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Changes of Nutrients and Phytoplankton Chlorophyll-a in a Large Shallow Lake, Taihu, China: An 8-Year Investigation

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Abstract

Inter-annual changes of total nitrogen (TN) and total phosphorus (TP) and phytoplankton chlorophyll-a (Chla) in a large shallow lake, Taihu China, were analysed using the monthly monitoring data covering the period of 1991–1999. The concentrations of TN, TP and Chla showed marked gradients in the lake from high values near the northern river input in the inner Meiliang Bay towards lower concentrations the lake centre. TN was always much greater than TP (7:1 by weight) indicating that nitrogen was not a limiting factor in the lake. Annual averages of TN, TP and Chla increased until 1996 declining thereafter possibly because of the controlling of wastewater discharged from the catchment area by the local government. The internal nutrient loading in the lake was low because of the well-mixed condition and the low organic content of superficial sediment. Our results suggest that the recovery process in the lake might have started in 1996.

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... For example, water holding capacity of forests and grasslands has a significant positive effect on water quality (Zhang et al., 2011). The mixed farming and fertilizer application in cropland and the dense population in urban residential land, along with the development of industry, are the main causes of nutrient changes such as N and P in lakes (Chen et al., 2003;Deng, 2020;Pu et al., 2020;Reichert & Schuwirth, 2010). Therefore, different land use may reflect varying types of human activities. ...
... [TN] was positively correlated with latitude and negatively correlated with MAP (Fig. 5a, c), possibly due to the fact that northern ELR has a relatively large area of cropland and urban residential lands (Figs. 2 and 3). The lakes there typically receive long periods of high nutrient loading from agriculture, human activities, and industrial pollution (Chen et al., 2003;Han et al., 2011;Pu et al., 2020). Our analysis indicated that [TP] peaked at 18-20 °C water temperature (Fig. 5b), consistent with Fig. 4b that showed growth limitations in phytoplankton at high temperatures > 25 °C (Liu et al., 2011). ...
... Lakes with high [TP] were distributed in eastern and lowaltitude areas in China, which tended to have a relatively large proportion of cropland and urban residential lands. Some studies argued that these lakes receive nutrient loads from agriculture and human activities such as industrial pollution (Chen et al., 2003;Deng, 2020;Han et al., 2011;Pu et al., 2020). Our SEM analysis showed that high [TN] and [TP] often increased [DC] in lakes (Fig. 9). ...
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Given the differences in geomorphology, climate, hydrology, and human activities in various regions, lake chemometrics may also vary. However, the spatial distribution of lake chemistry and the factors affecting such pattern are still unclear. Here, we collected data for carbon, nitrogen, and phosphorus from published literature and databases in 224 lakes and calculated the trophic status index to represent the nutrient classification state of lakes. We found that lakes with high carbon concentrations were located in the Tibet-Qinghai Limnetic Region of western China, whereas lakes with high nitrogen and phosphorus concentrations were located in the Inner Mongolia-Xinjiang Limnetic Region and Northeast Limnetic Region of northern China. Areas with larger cropland and urban residential land (such as the junction of the three lake regions, i.e., the Northeast Limnetic Region, East Limnetic Region, and Inner Mongolia-Xinjiang Limnetic Region) tended to have lakes with high nitrogen and phosphorus concentrations. Our analysis suggested that spatial distribution of carbon, nitrogen, and phosphorus concentrations reflect the effect of climate, geomorphology, and land use in each lake region and nationwide.
... At each site, water samples were taken by mixing the surface (0.5 m below the surface), middle, and bottom (0.5 m above the bottom) layers of the water. Physicochemical variables such as transparency, water temperature, pH and nutrient concentrations (total nitrogen: TN and total phosphorus: TP) were analysed following Chinese standard methods (see Chen et al., 2003a;Chen et al., 2003b for details). Phytoplankton samples were fixed with Lugol's iodine solution and sedimented for 48 h prior to counting on a microscope (Chen et al., 2003a). ...
... Physicochemical variables such as transparency, water temperature, pH and nutrient concentrations (total nitrogen: TN and total phosphorus: TP) were analysed following Chinese standard methods (see Chen et al., 2003a;Chen et al., 2003b for details). Phytoplankton samples were fixed with Lugol's iodine solution and sedimented for 48 h prior to counting on a microscope (Chen et al., 2003a). Phytoplankton species were identified at the species or genus level and counted according to Hu and Wei (2006). ...
Article
Understanding the relative effect sizes of climate-related environmental variables and nutrients on the high annual variation in the phytoplankton biomass in eutrophic lakes is important for lake management efforts. In this study, we used a data set of phytoplankton dynamics in eutrophic Lake Taihu that cover more than two decades (1993-2015) to show the variation in and the drivers of phytoplankton biomass under complex, fluctuating environmental conditions. Our results showed that the phytoplankton biomass increased slowly over the studied period despite the recent decrease in nutrient levels. The distribution of the phytoplankton biomass expanded spatially towards the central lake region, and seasonally towards the autumn and winter. Nutrients were still the primary predictors of the long-term phytoplankton biomass trend. The effect size of climate-related variables was also high and close to the effect size of nutrients. Among the climate-related variables, wind speed and underwater available light were more important predictors than temperature. The biomass of the phytoplankton taxonomic groups showed different responses to the environmental variables based on their niches. However, the compensatory dynamics affecting biomass were weak at phylum level, and synchronous dynamics drove the variation in total biomass. Our findings highlight the effect of climate-related variables on the phytoplankton biomass in Lake Taihu, which has experienced high nutrient loadings and concentrations for more than two decades. Therefore, changes in climate-related variables, such as wind speed and underwater available light, should be considered when evaluating the amount that nutrients should be reduced in Lake Taihu for future lake management.
... Therefore, understanding the ecological processes, as well as abiotic and biotic factors that contribute to absolute and relative abundances of taxa in these communities are major goals of basic and applied community ecology. Metrics, such as species richness and the Shannon-Wiener diversity index, represent important tools for the characterization of changes in phytoplankton communities in aquatic ecosystems [3][4][5]. ...
... Meanwhile, at that time, the community was dominated by Bacillariophyta-Chlorophyta in TH3, which is in the southwest of the lake. Concentrations of nutrients (Nitrogen: 0.15 mg/L, PO 4 3− P: 0.05 mg/L) and pollutants (COD Mn : 1.90 mg/L) in the whole Tai Lake were also less than those measured here (Table 1). Since 1980s, cell density of phytoplankton increased in the rate of 5.8 times per year. ...
