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1.
The spatial and seasonal variability of primary production in the Japan Sea from 1998 to 2002 was estimated using a satellite primary production model. A size-fractionated primary production model was validated by in situ primary production data measured in the Japan Sea. Estimated primary production and in situ primary production showed a good positive correlation. Estimated primary production showed spatial variability. Annual primary production levels were 170, 161, 191 and 222 gC m−2year−1 at the Russian coast, in the middle of the Japan Basin, the southeastern area and the southwestern area, respectively. It was higher to the south around 40°N than to the north, and higher in the western area than in the eastern one. Peaks of primary production appeared twice, in spring and fall, in the southern area, while a single peak appeared in the northern area. Primary production along the Russian coast was higher than in other areas during summer. The spring bloom contributed 42% to the annual primary production in these four areas. Furthermore, estimated primary production showed an interannual variability that was largest in spring. Primary production in fall also showed interannual variability, especially in the middle of the Japan Basin and the southwestern area. This corresponded mainly to the size of the phytoplankton bloom in each year. Winter convection by wind and the depth of nutrient-rich, cold subsurface water underlying the Tsushima Current may contribute to the nutrient supply to upper layer and interannual variations of primary production in spring.  相似文献   

2.
The seasonal abundance of the dominant dinoflagellate, Ceratium fusus, was investigated from January 2000 to December 2003 in a coastal region of Sagami Bay, Japan. The growth of this species was also examined under laboratory conditions. In Sagami Bay, C. fusus increased significantly from April to September, and decreased from November to February, though it was found at all times through out the observation period. C. fusus increased markedly in September 2001 and August 2003 after heavy rainfalls that produced pycnoclines. Rapid growth was observed over a salinity range of 24 to 30, with the highest specific rate of 0.59 d−1 measured under the following conditions: salinity 27, temperature 24°C, photon irradiance 600 μmol m−2s−1. The growth rate of C. fusus increased with increasing irradiance from 58 to 216 μmol m−2s−1, plateauing between 216 and 796 μmol m−2s−1 under all temperature and salinity treatments (except at a temperature of 12°C). Both field and laboratory experiments indicated that C. fusus has the ability to grow under wide ranges of water temperatures (14–28°C), salinities (20–34), and photon irradiance (50–800 μmol m−2s−1); it is also able to grow at low nutrient concentrations. This physiological flexibility ensures that populations persist when bloom conditions come to an end.  相似文献   

3.
The abundance of a scyphomedusae, Aurelia aurita and Chrysaora melanaster, and a ctenophore, Bolinopsis mikado, in Tokyo Bay was investigated from 1995 to 1997. Aurelia aurita appeared throughout the year with a peak in abundance occurring from spring to summer. The average abundance and biomass during this period for the three successive years was 4.8, 43.8 and 3.2 ind. m−2, and 1.02, 10.0 and 0.42 gC m−2, respectively. The values in 1995 and 1997 were comparable with those previously reported for A. aurita abundance from 1990 to 1992. Values were very high in 1996, but the size composition of the bell diameter did not differ from other years, which suggested the absence of food limitation for A. aurita in 1996. C. melanaster was scarce over the survey period (<1.0 ind. m−2) while Bolinopsis mikado was more abundant during September to December, with maximum values of 172 ind. m−2 and 0.33 gC m−2 observed in December 1997. The weight-specific clearance rate for A. aurita on zooplankton (mainly copepods and their nauplii) was 0.16 ± 0.05 lgWW−1 h−1 (n = 13). Population clearance rate peaked from spring to summer, with average levels of 14.2%, 162% and 5.0% day−1 obtained from spring to summer for respective years. Population clearance rates for B. mikado, calculated based on minimum carbon requirements, was 7.1% day−1 in December 1997. Consequently, the trophic role of gelatinous zooplankton as predators in Tokyo Bay is important all the year round, considering the high impact of A. aurita from spring to summer and B. mikado from autumn to winter.  相似文献   

