Morphological comparison and molecular marker screening of three Skeletonema species found in Changjiang(Yangtze)River Basin

In our recent investigations of diatom diversity,we studied three species,namely,Skeletonema costatum,Skeletonema subsalsum,and Skeletonema potamos.Although they have been found frequently in Changjiang(Yangtze)River Basin,their morphological and molecular identification is difficult in taxonomy.Therefore,to integrate morphological and molecular biological approaches,we compared systematically their morphological characters and performed phylogenetic analysis.Twelve strains of Skeletonema were collected and isolated from Shanghai and Jiangsu,China,and their morphological characteristics were examined by light microscopy(LM)and the scanning electron microscopy(SEM).Based on morphological comparison,we determined that S.potamos is easy to distinguish from the other two species.The heavily silicified areolae,undulated or cleft distal ends of terminal fultoportula processes(TFPPs),absence of basal pores of fultoportula processes(FPPs),the rootlike protrusions of FPPs,and no interlocking connection are the stable characteristics that can be used to identify S.potamos.However,there are only two features that can distinguish S.costatum from S.subsalsum,namely the location of terminal rimoportulae(TRPs)and the distal shape of TFPPs.In addition,we amplified and sequenced nine common genetic markers from the strains,from which 101 sequences were obtained,constructed phylogenetic trees based on the nine genes and evaluated that seven genes can be used to identify S.potamos,and revealed that S.subsalsum is the closest known relative of S.costatum,and only ATP synthetase beta-subunit gene(atp B)is able to distinguish them from each other,which strongly support that it is an effective molecular marker for Skeletonema.This work provided a theoretical basis for the taxonomic study of Skeletonema.

Inter-annual variations of dissolved oxygen and hypoxia off the northern Changjiang River(Yangtze River) Estuary in summer from 1997 to 2014

Hypoxia off the Changjiang River Estuary has been the subject of much attention,yet systematic observations have been lacking,resulting in a lack of knowledge regarding its long-term change and drivers.By revisiting the repeated surveys of dissolved oxygen(DO) and other relevant hydrographic parameters along the section from the Changjiang River Estuary to the Jeju-do in the summer from 1997 to 2014,rather different trends were revealed for the dual low-DO cores.The nearshore low-DO core,located close to the river mouth and relatively stable,shows that hypoxia has become more severe with the lowest DO descen ding at a rate of -0.07 mg/(L·a) and the thickness of low-DO zone rising at a rate of 0.43 m/a.The offshore core,centered around 40-m isobath but moving back and forth between 123.5°-125°E,shows large fluctuations in the minimum DO concentration,with the thickness of low-DO zone falling at a rate of -1.55 m/a.The probable factors affecting the minimum DO concentration in the two regions also vary.In the nearshore region,the decreasing minimum DO is driven by the increase in both stratification and primary productivity,with the enhanced extension of the Changjiang River Diluted Water(CDW) strengthening stratification.In the offshore region,the fluctuating trend of the minimum DO concentration indicates that both DO loss and DO supplement are distinct.The DO loss is primarily attributed to bottom apparent oxygen utilization caused by the organic matter decay and is also relevant to the advection of low-DO water from the nearshore region.The DO supplement is primarily due to weakened stratification.Our analysis also shows that the minimum DO concentration in the nearshore region was extremely low in 1998,2003,2007 and 2010,related to El Ni?o signal in these summers.

Effects of phosphorus limitation on sinking velocities of phytoplankton during summer in the Changjiang River Estuary