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Background Eutrophication of freshwater systems can result in blooms of phytoplankton, in many cases cyanobacteria. This can lead to shifts in structure and functions of phytoplankton communities adversely affecting the quality of drinking water sources, which in turn impairs public health. Relationships between structures of phytoplankton communities and concentrations of the toxicant, microcystin–leucine–arginine (MC-LR), have not been well examined in large shallow lakes. The present study investigated phytoplankton communities at seven locations from January to December of 2015 in Tai Lake, and relationships between structures and diversities of phytoplankton communities and water quality parameters, including concentrations of MC-LR and metals, were analyzed. Results A total of 124 taxa of phytoplankton were observed, and the predominant taxa were Microcystis sp. and Dolichospermum flos-aquae of Cyanophyta and Planctonema sp. of Chlorophyta. The greatest diversities of phytoplankton communities, as indicated by species richness, Simpson, Shannon–Wiener, the Berger and Parker, and the Pielou evenness indices, were observed in spring. Furthermore, productivity of phytoplankton was significantly and negatively correlated with diversities. These results demonstrated that Simpson, Shannon–Wiener, the Berger and Parker, and the Pielou evenness indices of phytoplankton communities were significantly related to trophic status and overall primary productivity in Tai Lake. In addition, temperature of surface water, pH, permanganate index, biochemical oxygen demand, total phosphorus, arsenic, total nitrogen/total phosphorous ratio, and MC-LR were the main factors associated with structures of phytoplankton communities in Tai Lake. Conclusion The present study provided helpful information on phytoplankton community structure and diversity in Tai Lake from January to December of 2015. Our findings demonstrated that Simpson, Shannon–Wiener, the Berger and Parker, and the Pielou evenness indices could be used to assess and monitor for status and trends in water quality of Tai Lake. In addition, MC-LR was one of the main factors associated with structures of phytoplankton communities in Tai Lake. The findings may help to address important ecological questions about the impact of a changing environment on biodiversity of lake ecosystems and the control of algae bloom. Further studies are needed to explore the relationship between MC-LR and phytoplankton communities in the laboratory.
... The eutrophication of Lake Taihu began in 1980s (Qin 2013), especially in the late 1980s, when the Meiliang Bay in the northern part of Taihu Lake experienced cyanobacteria blooms that later extended to the entire northwest region of Taihu Lake (Chen et al. 2003). After 1990, N and P concentrations were much higher than in the 1980s (Chen et al. 2003. ...
... The eutrophication of Lake Taihu began in 1980s (Qin 2013), especially in the late 1980s, when the Meiliang Bay in the northern part of Taihu Lake experienced cyanobacteria blooms that later extended to the entire northwest region of Taihu Lake (Chen et al. 2003). After 1990, N and P concentrations were much higher than in the 1980s (Chen et al. 2003. Increasing anthropogenic activities have resulted in the eutrophication of Lake Taihu (Cao et al. 2018). ...
Article
Xu X, Liu H, Jiao F, Ren Y, Gong H, Lin Z, and Huang C. 2020. Influence of climate change and human activity on total nitrogen and total phosphorus: a case study of Lake Taihu, China. Lake Reserv Manage. XX:XXX–XXX. Climate change and human activities can influence lake total nitrogen (TN) and total phosphorus (TP), affecting the overall health of the lake. These factors must be considered for planning and management of lakes in order to maintain their ecosystem integrity and sustain societal development. Using the Ensemble Empirical Mode Decomposition Method (EEMD) and the nonparametric Mann–Kendall test, the changes of TN and TP and their relationship to climate change and human activities were quantitatively evaluated on multiple time scales ranging from 1952 to 2010 using Meiliang Bay of Lake Taihu (China) for a case study. Patterns of TN change could be divided into 4 time scales: 2.73, 5.89, 25.33, and 45 yr, with an evident increasing long-term trend. Patterns of TP change were divided into 2.49, 6.4, 11.5, and 43 yr time scales with an increasing long-term trend. On short time scales, TN and TP were positively correlated with gross domestic product (GDP) and urban area, and negatively correlated with crop area and animal production. For the long-term trends, TN and TP were positively correlated with temperature, GDP, urban area, and animal production, and negatively correlated with precipitation and crop area. Both TN and TP abruptly changed in 2000, consistent with the abrupt changes in temperature, precipitation, and urban area. Collectively, results revealed that specific human activities in the watershed affected TN and TP in the sediments both on short-term and long-term scales, while global climate change affected TN and TP in the sediments on long-term scales. These results suggest that climate change and human activities must be considered to manage and protect lakes.
... It is a very challenging task to estimate TP concentration by the sensor because phosphorus distribution is heterogeneous in nature. But, some research work revealed that if TP attention is high, then chlorophyll is also increasing (Vollenweider 1976;McQueen et al. 1986;Chen et al. 2003;Müller-Navarra et al. 2004). The different spectral band has a remarkable contribution on TP estimation described in Table 5. Landsat 7 ETM+ Wang et al. (2006) Landsat 5 TM Rundquist et al. (1996) MODIS Terra, Aqua ...
... In this empirical relationship, the multicomponent regression model is quite a common practice to assess and understand the signature of the water surface. The genetic algorithms (Chen 2003;Chen et al. 2008), multiple linear regression (Baban 1993;Dekker and Peters 1993;Rundquist et al. 1996;Flink et al. 2001;Alparslan et al. 2007;Hicks et al. 2013), linear mixture modelling (Tyler et al. 2006;Bonansea et al. 2015), and partial linear regression (Song et al. 2012b) are effective and popular linear regression approaches for water quality modelling . Apart from the linear methods, there are few non-linear approaches like neural network (Panda et al. 2004;Giardino et al. 2013;Peterson et al. 2018;Peterson et al. 2020) and support vector regression method (Wang et al. 2010;Wang et al. 2017 Maier andKeller 2018;Peterson et al. 2019) that are getting enormous recognition due to their ability of trend analysis through statistical performance for remote sensing-based water quality data. ...
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Evaluation of water quality is a priority work nowadays. In order to monitor and map, the water quality for a wide range on different scales (spatial, temporal), the geospatial technique has the potential to minimize the field and laboratory work. The review has emphasized the advance of remote sensing for the effectiveness of spectral analysis, bio-optical estimation, empirical method, and application of machine learning for water quality assessment. The water quality parameters (turbidity, suspended particles, chlorophyll, etc.) and their retrieval techniques are described in a scientific manner. Available satellite, bands, resolution, and spectrum ranges for specific parameters are critically described in this review with challenges in remote sensing for water quality analysis, considering non-optical active parameters. The application of statistical programmes like linear (multiple regression analysis) and non-linear approaches is discussed for better assessment of water quality. Emphasis is given on comparison between different models to increase the accuracy level of remote sensing of water quality assessment. A direction is suggested for future development in the field of estimation of water pollution assessment through geospatial techniques.
... The results of this study is supported by Chen [21], which stated that the main cause of the ecological change has been generally attributed to nutrient load from urban and agricultural human activities together with climate change. As a consequence, the increase in nutrients load is likely to have caused the recent eutrophication of the lake ecosystem owing to increased intensification of agriculture. ...
