Showing papers on "Water column published in 1988"

Denitrification in freshwater and coastal marine ecosystems: Ecological and geochemical significance

Abstract: Denitrification occurs in essentially all river, lake, and coastal marine ecosystems that have been studied. In general, the range of denitrification rates measured in coastal marine sediments is greater than that measured in lake or river sediments. In various estuarine and coastal marine sediments, rates commonly range between 50 and 250 µmol N m−2 h−1, with extremes from 0 to 1,067. Rates of denitrification in lake sediments measured at near-ambient conditions range from 2 to 171 µmol N m−2 h−1. Denitrification rates in river and stream sediments range from 0 to 345 µmol N m−2 h−1. The higher rates are from systems that receive substantial amounts of anthropogenic nutrient input. In lakes, denitrification also occurs in low oxygen hypolimnetic waters, where rates generally range from 0.2 to 1.9 µmol N liter−1 d−1. In lakes where denitrification rates in both the water and sediments have been measured, denitrification is greater in the sediments. The major source of nitrate for denitrification in most river, lake, and coastal marine sediments underlying an aerobic water column is nitrate produced in the sediments, not nitrate diffusing into the sediments from the overlying water. During the mineralization of organic matter in sediments, a major portion of the mineralized nitrogen is lost from the ecosystem via denitrification. In freshwater sediments, denitrification appears to remove a larger percentage of the mineralized nitrogen. N2 fluxes accounted for 76–100% of the sediment-water nitrogen flux in rivers and lakes, but only 15–70% in estuarine and coastal marine sediments. Benthic N2O fluxes were always small compared to N, fluxes. The loss of nitrogen via denitrification exceeds the input of nitrogen via N2 fixation in almost all river, lake, and coastal marine ecosystems in which both processes have been measured. Denitrification is also important relative to other inputs of fixed N in both freshwater and coastal marine ecosystems. In the two rivers where both denitrification measurements and N input data were available, denitrification removed an amount of nitrogen equivalent to 7 and 35% of the external nitrogen loading. In six lakes and six estuaries where data are available, denitrification is estimated to remove an amount of nitrogen equivalent to between 1 and 36% of the input to the lakes and between 20 and 50% of the input to the estuaries.

Nuisance phytoplankton blooms in coastal, estuarine, and inland waters1

Abstract: Multiple interacting physical, chemical, and biotic factors, in proper combination, lead to the development and persistence of nuisance algal blooms. Upon examining combinations of environmental conditions most likely to elicit nuisance blooms, commonalities and analog situations become more apparent among coastal marine (dinoflagellate-dominated), estuarine (dinoflagellate- and cyanobacteria-dominated), and freshwater (cyanobacteria-dominated) ecosystems. A combination of the following hydrological, chemical, and biotic factors will most likely lead to bloom-sensitive waters: a horizontally distinct water mass; a vertically stratified water column; warm weather conditions, as typified by dry monsoon tropical climates and summer seasons in temperate zones; high incident photosynthetically active radiation (PAR); enhanced allochthonous organic matter loading (both as DOC and POC); enhanced allochthonous inorganic nutrient loading (nitrogen and/or phosphorus); adequate availability of essential metals, supplied by terrigenous inputs or upwelling; underlying sediments physically and nutritionally suitable as “seed beds” for resting cysts and akinetes; algal-bacterial synergism, which exhibits positive impacts on phycosphere nutrient cycling; algal-micrograzer (protists and rotifers) synergism, which also enhances nutrient cycling without consumption of filamentous and colonial nuisance taxa; and selective (for non-nuisance taxa) activities of macrograzers (crustacean zooplankton, larval fish). Nuisance bloom taxa share numerous additional physiological and ecological characteristics, including limited heterotrophic capabilities, high degrees of motility, and toxicity. Given such a set of commonalities, it would appear useful and timely to identify and address generally applicable criteria for deeming a water body “bloom sensitive” and to incorporate such criteria into the design of water quality management strategies applicable to both coastal marine and freshwater habitats.

