Showing papers on "Water column published in 1987"

Turbidity as a control on phytoplankton biomass and productivity in estuaries

Abstract: In many coastal plain estuaries light attenuation by suspended sediments confines the photic zone to a small fraction of the water column, such that light limitation is a major control on phytoplankon production and turnover rate. For a variety of estuarine systems (e.g. San Francisco Bay, Puget Sound, Delaware Bay, Hudson River plume), photic-zone productivity can be estimated as a function of phytoplankton biomass times mean irradiance of the photic zone. Net water column productivity also varies with light availability, and in San Francisco Bay net productivity is zero (estimated respiratory loss of phytoplankton balances photosynthesis) when the ratio of photic depth ( Z p ) to mixed depth ( Z m ) is less than about 0.2. Thus whenever Z p : Z m Much of the spatial and temporal variability of phytoplankton biomass or productivity in estuaries is explained by variations in the ratio of photic depth to mixed depth. For example, phytoplankton blooms often coincide with stratification events that reduce the depth of the surface mixed layer (increase Z p : Z m ). Shallow estuarine embayments (high Z p : Z m ) are often characterized by high phytoplankton biomass relative to adjacent channels (low Z p : Z m ). Many estuaries have longitudinal gradients in productivity that mirror the distribution of suspended sediments: productivity is low near the riverine source of sediments (low Z p : Z m ) and increases toward the estuary mouth where turbidity decreases. Some of these generalizations are qualitative in nature, and detailed understanding of the interaction between turbidity and estuarine phytoplankton dynamics requires improved understanding of vertical mixing rates and phytoplankton respiration.

Climate and Chlorophyll a: Long-Term Trends in the Central North Pacific Ocean

Abstract: Since 1968 a significant increase in total chlorophyll a in the water column during the summer in the central North Pacific Ocean has been observed. A concomitant increase in winter winds and a decrease in sea surface temperature suggest that long-period fluctuations in atmospheric characteristics have changed the carrying capacity of the central Pacific epipelagic ecosystem.

Geographical variation of the water column distrubution of suspended particulate organic nitrogen and its 15N natural abundance in the Pacific and its marginal seas

Abstract: The water column distribution of suspended particulate organic nitrogen (PON) and its natural abundance ratio of 15N: 14N were investigated to a depth of ∼4000 m at 13 stations in the North Pacific, and the South China, Philippine and Bering seas. At two stations in the northern North Pacific, sediment trap experiments were also carried out. The δ15N of PON ranged from −1.5 to 23.3 per mil. The 15N natural abundance of PON increased with depth between 0 and 200 m, while the PON concentration decreased sharply in the same depth range. In the vertical profiles, the PON in the deep water was, on an average, enriched with 15N by approximately 6 per mil as compared with that in the euphotic zone. These findings imply that the vertical transport of organic matter is mediated primarily by rapidly sinking particles, and that most of the decomposition of organic matter takes place in the shallow layer beneath the bottom of the euphotic zone (<200 m) in a similar manner at all locations. The average 15N abundance of PON in the water column was higher in the eastern tropical and central gyre portions of the Pacific than in the western Pacific, the South China Sea, the Philippine Sea, and the Bering Sea. Year-round stratification, the influence of 15N enriched nitrate produced during denitrification and the lack of significant nitrogen fixation in the surface layer probably caused the 15N enrichment in the eastern tropical Pacific.

Seasonal and Spatial Variations in Mercury Methylation and Demethylation in an Oligotrophic Lake

