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1.
Seasonal and interannual variations in physicochemical properties were investigated in the neritic area of Sagami Bay, Kanagawa, Japan, from December 2000 to December 2005. Physicochemical properties (i.e. temperature, salinity, density, dissolved oxygen and dissolved inorganic nutrient concentration) revealed clear seasonal variations, which were similar to each other during all 5 years. Temperature, salinity and dissolved inorganic nutrients showed rapid, drastic variations within a few days and/or weeks. These variations are related to sea levels, principally due to the shifting effects of the Kuroshio Current axis: they were strongly affected by the Kuroshio Water and other waters, when sea level difference was greater than ca. 35 cm and lower than ca. 15 cm, respectively. Temperature difference (DF T ) increased with sea level difference, and the difference of salinity and dissolved inorganic nutrients (NH4 +-N, NO3 −+NO2 −-N, NH4 ++NO3 −+NO2 −-N, PO4 3−-P and SiO2-Si) increased and decreased with DF T , respectively. All these correlations are significant. Total dissolved inorganic nitrogen (N), phosphate (P) and silicate (Si) revealed seasonal variations in the ranges of 0.57–16.08, 0.0070–0.91 and 0.22–46.38 μM, respectively. From the regression equations between these elements allowed the following relation to be obtained; Si:N:P = 14.8:13.4:1. Dissolved inorganic nutrients were characterized by Si and/or P deficiency, especially in the upper layer (0–20 m depth) during summer. Single and/or combined elements are discussed on the basis of potential and stoichiometric nutrient limitations, which could restrict phytoplankton (diatom) growth as a limiting factor.  相似文献   

2.
Nutrient-enrichment bottle experiments in the northwestern Indian Ocean surface waters were conducted to investigate phytoplankton growth following enrichments with either NH4+, NO3−, Fe or Fe + NO3−. Stimulation of phytoplankton growth could be achieved by the addition of either NH4+ or NO3− under the ambient Fe concentrations, but the most significant increases in Chl a, POC, and cell densities were observed in the Fe + NO3−-amended culture. Iron addition caused more rapid responses of phytoplankton growth in the Fe + NO3− treatment than those in the NO3− and NH4− treatment. However, the Fe-enrichment treatment revealed minimal growth of phytoplankton because of severe major nutrient deficiency and was similar to the control treatment. Increases in the cell density of diatoms and spherical phytoplankton cells (< 10 μm) were significant in the NH4+-enriched samples, whereas NO3− enrichment alone had little effect on the diatoms. Simultaneous addition of Fe and NO3− stimulated maximal growth of phytoplankton, in particular in diatoms, coccolithophorids and Phaeocystis type colonies. However, the dominance of coccolithophorids and Phaeocystis type colonies in the Fe + NO3− treatment may be interpreted as resulting from Si-limitation. The high N/P ratio for phytoplankton nutrient uptake in the N-amended culture indicates the possibility of some P-limited growth. From these results, we conclude that in the northwestern Indian Ocean, Fe and major nutrients are co-limiting phytoplankton production during the northeast monsoon. Iron appeared to affect the ability of phytoplankton to respond quickly to transient nutrient inputs.  相似文献   

3.
Concentrations of particulate organic nitrogen (PN), dissolved inorganic nitrogen (DIN), and their nitrogen isotope ratios (δ 15N) in the Kiso-Sansen Rivers were determined from monthly observations over the course of a year to assess variations in the form and sources of riverine nitrogen discharged into Ise Bay. The δ 15N values of NO3 − observed in the Kiso-Sansen Rivers showed a logarithmic decreasing trend from 8 to 0‰, which varied with the river discharge, indicating mixing between point sources with high δ 15N and non-point sources with low δ 15N. The influence of isotope fractionation of in situ biogeochemical processes (mainly DIN assimilation by phytoplankton) on δ 15N of NO3 − was negligible, because sufficient concentrations of NH4 + for phytoplankton demand would inhibit the assimilation of NO3 −. A simple relationship between river discharge and δ 15N of NO3 − showed that the fraction of total NO3 − flux arising from point sources increased from 4.0–6.3% (1.1–1.8 tN day−1) during higher discharge (>600 m3 s−1) to 30.2–48.3% (2.6–4.1 tN day−1) during lower discharge (<300 m3 s−1). Riverine NO3 − discharge from the Kiso-Sansen Rivers can explain 75% of the variations in surface NO3 − at the head of Ise Bay over the year.  相似文献   

