Distribution of Dissolved Inorganic Carbon (DIC) and Its Related Parameters in Seawater of the North Yellow Sea and off the Qingdao Coast in October, 2007

Data on the distribution of dissolved inorganic carbon (DIC) were obtained from two cruises in the North Yellow Sea (NYS) and off the Qingdao Coast (QC) in October, 2007. Carbonate parameters were calculated. The concentrations of DIC are from 1.896-2.229 mmolL-1 in the NYS and from 1.939-2.032 mmolL-1 off the QC. In the southwest of the NYS, DIC in the upper layers decreases from the north of the SP (Shandong Peninsula) shelf to the center of the NYS; whereas in the lower layers DIC increases from the north of the SP shelf to the center of the NYS and South Yellow Sea. In the northeast of the NYS, DIC in all layers in- creases from the YR (Yalu River) estuary to the centre of the NYS. The distribution of DIC in NYS can be used as an indicator of Yellow Sea Cold Water Mass (YSCWM). Air-sea CO2 fluxes were calculated using three models and the results suggest that both the NYS and the QC waters are potential sources of atmospheric CO2 in October.

Stable isotopic composition of riverine dissolved inorganic carbon of the Xijiang River Inner Estuary

For researching the spatio-temporal variation of the stable isotopic composition of the riverine dissolved inorganic carbon（DIC）,we had carried out a survey throughout the hydrologic year during which theδ^13CDIC of the surface water and its physicochemical parameter were examined along the Xijiang River Inner Estuarine waterway from September 2006 to June 2007.There was a striking seasonal variation on the averageδ^13CDIC,as the averageδ^13CDIC in summer（-13.91‰）or autumn（-13.09‰）was much less than those in spring（-11.71‰）or winter（-12.26‰）.The riverineδ13C DIC was controlled by decomposed condition of the riverine organic matter linking the seasonal variation of the physicochemical parameter in the surface water according to the correlation analysis which indicated notable relations betweenδ^13CDIC and water temperature（p=0.000;r=-0.569）or betweenδ^13CDIC and oxide-reduction potential（p=0.000;r=0.646）.The striking positive correlation between δ^13CDIC and the sampling distance happened in the summer rainy season,while striking negative correlation happened in the spring dry season,indicating that river-sea interaction influenced water physicochemical parameters and controlled the riverine DIC property in the survey waterway.In view of the riverineδ^13CDIC decreasing for the decomposition of the terrestrial organic matter in the rainy season in summer and increasing for the briny invaded zone extending in the spring dry season along the waterway from the Makou gauging station to the Modaomen outlet,theδ^13CDIC spatio-temporal variation was closely related to the geographical environment of the Xijiang drainage basin.

Damming effects on dissolved inorganic carbon in different kinds of reservoirs in Jialing River,Southwest China

To assess the effects of river damming on dissolved inorganic carbon in the Jialing River, a total of 40 water samples, including inflow, outflow, and stratified water in four cascade reservoirs(Tingzikou, Xinzheng,Dongxiguan, Caojie) were collected in January and July,2016. The major cations, anions, and δ^(13)C_(DIC) values were analyzed. It was found that the dissolved compositions are dominated by carbonate weathering, while sulfuric acids may play a relatively important role during carbonate weathering and increasing DIC concentration. Different reservoirs had variable characteristics of water physiochemical stratification. The DIC concentrations of reservoir water were lower in summer than those in winter due to the dilute effects and intensive aquatic photosynthesis, as well as imported tributaries. The δ^(13)C_(DIC) values in Tingzikou Reservoir were higher during summer than those in winter,which indicated that intensive photosynthesis increased the δ^(13)C_(DIC) values in residual water, but a similar trend was not obvious in other reservoirs. Except for in Xinzheng Reservoir, the δ^(13)C_(DIC) values in inflow and outflow reservoir water were lower than those in the surface water of stratified sampling in summer. For stratified sampling, it could be found that, in summer, the Tingzikou Reservoir δ^(13)C_(DIC) values significantly decreased with water depthdue to the anaerobic breakdown of organic matter. The significant correlation(p<0.01 or 0.05) between the DIC concentrations, the δ^(13)C_(DIC) values and anthropogenic species(Na^++K^+, Cl~–, SO_4^(2-) and NO_3^-) showed that the isotope composition of DIC can be a useful tracer of contaminants. In total, Tingzikou Reservoir showed lacustrine features, Xinzheng Reservoir and Dongxiguan Reservoir had "transitional'' features, and Caojie Reservoir had a total of "fluvial'' features. Generally, cascade reservoirs in the Jialing River exhibited natural river features rather than typical lake features due to characteristics of reservoir water in physiochemical stratification, spatiotemporal variations of DIC concentrations and isotopic compositions. It is evident that the dissolved inorganic carbon dynamics of natural rivers had been partly remolded by dam building.