Abstract: Microbial mercury methylation and methylmercury decomposition were examined in Lake Clara, an oligotrophic northern Wisconsin seepage lake, using radioisotopic tracers. Methylation activity was near background in the water column, was greatest in the profundal surficial sediments, and decreased with depth in sediment cores. Active demethylation occurred in the water column but was variable. Demethylation was greatest in the surficial sediments and decreased slightly with sediment depth. The methylation/demethylation ratio (M/D) was >1 in the water column, exhibited a sharp peak in surface sediments, and decreased in deeper sediments. Methylation and demethylation activity varied in surface sediments collected along a lake transect. The M/D ratio in surface sediments ranged from 1.4 to 5.8. Methylation in attached microbial communities was near background, while demethylation was high. The M/D ratios in the attached communities were all <0.20. Methylation activity in surface sediments incubated at in situ temperature increased from spring to late summer and decreased in the fall. Demethylation increased from early to midsummer and then declined. The M/D ratio in surface sediments increased from mid- to late summer, and decreased in the fall. These results indicate that the greatest potential for methylation in Lake Clara occurs in the surficial sediments and that methylation in surficial sediments is greatest from mid-July through September. In addition, the net rate of methylmercury production may be significantly affected by demethylation.

Measurements of Specific Rates of Net Methyl Mercury Production in the Water Column and Surface Sediments of Acidified and Circumneutral Lakes

Abstract: Specific rates of mercury methylation and demethylation were determined for water and surficial sediment samples taken from several lakes located in the Experimental Lakes Area, northwestern Ontari...

Trends in oxygen content 1911–1984 and occurrence of benthic mortality in the northern Adriatic Sea

Abstract: Trends of dissolved oxygen content of the surface and bottom layers of the northern Adriatic Sea are analysed for the period 1911–1984. An increase in the surface layer and a decrease in the bottom layer are observed in all seasons except winter. Although the oxygen content of the water column as a whole has not changed significantly, it is inferred, from the increasing difference between the surface and the bottom layer, that the primary productivity of the northern Adriatic Sea is increasing. As the average midsummer oxygen content of the bottom layer decreases, the frequency of mass mortality in the benthic fauna is expected to increase, especially in the northern and western subareas.

Nutrient fluxes during extended blooms of Arctic ice algae

Abstract: Estimates of nutrient demand by dense mats of ice algae in the high Arctic indicate that substantial nutrient fluxes are necessary to satisfy the observed growth over the 2-month bloom. In our study area, Barrow Strait, the quantity of nutrients in the surface-mixed layer is about 3–10 times greater than estimates of total demand during the bloom, and nutrient fluxes in the water column are estimated to be of the same order of magnitude as algal demand. The fluxes in the water column are predicted to vary by more than an order of magnitude over the fortnightly tidal cycle, assuming that fluxes depend upon the strength of tidal currents and the vertical nutrient gradients. In the latter half of the bloom, when biomass levels are high, it appears that established populations of ice algae may experience cyclic conditions of nutrient limitation during neap tides when nutrient fluxes are minimal. Contributions from regeneration and brine exclusion from the ice sheet appear to satisfy only a portion of the bloom's total requirement for nutrients.

Spring distributions of density, nutrients, and phytoplankton biomass in the ice edge zone of the Weddell‐Scotia Sea

Abstract: We collected data on temperature, salinity, nutrient concentrations (nitrate, nitrite, phosphate, and silicic acid), and phytoplankton biomass (chlorophyll a, particulate carbon, nitrogen, and biogenic silica) in the upper 150 m in the marginal ice zone of the eastern Scotia Sea and northwestern Weddell Sea during November and early December of 1983. A distinct hydrographic front separating Drake Passage water from Weddell and Scotia sea surface waters was located at approximately 59°S and was the site of a consistent maximum in phytoplankton biomass. In addition, there was a pronounced phytoplankton biomass maximum associated with a surface salinity minimum near the northern limit of pack ice in the waters of the Weddell-Scotia confluence that characterized the western portion of the study area. In the eastern half of the study area, characterized by largely unmodified Weddell Sea surface water, the phytoplankton biomass near the ice edge was 2–5 times lower than that in the Weddell-Scotia confluence but was increasing with time. The water column structure, nutrient fields, and phytoplankton biomass distribution all suggest that the high phytoplankton biomass in the ice edge zone of the Weddell-Scotia confluence and the lower but temporally increasing biomass near the ice edge in unmodified Weddell Sea water reflect ice edge phytoplankton blooms in different stages of their seasonal development. A bloom had become well established in the waters of the Weddell-Scotia confluence by mid-November, but the ice-free, vertically stable near-surface water column necessary for enhanced phytoplankton growth had apparently not been present long enough for high biomass levels to develop within the Weddell Sea proper.

