taxonomic composition). A sixfold variation in Ψ* was observed with time of year and strongly associated with the high seasonality in incident irradiance characteristic of these polar sampling sites. Variability in daily incident irradiance as influenced by cloudiness and variation in chlorophyll content were responsible for an additional twofold variation in Ψ*. Finally, the taxonomic dependency of Ψ* was demonstrated for the first time. For identical chlorophyll content and surface irradiance, mean Ψ* values of 0.114±0.051 m2 g Chl α−1 were recorded for diatom blooms and 0.053±0.011 m2 g Chl α−1 for cryptophyte‐dominated populations. Results illustrate the validity of Ψ*‐based approaches for estimating primary production for the Southern Ocean but emphasize the need to address taxonspecific photophysiology to better estimate primary production on smaller spatio‐temporal scales.

Remote estimation of chlorophyll content in higher plant leaves

Indices for the non-destructive estimation of chlorophyll content were formulated using various instruments to measure reflectance and absorption spectra in visible and near-infrared ranges, as well as chlorophyll contents from several non-related species from different climatic regions. The proposed new algorithms are simple ratios between percentage reflectance at spectral regions that are highly sensitive (540 to 630nm and around 700nm) and insensitive (nearinfrared) to variations in chlorophyll content: R NIR / R 700 and R NIR / R 550. The developed algorithms predicting leaf chemistry from the leaf optics were validated for nine plant species in the range of chlorophyll content from 0.27 to 62.9mug cm -2. An error of less than 4.2 mugcm -2 in chlorophyll prediction was achieved. The use of green and red (near 700nm) channels increases the sensitivity of NDVI to chlorophyll content by about five-fold.

Effects of microbial particles on oceanic optics: Methodology for radiative transfer modeling and example simulations

Radiative transfer numerical modeling provides a powerful means of separating and understanding the effects of various types of microbial particles on oceanic light fields. We illustrate the methodology for achieving this separation and provide various idealized examples. We begin with a database of the single-particle optical properties of marine microbial particles and then construct the total absorption and scattering properties of natural waters for given concentrations of the various particle types. When used as input to the Hydrolight radiative transfer numerical model, these absorption and scattering properties generate underwater light fields. Because this modeling process rests upon the optical properties of the individual microbial components, rather than just on the total absorption and scattering properties of a water body, it is possible to analyze the effects of the various particulate components on quantities such as diffuse attenuation coefficients and remote-sensing refiectances. We find that different microbial compositions in two water bodies can give considerably different optical properties, even though the chlorophyll concentration is the same in each of the water bodies. Our simulations show how variability in chlorophyll concentrations obtained from remotely sensed ocean color signals can be explained by the detailed composition of the water body. This approach suggests that it may be possible to distinguish between blooms of small picophytoplankton and larger nanophytoplankton by using remotely sensed signals.

Biogeochemical characterization of suspended particulate matter in the Columbia River estuary

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 160:173-184 (1997) - doi:10.3354/meps160173 Biogeochemical characterization of suspended particulate matter in the Columbia River estuary F. G. Prahl*, L. F. Small, B. Eversmeyer College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA *E-mail: fprahl@oce.orst.edu In order to understand what controls the composition of suspended particulate material (SPM) in estuarine turbidity maxima (ETM), a set of SPM samples collected in the Columbia River and estuary (northwestern USA) during 3 seasons (fall 1990, summer 1991, spring 1992) was analyzed for detrital mineral (Min), total organic matter [OM, as 2 x particulate organic carbon (POC)], biogenic silica (BSi), chlorophyll a, δ13C, and lignin. In most samples, Min, OM and BSi collectively accounted for 100% of total SPM mass, although their relative importance changed seasonally. The ETM was a trap for organic matter during all 3 seasons, which can explain the intense microbial activity and microcrustacean grazing observed previously. The organic matter was particularly rich in chlorophyll a in late spring to early summer. The source of this seasonal enrichment was mainly riverine phytoplankton. The organic matter contribution to ETM from the ocean was minor compared to the river, but apparently not negligible. Despite large seasonal variations in chlorophyll content, the δ13C of POC concentrated in ETM remained nearly constant between -26 and -25.5o/oo. Vascular plant debris, as depicted by lignin phenol content, always comprised a minor fraction of the organic matter in ETM, although ETM had higher lignin levels than the OM of surrounding waters. Intertidal mudflats are if not an additional source of organic matter at least an important site for transforming riverine organic matter that is ultimately concentrated in ETM. Columbia River estuary · Estuarine turbidity maxima (ETM) · Mudflats · Suspended particulate material (SPM) · Particulate organic carbon (POC) · Chlorophyll · Lignin · Aluminum · Manganese Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 160. Publication date: December 15, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Recovery of Digital Information Stored in Living Plant Leaf Photosynthetic Apparatus as Fluorescence Signals

