Xiangxi Bay Research Articles

Effects of Reservoir Impounding on Key Ecological Factors in the Three Gorges Region

According to the analyzing of the monitoring data of key ecological factors, such as concentration of total phosphorus (TP), concentration of total nitrogen (TN), and algae cell density during 2002-2005 in the reservoir region, we can find that the number of algae species and the cell density are significant increase, nutrient concentration in Xiangxi Bay also has marked increasing tendency after impounding. It creates a necessary condition for the outbreaking of algal blooms in the tributary bay. Hydraulic structures locates in the tributaries upstream are suggested to be used to regulate and control water quality in the bays.

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

AbstractAlgal 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. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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

ABSTRACT 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 R2 values of observed and predicted data were 0.85 for training and 0.89 for validating. In 7-days-ahead forecasting, the R2 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.

Diel vertical migration of Peridiniopsis niei, Liu et al., a new species of dinoflagellates in an eutrophic bay of Three-Gorge Reservoir, China

In spring, a typical dinoflagellate (Peridiniopsis niei Liu et al.) constitutes most of the phytoplankton biomass in most of eutrophic bay of Three-Gorge Reservoir (TGR, China). There are few field observations on vertical migration of the members of the genus Peridiniopsis. We studied diel vertical migration of the new species (Peridiniopsis niei) at sampling stations A and B in an eutrophic bay (Xiangxi Bay) of TGR during both day and night in March 2007. The present study suggests that vertical migration by Peridiniopsis niei is similar in nature to the migration patterns observed for other dinoflagellates. Solar irradiance incident was an important factor regulating the ascent and descent of Peridiniopsis niei. The vertical descent of Peridiniopsis niei during nighttime was restricted when the thermocline (Temperature gradient >1°C m−1) was present in the station B.

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

AbstractFrom July 2003 to June 2005, investigations of rotifer temporal and spatial distributions were car‐ried 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 succes‐sion 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. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Using temporal coherence to determine the responses of water clarity to hydrological processes in a giant subtropical canyon-shaped reservoir (China)

Investigating whether different locations of a large lake exhibit synchronous or asynchronous fluctuations in limnological characteristics is essential to lake management. If synchronous fluctuations (termed as “temporal coherence”) among sites are found to prevail, regional factors are likely to be the drivers; otherwise, local factors may be dominant. Here, this idea is tested at two spatial scales: the large scale being the mainstream of Three-Gorges reservoir (TGR, China) and the small scale being Xiangxi Bay of TGR. Data of transparency and chlorophyll a were gathered monthly at 26 sampling sites from July 2003 to July 2006 to evaluate temporal coherence for water clarity. High spatial and temporal variation in transparency (4–510 cm) and chlorophyll a (0.1–190.2 μ g/L) mark the system. For the mainstream of TGR, significant high temporal coherence of water clarity among sites (correlation analysis: 0.872 ≤ r ≤ 0.991, mean r = 0.960) was detected and the among-site correlations showed no significant relationship with geographical distance (Mantel test: r = −0.186, p > 0.05) or chlorophyll a (Mantel test: r = 0.249, p > 0.05). By contrast within Xiangxi Bay, lower synchronous fluctuations (correlation analysis: 0.396 ≤ r ≤ 0.971, mean r = 0.785) occurred, and the among-site correlations decreased with an increase in geographical distance (Mantel test: r = −0.715, p < 0.01) and a decrease in temporal coherence of chlorophyll a (Mantel test: r = 0.893, p < 0.01). Seasonal dynamics of water clarity were very well explained by inflow discharges (regression analysis: 0.771 ≤ R 2 ≤ 0.906) and water residence time (0.782 ≤ R 2 ≤ 0.918) in the mainstream, but not in Xiangxi Bay. The high coherency of the dynamics of water clarity in TGR mainstream is likely caused by regional hydrological processes driven by subtropical monsoon climate. For Xiangxi Bay, local processes such as phytoplankton dynamics may override the regional effects of hydrological processes, because the water clarity of this bay is strongly determined by phytoplankton bloom dynamics.