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Lake Ziway is shallow freshwater located in Northern part of Ethiopian Rift Valley. Expansions of the flower industry, fisheries, intensive agricultural activities, fast population growth lead to deterioration of water quality and depletion of aquatic biota. The objectives of the present study are to evaluate the spatial and temporal variations in the external nutrient load and determine the trophic status of Lake Ziway in 2014 and 2015. The nutrients and Chlorophyll-a were measured according to the standard procedures outlined in APHA, 1999. From the result Ketar and Meki Rivers catchment showed the major sources of external nutrient loads to the lake ecosystem. The mean external soluble reactive phosphorus (SRP), total phosphorus (TP), total inorganic nitrogen (TIN) and total nitrogen (TN) loads to Lake Ziway were 230, 2772, 4925 and 24016 kg day-1, respectively. A general trend which was expected that the nutrient loads would be much higher in rainy season than in dry season. The mean concentrations of trophic state variables for TN, TP and Chla were 6700, 212 and 42 mg L-1, respectively. The mean values of TSI-TP, TSI-Chl-a, TSI-TN and TSI-SD were 79, 66, 81 and 83, respectively and the overall evaluation of Carlson Trophic State Index (CTSI) of Lake Ziway was 77. Therefore, the lake is under eutrophic condition. The mean values of TN: TP ratio was 48 which were very high. The trophic state index determined with chlorophyll-a showed lower value than those determined with all trophic state indices values of TN, TP, and SD which indicated that non-algal turbidity affected light attenuation for algal growth. This suggested that phosphorus was the limiting nutrient in Lake Ziway. Due to its importance as being the lake is an intensive agricultural site, management solutions must be urgently developed in order to avoid the destruction of the lake.
... The effect of water transfer on water transport processes in the lake is strongly influenced by hydrodynamic conditions induced by wind, and is also influenced by the water transfer routs and flow discharge (Hu et al 2010, Li et al 2013. Taihu Lake was oligotrophic as recently as the 1950s and 1960s, with Chl-a concentrations of about 2 mg m −3 and total phosphorus (TP) of about 10 mg m −3 (Chen et al 2003). However, since the late 1980s, the water quality of this lake has severely deteriorated and algal blooms have become a frequent nuisance (especially in Meiliang Bay, the most eutrophic region). ...
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An algal bloom is a complex hydro-biological phenomenon driven by multi-attribute environmental processes and thus is still difficult to predict. In this paper, a comprehensive modelling framework for forecasting algal bloom risks in shallow lakes is presented, which is based on long-term field observation and modelling of eutrophic shallow lakes. In the procedure, the major factors and their suitable ranges are investigated, and the individual influence of various driving factors is evaluated quantitatively, using an integrated approach of orthogonal design and regression analysis. By analyzing the possible combined effects of the major driving factors and the relationship between algal bloom risk and major bloom-driving factors, a cost-effective environmentally driven risk assessment model is developed to forecast the likelihood of algal bloom occurrence, through a parameter optimization and prediction comparison routine. The risk model has been calibrated and validated against long-term field observations of algal blooms in Taihu Lake, with the prediction accuracy higher than 70%, which only requires readily available meteorological and water quality data. It is noted that for the closed shallow lake, the influence of hydrodynamics can be indirectly reflected by the variation of wind speed; and, TP, water temperature (WT), photosynthetically active radiation (PAR), and average wind speed (AWS) could be used as major bloom-driving factors in Taihu Lake generally. This study provides a practical framework for the development of algal bloom early warning schemes for shallow lakes and helps to understand the combined function of complex bloom-driving factors.
... The analytical process is schematically shown in Figure 2. Generalized linear mixed models (GLMMs) (Bolker et al., 2009) were used to detect the key environment drivers (i.e., light, temperature, and nutrient) correlated to phytoplankton biomass (Chl a) during the period of field monitoring. In present study, we used Chl a as a measure of algal biomass according to previous studies in both freshwater and marine ecosystems (Carlson, 1977;Barlow et al., 1993;Schlüter et al., 2000;Chen et al., 2003). Sampling site within the lake was introduced as a random effect in the model to avoid pseudoreplication by introducing correlation among species (Hurlbert, 1984). ...
Article
The occurrence of algal blooms in drinking water sources and recreational water bodies have been increasing and causing severe environmental problems worldwide, particularly when blooms dominated by Microcystis spp. Bloom prediction and early warning mechanisms are becoming increasingly important for preventing harmful algal blooms in freshwater ecosystems. Chlorophyll fluorescence parameters (CFpars) have been widely used to evaluate growth scope and photosynthetic efficiency of phytoplankton. According to our 2-year monthly monitor datasets in Lake Erhai, a simple but convenient method was established to predict Microcystis blooms and algal cell densities based on a CFpar representing maximal photochemical quantum yield of Photosystems II (PSII) of algae. Generalized linear mixed models, used to identify the key factors related to the phytoplankton biomass in Lake Erhai, showed significant correlations between Chl a concentration and both the light attenuation coefficient and water temperature. We fitted seasonal trends of CFpars (F v /F m and F/F m) and algal cell densities into the trigonometric regression to predict their seasonal variations and the autocorrelation function was applied to calculate the time lag between them. We found that the time lag only existed between F v /F m from blue channel and algal cell densities even both F v /F m and F/F m show the significant non-linear dynamics relationships with algal cell densities. The peak values of total algal cell density, cyanobacteria density and Microcystis density followed the foregoing peak value of F v /F m from blue channel with a time lagged around 40 days. Therefore, we could predict the possibilities of Microcystis bloom and estimate the algal cell densities in Lake Erhai ahead of 40 days based on the trends of F v /F m values from blue channel. The results from our study implies that the corresponding critical thresholds between F v /F m value and bloom occurrence, which might give new insight into prediction of cyanobacteria blooms and provide a convenient and efficient way for establishment of early warning of cyanobacteria bloom in eutrophic aquatic ecosystems.
... Previous studies have found that Chl-a size characteristics in lakes, estuaries and other waters varied linearly with the nutrient gradient of the water body (Wang et al. 2012;Li et al. 2013;Soria-P ıriz et al. 2017). In our study, the concentration of total Chl-a increased with eutrophication, which is consistent with results from other waters (Chen et al. 2003;Xu et al. 2010;Wang et al. 2015). The total Chl-a concentration of G3 was significantly higher than that of G1 and G2. ...
Article
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Spatio-temporal patterns in chlorophyll a (Chl-a) from size-fractionated phytoplankton were examined in the Pearl River (PR), China, during 2015 and 2016. The concentration of total Chl-a was a good indicator of spatial patterns, since it increased along a nutrient gradient. A nonmetric multidimensional scaling (NMDS) model showed clearly a spatial pattern in the distribution of size-fractionated Chl-a, dividing the study area into three groups of sampling sites. The three groups represented sites at the West River (G1), the central Pearl River Delta (G2) and the Guangzhou City center (G3). Temporal changes in physicochemical factors among the three groups were not obvious. And the Linear Discriminant Analysis (LDA) model showed G1 and G2 were mostly explained by physical factors, G3 was closely associated with chemical factors. The potential of using size-fractionated Chl-a data as an indicator of water quality was compared using two other size-based methods; the morphological traits of the algae Aulacoseira granulata and using functional groups (FGs) combined with trait-based (algae volume) classifications of benthic diatoms. Our study indicated that size-based methods of phytoplankton research could make a useful contribution to determine spatio-temporal patterns in the studied area, providing greater insight into phytoplankton dynamics and enabling better managements of water quality.