A CCD (charge-coupled device)-equipped, imaging spectroscopic instrument is discussed that can be reversible and rapidly reconfigured to image photosynthetic fluorescence, allowing two-dimensional spatial estimates of fluorescence quantum yield ( Y′). Y′ images of leaf areas with immediately functional photosynthetic apparatus appear smooth and uniform and are much less affected by variations in chlorophyll content and light path through the leaf. However, areas of the leaf where the photosynthetic apparatus has different light history, pathology, or other damage generate different Y′ value images. This characteristic allowed storage and recovery of images from leaves. Extending this finding, we prepared binary data coding for the value of π to 99 decimal places (100 digits), on living leaves. The images containing the binary codes for these digits can be “read” by eye, because the human brain interprets visual data with great skill. However, it was necessary to enhance the images to facilitate instrument “reading”. A program was developed to enhance the images and “read” the data images with no errors. The photosynthetic mechanism involved (nonphotochemical quenching), the role of leaf age and germplasm variation, and the potential applications of this finding in terms of bioelectronics are discussed.

Non-Destructive Determination of Chlorophyll Content of Leaves of a Green and an Aurea Mutant of Tobacco by Reflectance Measurements

Summary Reflectance spectra from 400 to 800 nm with a spectral resolution of 1 nm and the content of photosynthetic pigments were acquired for leaves of an aurea mutant and a green tobacco ( Nicotiana tabacum L.) covering a range of chlorophyll a content from 7 to 30.8 μ cm -2 and total chlorophyll a + b level from 8.4 to 41.4 μg cm -2 leaf area. At a chlorophyll a content of more than 7 μg cm -2 leaf area the reflectance near 670 to 680 nm was not sensitive to a variation in chlorophyll content due to saturation of the relationship ≪absorption vs. chlorophyll content≫. The wavelength position of the red reflectance minimum (Rmin) in the main red absorption bands of in vivo chlorophyll a proved to be independent of the chlorophyll content of leaves and thus is not suitable for chlorophyll determination. Maximum sensitivity of leaf reflectance to variation in chlorophyll content was, however, found in a wide spectral range from 530 to 630 nm and near 700 nm. The wavelength of the red edge position of the reflectance spectrum (inflection point IP) in the range of 694 to 706 nm correlated very closely with the leaves' chlorophyll content in a curvilinear manner. The Ip is also closely correlated in a linear manner with the reflectance signals at 550 and 700 nm. Reflectances near 700 nm and 550 nm were found to be sensitive indicators of the red edge position and the chlorophyll content of leaves as well. The ratios of reflectances in the near infra-red range of the spectrum (above 750 nm) to that at 700 nm and at 550 nm, R NiR /R700 (or R750/R700) and R nir /R550 (or R750/R550), were directly proportional (r 2 >0.93) to the leaves' chlorophyll content. These two novel indices for chlorophyll determination (R750/R700 and R750/R550) allowed the estimation of leaf chlorophyll content with an error of less than 2.1 μg cm -2 . The two new vegetation indices, R750/R700 and R750/R550, are linearily correlated to the chlorophyll content. They exhibit a more than 6 times wider dynamic range than the widely used Normalized Difference Vegetation Index NDVT. The new vegetation index ratios are very sensitive to changes in chlorophyll content at low, medium and high chlorophyll content which is not the case for the NDVI. This suggests the application of the new indices R750/R700 and R750/R550 in the near and remote sensing of the chlorophyll content of terrestrial vegetation.

