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1.
Nitrification rates, as oxidation of 15N-labelled ammonium and loss of nitrite from N-Serve treated samples, were measured in Kochi backwaters during three seasons. Nitrification rates ranged from undetectable to 166 nmol N L−1 h−1 in the water column and up to 17 nmol N (g wet wt)−1 h−1 in sediments. Nitrification rates were higher in intermediate salinities than in either freshwater or seawater end. Within this salinity range, nitrification rates could be related to ammonium concentrations. As shown by the relation between ammonification and nitrification rates, it is also likely that nitrification is more regulated by renewal rates, rather than by in situ concentrations, of substrate. Among other environmental parameters, temperature and pH may have an influence on nitrification. Potential nitrification rates calculated from loss of nitrite from N-Serve treated, nitrite-enriched samples were about 800 nmol N L−1 h−1 in the water column and 40 nmol N (g wet wt)−1 h−1 in sediments. While these rates are in balance with those of biological ammonium production they may be inadequate to mitigate ammonium pollution in this estuary.  相似文献   

2.
《Marine Chemistry》2007,103(1-2):84-96
An isotope dilution method has been developed to determine by gas chromatography/mass spectrometry (GC/MS) the rates of ammonium and nitrite oxidation in severely oligotrophic marine waters. The method is based on the formation of sudan-1 from nitrite, or from nitrate following reduction to nitrite. Samples were collected by solid phase extraction and purified by high performance liquid chromatography (HPLC). A deuterated sudan-1 internal standard was synthesized, purified by HPLC and used for quantitative analysis. Concentrations of NO2− and NO3− were generally < 2 nmol/kg and < 5 nmol/kg respectively, typical of oligotrophic surface waters, and turnover times for the inorganic N pools ranged from < 1 day to > 10 days. Significant rates of nitrification were measured in the surface oligotrophic ocean, with rates of ammonium and nitrite oxidation generally within the range of 10–500 pmol/kg/h. Consequently, a significant proportion of daily NO3− assimilation by marine phytoplankton is regenerated, and not new. In a case study of the oligotrophic gyre of the North Atlantic, the influence of NH4+ regeneration and nitrification on f-ratio values suggests that in the oligotrophic ocean, f-ratio values may be significantly, and sometimes grossly, overestimated.  相似文献   

3.
Nitrogen isotope compositions of particulate organic matter and nitrate were analyzed for seawater sampled at five stations at the Alaskan Gyre, Western Subarctic Gyre and East China Sea, focusing on the samples from the surface to 5000 m water to characterize the nitrogen cycling in the subarctic North Pacific Ocean and its marginal sea. The 15N of particulate organic matter showed little agreement with a conceptual closed model that interprets isotopic variation as being caused by isotope discrimination on nitrate utilization. The 15N and 13C of particulate organic matter varied with the water depth. A correlation between isotope compositions and C/N elemental ratio was found generally at all stations, although some irregular data were also found in deep layers. We developed a hypothetical nitrogen balance model based on N2 fixation and denitrification in seawater and attempted to apply it to distinguish nutrient cycling using both 15N-NO3 – and N* variation in seawater. This model was applied to the observed data set of 15N-NO3 – and N* in the North Pacific water and estimated the 15N-NO3 – of primordial nitrate in the North Pacific deep water as 4.8. The North Pacific intermediate water for all stations showed similar 15N-NO3 – and N* values of 6 and –3 µmol/kg, respectively, suggesting a similar nitrogen biogeochemistry. In the East China Sea, analysis showed evidence of water exchange with the North Pacific intermediate water but a significant influence of nitrogen from the river runoff was found in depths shallower than 400 m.  相似文献   