The sinking of phytoplankton is critical to organic matter transportation in the ocean and it is an essential process for the formation of coastal hypoxic zones.This study was based on a field investigation conducted during the summer of 2022 in the Changjiang River(Yangtze River) Estuary(CJE) and its adjacent waters.The settling column method was employed to measure the sinking velocity(SV) of different size fractions of phytoplankton at the surface of the sea and to analyze their environmental control mechanisms.The findings reveal significant spatial variation in phytoplankton SV(-0.55-2.41 m/d) within the CJE.High-speed sinking was predominantly observed in phosphate-depleted regions beyond the CJE front.At the same time,an upward trend was more commonly observed in the phosphate-rich regions near the CJE mouth.The SV ranges for different sizefractionated phytoplankton,including micro-(>20 μm),nano-(2-20 μm),and picophytoplankton(0.7-2 μm),were-0.50-4.74 m/d,-1.04-1.59 m/d,and-1.24-1.65 m/d,respectively.Correlation analysis revealed a significant negative correlation between SV and dissolved inorganic phosphorus(DIP),implying that the influence of DIP contributes to SV.The variations in phytoplankton alkaline phosphatase activity suggested a significant increase in SV across all size fractions in the event of phosphorus limitation.Phytoplankton communities with limited photo synthetic capacity(maximum photochemical efficience,Fv/Fm <0.3) were found to have higher SV than that of communities with strong capacity,suggesting a link between sinking and alterations in physiological conditions due to phosphate depletion.The findings from the in situ phosphate enrichment experiments confirmed a marked decrease in SV following phosphate supplementation.These findings suggest that phosphorus limitation is the primary driver of elevated SV in the CJE.This study enhances the comprehension of the potential mechanisms underlying hypoxic zone formation in the CJE,providing novel insights into how nearshore eutrophication influences organic carbon migration.

Responding of zooplankton to environmental factor changes in the Changjiang River estuarine regions in spring-summer from 2016 to 2020

The estuarine areas are under frequent influence from freshwater intrusion and ocean currents,in which zooplankton species are diversified and variable as they are sensitive to physio-chemical variations in water.Therefore,understanding the relationships between zooplankton and environmental factors help us know the water quality.To achieve co-existence with species in similar ecological group or habit,they could inevitably alter themselves to fit the ecology and adjust the function according to the competitive exclusion in ecological theory.However,information of the co-existence of dominant species in the Changjiang(Yangtze)River estuary(CRE)and adjacent waters remains scarce.We explored the relationships between dominant zooplankton and environmental factors in the study region in spring-summer from 2016 to 2020,involving particularly the composition of dominant species,ecological groups,their relationships with environmental factors,and co-existence of important species,using the non-multidimensional scale analysis(nMDS)method and redundancy analysis.Results show that Labidocera euchaeta and Tortanus vermiculus were dominant species in the study scope.The turnover rate of dominant zooplankton was greater(>50%)in spring while the species number was higher in summer.The dominant species were estuarine,offshore,and eurytopic based on the adaptation to salinity.In spring,the ecological groups were dominated by estuarine species,while in summer by estuarine and offshore species.In addition,the nMDS showed that the dominant species in the same ecological group were more dispersed and not prominently clustered;the dominant species were staggered among different ecological groups.The temperature,salinity,pH,dissolved oxygen,and chlorophyll a were the main environmental factors on the distribution of the dominant species in spring,while in summer were dissolved oxygen,temperature,salinity,and pH.The domination of medusae of Nemopsis bachei and Pleurobrachia globosa in zooplankton community in spring,and the continuous decrease in abundance of L.euchaeta reflected the effects of local climate change.The temperature and salinity changes in different years and the subsequent response of zooplankton reflected the influence of freshwater intrusion and/or ocean currents.Zooplankton in similar ecological habits exhibited the competitive exclusion in terms of co-existence.

Coastal hypoxia response to the coupling of catastrophic flood,extreme marine heatwave and typhoon:a case study off the Changjiang River Estuary in summer 2020

Massive bodies of low-oxygen bottom waters are found in coastal areas worldwide,which are detrimental to coastal ecosystems.In summer 2020,the response of coastal hypoxia to extreme weather events,including a catastrophic flooding,an extreme marine heatwave,and Typhoon Bavi,is investigated based on multiple satellite,four cruises,and mooring observations.The extensive fan-shaped hypoxia zone presents significant northward extension during July-September 2020,and is estimated as large as 13 000 km^(2) with rather low oxygen minimum(0.42 mg/L) during its peak in 28-30 August.This severe hypoxia is attributed to the persistent strong stratification,which is indicated by flood-induced larger amount of riverine freshwater input and subsequent marine heatwave off the Changjiang River Estuary.Moreover,the Typhoon Bavi has limited effect on the marine heatwave and coastal hypoxia in summer 2020.