The effects of light acclimation during and after foliage expansion on photosynthesis ofAbies amabilis foliage within the canopy.

Variation in the photosynthetic function ofAbies amabilis foliage within a canopy was examined and related to three different processes that affect foliage function: foliage aging, sun-shade acclimation that occurred while foliage was expanding, and reacclimation after expansion was complete. Foliage produced in the sun had higher photosynthesis at light saturation (A max, μmol·m-2·s-1), dark respiration (μmol·m-2·s-1), nitrogen content (g·m-2), chlorophyll content (g·m-2), and chlorophylla:b ratio, and a lower chlorophyll to nitrogen ratio (chl:N), than foliage produced in the shade. As sun foliage becomes shaded, it becomes physiologically similar to shade foliage, even though it still retains a sun morphology. Shaded sun foliage exhibited lowerA max, dark respiration, nitrogen content, and chlorophylla:b ratio, and a higher chl:N ratio than sun foliage of the same age remaining in the open. However, shaded sun foliage had a higher chlorophyll content than sun foliage remaining in the open, even though true shade foliage had a lower chlorophyll content than sun foliage. This anomaly arises because as sun foliage becomes shaded, it retains a higher nitrogen content than shade foliage in a similar light environment, but the two forms have similar chl:N ratios. Within the canopy, most physiological indicators were more strongly correlated with the current light environment than with foliage age or leaf thickness, with the exception of chlorophyll content.A max decreased significantly with both decreasing current light environment of the foliage and increasing foliage age. The same trend with current light and age was found for the chlorophylla:b ratio. Foliage nitrogen content also decreased with a decrease in current light environment, but no distinct pattern was found with foliage age. Leaf thickness was also important for predicting leaf nitrogen content: thicker leaves had more nitrogen than thinner leaves regardless of light environment or age. The chl:N ratio had a strong negative correlation with the current light environment, and, as with nitrogen content, no distinct pattern was found with foliage age. Chlorophyll content of the foliage was not well correlated with any of the three predictor variables: current light environment, foliage age or leaf thickness. On the other hand, chlorophyll content was positively correlated with the amount of nitrogen in a leaf, and once nitrogen was considered, the current light environment was also highly significant in explaining the variation in chlorophyll content. It has been suggested that the redistribution of nitrogen both within and between leaves is a mechanism for photosynthetic acclimation to the current light environment. Within theseA. amabilis canopies, both leaf nitrogen and the chl:N ratio were strongly correlated with the current light environment, but only weakly with leaf age, supporting the idea that changing light is the driving force for the redistribution of nitrogen both within and between leaves. Thus, our results support previous theories on nitrogen distribution and partitioning. However,A max was significantly affected by both foliage age and the current light environment, indicating that changes in light alone are not enough to explain changes inA max with time.

Quantitative estimation of chlorophyll- a using reflectance spectra: Experiments with autumn chestnut and maple leaves

The signature analysis of reflectance spectra of autumn Aesculus hippocastanum L. and Acer platanoides L. leaves revealed spectral bands maximally (near 550 and 705 nm) and minimally (at more than 750 nm) sensitive to variation in chlorophyll content, which can serve as sensitive indicators of early stages of leaf senescence. Several functions of reflectance directly proportional to chlorophyll- a have been found. These make it possible to determine chlorophyll accurately with a background of high pigment concentration.

