Temporal Coherence of Chlorophyll a during a Spring Phytoplankton Bloom in Xiangxi Bay of Three-Gorges Reservoir, China

Algal bloom phenomenon was defined as "the rapid growth of one or more phytoplankton species which leads to a rapid increase in the biomass of phytoplankton", yet most estimates of temporal coherence are based on yearly or monthly sampling frequencies and little is known of how synchrony varies among phytoplankton or of the causes of temporal coherence during spring algal bloom. In this study, data of chlorophyll a and related environmental parameters were weekly gathered at 15 sampling sites in Xiangxi Bay of Three-Gorges Reservoir (TGR, China) to evaluate patterns of temporal coherence for phytoplankton during spring bloom and test if spatial heterogeneity of nutrient and inorganic suspended particles within a single ecosystem influences synchrony of spring phytoplankton dynamics. There is a clear spatial and temporal variation in chlorophyll a across Xiangxi Bay. The degree of temporal coherence for chlorophyll a between pairs of sites located in Xiangxi Bay ranged from -0.367 to 0.952 with mean and median values of 0.349 and 0.321, respectively. Low levels of temporal coherence were often detected among the three stretches of the bay (Down reach, middle reach and upper reach), while high levels of temporal coherence were often found within the same reach of the bay. The relative difference of DIN between pair sites was the strong predictor of temporal coherence for chlorophyll a in down and middle reach of the bay, while the relative difference in Anorganic Suspended Solids was the important factor regulating temporal coherence in middle and upper reach. Contrary to many studies, these results illustrate that, in a small geographic area (a single reservoir bay of approximately 25 km), spatial heterogeneity influence synchrony of phytoplankton dynamics during spring bloom and local processes may override the effects of regional processes or dispersal.

Evolution of freshwater plumes and salinity fronts in the northern Bay of Bengal

[1] The evolution of freshwater plumes and the associated salinity fronts in the northern Bay of Bengal ( henceforth the bay) is studied using rotated empirical orthogonal function (REOF) analysis and extended associate pattern analysis (EAPA). The results show that sea surface salinity distribution is featured by eastern-bay and western-bay plumes in the northern bay during different seasons. The western-bay plume begins in early July, peaks in late August, and then turns into a bay-shaped plume with the two plumes in either side of the bay, which peaks in late October. The southward extension of the western-bay plume can be explained by the southwestward geostrophic flow associated with the cyclonic gyre in the northern bay, which counters the northeastward Ekman drift driven by wind stress. The offshore expansion of the western-bay plume is induced by the offshore Ekman drift which also produces a salinity front near the east coast of India. The bay-shaped plume appears when the cyclonic gyre shifts westward and a weak anticyclonic gyre occupies the northeastern bay. As the season advances, the western part of the bay-shaped plume decays while the eastern part persists until the following June, which is believed to be associated with the anticyclonic gyre in the northern bay. The evolution of the plumes except the eastern part of the bay-shaped plume in fall can be partly explained by the seasonal variation of mass transport associated with the Sverdrup balance. The fact that the western-bay (eastern-bay) plume appears when surface freshwater flux in the northeastern bay increases ( decreases) dramatically suggests that the plumes are not produced directly by surface freshwater flux. River discharge seems to be the freshwater source for the plumes and has little to do with the evolution of the plumes.

Studies on growth rate and grazing mortality rate by microzooplankton of size-fractionated phytoplankton in spring and summer in the Jiaozhou Bay, China

Dilution experiments were performed to examine the growth rate and grazing mortality rate of size-fractionated phytoplankton at three typical stations, inside and outside the bay, in the spring and summer of 2003 in the Jiaozhou Bay, China. in spring, the phytoplankton community structure was similar among the three stations, and was mainly composed of nanophytoplankton, such as, Skeletonema costatum and Cylindrotheca closterium. The structure became significantly different for the three stations in summer, when the dominant species at Stas A, B and C were Chaetoceros curvisetus, Pseudo-nitzschia delicatissima, C. affinis, C. debilis, Coscinodiscus oculus-iridis and Paralia sulcata respectively. Tintinnopsis beroidea and T. tsingtaoensis were the dominant species in spring, whereas the microzooplankton was apparently dominated by Strombidium sp. in summer. Pico- and nanophytoplankton had a relatively greater growth rate than microzooplankton both in spring and summer. The growth rate and grazing mortality rate were 0.18 similar to 0.44 and 0.12 similar to 1.47 d(-1) for the total phytoplankton and 0.20 similar to 0.55 and 0.21 similar to 0.37 d-1 for nanophytoplankton in spring respectively. In summer, the growth rate and grazing mortality rate were 0.38 similar to 0.71 and 0.27 similar to 0.60 d-1 for the total phytoplankton and 0.11 similar to 1.18 and 0.41 similar to 0.72 d(-1) for nano- and microphytoplankton respectively. The carbon flux consumed by microzooplankton per day was 7.68 similar to 39.81 mg/m(3) in spring and 12.03 similar to 138.22 mg/m(3) in summer respectively. Microzooplankton ingested 17.56%similar to 92.19% of the phytoplankton standing stocks and 31.77%similar to 467.88% of the potential primary productivity in spring; in contrast, they ingested 34.60%similar to 83.04% of the phytoplankton standing stocks and 71.28%similar to 98.80% of the potential primary productivity in summer. Pico- and nanophytoplankton appeared to have relatively greater rates of growth and grazing mortality than microphytoplankton during the experimental period. The grazing rate of microzooplankton in summer was a little bit greater than that in spring because of the relatively higher incubation temperature and different dominant microzooplankton species. Microzooplankton preferred ingesting nanophytoplankton to microphytoplankton in spring, while they preferred ingesting picophytoplankton to nanophytoplankton and microphytoplankton in summer. Compared with the results of dilution experiments performed in various waters worldwide, the results are in the middle range.