4.
A Geographic Information System (GIS)-aided flow-tracking technique was adopted to investigate nutrient exchange rates between specific benthic communities and overlying seawater in a fringing reef of Ishigaki Island, subtropical Northwestern Pacific. Net exchange rates of NO3 −, NO2 −, NH4 +, PO4 3−, Total-N and Total-P were estimated from concentration changes along the drogue trajectories, each of which was tracked by the Global Positioning System and plotted on a benthic map to determine the types of benthic habitat over which the drogue had passed. The observed nutrient exchange rates were compared between 5 typical benthic zones (branched-coral (B) and Heliopora communities (H), seaweed-reefrock zone (W), bare sand area (S), and seagrass meadow (G)). The dependence of nutrient exchange rates on nutrient concentrations, physical conditions and benthic characteristics was analyzed by multiple regression analysis with the aid of GIS. The spatial correlation between nutrient exchange rates and benthic characteristics was confirmed, especially for NO3 − and PO4 3−, which were usually absorbed in hydrographically upstream zones B and W and regenerated in downstream zones H and G. NO3 − uptake in zones B and W was concentration-dependent, and the uptake rate coefficient was estimated to be 0.58 and 0.67 m h−1, respectively. Both nutrient uptake in zone W and regeneration in zone H were enhanced in summer. The net regeneration ratio of NO3 −/PO4 3− in zone H in summer ranged 5.2 to 34 (mean, 17.4), which was somewhat higher than previously measured NO3 −/PO4 3− for sediment pore waters around this zone (1.1–8.5). Nutrient exchanges in zone S were relatively small, indicating semi-closed nutrient cycling at the sediment-water interface of this zone. NH4 + efflux from sediments was suggested in zone G. The data suggest that the spatial pattern of nutrient dynamics over the reef flat community was constrained by zonation of benthic biota, and that abiotic factors such as nutrient concentrations and flow rates, influenced nutrient exchange rates only in absorption-dominated communities such as zones B and W.  相似文献   

5.
We report the first application of a biogeochemical model in which the major elemental composition of the phytoplankton is flexible, and responds to changing light and nutrient conditions. The model includes two phytoplankton groups: diatoms and non-siliceous picoplankton. Both fix C in accordance with photosynthesis-irradiance relationships used in other models and take up NO3− and NH4+ (and Si(OH)4 for diatoms) following Michaelis-Menten kinetics. The model allows for light dependence of photosynthesis and NO3− uptake, and for the observed near-total light independence of NH4+ uptake and Si(OH)4 uptake. It tracks the resulting C/N ratios of both phytoplankton groups and Si/N ratio of diatoms, and permits uptake of C, N and Si to proceed independently of one another when those ratios are close to those of nutrient-replete phytoplankton. When the C/N or Si/N ratio of either phytoplankton group indicates that its growth is limited by N, Si or light, uptake of non-limiting elements is controlled by the content of the limiting element in accordance with the cell-quota formulation of Droop (J. Mar. Biol. Ass. U.K 54 (1974) 825).We applied this model to the Bermuda Atlantic Time-series Study (BATS) site in the western Sargasso Sea. The model was tuned to produce vertical profiles and time courses of [NO3−], [NH4+] and [Si(OH)4] that are consistent with the data, by adjusting the kinetic parameters for N and Si uptake and the rate of nitrification. The model then reproduces the observed time courses of chlorophyll-a, particulate organic carbon and nitrogen, biogenic silica, primary productivity, biogenic silica production and POC export with no further tuning. Simulated C/N and Si/N ratios of the phytoplankton indicate that N is the main growth-limiting nutrient throughout the thermally stratified period and that [Si(OH)4], although always limiting to the rate of Si uptake by diatoms, seldom limits their growth rate. The model requires significant nitrification in the upper 200 m to yield realistic time courses and vertical profiles of [NH4+] and [NO3−], suggesting that NO3− is not supplied to the upper water column entirely by physical processes. A nitrification-corrected f-ratio (fNC), calculated for the upper 200 m as: (NO3− uptake—nitrification)/(NO3− uptake+NH4+ uptake) has annual values ranging from only 0.05–0.09, implying that 90–95% of the N taken up annually by phytoplankton is supplied by biological regeneration (including nitrification) in the upper 200 m. Reported discrepancies between estimates of organic C export based on seasonal chemical changes and POC export measured at the BATS site can be almost completely resolved if there is significant regeneration of NO3− via organic-matter decomposition in the upper 200 m.  相似文献   