4.
The incidence of a large scale Trichodesmium erythraeum bloom along the southwest coast of India (Arabian Sea) observed in May 2005 is reported. Around 4802 filaments of T. erythraeum ml−1 seawater was observed and a colony consisted of 3.6 × 105 cells. The bloom was predominant off Suratkal (12° 59′N and 74° 31′E) with a depth of about 47 m, covering an area of 7 km in length and 2 km width. The concentrations of Zinc, Cadmium, Lead, Copper, Nickel and Cobalt were determined in samples collected from the bloom and non-bloom sites using stripping voltammetry. The observed hydrographical and meteorological parameters were found to be favorable for the bloom. The concentrations of Zinc, Cadmium and Nickel were found to be higher at bloom stations, while the concentrations of Lead, Copper and Cobalt were found to be very low at bloom stations. Elevated concentrations of Cadmium and Cobalt were observed at Valappad mainly due to the decomposition of detrital material produced in the bloom. Statistically significant differences (P > 0.01) in metal concentrations between the bloom and non-bloom stations were not observed except for Copper. Metals such as Lead, Copper and Cobalt were removed from the seawater at all places where bloom was observed. Cadmium was found to be slowly released during the decaying process of the bloom.  相似文献   

5.
Chemical profiles of both oxidized (nitrate and sulfate) and reduced (ammonium, sulfide, acid-volatile sulfide [AVS], and pyrite) materials and the corresponding distribution of denitrifier microbial communities were measured at low tide in sediments at Guandu in the estuary of the Tanshui River, northern Taiwan in August 2002. Denitrifier strains were isolated for physiological and phylogenic analyses. Based on the distribution of nitrogenous compounds and denitrifier abundances, the vertical profile of Guandu sediments could be separated into four layers: a mixed layer (the top 1 cm of depth, respectively containing 0.82–2.37 and 535.9–475.0 μM of nitrate and ammonium), a nitrate-concentrated layer (1–5 cm in depth, 2.37–0.53 and 475.0–1192.1 μM, respectively), a denitrifier-aggregation layer (5–7 cm in depth, 0.53–0.72 and 1192.1–1430.1 μM, respectively), and an ammonium-enriched layer (7–12 cm in depth, 0.72–0.78 and 1430.1–2196.6 μM, respectively). Denitrifier strains were detected in all layers except for the mixed layer. A variety of metabolic processes by these strains may occur in different layers. Bacillus jeotgali-, Bacillus sphaericus-, and Bacillus firmus-related strains isolated from the nitrate-concentrated layer may be involved in the nitrification-denitrification coupling process due to the relatively low nitrate concentrations (maximum = 2.37 μM), and may contribute to denitrification not nitrification. Bacillus bataviensis- and B. jeotgali-related strains isolated from the denitrifier-aggregation layer comprised the predominant denitrifier population (3.64 × 104 cells/g of denitrifier abundance). They possess the ability of dissimilatory nitrate reduction to ammonium (DNRA). Bacillus jeotgali-related strains and two newly identified strains of GD0705 and GD0706 isolated from the ammonium-enriched layer possibly use fermentative processes as the main metabolic pathway instead of denitrification when nitrate is scarce, and this further supports the high ammonium concentrations (up to 2.20 mM) found in the Guandu sediments. In addition, spore formation also enhances the chance of survival of these strains in the face with such a nitrate-deficient environment.  相似文献   

6.
Axenic cultures of the microalgae species, Dunaliella tertiolecta and Phaeodactylum tricornutum were grown at arsenic (As) concentrations typically found in uncontaminated marine environments ( 2 µg L− 1) under different phosphorus concentrations. D. tertiolecta accumulated higher arsenic concentrations (mean: 13.7 ± 0.7 µg g− 1 dry mass) than P. tricornutum (mean: 1.9 ± 0.2 µg g−1 dry mass). Media phosphorus concentrations (0.6–3 mg/L) had little influence on microalgae growth rates or arsenic accumulation. Arsenic was present as lipid bound (29–38%; 4.2–9.5%), water-soluble (20–29%; 26–34%) and residue bound (41–45%; 57–69%) arsenic species in D. tertiolecta and P. tricornutum respectively. Hydrolysed lipids contained mostly glycerol arsenoribose (OH- ribose), dimethylarsinate (DMA) and inorganic arsenic (As(V)) moieties. Water-soluble species of microalgae were very different. D. tertiolecta contained inorganic arsenic (54–86%) with variable amounts of DMA (7.4–20%), arsenoriboses (5–25%) and traces of methylarsonate (MA) ( 1%). P. tricornutum contained mostly DMA (32–56%) and phosphate arsenoribose (PO4-ribose, 23–49%) and small amounts of OH-ribose (3.8–6.5%) and As(V) (9–16%). Both microalgae contained an unknown cationic arsenic species. The residue fractions of both microalgae contained predominately inorganic arsenic (99–100%). These results show that at natural seawater arsenic concentrations, both algae take up substantial amounts of inorganic arsenic that is complexed with structural elements or sequestered in vacuoles as stable complexes. A significant portion is also incorporated into lipids. Arsenic is metabolised to simple methylated species and arsenoriboses.  相似文献   