4.
赵亮  李夏  张芳 《海洋与湖沼》2016,47(3):564-571
近十年来,我国黄、东海沙海蜇的数量呈上下波动趋势,除2008、2010、2011、2013年为不暴发年外,其余年份均为暴发年或弱暴发年(本文界定沙海蜇平均丰度范围为2—10ind./100m2为暴发年,1—2ind./100m2为弱暴发年,0—1ind./100m2为不暴发年)。为研究沙海蜇数量年际变化的原因,本文借助同化的海洋模式结果,分析了2006—2013年南黄海沙海蜇平均丰度与表底层海水温度的关系、与不同温度持续时间的关系。研究结果发现,在海州湾附近,对于暴发年2007年和2009年,春季底层海水10—18°C持续时间为130天,比不暴发年2010年和2011年多近15天。在长江口区域,不暴发年2008年和2011年夏秋季底层海水18—25°C持续时间较长,约80天,比暴发年2007年多20天。在长江口、苏北近岸以及海州湾区域,春季底层海水10—18°C持续时间越长,南黄海水母丰度呈现越大的趋势;夏秋季底层海水18—25°C持续时间越长,第二年水母生物量则越大。结果支持和验证了春季底层10—18°C持续时间长有利于当年水母暴发及夏秋季底层18—25°C持续时间长有利于来年水母暴发的推论。本文通过分析沙海蜇丰度和温度变化的关系,可以为将来预测该水母数量提供基础。  相似文献   

5.
The concentrations of Cu, Ni and Cd were determined in Funka Bay during a spring phytoplankton bloom, consisting of diatoms. Just after the bloom, both dissolved Cd and nutrients were removed in the euphotic zone. However, the removal ratio of Cd to phosphate was very different from that in seawater. The removal of Cd took place at a Cd/phosphate ratio of 0.07×10−3, which was lower than in seawater before the bloom (0.25×10−3), leading to an increase in this ratio in seawater exceeding 0.7×10−3 at the end of the bloom. Elevated concentrations of Cd and phosphate were observed in the deeper layer after the bloom due to the decomposition of detrital materials produced in the bloom. The ratio of Cd/phosphate in the regeneration step was 0.24×10−3 which was different from the removal ratio of 0.07×10−3. These observations suggest that the high Cd/phosphate ratio in the regeneration would reflect a relatively high regeneration rate of Cd than that of phosphate. No significant decrease in Cu and Ni concentrations was observed during the development of the bloom, suggesting that biological removal of these metals was not so significant during the spring bloom. The concentrations of Cd, Cu and silicate in surface waters increased after the bloom with decreasing salinity due to the influence of a spring thaw.  相似文献   

6.
In order to detect iron (Fe) stress in micro-sized (20–200 μm) diatoms in the Oyashio region, western subarctic Pacific during spring, immunological ferredoxin/flavodoxin assays were applied to samples collected from the surface layer in May 2005. Concomitantly, the community composition of the micro-sized phytoplankton and hydrographic conditions, including dissolved Fe and macronutrient concentrations, were also examined. Chlorophyll (Chl) a concentrations were <2 mg m−3 at all sampling stations, except at a station where the Chl a level was 9.0 mg m−3 and a micro-sized diatom bloom occurred. A high abundance of ferredoxin in micro-sized diatoms was detected only at a rather near-shore station where dissolved Fe and macronutrient concentrations were higher, indicating that the micro-sized diatoms did not suffer from iron deficiency. On the other hand, flavodoxin in micro-sized diatoms was often observed at the other stations, including the bloom station, where macronutrients were replete but dissolved Fe concentration was low (0.31 nM). A significant amount of chlorophyllide a, a degradation product of Chl a, was also observed at the bloom station, suggesting a decline of the diatom bloom. The micro-sized phytoplankton species at all the stations were mainly composed of the diatoms Thalassiosira, Chaetoceros, and Fragilariopsis spp. Our study indicates that micro-sized diatoms were stressed by Fe bioavailability during the spring season in the Oyashio region  相似文献   