Photochemical production of dissolved inorganic carbon from suwannee river humic acid

The photochemical mineralization of dissolved organic carbon(DOC) to dissolved inorganic carbon(DIC) is a key process in carbon cycling.Using a Suntest CPS solar simulator,Suwannee River humic acid(SRHA) was photooxidated to examine the effects of O2 levels,the wavelength of incident light,and the concentration of Fe on the photoproduction of DIC.Increasing the O2 abundance enhanced photodegradation of SRHA.The rate of DIC photoproduction under air saturation in the first 24 h(4.40 μmol/(L h)) was increased by a factor of 1.56 under O2 saturation,but fell by only 36% under N2 saturation.To evaluate the relative importance of UV-B,UV-A,and visible radiation in the photodegradation,we examined the above process using Mylar-d films and UF-3 and UF-4 plexiglass filters.The results indicated that the UV-B,UV-A and visible wavelengths accounted for 31.8%,32.6% and 25.6%,respectively,of DIC production with simulated sunlight irradiation.The above results also indicated that photoproduction of DIC could take place in natural water at depths greater than those that UV light can reach.When 20 μmol/L desferrioxamine mesylate(DFOM,a strong Fe complexing ligand) was added,the rate of DIC photoproduction fell to 55.6% that of the original SRHA samples with 5.46 μmol/L Fe.

Stable isotope geochemical characteristics of dissolved inorganic carbon in the Jiulong River Estuary, Fujian Province, China

The isotopic composition of dissolved inorganic carbon(DIC) in estuarine environments has been studied for its significant role in determining the isotopic composition of inorganic/organic matter and its applications to the study of various natural processes. In this paper, based on the stable isotope geochemical characteristics of dissolved inorganic carbon in the Jiulong River Estuary, the following conclusions are drawn:(1) δ13CDIC values are mainly controlled by the mixing ratio of fresh water and sea water;(2) δ13Cphytoplankton values are linearly related to the δ13CDIC values;(3) δ13CPOM values for the Jiulong River Estuary are affected by anthropogenic pollution significantly; and(4) the comprehensive analysis of δ13Cphytoplankton, δ13CPOM and δ13CDIC shows that along with increasing salinity, the proportion of POM derived from the degradation of phytoplanktons gradually increases.

The influence of macronitrogen (NO_3^- and NH_4^+) addition with U lva pertusa on dissolved inorganic carbon system

The influence of macronitrogen （NO3 and NH＋） addition with Ulva pertusa on dissolved inorganic carbon system in seawater was studied. The results indicate that p（C02） and HCO3 concentration decrease significantly, while pH and CO32- concentration increase significantly. When the con- centration of NO3 was less than 71 μmol/dm3 or NH4＋ was less than 49.7μmol/dm3, dissolved inorganic carbon （DIC） absorption rates by Ulva pertusa generally increased with the increasing of nitrogen concentration. The DIC decreased 151 μmol/dm3 with the addition of 71 μmol/dm3 NO3 and decreased 232 μmol/dm3 with the addition of 49.7 μmol/dm3 NH＋ after the experiment compared with DIC measured without nitrogen addition. A significant negative-correlation was found between Ac（DIC） and growth rate （#） of Ulva pertusa （r =- 0.91, P 〈0.000 1, n=11）. NH＋ had more influence on the species of inorganic carbon system than NO3.