... It is the core of the Yangtze River delta region, and homes to several megacities (e.g., Shanghai, Hangzhou, etc.) in China. Cyanobacteria blooms erupt frequently north of the Taihu Lake (Chen et al., 2003), and lead to serious drinking water crisis in the city of Wuxi in 2007 (Li et al., 2014b;Liu et al., 2012;Zhang et al., 2008). Fast urbanization leads to deterioration of water quality in the rivers that feed into the Taihu Lake. ...
Article
In this study, we focus on the measurement of different nitrogen (N) forms and investigate the spatial-temporal variability of degradation coefficient in river channels. We aim to provide a new approach of deriving in-situ degradation coefficients of different N forms, and highlight factors that determine the spatial-temporal variability of degradation coefficients. Our results are based on a two-year field survey in 34 channels around the Taihu Lake Basin, eastern China. The derived degradation coefficients of different N forms based our newly-developed experimental device are: degradation coefficients of TN, NH4+-N and NO3-N range from 0.006-0.449 d-1, 0.022-1.175 d-1 and -0.096-2.402 d-1, respectively. The degradation coefficients of N show strong dependence on N concentration and water temperature. The seasonal difference of water temperature and N concentration leads to spatial-temporal variability of degradation coefficients. The derived degradation coefficients of N are further verified through one-dimensional water quality model simulations. The degradation coefficient obtained in this study and the influencing factors of its spatial-temporal variability provide invaluable reference for studies in aquatic environment.
... 117 In general, total phosphorus does not directly reflect optical signals in water, but is closely related to other water quality parameters such as phytoplankton, 118 total suspended matter (TSM), turbidity and Secchi disk depth (SDD). 119 Many studies have shown that the concentration of TP in water is positively correlated with the concentration of chl-a, 120 while the depth of the Secchi disc decreases with an increase in the TP concentration. These studies suggested that both the chl-a concentration and Secchi disc depth can be considered as representative parameters for indirect prediction of the TP concentration in water. ...
Article
Phosphorus species are the sum of naturally evolved phosphorus elements with diverse forms of existence and unique properties. The detection and analysis to the optical properties of unknown phosphorus species via direct or indirect strategies offers unique advantages in understanding the growth processes and existence characteristics of various chemicals and microorganisms in water environment. This review highlights recent advances and future trends in total phosphorus detection methods of water, including photoelectric strategies, spectroscopy techniques, and modeling algorithms. These methods effectively explore the dynamic changes of total phosphorus content in complex water environments to reveal important signals in water, which is of great guiding significance for achieving accurate detection of water quality and promoting social development. We also discuss some extended strategies for its measuring and predicting via rational design and cross-combination, which may help to inspire future design of more accurate and intelligent detection models or systems. The strategies based on these types of total phosphorus detection provide a versatile platform for the novel sensors and thereby show great potential in the development of future water quality detection applications.
... Water is an essential component of all organisms worldwide. There are huge amounts of multi-pollutants that entering the water bodies and affecting the ecosystem livings, than including the nature and anthropogenic activities, such as urban runoff, wastewater, industries and agriculture (Chen et al., 2003;Bai et al., 2009;Mohamed., 2012 andSharif et al., 2015). Annually, high concentrations of pollutants adversely affect the life of the fish and the aquatic environment within short and long-term (Massoud et al., 2006). ...
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Scylla olivacea is the most prevalent edible mud crab species in Peninsular Malaysia. However, mud crab can accumulate high contaminations from the surrounding environment resulting in health risk to consumers. Thus, this study was conducted to determine the selected heavy metal accumulative concentrations in Scylla olivacea from Sungai Merbok, Kedah. Adult crab samples were collected every three months for one year (August 2017, November 2017, February 2018 and May 2018) from selected areas in Sungai Merbok, Kedah. The heavy metal accumulation levels in the crab tissues were determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The concentration of heavy metals ranged from 0 to 4.81 ppm for Chromium (Cr), 0 to 0.49 ppm for Manganese (Mn), 0 to 8.3 ppm for Iron (Fe), 0 to 0.33 ppm for Nickle (Ni), 3.2 to 66.07 ppm for Zinc (Zn), 0.33 to 2.55 ppm for Arsenic (As), 0.11 to 0.77 ppm for Lead (Pb), and below the detectable limit for cadmium (Cd). The mean concentration of Cr, Fe and as were 1.52 ± 2.26 ppm, 2.09 ± 4.14 ppm and 1.68 ± 0.95 ppm respectively, slightly higher than the maximum permissible limits set by Joint Food and Agriculture Organization/ World Health Organization Expert Committee on Food Additives (JECFA) and Malaysian Food Regulation. This study indicated that the accumulation of Cr, Fe and as was high in the edible tissues of Scylla olivacea from Sungai Merbok, Kedah, which can trigger adverse effects on consumer’s health. Hence, a detailed investigation needs to be addressed to determine the pollution status in crabs inhabiting along the Sungai Merbok waters.
... The experiment was initiated by adding 7 g Microcystis detritus (labelled and powdered) to the 21 mesocosms on day 0, which is equivalent to 350 µg L −1 chlorophyll-a in the natural water column (unpublished data), while the other mesocosms (3 replicates) acted as controls. The simulated concentration of chlorophyll-a was similar to that in the study of Chen et al. [48] but much lower than the concentration reported by Qin et al. [42] during the cyanobacteria blooming phase in Lake Taihu. The average concentration of Chl-a on day 0 was 25.4 ± 4.2 µg L −1 . ...
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Eutrophication of lakes often results in dominance of cyanobacteria, which may potentially lead to serious blooms and toxic water. However, cyanobacterial detritus may act as an important carbon source for aquatic organisms. Using stable isotope carbon (13 C) as a tracer, we assessed the carbon transfer from cyanobacteria to pelagic and benthic consumers in a 28-day outdoor mesocosm (~130 L) labelling experiment established in Lake Taihu, China, during a Microcystis aeruginosa bloom. The different organisms were labelled differently after addition of the labelled Microcystis detritus to the water. δ 13 C of particulate organic matter and of cladoceran zooplankton peaked earlier than for larger invertebrate consumers. Among the pelagic species, Daphnia similis had the highest ∆δ 13 C, while the two snail species Radix swinhoei and Bellamya aeruginosa had lower but similar ∆δ 13 C. The bivalves showed relatively modest changes in δ 13 C. The δ 13 C of Anodonta woodiana and Unio douglasiae showed a marginal though not significant increase, while a marked increase occurred for Arconaia lanceolate peaking on day 20, and Corbicula fluminea a slight increase peaking on day 9. Our results suggest that carbon from cyanobacteria can be incorporated by pelagic and some benthic consumers and eventually be transferred to higher trophic levels. Cyanobacterial carbon may, therefore, be considered an important carbon source supporting the entire food web during blooms, even if the cyanobacteria are not consumed directly.
... Located in the southeastern part of China, Taihu Lake is the third largest fresh water lake in China. Like most large shallow lakes all over the world and as a typical shallow lake around the middle and lower reaches of the Yangtze River, Taihu Lake is suffering from the threat of eutrophication [1][2][3]. Considering the multi-functionality of Taihu Lake, both as an economic resource (such as supplying drinking water, and providing flood control, irrigation, water transport, and recreation) and as a valuable ecological resource, the water quality issue and consequential algae bloom problem have caused, and are still causing huge losses to this regional industrial and economic center, ever since 1987 [4][5][6][7]. ...