6.
The influence of macronitrogen (NO - 3 and NH + 4 ) addition with Ulva pertusa on dissolved inorganic carbon system in seawater was studied. The results indicate that p(CO 2 ) and HCO 3 concentration decrease significantly, while pH and CO 2- 3 concentration increase significantly. When the concentration of NO 3 was less than 71 μmol/dm 3 or NH + 4 was less than 49.7 μmol/dm 3 , dissolved inorganic carbon (DIC) absorption rates by Ulva pertusa generally increased with the increasing of nitrogen concentration. The DIC decreased 151 μmol/dm 3 with the addition of 71 μmol/dm 3 NO 3 and decreased 232 μmol/dm 3 with the addition of 49.7 μmol/dm 3 NH + 4 after the experiment compared with DIC measured without nitrogen addition. A significant negative-correlation was found between c(DIC) and growth rate (μ) of Ulva pertusa (r = -0.91, P <0.000 1, n=11). NH + 4 had more influence on the species of inorganic carbon system than NO 3 .  相似文献   

7.
Temporal changes in nitrogen isotopic composition (δ15N) of the NO3 − pool in the water column below the pycnocline in Ise Bay, Japan were investigated to evaluate the effect of nitrification on the change in the δ15N in the water column. The δ15N of NO3 − in the lower layers varied from −8.5‰ in May to +8.4‰ in July in response to the development of seasonal hypoxia and conversion from NH4 + to NO3 −. The significantly 15N-depleted NO3 − in May most likely arose from nitrification in the water column. The calculated apparent isotopic discrimination for water column nitrification (ɛnit = δ15Nsubstrate − δ15Nproduct) was 24.5‰, which lies within the range of previous laboratory-based estimates. Though prominent deficits of NO3 − from hypoxic bottom waters due to denitrification were revealed in July, the isotopic discrimination of denitrification in the sediments was low (ɛdenit = ∼1‰). δ15NNO3 in the hypoxic lower layer mainly reflects the isotopic effect of water column nitrification, given that water column nitrification is not directly linked with sedimentary denitrification and the effect of sedimentary denitrification on the change in δ15NNO3 is relatively small.  相似文献   

8.
浒苔对NH+4-N与NO-3-N吸收的相互作用   总被引：1，自引：0，他引：1  
在国内首次研究了大型海洋绿潮藻浒苔(Ulva prolifera)对NH4+-N与NO 3--N两种氮源的选择吸收作用。结果表明:当两种氮源等浓度比例存在时,随着NH4+-N与NO3--N浓度升高,藻体对NH4+-N的吸收速率逐渐升高,而对NO3--N吸收受到抑制;当NO3--N和NH 4+-N高浓度比存在时,藻体对NH4-N的吸收速率随着NO3--N/NH4+-N比例的升高和NH4-N浓度的下降而降低;当NO3--N和NH4+-N低浓度比存在时,藻体对NH+4-N保持较高的吸收速率,而对NO3--N的吸收效率随着NO3--N浓度的降低而降低;浒苔具有同时利用水体中较高浓度的NH+4-N和NO3--N的能力,只有当NH4+-N或NO3--N浓度较低时,才以吸收相对应的氮源为主。这说明浒苔能够快速、大量地吸收水体中氮源,为爆发性增殖贮备物质条件。同时,即便两种氮源同时存在,浒苔对NH+4-N的吸收速率也远高于对NO3--N的吸收速率,因此,控制NH4+-N的大量输入仍是预防浒苔绿潮爆发的关键。  相似文献   