Distributions of dissolved inorganic carbon and total alkalinity in the Western Arctic Ocean

The third Chinese National Arctic Research Expedition （3rd CHINARE-Arctic in 2008） was carried out from July to September 2008. During the survey, numerous sea water samples were taken for CO2 parameter measurement （including total alkalinity TA and total dissolved inorganic carbon DIC）.The distribution of COs parameters in the Western Arctic Ocean was determined, and the controlling factors are addressed. The ranges of summertime TA, normalized TA （nTA）, DIC and normalized DIC （nDIC） in the surface seawater were 1 757 2 229 umol.kg 1 2 383-2 722 umol.kg-1, 1 681 2 034 pmol.kg 1, 2 119--2 600 umol.kg-1, respectively. Because of dilution from ice meltwater, the surface TA and DIC concentrations were relatively low. TA in the upper 100 m to the south of 78°N had good correlation with salinity, showing a conservative behavior. The distribution followed the seawater-river mixing line at salinity 〉30, then followed the seawater mixing line （diluted by river water to salinity = 30） with the ice meltwater. The DIC distribution in the Chukchi Sea was dominated by biological production or respiration of organic matter, whereas conservative mixing dominated the mixed layer TA distribution in the ice-free Canada Basin.

The stable isotope geochemical characteristics of dissolved inorganic carbon in northern South China Sea

The isotopic composition of dissolved inorganic carbon (DIC) in marine and estuarine environments has been studied in some detail because of its role in determining the isotopic composition of inorganic/organic matter and its applications to the study of various natural processes. The δ13CDIC values of sea water are controlled by the sources and sinks of carbon and the results from isotope fractionation among solid, dissolved and gaseous phases. In this paper, based on the description of the stable isotope geochemical characteristics of dissolved inorganic carbon in northern South China Sea, the following conclusions were drawn: 1) the δ13CDIC values of natural waters are controlled by the sources and sinks of carbon and the results from isotope fractionation among solid, dissolved and gaseous phases. And the low seawater δ13CDIC values of northern South China Sea are accompanied by a low level of sea primary productivity in this region; 2) according to the parameter relationship (δ13CDIC-1.1 PO4) between δ13CDIC and PO4, it is indicated that northern South China Sea is the source of atmospheric CO2; and 3) nitrogen (N) and phosphorus (P) are the elements which are the basis for phytoplankton growth. Based on the analysis of seawater δ13CDIC values and PO4 and NO3+NO2 concentrations, our data show that N is a limiting nutrient in northern South China Sea.

Sources of dissolved inorganic carbon in rivers from the Changbaishan area, an active volcanic zone in North Eastern China

Major elements and carbon isotopes of dissolved inorganic carbon(DIC)have been measured in the waters of Changbaishan mountain,a volcanic area in northeastern China,between June and September 2016 to decipher the origin of the CO_2 involved in chemical weathering reactions.Spatial variations of major elements ratios measured in water samples can be explained by a change of the chemical composition of the volcanic rocks between the volcanic cone(trachytes)and the basaltic shield as evidenced by the variations in the composition of these rocks.Hence,DIC results from the neutralization of CO_2 by silicate rocks.DIC concentrations vary from 0.3 to 2.5 mmol/L and carbon isotopic compositions of DIC measured in rivers vary from-14.2‰to 3.5‰.At a first order,the DIC transported by rivers is derived from the chemical weathering’s consumption of CO_2 with a magmatic origin,enriched in^(13)C(-5%)and biogenic soil CO_2 with lower isotopic compositions.The highest δ^(13)C values likely result from C isotopes fractionation during CO_2 degassing in rivers.A mass balance based on carbon isotopes suggest that the contribution of magmatic CO_2 varied from less than 20%to more than 70%.Uncertainties in this calculation associated with CO_2 degassing in rivers are difficult to quantify,and the consequence of CO_2 degassing would be an overestimation of the contribution of DIC derived from the neutralization of magmatic CO_2 by silicate rocks.

