Showing papers on "Water column published in 1977"
TL;DR: In this paper, vertical profiles of light scattering from over 1000 L-DGO nephelometer stations in the Atlantic Ocean have been used to calculate mass concentrations of suspended particles based on a calibration from the western North American Basin.
298 citations
TL;DR: All species appeared to show less habitat segregation in spring when temperatures rose and food was abundant, and more habitat segregation during the summer when temperatures rise and food is abundant.
Abstract: The seasonal distributions and abundances of 15 littoral zone fish species were determined from May to October 1976 in a small Michigan lake. A team of divers performed seven censuses along a set of transects which encompassed nearly the entire littoral region of the lake; additional dives enabled us to determine vertical distributions and migration patterns to and from overwintering areas. All species appeared to show less habitat segregation in spring when temperatures rose and food was abundant. Species distributions and abundances were quite constant during the summer and considerable habitat segregation was apparent. The bluegill (Lepomis macrochirus) was the dominant species and was studied in greater detail. Small bluegills (<80 mm total length) were confined throughout the year to the vegetation apparently to avoid predation; larger fish moved up in the water column. This species overwintered in two localized regions of tall perennial vegetation in the deep littoral apparently in response...
166 citations
TL;DR: Temperature, salinity, bottom-sediment type, and zinc concentration all influenced Cd uptake by 4 marine bivalves in short-term static assay systems using 109Cd as a tracer in order to demonstrate differences in uptake rates among organisms tested.
Abstract: Temperature, salinity, bottom-sediment type, and zinc concentration all influenced Cd uptake by 4 marine bivalves (Mya arenaria, Mytilus edulis, Mulinia lateralis and Nucula proxima) in short-term static assay systems using 109Cd as a tracer. The experimental system consisted of aquaria containing 20 l of seawater maintained under controlled light and temperature conditions. The water contained either 5 or 20 μg/l Cd and tracer. Distribution and kinetics of the metal were monitored in the water column and organisms. The results demonstrate that Cd uptake rates differed widely among the organisms tested. An increase in temperature increased Cd uptake rate by all test organisms. A decrease in salinity increased Cd uptake by all organisms tested. The presence of bottom sediment depresses Cd accumulation in some benthic animals. Zinc in concentrations of 0.5 mg/l substantially decreased Cd uptake by Mytilus edulis and Mulinia lateralis. It is suggested that all important species and environmental variables be considered when studying heavy-metal uptake by marine organisms or when establishing water-quality criteria.
134 citations
TL;DR: The magnitude of nitrogen fixation in the gyre is seasonally dependent, with high rates in late summer and autumn, and data suggest that during these months of stratification, biological fixation of nitrogen amounts to about 33 μg-at N/m2/day.
Abstract: The magnitude and physiological characteristics of biological nitrogen fixation have been studied in the oligotrophic waters of the North pacific gyre. The filamentous blue-green algae Trichodesmium spp. and Richelia intracellularis were the important nitrogen-fixing phytoplankton. Most of the nitrogen fixation occurs in the upper 40 m of the water column, with detectable fixation as deep as 90 m, which corresponds to about the 1 % light depth. There was no evidence of photoinhibition of nitrogen fixation, although CO2 reduction was depressed slightly at the highest light levels. The rate of nitrogen fixation in the water column varied throughout the day, being highest in mid-morning and in late afternoon. Relatively high fixation rates were also found during periods of darkness. Elevated oxygen concentrations had a marked inhibitory effect on rates of nitrogen fixation, a pO2 of 0.4 atm causing a 75% inhibition. Data from studies of nitrogen fixation and assimilation rates of 15N-labelled nitrate, ammonium, and urea indicate that nitrogen fixation furnished about 3% of the total daily fixed nitrogen requirement for phytoplankton growth. Studies with isolated colonies of Trichodesmium spp. indicated that 100% of their nitrogen requirement was met by nitrogen fixation. Chemical composition of the Trichodesmium colonies showed that the C:N ratio was 4.1 and that their phosphorus content relative to carbon or nitrogen was much lower than that of the total particulate material in the water column. Elevated ratios of carbon: adenosine triphosphate (ATP) also suggest that phosphorus deficiency may be limiting the growth of Trichodesmium. The magnitude of nitrogen fixation in the gyre is seasonally dependent, with high rates in late summer and autumn. At these times the water column is stratified, with phosphate and nitrate barely detectable in the upper 100 m. Our data suggest that during these months of stratification, biological fixation of nitrogen amounts to about 33 μg-at N/m2/day.