9.
In the present study, we have investigated the conditions influencing encystment and excystment in the dinoflagellate Gyrodinium instriatum under laboratory conditions. We incubated G. instriatum in modified whole SWM-3 culture medium and in versions of modified SWM-3 from which NO3 −, PO4 3−, NO3 − + PO4 3−, or Si had been omitted and observed encystment. Percentage encystment was high in the media without N and without P, while the percentage encystment in the medium lacking both N and P was highest. Moreover, to investigate N or P concentration which induced the encystment, Gyrodinium instriatum was also incubated in media with different concentrations of inorganic N and P; the concentrations of NO2 − + NO3 − and PO4 3− were measured over time. The precursors of cysts appeared within 2 or 3 days of a decrease in NO2 − + NO3 − or PO4 3− concentration to values lower than 1 μM or 0.2 μM, respectively. When cysts produced in the laboratory were incubated, we observed excystment after 8–37 days, without a mandatory period of darkness or low temperature. We incubated cysts collected from nature at different temperatures or in the dark or light and observed excystments. Natural cysts excysted at temperatures from 10 to 30°C, in both light and dark, but excystment was delayed at low temperatures. These studies indicate that G. instriatum encysts in low N or P concentration and excysts over a wide temperature range, regardless of light conditions, after short dormancy periods.  相似文献   

10.
This study investigates the biogeochemical processes that control the benthic fluxes of dissolved nitrogen (N) species in Boknis Eck – a 28 m deep site in the Eckernförde Bay (southwestern Baltic Sea). Bottom water oxygen concentrations (O2−BW) fluctuate greatly over the year at Boknis Eck, being well-oxygenated in winter and experiencing severe bottom water hypoxia and even anoxia in late summer. The present communication addresses the winter situation (February 2010). Fluxes of ammonium (NH4+), nitrate (NO3−) and nitrite (NO2−) were simulated using a benthic model that accounted for transport and biogeochemical reactions and constrained with ex situ flux measurements and sediment geochemical analysis. The sediments were a net sink for NO3− (−0.35 mmol m−2 d−1 of NO3−), of which 75% was ascribed to dissimilatory reduction of nitrate to ammonium (DNRA) by sulfide oxidizing bacteria, and 25% to NO3− reduction to NO2− by denitrifying microorganisms. NH4+ fluxes were high (1.74 mmol m−2 d−1 of NH4+), mainly due to the degradation of organic nitrogen, and directed out of the sediment. NO2− fluxes were negligible. The sediments in Boknis Eck are, therefore, a net source of dissolved inorganic nitrogen (DIN = NO3− + NO2− + NH4+) during winter. This is in large part due to bioirrigation, which accounts for 76% of the benthic efflux of NH4+, thus reducing the capacity for nitrification of NH4+. The combined rate of fixed N loss by denitrification and anammox was estimated at 0.08 mmol m−2 d−1 of N2, which is at the lower end of previously reported values. A systematic sensitivity analysis revealed that denitrification and anammox respond strongly and positively to the concentration of NO3− in the bottom water (NO3−BW). Higher O2−BW decreases DNRA and denitrification but stimulates both anammox and the contribution of anammox to total N2 production (%Ramx). A complete mechanistic explanation of these findings is provided. Our analysis indicates that nitrification is the geochemical driving force behind the observed correlation between %Ramx and water depth in the seminal study of Dalsgaard et al. (2005). Despite remaining uncertainties, the results provide a general mechanistic framework for interpreting the existing knowledge of N-turnover processes and fluxes in continental margin sediments, as well as predicting the types of environment where these reactions are expected to occur prominently.  相似文献   

11.
A 24 hour time series survey was carried out during a spring tide (tidal range ca.2 m) of May 1995 on a tidal estuary in the Seto Inland Sea, Japan, in the context of an integrated program planned to quantify the dynamics of biophilic elements (carbon, nitrogen and phosphorus) and the roles played by the macrobenthos on the processes. Three stations were set along a transect line of about 1.4 km, which linked the river to the rear to the innermost part of the subtidal zone. Every hour, at each station, measurements were made of surface water temperature, salinity and dissolved oxygen concentration, and surface water was collected for the determination of nutrients [NH4 +−N, (NO3 −+NO2 −)−N, PO4 3−−P and Si (OH)4−Si]. During the ebb flow, riverine input of silicate and nitrate+nitrite significantly increased the concentrations of both the intertidal and the subtidal stations. Conversely, during the high tide, river nutrient concentrations were lowered by the mixing of fresh water with sea water. As a result, best (inverse) correlations were found at the river station for salinity against silicate (y=-2.9 Sal.+110.7,r 2=0.879) and nitrate+nitrite (y=-1.3 Sal.+48.4,r 2=0.796). In contrast, ammonium nitrogen concentrations were higher at intermediate salinities. Indeed, no significant correlation was found between salinity and ammonium. The effect of the macrobenthos, which is abundant on the intertidal flat, is discussed as a biological component that influences the processes of nutrient regeneration within the estuary. The effect of the tidal amplitude is an important one in determining the extent of the variations in nutrient concentrations at all three stations, which were stronger between the lower low tide and the higher high tide.  相似文献   

