Abundance and Biomass of Benthic Bacteria in Jiaozhou Bay, China

The abundance and biomass of benthic heterotrophic bacteria were investigated for the 4 typical sampling stations in the northern muddy part of Jiaozhou Bay, estuary of the Dagu River, raft culturing and nearby areas of Huangdao in March, June, August and December, 2002. The abundance and biomass range from 0.98×10⁷ to 16.87×10⁷ cells g⁻¹ sediment and 0.45 to 7.08 μg C g⁻¹ sediment, respectively. Correlation analysis showed that heterotrophic bacterial abundance and biomass are significantly correlated to water temperature (R=0.79 and 0.83, respectively,P<0.01).     

Characteristics of nutrients in the Jiulong River and its impact on Xiamen Water, China

Water samples were collected at 20 sites on 4 occasions in 2009(twice in May,and once in both August and November) along the Jiulong River,South China to examine how nutrient inputs from the Jiulong River could affect the nutrient status of the Xiamen Water.Samples were analyzed for nitrite(NO2-N),nitrate(NO3-N),ammonium(NH4-N),phosphate(PO4-P),silicate(SiO3-Si),salinity,and temperature,to determine the nutrient and trophic status of the river.The results indicate that nutrients are derived mainly from river runoff.NO3-N was the main form of DIN in most parts of the river.In addition,NO3-N,DIN,and SiO3-Si behave conservatively.There is a surplus of DIN and SiO3-Si in the river,and PO4-P is a limitation on phytoplankton growth.The concentration of DIN is typically above 0.60 mg/dm3,and higher than 1.00 mg/dm3in most parts of the river.The concentration of PO4-P is typically above 0.02 mg/dm3,while the concentration of SiO3-Si is higher than 1.00 mg/dm3.Between 2003 and 2008,samples were collected 3 times per year(May,August and November) at 27 sites in the Xiamen Water and analyzed for NO2-N,NO3-N,NH4-N,PO4-P,salinity,and temperature.We discovered that the Jiulong River was the key source of DIN into the Xiamen Water,but not PO4-P,indicating the reason of the N/P molar ratio imbalance in the Xiamen Water.In the future,the effects of high DIN concentrations on the phytoplankton communities and marine ecosystems of the Xiamen Water shall be studied.     

Nutrient and eutrophication characteristics of the Dongshan Bay,South China

We recorded NO 3-N, NO 2-N, NH 4-N, PO 4-P, SiO 3-Si, salinity, and temperature data at 10 stations in the Dongshan Bay in May, June, July, August, October, and November 2008, analyzing nutrient and eutrophication characteristics. The mean concentration of dissolved inorganic nitrogen(DIN) was 0.30–0.40 mg/dm 3; generally, NO 3-N was the main form in most areas. The mean concentrations of PO 4-P and SiO 3-Si were 0.040–0.060 mg/dm 3 and 1.00–1.50 mg/dm 3, respectively. We proved that the majority of the SiO 3-Si in the Dongshan Bay came from the Zhangjiang River, with some coming from the Bachimen Strait. DIN originated from both the Zhangjiang River and the Bachimen Strait. Most PO 4-P originated from the Bachimen Strait, and some came from the Zhangjiang River. We found that P was an overall limiting factor to the phytoplankton community in most of the Dongshan Bay, and that Si and N were in surplus. However, near the Bachimen Strait Si became a limiting factor, especially for diatoms, while P and N were in comparative surplus. We used a potential eutrophication assessment method to analyze eutrophication, and showed that the most serious eutrophication occurred near the Zhangjiang River estuary and near the Bachimen Strait. In 2008, DIN levels were four times higher than that in 1988; PO 4-P levels were threefold higher, while SiO 3-Si was approximately double. Dissolved nutrients increased between 1988 and 2008. DIN increased at the greatest rate comparing to PO 4-P and SiO 3-Si, thus the N/P and N/Si mol ratios increased. Further studies on the effects of high DIN concentrations on the phytoplankton communities and marine ecosystems of the Dongshan Bay are needed.     