Phytoplankton, nutrients, and turbidity in the Chesapeake, Delaware, and Hudson estuaries

Abstract: Estuaries receive continuous inputs of nutrients from their freshwater sources, but the fate of the inputs is poorly known. In order to document nutrient removal from the water column by phytoplankton, we measured the distributions of turbidity, nutrients, and phytoplankton across the salinity gradients of three estuaries: Chesapeake Bay, Delaware Bay, and the Hudson river estuary. Mixing diagrams were used to distinguish between conservative and non-conservative behavior; i.e. between loss from the water column and export to the estuarine plume on the shelf. In Chesapeake and Delaware Bays, we frequently observed a turbidity maximum in the oligohaline region, a chlorophyll maximum in clearer waters seaward of the turbidity maximum, and a nutrient-depleted zone at the highest salinities. In the Hudson River estuary, mixing diagrams were dominated by lateral waste inputs from New York City, and nutrient removal could not be estimated. In Chesapeake Bay, there was consistent removal of total N, nitrate, phosphate, and silicate from the water column, whereas in Delaware Bay, total N, ammonium, total P, and phosphate were removed. Total N and P removal in the Chesapeake and Delaware are estimated as ca. 50%, except for TP in the Chesapeake, which appeared to be conservative. Phytoplankton accumulation was associated with inorganic nutrient removal, suggesting that phytoplankton uptake was a major process responsible for nutrient removal. In the high salinity zone near and in the shelf plume, an index of nutrient limitation suggested no limitation in the Hudson, slight or no limitation in the Delaware, and widespread limitation in the Chesapeake, especially for P. These observations and information from the literature are summarized as a conceptual model of the chemical and biological structure of estuaries.

Pelagic-benthic coupling on the shelf of the northern Bering and Chukchi Seas. I. Food supply source and benthic bio-mass

Abstract: The shelf waters of the northern Bering and Chukchi Seas are ice-covered for 7 mo of the year, but despite thls harsh environment, they are characterized by high benthic biomass. Coupling between water column primary production and the benthos was investigated in summers 1984 to 1986 by measurements of sediment characteristics in relation to those of the water column. Low surface sediment C/N ratios (5.8 to 7.6) suggested a higher quality, nitrogen-rich marine carbon supply to the benthos in the highly productive (ca 250 to 300 g C m-' yr-') Bering Shelf-Anadyr Water (BSAW) compared to lower quality, higher C/N ratios (7 7 to 14 0) in sediment under the less productive (ca 50 g C m-' yr-l) Alaska Coastal Water (ACW). Stable carbon isotope ratios suggested a manne origin for organic matter in BSAW compared to a mixture of manne and terrestrial input in ACW. Mean benthic biomass was significantly different between water locations, with mean benthic biomass decreasing from 20.2 g C m-* under BSAW to 6.3 g C m-2 under ACW Summer benthic biomass remained seasonally constant for the 3 yr. Benthic communities underlying BSAW received a high quality marine food supply on a regular basis interannually, while those in ACW received an interannually variable amount of temgenous organic matter in addition to marine organic matter. We conclude that the quality and quantity of organic carbon deposited to the benthos directly influence benthic biomass.

Organic matter sources to the water column and surficial sediments of a marine bay

Abstract: Sediment trap and net plankton samples were collected monthly for a year at three depths in a marine bay (Dabob Bay, Washington). These materials and subsamples from a sediment box core were analyzed for lignin oxidation products as well as elemental and stable carbon isotope compositions. The sediment core was compositionally uniform over its entire 50-cm length. The elemental and lignin compositions of the sediment trap and core samples indicate nitrogen-rich (atomic C : N = 7.5) plankton-derived organic matter mixed with vascular plant debris. At most, vascular plant debris accounts for 10% (nonwinter months) to 35% (winter months) of the total organic carbon in the upper water column (30 m) sediment trap samples and consists predominantly of gymnosperm wood along with some nonwoody gymnosperm tissues and angiosperm woods. Bulk land-derived organic matter in Dabob Bay contains a maximum of 50% vascular plant debris and comprises an average of one-third of the total organic carbon in the sediment trap samples and two-thirds of the total organic carbon in the underlying sediments. Lignin in the sediment trap and core samples shows evidence (from elevated vanillic acid:vanillin ratios) of white-rot fungal degradation before (but not after) introduction to the water column at the study site. Vascular plant debris introduced to the bay has already lost almost half of its initial bulk polysaccharide. Glucose yields are particularly low whereas rhamnose and fucose are obtained in excess of expected yields and must have additional sources. Lignin and neutral sugars together account for ~20% of the total organic carbon in the sediment trap and core samples. Overall, the sediments of Dabob Bay compositionally resemble the gymnosperm wood-rich particulate material introduced to the overlying water column during winter and poorly record the input of plankton and other types of vascular plant debris during nonwinter months.

