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1.
We present the results of multiparametric observations designed to follow the phytoplankton dynamics and interrelated physical, chemical and biological processes in the Gulf of Finland (Baltic Sea). Data were acquired by an autonomous moored water column profiler, an acoustic Doppler current profiler, a flow-through system installed aboard a ferry and by profiling and discrete water sampling aboard research vessels in July and August 2009. The main aim of the study was to investigate the processes responsible for the formation and maintenance of sub-surface maxima of phytoplankton biomass. We suggest that the environmental conditions caused by the prevailing atmospheric and oceanographic forcing (wind; vertical stratification; basin-wide, mesoscale and sub-mesoscale processes) are preferred by certain species/taxonomic groups and explain the migration patterns of phytoplankton. Nocturnal downward migration of phytoplankton with a swimming speed up to 1.6 m h−1 occurred when the community was dominated by the dinoflagellate Heterocapsa triquetra. The observed splitting of the population into two vertically separated biomass maxima suggests that the H. triquetra cells, which reached the sub-surface layers with high nutrient concentrations, experienced bi-diurnal or asynchronous (when swimming upwards) vertical migration. The most intense sub-surface biomass maxima, on some occasions with the biomass much higher than that in the surface layer, were detected in connection to the sub-mesoscale intrusions below the depth of the strongest vertical density gradient.  相似文献   

2.
Forward-Looking Infrared (FLIR) nighttime thermal images were used to extract the thermal and morphological properties for the surface of a blocky-to-rubbley lava mass active within the summit crater of the Caliente vent at Santiaguito lava dome (Guatemala). Thermally the crater was characterized by three concentric regions: a hot outer annulus of loose fine material at 150–400°C, an inner cold annulus of blocky lava at 40–80°C, and a warm central core at 100–200°C comprising younger, hotter lava. Intermittent explosions resulted in thermal renewal of some surfaces, mostly across the outer annulus where loose, fine, fill material was ejected to expose hotter, underlying, material. Surface heat flux densities (radiative + free convection) were dominated by losses from the outer annulus (0.3–1.5 × 104  s−1m−2), followed by the hot central core (0.1–0.4 × 104 J s−1m−2) and cold annulus (0.04–0.1 × 104 J s−1m−2). Overall surface power output was also dominated by the outer annulus region (31–176 MJ s−1), but the cold annulus contributed equal power (2.41–7.07 MJ s−1) as the hot central core (2.68–6.92 MJ s−1) due to its greater area. Cooled surfaces (i.e. the upper thermal boundary layer separating surface temperatures from underlying material at magmatic temperatures) across the central core and cold annulus had estimated thicknesses, based on simple conductive model, of 0.3–2.2 and 1.5–4.3 m. The stability of the thermal structure through time and between explosions indicates that it is linked to a deeper structural control likely comprising a central massive plug, feeding lava flow from the SW rim of the crater, surrounded by an arcuate, marginal fracture zone through which heat and mass can preferentially flow.  相似文献   