7.
We measured the ammonium excretion, phosphate excretion and respiration rates of the scyphomedusa Aurelia aurita from Ondo Strait, in the central part of the Inland Sea of Japan, at 28 and 20°C. The rates measured at 28°C were converted to those at 20°C using the Q10 values, i.e. 1.56, 1.57 and 2.80, for ammonium excretion, phosphate excretion and respiration rates, respectively. The composite relationships between metabolic rates and wet weight of a medusa (WW, g, range 11–1330 g) at 20°C were expressed by the following allometric equations. For ammonium excretion rate (N, μmoles N medusa−1d−1): N = 0.497WW 1.09, phosphate excretion rate (P, μmoles P medusa−1d−1): P = 0.453WW 0.84, and respiration rate (R, μmoles O2 medusa−1d−1): R = 96.9WW 1.06. Mean O:N ratios (i.e. atomic ratios of 16.9 and 11.0 at 28 and 20°C, respectively) indicated that the metabolism of A. aurita medusae was protein-dominated. These metabolic parameters enabled us to estimate the nitrogen and phosphorus regeneration rates of an A. aurita medusa population typical of early summer in the Ondo Strait (means of water temperature, medusa individual weight and population biomass: 20°C, 200 g WW and 50.8 g WW m−3, respectively). Regenerated nitrogen and phosphorus were equivalent to 10.0 and 21.6% of phytoplankton uptake rates, respectively, nearly twice that estimated for mesozooplankton, demonstrating that A. aurita medusae are key components of the plankton community, influencing the trophic and nutrient dynamics in the Ondo Strait during early summer.  相似文献   

8.
A sediment trap experiment was carried out in conjunction with an over flight of Ocean Color Temperature Scanner (OCTS) on board Advanced Earth Observing Satellite (ADEOS) at 40°N, 143°E off Sanriku in April to May 1997. Short term variability of particle fluxes was examined at depths of 450 m and 600 m from April 6 to May 1 with a sampling interval of two days, and at 450 m with one day interval from 2nd to 10th May. Daily averaged mass flux at 450 m and 600 m was 815 mg m−2d−1 and 862 mg m−2d−1, respectively. A sharp increase in mass flux was observed during the period from April 26 to April 29 with the highest mass flux of 8 g m−2d−1. About 85% of the total mass flux for the entire duration (26 days) was collected within these 4 days. Trapped material during the peak flux period was mainly composed of diatoms dominated byThalassiosira spp. and resting spores ofChaetoceros spp. This suggested that the peak flux was the result of (a) diatom bloom(s) in the euphotic column. Current meter records at 420 m showed that on April 26 and 27, the period when the peak flux was observed, the southwestward current had diminished in strength and changed its direction northwestward. Low current speeds appeared to have enhanced trap efficiency to help form the peak flux. A time series of OCTS Intensive-LAC (Local Area Coverage: Region B) images from mid-March to early May was examined todetect phytoplankton bloom(s). In the March 26th Chl image, high concentration region was restricted to the southwest off Cape Erimo, but spread around the warm core ring (WCR) 93A by April 10. East of the WCR93A, high Chl concentration remained steady until May, but to the west of the WCR93A, Chl decreased rapidly before the 19th of April. From this observation we suspect that the peak flux observed at the end of April originated from a bloom, which ceased on the 17th or 18th of April, in the region north of 40°N and west of 143°E. Taking the current meter records into account, the source region for the trapped material is most likely around southwest of the Cape Erimo.  相似文献   

9.
A global ocean inverse model that includes the 3D ocean circulation as well as the production, sinking and remineralization of biogenic particulate matter is used to estimate the carbon export flux in the Pacific, north of 10°S. The model exploits the existing large datasets for hydrographic parameters, dissolved oxygen, nutrients and carbon, and determines optimal export production rates by fitting the model to the observed water column distributions by means of the “adjoint method”. In the model, the observations can be explained satisfactorily with an integrated carbon export production of about 3 Gt C yr−1 (equivalent to 3⋅1015 gC yr−1) for the considered zone of the Pacific Ocean. This amounts to about a third of the global ocean carbon export of 9.6 Gt C yr−1 in the model. The highest export fluxes occur in the coastal upwelling region off northwestern America and in the tropical eastern Pacific. Due to the large surface area, the open-ocean, oligotrophic region in the central North Pacific also contributes significantly to the total North Pacific export flux (0.45 Gt C yr−1), despite the rather small average flux densities in this region (13 gC m−2yr−1). Model e-ratios (calculated here as ratios of model export production to primary production, as inferred from satellite observations) range from as high a value as 0.4 in the tropical Pacific to 0.17 in the oligotrophic central north Pacific. Model e-ratios in the northeastern Pacific upwelling regions amount to about 0.3 and are lower than previous estimates. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