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As the third largest fresh water lake in China, Taihu Lake is suffering from serious eutrophication, where nutrient loading from tributary and surrounding river networks is one of the main contributors. In this study, water age is used to investigate the impacts of tributary discharge and wind influence on nutrient status in Taihu Lake, quantitatively. On the base of sub-basins of upstream catchments and boundary conditions of the lake, multiple inflow tributaries are categorized into three groups. For each group, the water age has been computed accordingly. A well-calibrated and validated three-dimensional Delft3D model is used to investigate both spatial and temporal heterogeneity of water age. Changes in wind direction lead to changes in both the average value and spatial pattern of water age, while the impact of wind speed differs in each tributary group. Water age decreases with higher inflow discharge from tributaries; however, discharge effects are less significant than that of wind. Wind speed decline, such as that induced by climate change, has negative effects on both internal and external nutrient source release, and results in water quality deterioration. Water age is proved to be an effective indicator of water exchange efficiency, which may help decision-makers to carry out integrated water management at a complex basin scale.
... Moreover, the streams assume an imperative job in absorbing municipal and industrial effluent and runoff from agricultural land and the enclose zone in a watershed (Sigua et al., 2003;Chowdhury et al., 2018). As reported by Chen et al. (2003), waterways include the most essential water assets for water system throughout residential water supply, and nowadays, likewise, extraordinary purposes in a watershed, thusly tending to energize certified sterile and natural issues. Therefore, repulsion and controlling of conduit sullying and strong evaluation of water quality are a fundamental stipulation for effective organization. ...
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This study was carried out to determine the preliminary water quality status of stream at UiTM Pahang Branch, Jengka Campus based on the physicochemical and biological parameters. The sampling was conducted on rainy season with seven sampling points that were selected along the stream.
... The water temperature, dissolved oxygen (DO), pH and conductivity were monitored on site using a multiparameter meter (model 6600; Yellow Spring Instruments, USA). Nutrient concentrations were analyzed following Chinese standard methods (see Chen et al. 2003a, Chen et al. 2003b for details). The diel mean temperature (MT) and diel temperature difference (DTD) were calculated based on the monitoring data. ...
Article
Diel temperature fluctuation might promote the dominance of cyanobacteria and result in the advance of bloom onset timing in spring. However, knowledge of how temperature fluctuations impact phytoplankton shift and then favor cyanobacterial growth in spring is limited. In this study, we analyzed photosynthesis and growth responses of phytoplankton species to different temperature fluctuation patterns in the laboratory. We also performed daily monitoring to detect the relationship between phytoplankton groups and diel temperature fluctuations. The results of the laboratory experiments suggested that the photosynthetic performance and growth rate of Microcystis aeruginosa were better adapted to temperature fluctuations than those of Chlorella pyrenoidosa and Cyclotella meneghiniana. Temperature fluctuations slowed the proliferation of Ch. pyrenoidosa and Cy. meneghiniana, while promoting M. aeruginosa. Moreover, the response dynamics of different phytoplankton species to diel temperature fluctuations depended on the mean temperature. The results from the field also indicated that there was a positive relationship between cyanobacterial biomass and diel temperature fluctuations. Our study offers further understanding of the effect of temperature fluctuation on phytoplankton composition shift and the formation of cyanobacterial dominance in spring.
... Rapid development and lack of suitable environmental controls has led to large inputs of pollutants from industry and agricultural waste into Taihu and its tributaries, intensifying water quality deterioration (Wang et al., 2009). Ergo, this previously oligotrophic, diatom-dominated lake (Chen et al., 2003a(Chen et al., , 2003b is now subject to hypereutrophication, and cyanobacterial HABs have occurred every summer in the northern part of the lake since the mid-1980s (Qin et al., 2007). During the summer of 1990, a largescale cyanobacterial HAB occurred in Taihu, causing 116 factories to halt work (Guo, 2007;Xu et al., 2010). ...
Article
Eutrophication or excessive nutrient richness is an impairment of many freshwater ecosystems and a prominent cause of harmful algal blooms. It is generally accepted that nitrogen and phosphorus nutrients are the primary causative factor, however, for systems subject to large anthropogenic perturbation, this may no longer be true, and the role of micronutrients is often overlooked. Here we report a study on Lake Tai (Taihu), a large, spatially diverse and hypereutrophic lake in China. We performed small-scale mesocosm nutrient limitation bioassays using boron, iron, cobalt, copper, molybdenum, nitrogen and phosphorus on phytoplankton communities sampled from different locations in Taihu to test the relative effects of micronutrients on in situ algal assemblages. In addition to commonly-used methods of chemical and biological analysis (including algal phytoplankton counting), we used flow cytometry coupled with data-driven analysis to monitor changes to algal assemblages. We found statistically significant effects of limitation or co-limitation for boron, cobalt, copper and iron. For copper at one location chlorophyll-a was over four times higher for amendment with copper, nitrogen and phosphorous than for the latter two alone. Since copper is often proposed as amendment for the environmental management of harmful algal blooms, this result is significant. We have three primary conclusions: first, the strong effects for Cu that we report here are mutually consistent across chlorophyll-a results, count data, and results determined from a data-driven approach to flow cytometry. Given that we cannot rule out a role for a Fe-Cu homeostatic link in causing these effects, future research into MNs and how they interact with N, P, and other MNs should be pursued to explore new interventions for effective management of HABs. Second, in view of the stimulatory effect that Cu exhibited, management of HABs with Cu as an algal biocide may not always be advisable. Third, our approach to flow cytometry offers data confirming our results from chemical and biological analysis, however also holds promise for future development as a high-throughput tool for use in understanding changes in algal assemblages. The results from this study concur with a small and emerging body of literature suggesting that the potential role of micronutrients in eutrophication requires further consideration in environmental management.
... Meiliang Bay is located in the northwest region of Lake Taihu ( Figure 1) and has been reported to be one of the most eutrophic Bays in the lake . The surface area of the Bay is nearly 100 km 2 , and the average depth is about 1.8 m (Chen, Fan, Teubner, & Dokulil, 2003). Six sampling sites covering Meiliang Bay and the open-water region of the lake were selected. ...
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In this study, algal growth potential tests were performed in water samples collected from six sampling sites in Meiliang Bay, Lake Taihu. The potential release of soluble reactive phosphorus (SRP) by enzymatic hydrolysis of enzymatically hydrolyzable phosphorus (EHP) was simultaneously evaluated. Results show that all studied regions were in highly eutrophic states, with additional nitrogen (N) or phosphorus (P) inputs, inducing negligible further increase in algal growth. EHP in water could be rapidly transformed into SRP, further supporting the proliferation of algal blooms. The shortest EHP mineralization time was calculated as 69 minutes; therefore, limiting specific nutrient inputs alone in extremely eutrophic lakes can have a limited effect on suppressing the proliferation of algal blooms. Methods to establish a suitable environmental fate for excessive nitrogen and phosphorus nutrients may be more effective and provide more significant results. Practitioner points • N and P were no longer serving as the limiting factors in Meiliang Bay. • Enzymatically hydrolysable phosphorus could be hydrolyzed into soluble reactive phosphorus in a very short period during algal blooms. • Both enzymatically hydrolysable phosphorus and soluble reactive phosphorus are required to be curbed in practical eutrophication control.