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

ABSTRACT 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.

Seasonal dynamics of suspended solids in a giant subtropical reservoir (China) in relation to internal processes and hydrological features

To explore the factors regulating seasonal variation of total suspended solids (TSS) and its two fractions in a giant dendritic reservoir (the Three-Gorges Reservoir of China, TGR) in the subtropical monsoon region, suspended solids, chlorophyll a (a surrogate for lake internal processes) and water residence time (an index of hydrologic flushing) were examined monthly from August 2005 to July 2006. TSS ranged from 0.6 to 200.3 mg/L and from 0.6 to 78 mg/L respectively in the mainstream and in a typical reservoir-bay (the Xiangxi Bay) of the TGR,. TSS exhibited a typical seasonal pattern in the mainstream rather than in the Xiangxi Bay of the TGR. The fraction of non-volatile suspended solids (NVSS) was often more dominant in the mainstream than in the Xiangxi Bay, especially during the flood season. Regressions analysis showed that 87.6% and 89.8 % of seasonal variation in TSS and NVSS of the mainstream, respectively, are explained by water residence time . In contrast, suspended solids (particularly volatile suspended solids, VSS) of the Xiangxi Bay displayed significant correlation with algal biomass, and no correlation with hydrological parameters. It implies that the Xiangxi Bay was a more autochthonous system than the mainstream of the TGR where exogenous influences were the more determinant factors.

Influence Factors Analysis to Chlorophyll a of Spring Algal Bloom in Xiangxi Bay of Three Gorges Reservoir

To study the relationship between environmental variables and chlorophyll a of spring algal bloom in Xiangxi Bay of Three Gorges Reservoir, stepwise multiple binomial regression and grey relative analysis methods were adopted. In surveys, 13 stations have been investigated and 143 samples were collected weekly from March 4 to May 13 in 2007. The study shows environmental variables (turbidity, total nitrogen, dissolved oxygen, total phosphates and silicate) are key factors during algal bloom. The grey relative values and their permutation indicated that turbidity was the most important factor and had comprehensive effect on chlorophyll a. The more number of interactive variables is found to be an indication of biochemical activity during spring algal bloom in Xiangxi Bay such as DO×TN, Turb×TP and so on. There was good linear relationship between chlorophyll a and the interaction of DO with TN ( , ).The interac-tion of nutrients (TP×TN, TP×SiO4, TN×SiO4) had significant influence to chlorophyll a and probably determined the inter-specific competition at different nutrient concentrations.

Dynamics of main nutrient input to Xiangxi Bay of the Three-Gorges Reservoir

Based on routine monitoring data in Xiangxi River and its main tributary Gaolan River from September 2000 to June 2005, this paper estimates the contribution of riverine nutrients, and analyzes the monthly dynamics of concentrations and fluxes of nutrients. The results show that Xiangxi Bay annually receives 1623.49 tons of total nitrogen (TN) and 331.85 tons of total phosphorus; Xiangxi River alone accounts for 68.50% of the total nitrogen fluxes and 91.74% of the total phosphorus fluxes. In these two rivers, dissolved inorganic nitrogen (DIN) is the dominating form of nitrogen; fluxes of DIN and TN are high during summer (July), mid-spring and autumn, and relatively low in winter; non-point source pollutants that flow into rivers are the most important pathway of nitrogen. Orthophosphate is the dominating form of phosphorus in Xiangxi River, relatively low in Gaolan River; fluxes of phosphorus are high during summer and late spring, relatively low during winter and late autumn in Gaolan River, but fluctuate irregularly in Xiangxi River; phosphorus in Gaolan River is mainly caused by non-point source pollutants, while point source pollutants of phosphorus play an important role in Xiangxi River. Soil erosion probably represents the major way of non-point source pollutants, while the drainages of phosphorus diggings and factory discharges play the most important role in the point source pollutants of phosphorus. This research suggests that measures must be taken to control the point source pollutants of phosphorus in Xiangxi River in order to protect Xiangxi Bay of the Three-Gorges Reservoir.