12.
In Tokyo Bay the concentrations of dissolved gaseous mercury (DGM) in the surface seawater and total gaseous mercury (TGM) over the sea were measured during December 2003, October 2004 and January 2005. Based on these data, the evasional fluxes of mercury from the sea surface were estimated using a gas exchange model. In addition, an automatic wet and dry deposition sampler was used to measure the wet and dry depositional fluxes of mercury from December 2003 to November 2004 at three locations in and near Tokyo Bay. The results indicate that the average DGM and TGM levels of seven locations are 52 ± 26 ng m−3 and 1.9 ± 0.6 ng m−3, respectively, which shows that the surface seawater in Tokyo Bay is supersaturated with gaseous mercury, leading to an average mercury evasional flux of 140 ± 120 ng m−2d−1. On the other hand, the annual average wet and dry depositional fluxes of mercury at three locations were 19 ± 3 μg m−2yr−1 and 20 ± 9 μg m−2yr−1, respectively. These depositional fluxes correspond to the daily average total depositional flux of 110 ± 20 ng m−2d−1. Thus, it is suggested that in Tokyo Bay, the evasional fluxes of mercury are comparable to the depositional fluxes.  相似文献   

13.
The first estimates of uptake kinetic parameters for NH4+, NO3−, and urea in the Ross Sea, Antarctica were measured on three cruises during austral late winter–early spring 1996 (pre-bloom), late spring 1997 (bloom development), and summer 1997 (bloom decline). Nitrogen (N) uptake experiments were conducted with water collected at the 50% light penetration depth using trace-metal clean protocols and 15N tracer techniques. At all sites, ambient NO3− concentrations ranged from 5.8 to 30.5 μg-at N l−1 and silicic acid concentrations were greater than 62.0 μg-at Si l−1. The following trends were observed. First, based on maximum uptake rates (Vmax), apparent N utilization followed the order NO3−>NH4+>urea during the pre-bloom and bloom development cruises. During the summer cruise, as the bloom was declining, the apparent order of utilization was NH4+>NO3−>urea. Second, evidence for possible repression of NO3− uptake by elevated NH4+ concentrations was only observed at one site. Third, the kinetic parameters of NH4+ uptake rates corrected for isotope dilution were compared with the kinetic parameters determined from uncorrected rates. In this comparison, the measure of substrate affinity, α (α=Vmax/Ks) increased by an average of 4.6-fold when rates were corrected for isotope dilution, but values of Vmax remained unchanged. Fourth, using bacterial production data, the magnitude of bacterial N uptake was estimated. Assuming that all bacterial N demands were met with NH4+, the estimated bacterial portion of NH4+ uptake ranged from <1%, when the ratio of bacteria to autotrophic biomass was low, to 35%, when bacterial abundance and biomass were highest. Finally, dramatic changes in NH4+ uptake capacity were observed at one station (Stn. O), where kinetic parameters were measured during all three cruises. We hypothesize that a mutualistic relationship exists between phytoplankton and heterotrophic bacteria, and that the creation of microzones of high NH4+ concentrations contributed to the changes seen at this station.  相似文献   

14.
Estimating nitrogen transformation rates in aquatic ecosystems by isotope dilution techniques is simplified by directly measuring nitrogen isotopic ratios for NH4+ in the water using high performance cation exchange liquid chromatography (HPLC). Modifications of HPLC conditions and implementation of a median-area method for retention time determination improved and linearized a previously reported sigmoid relationship between the retention time shift (RTshift) of the NH4+ peak and the ratio of [15NH4+]: [Total NH4+] in seawater fortified with 15NH4+. Increasing the temperature of the HPLC column from 47 to 85 °C increased mobile phase buffer flow rate relative to column back pressure, decreased the retention time for NH4+, and allowed the buffer pH to be optimized relative to the pK of NH4+. The use of median-area rather than maximum-height to define the retention time of NH4+ further improved the linearity (r > 0.995) of the relationship between the ratio [15NH4+]: [Total NH4+] and RTshift over the range of isotope ratios. Reduction of NO3− to NH4+ by adding zinc dust to acidified (pH 2) seawater or lakewater samples, followed by pH neutralization, and subsequent analysis of NH4+ isotope ratios by HPLC, extended application of the method to isotope dilution experiments with NO3−. Advantages of this direct-injection method over mass-measurement approaches traditionally used for isotope dilution experiments include small sample size and minimal sample preparation.  相似文献   

