1 Introduction

Oceans significantly devote numerous climatic important biogases, especially those containing CO2, O2, and dimethylsulfide (DMS), to the global emissions (Carpenter et al., 2012). CO2 emission from oceans to atmosphere is a key process in global climate change, and that from rivers and their estuaries also has been extensively investigated (Chen and Borges, 2009; Chen et al., 2012, 2013).DMS is the dominant volatile sulfur compound emitted from the ocean to the atmosphere (Lovelock et al., 1972;Stefels et al., 2007). Observations in the marine boundary layer were conducted in terms of its significant role in climate regulation and acid rain formation (Turner et al.,1996; Yang et al., 2009), although Quinn and Bates (2011)consider that a DMS biological control over cloud condensation nuclei probably does not exist. Dissolved oxygen (DO) represents the functionality and behavior of an ecosystem (Ross et al., 2001). Numerous phenomena involving marine hypoxia occur worldwide (Conley et al.,2011; Wang et al., 2016); thus, DO in aquatic systems is widely explored. Estuaries provide habitats for a large number of organisms and support very high productivity,which play a critically important role in the global oceanic substance cycles and have recently received increasing attention.

[10]赵月枝.国家、市场与社会：从全球视野和批判角度审视中国传播与权力的关系[J].传播与社会学刊，2007（2）

Various mechanisms, including respiration, decomposition, uptake from the atmosphere, and carbonate formation, can increase the levels of CO2 in seawater (Carpenter and Nightingale, 2015). Thus far, studies on CO2 in seawater have focused on sea-to-air CO2 flux in different seasons and regions, and also many in-depth researches have been carried out (Chou et al., 2009a; Zhai et al.,2014). They found that spatial variations of CO2 parame-ters closely corresponded to the distributions of various water types and had different causes including water mixing, high biological production and the modulation of chemical buffering capacity. These researches help to better understand the sea surface carbonate chemistry dynamics in marine systems. Considering the critical roles of estuarine plumes in land-ocean interaction and large uncertainties in drainage areas (Xue et al., 2016;Zhai and Dai, 2009), further observation and estimation of CO2 systems is essential.

DO level in natural aquatic systems is an important parameter of biogenic elements, whose distributions and variations can elucidate atmosphere-ocean interactions,net primary production, and carbon remineralization. The atmosphere and aquatic plant photosynthesis are the two main sources of DO in seawater. Thus, DO can indicate the activity of marine phytoplankton (Ginders et al., 2016;Yin et al., 2004). DO is essential not only for marine life but also for organic matter decomposition because this process consumes oxygen (Gao and Song, 2008). Furthermore, the production and consumption of O2 are often related to CO2 variations in marine ecosystems.

DMS is produced through the enzymatic cleavage of dimethylsulfoniopropionate (DMSP), which exists in marine phytoplankton and functions as an osmolyte, cryoprotectant, anti-oxidant, grazing defender, or chemoattractant (Gage et al., 1997; Malin and Kirst, 1997). DMS is exudated from intact algae by DMSP-lyase, which is found in algae (Steinke et al., 2007) and bacteria (Ledyard and Dacey, 1994); this process is quantitatively not significant (Laroche et al., 1999). Moreover, DMS is substantially released through senescent algal cell lysis.Other biological processes, such as viral attack (Hill et al.,1998; Zubkov et al., 2002) and zooplankton grazing (Dacey and Wakeham, 1986; Wolfe et al., 2000), may be implicated in accelerating DMS production. DMS is removed from the ocean through the following three pathways: emission to the atmosphere, bacterial consumption(Gonzalez et al., 1999), and photo-oxidation into dimethylsulfoxide and other oxidation products (Lee and de Mora, 1999). However, the biogeochemistry of DMS in coastal ecosystems remains poorly understood.

Considerable efforts have been devoted to investigating O2 (Gao and Song, 2008; Minami et al., 1999), CO2(Wang et al., 2000; Zhai et al., 2007; Zhang et al., 2014a),and DMS (Yang et al., 2009; Zhang et al., 2014b) separately. However, only a few studies have explored O2,CO2, and DMS simultaneously (Delille et al., 2007; Tortell et al., 2011, 2012a, 2012b), and most of them studied on the biogeochemistry of O2, CO2, and DMS in sea ice zone. They reported spatial distribution of pCO2, ΔO2/Ar and DMS in different seasons (spring and summer) and different regions (Ross Sea and Amundsen Sea) of the Southern Ocean. The strength of correlation between pCO2, ΔO2/Ar and DMS differed in different seasons and affected by different factors such as sea ice cover, surface hydrography, and phytoplankton biomass and taxonomic composition. They generally drew a conclusion that the study areas acted as an overall net sink for atmospheric CO2 and a DMS source during the time of cruises. Future studies were suggested to explore more information on the microbial production and consumption of DMS and increase the temporal coverage of gas measurements in different regions to constrain the annual sea-to-air fluxes of CO2 and DMS in this system and its relative contribution to total Southern Ocean gas cycling. To our best knowledge, the joint temporal survey of pCO2, O2 and DMS has yet not been conducted in coastal waters, which has been demonstrated to play a significant role in climate regulation. To improve understanding of the biogeochemical processes and their influence on local climate model, in the present study, we investigated the distributions and relationships among O2, CO2, and DMS in the Changjiang Estuary and its adjacent waters in summer.This study may contribute to research on carbon and sulfur cycles in the ocean and is of great significance in ecology and biology (Carpenter et al., 2012).

2 Materials and Methods

2.1 Study Area

where K is the gas transfer coefficient related to wind velocity and [DMS] is the concentration of dissolved DMS in the surface water. In this case, the atmospheric DMS concentration is negligible relative to dissolved DMS levels. There are several empirical gas exchange models to estimate K (Liss and Merlivat, 1986; Nightingale et al., 2000; Wanninkhof, 1992). In this study, we used the model of Wanninkhof (1992) to estimate K values.

一是考核主体不明晰，即由谁来进行评估尚无定论。无论是以中国管理科学研究院或者是武汉大学中国科学评价研究中心为代表的民间机构，还是以教育部学位与研究生教育发展中心为代表的半官方机构，其合法性和权威性一直都备受外界质疑，其中立性也饱受诟病。二是考核对象分类不清。未能对被考核对象进行详细分类是国内高校绩效评估结果引发外界争议的一个重要原因。三是考核标准有待规范。国内高校绩效评估尚没有提出一个完整和公认的绩效评价指标体系，不同评价体系选用的指标差异较大，其评价结果也大不相同。

复测从全国华东、西北、华中、西南、华南、东北和华北7个地区选取共计484名高职院校数学教师参与调查，最终收回有效量表484份，量表有效率为100%．使用SPSS17.0软件，先针对量表的所有项目进行整体探索性因素分析，在取得因素构面基础上进行分层面探索性因素分析，即以分量表的个别题项进行因素分析，从而形成一份具有较好建构效度的量表．

2.2 Sampling

The net sea-to-air CO2 exchange flux (F) was calculated based on the formula:

3.问卷调查法：本课题除运用比较分析法外，还通过问卷调查法对结果进行验证，以提升结论的可靠性。利用云课堂平台相关功能实施调查，了解学生对教师教学态度、教学方法和教学效果等方面的满意程度，问卷针对全体学生。

Fig.1 Location of the sampling stations in the Changjiang(Yangtze) Estuary and its adjacent waters in June 2014.Arrows indicate the direction of the currents (Liu et al.,2007). YSCC, Yellow Sea Coastal Current; CRDW,Changjiang River Diluted Water; ZMCC, Zhe-Min Coastal Current; TWC, Taiwan Warm Current.