Spatiotemporal changes of biogenic elements in the Changjiang River Estuary and adjacent waters in summer over the last decade

The long-term spatiotemporal changes of surface biogenic elements in the Changjiang River Estuary and adjacent waters during the summer of 2008–2016 were analyzed in this study.The concentrations of dissolved inorganic nitrogen(DIN),soluble reactive phosphate(PO_(4)^(3−))and silicate(SiO_(3)^(2−))were generally stable,with a slight decrease of DIN and PO_(4)^(3−),and a slight increase of SiO_(3)^(2−),which mainly occurred in the estuarine waters.The grey correlation analysis was carried out between biogenic elements and chlorophyll a(Chl-a).Results showed that compared with the absolute values of biogenic elements,the correlations between the concentration ratio of nitrogen to phosphorus(N/P),ratio of silicon to nitrogen(Si/N)and Chl-a were closer,indicating the important influence on phytoplankton by the structure of biogenic elements.The study area was generally in a state of potential P limitation,and could have potential impact on the phytoplankton community,triggering the shift of red tide dominant species from diatoms to dinoflagellates.

Diel,seasonal,and annual variations of fish assemblages in intertidal creeks of the Changjiang River estuary

The use patterns of salt marsh habitats by fish assemblages were investigated in two welldeveloped intertidal creeks in the Changjiang(Yangtze)River estuary on spatial and temporal scales.Samples were collected using fyke nets at two sites during day and night in each season throughout four years.Notable changes in fish assemblages were detected over seasonal and interannual cycles,with many more marine species present in winter assemblages,whereas freshwater and estuarine species characterized the other seasonal samplings.The appearance of catadromous species in intertidal creeks mainly depended upon their specific physiological requirements,such as spawning migration.No significant diel shifts were observed in fish assemblages.This diel pattern may be a combined consequence of avian predation pressure and other drivers(i.e.,inherent living behaviors,food availability,and predation by piscivorous fishes).The spatial difference in fish community was insignificant even though the two intertidal creeks were different in size.Intertidal creeks with different size could possess similar ecological value for fish fauna.Redundancy analysis(RDA)showed that biological factors exerted greater effects on fish assemblages than physical variables.Temporal variations were strongly facilitated by food availability,but negatively impacted by avian predation.Salinity,water temperature,and river runoff had weak influence on temporal variations of fish communities.The lengthfrequency distribution showed that the fish collected in these two sites mainly consisted of young-of-year and juvenile fish,which confirmed that the creeks provided important nursery and forage roles in the process of fish ontogenetic development.Further,we proposed that salt marsh conservation management should be equally applied to all well-developed intertidal creeks regardless of creek size.

Diatom-based dissolved inorganic nitrogen reconstruction in the Changjiang River estuary and its adjacent areas

A five-component weighted average partial least squares(WA-PLS)calibration model was developed by analysing diatom assemblages in 34 surface sediment samples(collected in 2015)from the Changjiang River estuary(CRE)and its adjacent areas to infer dissolved inorganic nitrogen(DIN)concentrations.Eighteen additional sets of surface sediment diatoms and corresponding upper water DIN data(collected in 2012)were used to evaluate the accuracy of the model,and the relationship between observed and diatom-inferred DIN(DI-DIN)values(R2=0.85)illustrated the strong performance of the transfer function,indicating that precise reconstructions of former DIN are possible.The diatom-DIN transfer function was applied to the diatom record from a sediment core DH8-2(1962‒2012)collected in the Fujian-Zhejiang area south of the CRE.The reconstruction based on the DI-DIN model showed a significant DIN increase from 1962-2012,reflecting the influence of human activities on the very large increase in eutrophication.Three distinct periods can be seen from the changes in DIN and diatom taxa.In the 1962-1972 period,the DIN content was relatively low,with an average of 5.94μmol/L,and more than 80%of the diatom species identified were benthic taxa.In the 1972-2004 period,as the impact of human activities intensified,large nutrient inputs caused the DIN content to increase,with an average of 8.25μmol/L.The nutrient inputs also caused a significant change in the nutrient components and a distinct increase in small planktonic taxa.In the 2004-2012 period,the DIN content continued to rise,fluctuating at approximately 10μmol/L.A continuous increase in the frequency of planktonic taxa(up to 65.48%)indicated that eutrophication was further intensified,which was confirmed by the transformation from diatom-induced red tide to dinoflagellate-induced red tide during this period.