10.
Sea surface pCO2 was monitored during 49 cruises from February 1997 to December 1999 along a section perpendicular to the central California Coast. Continuous measurements of the ocean–atmosphere difference of pCO2 were made on a mooring in the same region from July 1997 to December 1999. The El Niño/La Niña cycle of 1997–1999 had a significant influence on local ocean–atmosphere CO2 transfer. During the warm anomaly associated with El Niño, upwelling was suppressed and average sea surface pCO2 was below atmospheric level. High rainfall and river runoff in the late winter and early spring of 1998 produced areas where pCO2 was depressed by as much as 100 μatm. A flux ranging from 0.3 to 0.7 mol C m−2 y−1 from the atmosphere into the ocean was estimated for the El Niño period from wind and ΔpCO2 data. Temperatures and upwelling returned to near normal in the summer of 1998, but a cold anomaly developed during autumn of that year. Temperature and pCO2 data indicate that upwelling continued throughout much of the 1998–1999 winter and intensified significantly in the spring of 1999. During strong upwelling events, the estimate of ocean to atmosphere flux approached rates of 50 mol C m−2 y−1. The estimate for the average CO2 flux from July 1998 to July 1999 was 1.5–2.2 mol C m−2 y−1 from the ocean to the atmosphere. While the flux estimate for the El Niño time period may be applicable to a larger area, the high ocean to atmosphere fluxes during La Niña might be the result of sampling near a zone of intense upwelling.  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.
Time-series measurements of dissolved inorganic carbon (DIC) and nutrient concentrations were conducted in the northwestern North Pacific from October 2002 to August 2004. Assuming that data obtained in different years represented time-series seasonal data for a single year, vertical distributions of DIC and nutrients showed large seasonal variabilities in the surface layer (∼100 m). Seasonal variabilities in normalized DIC (nDIC) and nitrate concentrations at the sea surface were estimated to be 81–113 μmol kg−1 and 12.7–15.7 μmol kg−1, respectively, in the Western Subarctic Gyre. The variability in nutrients between May and July was generally at least double that in other seasons. In the Western Subarctic Gyre, estimations based on statistical analyses revealed that seasonal new production was 39–61 gC m−2 and tended to be higher in the southwestern regions or coastal regions. The seasonal new productions in the northwestern North Pacific were two or more times higher than in the North Pacific subtropical gyre and the northeastern North Pacific. It is likely that this difference is due to spatial variations in the concentrations of trace metals and the species of phytoplankton present. In addition, from estimations of surface pCO2 it was verified that the Western Subarctic Gyre is a source of atmospheric CO2 between February and May and a sink for CO2 between July and October.  相似文献   

13.
The values and seasonal variations of the primary production and chlorophyll a content were investigated in the Russian sector of the Southeastern Baltic in 2003–2007. The annual average values of the primary production and chlorophyll content for this area were 231 gC m−2 year−1 and 2.9 mg/m3, respectively; i.e., they corresponded to the mesotrophic level according to the trophic classification. The spatial distribution of the primary production and the chlorophyll concentrations in the different seasons and the annual average increased values exhibited at the northern coast of the Sambian Peninsula and the Curonian Spit were determined. In these areas, the values of the primary production and the chlorophyll concentrations corresponded to the eutrophic level.  相似文献   