15.
The egg production rate (EPR) of Calanus sinicus was measured from March 2007 to April 2010 at three stations along the Korean coast of the Yellow Sea (in coastal waters off Saemangum, Yeongheungdo, and Asan Bay) to estimate in situ maximum egg production rate (MEPR) and to understand whether the females were limited in their growth or fecundity in the field. The mean EPR of C. sinicus at each sampling date ranged from 10.3–34.9 eggs female−1 d−1 (mean 23.4 eggs female−1 d−1), and the EPR of individual copepods ranged from 0–81 eggs female−1 d−1. The mean EPR was positively correlated with the body weight of female copepods. The MEPR at each sampling date ranged from 40–81 eggs female−1 d−1 (mean 50.4 eggs female−1 d−1). Over 84% of eggs spawned hatched successfully. The weight-specific growth rate (WSGR) ranged from 0.038–0.111 d−1 (mean 0.082 d−1), indicating that 3.8–11.1% of the carbon in an adult female was produced daily as female growth. The WSGR was negatively correlated with water temperature. The ratio of mean EPR to observed mean MEPR ranged from 20–70% (mean 46%), indicating that ∼54% of a female’s growth might be limited in the field. We suggest that the ratio of observed EPR to mean MEPR of copepod can be applied to understand how the copepod responds to environmental changes, as well as EPR and hatching success.  相似文献   

16.
In-situ measurements of benthic fluxes of oxygen and nutrients were made in the subtidal region of the Mandovi estuary during premonsoon and monsoon seasons to understand the role of sediment–water exchange processes in the estuarine ecosystem. The Mandovi estuary is a shallow, highly dynamic, macrotidal estuary which experiences marine condition in the premonsoon season and nearly fresh water condition in the monsoon season. The benthic flux of nutrients exhibited strong seasonality, being higher in the premonsoon compared to the monsoon season which explains the higher ecosystem productivity in the dry season in spite of negligible riverine nutrient input. NH4+ was the major form of released N comprising 70–100% of DIN flux. The benthic respiration rate varied from −98.91 to −35.13 mmol m−2 d−1, NH4+ flux from 5.15 to 0.836 mmol m−2 d−1, NO3− + NO2− from 0.06 to −1.06 mmol m−2 d−1, DIP from 0.12 to 0.23 mmol m−2 d−1 and SiO44− from 5.78 to 0.41 mmol m−2 d−1 between premonsoon to monsoon period. The estuarine sediment acted as a net source of DIN in the premonsoon season, but changed to a net sink in the monsoon season. Variation in salinity seemed to control NH4+ flux considerably. Macrofaunal activities, especially bioturbation, enhanced the fluxes 2–25 times. The estuarine sediment was observed to be a huge reservoir of NH4+, PO43− and SiO44− and acted as a net sink of combined N because of the high rate of benthic denitrification as it could remove 22% of riverine DIN influx thereby protecting the eco system from eutrophication and consequent degradation. The estuarine sediment was responsible for ∼30–50% of the total community respiration in the estuary. The benthic supply of DIN, PO43− and SiO44− can potentially meet 49%, 25% and 55% of algal N, P and Si demand, respectively, in the estuary. Based on these observations we hypothesize that it is mainly benthic NH4+ efflux that sustains high estuarine productivity in the NO3− depleted dry season.  相似文献   

17.
Nutrient fluxes were measured between Fourleague Bay, a shallow Louisiana estuary, and the Gulf of Mexico every 3 h between February 1 and April 30, 1994 to determine how high velocity winds associated with cold fronts and peak Atchafalaya River discharge influenced transport. Net water fluxes were ebb-dominated throughout the study because of wind forcing and high volumes of water entering the northern Bay from the Atchafalaya River. Flushing time of the Bay averaged <8 days; however, more rapid flushing occurred in response to northerly winds with approximately 56% of the volume of the Bay exported to the Gulf in 1 day during the strongest flushing event. Higher nitrate+nitrite (NO2+NO3), total nitrogen (TN), and total phosphorus (TP) concentrations were indicative of Atchafalaya River input and fluxes were greater when influenced by high velocity northerly winds associated with frontal passage. Net exports of NO2+NO3, TN, and TP were 43.5, 98.5, and 13.6 g s−1, respectively, for the 89-day study. An average of 10.6 g s−1 of ammonium (NH4) was exported to the Gulf over the study; however, concentrations were lower when associated with riverine influence and wind-driven exports suggesting the importance of biological processes. Phosphate (PO4) fluxes were nearly balanced over the study with fairly stable concentrations indicating a well-buffered system. The results indicate that the high energy subsidy provided by natural pulsing events such as atmospheric cold fronts and seasonal river discharge are efficient mechanisms of nutrient delivery to adjacent wetlands and nearshore coastal ecosystems and are important in maintaining coastal sustainability.  相似文献   