127 citations
TL;DR: Most of the variability in the bacterial population estimates could have been explained by five of the regressor variables and that the factors most likely to provide more information would include some measure of predation and lake retention time.
Abstract: SUMMARY. The difference between the results of viable and total counting procedures for bacteria are exemplified by vertical profiles from a deep and a shallow lake and from seasonal changes in the epilimnion and hypolimnion of a shallow eutrophic lake. The viable count was, on average, 0.25% of the total count, the greatest difference being noted in the anoxic hypolimnion, probably due to the inadequacy of the viable counting procedure for the isolation of bacteria from such samples. There was a general trend for the more nutrient-rich waters to support larger bacterial populations but such observations did not provide any further information on the factors responsible for the population changes observed. Seasonal fluctuations in the counts are studied and the qualitative and quantitative changes resulting from artificial enclosure of water are discussed. Not all the temporal changes could be explained and short-term changes resulting from nutrient additions to the experimental enclosures were not always reproducible. Horizontal variability was examined, found to be significant and could play an important role where water movement and turbulence is considerable. Results from six sites sampled between 1969 and 1974, representing total and viable bacterial population estimates and a total of eighteen independent or regressor variables were then subjected to principal components analysis. Results taken from the whole water column showed the overwhelming effect of the process of stratification on the bacterial population accounting for 30%-60% of its variability. Secondary components representing algal productivity could account for 10% to 20% of the variability. Many of the chosen regressor variables were acting as measures of the same phenomenon without providing significant information on what affected the bacterial population. To overcome this problem results from the hypolimnion and epilimnion were analysed separately. The analysis demonstrated the importance of seasonal changes in nutrient concentrations in the epilimnion and the development of anoxic conditions in the hypolimnion. Algal biomass, phosphate concentration and the interaction of pH and ammonia appeared to be important. It was concluded that most of the variability in the bacterial population estimates could have been explained by five of the regressor variables and that the factors most likely to provide more information would include some measure of predation and lake retention time.
122 citations
TL;DR: In this paper, a pycnocline builds up in September due to seepage of seawater to the surface, leading to a rapid development of anoxic conditions with up to 39 ppm H2S, a decrease in pH from top to bottom, redox potential gradients (+390 to −185 mV), and extremely pronounced light absorption are observed during the period of stratification which lasts from Sepember to July.
Abstract: In Solar Lake, a basin at the edge of the sea filled with brine and shielded from the wind, a pycnocline builds up in September due to seepage of seawater to the surface. Solar heating produces a mesothermic temperature curve with a maximum up to 60.5°C at 2.5–3-m depth and decreasing temperatures toward the bottom (40°C at 5 m). The temperature profile together with a supply of nutrients from seepage leads to the development of several bacterial plates and a benthic cyanobacterial bloom. A rapid development of anoxic conditions with up to 39 ppm H2S, a decrease in pH from top to bottom (8–6.9), redox potential gradients (+390 to −185 mV), and extremely pronounced light absorption are observed during the period of stratification which lasts from Sepember to July. With increasing solar energy, the seawater supply no longer compensates for the evaporation rate of 3.0 m yr−1 and the mesothermy becomes unstable. During a short period of holomixis, lasting from 4–13 weeks, the temperature is 27°C throughout the water column. The sediments of Solar Lake preserve a record of the last 4,600 years from the conditions of a marine lagoon to the development of the limnological cycle presented here.
103 citations
TL;DR: In this paper, the influence of tidal mixing on the temperature structure of the water column and the availability of light and nutrients for phytoplankton growth in this region have been described.