Characteristics of dissolved inorganic carbon in produced water from coalbed methane wells and its geological significance

Based on long-term dynamic tracing of dissolved inorganic carbon(DIC)and stable carbon isotope(δ13CDIC)in produced water from 20 coalbed methane(CBM)wells in western Guizhou,the spatial-temporal dynamic variations ofδ13CDIC of the GP well group produced in multi-layer commingled manner were analyzed,and the relationship between the value ofδ13CDIC and CBM productivity was examined.The produced water samples of typical wells in the GP well group were amplified and sequenced using 16S rDNA,and a geological response model ofδ13CDIC in produced water from CBM wells with multi-coal seams was put forward.The research shows that:δ13CDIC in produced water from medium-rank coal seams commonly show positive anomalies,the produced water contains more than 15 species of methanogens,and Methanobacterium is the dominant genus.The dominant methanogens sequence numbers in the produced water are positively correlated withδ13CDIC,and the positive anomaly of v is caused by reduction of methanogens,and especially hydrogenotrophic methanogens.Vertical segmentation of sedimentary facies and lithology in stratum with multi-coal seams will result in permeability and water cut segmentation,which will lead to the segmentation ofδ13CDIC and archaea community in produced water,so in the strata with better permeability and high water cut,theδ13CDIC of the produced water is abnormally enriched,and the dominant archaea is mainly Methanobacterium.In the strata with weak permeability and low water cut,theδ13CDIC of the produced water is small,and the microbial action is weak.The shallow layer close to the coal seam outcrop is likely to be affected by meteoric precipitation,so theδ13CDIC of the produced water is smaller.The geological response model ofδ13CDIC in produced water from multi-coal seams CBM wells in the medium-rank coal reveals the geological mechanism and microbial action mechanism of theδ13CDIC difference in the produced water from the multi-coal seams CBM wells.It also provides effective geochemical evidence for the superimposed fluid system controlled by sedimentary facies,and can also be used for the contribution analysis of the produced gas and water by the multi-layer CBM wells.

The Correlation between the Variation of Dissolved Inorganic Carbon Content and Cyanobacterial Blooms in Fubao Bay of Dianchi Lake

To explore variation of dissolved inorganic carbon content( DIC) caused by cyanobacterial blooms and provide a basis for formulating effective preventive and control measures of cyanobacterial blooms,the concentration of inorganic carbon and the concentration of planktonic algae were studied by sampling method,and the distribution and variation of the DIC and physicochemical factors in the ecological restoration area of Fubao Bay of Dianchi Lake were analyzed. Results indicated that the distribution of chlorophyll-a was significantly positive correlated with CO_3^(2-)( P < 0. 01) and pH values( P < 0. 05); and the distribution of chlorophyll-a was significantly negative correlated with CO_2( P <0. 01),DIC and HCO_3^-( P < 0. 05). In conclusion,the outbreak and extinction of cyanobacterial blooms is one of the important reasons for the variation of inorganic carbon form and concentration.

