High Silicate Concentrations Research Articles

What Caused the Summer Replacement of Dominant Planktonic Algae in Lake Barato?

Dense water blooms of blue-green algae (Microcystis aeruginosa and Apha-nizomenon flos-aquae) had been observed in hypertrophic Lake Barato in the 1980s, but have not reappeared since 1990. Instead of these water blooms, diatoms (Melosira spp. and Cyclotella spp.) have dominated in summer. Orthophosphate (PO4-P) had been detected throughout the year, but since 1990 has apparently become depleted during May and June. In 1991, PO4-P concentrations increased in August and/or September, as did the biomass of blue-green algae (Anabaena spiroides or Phormidium spp.). These observations suggested that diatoms adapted to higher phosphorus limitation under conditions of low water temperature and high silicate concentration. Diatoms thus continued their dominance over blue-green algae because the latter could not grow in early summer due to a lack of PO4-P, most of which was taken up by the diatoms.

The influence of advection on the spatial variability of nutrient concentrations on the Texas-Louisiana continental shelf

Water column nutrient concentrations are presented for winter 1989 over the continental margin of the northwest Gulf of Mexico. Three physical processes advect waters of different nutrient concentrations onto the Texas-Louisiana shelf. These advection processes: (1) river discharge; (2) bay discharge; and (3) shelf-edge upwelling, influence the large-scale spatial variations of nutrient concentrations observed over the shelf. On the inner shelf near Atchafalaya Bay, river discharge injects high concentrations of silicate, phosphate, nitrate and nitrite into near surface water. Farther west, near Galveston and Port Aransas, inner shelf waters have high silicate and phosphate concentrations due to nutrient enrichment in the discharges from Galveston Bay and Corpus Christi Bay. Finally, upwelling at the shelf edge can introduce high nutrient midwater near the base of the mixed layer over the outer shelf. This upwelled water usually has higher silicate, phosphate and nitrate concentrations than those in the overlying surface water. However, if upwelled from below the nitrite maximum, the upwelled water can have quite low nitrite concentrations. The shelf edge upwelling is a result of bottom Ekman upwelling caused by a northeastward current on the outer shelf. At the shelf edge off Galveston the data show that upwelling was not occurring at the time of the study but dissolved oxygen saturation levels and nutrient concentrations show that it had occurred.

Selective and sensitive spectrophotometric determination of tetrafluoroborate in waste water after ion-pair extraction using bis[2-(5-chloro-2-pyridylazo)-5-diethylaminophenolato]cobalt(III) as a counter ion

A simple, selective and sensitive method has been proposed for the ion-pair extraction and spectrophotometric determination of tetrafluoroborate in waste water. Tetrafluoroborate is extracted as an ion pair with bis[2-(5-chloro-2-pyridylazo)-5-diethylaminophenolato]cobalt(III) into chlorobenzene. The absorbance of the organic phase is measured at 567 nm against a reagent blank. Beer's law is obeyed over the concentration range 0.05–1.0 mg l–1 of tetrafluoroborate and the detection limit (three times the standard deviation of the blank) was 0.009 mg l–1. Relative standard deviations were 0.6–2.0%. Nitrate seriously interferes with the determination but can be decomposed by shaking with zinc powder after adjusting the acidity with 0.05 mol l–1 sulfuric acid. The proposed method can be applied satisfactorily to the determination of tetrafluoroborate in industrial and laboratory waste waters containing high concentrations of fluoride, chloride, nitrate, sulfate, borate, silicate and many other metal ions.

A toxic dinoflagellate bloom and PSP production associated with upwelling in Golfo Nuevo, Patagonia, Argentina

In 1980 Paralytic Shellfish Poison (PSP) was detected for the first time in Patagonia (Argentina), and has been recurring since during spring and summer. Human intoxicantions were recorded during the 1987/88 sumer due to ingestion of mussles. In January, concentrations of 750 000 cell l−1 were observed, decreasing to 3100 cells l−1 twenty days later. At the same time, values of 66 150. Mouse Unit (MU) 100 g−1 of meat were measured in Aulacomya ater (a bivalve mollusk). A decrease in the concentration of toxic plankton resulted in a concomitant decrease in MU values. The mean detoxification time was 7.6 days. However, mussels retained toxicity up to 50 days after the disappearance of cells. The upwelling of cold waters at the beginning of summer, could have been one of the causes that favoured a bloom of Alexandrium excavatum and of Prorocentrum micans. In March, an abundance of the diatom Skeletonema costatum coincided with high concentrations of silicate.