Abstract: DURING the summer of 1976, for the second successive year, blooms of the dinoflagellate Gyrodinium aureolum Hulburt have occurred at the western entrance to the English Channel. The influence of tidal mixing on the temperature structure of the water column and the availability of light and nutrients for phytoplankton growth in this region have already been described1,2. Here we report a frontal movement in response to the cycle of tidal mixing induced by the alternation of neap and spring tides, and suggest that plant populations both in surface water on the stratified side of the front and in the thermocline are dependent on the associated periodic release of nitrate and inorganic phosphate from the cold, nutrient-rich, bottom layer. We also describe the effects of phytoplankton on nutrient gradients across the thermocline.
90 citations
TL;DR: The results were used as measures of the concentration and distribution of organic detritus in the coastal waters of Caminada and Barataria bays, Louisiana, and the Gulf of Mexico as discussed by the authors.
77 citations
TL;DR: The experiments confirm that some marine dinoflagellates have access to subthermocline nutrient pools and that these same species may also exhibit spatial and temporal patchiness in response to countercurrent flow across the thermocline.
Abstract: In experiments in a 10 m, thermally stratified seawater column, Cachonina niei crossed a 5°C gradient during a 4-m diurnal vertical migration, while Amphidinium carteri remained in the upper, isothermal, part of the water column during a 1-m diurnal vertical migration. The experiments confirm that some marine dinoflagellates have access to subthermocline nutrient pools. These same species may also exhibit spatial and temporal patchiness in response to countercurrent flow across the thermocline.
75 citations
TL;DR: A detailed study of the distribution of methane in this highly productive coastal environment was carried out in this paper, where the authors identified the relative importance for methane supply to the coastal mixed layer of in situ biological production and of eddy diffusive and advective transport of methane-rich water which has been in contact with the bottom at the coast.
Abstract: Nine stations were occupied in the vicinity of Walvis Bay, Namibia, during a detailed study of the distribution of methane in this highly productive coastal environment The principal features of the observed coastal methane distribution included (1) excess methane in the mixed layer of from 2 times to greater than 300 times solubility equilibrium with the atmosphere, (2) a subsurface maximum, located in the top of the pycnocline, at which concentrations ranged from 26 to 440 times solubility equilibrium, (3) an intermediate depth minimum, where concentrations were comparable to those offshore at similar depths and which we attribute to the influence of onshore movement of subsurface offshore water, and (4) a bottom maximum, which we attribute to input of methane to the water column from the anoxic sediments in the Walvis Bay area An attempt was made to identify the relative importance for methane supply to the coastal mixed layer of in situ biological production and of eddy diffusive and advective transport of methane-rich water which has been in contact with the bottom at the coast Calculations suggest that both in situ production and physical processes are major sources of excess methane for the highly productive coastal surface waters However, the complicated circulation patterns make quantification extremely difficult
69 citations
TL;DR: In this article, the authors constructed a budget for the water column which balances the rate of radon input against the radon loss for two regions, one of which is broad and shallow and the other narrow and deep.
Abstract: Radon 222 concentrations in waters of the Hudson River estuary show little consistent vertical, axial, or seasonal variation. The median of 106 summer measurements is 1.43 +- 0.25 dpm/1, and the median of 17 winter measurements is 1.30 +- 0.35 dpm/1. A budget is constructed for the water column which balances the rate of radon input against the rate of radon loss for two regions, one of which is broad and shallow and the other narrow and deep. The primary supply of radon for these two regions is from the sediments (75--90%), with minor inputs from radium 226 decay in the water column, stream runoff, and tidal pumping of groundwater. Loss of radon occurs by evasion to the atmosphere and decay in the water column in roughly equal amounts. The activity of mobile radon in sediments (per wet sediment volume) is 0.33 +- 0.10 dpm/cm/sup 3/ in the broad, shallow area of the estuary and 0.42 +- 0.11 dpm/cm/sup 3/ in the narrow, deep reach immediately upstream. When these value are used, the flux supplied by molecular diffusion is approximately 40% of the total input. Constant physical stirring of the upper few centimeters of sediments by bottom currents over largemore » areas and stochastic reworking to somewhat greater depth in localized sediment deposits appear to be primarily responsible for augmenting the flux from sediments provided by molecular diffusion.« less
01 Jan 1977
TL;DR: The isotopic compositions of nitrogen in lake water, plankton samples and the organic-N fractions extracted from sediments at selected stations in Lake Superior are presented in this paper, where the authors emphasize the need for a better understanding of the autogenous isotopic fractionation before the isotopic method can be used to fingerprint the sources of nitrogen.
