Showing papers on "Water column published in 1981"

Primary production and standing crop of phytoplankton along the ice-edge in the Weddell Sea

Abstract: Chlorophyll a, phaepoigments, primary production, nannoplankton, inorganic nutrients, and physical measurements were made in the upper water column at 17 stations occupied in the Weddell Sea in February and March 1977. The most conspicuous feature is the marked contrast between the low standing crop and primary productivity of the northern and central regions, compared with the much more productive shelf waters at the head of the Weddell Sea. Chlorophyll a in the euphotic zone was 4.36 ± 1.75 mg m−2 for the former regions and 31.6 ± 9.5 mg m−2 for the southern stations. Production in the water columns of the southern stations (0.41 ± 0.23 g C m−2 day−1) was approximately four times that at the northern-central ones (0.104 ± 0.092 g C m−2 day−1). Based on plant carbon: chlorophyll a ratio of 30 ± 10 estimated in the present study, an average specific growth rate (μ) of 0.71 was calculated. The nutrient concentrations showed an inverse distribution compared with those of chlorophyll a and primary production; higher nutrient concentrations were recorded at the northern stations than at the southern waters. Phosphate: nitrate: silicate ratios in the water column suggested the importance of nitrate for phytoplankton production. A significant relationship (P < 0.001) between chlorophyll a concentration and day-zooplankton biomass and a significantly higher ratio (P < 0.06) of night-to-day catch of zooplankton in the northern-central regions than in the southern region were found. This suggests that zooplankton do not need to migrate vertically in the southern regions due to abundance of food supply, whereas in the northern-central regions zooplankton must migrate upwards during the night to consume available food produced through the photosynthetic process. The study demonstrates that water column stability, grazing, and proximity to land masses are the most significant factors controlling phytoplankton production in the Weddell Sea.

Energy flow in the Ythan Estuary, Aberdeenshire, Scotland

Abstract: A steady-state energy flow model has been constructed for the Ythan estuary. Nutrient and particulate organic carbon flux has been described in relation to freshwater drainage and tidal action. No rates of retention however, could be provided. Organic C to organic N ratios of detritus vary from 1:14 to 1:200 in the water column, whilst this ratio is 1:8 in the sediments of the mudflats. Primary production by benthic macrophytes, benthic algae and phytoplankton amounts to 631 g C m −2 year −1 whilst the production for zooplankton is 0·8 g C m −2 year −1 , for meiofauna 19·5 g C m −2 year −1 and for macrofauna 48·8 g C m −2 year −1 . The efficiency of energy transfer between the invertebrate macrofauna and vertebrate predators approximates to 54·2% which is higher than that recorded hitherto in various aquatic ecosystems.

Primary production in a turbid estuary

Abstract: The primary production in the Bristol Channel, U.K., was studied from 1973 to 1977: in this estuary, the euphotic zone extends from less than 0.5 m to greater than 10m and there is a large riverine input of inorganic nutrients. The standing stock of phytoplankton chlorophyll a was measured in 1973 and 1974 and was similar throughout the Bristol Channel but the rate of primary production was much greater where the water was less turbid. The estimated primary production was 6.8g C m−2 for the most turbid region and 164.9g C m−2 for the Outer Bristol Channel. A larger proportion of the annual primary production occurred in the spring in the Outer Channel than in the most turbid regions. Phaeocystis developed into blooms in some, but not all, years and exhibited a different light saturation curve to other phytoplankton populations. Serial incubations of short duration gave higher fixation rates than day-long incubations and it is argued that photoinhibition is probably insignificant in a mixed water column. Excretion rates of dissolved organic carbon by phytoplankton were always low.

Reduction of sulfur compounds in the sediments of a eutrophic lake basin.

Abstract: Concentrations of various sulfur compounds (SO42−, H2S, S0, acid-volatile sulfide, and total sulfur) were determined in the profundal sediments and overlying water column of a shallow eutrophic lake. Low concentrations of sulfate relative to those of acid-volatile sulfide and total sulfur and a decrease in total sulfur with sediment depth implied that the contribution of dissimilatory sulfur reduction to H2S production was relatively minor. Addition of 1.0 mM Na235SO4 to upper sediments in laboratory experiments resulted in the production of H235S with no apparent lag. Kinetic experiments with 35S demonstrated an apparent Km of 0.068 mmol of SO42− reduced per liter of sediment per day, whereas tracer experiments with 35S indicated an average turnover time of the sediment sulfate pool of 1.5 h. Total sulfate reduction in a sediment depth profile to 15 cm was 15.3 mmol of sulfate reduced per m2 per day, which corresponds to a mineralization of 30% of the particulate organic matter entering the sediment. Reduction of 35S0 occurred at a slower rate. These results demonstrated that high rates of sulfate reduction occur in these sediments despite low concentrations of oxidized inorganic compounds and that this reduction can be important in the anaerobic mineralization of organic carbon.