2.3 Analytical Methods

According to the report of Mauna Loa Observation in Hawaii, CO2 concentration in the atmosphere reached 400 ppm (about 384 µatm) in April 2014; the average pCO2 values of Changjiang Estuary showed that it acted as a CO2 sink to the atmosphere in June 2014. Chen et al.(2008) reported pCO2 values of 181-712 µatm in the outer Changjiang Estuary on August 26-27, 2003, with a mean value of 380 µatm, which was close to atmospheric CO2 at the time. Thus, the values of our observation are almost in accordance with that reported by Chen et al.(2008). Throughout the study area, the sea-to-air fluxes of CO2 exhibited considerable spatial variability, which was related to the sea-to-air pCO2 difference and wind speed.Chen et al. (2012) summarized that significant river plumes such as Amazon, Mississippi, Congo, Ganges and Pearl River plumes acted as sink of CO2. Zhai and Dai(2009) indicated that the sea-to-air CO2 flux of the outer Changjiang Estuary was −4.9 ± 4.0 mmol m−2 d−1 in summer; the results showed that the sea-to-air CO2 flux of the Louisiana shelf was −2.0 ± 0.20 mmol m−2 d−1 in August 2007 (Huang et al., 2015). Huang et al. (2015) also demonstrated that the same place might act as sink or source in different seasons and years.

根据城市用水情况，清水池设计2座，单池有效容积1.25万m3，池内溢流及放空，清水池顶部设置绿化覆盖。供水时变化系数为Kh=1.25，设置5台Q=1620m3/h，H=68m，N=450kW自吸式离心泵向城市管网供水。

pH was determined on board at a constant temperature of 28℃ using a PB-10 pH meter equipped with a pH/ATC electrode (Sartorius Ltd., Germany), calibrated according to the National Bureau Standard (NBS scale) of 4.00, 6.86, and 9.18. Precision levels were about ± 0.01.As described in Zhang et al. (2010), DIC was determined by acid extraction using a Shimadzu TOC-5000 Analyzer(Shimadzu Co., Japan). The coefficient of variance of the instrument was less than 1.5% and the precision of the DIC measurements was ± 5 μmol L−1 (Zhang et al., 2014a).Certified reference materials (Batch 122) from A. G.Dickson of Scripps Institution of Oceanography were used to calibrate DIC (2042.29 ± 0.59 μmol kg−1). The partial pressure of CO2 (pCO2) was calculated from pH and DIC respectively by using CO2SYS software (Pierrot et al., 2006) with equilibrium constants from Mehrbach et al. (1973), and KHSO4 described by Dickson (1990).

DO was measured in accordance with the Winkler method (Dickson, 1994). Oxygen solubility was then quantified through a thermodynamic equation proposed by Weiss (1970):

where C is the oxygen solubility (mL L−1), T is the thermodynamic temperature, and S is the salinity. Oxygen saturation was determined as DO concentration (mL L−1)divided by the solubility of O2 at the corresponding temperature and salinity in the field.

DMS concentration in the samples was analyzed using a purge-and-trap technique modified from the method of Andreae and Barnard (1983) in an Agilent 6850 gas chromatograph (GC) equipped with a flame photometric detector and a 3 m glass column (10% DEGS on Chromosorb W-AW-DMCS). Briefly, DMS was extracted with ultrapure nitrogen for 3 min at a flow rate of 200 mL min−1, dried using a glass tube containing CaCl2,and trapped in a loop of Teflon tubing at the temperature of liquid nitrogen (−196℃). The trapped gases were desorbed with hot water (90℃) and analyzed on the GC.For calibration, gravimetrically prepared standards of DMS in ethanol solution were analyzed using the same procedure as that used for the samples. The analytical precision was generally higher than 10%, and the detection limit was approximately 0.4 nmol L−1 DMS (Yang et al., 2015).

The concentrations of phosphate, silicate, nitrite, nitrate,and ammonia nitrogen were determined using an Auto Analyzer 3 (SEAL Analytical, USA) in accordance with the procedure described by Strickland and Parsons (1972).The precision were both 0.3%, and the detection limits were 0.024, 0.030, 0.003, 0.015 and 0.040 μmol L−1, respectively.

2.4 Sea-to-Air Fluxes Estimation

The DMS sea-to-air flux was calculated according to the equation

The Changjiang (Yangtze) River is a massive body of water involved in the transport and transformation of nutrients and organic compounds from the land to the ocean(Zhang, 1996; Zhang et al., 2014a). The Changjiang River originates from the Qinghai–Tibetan plateau and discharges to the East China Sea (ECS); the total length of the river stretches to 6300 km (Zhang et al., 2014a).The water discharge of Changjiang River reaches approximately 944 × 109 m3 yr−1 at the estuary mouth (Dai and Trenberth, 2002). The estuary mouth is divided into two branches by the Chongming Island, and more than 95% of the river flow empties into the ECS through the South Branch (Zhai et al., 2007). The drainage area covers 1.8 × 106 km2 and nearly accounts for 20% of the total terrestrial area of China (Chen et al., 2002). The Changjiang Estuary, which is currently about 120 km long and more than 90 km wide at its outer limit, is a mesotidal estuary and characterized by complex morphological characteristics associated with multi-step bifurcations (Li and Zhang, 1998; Yang et al., 2003). Harmful algal bloom caused by eutrophication and hypoxic phenomenon occurs frequently in the adjacent area of the Changjiang Estuary. This hypoxic phenomenon affects CO2 emission, O2 distribution, and DMS production in the seawater and causes heavy stress on the estuary and coastal environment (Rabalais and Turner, 2001).

Sampling was conducted on board the R/V ‘Runjiang 1’ in the Changjiang Estuary and its adjacent area from June 7 to 14, 2014. The location of sampling stations is represented by black dots in Fig.1. The cruise included 32 grid stations and 2 transects (E and F). In the previous cruise, the hypoxic phenomenon was observed in these two transects. Water samples were collected in 5 L Niskin bottles and DO was sampled according to the Winkler method. Each DMS water sample (2 mL) was collected into a glass bubbling chamber after being filtered through a glass fiber filter (GF/F). The samples for determination of dissolved inorganic carbon (DIC) were pressure filtered through a 0.45 µm cellulose acetate membrane to remove particulate sediment and organic material; the DIC samples were then stored into soda-lime glass bottles with 100 µL of saturated HgCl2 solution. The sampling procedures were performed immediately to minimize gas escape. DIC was determined within 20 days upon sampling. Temperature, salinity, and depth were synchronously obtained using an AAQ1183 multi-parameter controller (ALEC Co., Japan) and a 300K L-ADCP (RDI Co.,USA). Wind speed was measured at the height of 10 m above the sea surface using the Model 27600-4X Shipborne Weather Instrument (Young, US).

（4）按照国家标准《鲜柑橘》，在石门县采集的252件柑橘样品大部分属于优等果，优等果比率达91%。重金属超标率较低，仅少量样品汞、砷超标。

The parameters showed regular variations with increasing depth. The temperature of transect E decreased from 24.0℃ to 17.8℃, with average value of 20.9℃,from the surface to the bottom; similarly, the temperature of transect F decreased from 24.9℃ to 18.3℃, with an average value of 22.4℃ (Figs.5 and 6). By contrast, the salinities of transects E and F increased from 27.6 to 34.7 and from 32.3 to 34.7, respectively, as depth increased(Figs.5 and 6), with average values of 32.5 and 34.0, respectively. The Chl a concentrations of transect E varied from 2.92 μg L−1 to 0.01 μg L−1 (Fig.5), with a mean of 0.52 μg L−1 and maximum value at 10 m depth of station E5. However, the concentrations of Chl a at transect F were almost below 0.10 μg L−1 (Fig.6) and exhibited a minimal decrease with increasing depth except a minimal increase below 40 m of station F7.