Seasonality in East Africa's coastal waters

Abstract: A review of existing literature and data on seasonal patterns in East Africa's coastal waters indicates distinct seasonality in physical, chemical and biological oceanographic parameters. Seasonal patterns are dictated by the behavior of the Inter-Tropical Convergence Zone (ITCZ) which creates 2 distinct seasons the northeast and southeast monsoons. SE monsoon (March to October) meteorological parameters are characterized by high cloud cover, rainfall, river discharge, terrestrial runoff and wind energy while solar insolation and temperatures are low; SE monsoon oceanographic parameters are characterized by cool water, a deep thermocline, high water-column mixing and wave energy, fast currents, low s a h ~ t y and high phosphorus. These parameters are reversed during the NE monsoon. Nitrogen availability and planktonic primary productivity are high along the Somali coast and estuarine and river discharge areas during the southeast monsoons due to nutrient upwelling and terrestrial runoff. In near-shore waters off Tanzania, nitrogen fixation is the major source of nitrogen and is highest during NE monsoons when the water column is stable. Coral reef benthic algal biomass and diversity is greatest during the SE monsoons. Fish catch and reproduction are highest during NE monsoons in Kenya and Tanzania. Transition periods between monsoons may also be important times in determining productivity and reproduction.

Fluxes and reactivities of organic matter in a coastal marine bay

Abstract: Vertical fluxes of bulk particulate material, organic carbon, nitrogen, lignin-derived phenols, and neutral sugars through the water column and into surface sediments of Dabob Bay, Washington, were determined monthly for 1 yr by sediment trap deployments at 30, 60, and 90 m at a site 110 m deep. Vertical fluxes of sinking bulk particulate material in this marine bay were elevated during winter and increased in consistent proportion to sediment trap deployment depth throughout the year. Although annual average particle fluxes at 30 and 60 m bracketed the mean accumulation rate of the underlying sediment, the flux at 90 m was higher by a factor of 2 due to resuspension, horizontal advection, or both. The monthly fluxes of lignin-derived phenols paralleled those of total particulate material, indicating a common riverine origin. The annual average fluxes of vanillyl and cinnamyl phenols through the water column closely matched the corresponding accumulation rates in the underlying sediment, whereas about a third of the total syringyl phenol input was degraded at the watersediment interface. Although p-hydroxyacetophenone exhibited a stability typical of lignin-derived phenols, the distinctly higher reactivities (> 60% degradation) ofp-hydroxybenzaldehyde and p-hydroxybenzoic acid indicate a predominantly nonlignin source. On average, 60 and 70%, respectively, of the total particulate organic carbon and nitrogen and 65-75% of all neutral sugars settling through the midwater column were degraded at the watersediment interface. The elemental and carbohydrate composition of the degraded material was similar to that of local net plankton except for higher percentages of glucose and total neutral sugars. Land-derived organic material accounted for about one-third of the total organic carbon passing through the midwater column and two-thirds of the organic carbon accumulating in the underlying sediments. The amounts of plankton-derived organic matter sinking through the midwater column and being preserved in the sediments below corresponded to 14 and 3% of the annual mean primary productivity. Plankton-derived organic matter exhibited about 5 times the reactivity of local land-derived organic matter at the water-sediment interface of Dabob Bay and supported essentially all of the benthic respiration.