TL;DR: In this article, the authors measured the photosynthetic potential of phytoplankton in Lake Tahoe and demonstrated the importance of these populations in influencing the vernal bloom.
Abstract: Biomass, chlorophyll a, and photosynthetic potential of phytoplankton were measured year-round throughout a 450-m water column of ultraoligotrophic Lake Tahoe. Phytoplankton biomass was uniform from the surface to the maximum depth while the lake mixed completely in March, but was lower in aphotic waters during thermal stratification. Aphotic chlorophyll a concentrations decreaked progressively in fall and reached a miniI~UI~ of 17% of mean euphotic concentrations in January, before the mixing depth exceedcd the euphotic depth. Photosynthetic rates measured in an incubator under constant light conditions were significantly correlated with pigment concentrations in both euphotic and aphotic phytoplankton and demonstrated viability of the aphotic phytoplankton throughout the year. High surface : volume ratios of the small species dominating the phytoplankton assemblage suggest low sinking velocities. Extremely slow decomposition is postulated to explain the vertical pigment concentration gradients in the aphotic zone. Re-entry of viable aphotic phytoplankton into the euphotic zone during deep mixing of the lake can diminish the dilution of euphotic phytoplankton, thereby increasing the magnitude of the subsequent vernal bloom. In deep lakes and oceans phytoplankton are lost as a result of sinking into aphotic layers. Algal cells decay by bacteria1 attack and autolysis, thereby releasing nutrients which can be reintroduced to euphotic waters by vertical mixing or upwelling. These processes have been studied in Lake Tahoe ( Paerl et al. 1975a,h). In spite of its high transparency (Secchi depths vary between 20 and 40 m), twothirds of Lake Tahoe’s water volume is aphotic because of its great mean depth (313 m). In eutrophic lakes the aphotic degradation of phytoplankton occurs under anaerobic and frequently toxic conditions ( e.g. development of H2S). In Lake Tahoe, however, even the deepest layers remain fully oxygenated. Environmental conditions in deep euphotic and aphotic waters are similar except for the lack of light and enhanced (but still very low ) nutrient levels. Phytoplankters on the average have to sink from deep in the cu--’ Present address : Technische Universitaet Berlin, Institut fuer Oekologie-Limnologie, EngleralIce 19-21, D-l Berlin 33, West Germany. a Present address: Department of Scientific and Industrial Research, Ecology Division, Vreshwatcr Section, P.O. Box 415, Taupo, New Zealand. photic zone through a water column of about 200 m before reaching the lake bottom. Because of the extreme clarity of the lake, layers of water at different optical depths are farther apart than in a less transparent environment. In high altitude and high latitude lakes phytoplankton can endure extended periods of extremely low light intensities or complete darkness under thick ice and snow cover (Rodhe 1955; Tilzer 1972; KaIff and Welch 1974). In Lake Tahoe, which never freezes, previous work has revealed the existence of high phytoplankton biomass in deep aphotic layers (Kiefer et al. 1972). We here provide evidence for the viability of these populations throughout the year by measuring their photosynthetic potential under constant light and temperature. We then evaluate their importance in influencing the vernal bloom. R. C. Richards helped with sampling, S. Paulson with sample analyses, R. L. Leonard, R. C. Richards, and B. Jost reviewed the text. P. Towns typed the final manuscript. The work was supported by NSF-RANN grants GI-22 and AEN 7422675, LIMNOLOGY AND OCEANOGRAPIIY 84 JANUARY 1977, V. 22( 1) Viability of nphotic phytoplankton 85 Materials and methods Between March 1974 and March J-975, phytoplankton samples were collected at monthly intervals from 13 depths throughout a midlake water column with opaque, nonmetallic Van Dorn water bottles. Chlorophyll a concentrations were determined in 3.5-4.0 liters of water filtered through Whatman GF/C filters followed by extraction in 90% acetone. Absorbance