Eddy-induced oscillations of the pycnocline affect the floristic composition and depth distribution of phytoplankton in the subtropical Pacific

Changes in the phytoplankton population caused by a wind-induced mesoscale eddy, first located off the Hawaiian chain on 29 August 1989, were examined from 6 to 12 September 1989. These cyclonic eddies produce upwelling of nutrient-rich water into the photic zone which may induce changes in the distribution of phytoplankton. The eddy affected the depth, magnitude and composition of the chlorophyll maximum. The eddy produced an upward shift in the distribution of phytoplankton, shoaling the chlorophyll maximum to 30 m. Pigment concentrations at the chlorophyll maximum were enriched up to 2.2 times inside the eddy. Outside the eddy, the upper mixed layer (UML, ≤50 m) was dominated by cyanobacteria whereas the deep chlorophyll maximum (DCM) was dominated by prochlorophytes, chlorophytes and chrysophytes. Inside the eddy, the UML showed an increase in deep water taxa but little change in cyanobacteria. The observed population changes probably resulted from increased growth rates and vertical transport of cells. Based on projections of the track of the eddy, we inferred that its trail created an area of enhanced chlorophyll that was not quickly consumed, and concluded that coupling between phytoplankton and grazers was weak. The presence of such cyclonic eddies may explain some of the variability in chlorophyll concentration found in the oligotrophic subtropical Pacific.

Estimation of the processes controlling variability in phytoplankton pigment distributions on the southeastern U.S. continental shelf

A series of five CZCS images from the southeastern U.S. continental shelf for April 10–16, 1980, were combined with concurrent moored current meter measurements to estimate the processes controlling the observed variability in chlorophyll concentration and distribution in this region. The approach used for this analysis is a series of calculations with the equation governing the space and time distribution of a nonconservative quantity such as chlorophyll. The CZCS chlorophyll distributions and current meter measurements allow estimation of the terms in the governing equation which gives an indication of the relative contribution of advective, diffusive, and local processes in producing the observed chlorophyll distributions on the southeastern U.S. continental shelf. The estimates of the terms in the governing equation from observations show that advective, diffusive, and local processes all contribute to the phytoplankton distributions and that the relative contribution of each changes with time and location. For the 5 days considered in this analysis, the order of importance of processes controlling variability in phytoplankton distributions determined from observations was biologicalvertical processes (36%), diffusion (33%), advection (16%), and local time change (15%). As a comparison, a similar series of calculations were performed with simulated chlorophyll distributions obtained from a numerical physical‐biological model constructed for the southeastern U.S. continental shelf ecosystem that used circulation fields derived from an optimal interpolation of the current meter observations. The ranking of the importance of processes obtained from the simulated distributions is; advection (32%), biological‐vertical processes (27%), diffusion (20%), and local time change (21%). Thus the two approaches provide different estimates of the processes controlling phytoplankton variability on the southeastern U.S. continental shelf. The most likely cause of the different results obtained with the two methods is error introduced into the calculations by the transient nature and sharp gradients associated with Gulf Stream frontal eddies. In spite of these results, the approach described in this analysis may have promise for computing chlorophyll budgets from ocean color measurements obtained in less dynamic environments.

Denitrification in nitrate‐rich streams: Diurnal and seasonal variation related to benthic oxygen metabolism

Seasonal variation of chlorophyll content, photosynthesis, O2 respiration, and denitrification was measured under light and dark conditions in the sediment of a nutrient‐rich Danish lowland stream. Exponential growth of benthic microalgae was observed in early spring (April–May) and photosynthetic capacity persisted until fall. The benthic algae were a major C source for heterotrophic activity as indicated by a close correlation between O2 respiration and Chl content in the sediment. Denitrification activity was related to Chl content, NO3− availability, and O2 conditions. Diffusion from the overlying water was always the major NO3− source for denitrification. Under lighted conditions, photosynthetic O2 production increased the oxic zone and reduced denitrification activity by up to 85% in spring. A simple diffusion‐reaction model allowed denitrification rates to be estimated from O2 respiration rates and concentrations of O2 and NO3− in the stream water. Throughout the season, estimated denitrification rates correlated well with those actually measured. The model demonstrated that denitrification activity was controlled primarily by the thickness of the oxic surface layer which served as a diffusion barrier for NO3− to the denitrification zone.

