Changes of nutrient concentrations and N: P: Si ratios and their possible impacts on the Huanghai Sea ecosystem

To investigate the impacts of nutrient concentrations and N:P:Si ratios on the ecosystem of the Huanghai Sea (Yellow Sea), the current status and long-term variation of nutrients concentrations and ratios as well as phytoplankton community structure in the Huanghai Sea were collected and analyzed. The results reveal great annual and seasonal fluctuations in the nutrient concentrations and N:P:Si ratios during 1998-2008 with no clear pattern observed in the whole region. Yet on a seasonal scale of spring and in the coastal regions such as the Jiaozhou Bay and Sanggou Bay, the increase of DIN concentration and N:P ratio as well as the decrease of phosphate and silicate concentrations and Si:N ratios were relatively significant. Many pelagic ecosystem changes have occurred concurrent with these changes of the nutrient regime, such as the recent increase of primary production, changes of phytoplankton chlorophyll a biomass and abundance, an increase of eutrophication, and occurrence of HABs. In addition, new trends in the variation of nutrients seem to be developing in some particular transect such as 36°N, which suggests that long-term and systematic ecosystem monitoring in the Huanghai Sea is necessary.     

南黄海浮游植物季节性变化的数值模拟与影响因子分析

用三维物理-生物耦合模式研究南黄海浮游植物(以叶绿素a为指标)的季节变化.对于物理模式采用Princeton ocean model(POM),对于生物模式考虑溶解无机营养盐(氮、磷、硅)、浮游植物、食草性浮游动物和碎屑.给定已知的初始场和外加边界强迫,模拟了观测到叶绿素a的主要时、空分布特征,如浮游植物的春、秋季水华和夏季次表层叶绿素a极大值现象等.研究表明,浮游植物春季水华最先发生于黄海中央海域,主要原因是该海域透明度较高,流速较小.春季水华开始于垂直对流减弱和层化开始形成之前(约3月底至4月上旬),显著地依赖水层的稳定性.水体层化以后(约5～9月)叶绿素a浓度高值区分布在南黄海的南部和锋区.夏季的南黄海中央海域,由于上混合层营养盐几乎耗尽,限制了浮游植物的生长,在紧贴温跃层下部的真光层,具有丰富的营养盐和合适的光照,次表层叶绿素a极大值得以形成.秋季(约9～11月份,略迟于海表面开始降温的时间,随地点不同而异)随垂直混合的增强,有利于营养盐向上输运,浮游植物出现一次较小的峰值.     

An ecosystem model with iron limitation of primary production in the equatorial Pacific at 140°W

We construct a one-dimensional ecosystem model (nitrate, ammonium, phytoplankton, zooplnakton and detritus) with simple physics and biology in order to focus on the structural relations and intrinsic properties of the food web that characterizes the biological regime in the central equatorial Pacific at 140°W. When possible, data collected during the EgPac and other cruises were used to calibrate model parameters for two simulations that differ in the limiting nutrient, i.e. nitrogen or iron. Both simulations show annual results in good agreement with the data, but phytoplankton biomass and primary production show a more pronounced annual variability when iron is used as the limiting nutrient. This more realistically reproduces the variability of biological production and illustrates the greater coupling between vertical physical processes and biological production when the limiting nutrient is iron rather than nitrogen. The iron simulation also illustrates how iron supply controls primary production variability, how grazingbalances primary production and controls phytoplankton biomass, and how both iron supply and grazingcontrol primary production. These results suggest that it is not possible to capture primary production variability in the central equatorial Pacific with biological models using nitrogen as the limiting nutrient. Other indirect results of this modeling study were: (1) partitioning of export production between dissolved and particulate matter is almost equal, suggesting that the importance of DOC export may have been previously overestimated; (2) lateral export of live biomass has to be taken into account in order to balance the nitrogen budget on the equator at 140°W; and (3) preferential uptake of ammonium (i.e. nitrate uptake inhibition by ammonium) associated with high regeneration of nitrogen (low f ratio as a consequence of the food web structure imposed by iron limitation) largely accounts for the surface build-up of upwelled nitrate.     