Vertical structure of tidal currents in the Xuliujing Section of Changjiang River Estuary

Three long-term fixed acoustic Doppler current profilers were first used for investigating the vertical structure of tidal currents in Xuliujing Section of Changjiang River Estuary.Moreover,three different periods(spring,summer and fall)were also considered for investigating seasonal variations.The semi-diurnal tides were the most energetic,with along-channel speed of up to 80 cm/s for M_(2)constituent,which dominates at all stations with percent energy up to 65%–75%during seasons.The shape of tidal ellipses of the most energetic semi-diurnal constituent M_(2)showed obvious polarization of the flow paralleling to the riverbank,with the minor semi-axis being generally less than 20%of the major one.The maximum velocity of mean current is appeared in top layers at all the three stations,and the velocity decreased with the depth.The seasonal variations of direction are also observed,which is probably caused by complex local topography since the erosion and deposition in riverbed.Observed vertical variation of four parameters of M_(2)ellipses,agreed well with the optimally fit frictional solutions in top and middle layers.However,there was an obvious difference between frictional model and observed data in the lower water column.Discrepancies are probably on account of stratification,which strengthens in summer and fall due to the freshening influence of the Changjiang River Estuary outflow.

Prokaryotic diversity and community composition in the surface sediments of the Changjiang River Estuary in summer

Microorganisms are fundamental for the functioning of marine ecosystems and are involved in the decomposition of organic matter, transformation of nutrients and circulation of biologically-important chemicals. Based on the complexity of the natural geographic characteristics of the Changjiang River Estuary, the geographic distribution of sedimentary microorganisms and the causes of this distribution are largely unexplored. In this work, the surface sediment samples from the adjacent sea area of the Changjiang River Estuary were collected. Their prokaryotic diversity was examined by high-throughput sequencing technology, and the environmental factors of the bacterial community were investigated. The results indicated that the distribution of prokaryotic communities in the sediments of the study areas showed obvious spatial heterogeneity. The sampling sequences divided the sample regions into three distinct clusters. Each geographic region had a unique community structure, although Proteobacteria, Bacteroidota, Desulfobacterota, Acidobacteriota, and Actinobacteriota all existed in these three branches. Canonical correspondence analysis demonstrated that prokaryotic diversity and community distribution were significantly correlated with the geographic location of sediment, seawater depth, and in particular, nutrient content(e.g., total phosphorus, total organic carbon and dissolved oxygen). Moreover, it was found for the first time that the metal ions obviously affected the composition and distribution of the prokaryotic community in this area. In general, this work provides new insights into the structural characteristics and driving factors of prokaryotic communities under the background of the ever-changing Changjiang River Estuary.

Prediction of discharge in a tidal river using the LSTM-based sequence-to-sequence models

The complexity of river-tide interaction poses a significant challenge in predicting discharge in tidal rivers.Long short-term memory(LSTM)networks excel in processing and predicting crucial events with extended intervals and time delays in time series data.Additionally,the sequence-to-sequence(Seq2Seq)model,known for handling temporal relationships,adapting to variable-length sequences,effectively capturing historical information,and accommodating various influencing factors,emerges as a robust and flexible tool in discharge forecasting.In this study,we introduce the application of LSTM-based Seq2Seq models for the first time in forecasting the discharge of a tidal reach of the Changjiang River(Yangtze River)Estuary.This study focuses on discharge forecasting using three key input characteristics:flow velocity,water level,and discharge,which means the structure of multiple input and single output is adopted.The experiment used the discharge data of the whole year of 2020,of which the first 80%is used as the training set,and the last 20%is used as the test set.This means that the data covers different tidal cycles,which helps to test the forecasting effect of different models in different tidal cycles and different runoff.The experimental results indicate that the proposed models demonstrate advantages in long-term,mid-term,and short-term discharge forecasting.The Seq2Seq models improved by 6%-60%and 5%-20%of the relative standard deviation compared to the harmonic analysis models and improved back propagation neural network models in discharge prediction,respectively.In addition,the relative accuracy of the Seq2Seq model is 1%to 3%higher than that of the LSTM model.Analytical assessment of the prediction errors shows that the Seq2Seq models are insensitive to the forecast lead time and they can capture characteristic values such as maximum flood tide flow and maximum ebb tide flow in the tidal cycle well.This indicates the significance of the Seq2Seq models.