Variation in Chlorophyll Content of Rice Flag Leaf Lamina and Sheath

Variation in Chlorophyll Content of Rice Flag Leaf Lamina and Sheath

Differences between genotypes of tomato (Lycopersicon esculentum Mill.) in net photosynthesis, light absorption by leaves, chlorophyll content and specific leaf fresh weight under low-energy conditions.

Differences in net photosynthesis between tomato genotypes, grown under low light intensity and, from day 30, at 3 night temperatures, were largely due to differences in the capacity of the leaves to absorb light. Variation in chlorophyll content and leaf thickness largely explained the differences in light absorption. Genotypes with large thin leaves and a high chlorophyll content were thought to be best adapted to low-energy conditions. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Effects of light intensity and nutrient availability on diel patterns of cell metabolism and growth in populations of Synechococcus spp.

Between July 21 and August 8, 1984, phytoplankton were collected from the surface (2 m) and/or chlorophyll maximum of a neritic front, warm-core eddy 84-E and Wilkinson's Basin in the Northwest Atlantic Ocean and incubated up to 38 h in 200-liter vats. Effects of light intensity and nutrient availability on diel patterns of cell metabolism were analyzed in a 0.6- to 1-μm fraction, where Synechococcus spp. represented 80 to 100% of the total photoautotrophs. Populations held under in situ conditions exhibited daytime peaks in photosynthetic potential (Pmax) that were an order of magnitude higher than nighttime Pmax values. Daytime phasing of Pmax peaks had no relationship to asynchronous fluctuations in cellular activities of ribulose 1,5 bisphosphate carboxylase (RUBPCase) or phosphoenol pyruvate carboxylase (PEPCase), or to variations in chlorophyll content. Daytime Pmax peaks were about 12 h out of phase with nighttime maxima in the frequency of dividing cells (FDC). The phase relationship between Pmax and FDC could be altered by manipulating environmental conditions. High light exposure of depp populations did not affect timing of the Pmax peak, but its magnitude increased and coincided with increased RUBPCase activity and chlorophyll photobleaching. In the eddy population, a major shift in the timing of peak Pmax was induced when increased light intensity was accompanied by nutrient enrichment. This change coincided with major increases in cellular chlorophyll and carboxylating enzyme activity. Lowering irradiance and/or increasing nutrient availability elicited different diel pattern in cellular metabolism in surface populations from the eddy and from Wilkinson's Basin that appeared linked to differences in the nutrient status of the cells. Rates of cell division estimated from the percentage of dividing cells in preserved samples were 0.83 divisions d-1 in surface warm-core eddy populations, supporting the view that carbon and nitrogen turnover rates in oligotrophic waters can be sufficient to promote near optimal growth of Synechococcus spp.

Sedimentation, Resuspension, and Oxygen Depletion in Lake Erie (1979)

Oxygen depletion in Lake Erie's central basin hypolimnion is ultimately sustained by the respiration rate of organisms using organic matter which is produced in the trophogenic zone. Although other transformations are certainly important, they are nevertheless driven by the decomposition of organic carbon both in the water column and in the sediments. Rates of transport of particulate organic carbon to the hypolimnion and sediments were estimated using sediment traps. Corrections for sediment resuspension were necessary even during the summer period when the lake is stratified. Particulate organic carbon concentrations in the hypolimnion were partially independent of short-term variations in chlorophyll concentration. The net downflux of carbon to the hypolimnion appeared less than that required to support the observed oxygen depletion. Sediment resuspension accounted for much of the particulate material caught by the sediment traps in the central basin. It is concluded that organic material stored in the surficial sediments is made available to the water column through frequent resuspension. Of total phosphorus in the trap samples, an average of 42% was potentially bioavailable (NaOH extraction).