Dispersal of Benthic Meiofauna by Wave and Current Action in Bogue Sound, North Carolina, USA

Abstract: . Results from sediment trap experiments in Bogue Sound, North Carolina, indicate that meiofauna from a wide variety of taxa and benthic habitats are regularly suspended in the subtidal water column. Interstitial species are estimated to account for 10–30 % of the suspended meiofauna. Measurements of suspended nematode concentrations, when compared with wind and current velocity records, suggest that in Bogue Sound, shoaling and breaking waves are more important than tidal currents in controlling meiofauna erosion and deposition. Linear regression analysis indicates that 80% (r = 0.907) of the variation in suspended nematode density is correlated with changes in the mean onshore-offshore component of local wind velocity. Nematode turnover associated with spring and summer coastal wind patterns is estimated to be several hundred animals per m2per day. Once suspended, meiofauna may be carried up to 10 km per day by residual currents in the Sound. Although erosion, transport and deposition of benthic nematodes by wave and current action appears to provide an effective means of dispersal along continental coastlines, the high settling velocity of nematodes suspended in Bogue Sound (on the order of 10-4m s-1) suggests that net downward flux in shelf and slope waters probably prevents their dispersal across ocean basins by surface currents.

Methane in the upper water column of the northwestern Gulf of Mexico

Abstract: Shallow subsurface dissolved methane maxima were commonly observed in the northwestern Gulf of Mexico during a series of cruises between 1975 and 1977. Although there were often several methane maxima at various depths at any one particular station, the most prevalent and widespread occurred over a narrow band of σt, in a range from 24 to 26 and could be traced as layers extending along and outward from the continental shelf. These layers generally followed the local stratification and were associated with the upper part of the pycnocline. Advection was undoubtedly of importance in determining the extent and distribution of these methane maxima layers, but in situ production appears to have supported them. Some vertical profiles revealed associations between methane, ATP, and suspended matter maxima. It is postulated that methane forms in situ in reducing microenvironments associated with suspended participates, which are advected from the shelf or which have accumulated in the upper pycnocline due to increase in buoyancy forces.

Laboratory experiments on the diurnal vertical migration of marine dinoflagellates through temperature gradients

Abstract: The diurnal vertical migrations of 4 marine dinoflagellates (Cachonina niei, Ceratium furca, Gymnodinium splendens, and Prorocentrum micans) were studied in a thermally-stratified Plexiglas column (1.70 m deep, 0.61 m diameter). All species migrated through temperature gradients exceeding 7 C°. Some species exhibited altered migration patterns at different salinities either between experiments or compared to observations by other investigators. P. micans exhibited complex changes in swimming speed that depended both on temperature and on the light cycle. These changes provide insight into the possible time course of a field organism's diurnal exposure to physical variability in the water column. P. micans exhibited compositional changes in response to the light cycle, but not to the cross-thermocline temperature differential. A multi-parameter response matrix is required to model coupling between organisms and biologically-active physical mechanisms realistically.

Tidal Variation in Sediment Densities of Marine Benthic Copepods

Abstract: Recent studies have shown that meiofauna frequently occur in the water column and may be highly mobile due to suspension by water currents or any process that disturbs the sediments. We hypothesized that tidal variability in meiofauna sediment densities and distributions may be significant. As a test of this hypothesis, replicate sediment cores were collected in intertidal, slope (creekbank just below water level), and subtidal muds to determine if densities of benthic copepods varied over a tidal cycle. As determined by analysis of variance, the number of copepods within each area clearly varied with the stage of the tide. In the intertidal and subtidal areas there were significantly more copepods in the sediment at both slack high and low tide than at flooding or ebbing tides. This pattern may be due to resuspension of meiofaunal copepods from the sediment into the water column via tidal current action. At the slope site such a tidal response was more complex and observations on the distribution of certain species in the 3 areas suggest that movement of animals occurred between intertidal and slope areas. All intertidal species did not display the same tidal response, and in the slope and subtidal areas all developmental stages (adults, copepodites, nauplii) did not display the same tidal response. These differences were likely due to differences in the size and/or behavior of adults vs juveniles. The processes which likely act to redistribute mud-meiofauna in many systems have hitherto been largely ignored, yet may have important consequences for the communities.