7.
Seventy-nine total-mercury analyses of seawater samples, collected from the surface down to 5,700 m depth in the northeastern Pacific Ocean and in the South Polar seas, showed a homogeneous distribution of mercury with depth at all stations, although its absolute concentration in the northeastern Pacific (12–30 ng/kg) was 3 to 5 times less than that in the polar waters (50–150 ng/kg). The high concentrations are ascribed to an input of mercury resulting from submarine volcanism.The mercury content was also determined in 8 surface-film samples, 3 sediment cores (0–30 cm), 2 pack-ice samples and 1 sample each of snow and sea smoke.  相似文献   

8.
A continuous flow method for the determination of ammonium concentration in seawater from a nanomolar to a micromolar level is described. To prevent spurious peaks derived from salinity difference, a gas-permeable hydrophobic membrane filter was used to separate the manifold into an outgassing section and an indophenol blue reaction section. The indophenol blue reaction section was adopted for colorimetric analysis and is equipped with a 1-m path length liquid capillary cell and a fiber-optic spectrometer, which is able to record the absorbance at multiple wavelengths. The minimum detection limit at wavelength 630 nm is 5.5 ± 1.8 nM, and the calibration curves are linear to at least 2,000 nM. In addition, the minimum detection limit at wavelength 530 nm was 13 ± 5.3 nM, and linear calibration curves were observed until at least 10,000 nM. The slopes of the calibration curves were similar for standards prepared using filtered seawater and ultrapure water. The ammonium concentration of the ultrapure water was similar to those of ion-exchanged water and unfiltered low-nutrient seawater, but was significantly lower than those of filtered seawater and solutions that contained sodium hydroxide. Therefore, ultrapure water is optimal for both blank and standard preparations because of its stable quality and availability. Given its large concentration range and the use of readily available blanks, this method is suitable for the determination of ammonium concentration and helps our understanding of ammonium dynamics in the ocean.  相似文献   

9.
Sediments and overlying water collected using Multiple Corer (MC) and Box Corer (BC) at three stations in Suruga Bay were compared from the view points of meiobenthic and chemical characteristics. Dissolved oxygen, pH, ammonium and nitrite concentrations of the overlying waters were lower, whereas nitrate and phosphate concentrations were higher constantly in the samples collected by MC than those by BC, suggesting contamination of surface seawater in the BC samples. Sediments were sliced into 0–1, 1–2 and 2–3 cm layers, and water content and Eh, and abundance of meiofauna were analyzed. Water content in MC samples was always higher than BC ones. For the whole meiobenthos, MC collected significantly more individuals than BC at only one out of three stations, whereas for harpacticoid copepods, which aggregated to the surface layer of the sediment, MC constantly collected significantly more individuals than BC. In the vertical profiles of both water content and meiofaunal density, data of 0–1, and 1–2 cm layers in the BC samples were similar to those of 1–2 and 2–3 cm layers in the MC samples, respectively. These results suggested only MC can collect the real sediment surface (so called fluffy layer), which was lost due to bow wave effects in the BC samples.  相似文献   