18.
The relation between trophic regime and phytoplankton composition and function in oceanic systems is well accepted in oceanography. However, the relative dynamics and carbon cycling contributions of different phytoplankton groups across gradients of ocean richness are not fully understood. In this work we investigated phytoplankton dynamics along two transects from the NW African coastal upwelling to open-ocean waters of the north Atlantic subtropical gyre. We adopted a pigment-based approach to characterize community structure and to quantify group-specific growth and grazing rates and associated carbon fluxes. Changes in pigment cell concentration during the incubation experiments due to photoadaptation were corrected to obtain reliable rates. The oceanic region was dominated by Prochlorococcus (PRO) (45±7% of total chlorophyll a) while diatoms dominated in upwelling waters (40±37%). Phytoplankton grew faster (μ=0.78±0.26 d−1) and free of nutrient limitation (μ/μn=0.98±0.42) in the coastal upwelling region, with all groups growing at similar rates. In oceanic waters, the growth rate of bulk phytoplankton was lower (μ=0.52±0.16 d−1) and nutrient limited (μ/μn=0.68±0.19 d−1). Diatoms (0.80±0.39 d−1) and Synechococcus (SYN) (0.72±0.25 d−1) grew faster than Prymnesiophyceae (PRYMN) (0.62±0.26 d−1) and PRO (0.46±0.18 d−1). The growth rates of PRO and SYN were moderately nutrient limited (μ/μn=0.81 and 0.91, respectively), while the limitation for diatoms (μ/μn=0.71) and PRYMN (μ/μn=0.37) was more severe. Microzooplankton grazing rate was higher in upwelling (0.68±0.32 d−1) than in oceanic waters (0.37±0.19 d−1), but represented the main loss pathway for phytoplankton in both systems (m/μ=0.90±0.32 and 0.69±0.24, respectively). Carbon flux through phytoplankton, produced and grazed, increased from offshore to coastal (∼2 to ∼200 μg C L−1 d−1), with diatoms dominating the flux in the upwelling region (52%) while PRYMN (40%) and PRO (30%) dominated in the open ocean.  相似文献   

19.
桑沟湾养殖海域营养盐和沉积物-水界面扩散通量研究   总被引：7，自引：0，他引：7  
利用2006年4,7,11月和2007年1月4个航次对桑沟湾养殖海域的观测资料,分析了该海域营养盐分布、结构特征、主要控制过程以及沉积物-水界面扩散通量,结果表明,该海域的营养盐分布具有明显的季节变化,海水中NO3-,NO2-,PO43-,DOP,TDP和SiO32-浓度皆是秋季最高,而NH4+,DON,TDN浓度则为夏季最高;各种营养盐的最低值除DON外都出现在春季。春季湾内外海水交换不畅,再加上大型藻类海带等生长旺盛期的消耗,使营养盐浓度处于较低水平,在夏秋两季丰水期沿岸河流注入对该海域营养盐的影响较大,冬季无机营养盐浓度分布主要受沿岸流的影响。磷的结构变化较大,其中DOP百分含量在夏季最高,达到81%。从春季到秋季海水中TDN的结构变化从以DON为主转变成以DIN为主。硅和氮的原子比值全年变化不大,硅和氮和氮和磷原子比值春夏两季的高于秋冬季的。分析营养盐化学计量限制标准和浮游植物生长的最低阈值结果表明,磷是春夏两季桑沟湾浮游植物生长的限制性因素;春季硅浓度低于浮游植物生长的最低阀值,也是一个潜在的限制因素。计算结果显示桑沟湾沉积物释放的NH4+,SiO32-和PO43-对初级生产力的贡献较小,与其他浅海环境相比,桑沟湾沉积物-水界面的营养盐通量处于较低或中等水平。  相似文献   