从表1和表2可以看出，本文提出的LSTM算法相对于传统的随机森林算法以及逻辑回归算法具有更高的预测精度。由于深度学习算法在训练海量数据的过程中，可以自主学习数据中隐藏的信息，并使其对于错误和离群点更加具有鲁棒性。随着数据量的增加，LSTM算法的预测精度会有进一步的提升。由此通过多次的迭代，最终训练出高精度预测模型。

where P is atmospheric pressure; VP(H2O, s/w) is saturated water vapor pressure calculated according to the Weiss and Price (1980) formula; xCO2 is calculated as 400 ppm consistently according to the report of Mauna Loa Observation in Hawaii.

3 Results

3.1 Hydrological Parameters

Fig.2 Temperature-salinity diagrams with O2 saturation, pCO2, and DMS concentrations in surface water. The dominant water masses are classified as previously described (Chou et al., 2009; Sun et al., 2015) and indicated by rectangular outlines. YSW, Yellow Sea Water; CRDW, Changjiang River Diluted Water; CRDW+YSW, mixed CRDW and YSW,ZMCCW, Zhe-Min Coastal Current Water; TWCW, Taiwan Warm Current Water.

Throughout the study area, the temperature of surface water ranged from 19.7℃ to 24.9℃ with a mean of 22.4℃;the salinity increased from the inner estuary to the outer estuary within 14.1-34.2, with an average value of 28.8.On the basis of the temperature-salinity (T-S) diagrams(Fig.2) and the classification described by Chou et al.(2009a) and Sun et al. (2015), surface waters were divided into five categories: 1) Yellow Sea Water (YSW);2) Changjiang River Diluted Water (CRDW); 3) mixed CRDW and YSW (CRDW+YSW); 4) Zhe-Min Coastal Current Water (ZMCCW); 5) Taiwan Warm Current Water (TWCW). The YSW with high salinity (30.6-31.4)and low temperature (19.7-20.9℃) affected stations at transect A in the north of study area, while the CRDW with low salinity (14.1-26.6) and high temperature(20.9-3.3) influenced stations near the Changjiang Estuary (stations B2, B3, C2, C3, C5, D2, D3 and D5). Stations B5, B7 and B9 impacted by both the YSW and the CRDW presented moderate salinity (27.4-28.9) and temperature (21.3-21.5℃), and station E1 also showed relatively moderate salinity (27.6) and temperature(22.1℃) due to the effect of the ZMCCW. The TWCW affected the mid-shelf of the ECS, as indicated by high salinity (29.7-34.2) and high temperature (21.5-24.9℃)in the southwestern region of the ECS (stations C7, C9,C11, D7, D9, D11, E5, E7, E9, F1, F3, F5, F7 and F9).This distribution of water types is generally consistent with the known summer circulation pattern in the study area (Fig.1).

Fig.3 Horizontal distributions of temperature (℃) (a), salinity (b), Chl a (μg L−1) (c), O2 saturation (%) (d), pCO2 (μatm) (e),and DMS (nmol L−1) (f) in the surface water.

3.2 Distributions of O2, CO2, DMS, and Related Parameters in Surface Water

The Chl a concentrations in the surface water ranged from 0.01 μg L−1 to 6.75 μg L−1 (Fig.3), with a mean of 1.05 μg L−1. Surface water samples were almost all oversaturated in O2 with a range of 89%-167% (Fig.3) and mean value of 110%. High oxygen saturation (reached up to 135%) was found in seawater junction between the Changjiang Estuary and the Hangzhou Bay. The average pCO2 varied from 91 µatm to 640 µatm (Fig.3), with a mean of 374 µatm. The regions with high Chl a contents,maximum O2 saturation level, and minimum pCO2 basically overlapped in the junction waters of the Changjiang Estuary and the Hangzhou Bay (stations C5 and D5). The DMS concentrations ranged from 1.10 nmol L−1 to 27.50 nmol L−1 (Fig.3), with an average value of 8.53 nmol L−1. The highest DMS concentration was measured at station E3, whereas the lowest concentration was found at station C2.

总之，在网络技术的驱动下，实现倒逼新闻传播教育的转型与创新，无论从培养目标的设定，还是从教学体系的构成和具体教学内容的设计上，抑或是在实践教学条件的建设和教学方法的更新上，都需要摒弃老观念老方法，要有“壮士断腕”的气概，才能让我们的教育不负时代，不负使命。

Fig.4 shows the variations in O2 saturation, pCO2, and DMS concentrations with increasing salinity. The O2 saturation levels increased from unsaturation (95%) to the maximum saturation (167%) at the salinity of 22 and then decreased to unsaturation at the salinity of 25. At salinity＞ 25, the O2 saturation level fluctuated around 100%.Conversely, the pCO2 values decreased from a high value(＞600 µatm) to the minimum value (91 µatm) at the salinity of 22 and then increased to a high value (＞ 600 µatm)at the salinity of 25. At salinity ＞ 25, pCO2 fluctuated around 400 µatm. DMS concentration was extremely low(＜5 nmol L−1) at salinity ＜ 25 and increased gradually to the maximum value (27.50 nmol L−1) at the salinity of 30.At salinity ＞ 30, the DMS concentration fluctuated around 10 nmol L−1.

The sea-to-air fluxes of DMS observed in this study ranged from 0.26 μmol m−2 d−1 to 62.77μmol m−2 d−1, with an average of 8.24 μmol m−2 d−1. Because of the different T and S in different stations, the atmospheric pCO2 also had small differences. The average atmospheric pCO2 is 384µatm and the average ΔpCO2 is −10 ± 144 µatm. The sea-to-air CO2 exchange fluxes varied from −107.7 mmol m−2 d−1 to 31.6 mmol m−2 d−1, with an average of −3.7 mmol m−2 d−1.

Fig.4 Plots of O2 saturation, pCO2, DMS concentrations versus salinity in the surface water.

Fig.5 Vertical profiles of temperature (℃) (a), salinity (b), Chl a (μg L−1) (c), O2 saturation (%) (d), pCO2 (μatm) (e), and DMS (nmol L−1) (f) at transect E.

3.3 Distributions of O2, CO2, DMS, and Related Parameters at Transects E and F

where KH is the solubility of CO2 (Weiss 1974), and ΔpCO2 is the difference between the pCO2 of water and atmosphere. Gas transfer velocity k is calculated according to the Wanninkhof (1992) empirical function of short-term wind speed; u is the field-measured wind speed at 10 m height. In order to be consistent with the DMS flux and be compared with previous data, Sc is the Schmidt number for CO2 (a function of water temperature)as calculated by Wanninkhof (1992).

根据工程设计要求，结合场址具体情况，为减小对正常通车的影响，并保证施工安全，决定采用支架的方法进行施工。横跨既有高速公路段布置贝雷梁实现架空，在梁体以下部分采用工字钢作为支墩。

At transects E and F, O2 saturation uniformly declined from the surface to the bottom except in stations E3 and F3. The lowest DO concentrations of 2.26 and 2.93 mg L−1 were found at stations E3 and F3, respectively, which specifically coincided with the hypoxic zone situated at the longitude of 123˚E. At these two stations, the O2 saturation sharply decreased from 133% to 59% (station E3) and from 106% to 80% (station F3) at depth of 10-20 m. The O2 saturation levels at transects E and F ranged from 54% to 133% and from 66% to 119%, respectively(Figs.5 and 6), with mean values of 91% and 88%, respectively. The pCO2 at transect E increased from 224µatm to 1060 µatm (mean: 608 µatm), and that at transfect F increased from 278 µatm to 763 µatm (mean = 531µatm; Figs.5 and 6) with increasing depth; this finding demonstrated a pattern opposite that of the distribution of O2 saturation. The distribution of DMS concentrations exhibited a trend similar to that of O2 saturation, including the findings at stations E3 and F3. The DMS concentrations varied from 1.37 nmol L−1 to 27.50 nmol L−1 and from 1.32 nmol L−1 to 20.21 nmol L−1 at transects E and F,respectively (Figs.5 and 6), with average values of 7.33 and 3.08 nmol L−1, respectively.