Geochemical Evidence for Modern Sediment Accumulation on the Continental Shelf off Southern New England

Abstract: An area of fine-grained sediment approximately 170 km 74 km in size, located in water depths between 60 m and 150 m, south of Martha's Vineyard, Mass., is a site of modern sediment deposition. The 14C ages systematically increase with sediment depth from about 1,300 years B.P. at the surface to 8,000-10,000 years B.P. at the depth of maximum core penetration. The old age for the surface sediments probably results from a combination of deposition of old carbon and faunal mixing. In the finest sediments, the sedimentation rates were approximately 130 cm/1,000 yrs when deposition began and have decreased to about 25 cm/1,000 yrs. The decreasing sedimentation rate reflects a diminishing source of fine sediments, which presuma ly came from the Georges Bank and Nantucket Shoals area. Inventories of excess 210Pb in undisturbed cores average 70 dpm/cm2 (disintegrations per minute per square centimeter), more than two times higher than the flux of 210Pb from the atmosphere and from 226Ra decay in the overlying water. This additional influx of 210Pb either must be with new fine-grained sediment material or from solutions that are stripped of their 210Pb by particulates in the bottom nepheloid layer. Stable Pb concentrations in surface sediments are about 28 ppm, as much as two times higher than concentrations at depth. The high accumulation rates, 210Pb inventories, and trace-metal profiles imply that this area is a modern sink for fine-grained sediments and for pollutants associated with particulate matter in the water column. To our knowledge, this is the only site of present-day natural deposition on the Continental Shelf off the eastern United States, exclusive of the Gulf of Maine. Because the net currents on the outer half of this Continental Shelf flow from northeast to southwest, this fine-grained deposit may receive its sediments and possible contaminants from the Nantucket Shoals and Georges Bank regions.

Supply of iron and manganese to an anoxic lake basin

Abstract: In seasonally anoxic lakes, the dynamic cycling of iron and manganese makes possible the study of geochemical cycling and processes of mineral formation, while the rapid lake processes may be a model for the analogous but slower oceanic processes. We have now measured concentration–depth profiles for iron and manganese to assess the flux of these elements from the sediments. The seasonal accumulation of iron in lake water can be accounted for by supply from the sediment, but the manganese profiles suggest that the major source of manganese is dissolution from particular material sedimenting through the water column.

Statistical analysis of estuarine profiles: Application to manganese and ammonium in the Tamar Estuary

Abstract: Results from numerical modelling of the Tamar Estuary suggest that the observed maxima in manganese and ammonium concentrations may be due to mixing of interstitial water rich in these components into the water column. A mathematical formulation of this proposal results in predictions which are tested statistically, using field measurements of water and interstitial liquid concentrations, with positive results.

Vertical distributions and diel migrations of Euthecosomata in the northwest Sargasso Sea

Abstract: Vertical distributions and seasonal variations in abundance of nine abundant or frequent pteropod species or subspecies in the northwest Sargasso Sea are described. Factor analyses yielded two groups, diel migrators and non-migrators. In terms of water column abundances, tows taken in August and November are similar, as are tows in December and April. Most species show significant within-species agreement in depth distribution over the year but high variability in abundance. Regression analyses using environmental parameters as independent variables show significant correlations of species abundances with temperature.

Methylmercury production in the marine water column

Abstract: Although the biosynthesis of methylmercury in sediments is well established1, this is not necessarily the exclusive natural source of methylmercury entering the marine food chain, particularly commercial fish and shellfish species for human consumption. An examination of mercury levels in freshwater fish2, collected from a lake with a history of industrial mercury contamination, suggested that levels in fish are controlled in part by mercury in suspension and it followed that methylation should occur in the water column. Although methylmercury is present in seawater in coastal areas receiving discharges of waste containing either inorganic mercury3 or methylmercury4 there is no evidence that methylmercury is actually formed in the water column. We now present data which demonstrate that inorganic mercury can be methylated in the water column and we compare this production with that known to occur in marine sediments.

Oxygen Availability and Seasonal Migrations of Ciliated Protozoa in a Freshwater Lake

Abstract: Migrations of ciliated protozoa between the benthos and water column of a productive lake are reversible and linked to seasonal changes in oxygen availability. Maximum densities of planktonic populations are maintained for periods of several months at depths where the oxygen concentration is 1 mgl-1 or less. With the possible exception of one genus (Loxodes) there was no evidence for periodic vertical migration within a season. The supposed unconditional requirement for oxygen in large free-living ciliates is questioned.