The record of Ontong Java Plateau: Main results of ODP Leg 130

The drilling campaign of ODP Leg 130 on Ontong Java Plateau resulted in the recovery of complete Neogene sections at several depths, providing materials for detailed biostratigraphic and paleoceanographic studies in the western equatorial Pacific. The acquisition of extensive logging records and high-resolution physical-property data allow detailed correlation from hole to hole and from site to site and provide the basis for a paleoceanographic interpretation of acoustic reflectors. We drilled 16 holes at 5 sites on the north-eastern flank of the plateau (Sites 803 through 807). All sites are close to the equator, at water depths ranging from 2,500 m to 3,900 m. Sites 803 and 807 penetrated into basement (26 m and 149 m, respectively). The K/T boundary was recovered at both of these sites. Neogene sedimentation rates decrease with depth, as expected, but this decrease is much greater than calculated from carbonate content, under the assumption that carbonate dissolution is the sole cause of the decrease. At any one site, sedimentation rates vary by a factor of more than two, with a striking maximum in the latest Miocene to early Pliocene, and strong minima in late early to early middle Miocene and in the Pleistocene. Many acoustic reflectors correlate between sites, within the limits of stratigraphic resolution. This suggests paleoceanographic events as a cause, generating changes in physical properties of sediments at the time of deposition. Many of the reflectors occur at carbonate reduction events (CRE's). Some apparently are the product of diagenetic enhancement of property changes, as, for example, within the ooze/chalk transition (which is diachronous). The interval corresponding to the Cretaceous/Tertiary (K/T) transition in the area is characterized by the presence of a deep CCD. The sequence at one site is calcareous; that at the other, is not. The fact that the two K/T sections recovered occur in sequences with major hiatuses suggests special conditions for preservation during the transition. We propose early cementation caused by high silicate concentrations in an ocean with greatly reduced productivity. The basalt cored at Sites 803 and 807 is predominantly aphyric to sparsely olivine or plagioclase phyric; the last flows are Albian to Aptian in age. At Site 807, pillow lavas buried sediments. One very thick flow (∼28 m) was penetrated here, possibly a flood basalt, indicative of massive outpourings on Ontong Java Plateau during the middle Cretaceous.

Recirculating components to the deep boundary current of the northern North Atlantic

The meridional overturning system of the North Atlantic is conventionally thought of as transporting warm water (≡ ≥4°C) to high latitudes and covd water to low latitudes. The northern cold water sources for this system are dense overflow from the Nordic Seas and less dense water from the labrador Sea (LSW). The overflow components are carried westward by a deep northern boundary current (DNBC) that is shown here actually to begin southeast of the overflow regions. The DNBC lies along the southern side of a system of islands and submarine ridges that divides the Nordic Seas from the subpolar basins. The overflows act to increase the transport of the DNBC, and this transport is further increased through the entrainment of warm waters. Once inside the Labrador Sea, the DNBC is joined by LSW before continuing south to low latitudes as a cold, deep western boundary current (DWBC). However, published transport estimates are larger than can be explained by warm water entrainment alone, thus indicating entrainment also of recirculating cold components, the subject of this paper. Their sources are shown to be the LSW and cold abyssal waters originating from the southern hemisphere. The LSW is entrained downward into the denser part of the DNBC and laterally into the upper part of the DWBC, whereas the cold abyssal waters are supplied by an eastern-intensified northward flow in the eastern Atlantic (that serves as the initial source of the DNBC) and by a similar northward flow in the western Atlantic. The meridional overturning system described includes recirculations and poleward transport of cold water in addition tothe components described by the conventional system. The cold abyssal waters in both the eastern and western basins have relatively low levels of oxygen and high concentrations of silicate reflecting their southern origin, but their influence in the northwestern Atlantic is somewhat obscurred by strong recirculating cyclonic gyres in the Newfoundland and Labrador Basins. This influence is detected by a deep silicate maximum extending poleward from the mid-latitude western Atlantic through the two gyres with eastern concentration and recirculating back (diluted) toward the south in the DWBC within the respective basins. Such a maximum also extends northward through the Irminger Basin into the DNBC, but there is an ambiguity as to whether this is a direct extension of the signal from the south in the western basin, or if it comes from the mid-latitude eastern basin by way of westward flow through the Charlie-Gibbs Fracture Zone; it is perhaps consequence of both. Estimates of the volume transports of the various recirculating cold components indicate that they supply about as much water to the deep boundary currents as do the combined cold water sources in the north.