Inorganic Carbon Parameters Responding to Summer Hypoxia Outside the Changjiang Estuary and the Related Implications

The eutrophication,hypoxia and coastal acidification are attracting more and more attention.In this study,inorganic carbon parameters,including dissolved inorganic carbon (DIC) ,total alkalinity (TA) and calculated partial pressure of CO2 (pCO2) ,obtained from a summer cruise in August,2009,were used to investigate their integrated response to biological processes accompanying the oxygen depletion in the areas off the Changjiang Estuary.According to the observations,the typical hypoxia occurred in the bottom water just outside the Changjiang Estuary with Dissolved Oxygen (DO) lower than 2.00 mg L 1.The biological uptake in the surface water and the decomposition of organic matter in the bottom water were fully coupled with each other.The high concentration of Chl_a (Chl_a=10.9μg L 1) and DO (9.25 mg L 1) ,profoundly decreased DIC concentration (1828μmol kg 1) and elevated pH (8.42) was observed in the surface water.The correspondingly increased DIC and depletion of oxygen were observed in the bottom water.The semi-quantitative analysis proved that the locally-produced phytoplankton,determined by primary productivity,was deposited to the bottom and contributed about 76%of total amount of the organic carbon decomposition in the bottom.However,in the bottom hypoxia (DO=2.05 mg L 1) area observed in the Southern Zhejiang coastal water,the responding patterns of inorganic carbon parameters deviated from the previous one.The expanding of Changjiang Diluted Water (CDW) ,the adding of Hangzhou Bay water (with high DIC concentration) and Coastal Current together modify the DIC background value in this area,and the local degeneration and upwelling process may also help to offset the local DIC removed by net biological uptake in surface water.In addition,when the mixing occurring in autumn,which may break the summer stratification,the excess release of high DIC in the bottom water to the subsurface water could have an important influence on coastal acidification and the CO2uptake capacity in this area.

The Effects of Estuarine Processes on the Fluxes of Inorganic and Organic Carbon in the Yellow River Estuary

Riverine carbon flux is an important component of the global carbon cycle. The spatial and temporal variations of organic and inorganic carbon were examined during both dry and wet seasons in the Yellow River estuary. Concentrations of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in the Yellow River during dry seasons were higher than those during wet seasons. The effective concentrations of DOC (CDOC*) were higher than the observed DOC at zero salinity. This input of DOC in the Yellow River estuary was due to sediment desorption processes in low salinity regions. In contrast to DOC, the effective concen- trations of DIC were 10% lower than the DIC measured at freshwater end, and the loss of DIC was caused by CaCO3 precipitation in low salinity region. Particulate organic carbon (POC) and particulate inorganic carbon (PIC) contents of the particles stabilized to constant values (0.5%±0.05% and 1.8%±0.2%, respectively) within the turbidity maximum zone (TMZ) and showed no noticeable seasonal variations. A rapid drop of PIC and rise of POC occurred simultaneously outside the TMZ due to an intense dilution of riverine inorganic-rich particles being transported into a pool of aquatic organic-poor particles outside the TMZ. Annually, the Yellow River transported 6.95×105 t of DIC, 0.64×105 t of DOC, 78.58×105 t of PIC and 2.29×105 t of POC to the sea.

RIVERINE INORGANIC CARBON DYNAMICS:OVERVIEW AND PERSPECTIVE

Inorganic carbon, the great part of the riverine carbon exported to the ocean, plays an important role in the global carbon cycle and ultimately impacts the coupled carbon-climate system. An overview was made on both methods and results of the riverine inorganic carbon researches. In addition to routine in situ survey, measurement and calculation, the direct precipitation method and the gas evolution technique were commonly used to analyze dissolved inorganic carbon in natural water samples. Soil CO2, carbonate minerals and atmospheric CO2 incorporated into riverine inorganic carbon pool via different means, with bicarbonate ion being the dominant component. The concentration of inorganic carbon, the composition of carbon isotopes (δ13C and Δ14C), and their temporal or spatial variations in the streams were controlled by carbon input, output and changes of carbon biogeochemistry within the riverine system. More accurate flux estimation, better understanding of different influential processes, and quantitative determination of various inputs or outputs need to be well researched in future.