Abundance and spatial dynamics of bacterioplankton in the Seven Rila Lakes, Bulgaria

In the high mountain oligotrophic Seven Rila Lakes (2 095–2 535 m a.s.l.) bacterial abundance was recorded in July and September 2006. In July, bacterial abundance (average (3.32±2.5)×10⁵ cell/ml) in the lakes correlated negatively with elevation, while in September (average (26.39±7.1)×10⁵ cell/ml) this pattern was altered and the greatest abundance of bacteria occurred at the highest ((39.05±1.5)×10⁵ cell/ml) and the lowest ((30.63±6.0)×10⁵ cell/ml) elevated lakes. Regression analyses suggested that the principal factor controlling bacterial abundance, in both July and September, was inorganic nitrogen (NO₃-N and NH₄-N; R ²=0.70, P<0.05). Other major regulating factors were temperature (R ²=0.66, P<0.03) in July and filter-feeding zooplankton (R ²=0.95, P<0.01) in September. All factors, except NO₃-N, had a positive effect on bacterial abundance.     

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 = 10.9 μg L^?1) and DO (9.25 mg L^?1), profoundly decreased DIC concentration (1828 μmol 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 CO₂ uptake capacity in this area.     

Distribution and abundance of pelagic tunicates in the North Yellow Sea

In this paper, the distribution patterns and abundance of pelagic tunicates in the North Yellow Sea of China during the period 2006-2007 were analyzed. Zooplankton samples were obtained with vertical towing from bottom to surface using a WP2 plankton net(200 μm mesh size; mouth area: 0.25 m2). Five species belonging to two classes were identified: Oikopleura dioica, O. longicauda and Fritillaria borealis belonging to class Appendicularia; Salpa fusiformis and Doliolum denticulatum of class Thaliacea. O. dioica and O. longicauda were the dominant species, occurring in the samples of all four seasons, with different distribution patterns. Their maximum abundance were 1664.7 ind. m-3(spring) and 1031.7 ind. m-3(spring) respectively. Following Oikopleura spp. were D. denticulatum, which was found only in autumn with an average abundance of 149.6 ind. m-3, and S. fusiformis, which was detected all the year long except for autumn with low abundance(max. abundance 289.4 ind. m-3 in summer). Only a very small amount of F. borealis was detected in summer samples, with an average abundance of 2.7 ind. m-3. The relationship between tunicates abundances and the environmental factors was analyzed using the stepwise regression model for each species. The variation of appendicularian abundance showed a significant correlation with the surface water temperature and with the concentration of Chl-a. No relationship was found between tunicates abundance and salinity, likely due to the slight changes in surface salinity of the studied area during the four seasons. Salps abundance and that of doliolids were significantly correlated to bottom water temperature, indicating that these two species(S. fusiformis and D. denticulatum) migrate vertically in the water column. In particular D. denticulatum, known to be a warm water species, showed not only an important correlation with water temperature, but also a spatial distribution connected to the warm currents in the North Yellow Sea. The occurrence of D. denticulatum represents an interesting result never found in past research work. Water temperature, algal distribution and currents were the most relevant environmental factors influencing the tunicate abundance and distribution in the North Yellow Sea. Further research is needed in order to get more information on the ecology of these organisms and to better understand their role in the ecosystem including the oceanic food web.     

Seasonal succession of phytoplankton in response to the variation of environmental factors in the Gaolan River, Three Gorges Reservoir, China

To understand the responses of a freshwater ecosystem to the impoundment of the Three Gorges Reservoir (TGR), phytoplankton was monitored in the tributaries of the TGR area. From August 2010 to July 2011, algal species composition, abundance, chlorophyll a and other environmental parameters were investigated in the Gaolan River, which is a tributary of Xiangxi River. Thirty-one algal genera from seven phyla were identified. Results show that the lowest concentrations of total phosphorus (TP) and total nitrogen (TN) were 0.06 mg/L and 1.08 mg/L, respectively. The values of TP and TN exceeded the threshold concentration of the eutrophic state suggested for freshwater bodies. In the Gaolan River, the succession of phytoplankton showed clear seasonal characteristics. Different dominant species were observed among seasons under the control of environment factors. In spring and summer, the dominant species were Nitzschia sp. and Aphanizomenon flos-aquae (L.) Ralfs, the limiting nutrient was NO ₃ ^? -N, and the key environmental factor for phytoplankton population succession was water temperature (WT). In autumn and winter, the dominant species were A. flos-aquae and Chlorella sp., the limiting nutrient was PO ₄ ^3? -P, and the key environmental factors were transparency and WT. This study illustrates the influence of physical and chemical factors on phytoplankton seasonal succession in a tributary of TGR since the downstream regions of Xiangxi River and Gaolan River became reservoirs after impoundment of the Three Gorges Dam. We suggest that this activity has significantly affected water quality in the dam area.     