Trophic Status of the South-Eastern Baltic Sea: A Comparison of Coastal and Open Areas

Primary production, nutrient concentrations, phytoplankton biomass (incl. chlorophyll a) and water transparency (Secchi depth), are important indicators of eutrophication. Earlier basin-wide primary production estimates for the Baltic Sea, a shallow shelf sea, were based mainly on open-sea data, neglecting the fundamentally different conditions in the large river plumes, which might have substantially higher production. Mean values of the period 1993–1997 of nutrient concentrations (phosphate, nitrate, ammonium and silicate), phytoplankton biomass, chlorophyll a (chl a) concentration, turbidity and primary production were calculated in the plumes of the rivers Oder, Vistula and Daugava and Klaipeda Strait as well as the open waters of the Arkona Sea, Bornholm Sea, eastern Gotland Sea and the Gulf of Riga. In the plumes, these values, except for primary production, were significantly higher than in the open waters. N:P ratios in the plumes were >16 (with some exceptions in summer and autumn), indicating potential P-limitation of phytoplankton growth, whereas they were <16 in the open Baltic Proper, indicating potential N-limitation. On the basis of in situ phytoplankton primary production, phytoplankton biomass and nutrient concentrations, the large river plumes and the Gulf of Riga could be characterized as eutrophic and the outer parts of the coastal waters and the open sea as mesotrophic. Using salinity to define the border of the plumes, their mean extension was calculated by means of a circulation model. Taking into account the contribution of coastal waters, the primary production in the Baltic Proper and the Gulf of Riga was 42·6 and 4·3×10⁶ t C yr⁻¹, respectively. Hence, an annual phytoplankton primary production in the whole Baltic Sea was estimated at 62×10⁶ t C yr⁻¹. The separate consideration of the plumes had only a minor effect on the estimation of total primary production in comparison with an estimate based on open sea data only. There is evidence for a doubling of primary production in the last two decades. Moreover, a replacement of diatoms by dinoflagellates during the spring bloom was noticed in the open sea but not in the coastal waters. A scheme for trophic classification of the Baltic Sea, based on phytoplankton primary production and biomass, chl a and nutrient concentrations, is proposed.     

1999年渤海浮游植物生物量的数值模拟

以浮游植物量、浮游动物量、营养盐浓度 (包括无机氮和无机磷 )以及碎屑量为生态变量 ,在HAMSOM水动力学模式的基础上构建了 1个三维浮游生态动力学NPZD模型。采用此模型研究了渤海 1999年浮游植物量和初级生产力的变化情况 ,模拟结果与实测基本相符。模拟结果表明 :1999年渤海浮游植物量的变化大致呈双峰分布 ,春季水华出现在4,5月份 ,秋季水华出现在 9,10月份 ;受透明度和局地水深的影响 ,渤海湾和辽东湾北部浮游植物量的年变化呈夏季大、冬季小的单峰分布。 1999年渤海不同海区初级生产力的变化特征是 :除莱州湾一年中有春、夏 2个峰值外 ,其它 3个海区都是夏季高、冬季低的单峰分布 ;1999年整个渤海年平均的初级生产力为 2 5 7mgC/m2 /d。     

A modelling study of ecosystem dynamics and nutrient cycling in the Humber plume, UK

The European Regional Seas Ecosystem Model (ERSEM) has been coupled with a two-dimensional depth-averaged transport model of the Humber plume region and run to simulate 1988–1989. Simulations of the spatial and temporal variations in chlorophyll-a, nitrate, phosphate and suspended particulate matter distributions in winter, spring and summer show how the development of the spring bloom and subsequent maintenance of primary production is controlled by the physicochemical environment of the plume zone. Results are also shown for two stations, one characterised by the high nutrient and suspended matter concentrations of the plume and the other by the relatively low nutrient and sediment concentrations of the offshore waters. The modelled net primary production at the plume site was 105 g C m⁻² a⁻¹ and 127 g C m⁻² a⁻¹ offshore. Primary production was controlled by light limitation between October and March and by the availability of nutrients during the rest of the year. The phytoplankton nutrient demand is met by in-situ recycling processes during the summer. The likely effect of increasing and decreasing anthropogenic riverine inputs of nitrate and phosphate upon ecosystem function was also investigated. Modelling experiments indicate that increasing the nitrogen to silicate ratio in freshwater inputs increased the production of non-siliceous phytoplankton in the plume. The results of this model have been used to calculate the annual and quarterly mass balances describing the usage of inorganic nitrogen, phosphate and silicate within the plume zone for the period of the NERC North Sea survey (September 1988 to October 1989). The modelled Humber plume retains 3.9% of the freshwater dissolved inorganic nitrogen, 2.2% of the freshwater phosphate and 1.3% of the freshwater silicate input over the simulated seasonal cycle. The remainder is transported into the southern North Sea in either dissolved or particulate form. The reliability of these results is discussed.     