was read in 4-cm glass cells in a Beckman DB-G spectrophotometer. The trichromatic equations of Strickland and Parsons (1968) were used to calculate the amount of pigment. Pheopigments were analyzed after acidification. Since fairly constant C : ATP ratios have been found (HolmHansen and Booth 1966)) concentrations of ATP (adenosine triphosphate) were used as an approximate measure of live cellular carbon assuming a C : ATP ratio of 250 ( IIolm-Hansen and Booth 1966). Using the luciferin-luciferase ATP assay following extraction in 0.02 M tris buffer as modified by Holm-IIansen and Booth (1966) and as described by Holm-IIansen and Paerl ( 1972), we performed ATP analyses on 1-Z ter subsamples filtered through precombusted Whatman GF/C filters. Water for both analyses was strained through a 76-pm plankton net befort filtration, The photosynthetic potential of algal populations was examined by labeling subsamples with 0.5 ml of 14C-bicarbonate (specific activity 8.24 i microbial activity in Lake Tahoe is low. In two incubator experiments, euphotic phytoplankton was held in complete darkness in replicate 4-liter plastic containers at 7-8” C for 22 days. Samples were taken every 3-5 days and chlorophyll a and photosynthetic potential measured.
TL;DR: In this article, mass-balance calculations show that there is a net loss of Ca, Mg and Al from the watershed while there are a net uptake of H+, NO3 and NH4.
Abstract: Langtjern is an acid lake situated in south-central Norway, 516 m above sea level. The watershed is underlain by biotite gneisses and granites. Coniferous forests cover 63% of the watershed, while 16% is covered by peaty areas. The lake has a relatively large watershed (4.8 km2) in relation to lake size (0. 23 km2), and most of the water and chemicals reach the lake via the watershed and inflowing streams. Direct precipitation on the lake surface is less important.
The two major inflowing streams show rapid responses to influxes of acid precipitation (weighted annull mean pH 4.3) and long recovery periods between episodes. The fall and spring acid episodes have different impacss on the lake-water chemistry. The spring episode during which large amounss of H+ are released in the first phases of the snow melt reduces the pH in only the surface layers of the still ice-eovered lake and much of the inflowing pollutants are promptly discharged. In the fall, however, the acid inputs are readily mixed through the entire water column during the autumnal circulation period.
Assuming chloride as a conservative parameter, mass-balance calculations show that there is a net loss of Ca, Mg and Al from the watershed while there is a net uptake of H+, NO3 and NH4. SO4 and Na budgets balance. The net uptake of H+ in the watershed is directly related to net losses of other cations. The net uptake of NO3 and NH4 is most likely due to biological uptake by the forest ecosystem.
For the Langtjern itself the inputs of all major ions equal the outputs, except for H+ and NO3 which are retained by the lake. The neutralization of H+ in Langtjern varies seasonally, whereas only 10-20% is neutralized during spring, in the autumn 50-70% is neutralized.
TL;DR: Sediment traps that can greatly amplify the rate of sedimentation and automatically time the depositional process were set out in El Vado Lake and Morgan Lake (New Mexico), Lake Powell (Utah), and Pyramid Lake (Nevada) as mentioned in this paper.
Abstract: Sediment traps that can greatly amplify the rate of sedimentation and automatically time the depositional process were set out in El Vado Lake and Morgan Lake (New Mexico), Lake Powell (Utah), and Pyramid Lake (Nevada). In El Vado and Morgan lakes, sediment fluctuations on the scale of days were responsive to local weather factors, with the deposition rate in Morgan Lake greater near the bottom of the water column than near the top. Sedimentation in El Vado and Pyramid lakes appeared to have some diurnal control. Sedimentation in Pyramid Lake and Lake Powell, the two lakes fed by large rivers, was strongly influenced by river discharge and showed lag effects proportional to the distance of sediment transport.