Discussion on the Construction of Negotiation Mechanism of Cross-bounder Water Pollution Treatment in Changjiang River

In order to construct cooperation platform for the treatment of water pollution in Changjiang River,thoughts and revolution were performed from both central government and regional area two aspects.From the national level,Changjiang region water resources management cooperation counsel committee was constructed as the national cooperation platform;from the regional level,Changjiang region water resources management cooperation counsel committee was constructed as the platform of Changjiang cooperation platform.The two platforms built fine interaction mechanism to deal with the national water management and Changjiang regional water management.

Impact of the Three Gorges Dam on reproduction of four major Chinese carps species in the middle reaches of the Changjiang River

Silver carp(Hypophthalmichthys molitrix),bighead carp(Aristichthys nobilis),grass carp(Ctenopharyngodon idella),and black carp(Mylopharyngodon piceus) are the four major Chinese carps and are commercially important aquaculture species in China.Reproduction of these carp has declined since the construction of the Three Gorges Dam(TGD) due to an altered water flow and thermal regime in the Changjiang(Yangtze) River.However,details of the changes in reproduction of the four species are not well understood.To assess the impact of the TGD on reproduction of the four carp,we investigated their eggs and larvae at Yidu City,which is 80 km below the TGD,during 2005-2012.We examined differences in larval abundance of the four species in the Jianli section(350 km downstream of the TGD) before(1997-2002)and after(2003-2012) construction of the TGD.Based on these observations,the first spawning date of the four species was delayed a mean of about 25 days after the dam was constructed.Mean egg abundance in the Yidu section of the river was 249 million and mean larval abundance was 464 million,which were significant decreases since the 1980 s.Moreover,larval abundance in the Jianli section after the dam was constructed was significantly lower than that before construction(ANCOVA,P<0.05).The observed larval abundance accounted for only 24.66%of the predicted value in 2003 when the dam was first inundated.The present spawning grounds between the TGD and Yidu section of the river are very similar to those described in the 1980 s,and some spawning grounds exist upstream of the TGD.Large free-flowing stretches upstream of the TGD and the creation of artificially flooded downstream reaches are needed to stimulate spawning and effectively conserve these four major Chinese carps species.

Distribution patterns of phytoplankton in the Changjiang River estuary and adjacent waters in spring 2009

The Changjiang River estuary and adjacent waters are one of the most notable regions for red tides/harmful algal blooms in China's coastal waters.In this study,phytoplankton samples were collected and analyzed during the outbreak stage of red tides in May 2009.It was found that dinoflagellates,Prorocentrum donghaiense and Karenia mikimotoi,and diatoms,Skeletonema spp.and Paralia sulcata,were the major taxa dominating the phytoplankton community.Cluster analysis,non-metric multidimensional scaling(NMDS) and analysis of similarities(ANOSIM) was conducted on a data matrix including taxa composition and cell abundance of the phytoplankton samples.The analyses categorized the samples into three groups at a similarity level of 30%.Group Ⅰ was characterized by estuarine diatoms and distributed mainly in the highly turbid estuarine region.Group Ⅱ,which was dominated by the diatom Skeletonema spp.and represented the red tide of Skeletonema spp.,was situated around Group Ⅰ in the sea area west of 122°50'E.Group Ⅲ was characterized by a high proportion of dinoflagellates and was found further offshore compared with Groups Ⅰ and Ⅱ.Group Ⅲ was further divided into two subgroups(Ⅲ-S1 and Ⅲ-S2) at a similarity level of 40%.Group Ⅲ-S1 was characterized by the presence of the benthic diatom P.sulcata,representing phytoplankton samples collected either from the bottom or from the sea area affected by upwelling.GroupⅢ-S2 was dominated by dinoflagellates and represented red tides formed by P.donghaiense and K.mikimotoi.A gradual change of red-tide causative species was observed from the estuary to the offshore sea area,from diatoms to armored dinoflagellates and then unarmored dinoflagellates.Environmental factors associated with each group,and thus affecting the distribution of phytoplankton and red tides,are discussed.