... Taihu Lake is a typical large shallow lake with a surface area of 2338 km 2 [34]. Taihu Lake is the third-largest freshwater lakes in China, and it serves as an important source of drinking water for surrounding cities, for example, Wuxi and Suzhou. ...
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The influence of dredging season on sediment properties and nutrient fluxes across the sediment–water interface remains unknown. This study collected sediment cores from two sites with different pollution levels in Meiliang Bay, Taihu Lake (China). The samples were used in simulation experiments designed to elucidated the effects of dredging on internal loading in different seasons. The results showed that dredging the upper 30 cm of sediment could effectively reduce the contents of organic matter, total nitrogen, and total phosphorus in the sediments. Total biological activity in the dredged sediment was weaker (p < 0.05) than in the undredged sediment in all seasons for both the Inner Bay and Outer Bay, but the effect of 30-cm dredging on sediment oxygen demand was negligible. Dredging had a significant controlling effect on phosphorus release in both the Inner Bay and Outer Bay, and soluble reactive phosphorus (SRP) fluxes from the dredged cores were generally lower (p < 0.05) than from the undredged cores. In contrast, NH4+-N fluxes from the dredged cores were significantly higher (p < 0.05) than from the undredged cores in all seasons for both sites, this indicates short-term risk of NH4+-N release after dredging, and this risk is greatest in seasons with higher temperatures, especially for the Inner Bay. Dredging had a limited effect on NO2−-N and NO3−-N fluxes at both sites. These results suggest that dredging could be a useful approach for decreasing internal loading in Taihu Lake, and that the seasons with low temperature (non-growing season) are suitable for performing dredging projects.
... The Meiliang Bay and the Zhushan Bay were two other heavily polluted areas of Taihu Lake where TP and Chl-a contents were larger than in other regions, except in the northwestern region. The three regions with high concentrations of TP are mainly due to sediment and river nutrient inputs (Chen et al. 2003, Roy et al. 2011. As these three regions were affected by inflow rivers, the input of a large amount of nutrients and other pollutants led to water pollution. ...
... The preferred method is reducing the amount of nutrients in the water, but this is time-and cost-intensive (Dodds et al. 2008). Efforts in Taihu Lake revealed that lake restoration via nutrient reduction is challenging (Chen et al. 2003;Paerl et al. 2011;Xu et al. 2010). In addition to traditional methods (e.g., artificial mixing (Visser et al. 1996) and copper sulfate treatment (Van Hullebusch et al. 2003)), many other methods have recently been developed to control Microcystis blooms (Fan et al. 2019;Gu et al. 2016;Liu et al. 2016;Matthijs et al. 2012). ...
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Calcium peroxide (CP) has been widely applied in environmental remediation, but few studies have reported its application in controlling Microcystis blooms. To recognize its feasibility for mitigating Microcystis blooms, the properties of CP in terms of hydrogen peroxide (HP) release and phosphate removal were investigated at different CP doses, temperatures, and initial pH values. HP release kinetics followed the Higuchi model. Batch experiments conducted in this study suggested that the HP yield and release rate were positively correlated with the CP dose. Increasing temperature decreased the HP yield but accelerated the HP release rate. The phosphate removal kinetics were well simulated by the pseudo-second-order model. The batch experiments suggested that an increased CP dose enhanced the phosphate removal capacity, but it did not affect the phosphate removal rate. Moreover, increased temperature accelerated both phosphate removal capacity and rate. However, the initial pH of low-buffer-capacity solutions did not notably affect HP release and phosphate removal. According to laboratory experiments, HP released from CP could impair photosynthetic activity, resulting in Microcystis mortality. Furthermore, the reduced phosphate concentration in the solutions suggested that CP could facilitate the control of eutrophication, which directly reduced bloom formation. Hence, our results confirmed CP as a promising algicide for Microcystis bloom control, and it is worthwhile to develop novel methods for bloom mitigation based on CP. Graphic abstract
... The NH 3 -N/NO 3 − -N ratio ranged from 0.12 to 242.78 with an average value of 16.84. A high NH 3 -N/NO 3 − -N ratio meant that pollutants may be discharged from domestic sewage and livestock (Chen et al. 2003). The N/P ratio ranged from 2.28 to 48.55, with an average value of 18.68 indicating nitrogen or phosphorus limitation in different seasons (Xu et al. 2010). ...
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To regulate the water level and minimize the occurrence of water eutrophication in shallow lakes, dams and gates are often constructed in rivers. However, this practice may result in a deterioration of water quality in some estuaries. In the present study, using the correction of Nemerow pollution index (CNPI) and a redundancy analysis (RDA), water samples from different dammed rivers around Taihu Lake were compared to assess the pollution risk and identify the factors responsible for water eutrophication. The average total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC) concentrations, and chemical oxygen demand (CODMn) were 2.45 ± 2.28, 0.08 ± 0.06, 43.01 ± 18.75, and 10.78 ± 4.86 mg L−1, respectively. The CNPI values indicated that approximately 76.47% of the estuarine water was moderately polluted (1 < CNPI < 7.28). A positive correlation was observed between dam construction and nutrient concentrations (e.g., rTN = 0.38, p < 0.05; rTP = 0.89, p < 0.01). Under the effects of dam construction, land use change, estuary shape, and meteorological conditions, there was a clear spatial variation of the TN concentrations. Dams that were closed all year round accelerated the TN accumulation in the water around them. The pollution risk in a trumpet-shaped estuary was higher than that in other regions (t = 2.92, p = 0.02). Endogenous release of pollutants was an important factor that may have a priming effect on algal blooms and should be given more attention. In Wuli Lake, exogenous pollution was the dominant pollutant source. A total of 74.49% of the nitrogen losses with the runoff into the estuarine water in 2018 were derived from urban domestic sewage and constructed land, with the load being 4.40 times higher than in 2000. The RDA results revealed that dam construction was the main factor (43.70%) affecting water quality, while meteorological conditions, land use types, estuary shape, and other factors contributed 56.30%. Scientific regulation and control of dam operation is important to protect the water environment of Taihu Lake.
... Water samples were taken by mixing the surface (0.5 m below the surface), middle, and bottom (0.5m above the bottom) layers of the water. We followed national standard methods (Chen et al., 2003) to measure physical parameters (water depth and Secchi J o u r n a l P r e -p r o o f . Cyanobacteria as a carbon source for zooplankton in eutrophic Lake Taihu, China, measured by 13 C labeling and fatty acid biomarkers. ...