Long-term ecological interactions between nutrient and phytoplankton community in the Changjiang estuary

Both nitrate (NO₃⁻) and soluble reactive phosphate (PO₄³⁻) concentration in the freshwater end-member at the mouth of the Changjiang River have increased dramatically since the 1960s. Within the same period in the sea area, with surface salinity>30, NO₃⁻ concentration has shown an obvious increase, PO₄³⁻ has not changed greatly and dissolved reactive silica (SiO₃²⁻) has deceased dramatically. An examination of the elemental ratio of NO₃⁻ to PO₄³⁻ at the mouth of the Changjiang River did not show a systematic trend from the 1960s to 2000s largely because both nutrients increased simultaneously. In comparison, the elemental ratio of dissolved inorganic nitrogen (DIN) to PO₄³⁻ in surface seawater, with salinity>22, has shown a clearly increasing trend. Furthermore, an overall historical change of the SiO₃²⁻:PO₄³⁻ ratio has undergone a reverse trend in this area. Based on the changes of SiO₃²⁻:PO₄³⁻ and DIN:PO₄³⁻ ratios, we can conclude that an overall historical change of SiO₃²⁻:DIN ratio has decreased in this area from the 1950–1960s to 2000s. The argument that phytoplankton productivity in the Changjiang estuary has been enhanced by increasing nutrient input from the riverine transport was supported by these results. A comparative study analyzing the shift of phytoplankton composition from the mid-1980s to 2000s was also made. The results indicated that the average yearly percentage of diatom species in the Changjiang estuary has decreased from 84.6% during 1985–1986 to 69.8% during 2004–2005. Furthermore, the average yearly percentage of diatom abundance in the Changjiang estuary decreased from 99.5% during to 75.5% over the same time period, while the abundance of dinoflagellates has increased dramatically, from 0.7% to 25.4%.     

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 63.6×104     

Optimization of culture conditions and medium composition for the marine algicidal bacterium Alteromonas sp. DH46 by uniform design

Harmful algal blooms (HABs) have led to extensive ecological and environmental issues and huge economic losses. Various HAB control techniques have been developed, and biological methods have been paid more attention. Algicidal bacteria is a general designation for bacteria which inhibit algal growth in a direct or indirect manner, and kill or damage the algal cells. A metabolite which is strongly toxic to the dinoflagellate Alexandrium tamarense was produced by strain DH46 of the alga-lysing bacterium Alteromonas sp. The culture conditions were optimized using a single-factor test method. Factors including carbon source, nitrogen source, temperature, initial pH value, rotational speed and salinity were studied. The results showed that the cultivation of the bacteria at 28°C and 180 r min^?1 with initial pH 7 and 30 salt contcentration favored both the cell growth and the lysing effect of strain DH46. The optimal medium composition for strain DH46 was determined by means of uniform design experimentation, and the most important components influencing the cell density were tryptone, yeast extract, soluble starch, NaNO₃ and MgSO₄. When the following culture medium was used (tryptone 14.0g, yeast extract 1.63g, soluble starch 5.0 g, NaNO₃ 1.6 g, MgSO₄ 2.3 g in 1L), the largest bacterial dry weight (7.36 g L^?1) was obtained, which was an enhancement of 107% compared to the initial medium; and the algal lysis rate was as high as 98.4% which increased nearly 10% after optimization.     

Temporal and spatial variations of abundance of phycocyanin- and phycoerythrin-rich <Emphasis Type="Italic">Synechococcus</Emphasis> in Pearl River Estuary and adjacent coastal area

Three surveys were carried out in Pearl River Estuary and adjacent coastal area in May, August, and November, 2013, to investigate the temporal and spatial variations of abundance of phycoerythrin-rich Synechococcus (PE-rich SYN) and phycocyanin-rich Synechococcus (PC-rich SYN). The effects of environmental factors on the alternation of the different Synechococcus groups were also elucidated. PE-rich SYN was detected in three surveys, whereas PC-rich SYN was detected in May and August, but not in November. The highest abundances of PE-rich SYN and PC-rich SYN were recorded in August and May, with mean values of 74.17×10³ and 189.92×10³ cells mL^?1, respectively. From May to November, the relative abundance of PE-rich SYN increased, whereas that of PC-rich SYN declined. PE-rich and PC-rich SYN presented similar horizontal distributions with high abundance in the southern estuary in May, and in the western estuary in August. The abundances of PE-rich and PC-rich SYN were high at 27–32°C and salinity of 10–20. PC-rich SYN was not detected at < 24°C, and PC:PE-rich SYN decreased in abundance with salinity increase. When less than 20 mg L^?1, suspended particulate matter (SPM) was helpful for Synechococcus growth. PE-rich SYN decreased in abundance when the concentration of dissolved inorganic nitrogen increased in May and November, and the concentration of phosphate increased in November. However, PC-rich SYN abundance and nutrients showed no correlation. Principal component analysis and regression analysis indicated that PE-rich SYN significantly correlated with the principal components that were affected by environmental factors.     