Peaked abundance of Calanus sinicus earlier shifted in the Changjiang River (Yangtze River) Estuary:a comparable study between 1959,2002 and 2005

The sea surface temperature （SST） of the East China Sea （ECS） increased in the past decades, which may have a great impact on the ecosystem of the ECS, including the changes in planktonpopulation structure. In this paper, the changes in peaked abundance of Calanus sinicus in the Changjiang River （Yangtze River） Estuary were compared between 1959 and 2002, based on the data collected from the seasonally oceanographic cruises and those performed in spring of 2005. It was much higher in spring compared with that in other seasons both in 1959 and 2002. Furthermore, in spring 2005, the time for occurrence and decrease of the peaked C. sinicus abundance advanced about one month, accompanying the increase in the sea surface water temperature （SST）. It peaked in June and decreased in July in 1959, however, in 2005, it peaked in May and attenuated sharply in early June. The earlier decrease of peaked C. sinicus abundance may further deteriorate the ecosystem in the Changjiang River Estuary and north nearshore of the ECS.

Spatial distribution and deposition history of nonylphenol and bisphenol A in sediments from the Changjiang River(Yangtze River) Estuary and its adjacent East China Sea

Nonylphenol（NP） and bisphenol A（BPA） are endocrine disruptors causing harmful effects including feminization and carcinogenesis to various organisms,and consequently,their contamination in natural environment has received wide concerns.This study reports the distribution characteristics of NP and BPA in surface sediments and their deposition history based on a dated sediment core in the Changjiang River（Yangtze River） Estuary and its adjacent East China Sea.The contents of NP and BPA in surface sediments ranged from 1.56-35.8 and 0.72-13.2 ng/g（dry mass）,respectively,with high values recorded in the two mud zones,the Changjiang River Estuarine Mud Zone and the Zhejiang Coastal Mud Zone.High values in the Zhejiang Coastal Mud Zone suggest the possibility of long distance transport of both contaminants through the Changjiang riverine plume.The contents were not correlated with the distance from the pollution source,indicating other factors including particle deposition rate and sediment grain size obviously affecting the distribution pattern.NP was also detected in a sediment core at layers deposited from the year of 1971 to 2001 with contents of up to 20.9 ng/g（dry mass）.The deposition fluxes of NP varied from 0.68 to 17.9 ng/（cm^2 · a） with peaks and valleys reflecting the traces of economic development history in China during the previous three decades.BPA was detected at sediment layers deposited from 1973 to 2001 with contents of up to 3.66 ng/g.The fluxes of BPA varied from 0.62 to 3.13 ng/（cm^2 · a） showing a similar pattern as NP.The contents of NP and BPA also indicated potential risks on benthic organisms in the study area.

A STUDY ON THE RELATIONSHIPS OF THE NUTRIENTS NEAR THE CHANGJIANG RIVER ESTUARY WITH THE FLOW OF THE CHANGJIANG RIVER WATER

Investigations from August, 1985 to July , 1986 showed that the high concentration area of PO4-P , SiO3-Si and NO3-N gradually reduced with the reduction of the area of the Changjiang River diluted water from summer, autumn to winter , and that the seasonal distributions and variations of the nutrients concentrations were mainly controlled by the river flow and were also related to the growth and decline of phytoplankton . The conservation of SiO3-Si and NO3-N in the estuary in the flood season was poorer than that in the dry season .. The behaviour of PO4-P in the estuary shows that aside from -biological removal, buffering of PCU-P is possible in the estuary . The highest monthly average concentrations and annual average concentrations in the river mouth were respectively 0.88 and 0.57 umol/L for PO4-P,191.5 and 96.2 umol/L for SiO3-Si, and 81.6 and 58.6 umol/L for NOs-N . The Changjiang’s annual transports of PO4-P , SiO3-Si and NO3-N to the sea were about 1.4×104tons , 204.4×104 tons and 63.