Article
Across the globe, lake ecosystems are exposed to a variety of human disturbances. A notable example is shallow lakes where human-induced eutrophication or water level fluctuation may result in a switch from a clear-water, macrophyte-dominated state to a turbid, phytoplankton-dominated state. Yet, few investigations have described synchronous changes in biotic assemblage composition and food web framework under such a shift between alternative states. We used stable carbon and nitrogen isotopes to test the extent to which switching from macrophyte to phytoplankton dominance in Lake Gucheng, triggered by a water level increase, would alter ecosystem structure and change the basal resources supporting the food web. We found that invertebrates and fish compensated for a reduction of macrophyte and epiphyte resources by deriving more energy from the alternative pelagic energy channel, where benthic invertebrates act as crucial links between primary producers and higher consumers by transporting δ 13 C-depleted pelagic algae to the benthic zone. Although consumers can respond to large shifts in energy allocation and stabilize food web dynamics through their ability to feed across multiple energy pathways, our study suggest that energy subsidies may promote trophic cascades and enhance the stability of the turbid regime.
... However, the persistence of cyanobacteria in Taihu Lake is the result of a combination of nitrogen and phosphorus concentrations, prevailing southeasterly winds in summer, and temperature and precipitation (Chen et al., 2003). These factors are characterized by complexity, nonlinearity, and spatial and temporal heterogeneity . ...
Article
Understanding the sensitivity of the response of chlorophyll (Chla) to nutrients (e.g., nitrogen and phosphorus) concentrations is important for predicting cyanobacterial bloom risk. However, the processes by which nutrients in lake that affect cyanobacterial growth and outbreaks are nonlinear, gradual and spatially and temporally heterogeneous, and the single response thresholds of concentrations between nutrients and the Chla proposed in current studies maybe hardly reflect these characteristics. Due to three decades of rapid regional socio-economic development, the eutrophication in Taihu Lake of China is serious and there are cyanobacterial blooms every year. In this study, we quantified the interaction effects of different forms of nitrogen and phosphorus on Chla concentrations in lake water and sediment pore water. And a refined response threshold range with continuous variation was proposed to characterize the relationship between the Chla concentration and the NH4-N, total nitrogen (TN) and total phosphorus (TP) concentrations. The results showed that TP was the dominant factor influencing the spatial variation of cyanobacteria blooms in most areas of Taihu Lake, followed by TN. TP should therefore be the highest priority for future pollution load reduction in Taihu Lake. The effects of the interactions between the pollution factors were greater than the sum of them individually. NH4-N and dissolved inorganic phosphorus (DIP) are likely to be preferentially consumed by algae for growth and should be the focus of nutrient control efforts in Taihu Lake. For cyanobacterial risk prediction, prevention and control, NH4-N, TN and TP concentrations of 0.06 mg/L, 2.89 mg/L and 0.06 mg/L, respectively, can be used to indicate the beginning of cyanobacterial blooms in Taihu Lake, and concentrations of 0.34 mg/L, 4.67 mg/L and 0.11 mg/L, respectively, can be used as reference thresholds to indicate serious cyanobacterial blooms.
... Then, the chlorophyll a (Chl a) concentration was measured (18.61 μg L −1 ) and considered the low biomass in summer. Chlorophyll a concentration was similar to the annual average in the lake center, and therefore, this was considered as a control set [44]. Meanwhile, harvested algal scum were concentrated through 20-μm bolting silk to partly dewater and remove obvious impurities; then, these samples with 90% moisture were defined as algal organic matter. ...
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Cyanobacterial blooms caused by phytoplankton Microcystis have occurred successively since 1980 in Lake Taihu, China, which has led to difficulty collecting clean drinking water. The effects of cyanobacterial scum-derived dissolved organic matter (DOM) on microbial population variations and of algal-derived filtrate and algal residual exudative organic matter caused by the fraction procedure on nutrient mineralization are unclear. This study revealed the microbial-regulated transformation of DOM from a high-molecular-weight labile to a low-molecular-weight recalcitrant, which was characterized by three obvious stages. The bioavailability of DOM derived from cyanobacterial scum by lake microbes was investigated during 80-d dark degradation. Carbon substrates provided distinct growth strategy links to the free-living bacteria abundance variation, and this process was coupled with the regeneration of different forms of inorganic nutrients. The carryover effects of Microcystis cyanobacteria blooms can exist for a long time. We also found the transformation of different biological availability of DOM derived from two different cyanobacterial DOM fractions, which all coupled with the regeneration of different forms of inorganic nutrients. Our study provides new insights into the microbial degradation of cyanobacterial organic matter using a fractionation procedure, which suggests that the exudate and lysate from degradation products of cyanobacteria biomass have heterogeneous impacts on DOM cycling in aquatic environments.
... For bacterial and cyanobacterial community analyses, water samples (~ 1 500 mL) were further ltered through 0.22-µm pore-size polycarbonate membranes (50 mm, Jinteng®, Tianjin, China), and those membranes were stored at -80 o C until DNA extraction. The physicochemical parameters of the water samples were determined according to described previously [7] . Brie y, a Hydrolab HQ30D multiparameter water quality meter (HACH Company Co., Loveland, the USA) was used in situ to monitor the water temperature (TEMP), oxidation-reduction potential (ORP), pH value, and chlorophyll-a (Chl-a). ...
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Massive nitrogen and phosphorus input into aquatic ecosystems makes algal bloom one of the most concerning problems in China. Algal blooms not only threaten the health and stability of aquatic ecosystems but also influence the microbial community within. However, less is known regarding how algal bloom affects the spatiotemporal variation of the aquatic microbial community, including cyanobacteria and other bacteria. In this study, we used high-throughput sequencing to investigate how the cyanobacterial and bacterial community diversity and composition spatiotemporally vary along with main algal bloom phases in upstream rivers of a eutrophicated water source reservoir. For both cyanobacteria and bacteria, their diversities demonstrated temporal significance amongst different phases in each river, indicating the apparent impact of algal bloom. Dominant cyanobacterial taxa included Cyanobacteriales and Synechococcales , and dominant bacterial taxa comprised Acinetobacter , CL500-29, hgc I clade, Limnohabitans , Flavobacterium , Rhodoluna , Porphyrobacter , Rhodobacter , Pseudomonas , and Rhizobiales , whose relative abundance varied along with the algal bloom, rendering distinct community composition for each river. Non-metric multidimensional scaling analysis additionally indicated significant differences amongst different phases, and the linear discriminant analysis (LDA) with LDA effect size analysis (LEfSe) helped to identify the dominant species (OTUs) in each river at different phases. Canonical correlation analysis (CCA) or redundancy analysis (RDA) revealed distinct correlation patterns of cyanobacterial and bacterial communities with the environmental parameters, which implies their distinct ecological functions. In general, these results demonstrated the significant influence of algal bloom on microbial communities in a eutrophicated water source reservoir basin. These observations also arouse universal demands for strategies conserving the aquatic microbial equilibrium and alleviating algal blooms in reservoirs.
... However, changes in nutrient and Chl-a concentrations in each wetland did not occur simultaneously. Existing studies suggest that Chl-a abundance increases in environments with high nutrient levels [31,32]. In this study, the relationship between the two factors could be easily determined because only a specific period in the seasonal dynamics of nutrients and Chl-a in each wetland was monitored, and most of the wetlands with high nutrients were also rich in Chl-a. ...