20.
This investigation focused on the weaker and less well understood of the two Arabian Sea monsoonal wind phases, the NE Monsoon, which persists for 3–4 months in the October to February period. Historically, this period has been characterized as a time of very low nutrient availability and low biological production. As part of the US JGOFS Arabian Sea Process Study, 17 stations were sampled on a cruise in January 1995 (late NE Monsoon) and, 15 stations were sampled on a cruise in November 1995 (early NE Monsoon). Only the southern most stations (10° and 12°N) and one shallow coastal station were as nutrient-depleted as had been expected from the few relevant prior studies in this region. Experiments were conducted to ascertain the relative importance of different nitrogenous nutrients and the sufficiency of local regeneration processes in supplying nitrogenous nutrients utilized in primary production. Except for the southern oligotrophic stations, the euphotic zone concentrations of NO3− were typically 5–10-fold greater than those of NO2− and NH4+. There was considerable variation (20–40-fold) in nutrient concentration both within and between the two sections on each cruise. All nitrogenous nutrients were more abundant (2–4-fold) later in the NE Monsoon. Strong vertical gradients in euphotic zone NH4+ concentration, with higher concentrations at depth, were common. This was in contrast to the nearly uniform euphotic zone concentrations for both NO3− and NO2−. Half-saturation constants for uptake were higher for NO3− (1.7 μmol kg−1 (s.d.=0.88, n=8)) than for NH4+ (0.47 μmol kg−1 (s.d.=0.33, n=5)). Evidence for the suppressing effect of NH4+ on NO3− uptake was widespread, although not as severe as has been noted for some other regions. Both the degree of sensitivity of NO3− uptake to NH4+ concentration and the half-saturation constant for NO3− uptake were correlated with ambient NO3− concentration. The combined effect of high affinity for low concentrations of NH4+ and the effect of NH4+ concentration on NO3− uptake resulted in similarly low f-ratios, 0.15 (s.d.=0.07, n=15) and 0.13 (s.d.=0.08, n=17), for early and late observations in the NE Monsoon, respectively. Stations with high f-ratios had the lowest euphotic zone NH4+ concentrations, and these stations were either very near shore or far from shore in the most oligotrophic waters. At several stations, particularly early in the NE Monsoon, the utilization rates for NO2− were equal to or greater than 50% the utilization rates for NO3−. When converted with a Redfield C : N value of 6.7, the total N uptake rates measured in this study were commensurate with measurements of C productivity. While nutrient concentrations at some stations approached levels low enough to limit phytoplankton growth, light was shown to be very important in regulating N uptake at all stations in this study. Diel periodicity was observed for uptake of all nitrogenous nutrients at all stations. The amplitude of this periodicity was positively correlated with nutrient concentration. The strongest of these relationships occurred with NO3−. Ammonium concentration strongly influenced the vertical profiles for NO3− uptake as well as for NH4+ uptake. Both NO2− and NH4+ were regenerated within the euphotic zone at rates comparable to rates of uptake of these nutrients, and thus maintenance of mixed layer concentrations did not require diffusive or advective fluxes from other sources. Observed turnover times for NH4+ were typically less than one day. Rapid turnover and the strong light regulation of NH4+ uptake allowed the development and maintenance of vertical structure in NH4+ concentration within the euphotic zone. In spite of the strong positive effect of light on NO2− uptake and its strong negative effect on NO2− production, the combined effects of much longer turnover times for this nutrient and mixed layer dynamics resulted in nearly uniform NO2− concentrations within the euphotic zone. Responses of the NE Monsoon planktonic community to light and nutrients, in conjunction with mixed layer dynamics, allowed for efficient recycling of N within the mixed layer. As the NE Monsoon evolved and the mixed layer deepened convectively, NO2− and NO3− concentrations increased correspondingly with the entrainment of deeper water. Planktonic N productivity increased 2-fold, but without a significant change the new vs. recycled N proportionality. Consequently, NO3− turnover time increased from about 1 month to greater than 3 months. This reflected the overriding importance of recycling processes in supplying nitrogenous nutrients for primary production throughout the duration of the NE Monsoon. As a result, NO3− supplied to the euphotic zone during the NE Monsoon is, for the most part, conserved for utilization during the subsequent intermonsoon period.  相似文献   

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