Physical Control of Phytoplankton Production under Sea Ice (Manitounuk Sound, Hudson Bay)

Abstract: In polar and subpolar seas, there are numerous accounts of phytoplankton blooms in the upper water column under the ice. Various mechanisms have been invoked to explain these blooms: the seeding of the underlying surface water by algal cells (epontic flora) released from the melting ice, the optimization of light utilization by the cells, and the stabilization of the upper water column by the low-salinity melting water. From studies conducted in Manitounuk Sound (Hudson Bay), it is proposed that phytoplankton blooms under the ice probably result from the simultaneous deepening of both the photic layer (seasonal light increase) and the stratified layer (low-salinity melting water). In ice-covered seas, the release of ice algae superimposes itself on the phytoplankton bloom, resulting in the observed algal increase under melting ice.Key words: phytoplankton, under-ice blooms, ice flora, stability, nutrients, Hudson Bay

Estuarine dredge and fill activities: A review of impacts

Abstract: Dredge and fill activities in estuaries have many environmental effects, most, although not all, of them deleterious. These effects include reduced light penetration by increased turbidity; altered tidal exchange, mixing, and circulation; reduced nutrient outflow from marshes and swamps; increased saltwater intrusion; and creation of an environment highly susceptible to recurrent low dissolved oxygen levels. Coral, oysters, and barnacles are particularly vulnerable to the effects of siltation. Both estuarine flora and fauna may be harmed by contaminants released into the water column by dredging operations. Ways to mitigate the effects of dredge and fill operations include careful pre- and post-construction environmental studies; use of bridging to create roadbeds where coastal wetlands cannot be avoided; use of a turbidity diaper and other means to control turbidity; dredging during periods of low benthic populations or during tides that would carry coarser sediments away from productive areas such as oyster reefs; and thoughtful disposal of spoil, such as locating spoil sites on the uplands with proper diking.

The temporal and spatial distribution of planktonic and benthic protozoan communities in a small productive lake

Abstract: An investigation into the spatial and temporal distribution of protozoa in Esthwaite Water, a small eutrophic lake in the English Lake District, was carried out from mid-June until late September, 1977, during the period of summer stratification. Quantitative analyses of planktonic protozoan populations were performed on water samples collected at 1 m intervals throughout the water column and individual depth-time distribution profiles were constructed for the major ciliate species. Population density and species succession of the benthic protozoa was also studied.

Phytoplankton ecology in an Antarctic lake

Abstract: SUMMARY. The ecology of the phytoplankton of Heywood Lake, Signy Island, South Orkney Islands, Antarctica was investigated during 1969–72. The lake, which is ice-covered for 8–10 months per year, is moderately eutrophic due to enrichment by seal excreta. The annual cycle of the phytoplankton is described. During the winter (approximately May-September), very few algal cells could be detected in the water column and 14C fixation was below measurable limits. In spring (October-November), a rapidly-growing population of algae caused a large increase in the chlorophyll-a concentration (maximum value 170 mg m−2) but carbon fixation remained low, with values 3 g C m−2 day−1 were measured on bright days. Values for Assimilation Number were very high (maximum value 10.5 mg C h−1 mg−1 (chlorophyll-a) in January (1971) though temperatures never exceeded 8°C. In autumn, the phytoplankton regressed to winter levels. Both spring and summer algal populations probably overwinter as resting stages.

Calcite Dissolution: An in situ Study in the Panama Basin

Abstract: The results of an in situ study of calcite dissolution in the Panama Basin indicate that the rate of dissolution in the water column increases suddenly below a water depth of about 2800 meters. This coincides with the depth at which the calcium carbonate content of surface sediments begins to decrease rapidly or the sedimentary lysocline. Since this level of increased dissolution both in the water column and on the sea floor does not appear to be related to the transition from supersaturation to undersaturation with respect to carbonate, there may be a kinetic origin for the lysocline in this region.

External and internal factors regulating metabolic rates of an estuarine benthic community.

Abstract: The structure and metabolism of a soft-sediment estuarine macrofaunal community were measured over an annual cycle at two depth-contours in mesohaline Chesapeake Bay. Additional data for plankton productivity and respiration, as well as seston and sediment organics are also summarized for these communities. Benthic community respiration ranged from 0.24-3.38 g O2 m-2 d-1, and significant differences were detected between the two depths. Similarly, macroinfaunal standing stocks reached 11.2 and 32.3 g (ash free) m-2 for 3 m and 6 m depth communities, respectively, and both exhibited mid-summer declines in abundance. Inferences drawn from these data facilitated a partitioning of benthic community respiration into macrofaunal and meiofaunal/microbial components with a residual term, much of which could be explained statistically by interactions between these two components. A multi-variate statistical model developed from these data matched benthic respiration measurements within 1-2 S.E. Mass-balances of organic carbon were estimated for water column and benthos at the two depthcontours for early and late summer, as well as for an entire, time-weighted year. These various analyses led to the tentative conclusions that this benthic community was regulated by such internal factors as macrofaunal/meiofaunal grazing and "microbial gardening", and by external factors such as temperature and predation by nekton. However, it appears that the ultimate control for this community was the supply of energy from organic carbon.