Alleviating eutrophication by reducing the abundance of Cyanophyta due to dissolved inorganic carbon fertilization:Insights from Erhai Lake,China

The eutrophication of lakes is a global environmental problem.Regulating nitrogen(N)and phosphorus(P)on phytoplankton is considered to be the most important basis of lake eutrophication management.Therefore,the effects of dissolved inorganic carbon(DIC)on phytoplankton and its role in mitigating lake eutrophication have often been overlooked.In this study,the relationships between phytoplankton and DIC concentrations,carbon isotopic composition,nutrients(N and P),and hydrochemistry in the Erhai Lake(a karst lake)were investigated.The results showed that when the dissolved carbon dioxide(CO_(2)(aq))concentrations in the water were higher than 15μmol/L,the productivity of phytoplankton was controlled by the concentrations of TP and TN,especially by that of TP.When the N and P were sufficient and the CO_(2)(aq)concentrations were lower than 15μmol/L,the phytoplankton productivity was controlled by the concentrations of TP and DIC,especially by that of DIC.Additionally,DIC significantly affected the composition of the phytoplankton community in the lake(p<0.05).When the CO_(2)(aq)concentrations were higher than 15μmol/L,the relative abundance of Bacillariophyta and Chlorophyta was much higher than those of harmful Cyanophyta.Thus,high concentrations of CO_(2)(aq)can inhibit harmful Cyanophyta blooms.

菌藻共生系统对模拟油田驱采废水中PAM和DIC去除的处理

油田三元复合驱采废水中总溶解性无机碳(DIC)浓度高、总量大,现有以细菌为主的生物处理方法无法有效地处理DIC,尾水排放后会转化成CO_(2),违背了我国“碳减排”的总体目标。研究以旋转式菌藻共生生物膜系统处理模拟石油驱采废水,达到同步削减DIC和聚丙烯酰胺(PAM)的目的。文章探究了不同PAM、总碳(TC)、总氮(TN)浓度条件下,体系对PAM、总有机碳(TOC)、无机碳(IC)、溶液黏度的减排效果。结果表明,菌藻共生系统在有效地降低出水中DIC浓度的同时,对PAM降解效果明显;DIC的去除率能达到70%~80%,PAM的降解率可以达到60%~70%。投加共代谢氮源可以提高PAM的降解效果,但DIC去除效果明显下降。扫描电镜图像显示,处理后的PAM结构出现了明显的破坏。针对菌藻生物膜的16S rDNA高通量测序结果表明,藻类、细菌、真菌均在PAM和DIC的去除方面发挥了重要作用。

Photo-production of dissolved inorganic carbon from dissolved organic matter in contrasting coastal waters in the southwestern Taiwan Strait, China

Photo-production of dissolved inorganic carbon （DIC） from chromophoric dissolved organic matter （CDOM） is an important transformation process in marine carbon cycle, but little is known about this process in Chinese coastal systems. This study investigated an estuarine water sample and a coastal seawater sample from the subtropical waters in southeast of China. Water samples were exposed to natural sunlight and the absorption and fluorescence of CDOM as well as the DIC concentration were measured in the summer of 2009. The estuarine water had higher CDOM level, molecular weight and proportion of humic-like fluorescent components than the seawater that exhibited abundant tryptophan-like fluorescent component. After a 3-day irradiation, the CDOM level decreased by 45% in the estuarine water and 20% in the seawater, accompanied with a decrease in the molecular weight and aromaticity of DOM which was inferred from an increase in the absorption spectral slope parameter. The photo-degradation rates of all the five fluorescent components were also notable, in particular two humic-like components （C4 and C5） were removed by 78% and 69% in the estuarine water and by 69% and 56% in the seawater. The estuarine water had a higher photo-production rate of DIC than the seawater （4.4 vs. 2.5 μmol/（L-day））, in part due to its higher CDOM abundance. The differences in CDOM compositions between the twO types of waters might be responsible for the higher susceptibility of the estuarine water to photo-degradation and hence could also affect the photo-production process of DIC.