10.
The absorption of anthropogenic CO2 and atmospheric deposition of acidity can both contribute to the acidification of the global ocean. Rainfall pH measurements and chemical compositions monitored on the island of Bermuda since 1980, and a long-term seawater CO2 time-series (1983–2005) in the subtropical North Atlantic Ocean near Bermuda were used to evaluate the influence of acidic deposition on the acidification of oligotrophic waters of the North Atlantic Ocean and coastal waters of the coral reef ecosystem of Bermuda. Since the early 1980's, the average annual wet deposition of acidity at Bermuda was 15 ± 14 mmol m− 2 year− 1, while surface seawater pH decreased by 0.0017 ± 0.0001 pH units each year. The gradual acidification of subtropical gyre waters was primarily due to uptake of anthropogenic CO2. We estimate that direct atmospheric acid deposition contributed 2% to the acidification of surface waters in the subtropical North Atlantic Ocean, although this value likely represents an upper limit. Acidifying deposition had negligible influence on seawater CO2 chemistry of the Bermuda coral reef, with no evident impact on hard coral calcification.  相似文献   

11.
The oceanic biogeochemical cycles of many trace elements are dominated by their association with the growth, death, consumption and sinking of phytoplankton. The trace element content of marine phytoplankton reflects nutritional status, species composition, surface area to volume ratios, and interactions with bioactive and toxic elements in the ambient seawater. Despite the ecological and environmental importance of trace element assimilation by autotrophs, there are few modern measurements of trace elements in phytoplankton assemblages from the natural environment. Here we introduce a new method for collection and analysis of size-fractionated particulate samples from practical seawater volumes. We pay particular attention to accurate determination of trace element filter blanks which are typically the limiting factor for analysis of such samples. Metals were determined at very low detection limits by high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) for 11 elements (Ag, Al, Cd, Co, Cr, Cu, Fe, Mn, U, Zn and P, which is used as a biomass normalizer) in three types of polymer filters (0.45, 5.0, and 53 μm pore size) and a quartz fiber filter (0.8 μm pore size). To place these new determinations in a practical context, results are presented for a vertical profile of samples filtered from 1–4 l of coastal seawater (0.3–1.0 mg total solid dry weight) at a station off central California. The results demonstrate that the blanks of the evaluated filter types, precleaned appropriately, are sufficiently low to allow accurate determination of the trace metal content of three size-classes of phytoplankton. At the Pacific station, measured phytoplankton Zn content (as Zn/P) agrees with values predicted from single-species culture studies growing at seawater Zn concentrations expected for coastal waters. The new method has utility as a generally applicable and simple size fractionation technique, and allows determination of natural and pollutant elements in small samples of phytoplankton and particles in coastal, estuarine and offshore marine regimes.  相似文献   

12.
Climatological variability of picophytoplankton populations that consisted of >64% of total chlorophyll a concentrations was investigated in the equatorial Pacific. Flow cytometric analysis was conducted along the equator between 145°E and 160°W during three cruises in November–December 1999, January 2001, and January–February 2002. Those cruises were covering the La Niña (1999, 2001) and the pre-El Niño (2002) periods. According to the sea surface temperature (SST) and nitrate concentrations in the surface water, three regions were distinguished spatially, viz., the warm-water region with >28 °C SST and nitrate depletion (<0.1 μmol kg−1), the upwelling region with <28 °C SST and high nitrate (>4 μmol kg−1) water, and the in-between frontal zone with low nitrate (0.1–4 μmol kg−1). Picophytoplankton identified as the groups of Prochlorococcus, Synechococcus and picoeukaryotes showed a distinct spatial heterogeneity in abundance corresponding to the watermass distribution. Prochlorococcus was most abundant in the warm-water region, especially in the nitrate-depleted water with >150×103 cells ml−1, Synechococcus in the frontal zone with >15×103 cells ml−1, and picoeukaryotes in the upwelling region with >8×103 cells ml−1. The warm-water region extended eastward with eastward shift of the frontal zone and the upwelling region during the pre-El Niño period. On the contrary, these regions distributed westward during the La Niña period. These climatological fluctuations of the watermass significantly influenced the distribution of picophytoplankton populations. The most abundant area of Prochlorococcus and Synechococcus extended eastward and picoeukaryotes developed westward during the pre-El Niño period. The spatial heterogeneity of each picophytoplankton group is discussed here in association with spatial variations in nitrate supply, ambient ammonium concentration, and light field.  相似文献   