The atmospheric pCO2 was calibrated according to the atmospheric pressure and corrected to 100% humidity at in situ seawater surface temperature (T) and salinity (S)through the following equation (DOE, 1994):

Fig.6 Vertical profiles of temperature (℃) (a), salinity (b), Chl a (μg L−1) (c), O2 saturation (%) (d), pCO2 (μatm) (e), and DMS (nmol L−1) (f) at transect F.

At transect E, the maximum O2 saturation and DMS concentration were observed at 10 m above of station E3,where comparatively low pCO2 values (about 300 µatm)emerged. The minimum pCO2 was at the surface water of station E5 located near station E3. In addition, the minimum O2 saturation and maximum pCO2 appeared at 30 m below of station E3, extremely low DMS concentrations(about 1.50 nmol L−1) also occurred in this area. At transect F, the maximum O2 saturation and minimum pCO2 were found at the surface water of the nearest station (F1)from the coast, and the maximum DMS concentration was at the surface water of station F3, which is also near the coast. The minimum DMS concentration was consistent with the minimum O2 saturation at the bottom of station F3, while the maximum pCO2 was observed at the 75 m of the farthest station (F9) from the coast. The bottom layer (85 m) of station F9 also presented a quite high pCO2 value (696 µatm).

Fig.7 Vertical profiles of O2 saturation, pCO2, and DMS in different depths at stations E1 (a), E3 (b), E5 (c), E7 (d), E9 (e),F1 (f), F3 (g), F5 (h), F7 (i) and F9 (j).

As detected in each station (Fig.7), the vertical profiles of O2 saturation levels and DMS concentrations were characterized by high values that mostly occur near the surface. O2 was oversaturated in the surface water and exhibited reduced concentrations with increasing depth;O2 became unsaturated at the bottom. DMS concentration also decreased from the surface to the bottom (＜ 5 nmol L−1). In contrast, the pCO2 increased from 400 µatm in the surface water to 600-1100 µatm in the bottom seawater.Different stations presented similar patterns between the two transects. O2 saturation, pCO2, and DMS concentration exhibited the greatest differences between the surface and the bottom seawater at transects E and F.

4 Discussion

The O2 saturation level, pCO2, and DMS concentration are mainly affected by temperature, salinity, water masses,phytoplankton biomass, wind speed, nutrients, photosynthesis, respiration and oxidative decomposition of organic matter (Gao and Song, 2008; Lu et al., 2011; Yang et al.,2011; Zhai et al., 2007). In addition, pCO2 is influenced by the dilution of freshwater, as well as the precipitation and dissociation of CaCO3; DMS concentration is affected by the species type, algal density, growth phase of algae, and the removal of DMS (Delille et al., 2007; Liu et al., 2014). Therefore, the three active gases, namely, O2,CO2, and DMS, usually present complex distributions in coastal waters.

4.1 Relationships Among O2, CO2, DMS, and Related Parameters in Surface Water

The O2 in the surface water was oversaturated, which mainly suggests that the concentration of O2 produced by photosynthesis exceeds that consumed during respiration and oxidative decomposition of organic matter. Our results are consistent with that of Lu et al. (2011). In their study, the O2 saturation levels of the Changjiang Estuary in summer ranged from 87% to 173%, with an average of 114%.

For chlorophyll a (Chl a) analysis, 500 mL of water were filtered through gentle vacuum filtration by using Whatman GF/F filters. The filters were soaked in 10 mL of 90% acetone and then stored in the dark at 4℃. After 24 h, Chl a concentration was measured using an F-4500 fluorescence spectrophotometer (Hitachi, Ltd., Japan) by using the method described by Parsons et al. (1984).

The DMS concentrations obtained in our work were slightly higher than those measured by Yang et al. (2011)and Zhang et al. (2014b). Yang et al. (2011) reported DMS concentrations ranging from 1.79 nmol L−1 to 12.24 nmol L−1, with an average of 5.64 nmol L−1, in the ECS and the Yellow Sea in June–July 2006. Zhang et al.(2014b) obtained DMS concentrations that ranged from 0.63 nmol L−1 to 41.19 nmol L−1, with an average value of 5.30 nmol L−1, in the south Yellow Sea and the ECS in July 2011. The sea-to-air fluxes of DMS exhibited considerable spatial variability as well, which was related to the DMS concentration and wind speed. The lowest flux was recorded at station F1 which had the lowest wind speed. In contrast, station E1 with a high wind speed and a large DMS concentration displayed a very high flux.Generally, our result was lower than the previous values of 16.83 μmol m−2 d−1 in the ECS and Yellow Sea in summer (Yang et al., 2011), and 11.21 μmol m−2 d−1 in the south Yellow Sea and ECS during summer by Zhang et al.(2014b), which used the parameterization of Liss and Merlivat (1986) (with a lower flux estimate) to calculatethe flux of DMS. If using this model, the flux of DMS ranged from 0.11 μmol m−2 d−1 to 30.92 μmol m−2 d−1, with a mean of 2.55 μmol m−2 d−1. The low wind speeds during the cruise (an average of 3.2 m s−1) mainly resulted in the lower flux to the atmosphere.

Table 1 Correlation coefficients between O2 saturation, pCO2, DMS concentrations and other biogeochemical parameters in surface water and at transects E and F

Notes: *: significant at P＜0.05; **: significant at P＜0.01; ***: significant at P＜0.001. 1: TN (Total Nitrogen) = NH4+ + NO3－+ NO2－.

Temperature Salinity Chl a Wind speed TN1 PO43− SiO32−O2 saturation −0.008 −0.276 0.371 0.216 0.104 −0.327 0.028 pCO2 −0.224 −0.023 −0.040 −0.139 0.166 0.545*** 0.186 Surface DMS −0.160 0.204 −0.040 −0.033 −0.305 −0.300 −0.112 O2 saturation 0.823*** −0.680*** 0.379 - −0.278 −0.666*** 0.069 pCO2 −0.865*** 0.533** −0.466* - 0.463* 0.724*** 0.104 Transect E DMS 0.477* −0.768*** 0.030 - 0.028 −0.406* 0.358 O2 saturation 0.854*** −0.371 0.765* - −0.715*** −0.851*** −0.509**pCO2 −0.559** 0.628*** −0.695 - 0.371 0.548** 0.156 Transect F DMS 0.239 −0.408* 0.090 - −0.197 −0.217 −0.075

Although the O2 saturation level, pCO2 and DMS concentrations were not significantly correlated with temperature, salinity, Chl a, wind speed, and nutrients (Table 1), they were affected by terrestrial inputs, water masses and biological processes deeply. As shown in Fig.2, the pCO2 at stations affected by the YSW showed relatively high values compared to other regions, and the O2 saturation level fluctuated around 100% (lower than the mean value) in this region. The O2 saturation level and pCO2 both presented extremely low and high values in stations affected by the CRDW and moderate values at stations affected by the TWCW. As to DMS, it showed extremely low values at stations affected by the CRDW, moderate values at stations affected by the YSW and both low and high values at stations affected by the TWCW.

Further analysis showed that the pCO2 had a significant negative correlation, whereas the DMS concentrations showed different positive relationships with the O2 saturation level in different water masses (CRDW, YSW and TWCW, Fig.8). The slope of DMS-O2 saturation at stations affected by the CRDW was the lowest in the three different water masses, and it presented a comparatively good positive correlation between DMS concentrations and O2 saturation level at stations affected by the TWCW.The maximum O2 saturation level and minimum pCO2 occurred at stations affected by the CRDW because of the rich nutrients carried by the CRDW. The amount of nitrates and silicates reached approximately 30-50 µmolL−1 in this region, which is higher than those in other stations(almost below 10 µmol L−1). In addition to nutrients, the study area receives large amounts of inorganic carbon from terrestrial sources. DIC on the continental shelf contains a large oceanic component that may mask the DIC signal from terrestrial sources, therefore, DIC transport on the shelf is comparatively less obvious. To examine the DIC inputs from terrestrial sources, total excess DIC(DICT-excess) was calculated according to the following equation (Jiang et al., 2013):

Fig.8 Plots of pCO2 (a) and DMS (b) versus O2 saturation in the surface water.

in μmol kg−1, where DICi and DICocean are DIC concentrations of station i and the ocean end-member, respectively,and Si and Socean are salinities of station i and the ocean end-member, respectively. Total excess DIC represents all DIC sources or sinks (including all terrestrial inputs)except those from the open ocean.