3.
During the spring seasons of 1983, 1986 and 1987 the development of phytoplankton in Lake Zürich was investigated (from February to May) using samples taken at short term intervals. The aim was to describe the effects of the short term dynamics of environmental factors on the algal growth. The results could then be used to discuss the existing theories to assess the start of phytoplankton growth pulses in spring. Only 7 to 10 days without wind driven vertical mixing were required in spring to start the first growth pulse, despite of a still very unstable water column (sometimes inverse thermal stratification). Mainly flagellates andStephanodiscus hantzschii increased their biomass and achieved net growth rates of 0.1 and up to 0.65 d−1 respectively. During such a phase the mixing depth was always smaller than the euphotic depth. Later on, at the start of the spring bloom (=last growth pulse in spring before the clear water stage), the intensity of vertical mixing as well as the mixing depth were markedly reduced due to an increase in heat input and low wind. Then flagellates dominated (contribution up to 75.5% of the areal biomass reaching 60 g fresh weight m−2) and the growth rate rose to a maximum of 0.65 d−1. Standard models of critical depth considers that there is only a biomass increase if the mixing depth is smaller than the depth of a water layer positive balanced between production and respiration. This model for determining the beginning of a phytoplankton growth pulse in spring takes no account of the favorable light conditions for phytoplankton cells at calm and sunny days in February and March. The newly developed threshold value model takes these situations into account: It assumes that the phytoplankton biomass increases when the calculated effective light climate is equal or greater than a previously fixed threshold. The calculations are based on the mean light intensity within the mixed layer at windy days or within the euphotic depth (z eu) at calm days. In Lake Zürich a minimum of 0.2 106 J m−2d−1 (=0.9 mol quanta m−2d−1) has to be reached or surpassed in at least 3 days before an exponential increase of algal biomass can occur. The value does not depend on short term fluctuations in neither radiation nor mixing depth. It seems that this value is rather low comparing with those of investigations in other water bodies (up to 0.8 106 J m−2 d−1) but high related to values from algal cultures (0.02 106 J m−2d−1). As the weather can only be forecasted a few days ahead with any certainty the period for a more or less accurate prediction of an algal bloom is restricted to about 1 to 5 days.  相似文献   

4.
A critical factor controlling changes in the acidity of coastal waters is the alkalinity of the water. Concentrations of alkalinity are determined by supply from rivers and by in situ processes such as biological production and denitrification. A 2-year study based on 15 cruises in Liverpool Bay followed the seasonal cycles of changing concentrations of total alkalinity (TA) and total dissolved inorganic carbon (DIC) in relation to changes caused by the annual cycle of biological production during the mixing of river water into the Bay. Consistent annual cycles in concentrations of nutrients, TA and DIC were observed in both years. At a salinity of 31.5, the locus of primary production during the spring bloom, concentrations of NO x decreased by 25 ± 4 μmol kg−1 and DIC by 106 ± 16 μmol kg−1. Observed changes in TA were consistent with the uptake of protons during primary biological production. Concentrations of TA increased by 33 ± 8 μmol kg−1 (2009) and 33 ± 15 μmol kg−1 (2010). The impact of changes in organic matter on the measured TA appears likely to be small in this area. Thomas et al. (2009) suggested that denitrification may enhance the CO2 uptake of the North Sea by 25%, in contrast we find that although denitrification is a significant process in itself, it does not increase concentrations of TA relative to those of DIC and so does not increase buffer capacity and potential uptake of CO2 into shelf seawaters. For Liverpool Bay historical data suggest that higher concentrations of TA during periods of low flow are likely to contribute in part to the observed change in TA between winter and summer but the appropriate pattern cannot be identified in recent low-frequency river data. On a wider scale, data for the rivers Mersey, Rhine, Elbe and Weser show that patterns of seasonal change in concentrations of TA in river inputs differ between river systems.  相似文献   

5.
A month-long investigation of phytoplankton biomass and primary production (PP) was carried out during a harmful algal bloom (HAB) in Daya Bay, China, in 2003. During the bloom, the phytoplankton community was dominated by Scrippsiella trochoidea and Chattonella marina. The phytoplankton biomass (Chl a) and PP reached peak levels of 519.21 mg m−3 and 734.0 mgC m−3 h−1, respectively. Micro-phytoplankton was the key contributor to Chl a and PP in a cage-culture area and in the adjacent HAB-affected waters, with percentages of up to 82.91% and 84.94%, respectively. The HAB had complicated relationships with hydrological and meteorological factors in Daya Bay. However, the water around the cage-culture area always showed statistically greater phytoplankton biomass and nutrient loadings than in adjacent waters, suggesting that this was the “trigger area” of the bloom. The spatial and temporal distribution of diverse HABs in Daya Bay, their ecological characteristics, and their environmental impacts are also discussed in this paper.  相似文献   