TL;DR: Evans et al. as discussed by the authors collected bottom sediments and overlying waters from depths of 6 and 9 m in southeastern Lake Michigan, Copepod, cladoceran, and ostracod abundances were assessed in terms of known plankton.
Abstract: Cores of bottom sediments and overlying waters were collected from depths of 6 and 9 m in southeastern Lake Michigan, Copepod, cladoceran, and ostracod abundances were assessed in terms of known plankton. Species could be roughly divided into euplanktonic species showing no affinity for the sediments, epibenthic species occurring in the plankton but concentrated near the sediments, and benthic species inhabiting the sediments and rarely encountered in the plankton. While several epibenthic species left the sediments at night to enter the plankton, only a small fraction of the benthic species showed this migration. Epibenthic and benthic microcrustaceans in the lower 0.3 m of the water column accounted for 33-39s of the standing stock (by numbers) of the microcrustaceans within the 9-m depth contour. Preliminary information on the local food web indicates that the microcrustaceans have a significant role in the trophodynamics of the inshore area. Several of the species found in southeastern Lake Michigan are tolerant of eutrophic, mesotrophic, or moderately saline waters. Although the planktonic crustaceans of the open waters of the Great Lakes have been studied extensively, the epibenthic components have been largely overlooked, probably due to the technical difficulties in collecting from this habitat. Conventional zooplankton sampling gear (nets, water bottles) does not sample the organisms living on the sediments (benthic) or within a few centimeters of the sediments (epibenthic). Sampling gear such as dredges and grabs may collect epibenthic and benthic organisms, but the mesh sizes of screens in these devices and of the sieves used for washing samples are generally coarse (500 p) and do not retain the smallest organisms. Where special gear has been used, an abundant and diverse microfauna has been collected (Moore 1939; Cole 1955). Although the trophodynamics of the cpibenthic and benthic microfauna have not been well studied in temperate freshwaters, studies in Arctic ponds (Fenchel 1975), brackish waters (Jansson 1974)) and marine waters (McIntyre 1964) have shown that microfauna arc important in benthic communities both as competitors with the ’ This research was supported by the Indiana & Michigan Power Company. Great Lakes Research Division contribution 214. macrobenthos for food resources and as prey for benthic invertebrates and fish. In the Great Lakes, microbenthos probably have a similarly significant role. In summer 1974, we investigated the nearshore arca of southeastern Lake Michigan to determine the species composition and abundance of the epibenthic and benthic microfauna. The samples contained a diverse assemblage of organisms from a number of taxonomic groups. We here discuss primarily the copepods, cladocerans, and ostracods. The project was undertaken in cooperation with S. C. Mozley and we acknowledge his advice and help. Divers were J. Dorr and G. Gitschlag. Materials and methods Duplicate sediment cores were collected at five sites 80-100 m apart (Fig. 1) along two transects parallel to shore and extending southward from the intake structures of the Donald C. Cook Nuclear Plant in southeastern Lake Michigan. The plant was not operational in 1974 although water was occasionally drawn from the lake during periods of circulating-pump testing. Transect C (6-m depth contour) was sampled during the afternoon of 22 July 1974, LIMNOLOGY AND OCEANOGRAPHY 1059 NOVEMBER 1977, V. 22( 6) 1060 Evans and Stewart I Q DISCHARGE STRUCTURE
TL;DR: The vertical distribution of organic C, sulphate-chlorinity ratio, sulphide concentration, oxygen consumption rate and ETS activity was studied over a column of 35 cm in sediments of a natural tidal flat and of a large artificial indoor tidal flat as discussed by the authors.
TL;DR: The small influx of terrigenous sediment onto the continental margin off southern Spanish Sahara is evidenced by the carbonate-rich sands that cover the middle and outer shelf and by the low concentrations of land-derived grains suspended within the shelf and slope waters as mentioned in this paper.
TL;DR: It is shown that PCP persisted in leaf litter and sediments for at least seventeen months following contamination, which provides a potential for continuous contamination of the water column and biological magnification via detritus- and benthic-feeding organisms.