船基围隔条件下沙尘和营养盐添加对近海浮游植物群落结构的影响

为研究沙尘沉降和营养盐输入对中国陆架海域浮游植物群落结构的影响,于2017年3—4月在中国黄、东海进行沙尘和不同营养盐(NO^-₃、PO^-₄、尿素)添加的船基围隔培养实验。结果表明,与对照组相比,沙尘(2 mg/L)和尿素添加实验组的浮游植物群落细胞密度及群落结构变化不显著,叶绿素a含量差异不显著,优势种均为海链藻属 (Thalassiosira)。不同比值的氮、磷无机营养盐添加对水体中叶绿素a含量和细胞密度的影响不同,其中氮磷比为64∶1的实验组叶绿素a含量和细胞密度最高,分别为18.20 μg/L和7.86×10⁵cells/L。沙尘和营养盐添加对浮游植物群落的影响主要表现为叶绿素a含量、细胞密度峰值及不同优势种所占比例的差异,而各个实验组的种类组成及优势种具有一定的相似性。     

Modeling the effects of atmospheric nitrogen input on biological production in the Japan Sea

The effects of atmospheric nitrogen input on biological production in the Japan Sea have been investigated using a coupled physical-ecosystem model. Comparison between the cases with and without nitrogen deposition shows a relatively large effect on primary production in the southern Japan Sea during summer to autumn, when nitrogen deposition is high and nutrient is depleted in the surface layer. The atmospheric nitrogen deposition supports > 10% of the annual export production in the nearshore region along the Japanese coast. The importance of atmospheric input as a new nutrient will grow steadily with increasing deposition into the Japan Sea.     

中国近海区域浮游植物生态对气候变化的响应

我国近海区域对气候变化高度敏感,浮游植物生态的变化关系到我国近海生态安全.采用重构的遥感数据等资料,分析并综述我国近海区域浮游植物叶绿素a浓度、初级生产力和浮游植物群落结构对气候变化背景下海水升温、风场等环境因子的响应.结果表明,东(南)中国海叶绿素a浓度略有上升(下降)的趋势,但浮游植物群落结构和生物量有明显的变化;其中,微微型浮游植物和甲藻占比增加,小型浮游植物物种成为海区优势种,暖水性种分布区北扩,而这与气候变化背景下海洋热动力环境的长期变化及其对营养盐供给的影响关系密切.分析还指出了气候变化对我国近海区域海洋生态影响研究迫切需要开展的若干工作.     

渤黄海营养盐结构及其潜在限制作用的时空分布

根据2006-2007年4个季节的现场调查资料,分析探讨了渤海和黄海营养盐结构分布变化特征及其对浮游植物生长的潜在的限制状况.结果表明,渤黄海水体 Si/N/P 比值均偏离 Redfield 比值,季节变化明显;春夏冬季 N/P和 Si/P比值由近岸向远岸海域递减,高值区主要分布在黄河口、鸭绿江口及苏北近岸,秋季上层水体N/P和Si/P比值的分布趋势有所不同,高值区主要分布在南黄海的中部海域.受陆源输入的影响,近岸特别是河口区 N/P和 Si/P比值均较高,温跃层的生消变化和生物活动调控着黄海中部海域营养盐结构的变化.渤黄海浮游植物生长主要受P的潜在限制,部分季节受N、Si的潜在限制;营养盐限制状况存在着明显的时空变化及不同营养盐的同时或交替限制的现象.     