6.
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7.
The seasonal pattern of size-fractionated phytoplankton biomass, primary production and respiration was investigated along the longitudinal axis of the Nervión–Ibaizabal estuary (Bay of Biscay) from April 2003 to September 2004. Environmental factors influencing phytoplankton dynamics were also studied. Chlorophyll a biomass showed a longitudinal pattern of increase from the outer Abra bay to the inner estuary. On a seasonal scale, in the intermediate and inner estuary phytoplankton biomass maxima were registered in summer, the warmest and driest season, whereas in the outer bay chlorophyll a peaks occurred in May 2004, but were delayed to August 2003, likely due to a very rainy spring. Data suggest that river flow exerts a marked influence on the timing of phytoplankton biomass maxima in this estuary, decreased river flows providing a lowering of turbidity and an increase in water residence time needed for chlorophyll a to build up. Nutrient concentrations were high enough not to limit phytoplankton growth throughout the annual cycle, except silicate and occasionally phosphate in the outer bay during summer. Silicate concentration correlated positively with river flow, whereas ammonium and phosphate maximum values were generally measured in the mid-estuary, suggesting the importance of allochthonous anthropogenic sources. In the intermediate and inner estuary phytoplankton biomass was generally dominated by >8 μm size-fraction (ca. 60%), but in August 2003 <8 μm size-fraction increased its contribution in the intermediate estuary. It is argued that the lower nutrient concentrations measured in August 2003 than in August 2004 could have played a role. This is the first study in which phytoplankton primary production rates have been measured along the longitudinal axis of the Nervión–Ibaizabal estuary. Throughout the annual cycle these rates ranged from 0.001 to 3.163 g C m?3 d?1 and were comparable to those measured in nearby small estuaries of the Basque coast and other larger estuaries on the Bay of Biscay. Surface plankton community respiration rate maxima were measured during the spring 2004 chlorophyll a peak in the Abra bay and in summer months at the mid and inner estuary, coinciding with chlorophyll a biomass and primary production maxima. In general, respiration rates showed a positive correlation with temperature. In order to compare results from the Nervión–Ibaizabal estuary with other nearshore coastal and estuarine ecosystems within the Bay of Biscay a review of existing information on phytoplankton biomass and primary production dynamics was performed.  相似文献   

8.
Regions of freshwater influence (ROFIs) are dynamic areas within the coastal seas that experience cycles of stability driven by density gradients and the spring-neap tidal cycle. As a result, pulses of biological production may occur on a more frequent timescale than the classic seasonal cycle. Net community production (NCP) rates and chlorophyll a concentration are presented from a site within the ROFI of Liverpool Bay and compared to similar measurements made at a site outside the ROFI during 2009. The influence of water column stability on biological production in the ROFI was also investigated using high-frequency observations from a Cefas Smartbuoy. Both sites were autotrophic from spring to autumn before becoming heterotrophic over winter. NCP at the inshore site was estimated to range from 30.8 to 50.4 gC m−2 year−1. A linear relationship detected between chlorophyll a and NCP from both sites was used to estimate metabolic balance over 1 year at the ROFI site using high-resolution chlorophyll a concentrations from the Smartbuoy but was found to poorly replicate NCP rates compared to those derived from dissolved oxygen fluxes. There was no clear biological response to periods of stratification within the ROFI, and it is proposed that changes in light attenuation in the Liverpool Bay ROFI, driven not only by stratification but also by fluctuations in riverine sediment load, most likely play an important role in controlling phytoplankton growth in this region.  相似文献   

9.
Organic carbon release by phytoplankton and bacterial reassimilation   总被引：1，自引：0，他引：1  
The release of organic carbon by phytoplankton and its reassimilation by bacteria were studied in Lake Geneva during four daily kinetics, using14C techniques. Gentamycin was used to suppress bacterial activity. Size fractionation was used to measure14C fixation in 2 particulate fractions (≥1 μm and 0.2 to 1 μm) and in a third fraction: dissolved organic carbon. Measurements of bacterial biomass and14C glucose uptake as the H14CO 3 − uptake by samples prefractionated before incubation showed that the whole algae were retained on 1 μm pore size Nuclepore filters, but bacteria were retained on 1 μm and 0.2 μm filters. Concentration of 20 μg.ml−1 gentamycin resulted in incomplete bacterial inhibition while phytoplankton was affected. Phytoplankton released less of 20% of its photoassimilated carbon of which a large proportion was utilized by bacterioplankton.  相似文献   