14.
Vertical distributions of coccolithophores were observed in the depth range 0–50 m in the western subarctic Pacific and western Bering Sea in summer, 1997. Thirty-five species of coccolithophores were collected. Overall, Emiliania huxleyi var. huxleyi was the most abundant taxon, accounting for 82.8% of all coccolithophores, although it was less abundant in the western Bering Sea. Maximum abundance of this species was found in an area south of 41°N and east of 175°E (Transition Zone) reaching >10,000 cells L−1 in the water column. In addition to this species, Coccolithus pelagicus f. pelagicus, which accounted for 4.2% of the assemblage, was representative of the coccolithophore standing crop in the western part of the subarctic Pacific. Coccolithus pelagicus f. hyalinus was relatively abundant in the Bering Sea, accounting for 2.6% of the assemblage. Coccolithophore standing crops in the top 50 m were high south of 41°N (>241 × 106 cells m−2) and east of 170°E (542 × 106 cells m−2) where temperatures were higher than 12°C and salinities were greater than 34.2. The lowest standing crop was observed in the Bering Sea and Oyashio areas where temperatures were lower than 6–10°C and salinities were less than 33.0. From the coccolithophore volumes, the calcite stocks in the Transition, Subarctic, and the Bering Sea regions were estimated to be 73.0, 9.7, and 6.9 mg m−2, respectively, corresponding to calcite fluxes of 3.6, 0.5, and 0.3 mg m−2d−1 using Stoke's Law. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

15.
In order to examine the applicability of remotely-sensed ocean color for the estimation of phytoplankton biomass and primary production in the Oyashio region, the western subarctic Pacific, vertical distributions of chlorophylla concentration and primary production were observed in April and May 1997. Spring bloom was observed in both April and May, and the surface concentration of chlorophylla exceeded 40 mg m−3. The relationship between the standing stocks of chlorophylla within the layer from the sea surface to one optical depth (0–1/k layer) and the surface chlorophylla concentration is expressed as a Michaelis-Menten equation. The mean ratio of the standing stock of chlorophylla in the euphotic layer to that in the 0–1/k layer was 4.41, this ratio did not significantly differ from 4.61 which was obtained at homogeneous distribution of chlorophylla within the euphotic layer. These facts suggest that the distribution of chlorophylla could be assumed to be homogeneous in the euphotic layer during the spring bloom. Results of primary production measurements by simulatedin situ method were compared with those by an algorithm with two variables; chlorphylla and non-spectral PAR. Daily primary production in the euphotic layer estimated by the algorithm varied in a range of 38–274% of that estimated by incubation, although the primary productions by the algorithm agreed with those by the incubation at a half of stations. Primary production within the euphotic layer calculated using simply the surface data was the same as that estimated using vertical distribution of chlorophylla. These results show that the primary production in the euphotic layer may be estimated from the remote sensed measurements during the spring bloom in the Oyashio region.  相似文献   

16.
Factors controlling the timing of major (>10 mg chlorophyll a m−3) spring bloom events in the estuarine waters of the Solent, on the south coast of the UK, have been investigated. Winter to summer variations in chlorophyll a concentration together with relevant meteorological and hydrographical data have been analysed for 5 years (1988, 1992, 2001, 2002 and 2003). Mean water column irradiance is demonstrated to be the main factor controlling the timing of the first major spring bloom event, usually dominated by large chain-forming diatoms. When chlorophyll a concentration first exceeds 10 mg m−3 in spring (usually in May) the mean water column photosynthetic active radiation (PAR) averaged for one week prior to the sampling date was always >380 W h m−2 d−1. Prior to the main spring bloom event surface incident radiation and water turbidity combine to limit chlorophyll a concentration to levels <10 mg m−3. Chlorophyll a concentrations >10 mg m−3 do not occur in the Solent until almost the entire 10 m water column is within the euphotic zone (i.e. above 1% light level) and light extinction coefficient (k) is ca. ≤0.5 m−1. Statistically, river flow explains the largest percentage of the variations in k and the delayed bloom in June 2002 is due to increased cloud cover and high levels of rainfall in May, which caused a reduction in surface incident irradiance and increased turbidity. Chlorophyll a peaks during these major bloom events generally occur on spring tides when increased mixing rates favour net growth of diatoms.  相似文献   