Seasonal Patterns of Sedimentation and Their Associations with Benthic Communities in Xiangxi Bay of the Three Gorges Reservoir, China

ABSTRACT Sedimentation variables and benthic community data were collected at seven stations during four seasons in Xiangxi Bay of the Three Gorges Reservoir, China. Summer, the season of highest discharge into the reservoir, was characterized by the extreme sediment loading. The benthic macroinvertebrate community was dominated by oligochaetes across all seasons at most stations. In winter/spring, macroinvertebrate density and richness increased. Correspondence analysis showed that community structure differed among stations at the two ends of the bay in winter and among almost all stations in spring. However, no variable associated with sedimentation appeared to be associated with differences in the community.

Comparative study on macroinvertebrate communities along a reservoir cascade in Xiangxi River Basin

Three cascade reservoirs (Gudongkou Reservoir 1 (GR1), Gudongkou Reservoir 2 (GR2), and Xiangxi Bay of Three-Gorge Reservoir in Xiangxi River Basin, China were selected to investigate macroinvertebrate ecology in a cascade reservoir system. Principal Components Analysis (PCA) implied that water quality was degrading along the reservoir cascade. Non-metric Multidimensional Scaling (NMS) showed that sampling stations located in the lacustrine zone of a reservoir are representatives in comparing macroinvertebrate assemblages along the reservoir cascade. Oligochaetes were numerically dominant in both GR1 and Xiangxi Bay, and chironomids were dominant in GR2. A similar pattern was also exhibited in taxon composition. Benthic assemblages of the 3 reservoirs were all dominated by pollution-tolerant taxa in spite of their differences in water quality. Canonical Correspondence Analysis (CCA) disclosed that turbidity influenced the benthic assemblages significantly. Total organic carbon (TOC)/Turbidity was applied to determine the influence of organic matter on turbidity. The ratio in GR2 was the lowest among the 3 reservoirs, which implicated that the influence of organic matter on turbidity was smaller in GR2 than in the other 2 reservoirs, suggesting that inorganic matter contributed substantially to the turbidity of GR2.

Vertical Distribution and Migration of Planktonic Rotifers in Xiangxi Bay of the Three Gorges Reservoir, China

ABSTRACT We investigated diel vertical migrations (DVM) and distributions of rotifers in summer, 2004 and spring, 2005, in Xiangxi Bay of the Three Gorges Reservoir, China. Water temperature, pH, conductivity, and phytoplankton were closely related to rotifer vertical distribution, while dissolved oxygen had no relationship with the vertical distribution of rotifers. The species composition and population density of rotifers changed significantly between seasons. However, rotifer vertical distributions in both seasons were similar. They aggregated at specific depths in the water column. All the rotifer species inhabited the surface layers (0.5–5 m). Generally, the rotifers did not display DVM except for Polyarthra vulgaris (in summer), which performed reverse migration. The reason that rotifers did not perform DVM may be explained by the low abundance of competitors and predators and the high density of food resources at the surface strata.

Monthly change of community structure of zoobenthos in Xiangxi Bay after impoundment of the Three Gorges Teservoir, China