Hydrobiological variables as a regulatory factor on the abundance of heterotrophic flagellates in an urban pond

The seasonal abundance of flagellates has been monitored over a period of 1 year from December2013 to November 2014(divided into 4 conjugative seasons namely winter, spring, summer, and autumn) in an experimental pond located in Rajshahi City Corporation area, Bangladesh. To our knowledge, this study is the first to shed light on the occurrence and possible interrelationships among heterotrophic flagellates(HF),bacteria and zooplankton in Bangladesh and the result obtained by this study will be beneficial for similar water ecosystem all over the world. Standard methods were used to determine the prescribed hydrological parameters and zooplankton cell density. Maximum HF abundance(14 346.00 cells/mL) was found in the spring and the minimum(5 215.00 cells/mL) occurred in the summer. Inverse to HF, significantly(P0.05)higher zooplankton abundance was found during the winter(782.00±47.62 cells/mL) and the lowest value was found in the autumn(448.00±39.15 cells/mL). Whereas similar to the HF, total bacterial abundance was significantly higher during the spring((2.25±1.05)×10~5 cells/mL) and lower in the summer((0.79±0.06)×105 cells/mL). Multivariate analyses(ANOSIM and MDS) have shown significant seasonal differences for cell numbers where MDS ordination plot and cluster analysis based on similarity in the genera abundance of HF revealed overlapping condition between winter and spring. Canonical correspondence analysis(CCA) also showed a distinct separation among the genera based on the prevailing hydrological situation and indicated that temperature, pH, BOD_5, and NO_3~- were the most important environmental variables in determining the observed variation in HF community structure. Among the biological factors, zooplankton showed negative but total bacteria were positively correlated with HF abundance.     

Antifouling potential of bacteria isolated from a marine biofilm

Marine microorganisms are a new source of natural antifouling compounds. In this study, two bacterial strains, Kytococcus sedentarius QDG-B506 and Bacillus cereus QDG-B509, were isolated from a marine biofilm and identified. The bacteria fermentation broth could exert inhibitory effects on the growth of Skeletonema costatum and barnacle larvae. A procedure was employed to extract and identify the antifouling compounds. Firstly, a toxicity test was conducted by graduated pH and liquid-liquid extraction to determine the optimal extraction conditions. The best extraction conditions were found to be pH 2 and 100% petroleum ether. The EC50 value of the crude extract of K. sedentarius against the test microalgae was 236.7 ± 14.08 μg mL-1, and that of B. cereus was 290.6 ± 27.11 μg mL-1. Secondly, HLB SPE columns were used to purify the two crude extracts. After purification, the antifouling activities of the two extracts significantly increased: the EC50 of the K. sedentarius extract against the test microalgae was 86.4 ± 3.71 μg mL-1, and that of B. cereus was 92.6 ± 1.47 μg mL-1. These results suggest that the metabolites produced by the two bacterial strains are with high antifouling activities and they should be fatty acid compounds. Lastly, GC-MS was used for the structural elucidation of the compounds. The results show that the antifouling compounds produced by the two bacterial strains are myristic, palmitic and octadecanoic acids.     

Dual filtration effect of geochemical and biogeochemical processes in the Changjiang Estuary

Dissolved nutrients (NO ₃ ⁻ , PO₄ ³⁻, SiO₃ ²⁻) and oxygen, chlorophyll- a, pH, and Eh were measured on board during a cruise in August 1988 in the Changjiang Estuary region. Heavy metals, organic matter and carbonate contents were analyzed in laboratory. The results show that geochemical processes in the Changjiang Estuary have dual filtration effect: on the one hand geochemical filtration effect, reflected by ferromanganese oxide flocculation and sedimentation, occurs near the turbidity maximum, and leads to enrichment of heavy metals in suspended matter and sediments; on the other hand biogeochemical filtration, reflected by nutrients consumption, organic matter and carbonate sedimentation and enrichment of trace elements in suspended matter, occurs outside the plume water front. The biogeochemical filtration affects the environmental conditions; the dissolved oxygen and pH increase, in surface water and decrease in bottom water. The biogeochemical filtration effect outside the plume front is more important than the geochemical filtration effect near the turbidity maximum.     