Distribution and Molecular Weight of Dissolved DNA in Subtropical Estuarine and Oceanic Environments

Abstract: Dissolved DNA and a series of microbial biomass and activity parameters were measured in offshore, coastal, estuanne and coral reef environments of the southeast Gulf of Mexico. Oceanic concentrations of dissolved DNA ranged from 0.2 to 19 vg 1-' and decreased as a function of distance from shore and depth in the water column. Dissolved DNA concentrations were greater than half the particulate DNA content in offshore environments (Z = 63 + 45 O/O), but were a smaller percentage of particulate DNA in nearshore and estuarine environments (Z = 35 f 21 %). Dissolved DNA correlated better with bacterial parameters (i.e. bacterial direct counts, particulate DNA and thymidine incorporation) than with phytoplankton parameters (chlorophyll a, primary productivity). The molecular weight (MW) of dissolved DNA (determined by agarose gel electrophoresis) ranged from 0.12 kilobase pairs (kb; 7.75 X 104 daltons) to 35.2 kb (2.32 X 10' daltons) for estuarine samples, while an oligotrophic environment contained smaller MW DNA (range 0.24 to 14.27 kb). DNA fragments in this size range are sufficient to contain gene sequences. These results are discussed in terms of the potential for transformation by dissolved DNA.

Resuspension in the shallow sublittoral zone of a macrotidal estuarine environment: Wind influence1

Abstract: Several biological and physical variables were measured four times daily for 148 consecutive days at a fixed station to examine fluctuations of phytoplankton abundance in the littoral zone of the lower St. Lawrence estuary. On the seasonal scale, the pattern of variation of phytoplankton was characterized by a midsummer diatom bloom similar to that observed offshore in the pelagic zone. On the shorter time scale, chlorophyll a concentration in the littoral zone was highly variable and closely associated with variations in the wind field. No relationship, however, could be found between phytoplankton cell numbers and wind velocity. The possible influence of wind, tidalinduced upwelling, overturning eddies, and wave-induced mixing processes on resuspension was examined. The higher Chl a values observed irregularly at the sampling stations resulted from the mechanical resuspension of benthic diatoms due to wind, or wind-induced wave, mixing in the littoral zone. Wind velocities >4 m s-l were shown to cause significant resuspension of particulate organic matter (POC) in the water column. For winds >6 m s-l, there was no further increase in POC. These results suggest that the frequency of wind velocities > 4 m s- * plays a significant role on secondary production in the littoral zone by providing an increased food supply to benthic and planktonic filter feeders, especially at times when phytoplankton biomass is normally low in the water column.

High phytoplankton growth and production rates in the North Pacific subtropical gyre1,2

Abstract: Rates of phytoplankton growth and production were measured with 14C techniques at stations near the Hawaiian Islands and at about 28°N, 155°W in the North Pacific subtropical gyre during August and September 1985. Ratios of light-saturated assimilation averaged 9.5 ± 1.4 g C (g Chl a)−1 h−1 during the photoperiod. Doubling times in the upper 30 m of the water column averaged 14±3 h. Relative growth rates were estimated to be 85–90% of nutrient-saturated values. Over the upper 200 m of the water column photosynthetic rates uncorrected and corrected for grazing and phytoplankton respiration losses were 315 ± 26 and 450±37 mg C m−2 d−1, respectively. The former figure is comparable to the highest daily photosynthetic rates inferred from 14C studies at this station during 1968–1980 and is about twice the mean of those historical productivity numbers. These results contradict the paradigm of subtropical gyres as vast biological deserts characterized by constantly low biomass and low turnover rates limited by the supply of nutrients. However, further studies will be needed to determine whether these high growth and production rates are typical or atypical of the central regions of the oceans.