Specific oceanographic characteristics and phytoplankton responses influencing the primary production around the Ulleung Basin area in spring

The East Sea(Sea of Japan)is a marginal,semi-closed sea in the northwestern Pacific.The Ulleung Basin area,which is located near the subpolar front of the East Sea,is known to have high primary production and good fisheries in spring season.After episodic wind-driven events during the spring of 2017,horizontal and vertical profiles of physical chemical biological factors were investigated at 29 stations located in the Ulleung Basin area.In addition,growth responses of phytoplankton communities to nutrient additions were evaluated by bioassay experiments to understand the fluctuation of phytoplankton biomass.Because of strong northwestern wind,phytoplankton biomass was scattered and upwelling phenomenon might be suppressed in this season.The phytoplankton abundances in the coastal stations were significantly higher than offshore and island stations.In contrast,the nutrient and chlorophyll a(Chl a)concentrations and the phytoplankton biomass were quite low in all locations.Bacillariophyceae was dominated group(>75.1%for coastal,40.0%for offshore and 43.6%for island stations).In the algal bioassays,the phytoplankton production was stimulated by N availability.The in vivo Chl a values in the+N and+NP treatments were significantly higher than the values in the control and the+P treatments.Based on the field survey,the higher nutrients in coastal waters affected the growth of diatom assemblages,however,little prosperity of phytoplankton was observed in the offshore waters despite the injection of sufficient nutrients in bioassay experiments.The growth of phytoplankton depended on the initial cell density.All of results indicated that a dominant northwestern wind led to a limited nutrients condition at euphotic layers,and the low level of biomass supply from the coasts resulted in low primary production.Both supplying nutrients and introducing phytoplankton through the currents are critical to maintain the high productivity in the Ulleung Basin area of the East Sea.     

南海北部东沙天然气水合物区浮游植物生物量和生产力粒级结构特征及其环境影响分析

本文讨论了2013年5月南海东沙天然气水合物区浮游植物生物量和生产力粒级结构特征及其环境影响因素。结果表明，研究海域表现出典型的低营养盐、低叶绿素a、低生产力特征，浮游植物叶绿素a和初级生产力具有明显的次表层最大值现象。东沙海域生物量和初级生产力粒级结构差异性显著，从生物量和生产力贡献度来看，表现为微微型浮游植物> 微型浮游植物> 小型浮游植物。生物量的垂直分布结果表明，春季不同粒级类群浮游植物在真光层内的分布存在明显不同，比如小型浮游植物在真光层内分布较均匀；微型浮游植物则主要分布于近表层或真光层中部，而微微型浮游植物则主要分布于真光层中部和底部。微微型浮游植物在纬度较低的热带贫营养海区之所以能够占主导优势，最主要的原因是其极小的细胞体积和较大的表面积使其有利于营养竞争。相关性分析表明，南海东沙浮游植物各粒级生物量与温度、pH显著正相关，与硅酸盐、磷酸盐显著负相关；浮游植物各粒级生产力与温度显著正相关，与盐度、磷酸盐显著负相关。磷酸盐含量是影响东沙海域浮游植物粒级结构差异的重要因素之一，同时，光辐照度和水体的真光层深度对东沙天然气水合物区不同粒径浮游植物的垂直分布起着更为重要的调控作用。     

The Irish Sea: Is it eutrophic?

The question of whether the Irish Sea is eutrophic is addressed by reviewing the evidence for anthropogenic nutrient enrichment, elevated phytoplankton production and biomass and undesirable disturbance in the context of the EU and OSPAR definitions of eutrophication. Winter concentrations of dissolved available inorganic phosphate (DAIP), nitrogen (DAIN as nitrate and nitrite) and silicate (Si) in coastal waters and concentrations of DAIP and Si in offshore waters of the Irish Sea are elevated relative to winter Celtic Sea shelf break concentrations (0.5 μM DAIP, 7.7 μM DAIN and 2.7 μM Si). Significant, negative nutrient salinity relationships and analysis of the Isle of Man nutrient time-series indicate that the elevated Irish Sea levels of DAIP and DAIN are the result of anthropogenic enrichment with highest concentrations (≈2.0 μM DAIP, 30 μM DAIN and 17 μM Si) measured in near shore eastern Irish Sea waters.     