Seasonal distribution of bioaerosols in the coastal region of Qingdao

Bioaerosols were collected by using a six-stage bioaerosols sampler from September 2007 to August 2008 in the coastal region of Qingdao, China. The terrestrial and marine microbes(including bacteria and fungi) were analyzed in order to understand the distribution features of bioaerosols. The results show that the average monthly concentrations of terrestrial bacteria, marine bacteria, terrestrial fungi and marine fungi are in the ranges of 80–615 CFU m-3, 91–468 CFU m-3, 76–647 CFU m-3 and 231–1959 CFU m-3, respectively. The concentrations of terrestrial bacteria, marine bacteria, terrestrial fungi, marine fungi and total microbes are the highest in each microbial category during fall, high in spring, and the lowest in the summer and winter. The bacterial particles are coarse in spring, autumn and winter. The sizes of fungal particle present the log-normal distribution in all the seasons.     

Variation of bacteria biomass and its possible controlling factors in the East China Sea

Two surveys were performed for determining bacteria biomass (BB), temperature, salinity, chlorophyll a (chl-a) and nutrient concentrations at 11 stations with three sampling depths in the high-incidence regions of red tide in the East China Sea (ECS) in the spring of 2006. Temperature and salinity increased from nearshore to offshore region and from high latitude to low latitude in the two cruises of 2006. BB were between 0.3–5.2 mgC m⁻³ (about 2.1 mgC m⁻³ on average) and 0.2–6.0 mgC m⁻³ (about 2.7 mgC m⁻³ on average) respectively in the two cruises. BB in the surface layer decreased from the Changjiang River estuary to high sea and from low latitude to high latitude. The results showed that bacterial growth was regulated by temperature, primary production and inorganic nutrient concentrations depending on different hydrographic conditions. In the surface and middle layers where the primary production can supply enough organic substrate, temperature was the main factor to control bacteria biomass. BB showed a good correlation between the surface and middle layers in both cruises. The distribution of nutrients during both cruises showed a similar decreasing trend from nearshore region and high latitude to offshore region and low latitude. High BB values were mainly recorded from samples in the middle layer where chl-a concentrations were also high, indicating primary production being strongly correlated with temperature over the ECS shelf. In the offshore area, phosphate and silicate became limiting factors for phytoplankton growth with indirect influence on BB. Bacteria played an important role in nitrogen regeneration process turning organic nitrogen to inorganic forms such as NH₄ ⁺. The increasing ratio of NH₄ ⁺/DIN could be a proof of that.     

Seasonal dynamics of nitrogen and phosphorus in water and sediment of a multi-level ditch system in Sanjiang Plain,Northeast China

The multi-level ditch system developed in the Sanjiang Plain, Northeast China has sped up water drainage process hence transferred more pollutants from farmlands into the rivers of this region. Understanding the seasonal dynamics of nitrogen (N) and phosphorus (P) transportation in the ditch system and the role of different ditch size is thus crucial for water pollution control of the rivers in the Sanjiang Plain. In this study, an investigation was conducted in the Nongjiang watershed of the Sanjiang Plain to study the nutrient variation and the correlation between water and sediments in the ditch system in terms of ditch level. Water and sediments samples were collected in each ditch level in growing season at regular intervals (once per month), and TN, NO₃ ⁻N, NH₄ ⁺-N, TP, and PO₄ ³⁻-P were analyzed. The results show that nutrient contents in water were higher in June and July, especially in July, the contents of TN and TP were 3.21 mg/L and 0.84 mg/L in field ditch, 4.04 mg/L and 1.06 mg/L in lateral ditch, 2.46 mg/L and 0.70 mg/L in branch ditch, 1.92 mg/L and 0.63 mg/L in main ditch, respectively. In August and September, the nutrient contents in the water were relatively lower. The peak value of nutrient in ditch water had been moving from the field ditch to the main ditch over time, showing a remarkable impact of ditch system on river water environment. The nutrient transfer in ditch sediments could only be found in rainfall season. Nutrient contents in ditch sediment had effect on that in ditch water, but nutrients in ditch water and sediments had different origination. Ditch management in terms of the key factors is hence very important for protecting river water environment.     