Comparative transparency, depth of mixing, and stability of stratification in lakes of Cameroon, West Africa1

Abstract: Morphometry, oxygen concentration, temperature, and transparency were studied in 39 natural lakes in Cameroon, West Africa. Thermal profiles from 3 1 of the lakes and data from published studies were used to calculate stability of thermal stratification and evaluate morphological correlates of mixing depth. Twenty-six lakes showed some degree of stratification and 17 had distinct thermoclines and well-developed, anoxic hypolimnia. Total stability of the water column ranged from 0 to 5,784 J m-2. The high values were similar to or greater than those of other tropical and temperate lakes. Lake depth seems to exert a stronger influence on stability than does lake area, but depth or stability measures alone provide little information about heat distribution or mixing regime. A strong positive relationship between water transparency and thermocline depth in both tropical and temperate lakes suggests that reductions in buoyant resistance to vertical mixing, caused by deeper penetration of solar radiation, are important in establishing mixing depths in various lakes. Comparisons of persistent thermocline depth in tropical vs. temperate lakes, regardless of size, indicate that mixing depths in tropical lakes are often greater than those in their temperate counterparts. This difference is caused in part by the narrow ranges of temperature and smaller absolute density gradients in these tropical lakes, against which the mixed layer is deepened.

Planktonic bloom-forming Cyanobacteria and the eutrophication of lakes and rivers

Abstract: SUMMARY. 1. Eutrophication of water bodies involves the enrichment of plant nutrients, often followed by significant shifts in the phytoplankton towards Cyanobacteria. When comparing different aquatic systems, even with similar nutrient contents and in the same climatic region, inverse deductions are not valid; i.e. (a) the presence of Cyanobacteria does not necessarily indicate eutrophic conditions, or (b) eutrophic or even poly-trophic conditions do not necessarily support cyanobacterial development. 2. Above a threshold of 10 μg 1−1 total phosphorus, the development of Cyanobacteria can be described by physical factors, such as water column stability. By characterizing different forms of turbulence, the presence or absence of Cyanobacteria in lakes and rivers can be predicted. 3.When the turbulence of the water column is rather low, as it is in sheltered or meromictic lakes, Cyanobacteria can build up dense populations. In nutrient poor systems, species of Oscillatoria and (seldom) Aphanizomenon are dominating. 4.If the turbulence of the water column is high (mixing depth much greater than euphotic depth) or the mixing pattern is irregular, as in slowly flowing or regulated rivers, Cyanobacteria are outcompeted. 5. In the presence of frequent or permanent turbulence, but with mixing depths lower or not much greater than the euphotic zone (as it is the case in shallow, unstratified lakes, mostly eutrophic or even hypertrophic), Cyanobacteria can outgrow normally dominant r-strategists under conditions of low N:P ratios, high water temperatures, pH >9.0 or low light availabilities. 6. If turbulence is comparatively great (10 to $15 m) and stable for a longer period of time, some cyanobacteria are able to adapt. 7. Our statements are discussed on the basis of physiological characteristics.

Depositional model for shallow-marine manganese deposits around black shale basins

Abstract: Some of the world's largest and most valuable manganese resources formed as shallow-marine chemical sediments. We hypothesize that manganese deposition was on the margins of black shale (and related) facies of stratified seas. Manganese was deposited when deep anoxic water with high manganese solubility mixed with shallower oxygen-bearing water with low manganese solubility. The deposits show little or no evidence of volcanic contribution of manganese from nearby sources. The size of the manganese deposit varies with the vigor and dimensions of mixing and with the dissolved manganese content of anoxic deep water, the dilute ore-forming solution. The purity of the deposit depends on prior removal of dissolved iron from the system, primarily by pyrite precipitation in basinal environments, and on the absence of clastic dilution. Deposits may form one or two members of a zonal spectrum that includes sulfides, phosphorite, and barite. In many deposits there is evidence of great organic productivity, probably a by-product of vigorous mixing across stratification surfaces in the water column. Also common are primary sedimentary pisolites or oolites, glauconite, and biogenic silica.Manganese oxide facies deposition is preserved on oxic substrates in shallow water. Carbonate facies deposition can apparently be either on these oxic substrates or on reduced substrates in slightly deeper water. The reduced carbonate facies apparently forms by replacement of calcareous substrates by anoxic waters saturated with MnCO 3 , just below the water column redox interface. A single zoned deposit may show landward oxide facies and basinward reduced carbonate facies. Depositional regression may preserve the water column redox interface as a contact between overlying oxide facies and underlying carbonate facies manganese deposits.Stratigraphic evidence indicates that the deposits formed most commonly during high sea level stands in narrow time intervals when ocean anoxia was widespread. Eight manganese-precipitating modern environments and seven manganese deposits are described.