17.
We tracked the duration and intensity of the euphausiid spawning season through biweekly sampling along a transect off Newport, OR (latitude 44°40′N) over a six year period from 1996 to 2001. Our sampling consisted of vertical plankton tows, CTD casts, and collection of water for determination of chlorophyll a. Here, we report on data collected from two stations, 5 and 15 nautical miles (9.3 and 27.8 km) offshore. The density of euphausiid eggs in our samples was highly variable spatially and temporally; we saw the most striking differences in egg densities and length of the spawning season, when we compared spawning before and after 1999. This year corresponded to the time when the Pacific Decadal Oscillation switched from warm phase (pre-1999) to cool phase (1999–present). The years 1996 and 1997 were characterized by one large, late summer peak in egg density at our inshore station. 1998, an El Niño year, followed this pattern for our offshore station, but eggs were nearly absent at our inshore station. Starting in 1999, we saw multiple peaks in egg density and found that the spawning season extended from spring through early fall. For example, in spring (March–May) at the inshore station, the abundance of eggs increased from an average of 0.4 m−3 (1996–1998) to 51.3 m−3 (1999–2001), and for summer (July–September), 27.8 m−3 to 132.6 m−3 for the same time period. At the offshore station, egg abundances doubled over the same two time periods: 7 m−3 versus 11 m−3 (spring) and 55 m−3 versus 186 m−3 (summer). Peaks in egg densities were often associated with phytoplankton blooms, but not in a predictable way. Peaks in egg densities often followed cold-water upwelling events, especially at the inshore station. It is not yet clear whether this connection is due to changes in advection or changes in upwelling-induced productivity.  相似文献   

18.
During a cruise aboard the R/V Hakuho-maru in the northwestern North Pacific in the summer of 1998 the particle number concentrations and the major ionic components of size fractionated aerosols were measured to investigate the aerosol produced by marine biological activity. Continuous low concentrations of nitrate (<1.8 nmol m−3), similar to the marine air background level, were found over the northwestern North Pacific (40–45°N) and the Sea of Okhotsk (44–45°N). Over the Sea of Okhotsk, a high concentration of chlorophyll-a (5.4 mg m−3) in seawater was observed, and atmospheric concentrations of non sea-salt (nss-) sulfate (44 nmol m−3), methane sulfonic acid (MSA) (1.8 nmol m−3) and particle number in the size range of 0.1 < D < 0.5 μm (199 cm−3) were found to be 9, 7, and 2 times, respectively, higher than those in the background marine air. The increase in particle number concentrations mainly in the size range of 0.2 < D < 0.3 μm was likely caused by the increase of biogenic sulfate over the high productive region of the Sea of Okhotsk. In humid air conditions (R.H. > 96%), the increased biogenic sulfate that condensed the large amount of water vapor would not have sufficient solute mass to activate as cloud condensation nuclei (CNN) and would remain as aerosol particles in the marine air with frequent sea-fogs over the high productive region. Biogenic sulfate originating from dimethyl sulfide (DMS) would gradually grow into the CCN size and continuously supply a great number of CCN to the marine air in the northwestern North Pacific. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
The big Comacchio lagoons (NW Adriatic coast) have been experiencing a super-dense, long-term bloom of picocyanobacteria (PCB) since 1985. This bloom has caused profound transformations in their ecosystem and has resulted in the loss of valuable fish and clam resources. The composition, density and seasonal dynamics of this bloom and its impact on the ecosystem were studied between spring and autumn 1995 and in the summer of 2001. The density of the blooming phytoplankton assemblages varied from 8 to 35 × 106 cells ml−1, and biomass from 20 to 40 g m−3, thus demonstrating a quasi-stable status since 1993. The share of pico + nanocyanobacterial fraction of the total phytoplankton biomass was 98% in spring to early summer, and 92% in autumn. The remaining 0.2–5% comprised eukaryotic nano-algae. All components of the animal food web were found to be drastically depleted in the lagoons. Their biomass range in the open lagoons areas were: 2 to 20 mg m−3 of microzooplankton, 10 to 40 mg m−3 mesozooplankton, and 5 to 12 g m−2 macrozoobenthos. The share of filtering fauna in the whole ecosystem metabolism was less than 2%. The malfunction of the deteriorated animal food web resulted in the hyper-accumulation of non-grazed microplankton biomass and detritus in the water column and in bottom sediments. The sequence brought the acceleration of sulfide production and the accumulation of acid soluble sulfides in the upper sediment layer of up to 700–800 mg S dm−3 of wet silt. The results of this study provide evidence that the state of ecological collapse continues in the lagoons since 1993.  相似文献   

20.
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   

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