10.
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11.
Decompression experiments of a crystal-free rhyolitic liquid with ≈ 6.6 wt. % H2O were carried out at a pressure range from 250 MPa to 30–75 MPa in order to characterize effects of magma ascent rate and temperature on bubble nucleation kinetics, especially on the bubble number density (BND, the number of bubbles produced per unit volume of liquid). A first series of experiments at 800°C and fast decompression rates (10–90 MPa/s) produced huge BNDs (≈ 2 × 1014 m−3 at 10 MPa/s ; ≈ 2 × 1015 m−3 at 90 MPa/s), comparable to those in natural silicic pumices from Plinian eruptions (1015–1016 m−3). A second series of experiments at 700°C and 1 MPa/s produced BNDs (≈ 9×1012 m−3) close to those observed at 800°C and 1 MPa/s (≈ 6 × 1012 m−3), showing that temperature has an insignificant effect on BNDs at a given decompression rate. Our study strengthens the theory that the BNDs are good markers of the decompression rate of magmas in volcanic conduits, irrespective of temperature. Huge number densities of small bubbles in natural silicic pumices from Plinian eruptions imply that a major nucleation event occurs just below the fragmentation level, at which the decompression rate of ascending magmas is a maximum (≥ 1 MPa/s).  相似文献   

12.
Annual phytoplankton productivity in Lake Constance is about 300 g C m−2, a value typical for mesoeutrophic lakes. Seasonal variations in phytoplankton biomass and productivity are exceptionally great because of a sequence of factors controlling the production process. During winter productivity is controlled by low energy inputs and high respiratory losses due to deep water column mixing. Biomass is low and water transparancy high. The spring phytoplankton growth is triggered by the thermal stabilization of the water column. The summer phytoplankton biomass maximum mainly depends on phosphorus availability. However, biomass yields comprise only 15–20% of values to be expected from the Redfield ratio because large proportions of POM are detritus and non-algal biota. Moreover, sedimentation during the second half of the year removes biomass from the euphotic zone. Water transparency and thus vertical distribution of algal photosynthesis is highly dependent on phytoplankton biomass. Self-shading causes considerably smaller seasonal variations in areal biomass and photosynthetic rates than in volume-based values. By light-shade adaptation effects of seasonal fluctuations in mean daily surface radiance fluxes on algal photosynthesis can to a significant extent be compensated for. At any given level of biomass daylength is the major determinant of daily production rates. Dedicated to Professor Elster on his 80th birthday.  相似文献   

13.
Organic matter mineralisation in the hypolimnion of an eutrophic Maar lake   总被引：2，自引：0，他引：2  
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14.
The ocean takes up approximately 2 GT carbon per year due to the enhanced CO2 concentrations in the atmosphere. Several options have been suggested in order to reduce the emissions of CO2 into the atmosphere, and among these are CO2 storage in the deep ocean. Topographic effects of dissolution and transport from a CO2 lake located at 3,000-m depth have been studied using the z-coordinate model Massachusetts Institute of Technology general circulation model (MITgcm) and the σ-coordinate model Bergen ocean model (BOM). Both models have been coupled with the general ocean turbulence model (GOTM) in order to account for vertical subgrid processes. The chosen vertical turbulence mixing scheme includes the damping effect from stable stratification on the turbulence intensity. Three different topographic scenarios are presented: a flat bottom and the CO2 lake placed within a trench with depths of 10 and 20 m. The flat case scenario gives good correlation with previous numerical studies of dissolution from a CO2 lake. When topography is introduced, it is shown that the z-coordinate model and the σ-coordinate model give different circulation patterns in the trench. This leads to different dissolution rates, 0.1 μmol cm − 2 s − 1 for the scenario of a 20-m-deep trench using BOM and 0.005–0.02 μmol cm − 2 s − 1 for the same scenario using the MITgcm. The study is also relevant for leakages of CO2 stored in geological formations and to the ocean.  相似文献   