Inorganic carbon of sediments in the Yangtze River Estuary and Jiaozhou Bay

JGOFS results showed that the ocean is a major sink for the increasing atmospheric carbon dioxide resulting from human activity. However, the role of the coastal seas in the global carbon cycling is poorly understood. In the present work, the inorganic carbon (IC) in the Yangtze River Estuary and Jiaozhou Bay are studied as examples of offshore sediments. Sequential extraction was used to divide inorganic carbon in the sediments into five forms, NaCl form, NH3 H2O form, NaOH form, NH2OH HCl form and HCl form. Studied of their content and influencing factors were also showed that NaCl form < NH3 H2O form < NaOH form < NH2OH HCl form < HCl form, and that their influencing factors of pH, Eh, Es, water content, organic carbon, organic nitrogen, inorganic nitrogen, organic phosphorus and inorganic phosphorus on inorganic carbon can be divided into two groups, and that every factor has different influence on different form or on the same form in different environment. Different IC form may transform into each other in the early diagenetic process of sediment, but NaCl form, NH3 H2O form, NaOH form and NH2OH HCl form may convert to HCl form ultimately. So every IC form has different contribution to carbon cycling. This study showed that the contribution of various form of IC to the carbon cycle is in the order of NaOH form > NH2OH HCl form > NH3 H2O form > NaCl form > HCl form, and that the contribution of HCl form contributes little to carbon cycling, HCl form may be one of end-result of atmospheric CO2. So Yangtze River estuary sediment may absorb at least about 40.96x10(11) g atmospheric CO2 every year, which indicated that offshore sediment play an important role in absorbing atmospheric CO2.

Forecasting Daily Chlorophyll a Concentration during the Spring Phytoplankton Bloom Period in Xiangxi Bay of the Three-Gorges Reservoir by Means of a Recurrent Artificial Neural Network

A recurrent artificial neural network was used for 0-and 7-days-ahead forecasting of daily spring phytoplankton bloom dynamics in Xiangxi Bay of Three-Gorges Reservoir with meteorological, hydrological, and limnological parameters as input variables. Daily data from the depth of 0.5 m was used to train the model, and data from the depth of 2.0 m was used to validate the calibrated model. The trained model achieved reasonable accuracy in predicting the daily dynamics of chlorophyll a both in 0-and 7-days-ahead forecasting. In 0-day-ahead forecasting, the R-2 values of observed and predicted data were 0.85 for training and 0.89 for validating. In 7-days-ahead forecasting, the R-2 values of training and validating were 0.68 and 0.66, respectively. Sensitivity analysis indicated that most ecological relationships between chlorophyll a and input environmental variables in 0-and 7-days-ahead models were reasonable. In the 0-day model, Secchi depth, water temperature, and dissolved silicate were the most important factors influencing the daily dynamics of chlorophyll a. And in 7-days-ahead predicting model, chlorophyll a was sensitive to most environmental variables except water level, DO, and NH3N.

Seasonal variations in stable isotope ratios of two biomanipulation fishes and seston in a large pen culture in hypereutrophic Meiliang Bay, Lake Taihu

This paper reports on seasonal changes in stable carbon and nitrogen isotope ratios of seston and muscle tissue of silver carp and bighead carp during 2004 and 2005, focusing primarily on the carbon sources and trophic relationships among phytoplankton, zooplankton and silver carp and bighead carp in a large fish pen of Meiliang Bay (Lake Taihu, China). delta C-13 showed a minimal value in March 2005 and a maximal value in August 2005 in seston both inside and outside the pen, whereas delta N-15 of seston showed the minimum in winter and the maximum during algal blooms. A positive correlation between delta C-13 of silver carp and that of seston suggested that temporal variation Of delta C-13 in seston was preserved in fish via the food chain. The differences of delta C-13 among seston, zooplankton and muscle tissue of silver carp and bighead carp ranged only 0.2-1.7%, indicating that plankton production was the primary food source of filter-feeding fishes. According to a mass balance model, we estimated that the contributions of zooplankton to the diets of silver carp and bighead carp were 45.7% and 54.3%, respectively, based on the delta N-15 values of zooplankton and planktivorous fishes. (C) 2007 Elsevier B.V. All rights reserved