Distributions of picophytoplankton and phytoplankton pigments along a salinity gradient in the Changjiang River Estuary,China

We investigated the abundance of different picophytoplankton groups and the phytoplankton pigment ratio in relation to environmental factors such as nutrients and suspended solids along a salinity gradient in the Changjiang River Estuary. The average numbers of Synechococcus spp.(Syn) and picoeukaryotes(Euk) were(2.7 ±5.1) ×103 and(1.1±1.4) ×103 cells m L-1, respectively. Prochlorococcus spp.(Pro) was only found in the high-salinity brackish water with the concentration of 3.0×103 cells m L-1. Syn and Euk numbers both tended to increase offshore and Syn showed a larger variation in cell abundance than Euk. The contribution of picophytoplankton to total phytoplankton biomass increased with increasing salinity and decreasing nutrient concentrations from the estuary to the open ocean. The response of different picophytoplankton groups to environmental variables was different. Water temperature was more important in its control over Euk than over Syn, while nutrients were more important in their influence over Syn than over Euk. Phytoplankton pigment ratios were different in the three different ecological zones along the salinity gradient(i.e., freshwater zone with 0-5 range, fresh and saline water mixing zone with 5-20 range, and high-salinity brackish water zone with 20-32 range), where three different phytoplankton communities were discovered, suggesting that phytoplankton pigment ratios can be considered as a complementary indicator of phytoplankton community structure in the Changjiang River Estuary.     

The influence of key environmental variables on phytoplankton community structure in the estuary of tidal rivers around Luoyuan Bay,China

A total of 348 species belonging to 8 phyla and 125 genera were observed in seasonally sampled phytoplankton of tidal rivers from 13 sampling sites around Luoyuan Bay, and all field samplings were carried out in productive period(March/June/August/December) at ebb tide. Bacillariophyta species were the most abundant species, followed by Chlorophyta, Cyanophytes, Euglenophyta, Cryptophyta, Dinophyta, Xanthophyta and Chrysophytas. Seasonal distribution index(SDI) value ranged from 0.63 to 0.86, which meant that species found at those sites in 4 seasons tended to be largely different. Phytoplankton individuals ranged from 5.939×10~4 ind L~(-1) in winter to 75.31×10~4 ind L~(-1) in autumn. Phytoplankton biomass ranged from 0.620 mg L~(-1) in summer to 2.373 mg L~(-1) in autumn. The grey correlation analysis(GCA) showed that the nutrient variables played an important role in the influence on phytoplankton community in every season. The canonical correspondence analysis(CCA) revealed impact of environmental variables on the different species, most of Bacillariophyta species were negative correlation with nutrients(TP and NH_3-N) in the four seasons, Chlorophyta species and Cyanophyta species did not show obvious correlation with environment variables in every season. The combination of GRA analysis and CCA analysis provided a method to quantitatively reveal the correlation between phytoplankton community and environmental variables in water body of tidal rivers at this region.     

Temporal dynamics of phytoplankton communities in a semi-enclosed mariculture pond and their responses to environmental factors

Variations in physical-chemical factors, species composition, abundance and biomass of nano- and micro-phytoplankton assemblages, as well as their responses to environmental factors, were investigated over a complete cycle (6 months) in a semi-enclosed shrimp-farming pond near Qingdao, northern China. The aim was to establish the temporal patterns of phytoplankton communities and to evaluate protists as suitable bioindicators to water quality in mariculture systems. A total of 34 taxa with nine dominant species were identified, belonging to six taxonomic groups (dinoflagellates, diatoms, cryptophyceans, chlorophyceans, euglenophyceans and chrysophyceans). A single peak of protist abundance occurred in October, mainly due to chlorophyceans, diatoms and chrysophyceans. Two biomass peaks in July and October were primarily due to dinoflagellates and diatoms. Temporal patterns of the phytoplankton communities significantly correlated with the changes in nutrients, temperature and pH, especially phosphate, either alone or in combination with NO₃-N and NH₃-N. Species diversity, evenness and richness indices were clearly correlated with water temperature and/or salinity, whereas the biomass/abundance ratio showed a significant correlation with NO₃-N. The results suggest that phytoplankton are potentially useful bioindicators to water quality in semi-enclosed mariculture systems.