南黄海春季海水化学要素的分布特征及其受控因素

基于2007年4月对南黄海调查所得资料,对海水化学要素的分布特征及影响因素进行了探讨。结果表明,受浮游植物光合作用的影响,南黄海中北部上层海域出现了DO、pH的高值区以及营养盐的低值区,而底层则因有机物的分解,DO和pH较低而营养盐含量较高;受苏北沿岸水、长江冲淡水和/或台湾暖流前缘混合水的影响,南黄海西南部海域表、底层DO含量均较低,但却为营养盐的最高值区,且表层水中无机氮盈余状况的分布与该海域环流状况、尤其是苏北沿岸水的扩展途径密切相关,表现为无机氮相对过剩,而无机磷相对缺乏;南黄海西部沿岸流对营养盐往东南方向的输运态势较为明显,同时,首次从营养盐分布的角度揭示了这一水动力过程;受苏北沿岸水、黄海暖流以及两者之间的南黄海西部沿岸流主体的影响,南黄海斜断面上海水化学要素的分布具有明显的区域化特征和空间结构。     

Impact of open-ocean convection on nutrients,phytoplankton biomass and activity

We describe the impact of an open-ocean convection event on nutrient budgets, carbon budget, elemental stoichiometry, phytoplankton biomass and activity in the Northwestern Mediterranean Sea (NWM). In the convective episode examined here we estimated an input of nutrients to the surface layer of 7.0, 8.0 and 0.4×10⁸ mol of silicate, nitrate and phosphate, respectively. These quantities correspond to the annual nutrient input by river discharges and atmospheric depositions in the Gulf of Lion. Such nutrient input is sufficient to sustain new primary production from 46 to 63 g C m⁻² y⁻¹, which is the same order of magnitude found in the NWM open waters. Our results together with satellite data analysis, propose new scenarios that explain the origin of the spring phytoplankton bloom occurring in NWM.     

Bottom-up control of phytoplankton growth in spring blooms in Central Yellow Sea,China

The source and significance of three nutrients – nitrogen, phosphorous and silicon – were investigated by a modified dilution method performed on seawater samples from the Central Yellow Sea (CYS), in spring blooming period of 2007. This modified dilution method accounted for the phytoplankton growth rate, microzooplankton grazing mortality rate, the internal and external nutrient pools, as well as nutrients supplied through remineralization by microzooplankton grazing. The results indicate that phytoplankton growth during the bloom is mostly contributed by internal nutrient pools (K_I=0.062–1.730). The external nutrient pools (K_E=<0–0.362) are also of importance for phytoplankton growth during the bloom at some sampling sites. Furthermore, the contribution of the recycled-nutrient pool by remineralization (K_R=<0–0.751) is significant when microzooplankton grazing rate was higher than 0.5 d⁻¹ during the spring phytoplankton blooms in the Central Yellow Sea. Compared with internal phosphorus, internal nitrogen and silicon contribute more to the phytoplankton production at most sampling stations.     

Recent Primary Production and Small Phytoplankton Contribution in the Yellow Sea during the Summer in 2016

The high nutrient concentration associated with the mixing dynamics of two warm and cold water masses supports high primary production in the Yellow Sea. Although various environmental changes have been reported, no recent information on small phytoplankton contribution to the total primary production as an important indicator for marine ecosystem changes is currently available in the Yellow Sea. The major objective of this study is to determine the small (< 2 μm) phytoplankton contribution to the total primary production in the Yellow Sea during August, 2016. In this study, we found relatively lower chlorophyll a concentrations in the water column than those previously reported in the central waters of the Yellow Sea. Moreover, the overall contribution of small phytoplankton (53.1%) to the total chlorophyll a concentration was considerably higher in this study than that (10.7%) observed previously. Based on the N/P ratio (67.6 ± 36.6) observed in this study, which is significantly higher than the Redfield ratio (16), we believe that phytoplankton experienced P-limiting conditions during the study period. The average daily carbon uptake rate of total phytoplankton in this study was 291.1 mg C m^-2 d^-1 (± 165.0 mg C m^-2 d^-1) and the rate of small phytoplankton was 205.7 mg C m^-2 d^-1 (± 116.0 mg C m^-2 d^-1) which is 71.9% (± 8.8%) of the total daily carbon uptake rate. This contribution of small phytoplankton observed in this study appears to be higher than that reported previously. Our recent measured primary production is approximately 50% lower than the previous values decades ago. The higher contributions of small phytoplankton to the total chlorophyll a concentration and primary production might be caused by P-limited conditions and this resulted in lower chlorophyll a concentration and total primary production in this study compared to previous studies.     