15.
Forward Looking Infrared Radiometer (FLIR) cameras offer a unique view of explosive volcanism by providing an image of calibrated temperatures. In this study, 344 eruptive events at Stromboli volcano, Italy, were imaged in 2001–2004 with a FLIR camera operating at up to 30 Hz. The FLIR was effective at revealing both ash plumes and coarse ballistic scoria, and a wide range of eruption styles was recorded. Eruptions at Stromboli can generally be classified into two groups: Type 1 eruptions, which are dominated by coarse ballistic particles, and Type 2 eruptions, which consist of an optically-thick, ash-rich plume, with (Type 2a) or without (Type 2b) large numbers of ballistic particles. Furthermore, Type 2a plumes exhibited gas thrust velocities (>15 m s−1) while Type 2b plumes were limited to buoyant velocities (<15 m s−1) above the crater rim. A given vent would normally maintain a particular gross eruption style (Type 1 vs. 2) for days to weeks, indicating stability of the uppermost conduit on these timescales. Velocities at the crater rim had a range of 3–101 m s−1, with an overall mean value of 24 m s−1. Mean crater rim velocities by eruption style were: Type 1 = 34 m s−1, Type 2a = 31 m s−1, Type 2b = 7 m s−1. Eruption durations had a range of 6–41 s, with a mean of 15 s, similar among eruption styles. The ash in Type 2 eruptions originates from either backfilled material (crater wall slumping or ejecta rollback) or rheological changes in the uppermost magma column. Type 2a and 2b behaviors are shown to be a function of the overpressure of the bursting slug. In general, our imaging data support a broadening of the current paradigm for strombolian behavior, incorporating an uppermost conduit that can be more variable than is commonly considered.  相似文献   

16.
Main channel habitats of the Ohio, Missouri, and Upper Mississippi Rivers were surveyed during the summers of 2004, 2005 and 2006 using a probability-based sampling design to characterize inter-annual and inter-river variation in suspended chlorophyll a (CHLa) and related variables. Large (fivefold) differences in CHLa were observed with highest concentrations in the Upper Mississippi (32.3 ± 1.8 μg L−1), intermediate values in the Missouri (19.7 ± 1.1 μg L−1) and lowest concentrations in the Ohio (6.8 ± 0.5 μg L−1). Inter-annual variation was small in comparison to inter-river differences suggesting that basin-specific factors exert greater control over river-wide CHLa than regional-scale processes influencing climate and discharge. The rivers were characterized by variable but generally low light conditions as indicated by depth-averaged underwater irradiance <4 E m−2 day−1 and high ratios of channel depth to euphotic depth (>3). Despite poor light conditions, regression analyses revealed that TP was the best single predictor of CHLa (R 2 = 0.40), though models incorporating both light and TP performed better (R 2 = 0.60). Light and nutrient conditions varied widely within rivers and were inversely related, suggesting that riverine phytoplankton may experience shifts in resource limitation during transport. Inferred grazing and sedimentation losses were large yet CHLa concentrations did not decline downriver indicating that growth and loss processes were closely coupled. The contribution by algae to suspended particulate organic matter in these rivers (mean = 41%) was similar to that of lakes (39%) but lower relative to reservoirs (61%).  相似文献   