13.
In the spring of 1995, short-term variations in the concentration of particulate and dissolved dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) were monitored in the western Wadden Sea, a shallow coastal region in open connection with the North Sea. Significant correlations were found between abundance of Phaeocystis globosa and particulate DMSP; concentrations increased rapidly from 100 to 1650 nM in the middle of April. Highest DMS concentrations were found during the initial phase of the exponential growth of the bloom. DMS production and loss rates of DMSP and DMS were estimated experimentally during various phases of the bloom. DMS production and consumption were roughly in balance, with production only slightly exceeding consumption at the start of the bloom. Rates of production and consumption were highest during the exponential growth phase of Phaeocystis and declined in the course of the bloom (from 300–375 to less than 5 nmol dm−3 d−1). Demethylation of DMSP increased during the bloom (from 11 to 1300 nmol dm−3 d−1); it accounted for up to 100% of the DMSP loss at the end of the bloom. The shift from DMSP cleavage to demethylation in the course of a Phaeocystis bloom implies that DMS concentrations are not necessarily highest at the peak or towards the end of blooms.  相似文献   

14.
The esterification of two model vertebrate steroid hormones – estradiol (E2) and dehidroepiandrosterone (DHEA) – was studied in the oyster Crassostrea virginica. The activity of acyl-CoA:steroid acyltransferase was characterized in microsomal fractions isolated from oyster digestive glands. The apparent Km and Vmax values changed with the fatty acid acyl-CoA used (C20:4, C18:2, C18:1, C16:1, C18:0 or C16:0), and were in the range of 9–17 μM, and 35–74 pmol/min/mg protein for E2, and in the range of 45–120 μM, and 30–182 pmol/min/mg protein for DHEA. Kinetic parameters were also assessed in gonadal tissue. The enzyme saturated at similar concentrations, although conjugation rates were lower than in digestive gland. Preliminary data shows that tributyltin (TBT) in the low μM range (1–50) strongly inhibits E2 and DHEA esterification, the esterification of E2 being more sensitive to inhibition than that of DHEA. Overall, results indicate that apolar conjugation occurs in oysters, in both digestive gland and gonads, at a very similar rate to mammals, suggesting that this is a well conserved conjugation pathway during evolution. Esterification, together with other mechanisms, can modulate endogenous steroid levels in C. virginica, and might be a target for endocrine disrupters, such as TBT.  相似文献   

15.
为了优化蛏苗集约化平面流中间培育技术,研究了不同进水流速和苗种规格对缢蛏中间培育效果的影响,并分析了集约化平面流中间培育系统的水质状况。结果显示,不同进水流速对缢蛏稚贝生长影响显著,稚贝生长速率随进水流速增加而增加,但成活率下降。通过流速与成活率和体质量日增生长量的线性回归分析,估算0.163L/s为适宜的进水流速。在适宜流速和相同放苗重量下,大规格苗种(8万粒/kg)生长速度显著高于小规格苗种(18万粒/kg),但因为小规格组放苗数量多,小规格组单位面积质量较其高出23.72%。除低流速组以外,平面流中间培育过程对叶绿素a和铵态氮有良好的去除效果,去除率分别达到36.99%和3.88%以上,这表明平面流集约化中间培育在利用海水池塘水体进行苗种中间培育的同时,也起到了池塘养殖水体的净化作用。综合认为,在养殖密度0.5kg/m^2、流速0.163 L/s的培育条件下,可以保证水体自污染程度较低,缢蛏苗种生长较快,成活率在73.12%以上。  相似文献   