The calculated DICT-excess ranged from −119-856 μmol kg−1 with mean of 173 μmol kg−1. The high values appeared at stations 2 and 3 of transects B, C and D, while the low values emerged in the open ocean (stations 5, 7 and 9 of transects E and F). As shown in Fig.9, DICT-excess showed a significantly negative correlation with salinity in the surface water, suggesting strong input of DIC from terrestrial sources.

Fig.9 Plots of total excess DIC versus salinity in the surface water.

The low DMS values at stations affected by the CRDW were caused by many factors. Firstly, the fresh water phytoplankton species Pediastrum simplex dominated at stations affected by the CRDW because of low salinity(Luan et al., 2006). They could not produce DMS regardless of abundant O2. Secondly, Light limitation resulting from suspended sediments was stronger in the region.According to the hypothesized role of DMS(P) as a cellular antioxidant (Sunda et al., 2002), decreased light stress would lead to lower DMS production. Thirdly,Yang et al. (2014) reported that biological consumption rates of DMS exhibited a declining trend from inshore to offshore seawaters. Thus, the high DMS biological consumption rates at stations affected by the CRDW might lead to low DMS values. Conversely, high concentrations of DMS and good correlation between DMS and O2 saturation in TWCW were related to the composition and abundance of phytoplankton species in the ECS. In this region, abundant O2 promoted the growth of phytoplankton (Lu et al., 2011; Yang et al., 2011), and dinoflagellates and diatoms were the dominant phytoplankton. The number of diatoms was considerably higher than that of dinoflagellates, and dinoflagellates are considered high-DMSP-yielding algae which could produce large amounts of DMS mainly through DMSP enzymatic cleavage(Keller et al., 1989; Lin et al., 2008; Stefels, 2000; Wang et al., 2008). Although diatoms contained low DMSP,large amounts of diatoms could release high concentrations of DMS (Iverson et al., 1989; Yang et al., 2011).Also the low sea-to-air fluxes and biological consumption rates of DMS in TWCW resulted in high DMS concentrations.

4.2 Relationships Among O2, CO2, DMS, and related Parameters at Transects E and F

At transects E and F, larger O2 saturation and DMS values were found near the surface and the coast because of the strong photosynthesis in euphotic layer and higher Chl a contents near the coast, while larger pCO2 values were observed at the bottom of stations both near and far from the coast. This may be due to the excess carbonate derived from the Changjiang River and the decomposition of organic matter at the bottom layer. Meanwhile the O2 saturation level, pCO2, and DMS concentration showed different relationships with temperature, salinity, Chl a and nutrients at transects E and F. At transect E, the O2 saturation level, pCO2, and DMS concentration were significantly correlated with temperature, salinity, and phosphate content, but only pCO2 had correlations with Chl a and total nitrogen content (Table 1). Zhang et al.(2007) reported that the temperature of seawater decreases with increasing depth, and waters stratify in late spring and summer; hence, a layer of warmer and fresher water flows over a colder and saltier layer. In this case,oxygen is unable to reach the lower layer; as a result, low DO levels are detected at the bottom and high DO levels are found near the surface (Gao and Song 2008). Also because of the stratification of the water column, greater accumulation of respired CO2 in bottom waters during summer resulted in the negative correlation between pCO2 and temperature (Chou et al., 2009b). Furthermore,low salinity could increase algal DMSP lyase activity(Stefels, 2000; Steinke et al., 2002). Niki et al. (2007) and Visscher et al. (2003) also identified that low salinity shock enhances the production and release of DMS to the environment, which could explain the negative correlation between DMS concentration and salinity. At transect F, the O2 saturation level, pCO2 and DMS concentrations also showed different correlations with temperature, salinity, Chl a, and nutrients to different extents.

Sudden-change layers of O2 saturation were found at depths of 10-20 m at stations E3 and F3. In addition, an obvious hypoxic zone existed below the sudden-change layers until the bottom. This finding is similar to those reported in previous studies (Li et al., 2002; Shi et al.,2006; Tian et al., 1993); as such, the existence of the hypoxic zone may be attributed to the limited exchange between the oxygen-enriched surface water and bottom waters by the Taiwan Warm Current (Li et al., 2002). Organic detritus carried by the CRDW subsided in the hypoxic zone, which is an indentation at the front Changjiang River Delta. Hence, the oxidative decomposition of organic matter consumed abundant O2 and produced a large amount of CO2 (Shi et al., 2006). Zhu et al. (2016)also found that phytoplankton-driven dark plankton respiration is a key aspect of hypoxia studies. Under high levels of general background eutrophication, more blooms were found in estuaries and adjacent coastal zones; this observation suggested an increase in respiration from phytoplankton and heterotrophs. The paradox between heterotrophy and function as a CO2 sink was partially resolved by Chou et al. (2009b). In their study,the surface water acted as a CO2 sink, while the hypoxic phenomenon emerged and CO2 became supersaturated with the increasing depth. In the hypoxic zone (bottom layers of stations E3 and F3), the decreased phytoplankton biomass (low Chl a content) was the main reason resulting in low DMS concentrations. Diaz (2001) found that the numbers of hypoxic and anoxic environments increase in shallow coastal and estuarine areas, such as the Gulf of Mexico, Texas-Louisiana; Northern Adriatic Sea, Italy-Croatia; and Kattegat, Sweden-Denmark; these phenomena are most likely accelerated by eutrophication.Eutrophication, together with water-column stratification,usually produces abundant organic matter that promotes the development of hypoxia and anoxia; this finding is consistent with that described in our study on the Changjiang Estuary. The positive correlations between O2 saturation level and DMS concentration are similar to those reported by Yang (2000), and the negative correlations between O2 saturation levels and pCO2 resemble the results of Peng et al. (1987), as shown in Fig.7 at transects E and F.

（三）回归分析表明，党组织换届及书记选配、以权谋私现象、漠视和侵害师生员工利益现象等8个指标对党建工作评价的影响极显著。

5 Conclusions

This study is the first to investigate the distributions and relationships of O2, CO2 and DMS and their controlling factors in Changjiang (Yangtze) Estuary and its adjacent waters in summer. Our results indicated that the pCO2 was significantly and negatively correlated with the O2 saturation level, while the DMS concentration showed different positive relationships with the O2 saturation level in different water masses. In the surface water, the maximum of O2 saturation, the minimum of pCO2 were found in a similar area because of the rich nutrients carried by CRDW to this area and strong photosynthesis.The sea-to-air CO2 fluxes indicated that this region served as a sink of atmospheric CO2, and the sea-to-air DMS fluxes were lower than the surrounding sea areas because of the low wind speeds. At the two transects, a hypoxic zone was observed along the longitude of 123˚E in bottom waters. In the hypoxic zone, pCO2 increased because of the oxidative decomposition of the organic matter carried by the CRDW; meanwhile, DMS concentration declined in this area. Strong correlations appeared between the O2 saturation level, pCO2 and DMS concentrations at transects E and F. More details about factors affecting the distributions and relationships of O2, CO2, and DMS including the biological production and consumption rates of DMS, bacterial abundance and phytoplankton taxonomic composition should be explored to capture biogeochemical heterogeneity in this system.