Methane cycling in the sediments of Lake Washington

Abstract: Aerobic oxidation is important in the cycling of methane in the sediments of Lake Washington. About half of the methane flux from depth is oxidized to CO, in the upper 0.7 cm of the sediments and the remainder escapes into the water column. In terms of the total carbon budget of the lake, the upward flux of methane is insignificant with only about 2% of the carbon fixed by primary production being returned as methane. The upward flux of methane, however, does represent about 20% of the organic carbon decomposed within the sediments. In addition, methane oxidation consumes 7-10% of the total oxygen

Phytoplankton growth rates in a light-limited environment, San Francisco Bay

Abstract: San Francisco Bay has a high degree of spatial variability in physical properties (e.g. suspended sediment concentrations, water depths, vertical mixing rates) that affect biological pro- cesses. We used this setting to test the hypothesis that light availability is the primary control of phytoplankton growth in this turbid nutrient-rich estuary. In situ incubations (24 h), designed to simulate vertical mixing over the water column at 2 rates, were done at 4 sites. The photic depth to mixed depth ratio (Z,,:Z,) at the 4 sites ranged from 0.12 to 1.1. Phytoplankton growth rates were estimated by 14C assimilation and by changes in cell number. Growth rates were highest (approximately 2 divisions d-I) where the photic depth was large relative to the mixed depth, and small or negalive where Z,:& was small. Growth rate increased with total daily light exposure and fit a hyperbolic function that predicts maximum specific growth rate of about 2 divisions d-' and a compensation irradiance of about 1.4 Einst. m-2 d-l.

Pigment and lipid compositions of algal and bacterial communities in Ace Lake, Vestfold Hills, Antarctica

Abstract: The compositions of carotenoids, chlorophylls and lipids at four depths in Ace Lake have been determined as a means of studying the vertical zonation of species in the lake and for comparison with the lipids found in the bottom sediments. The four major species of phytoplankton found in the lake were identified by electron microscopy. The most abundant phytoplankter was Pyramimonas gelidicola McFadden (Chlorophyta, Prasinophyceae) which occurred in greatest numbers at 10 m, the base of the oxylimnion. The pigments and lipids at this depth were mainly derived from this alga. At 11 m (the top of the anoxylimnion) only traces of lipids and pigments attributable to P. gelidicola were found, indicating only limited settling of algal cells through to the anoxylimnion, at least in summer. The pigments at 11 m were dominated by bacteriochlorophylls c derived from green photosynthetic bacteria Chlorobium spp. These pigments were also abundant at 23 m suggesting the presence of intact bacterial cells which had settled out from higher in the water column. Major non-polar lipid classes in the sediments included sterols, alcohols, hydrocarbons and an unusual suite of very long-chain unsaturated ketones and esters which have not previously been reported from antarctic environments. Several novel compounds, not found previously in either sediments or organisms, are reported. These include tri- and tetra-unsaturated straight-chain C39 methyl ketones and C40 ethyl ketones and the methyl ester of a tetra-unsaturated straight-chain C36 fatty acid. The distributions of lipids in the sediment were markedly different from those in the water column indicating extensive bacterial degradation and recycling of labile lipids.