16.
β-dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) concentrations were recorded from September 1999 to September 2000 in two geographically close ecosystems, differently affected by eutrophication: the Little Bay of Toulon and the Niel Bay (N.W. Mediterranean Sea, France). Little Bay had higher nutrient levels ([NO3−]max. = 30.3 μM; [PO43−]max. = 0.46 μM) and higher chlorophyll a concentrations ([chl a]mean = 2.4 μg/L) compared to Niel Bay ([NO3−]max. = 19.7 μM; [PO43−]max. = 0.17 μM; [chl a]mean = 0.4 μg/L). In the two sites, we measured dissolved (DMSPd < 0.2 μm) and particulate DMSP (DMSPp > 0.2 μm) concentrations. The DMSPp was particularly analysed in the 0.2–5, 5–90 and > 90 μm fractions. In the eutrophicated Little Bay, DMSPd concentrations showed a clear seasonality with high values from January to March (124–148 nM). The temporal profile of the DMSPp concentrations was similar, peaking in February–March (38–59 nM). In the less eutrophic Niel Bay, DMSPp concentrations were much lower (6–9 nM in March–April), whereas DMSPd concentrations were relatively high (110–92 nM in February–March). DMS concentrations were elevated from the end of the winter to the spring in Little Bay, ranging from 3 nM in October to 134 nM in March. In the less eutrophic Niel Bay, lower DMS levels were observed, generally not exceeding 20 nM. Each particulate fraction (0.2–5; 5–90; > 90 μm) contained less DMSP in Niel Bay than in Little Bay. At both sites, the 5–90 μm fraction made up most of the DMSPp. This 5–90 μm fraction consisted of microphytoplankton, principally Dinophyceae and Bacillariophyceae. The 5–90 μm biomass calculated from cell biovolumes, was more abundant in Little Bay where the bloom at the end of the winter (165 μg/L in March) occurred at the same time as the DMSP peaks. The estimated DMSPp to biomass ratio for the 5–90 μm fraction was always higher in Little Bay than in Niel Bay. This suggests that the high DMSP levels recorded in Little Bay were not only due to a large Dinophyceae presence in this ecosystem. Indeed, the peak of DMSPp to biomass ratio obtained from cell biovolumes (0.23 nmol/μg in March) was consistent with the proliferation of Alexandrium minutum. This Dinophyceae species may account for between 50% (2894 cells/L) and 63% (4914 cells/L) of the total phytoplankton abundance in the Little Bay of Toulon.  相似文献   

17.
Standing stocks and production rates of phytoplankton and abundance of bacteria were investigated at 39 stations in the Seto Inland Sea, Japan during four crulses in October 1993, January, April and June 1994. Primary productivity was measured by the13C tracer method. Photosynthetic rate varied from 0.41 to 32.1 μgC/1/h with an average value of 4.67 μgC/l/h. Annual primary production was estimated to be 218 gC/m2/year. Annual primary production in this study was 1.8 times as high as the values which were previously reported at same area. The reason for the disagreement between our primary production value and previous values is not thought to be due to the difference of methods used for measuring primary production or the different Chl.a concentrations but to the method of estimating the primary production in the euphotic zone from thein vitro measurements. The distribution of bacterial cells in surface seawater was examined during the same cruises. Bacterial cell density ranged from 0.32 to 3.4×106 cells/ml. The density was relatively high in the eutrophic regions of Hiroshima Bay and Osaka Bay In addition, a high density of bacteria was also observed in an area within Suo Nada where Chl.a was relatively low. The disparity between Chla and bacterial density in Suo Nada suggests that bacterial abundance can be controlled by the availability of substrates other than phytoplankton exudate.  相似文献   

18.
Relationships between light intensity and substrate concentration and rates of assimilation and oxidation of ammonium by microorganisms were investigated at four stations off the Washington coast and three stations in the Southern California Bight. Ammonium oxidation rates were negatively correlated with light in the photic zone at all stations; light inhibition of nitrifying bacteria forms an important control over the depth distribution of ammonium oxidation activity. Both assimilation and oxidation were positively correlated with ammonium concentration at the Washington coast stations, where ambient ammonium concentrations were high. Light and ammonium assimilation rate were positively correlated at the Southern California Bight stations (within the photic zone; i.e., excluding depths greater than 150m), but unrelated at the Washington coast stations. Assimilation and oxidation have nearly opposite distribution patterns with depth in the water column, but phytoplankton and nitrifying bacteria probably compete for ammonium at depths near the bottom of the photic zone.  相似文献   