Late winter primary production and bacterial production in sea ice and seawater west of the Antarctic Peninsula

Abstract: The Southern Ocean is believed to be unproductive during winter due pnncipally to low irradiance. On the 1985 Wintercruise of the R N Polar Duke, considerable microbial blomass and rates of primary produchon and bactenal production were found in sea ice up to 1.79 m thick. Microbial activity associated with sea ice was equal to that found in several meters of underlying seawater. Downwelling irradiance was adequate for net production near the surface of ice-free water and in sea ice. Approximately 40 % of the newly fixed carbon incorporated by ice microalgae was assimilated into protein, suggesting that net growth was taking place without nutrient limitation. We propose that annual estimates of primary production should be revised upward by as much as 25 % to account for this unexpected productivity during late winter in the Southern Ocean. In addition, sea ice should be viewed as a concentrated source of microalgal carbon for grazers such as krill during late winter when phytoplankton in the water column are scarce. In situ observations by divers suggest that sea ice may also serve as an important nursery ground for larval knll during this time of year. We conclude that both the quantity of sea ice associated production and seasonal timing of this production are important factors in Antarctic trophodynamics.

Origin of diatom ooze belt in the Southern Ocean; implications for late Quaterary paleoceanography

Abstract: Diatom preservation patterns in surface sediments of the Pacific sector of the Southern Ocean were examined. A belt of well-preserved diatoms is bounded on the north and south by sediments containing poorly preserved diatoms. The northern boundary correlates closely with the Subantarctic Front and appears to result from reduced phytoplankton productivity caused by temperature effects on metabolic processes. The southern boundary is caused by the damping effect that late winter/early spring sea-ice has on diatom productivity in the water column. Our evidence suggests that the southern boundary represents the spring sea-ice position rather than summer position. When these data are applied to late Quaternary sections in the Pacific sector it appears that there was only a modest northward expansion of winter sea-ice cover during glacial maxima.

Proteolytic activity in coastal oceanic waters: depth distribution and relationship to bacterial populations

Abstract: Proteolytic activity and the role of bacteria in protein degradation in seawater were investigated during 2 cruises to the Santa Monica Basin. The rate of hydrolysis of L-leucyl-P-naphthylaniine was used as a measure of proteolytic activity, and was compared with bacterial numbers, production, and growth rates throughout the water column (905 m max. depth). Peak proteolytic activities in the upper 100 m of the water column were more than 10 times those of deeper waters, though the natural substrate concentrations (combined hydrolyzable amlno acids) in the Santa Monica Basin have prev~ously been found to vary by only 3 to 4-fold Sediment porewaters were assayed during one cruise and found to have 20 to 30 times more proteolytic activity than the peak water column samples from the same cruise, though the origin of this activity could not be determined. Most of the proteolytic activity in the water column was associated with particles the size of bacteria (0.2 to 0.8 pm) and, overall, total proteolytic activity was highly correlated with all bacterial variables tested. However, the average activities per cell were not related to average cell sizes, suggesting that proteolytic activity is not s~mply a function of bacterial biomass. In samples from one of the crulses, the average activities per cell covarled with bacterial growth rates (thymidme incorporation per cell), but this was not true for samples taken during the second cruise. Laboratory expenments using 'seawater cultures' indicated that neither changes in cell size nor growth rate alone could account for changes in the amount of proteolytic enzyme expressed by marine bacteria. These results suggest that proteolytic activity in the water column is primarily associated with bacteria and is likely to be controlled by a number of factors related to the bacterioplankton, including biomass and growth rates.

Evidence of recent lead pollution in deep north-east Atlantic sediments

Abstract: Today, the global lead emissions into the atmosphere from anthropogenic sources are about 200 times higher than in the past1 and dominate other lead pathways to the ocean. Exhaust from leaded gasoline is the major source of pollutant lead in the atmosphere2, and subsequently in the marine environment due to atmospheric deposition by wet and dry removal processes3,4. This pollution has already perturbed the biogeochemical cycle of lead in the open ocean2,3,5–7 especially in the north Atlantic. In surface waters, where lead is introduced mainly in the dissolved state, its residence time is relatively short (less than 5 years), as it is rapidly scavenged by, and transported with, participate matter5,7. The mean residence time of lead in the ocean is estimated to be ∼100 yr5,8. One can therefore expect to see some pollutant lead in the deep ocean surficial sediments. Here, we report lead concentrations in two short cores from the north-east Atlantic. Lead concentrations in surficial sediments (21.0 and 15.0 p.p.m. in the top cm) are higher than in the uppermost 10 cm of the cores (6.0 and 2.8 p.p.m.), and are likely to be enhanced from anthropogenic sources. The quantity of lead stored in these surficial sediments (5.7 and 2.5 µg cm−2) is of the same order as the amount of pollutant lead present in the dissolved state in the water column.