Concentrations of copepod nauplii associated with the nutrient-rich plume of the Mississippi River

During spring and summer, discharge plumes of the Mississippi River were located visually by water color. Temperature, salinity, nutrients, chlorophyll a and copepod nauplii were sampled coincidently in a cross-plume direction. Plume waters contained high concentrations of nitrate, silicate and chlorophyll during both spring and summer. Nitrate was depleted before silicate during summer but not during spring. During spring, concentrations of copepod nauplii (50–100 l −1) were similar to those reported in an earlier wintertime study in this region. Summertime concentrations of nauplii were much higher, sometimes 1000l −1. Nauplii were associated with plume waters. Strong seasonality in zooplankton production is suggested, with greatest production in summer. Consequently, a larger proportion of plume phytoplankton production should sink directly to the bottom during spring and a larger proportion of the summertime production should be consumed in the water column by grazers.

Sorption and desorption isotherms for silicate on gibbsite

Sorption and desorption of silicate on gibbsite were investigated. The sorption isotherm was complex, and consisted of Langmuir behavior at low silicate concentrations and Freundlich behavior at high silicate concentrations. The transition region was characterized by interaction between adsorbed silicate ions and multilayer adsorption or cluster formation; this corresponds to the onset of formation of a sodium aluminum silicate phase. The equilibrium sorption isotherm data reported here corroborate the scheme proposed to explain the sorption kinetics results reported elsewhere. The desorption data conformed to a Freundlich isotherm. In addition, desorption of silicate decreased with increasing silicate concentration in the solution, and reached a constant value at a solution concentration of 80 μgSiO2/cm3 and beyond. Desorption was larger at lower temperatures.

A comparative study of the trace metal fluxes of t the Bang Pakong and the Mae Klong Rivers, Thailand

Of the four major rivers draining into the Upper Gulf of Thailand, the Bang Pakong and the Mae Klong Rivers were selected for study of their inputs to the coastal zone because of their distinctive water characteristics. The Bank Pakong River drains acidic soils, while the Mae Klong is slightly alkaline and contains high concentrations of silicate and calcium. Both rivers were studied during the dry and wet seasons. It was found that, in the Bang Pakong, there appeared to be removal of some dissolved trace metals of particulates in the low-salinity region of the estuary, while this behaviour was not found in the Mae Klong River. In the Mae Klong, the high amount of particulates in the freshwater stretch of the river precipitated quickly in the low-salinity region.

Formation of Water-Soluble Silicate Gels by the Hydrolysis of a Diester of Dicarboxylic Acid Solubilized as Microemulsions

Summary Relatively inexpensive sodium silicate gels are attractive candidates for large-scale well conformance treatments. For a successful treatment, gelation must be delayed to permit proper placement of the silicate solution within the reservoir, to minimize rock/fluid interactions during placement, and to ensure long-term gel stability. We investigated each of these process phases, focusing on stable high-pH (≈11) sodium silicate solutions ranging up to 10 wt% SiO2 concentration. The addition of an acid or alcohol will cause these high-pH sodium silicate solutions to gel. To regulate the gelling time, an organic material that reacts with water to produce an alcohol and/or acid is often mixed with the silicate solution. An organic rather than inorganic compound is selected because the slow organic reaction rates yield a controlled gelation. The choice of the organic compound normally is quite limited because it must possess sufficient water solubility to be present in the quantities needed to cause gelling. This study shows that diesters, which hydrolize to produce both acid and alcohol, can be solubilized into silicate solutions as a microemulsion (not a macroemulsion), thus eliminating this limitation. All the rules developed with regard to selection of surfactants for EOR also apply to sodium silicate solutions. Field processes should use caustic preflushes to propagate silicate solutions deep into the formation. Long-term stability studies showed that, upon standing for several weeks, silicate gels tend to contract, expelling water. This process, called syneresis, clearly will affect the long-term effectiveness of a silicate treatment. We investigated syneresis over a wide range of silicate concentrations and temperatures. Gels formed from the high silicate concentrations exhibited the greatest degree of syneresis; up to an 80% decrease in volume. Increasing the temperature increased the syneresis. Some degree of syneresis may be desirable because all treated zones will retain residual permeability.