Abstract: The results of this investigation have shown that PCP persisted in leaf litter and sediments for at least seventeen months following contamination. This persistence provides a potential for continuous contamination of the water column and biological magnification via detritus- and benthic-feeding organisms. An investigation of these factors is presently underway.
TL;DR: In this paper, the interstitial reactive P (IRP) levels in Lake Mendota and Lake Wingra were evaluated as a function of season and water column and sediment depth.
TL;DR: In this article, a numerical study of the thermal front formed by cooling of the sea surface and inflow of the fresh water is made within a vertical two-dimensional plane without the rotation of the earth.
Abstract: A numerical study of characteristics of the front formed by cooling of the sea surface and inflow of the fresh water is made within a vertical two-dimensional plane without the rotation of the earth. The convective adjustment technique is employed to parameterize the small scale convective overturning process. A sharply edged shelf causing the marked difference of the heat capacity of the water columns between over the shelf (50 m depth) and in the deeper region (150 m depth), is responsible for the formation of a thermal front over the shelf edge and two cell circulations of the same sense with each other adjoining at the frontal region. Inflow of the fresh water at the upper region of the coast (which is equivalently replaced by the outflow of the salt from the same region) adds a circulation of the opposite sense to the above ones, which transports the water of low salinity and low temperature offshore and forms a sharp front both of temperature and salinity with the offshore water of high salinity and high temperature. This thermohaline front or “Oceanic front” has a remarkable character that the horizontal density gradient is minimal at the front due to the counteracting contributions of temperature and salinity to density. Response of this front to the sudden ceases of the surface cooling and the fresh water supply, is also studied in order to understand its transient behaviors.
TL;DR: The study revealed that dark bottle measurements of heterotrophic activity undrestimate total activity and can be justified as a means of assessing chemoheterotropich activity only, and Photocheterotrophy was shown to be quantitatively comparable to chemohetrophy within the pelagic zone.
Abstract: This study examines the occurrence of photoheterotrophy, the light—mediated assimilation of organic compounds at or near natural substrate concentrations, in the phytoplankton of a lake. The pelagic zone of Lawrence Lake, an oligotrophic, dimictic, hard—water lake in southwestern Michigan, was selected as the study site because extensive information is already available on its carbon cycle. The uptake of glucose by the plankton was monitored in both light and dark bottles over an annual period. Uptake was measured during 3 sampling periods throughput the daylight hours (i.e., sunrise, midday, and sunset) and at 3 depths within the water column (i.e., 2, 6, and 10 metres). The patterns of dark heterotrophic activity, chemoheterotrophy, and light—mediated heterotrophic activity, photoheterotrophy, were significantly related to the variables of months, depths, and time of day. Chemoheterotrophic activity generally increased throughout the daylight period and with greater depth within the water column. Maximal values were generally observed during the sunset—incubation series and at 10 metres depth. Generally high and uniform activities with respect to depth were observed during periods of water circulation. Increasing activity at greater depth during the stratified summer period was also observed. Maximal values for photoheterotrophy were observed during spring circulation and late summer stratification. Activity was generally greatest below 2 metres and during morning and midday incubation periods. There was an apparent shift during the daylight period in the area of maximal uptake from 2 and 6 metres in the morning to 6 and 10 metres as the day progressed. Chemoheterotrophy and photoheterotrophy are both temporally and spatially separated with respect to activity within the water colum on a diurnal as well as a seasonal basis. The study revealed that dark bottle measurements of heterotrophic activity undrestimate total activity and can be justified as a means of assessing chemoheterotropich activity only. Light bottle uptake values averaged 146% of dark bottle estimates during the light period. Photocheterotrophy was shown to be quantitatively comparable to chemoheterotrophy within the pelagic zone. Photoassimilation averaged 67.6% of chemoheterotrophic activity based on individual comparisons (N = 360) over an annual period. Photoheterotrophy represents an important step in our further understanding of the cycling of carbon within aquatic systems and of biological interactions within the planktonic community.