Tracers of chemical scavenging in the ocean: boundary effects and large-scale chemical fractionation

Abstract: Several nuclides in the natural radioactive decay series display a strong non-conservative behaviour in the oceanic water column because of their removal to the sediments by uptake at the solid—solution interface. This removal process is commonly referred to as scavenging, and it is believed to be important in governing the behaviour of many heavy metals and other trace substances in the ocean. Measurements of radioactive disequilibrium in seawater yield estimates of the rate at which scavenging occurs. Results show that removal times by scavenging are comparable to within-basin lateral mixing times. It follows that the distribution of the scavenged tracers should be sensitive to the spatial distribution of their sinks, and this has been demonstrated by observation, most notably in the case of 210 Pb. The distribution of 210 Pb suggests a strong control by intensified uptake at boundaries, especially at the ocean margins. This conclusion has been confirmed by sediment traps and by measurements of 210 Pb accumulations in the sediment column. A similar phenomenon of intensified scavenging at ocean margins has been observed for 231 Pa. Studies with 230 Th, on the other hand, show that its delivery to the sediments is mainly caused by the local flux of sinking particles. Thus two transport pathways for removal by scavenging are envisioned, one with a strong horizontal component due to the intensified uptake at the margins and the other with a strong vertical component due to the particle flux. Important large-scale chemical fractionations, best illustrated by comparative studies of 230 Th and 231 Pa, are produced by differential partitioning of elements between these two pathways. Model calculations suggest that horizontal mixing rate and particle flux are important variables controlling the partitioning of reactive chemical substances between pelagic sediments of the interior ocean and hemipelagic sediments of the ocean margins. Changes in the extent of this partitioning through time may be recorded as changes in the 230 Th/ 231 Pa ratio through the sediment column.

Cycling of dissolved rare earth elements in Chesapeake Bay

Abstract: The measurement of dissolved rare earth elements (REE) in the surface waters, water column of anoxic basins, and pore waters in Chesapeake Bay has provided new insights to the biogeochemistry and estuarine chemistry of REE. All dissolved REE from the riverine source show large-scale removal in the lower salinity zone (0-10‰). The shale-normalized pattern of dissolved Susquehanna River water is opposite in form to that of surface sediments in the Bay. The former is enriched in heavy REE (HREE) while the latter are enriched in light REE (LREE). Neither component has a flat pattern normally assumed for river- transported REE to the ocean. The dissolved LREE (i.e., La, Ce, Nd, Sm, and Eu) are enriched 3 to 9 times) in the oxygen-depleted deep waters over their concentrations in the oxic surface waters. In contrast, HREE (Er, Yb, and Lu) are slightly depleted. All REE concentrations in the two surface (0-2 cm) pore waters are greatly enriched (8-17 times; 43 times for Ce) relative to oxygen-depleted bottom waters and have relative abundances opposite to those of their sediments. While Ce has a positive anomaly in the pore waters, negative anomalies exist in the oxygen-depleted bottom waters. The REE are participating in a set of complex biogeochemical cycles within the water column and surface sediments. Fractionation of REE during these cycles leads to the preferential enrichment of LREE in the seasonally oxygen-depleted bottom waters. It is proposed that this fractionation is coupled to redox cycles of Mn and Fe and the interaction of dissolved REE with suspended particles and surficial sediments.

Abundance and distribution of krill in the ice edge zone of the Weddell Sea, austral spring 1983

Abstract: The effect of the ice edge zone on the abundance and distribution of Antarctic krill was investigated by acoustic and net sampling methods in the northwestern Weddell Sea during austral spring, 1983. The dominant acoustic target was Euphausia superba which occurred over the entire study area in the upper 100 m of the water column, either in aggregations or loosely defined layers. The vertical depth distribution under the pack ice was similar to that of open water. Average krill biomass under the ice ranged from 1 to 68 g m −2 and in open water range from 10 to 100 g m −2 . Another euphausiid, Thysanoessa macrura , appeared to be ubiquitous but was much less abundant than E. superba. T. macrura also formed aggregations. All stages were found in open water, but only adults and juveniles under the ice. A few adults and larvae of a third euphausiid, E. frigida , were found only in open water. Salps, which were abundant in open water, were not present under the pack ice. The pack ice directly influenced the abundance and distribution of young krill. Juvenile E. superba were much more abundant under the ice than in open water north of the ice edge. Numerous observations were made of juvenile krill feeding on the undersurface of ice floes where chlorophyll concentrations were much greater than in the water column below. These observations appear to indicate that the pack ice serves as a giant nursery area for young krill, providing a refugium from predators as well as a vast food resource that may be critical to the survival of overwintering juvenile E. superba .