Xiangxi Bay, a typical bay of the Three Gorges Reservoir (TGR) in China, was formed in June 2003 after the impoundment of the TGR. We investigated the community structure of zoobenthos in Xiangxi Bay from August 2003 to August 2004. Benthic abundance and biomass were calculated per unit area of sediment. A total of 26 taxa were identified. They included two families of Lamellibranchia (7.7% of the total taxa number), two families of Oligochaeta (50%), Chironomidae (38.5%), and one other animal (3.8%). The average density and biomass were 276 ind./m2 and 0.301 g/m2, respectively. Oligochaetes and chironomids constituted the major groups, and Limnodrilus hoffmeisteri, Procladius sp., Branchiura sowerbyi, Tubificidae sp1. and Polypedilum scalaenum group sp. were the common taxa in this reservoir system. Among them, L. hoffmeisteri and Procladius sp. were the dominant species, and contributed 37.0% and 28.3% of the total density, respectively. The standing crop of zoobenthos in Xiangxi Bay was relative low, compared with other similar reservoirs. Our studies demonstrate that the standing crop increased gradually with time. The total density and biomass in August 2004 were 8.8 and 14.3 times those of the initial impoundment, separately. Oligochaetes did not become the sole dominant group, indicating that the sediment loading in Xiangxi Bay may be not serious.

Spatial analysis for spring bloom and nutrient limitation in Xiangxi bay of three Gorges Reservoir

The spatial and temporal dynamics of physical variables, inorganic nutrients and phytoplankton chlorophyll a were investigated in Xiangxi Bay from 23 Feb. to 28 Apr. every six days, including one daily sampling site and one bidaily sampling site. The concentrations of nutrient variables showed ranges of 0.02-3.20 mg/L for dissolved silicate (Si); 0.06-2.40 mg/L for DIN (NH(4)N + NO(2)N + NO(3)N); 0.03-0.56 mg/L for PO(4)P and 0.22-193.37 microg/L for chlorophyll a, respectively. The concentration of chlorophyll a and inorganic nutrients were interpolated using GIS techniques. The results indicated that the spring bloom was occurred twice in space during the whole monitoring period (The first one: 26 Feb.-23 Mar.; the second one: 23 Mar.-28 Apr.). The concentration of DIN was always high in the mouth of Xiangxi Bay, and PO(4)P was high in the upstream of Xiangxi Bay during the whole bloom period. Si seems no obvious difference in space in the beginning of the spring bloom, but showed high heterogeneity in space and time with the development of spring bloom. By comparing the interpolated maps of chlorophyll a and inorganic variables, obvious consumptions of Si and DIN were found when the bloom status was serious. However, no obvious depletion of PO(4)P was found. Spatial regression analysis could explained most variation of Chl-a except at the begin of the first and second bloom. The result indicated that Si was the factor limiting Chl-a in space before achieved the max area of hypertrophic in the first and second bloom period. When Si was obviously exhausted, DIN became the factor limiting the Chl-a in space. Daily and bidaily monitoring of Site A and B, representing for high DIN: PO(4)P ratio and low DIN:PO(4)P ratio, indicated that the concentration of Si was decreased with times at both site A and B, and the dramatically drop of DIN was found in the end monitoring at site B. Multiple stepwise regression analysis indicated that Si was the most important factor affect the development of spring bloom both at site A and B in time series.

Daily Dynamics of Nutrients and Chlorophyll a during a Spring Phytoplankton Bloom in Xiangxi Bay of the Three Gorges Reservoir

ABSTRACT We studied the daily dynamics of nutrients (total phosphorus [TP], total nitrogen [TN], and dissolved silicate [SiO2]) and chlorophyll a (chl a) during a spring bloom in Xiangxi Bay of the Three Gorges Reservoir in year 2005. According to the daily dynamics of chl a, the bloom occurred in two stages (23 February–25 March and 26 March–28 April). The concentration of SiO2 decreased at different layers of the water column with the development of the bloom. However, the decrease of SiO2 in the layers with high concentration of chl a was more dramatic than in the layers with low concentration of chl a. The concentration of TP was lowest value a few days after the peak of chl a during the first bloom period, and the lowest value of TN was found a few days after the peak of chl a during the second bloom period. Correlative analyses indicated that SiO2 and TP were limiting factors in the first bloom period, and SiO2 and TN were limiting factors in the second bloom period.