The impact of damming on geochemical behavior of dissolved inorganic carbon in a karst river

To determine the impact of damming on the geochemical behavior of dissolved inorganic carbon(DIC)in the Wujiang River basin,field measurements and samples were collected semimonthly for a year.The surface waters of the reservoirs contained concentrations of chlorophyll a up to 5.6 times higher than the upstream river.Compared with the entering waters,the contributions of HCO3-and dissolved CO2to DIC decreased,and the contribution of CO32-to DIC and the carbon isotopic composition of DIC(d13CDIC)increased in the surface waters of the reservoirs,while in the waters released,the DIC species showed reverse geochemical behaviors.The d13CDICranged from-10.2%to 2.5%,indicating that significant contributions were from carbonate weathering,photosynthesis,and respiration.After the damming of a river,the bioactivity of phytoplankton was enhanced,and this affected the geochemistry of DIC compared to an unimpacted river and d13CDICcan be used to discern these changes.High-frequency monitoring of river-reservoir systems is necessary to evaluate the efflux of CO2and provide a better understanding of the carbon sinks and sources in the impounded river.

Dissolved inorganic carbon and its isotopic differentiation in cascade reservoirs in the Wujiang drainage basin

Three cascade reservoirs,built in different periods of time in the Wujiang drainage basin,were inves-tigated in this study.Samples were taken at the surface and also at 20,40,60,80 m depths in front of the dams in April,July,October of 2006 and January of 2007.Chemical parameters were calculated and the concentrations of dissolved inorganic carbon DIC and its isotopic composition(δ13CDIC) were de-termined.In surface waters,the δ13CDIC values are high in summer and autumn and low in winter and spring,while the DIC concentrations are relatively low in summer and autumn and relatively high in winter and spring.In the water column,the DIC concentrations increase while δ13CDIC values decrease with water depth.DIC in various reservoirs is significantly different in isotopic composition from that in natural rivers,but is close to that in natural lakes.In addition,in surface waters,the δ13CDIC values tend to become lower whereas the nutrition level tends to become higher with increasing age of the reser-voirs.The conclusion is that after dam blocking,changes took place in the hydrochemical properties of river water,and the impounding rivers developed toward lakes and swamps.In addition,differentiation in DIC isotopic composition may be used to some extent to trace the evolution process of a reservoir.

Stable-isotope probing of bacterial community for dissolved inorganic carbon utilization in Microcystis aeruginosa-dominated eutrophic water

Dissolved inorganic carbon(DIC) is an important source of carbon in aquatic ecosystems,especially under conditions of increased frequency of cyanobacterial bloom. However, the importance of bacteria in direct or indirect utilization of DIC has been widely overlooked in eutrophic freshwater. To identify the functional bacteria that can actively utilize DIC in eutrophic freshwater during cyanobacterial bloom, stable-isotope probing(SIP) experiments were conducted on eutrophic river water with or without inoculation with cyanobacteria(Microcystis aeruginosa). Our 16 S rRNA sequencing results revealed the significance of Betaproteobacteria, with similar relative abundance as Alphaproteobacteria, in the active assimilation of H^(13)CO^(3-) into their DNA directly or indirectly, which include autotrophic genera Betaproteobacterial ammonia-oxidizing bacteria. Other bacterial groups containing autotrophic members, e.g. Planctomycetes and Nitrospira, also presented higher abundance among free-living bacteria in water without cyanobacteria. Microcystis aggregates showed a preference for some specific bacterial members that may utilize H^(13)CO^(3-) metabolized by Microcystis as organic matter, e.g. Bacteroidetes(Cytophagales, Sphingobacteriales), and microcystindegrading bacteria Betaproteobacteria(Paucibacter/Burkholderiaceae). This study provides some valuable information regarding the functional bacteria that can actively utilize DIC in eutrophic freshwater.