Influence of environmental variables on the fish fauna of the deeper waters of a large Australian estuary

Abstract: Fish were collected by gill nets from the deeper waters of the Entrance Channel, basins and rivers of the large Peel-Harvey estuarine system (south-western Australia) in the wet (June to November) and dry (December to May) periods between August 1979 and July 1981. Simple-regression analysis showed that the number of species, abundance and biomass of fish in the rivers rose with increases in the salinity and temperature of both the surface and bottom of the water column. No such significant correlations were found in the Entrance Channel andbasins (Peel Inlet and Harvey Estuary), where salinity changes were far less marked. The number of species at sites throughout the estuary was inversely correlated with distance from the estuary mouth. Multiple-regression equations showed that, compared with the other environmental variables tested, bottom salinity had a greater influence on the nunber of species and abundance both in the rivers and in the system as a whole. These results indicate that salinity has a greater effect on the fauna in the deeper waters than in the shallows (cf. Loneragan et al., 1986). The larger fish which characterise the deeper waters may thus be less tolerant to low salinities than the smaller fish typically found in the shallows. Both classification and ordination separated the faunal composition of the rivers from those of the Entrance Channel and basins. The fauna of the two narrow and deeper sites in the rivers separated into wet- and dry-period components. Differences between the faunal composition of the riverine regions and those of the Entrance Channel and basins have been related to the much more variable and lower minimum salinities in the rivers. Species characteristic of the rivers included Amniataba caudavittatus, which is estuarine sensu stricto in south-western Australia, the semianadromous Nematalosa vlaminghi and the highly euryhaline Mugil cephalus. The indicator species for the Entrance Channel and basins were all marine species (Cnidoglanis macrocephalus, Hyporhamphus melanochir, Gerres subfasciatus and Pomatomus saltator).

Anoxic stratified oceans as a source of sulphur in sediment-hosted stratiform ZnPb deposits (Selwyn Basin, Yukon, Canada)

Abstract: Three periods of stagnation, viz. Middle Ordovician to Early Silurian, Early Devonian, and Late Devonian, have been recognized in the Selwyn Basin by extremely positive δ 34 S-values in pyrite. These δ 34 S-values in pyrite reflect almost complete bacterial sulphate reduction of sulphate to sulphide within a restricted anoxic layer of a stratified water column. W.C. Shanks and coworkers have reported a fourth anoxic event in the basin during the Early Cambrian. Each period of basin stagnation coincides with times when sedimentary Zn Pb-sulphide and barite deposits formed, while intervening periods correspond with the formation of stratiform barite deposits. The stratigraphic distribution of δ 34 S-values for pyrite are similar across the basin, whether near to or remote from mineralization, indicating a common seawater source of S. The generally parallel tracking of isotopic curves for sphalerite and galena with pyrite indicates that this sulphide also came from the bacterial reduction of sulphate within a stratified water column. This interpretation is supported by data on hydrothermal fluids that produced Zn Pb mineralization, which are near-neutral pH and range in temperature between 100° and 350°C. In such solutions, it is thermodynamically difficult to transport appreciable sulphide in the presence of Pb and Zn. Since these conditions apply to mineralizing fluids of many sedimentary-exhalative Zn Pb deposits, it follows that they too were likely S-poor, requiring an external seawater source of sulphide. This source is most effectively supplied by the sulphidic bottom layers of a stratified water column. This explains the correlation between anoxic events and Zn Pb sedimentary deposits, both within the Selwyn Basin and world-wide during the Phanerozoic. The latter observation also implies that the anoxic events within the Selwyn Basin were not controlled locally, but instead reflect periods of worldwide ocean stagnation.