（2）桥墩高度超过35m之后，为了使得墩身结构更具稳定性，可以采用薄壁墩的方式；对于高度不足50m的墩高，一般都会使用等截面薄壁实心墩；墩身高度在50m以上的桥梁结构可以使用变截面空心墩，而等截面也是一种不错的方式，效果也比较好。

Acknowledgements

We thank the captain and crew of the R/V ‘Runjiang 1’for their help during the in situ investigation. We are sincerely grateful to Wensheng Jiang, Lei Li, Anlong Li,Liangming Zhou and Tongtong Chen for assistance and cooperation during the research. We also thank two anonymous reviewers for their constructive comments,which greatly improved the manuscript. This work was financially supported by the National Key Research and Development Program of China (No. 2016YFA06 01301),the National Natural Science Foundation of China (Nos.41176062, 41676065), the Fundamental Research Funds for the Central Universities (No. 201564015), and the projection of the Education Ministration of China ‘A comprehensive practical education base for Marine Science in the Changjiang Estuary and its adjacent sea area’.

References

Andreae, M. O., and Barnard, W. R., 1983. Determination of trace quantities of dimethylsulfide in aqueous solutions. Analytical Chemistry, 55: 608-612.

Carpenter, L. J., Archer, S. D., and Beale, R., 2012. Oceanatmosphere trace gas exchange. Chemical Society Reviews,41: 6473-6506.

Carpenter, L. J., and Nightingale, P. D., 2015. Chemistry and release of gases from the surface ocean. Chemical Reviews,115: 4015-4034.

Chen, C. T. A., Zhai, W. D., and Dai, M. H., 2008. Riverine input and air-sea CO2 exchanges near the Changjiang (Yangtze) River Estuary: Status quo and implication on possible future changes in metabolic status. Continental Shelf Research, 28: 1476-1482.

Chen, C. T. A., and Borges, A. V., 2009. Reconciling opposing views on carbon cycling in the coastal ocean: Continental shelves as sinks and near-shore ecosystems as sources of atmospheric CO2. Deep Sea Research Part II: Topical Studiesin Oceanography, 56: 578-590.

Chen, C. T. A., Huang, T. H., Chen, Y. C., Bai, Y., He, X., and Kang, Y., 2013. Air-sea exchanges of CO2 in the world’s coastal seas. Biogeosciences, 10: 6509-6544.

Chen, C. T. A., Huang, T. H., Fu, Y. H., Bai, Y., and He, X.,2012. Strong sources of CO2 in upper estuaries become sinks of CO2 in large river plumes. Current Opinion in Environmental Sustainability, 4: 179-185.

Chen, J. S., Wang, F. Y., Xia, J. H., and Zhang, L. T., 2002.Major element chemistry of the Changjiang (Yangtze River).Chemical Geology, 187: 231-255.

Chou, W. C., Gong, G. C., Sheu, D. D., Hung, C. C., and Tseng,T. F., 2009a. Surface distributions of carbon chemistry parameters in the East China Sea in summer 2007. Journal of Geophysical Research: Oceans, 114: C07026.

Chou, W. C., Gong, G. C., Sheu, D. D., Jan, S., Hung, C. C., and Chen, C. C., 2009b. Reconciling the paradox that the heterotrophic waters of the East China Sea shelf act as a significant CO2 sink during the summertime: Evidence and implications. Geophysical Research Letters, 36: 139-156.

Conley, D. J., Carstensen, J., Aigars, J., Axe, P., Bonsdorff, E.,Eremina, T., Haahti, B. M., Humborg, C., Jonsson, P., Kotta,J., Lännegren, C., Larsson, U., Maximov, A., Medina, M. R.,Lysiak-Pastuszak, E., Remeikaitė-Nikienė, N., Walve, J.,Wilhelms, S., and Zillén, L., 2011. Hypoxia is increasing in the Coastal Zone of the Baltic Sea. Environmental Science &Technology, 45: 6777-6783.

Dacey, J. W. H., and Wakeham, S. G., 1986. Oceanic dimethylsulfide: Production during zooplankton grazing on phytoplankton. Science, 233: 1313-1316.

Dai, A. G., and Trenberth, K. E., 2002. Estimates of freshwater discharge from continents: latitudinal and seasonal variations.Journal of Hydrometeorology, 3: 666-687.

Delille, B., Jourdain, B., Borges, A. V., Tison, J. L., and Delille,D., 2007. Biogas (CO2, O2, dimethylsulfide) dynamics in spring Antarctic fast ice. Limnology and Oceanography, 52:1367-1379.

Diaz, R. J., 2001. Overview of hypoxia around the world. Journal of Environmental Quality, 30: 275-281.

Dickson, A. G., 1990. Standard potential of the reaction: AgCl(s)+1/2H2(g)=Ag(s)+ HCl(aq), and the standard acidity constant of the ion HSO4− in synthetic seawater from 273.15 to 318.15 K. Thermo, 22: 113-127.

Dickson, A. G., 1994. Determination of dissolved oxygen in sea water by Winkler titration. WHP Operations and Methods, 1-14.

DOE, 1994. Handbook of methods for the analysis of the various parameters of the carbon dioxide system in sea water,ver. 2, In: Dickson, A. G., and Goyet, C., eds., ORNL/CDIAC-74.

Gage, D. A., Rhodes, D., Nolte, K. D., Hicks, W. A., Leustek,T., Cooper, A. J., and Hanson, A. D., 1997. A new route for synthesis of dimethylsulphoniopropionate in marine algae.Nature, 387: 891-894.

Gao, X., and Song, J., 2008. Dissolved oxygen and O2 fluxMay 2003. Journal of Marine Systems, 74: 343-350.

Ginders, M. A., Collier, K. J., Duggan, I. C., and Hamilton, D. P.,2016. Influence of hydrological connectivity on plankton communities in natural and reconstructed side-arms of a Large New Zealand River. River Research and Applications,32: 1675-1686.

Gonzalez, J. M., Kiene, R. P., and Moran, M. A., 1999. Transformation of sulfur compounds by an abundant lineage of marine bacteria in the α-subclass of the class Proteobacteria.Applied and Environmental Microbiology, 65: 3810-3819.

Hill, R. W., White, B. A., Cottrell, M. T., and Dacey, J. W. H.,1998. Virus-mediated total release of dimethylsulfoniopropionate from marine phytoplankton: A potential climate process.Aquatic Microbial Ecology, 14: 1-6.

Huang, W. J., Cai, W. J., Wang, Y., Hu, X., Chen, B., Lohrenz,S. E., Chakraborty, S., He, R., Brandes, J., and Hopkinson, C.S., 2015. The response of inorganic carbon distributions and dynamics to upwelling-favorable winds on the northern Gulf of Mexico during summer. Continental Shelf Research, 111:211-222.

Iverson, R. L., Neaehoof, F. L., and Andreae, M. O., 1989.Production of dimethylsulfoniumpropionate and dimethyl sulphide by phytoplankton in estuarine and coastal waters.Limnology and Oceanography, 34: 53-67.

Jiang, L. Q., Cai, W. J., Wang, Y., and Bauer, J. E., 2013. Influence of terrestrial inputs on continental shelf carbon dioxide. Biogeosciences, 10: 839-849.

Keller, M. D., Bellows, W. K., and Guillard, R. R. L., 1989.Dimethyl sulfide production in marine phytoplankton, In:Biogenic Sulfur in the Environment. Saltzman, E. S., and Cooper, W. J., eds., American Chemical Society, 167-182.

Laroche, D., Vézina, A. F., Levasseur, M., Gosselin, M., Stefels,J., Keller, M. D., Matrai, P. A., and Kwint, R. L. J., 1999.DMSP synthesis and exudation in phytoplankton: A modeling approach. Marine Ecology Progress Series, 180: 37-49.