Temporal and Spatial Distributions of Rotifers in Xiangxi Bay of the Three Gorges Reservoir, China

From July 2003 to June 2005, investigations of rotifer temporal and spatial distributions were carried out in a bay of the Three Gorges Reservoir, Xiangxi Bay, which is the downstream segment of the Xiangxi River and the nearest bay to the Three Gorges Reservoir dam in Hubei Province, China. Thirteen sampling sites were selected. The results revealed a high species diversity, with 76 species, and 14 dominant species; i.e., Polyarthra vulgaris, Keratella cochlearis, Keratella valga, Synchaeta tremula, Synchaeta stylata, Trichocerca lophoessa, Trichocerca pusilla, Brachionus angularis, Brachionus calyciflorus, Brachionus forficula forficula, Ascomorpha ovalis, Conochilus unicornis, Ploesoma truncatum and Anuraeopsis fissa. After the first year of the reservoir impoundment, the rotifer community was dominated by ten species; one year later it was dominated by eight species. The community in 2003/2004 was dissimilar to that in 2004/2005, which resulted from the succession of the dominant species. The rotifer community exhibited a patchy distribution, with significant heterogeneity observed along the longitudinal axis. All rotifer communities could be divided into three groups, corresponding to the riverine, the transition and the lacustrine zone, respectively.

Spring Diatom Blooming Phases in a Representative Eutrophic Bay of the Three-Gorges Reservoir, China

We investigated dynamics of the phytoplankton community and abiotic factors in Xiangxi Bay of the Three-Gorge Reservoir, China, by daily sampling, a specific site during a spring algal bloom (February 23-April 28, 2005). Among the 76 taxa observed, Asterionella formosa and Cyclotella spp. were the dominants, accounting for 47.2% and 29.9% of the total abundance, respectively. We determined the five distinct developing phases of the bloom by analyzing the dissimilarity of physicochemical parameters. Simultaneously, six phytoplankton community groups were distinguished by TWINSPAN classifications. The pattern for algal community succession was similar to that for the bloom phase shift, and the structural complexity of communities significantly decreased over time. Water temperature and silicate were the main factors that related to the development of the bloom and the shifts of the phytoplankton community.

Controlling factors of spring-summer phytoplankton succession in Lake Taihu (Meiliang Bay, China)

The spring-summer successions of phytoplankton and crustacean zooplankton were examined weekly in Meiliang Bay of the subtropical Lake Taihu in 2004 and 2005. During the study period, the ecosystem of Meiliang Bay was characterized by (i) clearly declined nitrogen compounds (nitrate, TN, and ammonium) and slowly increased phosphorus compounds (TP and SRP), (ii) increased total phytoplankton density and rapid replacement of chlorophyta (mainly Ulothrix) by cyanobacteria (mainly Microcystis), and (iii) rapid replacement of large-sized crustaceans (Daphnia and Moina) by small-sized ones (Bosmina, Limnoithona, and Ceriodaphnia). Results from the CCA and correlation analysis indicate that the spring-summer phytoplankton succession was primarily controlled by abiotic factors. Cyanobacteria were mainly promoted by increased temperature and decreased concentrations of nitrogen compounds. The pure contribution of crustacean was low for the variation of phytoplankton suggesting a weak top-down control by crustacean zooplankton in the subtropical Lake Taihu.

In situ study on effect of food competition on diet shifts and growth of silver and bighead carps in large biomanipulation fish pens in Meiliang Bay, Lake Taihu

Silver and bighead carps were cultured in large fish pens to reduce the risks of cyanobacterial bloom outbreaks in Meiliang Bay, Lake Tauhu in 2004 and 2005. Diet compositions and growth rates of the carps were studied from April to November each year. Both carp species fed mainly on zooplankton (> 50% in diet) in 2004 when competition was low, but selected more phytoplankton in 2005 when competition was high. Silver carp had a broader diet breadth than did bighead carp. Higher densities and fewer food resources increased diet breadths but decreased the diet overlap in both types of carps. It can be predicted that silver and bighead carps would be released from diet competition and shift to feed mainly on zooplankton at low densities, decreasing the efficiency of controlling cyanobacterial blooms. Conclusively, when silver and bighead carps are used to control cyanobacterial blooms, a sufficiently high stocking density is very important for a successful practice.