Stratification and paleocirculation of the Late Cretaceous Western Interior Seaway of North America

Abstract: Paleotemperature and salinity profiles for the Western Interior Seaway are reconstructed by use of oxygen and carbon isotopic signatures of shell material Data have been gathered on different groups of molluscs distributed in three distinct habitat types: infaunal benthonic, epifaunal benthonic, and nektonic Isotopic variations and inferred environmental tolerances of the organisms were used to determine upper and lower temperature boundaries for each habitat group and therefore water-depth zones Water density for each temperature-salinity combination within a habitat range was calculated and used to develop a physically stable stratification model The results clearly show that the water column consisted of denser, more saline, warm bottom layers that were overlain by, and decoupled from, cooler, less saline intermediate layers It is proposed that this profile originated due to a surface current transporting runoff water from the western highlands toward the eastern shallow border of the seaway where evaporation and heating of surface water in a warm, humid atmosphere caused increased density and sinking, followed by westward return flow of the warm saline bottom water This model is compatible with known climatic and oceanographic information for the Cretaceous

Exchange of Nutrients Between Sediments and Water After 15 Years of Experimental Eutrophication

Abstract: Increases in the concentrations of nitrogen and phosphorus occurred in the water column of Lake 227 during 15 years of fertilization with phosphoric acid and sodium nitrate. The sources of the incr...

Distribution of indicator bacteria and Vibrio parahaemolyticus in sewage-polluted intertidal sediments.

Abstract: The impact of a sewage point source on the bacterial densities in an intertidal mud flat in Boston Harbor, Mass, was investigated The area, Savin Hill Cove, acts as a receiving basin for a combined storm and sewage outlet (CSO) Preliminary examination of sediments and overlying water at high tide demonstrated that fecal coliforms were present in sediments at abundances 2 to 4 orders of magnitude higher than in the overlying water column The following bacterial counts were determined from sediments along a sampling transect extending 460 m from the CSO: total bacteria by epifluorescent microscopy, heterotrophic bacteria by plate counts on nutrient-rich and nutrient-poor media, fecal coliforms and enterococci by membrane filtration, and Vibrio parahaemolyticus by a most-probable-number technique with a resuscitation step Median sediment grain size, average tidal exposure, carbon/nitrogen ratio, and total organic carbon were also measured All bacterial indices, except for V parahaemolyticus, declined significantly with distance from the outfall Multiple regression analysis indicated that tidal exposure (low tides) may affect densities of total bacteria Fecal coliforms and enterococci were still present in appreciable numbers in sediments as far as 460 m away from the CSO In contrast, V parahaemolyticus densities did not correlate with the other bacterial counts nor with any of the environmental parameters examined These results indicate that intertidal sediments which adjoin point sources of pollution are severely contaminated and should be considered as potentially hazardous reservoirs of sewage-borne diseases

Artificial radionuclides in the western Northwest Pacific (II):137Cs and239,240Pu inventories in water and sediment columns observed from 1980 to 1986

Abstract: Concentrations and inventories of137Cs and239,240Pu were determined in sea waters and sediments columns from the western North Pacific from 1980 to 1986. The239,240Pu/137Cs activity ratio in the water column shows a tendency to increase from the surface (10−3) to bottom waters (10−1), but the ratio in sediment is within a rather narrow range (10−2 to 10−1), indicating more effective removal of plutonium from the water column than137Cs. In regions south of 40‡N, the radionuclide inventories in the water column significantly exceed the estimated global fallout (stratospheric fallout due to the atmospheric nuclear explosion), especially in the case of239,240Pu. These excess inventories imply that local or close-in fallout derived from nuclear explosions in the equatorial North Pacific are well-preserved and retained in the regions, despite about 20 years since the atmospheric nuclear explosion moratorium. Data suggesting lateral transport of137Cs in surface water from north of 40‡N to southern regions is shown. Some data on90Sr contents are also shown.