Ledyard, K. M., and Dacey, J. W. H., 1994. Dimethylsulfide production from dimethylsulfoniopropionate by a marine bacterium. Marine Ecology Progress Series, 110: 95-103.

Lee, P. A., Mora, S. J. D., and Levasseur, M., 1999. A review of dimethylsulfoxide in aquatic environments. Atmosphere-Ocean, 37: 439-456.

Li, D., Zhang, J., Huang, D., Wu, Y., and Liang, J., 2002. Oxygen depletion off the Changjiang (Yangtze River) Estuary.Science in China Series D: Earth Sciences, 45: 1137-1146.

Li, J., and Zhang, C., 1998. Sediment resuspension and implications for turbidity maximum in the Changjiang Estuary. Marine Geology, 148: 117-124.

Lin, F. Z., Wu, Y. L., Yu, H. C., and Xian, W. W., 2008. Phytoplankton community structure in the Changjiang Estuary and its adjacent waters in 2004. Oceanologia et Limnologia Sinica, 39: 401-410 (in Chinese).

Liss, P. S., and Merlivat, L., 1986. Air-sea gas exchange rates:Introduction and synthesis. In: The Role of Air-Sea Exchange in Geochemical Cycling. Buat-Ménard, P., ed., Springer Netherlands, Berlin, 113-127.

Liu, C., Gao, C., Zhang, H., Chen, S., Deng, P., Yue, X., and Guo, X., 2014. Production of dimethylsulfide and acrylic acid from dimethylsulfoniopropionate during growth of three marine microalgae. Chinese Journal of Oceanology and Limnology, 32: 1270-1279.

Liu, J. P., Xu, K. H., Li, A. C., Milliman, J. D., Velozzi, D. M.,Xiao, S. B., and Yang, Z. S., 2007. Flux and fate of Yangtze River sediment delivered to the East China Sea. Geomorphology, 85: 208-224.

Lovelock, J. E., Maggs, R. J., and Rasmussen, R. A., 1972. Atmospheric dimethyl sulfide and the natural sulphur cycle.Nature, 237: 452-453.

Lu, Y., Li, H. L., Chen, J. F., Jin, H. Y., Chen, F. J., Gao, S. Q.,Wang, K., Wang, W. L., and Bai, Y. C., 2011. Seasonal variations of the surface dissolved oxygen saturation in Changjiang River Estuary and its adjacent waters. Journal of Marine Sciences, 29: 71-77 (in Chinese).

Luan, Q., Sun, J., Shen, Z., Song, S., and Wang, M., 2006.Phytoplankton assemblage of Yangtze River Estuary and the adjacent East China Sea in summer, 2004. Journal of Ocean University of China, 5: 123-131.

Malin, G., and Kirst, G. O., 1997. Algal production of dimethyl sulfide and its atmospheric role. Journal of Phycology, 33:889-896.

Mehrbach, C., Culberson, C. H., Hawley, J. E., and Pytkowicx,R. M., 1973. Measurement of the apparent dissociation constants of carbonic acid in seawater at atmospheric pressure.Limnology and Oceanography, 18: 897-907.

Minami, H., Kano, Y., and Ogawa, K., 1999. Long-term variations of potential temperature and dissolved oxygen of the Japan Sea Proper Water. Journal of Oceanography, 55: 197-205.

Nightingale, P. D., Malin, G., Law, C. S., Watson, A. J., Liss, P.S., Liddicoat, M. I., Boutin, J., and Upstill-Goddard, R. C.,2000. In situ evaluation of air-sea gas exchange parameterizations using novel conservative and volatile tracers. Global Biogeochemical Cycles, 14: 373-387.

Niki, T., Shimizu, M., Fujishiro, A., and Kinoshita, J., 2007.Effects of salinity downshock on dimethylsulfide production.Journal of Oceanography, 63: 873-877.

Parsons, T. R., Maita, Y., and Lalli, C. M., 1984. A Manual of Chemical and Biological Methods for Seawater Analysis.Pergamon Press, Oxford.

Peng, T. H., Takahashi, T., Broecker, W. S., and Olafsson, J.,1987. Seasonal variability of carbon dioxide, nutrients and oxygen in the northern North Atlantic surface water: Observations and a model. Tellus B, 39: 439-458.

Pierrot, D., Lewis, E., and Wallace, D. W. R., 2006. MS excel program developed for CO2 System Calculations. ORNL/CDIAC-105a. Carbon Dioxide Information Analysis Center,Oak Ridge National Laboratory, U.S. Department of Energy,Oak Ridge, Tennessee.

Quinn, P. K., and Bates, T. S., 2011. The case against climate regulation via oceanic phytoplankton sulphur emissions. Nature, 480: 51-56.

Rabalais, N. N., and Turner, R. E., 2001. Hypoxia in the northern Gulf of Mexico: Description, causes and change, In:Coastal Hypoxia: Consequences for Living Resources and Ecosystems. Rabalais, N. N., and Turner, R. E., eds., American Geophysical Union, Washington, D C, 1-36.

Ross, S. W., Dalton, D. A., Kramer, S., and Christensen, B. L.,2001. Physiological (antioxidant) responses of estuarine fishes to variability in dissolved oxygen. Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology, 130: 289-303.

Shi, X. Y., Lu, R., Zhang, C. S., and Wang, X. L., 2006. Distribution and main influence factors process of dissolved oxygen in the adjacent area of the Changjiang Estuary in autumn.Periodical of Ocean University of China, 36: 287-290 (in Chinese).

Stefels, J., 2000. Physiological aspects of the production and conversion of DMSP in marine algae and higher plants.Journal of Sea Research, 43: 183-197.

Stefels, J., Steinke, M., Turner, S., Malin, G., and Belviso, S.,2007. Environmental constraints on the production and removal of the climatically active gas dimethylsulphide (DMS)and implications for ecosystem modelling. Biogeochemistry,83: 245-275.

Steinke, M., Malin, G., Gibb, S. W., and Burkill, P. H., 2002.Vertical and temporal variability of DMSP lyase activity in a coccolithophorid bloom in the northern North Sea. Deep SeaResearch Part II: Topical Studies in Oceanography, 49: 3001-3016.

Steinke, M., Evans, C., Lee, G. A., and Malin, G., 2007. Substrate kinetics of DMSP-lyases in axenic cultures and mesocosm populations of Emiliania huxleyi. Aquatic Sciences, 69:352-359.

Strickland, J. D. H., and Parsons, T. R., 1972. A Practical Handbook of Seawater Analysis. Fisheries Research Board of Canada, Ottawa.

Sun, M. S., Zhang, G. L., Cao, X. P., Mao, X. Y., Li, J., and Ye,W. W., 2015. Methane distribution, flux, and budget in the East China Sea and Yellow Sea. Biogeosciences Discussions,12: 7017-7053.

Sunda, W., Kieber, D. J., Kiene, R. P., and Huntsman, S., 2002.An antioxidant function for DMSP and DMS in marine algae.Nature, 418: 317-320.

Takahashi, T., Olafsson, J., Goddard, J. G., Chipman, D. W., and Sutherland, S. C., 1993. Seasonal variation of CO2 and nutrients in the high-latitude surface oceans: A comparative study.Global Biogeochemical Cycles, 7: 843-878.

Tian, R. C., Hu, F. X., and Martin, J. M., 1993. Summer nutrient fronts in the Changjiang (Yangtze River) Estuary. Estuarine,Coastal and Shelf Science, 37: 27-41.

Tortell, P. D., Guéguen, C., Long, M. C., Payne, C. D., Lee, P.,and DiTullio, G. R., 2011. Spatial variability and temporal dynamics of surface water pCO2, ΔO2/Ar and dimethylsulfide in the Ross Sea, Antarctica. Deep Sea Research Part I:Oceanographic Research Papers, 58: 241-259.