Seasonal distribution of primary production,phytoplankton biomass and size distribution in the Greenland Sea

The study establishes an annual estimate for annual primary production of 81 g C m⁻² for the open Greenland Sea based on data from five cruises and literature data. This estimate agrees well with a model estimate based on nutrient utilisation but is a factor of 2–5 less than published primary production estimates made by remote sensing of this area. The seasonal distribution of particulate primary production in open Greenland Sea waters followed the seasonal distribution of surface irradiance with a peak in June, indicating that light is the primary factor governing primary production in the area. At stations along the ice edge, blooms were recorded in both June and August, suggesting a pattern of repeated blooms during the summer season at the ice edge. Subsurface phytoplankton peaks were a persistent feature in the open Greenland Sea from May to August. These peaks were consisted of actively photosynthesising phytoplankton and up to 90% of total water column particulate primary production was estimated to occur in association with these peaks. Diatoms dominated the phytoplankton community during the spring bloom and in the Polar Water during August. Size distribution analyses of the phytoplankton communities indicated that the relative abundance of large cells compared to small cells was greatest in May as compared to June and August. No significant differences were noted between June and August in the slope of the phytoplankton size distribution spectra. Inorganic nitrogen and phosphorus nutrients were measurable in surface waters on all cruises. Only in August were there some indications (altered Redfield ratios and higher nutrient concentrations in subsurface chlorophyll peaks than at the surface) of nutrient depletion of surface waters. Implications for food web structure and carbon flux of these patterns in phytoplankton activity and distribution are discussed.     

2011年春夏季黄海和东海微型浮游动物类群组成及其摄食的研究

为了解春夏季黄海和东海微型浮游动物类群及其摄食生态,于2011年春季和夏季在黄海、东海,通过稀释法测定浮游植物生长率及微型浮游动物对浮游植物的摄食率,同时应用显微分析技术研究了微型浮游动物丰度及其类群组成．结果表明：（1）春季,黄海、东海微型浮游动物丰度为1800～21833个／dm3,夏季的为67～6175个／dm3;春季,其微型浮游动物生物量为8．71-60．58ug/dm3,夏季的则为0．44～30．25ug／dm3（其生物量以c含量计）．（2）春季、夏季黄海和东海浮游植物的生长率及其标准偏差分别为0．78±0．35、1．62±0．83d-1,而春季的显著低于夏季（P〈0．05）．春季、夏季其微型浮游动物的摄食率及其标准偏差分别为0．98±0．32、0．92±0．57d-1,无显著性差异（p〉0．05）．春季,微型浮游动物摄食浮游植物现有生物量的61％±13％,占初级生产量的131％±58％;夏季,微型浮游动物摄食浮游植物现有生物量的54％±22％,占初级生产量的70％±44％．春、夏季,黄海和东海微型浮游动物对浮游植物初级生产量的摄食比例较高．     

东亚边缘海区浮游植物春华的纬向与年际变化

Combined studies of latitudinal and interannual variations of annual phytoplankton bloom peak in East Asian marginal seas(17°–58°N, including the northern South China Sea(SCS), Kuroshio waters, the Sea of Japan and the Okhotsk Sea) are rarely. Based on satellite-retrieved ten-year(2003–2012) median timing of the annual Chlorophyll a concentration(Chl a) climax, here we report that this annual spring bloom peak generally delays from the SCS in January to the Okhotsk Sea in June at a rate of(21.20±2.86) km/d(decadal median±SD). Spring bloom is dominant feature of the phytoplankton annual cycle over these regions, except for the SCS which features winter bloom. The fluctuation of the annual peak timing is mainly within ±48 d departured from the decadal median peak date, therefore this period(the decadal median peak date ±48 d) is defined as annual spring bloom period. As sea surface temperature rises, earlier spring bloom peak timing but decreasing averaged Chl a biomass in the spring bloom period due to insufficient light is evident in the Okhotsk Sea from 2003 to 2012. For the rest of three study domains, there are no significant interannual variance trend of the peak timing and the averaged Chl a biomass. Furthermore this change of spring phytoplankton bloom timing and magnitude in the Okhotsk Sea challenges previous prediction that ocean warming would enhance algal productivity at high latitudes.