Evidence for resuspension of rebound particles from near-bottom sediment traps

Abstract: Near-bottom sediment trap moorings were recovered at three sites in the North Equatorial Pacific Total particulate fluxes recorded within 30–350 m of the ocean floor were greater than those recorded in the mid-water column A simple two-component mixing model using the most organic-rich surface sediments sampled and an extrapolated mid-water column flux does not account for increases in the major biogenic components (organic carbon, calcium carbonate and opal) The resuspension of rebound particles (those particles) that have settled through the water column but have not become incorporated into the sediments) may account for the observed flux near the ocean floor

Water column productivity attributable to displaced benthic diatoms in well-mixed shallow estuaries

Abstract: We attempted to determine the extent to which benthic diatoms contribute to water column primary productivity in shallow-water estuaries and to elucidate the primary mechanisms responsible for suspending the diatoms. A perliminary study conducted in Mugu Lagoon, California indicated that productivity of ocean water entering the lagoon during flood tides was often several orders of magnitude less than that of the same water mass about 3 h later. Benthic pennate diatoms displaced from the sediments into the water column accounted for the increase. A more detailed study was conducted in Barataria Estuary, Louisiana where, for one month, daily measurements were made of benthic and water column productivity and several other environmental variables. During the month, the relationship between water column and benthic primary productivity varied from strongly negative to weakly negative to positive. K-systems analysis indicated that factors comprised of wave height, meteorological tides, astronomical tides, and benthic productivity and standing crop accounted for the full range of variation in water column productivity. Benthic pennate diatoms, represented an average of 74% of the diatom taxa in water column samples. We conclude that the primary productivity of well-mixed shallow estuarine waters is often greatly aumented by displaced benthic algae.

Hydrographic Patterns in McMurdo Sound, Antarctica and Their Relationship to Local Benthic Communities

Abstract: Measurements of hydrographic parameters (temperature, salinity, nitrate, nitrite, phosphate, chlorophyll a, phaeophytin, and oxygen) in McMurdo Sound, Antarctica during spring, 1984, before the regional phytoplankton bloom, and summer, 1984, after the peak of the bloom, indicate the several processes contribute to changes in the vertical and horizontal structure of the water column. Regional variation in the source of water masses within the Sound, ice cover patterns, and meltwater from the Ross Ice Shelf and nearby continental glaciers result in east-west and north-south gradients in the thermohaline, nutrient, and productivity characteristics of the Sound. These patterns are also related to the extremely variable structure and productivity of shallow water benthic macrofaunal communities in McMurdo Sound. Hydrographic patterns during Spring (November) were indicative of conditions at the end of winter prior to the spring phytoplankton bloom. The water column was nearly isothermal with temperatures near or below the surface freezing point of seawater with only a slight salinity increase with depth. Salinity was lower in the west Sound than in the east, probably in response to glacial meltwater input from the Ross Ice Shelf and/or terrestrial sources. Nutrient levels were high and nearly homogenous throughout the Sound. Chlorophyll a was low (<1.0 μg/l) throughout most of the Sound, but was lowest in the western sound, as expected from the circulation pattern (Barry and Dayton 1988). Oxygen was uniformly low during spring. The summer hydrographic distributions, estimated from samples collected during the decline of the regional plankton bloom, were dramatically different than in during spring. Both the salinity and temperature were vertically stratified at all sites, particularly in the west Sound. Temperatures near the surface were well above the freezing point and occasionally near or above 0°C. Near surface salinity in the western Sound was nearly fresh (0.4 ppt) at some locations in the southwestern Sound. Chlorophyll a was high throughout the Sound relative to spring concentrations, and nutrient levels (NO3, PO4) were strongly depressed near the surface, due mainly to phytoplankton uptake rather than by dilution. Primary productivity estimates based on the summer nitrate and phosphate deficits over 90 days were 1.96–2.02 and 0.39–1.02 gCm-2d-1 for the east and west sound, respectively. Nutrient ratios indicated that glacial meltwater from the Ross Ice Shelf and/or nearby terrestrial sources may be an important component of the summer meltwater input to the western Sound. Enhanced water column stability due to this input may prolong the maintenance of high water column stability as this water mass flows northward and result in particularly high productivity in northern McMurdo Sound.