Chemical oceanography of the Indian Ocean, north of the equator

Chemical oceanographic studies in the North Indian Ocean have revealed several interesting and unique features. These are caused by the diverse conditions prevailing in the area which include immense river runoff in the northeast (Bay of Bengal) and a large excess of evaporation over precipitation and runoff in the northwest (Arabian Sea, Persian Gulf and Red Sea), resulting in the formation of several low- and high-salinity water masses. The occurrence of coastal upwelling seasonally makes the region highly fertile, and the existence of Asian landmass, forming the northern boundary, prevents quick renewal of subsurface layers. Consequently, dissolved oxygen gets severely depleted below the thermocline and reducing conditions prevail at intermediate depths (ca. 150–1200m) resulting in the reduction of nitrate (denitrification). The North Indian Ocean may contribute up to 10% of the global marine denitrification. The “denitrified” nitrogen, when combined with the rate of photosynthetic production reaching below the euphotic zone, gives the average residence time of water between 75 and 1200m as 43–51 years. The inorganic nutrient concentrations in the subsurface layers are very high in close proximity of the euphotic zone. The two-layered circulation leads to an active recycling of nutrients. The presence of organic fractions of nitrogen and phosphorus in significant concentrations in the deep water suggest that oxidation of organic matter is incomplete even great depths. The relationships between the apparent oxygen utilization (AOU) and nutrients and the stoichiometric composition of organic matter, deduced from the oxidative ratios and by analysis of plankton, are not very different from other oceanic areas. Higher nutrients and lower oxygen concentrations occur in the bottom layer as compared to the overlying water column in deep waters of the Bay of Bengal and Arabian Sea, suggesting that considerable quantities of organic matter reach the deep-sea floor, probably as fecal pellets, and get oxidized in the bottom layer. Very high silicate concentrations occur in the bottom water, especially in the Arabian Sea, decreasing steadily southward, indicating the solution of diatomaceous sediments from the sea floor. The silicate-rich waters appear to move southward over the north-bound, silicate-poor bottom water, resulting in the occurrence of a deep silicate maximum. The calcium: chlorinity ratio in the North Indian Ocean is appreciably higher than the oceanic averages. This is probably due to: (1) a high rate of river runoff in relatively small area; and (2) excessive stripping of calcium at the surface associated with a high biological productivity and its subsequent addition and regeneration in the bottom waters. The upward flux of calcium appears to be higher than in other oceanic areas. Other major constituents investigated (fluoride and magnesium) do not show any anomally. The partial pressure of carbon dioxide in surface waters of the North Indian Ocean is higher than that in the atmosphere which results in a net flux of carbon dioxide from the sea to the atmosphere. Stagnation of intermediate layers, coupled with high organic productivity at the surface, results in high total carbon dioxide content at these levels. An increase in carbonate ion concentration occurs with depth in deep waters (>1000m). Calcite saturation depth varies from 1000 to 3000m, increasing proressively southward. The lysocline lies at about 4000m depth, while the carbonate critical depth is located at 4000–5100m. The lysocline appears to be related to the “critical carbonate ion concentration” of 90±5 μm kg −1.

Pathways of carbon assimilation in phytoplankton from the Antarctic Ocean1

The assimilation of [14C]bicarbonate into the major end‐products of photosynthesis was measured at five stations in the Southern Ocean. Under conditions of low light intensity and low temperature (<0°C) phytoplankton incorporated as much as 80% of the fixed carbon into lipid, with insigificant incorporation into protein. At higher temperatures (>0°C) and higher light intensities incorporation into lipid accounted for <20% of the fixed carbon, the synthesis of polysaccharide and (to a lesser extent) protein being more prominent. Populations showing high rates of incorporation of 14C into lipid have high PC:Chl ratios, high PC:PN ratios, and low C‐specific rates of 14C assimilation. All populations were dominated by diatoms. High concentrations of nitrate, phosphate, and silicate argue against the concept of nutrient limitation. This pattern of photosynthesis differs from that observed in many other parts of the oceans. It is suggested that the prominent synthesis of lipid is a response to extremely low temperatures and is enhanced by the additional stress of low light intensities.

Physical and biological characteristics of an upwelling at a station off La Jolla, California during 1971 1

A station located 1 km west of Scripps Institution of Oceanography pier La Jolla, California was occupied 15 times in the 57-day period from 9 February to 7 April, 1971. The condition of the environment and of the phytoplankton community was observed before, during and after a major upwelling (26 February to 1 March). Classical interaction between the environment and the phytoplankton was followed for three weeks after the strong WNW winds declined. The biological succession initiated by the upwelling ended on 22 March when a new water mass marked by a high silicate concentration apparently entered the area by surface transport.

Chemical aspects of the production of television tube screen. III. The dry screen

AbstractThe adhesion of phosphor to glass in the dried screen has been measured. It was found to depend on the quantity and composition of the solution left in the screen pores after removal of the bulk of the settling liquid. Adhesion was produced by drying of the solute. Delay between draining and drying allowed gelation to proceed, thereby reducing the quantity of dry binder available.Migration of solution through the screen towards the drying patch, if allowed to proceed for too long a time, caused uneven binder distribution.Measurement of the light output of screens under electron excitation confirmed the usual effect of variation in screen thickness on screen luminescence. Whilst controlling screen thickness, factors in settling were varied, but these factors were found to be irrelevant as long as good screen structure was maintained. Type and purity of potassium silicate had no effect within the usual settling range. Flocculation or very high silicate concentration depressed light output, but could be easily avoided.