Decreasing Reference Evapotranspiration in a Warming Climate-A Case of Changjiang (Yangtze) River Catchment During 1970-2000

This study deals with temporal trends in the Penman-Monteith reference evapotranspiration estimated from standard meteorological observations, observed pan evaporation, and four related meteorological variables during 1970-2000 in the Yangtze River catchment. Relative contributions of the four meteorological variables to changes in the reference evapotranspiration are quantified. The results show that both the reference evapotranspiration and the pan evaporation have significant decreasing trends in the upper, the middle as well as in the whole Changjiang （Yangtze） River catchment at the 5% significance level, while the air temperature shows a significant increasing trend. The decreasing trend detected in the reference evapotranspiration can be attributed to the significant decreasing trends in the net radiation and the wind speed.

Orthogonal design for optimization of pigment extraction from surface sediments of the Changjiang River Estuary

Using a suitable solvent for extracting pigments from sediment for high performance liquid chromatography（HPLC） analysis is critical for obtaining qualitative and quantitative estimates of phytoplanktonic and benthic algal biomass,as well as community composition. Five methodological factors（sample dehydration,extraction solvent,extraction duration,number of extractions,and ratio of solvent volume：sample weight） were studied using an L 9（3 4 ） orthogonal design in a sedimentary pigment extraction experiment on samples collected from the Changjiang large-river delta-front estuary（LDE）,using HPLC analysis. The results show that the optimal extraction method for sedimentary pigments should include freeze-drying samples prior to extraction. The effects of different factors on sedimentary pigment extraction were separated by the L 9（3 4 ） orthogonal design experiments and showed that the extraction solvent was the most important,with extraction duration the second most important,and numbers of extraction and ratio of solvent volume：sample weight was the least important. The mixed solvent treatment comprised of acetone,methanol and water（80：15：5,by volume） was best for polar pigment extraction,with 100% acetone better for apolar pigments. For most pigments employed in this study（i.e.,peridinin,fucoxanthin,alloxanthin,diatoxanthin,zeaxanthin,pheophytin-a and β-carotene） ,3 h was found to be enough time for extraction from these deltaic sediments. However,for chlorophyll-a,the most important pigment used for estimating algal biomass,12 h was needed. A small amount of solvent（3 ml） with duplicate extractions obtained the greatest amount and diversity of pigments. Unfortunately,no extraction method was found to be suitable for all pigments in sediments. The choice of extraction procedure should be made in accordance with the objective of each study,taking into consideration the properties of sediments and pigments in question.

The partial pressure of carbon dioxide and air-sea fluxes in the Changjiang River Estuary and adjacent Hangzhou Bay

The distributions of partial pressure of carbon dioxide （pCO2） in the surface waters of the Changjiang River Estuary and adjacent Hangzhou Bay were examined in the summer of 2010. Surface water pCO2 ranged from 751-2 095/zatm （1 atm=101 325 Pa） in the inner estuary, 177-1 036/zatm in the outer estuary, and 498-1 166 μatm in Hangzhou Bay. Overall, surface pCO2 behaved conservatively during the estuary mixing. In the inner estuary, surface pCO2 was relatively high due to urbanized pollution and a high respiration rate. The lowest pCO2 was observed in the outer estuary, which was apparently induced by a phytoplankton bloom because the dissolved oxygen and chlorophyll a were very high. The Changjiang River Estuary was a significant source of atmospheric CO2 and the degassing fluxes were estimated as 0-230 mmol/（m2.d） [61 mmol/（m2.d） on average] in the inner estuary. In contrast, the outer estuary acted as a CO2 sink.