Abstract: Low level nutrient enrichment of an enclosed water column caused increases in primary, secondary and tertiary production. In addition, increases in the amount of sediment material, heterotrophic activity and accumulation of major nutrients, nitrate and phosphate, were noted. In contrast, no change was observed in species diversity that could be attributed to nutrient enrichment. The combination of these effects is suggested as a diagnostic approach to examining the early effects of marine eutrophication.
TL;DR: Using the equation of continuity, vertical velocity profiles were calculated from horizontal current measuurements in the Oregon coastal upwelling system as mentioned in this paper, and a vertical velocity of 2 × 10 −2 cm s −1 was characteristic during a period of uplifting-favorable winds 11 km offshore in 100 m of water.
01 Oct 1977
TL;DR: Oscillatoria appears to be endemic to the shelf, is not necessarily contributed by the Gulf Stream nor are the blooms related to the subsurface Gulf Stream intrusions as discussed by the authors.
Abstract: Oscillatoria was found in the surface waters of the South Atlantic Bight during each of four seasonal cruises. There were large concentrations nearshore in September, December, and April while a shelf wide bloom with filament numbers as high as 36,000 l/sup -1/ prevailed in July. Oscillatoria appears to be endemic to the shelf, is not necessarily contributed by the Gulf Stream nor are the blooms related to the subsurface Gulf Stream intrusions. In July water column stability, high temperature and nutrient deficiency seemed to favor Oscillatoria but it is not clear why nearshore blooms occurred in September and December when unstable conditions, cooler water and relatively high nutrient loads existed. While we calculate that nitrogen fixation by Oscillatoria is not as important as the contribution of total nitrogen added from coastal and intrusion sources, the biomass and productivity represented by Oscillatoria must significantly influence secondary production on the shelf.
01 Jan 1977
TL;DR: A combined hydrographic-mineralogic survey of water masses and their suspended particulate matter was carried out over the continental shelf and upper slope adjacent to Sierra Leone and Liberia; it revealed a two-layered system with distinct clay signatures as discussed by the authors.
TL;DR: An extensive limnological study of a tropical African montane lake (Little Connemara Dam No. 3) was undertaken in 1975 to explain the discrepancy between the high nutrient content of the bottom muds and the oligotrophic status of the water column as discussed by the authors.
Abstract: SUMMARY. An extensive limnological study of a tropical African montane lake (Little Connemara Dam No. 3) was undertaken in 1975 to explain the discrepancy between the high nutrient content of the bottom muds and the oligotrophic status of the water column. Little Connemara Dam (No. 3) lies in a small dolerite catchment. The dolerite is strongly jointed allowing considerable water movement and it weathers easily under high rainfall. A number of homes are built in the small catchment.
The results of the study showed that the majority of the nutrients were being flushed into the lake from septic tanks via underground streams. As the dolerite weathers, large amounts of iron and manganese, but little calcium or carbonate, are released. The PO4-P in the water column is complexed with the Fe and Mn allowing only small concentrations for use by algae. Nitrogen enters the lake mainly as particulate nitrogen but is not significantly converted to soluble combined forms of nitrogen at the low pH values (6.2—6.7) found in the lake. Bioassay experiments indicated that combined forms of nitrogen limited phytoplankton growth.
01 Mar 1977
TL;DR: In this paper, the authors investigated the association of hydrocarbons and suspended sediments and the scavenging and sedimenting of hydrocarbon droplets by zooplankton.
Abstract: Results of hydrocarbon analyses of biota, water, sediment and seston are reported and discussed. In general these analyses show that the Alaskan OCS environments are free of petroleum at the present time. Petrogenic hydrocarbons were detected in intertidal sediments of the Beaufort Sea. It is not yet known to what extent, if at all, anthropogenic sources contribute to these hydrocarbons. Efforts to understand and quantify processes by which hydrocarbons in the water column are transported to the benthic environment are described. The two such processes investigated are the association of hydrocarbons and suspended sediments and the scavenging and sedimenting of hydrocarbon droplets by zooplankton. It appears that at least for the conditions of south central Alaska the formet process is not highly efficient. Results about the latter process is not highly effecient. Results about the latter process are not yet available. Brief descriptions of recently begun site specific studies are presented.