Methane and hydrogen in seawater (Atlantic Ocean)

Abstract: Measurements of dissolved methane and hydrogen from the Atlantic Ocean, between 50°N and 35°S, showed the surface water to be supersaturated, while the deep ocean water was in equilibrium or slightly undersaturated with respect to atmospheric CH4 and H2. Dissolved H2 was highest in surface water and decreased within the upper 100 m of the water column, whereas dissolved CH4 remained high within the entire euphotic water layer. There is evience for a diurnal variation of dissolved H2, with higher amplitudes at the water surface compared to 20m depth. Dissolved CH4 at 4 m depth also was measured using a continuously working equilibration technique which procided information on short-term fluctuations. The dissolved CH4 showed no diurnal variations and was independent of wind speed. Highest CH4 concentrations were observed in areas with high nutrient input, e.g. in the upwelling areas off West Africa, and correlated well with the observed chorophyll a concentrations. Based on an average CH4 saturation factor of about 1.1, the total source strength for atmospheric CH4 is calculated to about 1.5 Tg y−1.

Interrelationships among primary production, chlorophyll, and environmental conditions in frontal regions of the western Mediterranean Sea

Abstract: In May 1986, we investigated processes contributing to the unique characteristics of oceanic fronts in the western Mediterranean Sea. Simulated in situ measurements of 14C-based primary production were made in conjunction with precise chemical, physical and optical analyses coordinated with remote sensing. Eight transects consisting of 4–7 vertical stations were made across density fronts associated with the Almeria Gyre and the Algerian Current. A model was developed to describe the relationship between chlorophyll-specific primary production (mg C mg Chl−1h−1) and depth in the water column. Model regressions for Modified Atlantic Water (MAW, salinity = 36.5–36.8), Mediterranean water (37.6–38.0), and intermediate frontal water were not significantly different, and a single equation based on the pooled data was used to estimate regional production. East of 0° longitude, primary production integrated over the upper 100 m (ΣP) in Mediterranean water was 0.47 g C m−2 d−1 (range0.33–0.60) and 0.88 g C m−2 d−1 (range 0.50–1.30) in MAW and frontal regions. higher ΣP in MAW and frontal regions could be attributed partially to higher integrated chlorophyll, although locationof the chlorophyll maximum higher in the water column was also an important contributing factor. The chlorophyll maximum was shallower in MAW than in Mediterranean-type water. The depth of chlorophyll maxima generally coincided with the nitracline rahter than isopycnal surfaces, supporting the view that chlorophyll distributions and primary production were primarily influenced by nutrient supply.

Evidence from mesocosm studies for biological removal of dissolved aluminium from sea water

Abstract: The marine geochemical cycle of aluminium is relevant to such oceanographic processes as the diagenesis of aluminosilicate material1 and tracing atmospheric dust inputs to oceanic surface waters2–6; Al has also been used as a non-transient water mass tracer7. The principal inputs of aluminium to the oceans are from the atmosphere and rivers, and have been reasonably well quantified8–13. Processes controlling its removal from the water column are, however, not well understood and in the past they have been inferred only from measurements of its oceanic distribution2–6,12 and unrealistic laboratory culture experiments14. Here we report the results of a more realistic and controlled temporal study, using a 10-m mesocosm tank, of changes in dissolved aluminium levels and particulate aluminium flux during a diatom bloom. We find that rapid removal of dissolved aluminium occurs by a surface adsorption mechanism and/or incorporation into soft tissues of diatoms. These observations represent the first direct demonstration of the influence and mechanism of biogenic particle removal of aluminium.