Tortell, P. D., Long, M. C., Payne, C. D., Alderkamp, A.,Dutrieux, P., and Arrigo, K. R., 2012a. Spatial distribution of pCO2, ΔO2/Ar and dimethylsulfide (DMS) in polynya waters and the sea ice zone of the Amundsen Sea, Antarctica. Deep Sea Research Part II: Topical Studies in Oceanography, 71:77-93.

Tortell, P. D., Merzouk, A., Ianson, D., Pawlowicz, R., and Yelland, D. R., 2012b. Influence of regional climate forcing on surface water pCO2, ΔO2/Ar and dimethylsulfide (DMS)along the southern British Columbia coast. Continental Shelf Research, 47: 119-132.

Turner, S. M., Malin, G., Nightingale, P. D., and Liss, P. S.,1996. Seasonal variation of dimethyl sulphide in the North Sea and an assessment of fluxes to the atmosphere. Marine Chemistry, 54: 245-262.

Visscher, P. T., Baumgartner, L. K., Buckley, D. H., Rogers, D.R., Hogan, M. E., Raleigh, C. D., Turk, K. A., and Des Marais,D. J., 2003. Dimethyl sulphide and methanethiol formation in microbial mats: Potential pathways for biogenic signatures.Environmental Microbiology, 5: 296-308.

Wang, D., Sun, J., Zhou, F., and Wu, Y., 2008. Phytoplankton of Changjiang (Yangze River) Estuary hypoxia area and the adjacent East China Sea in June 2006. Oceanologia et Limnologia Sinica, 39: 619-627 (in Chinese with English abstract).

Wang, H., Dai, M., Liu, J., Kao, S. J., Zhang, C., Cai, W. J.,Wang, G., Qian, W., Zhao, M., and Sun, Z., 2016. Eutrophication-Driven Hypoxia in the East China Sea off the Changjiang Estuary. Environmental Science & Technology, 50: 2255-2263.

Wang, S. L., Chen, C. T. A., Hong, G. H., and Chung, C. S.,2000. Carbon dioxide and related parameters in the East China Sea. Continental Shelf Research, 20: 525-544.

Wanninkhof, R., 1992. Relationship between wind speed and gas exchange over the ocean. Journal of Geophysical Research, 97: 7373-7382.

Weiss, R. F., 1970. The solubility of nitrogen, oxygen and argon in water and seawater. Deep Sea Research and Oceanographic Abstracts, 17: 721-735.

Weiss, R. F., 1974. Carbon dioxide in water and seawater: The solubility of a non-ideal gas. Marine Chemistry, 2: 203-215.

Weiss, R. F., and Price, B. A., 1980. Nitrous oxide solubility in water and seawater. Marine Chemistry, 8: 347-359.

Wolfe, G. V., Levasseur, M., Cantin, G., and Michaud, S., 2000.DMSP and DMS dynamics and microzooplankton grazing in the Labrador Sea: Application of dilution technique. Deep Sea Research Part I: Oceanographic Research Papers, 47:2243- 2264.

Xue, L., Cai, W. J., Hu, X., Sabine, C., Jones, S., Sutton, A. J.,Jiang, L. Q., and Reimer, J. J., 2016. Sea surface carbon dioxide at the Georgia time series site (2006-2007): Air-sea flux and controlling processes. Progress in Oceanography,140: 14-26.

Yang, G. P., 2000. Spatial distributions of dimethylsulfide in the South China Sea. Deep Sea Research Part I: Oceanographic Research Papers, 47: 177-192.

Yang, G. P., Song, Y. Z., Zhang, H. H., Li, C. X., and Wu, G.W., 2014. Seasonal variation and biogeochemical cycling of dimethylsulfide (DMS) and dimethylsulfoniopropionate(DMSP) in the Yellow Sea and Bohai Sea. Journal of Geophysical Research: Oceans, 119: 8897-8915.

Yang, G. P., Zhang, H. H., Su, L. P., and Zhou, L. M., 2009.Biogenic emission of dimethylsulfide (DMS) from the North Yellow Sea, China and its contribution to sulfate in aerosol during summer. Atmospheric Environment, 43: 2196-2203.

Yang, G. P., Zhang, H. H., Zhou, L. M., and Yang, J., 2011.Temporal and spatial variations of dimethylsulfide (DMS)and dimethylsulfoniopropionate (DMSP) in the East China Sea and the Yellow Sea. Continental Shelf Research, 31:1325-1335.

Yang, G. P., Zhang, S. H., Zhang, H. H., Yang, J., and Liu, C.Y., 2015. Distribution of biogenic sulfur in the Bohai Sea and northern Yellow Sea and its contribution to atmospheric sulfate aerosol in the late fall. Marine Chemistry, 169: 23-32.

Yang, S. L., Belkin, I. M., Belkina, A. I., Zhao, Q. Y., Zhu, J.,and Ding, P. X., 2003. Delta response to decline in sediment supply from the Yangtze River: Evidence of the recent four decades and expectations for the next half-century. Estuarine,Coastal and Shelf Science, 57: 689-699.

Yin. K., Lin, Z., and Ke, Z., 2004. Temporal and spatial distribution of dissolved oxygen in the Pearl River Estuary and adjacent coastal waters. Continental Shelf Research, 24:1935-1948.

Zhai, W., and Dai, M., 2009. On the seasonal variation of airsea CO2 fluxes in the outer Changjiang (Yangtze River) Estuary, East China Sea. Marine Chemistry, 117: 2-10.

Zhai, W. D., Chen, J. F., Jin, H. Y., Li, H. L., Liu, J. W., He, X.Q., and Bai, Y., 2014. Spring carbonate chemistry dynamics of surface waters in the northern East China Sea: Water mixing, biological uptake of CO2, and chemical buffering capacity. Journal of Geophysical Research: Oceans, 119: 5638-5653.

Zhai, W., Dai, M., and Guo, X., 2007. Carbonate system and CO2 degassing fluxes in the inner estuary of Changjiang(Yangtze) River, China. Marine Chemistry, 107: 342-356.

Zhang, L., 1996. Nutrient elements in large Chinese estuaries.Continental Shelf Research, 16: 1023-1045.

Zhang, L., Xue, L., Song, M., and Jiang, C., 2010. Distribution of the surface partial pressure of CO2 in the southern Yellow Sea and its controls. Continental Shelf Research, 30: 293-304.

Zhang, L., Xue, M., Wang, M., Cai, W. J., Wang, L., and Yu, Z.,2014a. The spatiotemporal distribution of dissolved inorganic and organic carbon in the main stem of the Changjiang(Yangtze) River and the effect of the Three Gorges Reservoir. Journal of Geophysical Research: Biogeosciences, 119:741-757.

Zhang, S. H., Yang, G. P., Zhang, H. H., and Yang, J., 2014b.Spatial variation of biogenic sulfur in the south Yellow Sea and the East China Sea during summer and its contribution to atmospheric sulfate aerosol. Science of Total Environment,488: 157-167.

Zhang, Y., Zhang, J., Wu, Y., and Zhu, Z., 2007. Characteristics of dissolved oxygen and its affecting factors in the Yangtze Estuary. Environmental Science, 28: 1649-1654 (in Chinese).

Zhu, Z. Y., Hu, J., Song, G. D., Wu, Y., Zhang, J., and Liu, S. M.,2016. Phytoplankton-driven dark plankton respiration in the hypoxic zone off the Changjiang Estuary, revealed by in vitro incubations. Journal of Marine Systems, 154: 50-56.

Zubkov, M. V., Fuchs, B. M., Archer, S. D., Kiene, R. P., Amann,R., and Burkill, P. H., 2002. Rapid turnover of dissolved DMS and DMSP by defined bacterioplankton communities in the stratified euphotic zone of the North Sea. Deep Sea Research Part II: Topical Studies in Oceanography, 49: 3017-3038.