17.
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18.
During 2007–2008, three CO2 flux surveys were performed on El Chichón volcanic lake, Chiapas, Mexico, with an additional survey in April 2008 covering the entire crater floor (including the lake). The mean CO2 flux calculated by sequential Gaussian simulation from the lake was 1,190 (March 2007), 730 (December 2007) and 1,134 g m−2 day−1 (April 2008) with total emission rates of 164 ± 9.5 (March 2007), 59 ± 2.5 (December 2007) and 109 ± 6.6 t day−1 (April 2008). The mean CO2 flux estimated from the entire crater floor area was 1,102 g m−2 day−1 for April 2008 with a total emission rate of 144 ± 5.9 t day−1. Significant change in CO2 flux was not detected during the period of survey, and the mapping of the CO2 flux highlighted lineaments reflecting the main local and regional tectonic patterns. The 3He/4He ratio (as high as 8.1 R A) for gases in the El Chichón crater is generally higher than those observed at the neighbouring Transmexican Volcanic Belt and the Central American Volcanic Arc. The CO2/3He ratios for the high 3He/4He gases tend to have the MORB-like values (1.41 × 109), and the CO2/3He ratios for the lower 3He/4He gases fall within the range for the arc-type gases. The high 3He/4He ratios, the MORB-like CO2/3He ratios for the high 3He/4He gases and high proportion of MORB-CO2 (M = 25 ±15%) at El Chichón indicate a greater depth for the generation of magma when compared to typical arc volcanoes.  相似文献   

19.
This study combined water- and sediment flux measurements with mass balances of dissolved gas and inorganic matter to determine the importance of pelagic and benthic processes for whole-system metabolism in a eutrophic fluvial lake. Mass balances of dissolved O2, inorganic carbon (DIC), nitrogen (DIN), phosphorous (SRP), particulate N (PN) and P (PP) and Chl a were calculated at a nearly monthly frequency by means of repeated sampling at the lake inlet and outlet. Simultaneously, benthic fluxes of gas and nutrients, including denitrification rates, and the biomass of the dominant pleustophyte (Trapa natans) were measured, and fluxes of O2 and CO2 across the water–atmosphere interface were estimated from diel changes in outlet concentrations. On an annual scale, Middle Lake exhibited CO2 supersaturation, averaging 313% (range 86–562%), but was autotrophic with a net O2 production (6.35 ± 2.05 mol m−2 y−1), DIC consumption (−31.18 ± 18.77 mol m−2 y−1) and net export of Chl a downstream (8.38 ± 0.95 mol C m−2 y−1). Phytoplankton was the main driver of Middle Lake metabolism, with a net primary production estimated at 33.24 mol O2 m−2 y−1, corresponding to a sequestration of 4.18 and 0.26 mol m−2 y−1 of N and P, respectively. At peak biomass, T. natans covered about 18% of Middle Lake’s surface and fixed 2.46, 0.17 and 0.02 mol m−2 of C, N and P, respectively. Surficial sediments were a sink for O2 (−14.47 ± 0.65 mol O2 m−2 y−1) and a source of DIC and NH4 + (18.84 ± 2.80 mol DIC m−2 y−1 and 0.83 ± 0.16 mol NH4 + m−2 y−1), and dissipated nitrate via denitrification (1.44 ± 0.11 mol NO3 − m−2 y−1). Overall, nutrient uptake by primary producers and regeneration from sediments were a minor fraction of external loads. This work suggests that the creation of fluvial lakes can produce net autotrophic systems, with elevated rates of phytoplanktonic primary production, largely sustained by allochtonous nutrient inputs. These hypereutrophic aquatic bodies are net C sinks, although they simultaneously release CO2 to the atmosphere.  相似文献   

20.
Preliminary results of a seasonal study of the pelagic community at a station on the outer edge of the Cornwallis Estuary suggest that the seasonal variation in plankton community respiration (PCR) is related to organic inputs from nearby salt marshes. Annual phytoplankton production is low (<30 g C m−2 y−1) and exhibits a seasonal cycle very different from PCR. There is no indication that resuspension of benthic diatoms is an important energy input to the pelagic system. PCR, however, is quite high and exhibits a seasonal trend similar to the export of salt marsh detritus. Zooplankton densities (5–200 l−1) and biomass (<0.4 g m−3) appear to be much greater than could be supported by phytoplankton alone. The Cornwallis Estuary may be an estuarine system exhibiting a net export of organic matter to nearby offshore waters.  相似文献   

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