19.
Primary production was measured during two Lagrangian experiments in the Iberian upwelling. The first experiment, in a body of upwelled water, measured day-to-day changes in phytoplankton activity as the water mass moved south along the shelf break. Nutrient concentrations decreased over a five day period, with concomitant increases in phytoplankton biomass. Initially the maximum phytoplankton biomass was in the upper 10m but after four days, a sub-surface chlorophyll maximum was present at 30m. Depth-integrated primary production at the beginning of the experiment was 70mmolC.m−2.d−1 (838mgC.m−2.d−1) and reached a maximum of 88mmolC.m−2.d−1 (1053mgC.m−2.d−1) on day 3. On day 1, the picoplankton fraction (<2μm) was slightly more productive than larger (>5μm) phytoplankton, but the increase in overall production during the drift experiment was by these larger cells. Nitrate was the dominant nitrogen source. As nutrient concentrations declined, ammonium became increasingly more important as a nitrogen source and the f-ratio decreased from 0.7 to 0.5. Picoplankton cells (<2μm) were responsible for most (65–80%) of the ammonium uptake. The C:N:P uptake ratios were very close to the Redfield ratio for the first four days but as nutrients became depleted high C:N uptake ratios (11 to 43) were measured. Over the period of the experiment, nitrate concentration within the upper 40m decreased by 47.91mmolN.m−2. In vitro estimates, based on 15N nitrate uptake, accounted for 56% of the decrease in nitrate concentration observed in the drifting water mass. Ammonium uptake over the same four day period was 16.28mmolN.m−2, giving a total nitrogen uptake of 43.18mmolN.m−2.In the second experiment, an offshore filament was the focus and a water mass was sampled as it moved offshore. Nutrient concentrations were very low (nitrate was <10nmol l−1 and ammonium was 20–40nmol l−1). Primary production rate varied between 36mmolC.m−2.d−1 (436mgC.m−2.d−1) and 21mmolC.m−2.d−1 (249mgC.m−2.d−1). Picophytoplankton was the most productive fraction and was responsible for a constant proportion (ca 0.65) of the total carbon fixation. Uptake rates of both nitrate and ammonium were between 10 and 20% of those measured in the upwelling region. Urea could be a very significant nitrogen source in these waters with much higher uptake rates than nitrate or ammonium; urea turnover times were ca. one day but the source of the urea remains unknown. Urea uptake had a profound effect on calculated f ratios. If only nitrate and ammonium uptake was considered, f ratios were calculated to be 0.42–0.46 but inclusion of urea uptake reduced the f ratio to <0.1. The primary production of this oligotrophic off-shore filament was driven by regenerated nitrogen.  相似文献   

20.
Production of the marine calanoid copepod Acartia steueri was measured from 2 October 1991 to 8 October 1992 at a station in Ilkwang Bay, on the southeastern coast of Korea. Phytoplankton standing stock ranged over 1.0 to 9.3 mg chl.a m−3, and annual primary productivity (by the C-14 method) at three stations was estimated at 200 gC m−2 yr−1. Acartia steueri (nauplii + copepodids + adults) were present in the plankton throughout the year, with seasonal variation in abundance. Biomass of A. steueri, excluding the NI stage, was 0.01–4.55 mgC m−3 (mean: 0.68 mgC m−3) with peaks in November, February, May and July-early August, and relatively low biomass in September– January. Instantaneous growth rates of the nauplius stages were higher than the copepodid stages. Annual production of A. steueri was 25.1 mgC m−3 yr−1 (or 166 mgC m−2 yr−1), showing peaks in November, May and July–August with a small peak in February, and low production in December–April and September–October. There were no significant relationships between the daily production rate of A. steueri and temperature or chlorophyll a concentration, indicating that unknown other factors might be related to the variation of the production rate.  相似文献   

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