Article
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Hydrological characteristics of freshwater ecosystems are powerful determinants of the distribution of biological communities and changes in environmental factors. This study identified relationships between the wetland environment, rotifer community, and hydrological factors for 48 wetlands, to determine their impact on wetland conservation and management. Different hydrological factors produced different wetland environments, which influenced the rotifer community composition. The wetlands with “poor” “in/outflow function” and “shore stability” levels showed high conductivity, turbidity, depth, and concentrations of total nitrogen, total phosphorus, and chlorophyll a. In contrast, the dissolved oxygen levels and velocity were the highest in wetlands with “good” in/outflow function and shore stability variables. The nutritional status of each wetland affected the composition of the rotifer community. Some genera (Keratella, Brachionus, Anuraeopsis, Trichocerca, and Philodina) were found in wetlands with high concentrations of total nitrogen, total phosphorus, and chlorophyll a, and high turbidity and depth. In contrast, Ascomorpha and Ploesoma were found in wetlands with high dissolved oxygen levels and flow velocity. High densities of Lepadella, Lecane, and Testudinella were found in wetlands completely covered by macrophytes. The rotifer community distribution can be used to understand the trophic, current functional, and environmental status of wetlands.
... Taihu Lake is an important water body in Eastern China, as it provides drinking water and supplies various industries, including aquaculture, farming, and fisheries. However, it has attracted much research attention because of its severe pollution (Chen et al. 2003;Qin et al. 2007;Hai et al. 2010). Research has shown that the risks posed by heavy metals in Taihu Lake have increased since 1980 (Yao and Xue 2010). ...
Article
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In this study, nine heavy metals (Cd, Cr, As, Hg, Pb, Cu, Ni, Be, and Sb) in the sediments of 17 typical rivers on the western bank of Taihu Lake were determined. Several statistical methods were applied to analyze the distribution, sources, pollution status, and potential ecological risk of these metals. The mean concentrations of heavy metals in sediments other than Be exceeded their local background values. Geoaccumulation index and potential ecological risk index analyses demonstrated that most sediment samples were contaminated and may pose ecological risks, especially those from the Taihu Lake estuary. In particular, Cd concentrations indicated moderate contamination and potentially serious to severe ecological risk. Principal component, cluster, and correlation analyses demonstrated that Ni, Sb, Cr, and Cu were derived from industrial sources, whereas the other metals had complex origins.
... As an algal and macrophyte pigment involved in algae growth (Chen, Fan, Teubner, & Dokulil, 2003), chlorophyll-a is an important indicator to assess the state of eutrophication of water bodies (Nieto, Garciagonzalo, Fernandez, & Muniz, 2019;Phillips et al., 2008). Various models have been developed to forecast chlorophyll-a and assess eutrophication (Jimenosaez, Senentaparicio, Cecilia, & Perezsanchez, 2020). ...
Article
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Eutrophication and sporadic algal blooms occurring in the tributary bays of the Three Gorges Reservoir in Hubei, China, have become major environmental issues following impoundment. However, predicting eutrophication with traditional methods based on monthly monitoring data remains challenging. In order to explore the potential of data‐driven models in eutrophication prediction and establish reliable prediction data‐driven model based on monthly monitoring data. In this study, two ensemble‐learning models, random forests (RF) and gradient boosted decision trees (GBDT), were used to predict eutrophication in Zhuyi Bay. To address the target, three objectives were solved. First, RF and GBDT used to regress chlorophyll‐a concentrations showed good model fit across two monitoring data sets, with R² values of 0.809 and 0.822 for RF and 0.824 and 0.828 for GBDT. Second, the relative variable importance plots computed by ensemble‐learning models was calculated for selecting monitoring parameters and identify drivers of eutrophication. To improve model fit, it was more important to monitor key parameters of eutrophication (such as water transparency) than to increase sample size. Third, K‐Means++ modelling was used to partition eutrophication data into discrete levels. For three eutrophication levels, the classification accuracies of RF and GBDT were 0.8936 and 0.9064, respectively. When using only two eutrophication levels, accuracies for both models increased to 0.9617. This study suggests that ensemble‐learning models, and in particular GBDT (firstly used in eutrophication), show excellent fitting ability for eutrophication compared with other machine‐learning models and provided reliable eutrophication prediction method based on monthly monitoring data.
... The analytical process is schematically shown in Figure 2. Generalized linear mixed models (GLMMs) (Bolker et al., 2009) were used to detect the key environment drivers (i.e., light, temperature, and nutrient) correlated to phytoplankton biomass (Chl a) during the period of field monitoring. In present study, we used Chl a as a measure of algal biomass according to previous studies in both freshwater and marine ecosystems (Carlson, 1977;Barlow et al., 1993;Schlüter et al., 2000;Chen et al., 2003). Sampling site within the lake was introduced as a random effect in the model to avoid pseudoreplication by introducing correlation among species (Hurlbert, 1984). ...
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The occurrence of algal blooms in drinking water sources and recreational water bodies have been increasing and causing severe environmental problems worldwide, particularly when blooms dominated by Microcystis spp. Bloom prediction and early warning mechanisms are becoming increasingly important for preventing harmful algal blooms in freshwater ecosystems. Chlorophyll fluorescence parameters (CFpars) have been widely used to evaluate growth scope and photosynthetic efficiency of phytoplankton. According to our 2-year monthly monitor datasets in Lake Erhai, a simple but convenient method was established to predict Microcystis blooms and algal cell densities based on a CFpar representing maximal photochemical quantum yield of Photosystems II (PSII) of algae. Generalized linear mixed models, used to identify the key factors related to the phytoplankton biomass in Lake Erhai, showed significant correlations between Chl a concentration and both the light attenuation coefficient and water temperature. We fitted seasonal trends of CFpars (Fv/Fm and ΔF/Fm′) and algal cell densities into the trigonometric regression to predict their seasonal variations and the autocorrelation function was applied to calculate the time lag between them. We found that the time lag only existed between Fv/Fm from blue channel and algal cell densities even both Fv/Fm and ΔF/Fm′ show the significant non-linear dynamics relationships with algal cell densities. The peak values of total algal cell density, cyanobacteria density and Microcystis density followed the foregoing peak value of Fv/Fm from blue channel with a time lagged around 40 days. Therefore, we could predict the possibilities of Microcystis bloom and estimate the algal cell densities in Lake Erhai ahead of 40 days based on the trends of Fv/Fm values from blue channel. The results from our study implies that the corresponding critical thresholds between Fv/Fm value and bloom occurrence, which might give new insight into prediction of cyanobacteria blooms and provide a convenient and efficient way for establishment of early warning of cyanobacteria bloom in eutrophic aquatic ecosystems.
... The sampling site is located to the north of Taihu Lake in the inner bay of Meiliang Bay (Fig. S1), which is the most eutrophic part of the lake, with an area of 129 km 2 and an average depth of 1.9 m (Chen et al., 2003). The site-specific environment is described in our previous study (Wen et al., 2020). ...
Article
Internal nitrogen (N) loading of lakes is commonly controlled by sediment dredging, although its comprehensive effect on internal N loading remains unclear. Herein, we examined the long-term effects of sediment dredging on internal N loading from a new perspective on the N budget at the sediment-water interface (SWI) through a simulation of field dredging performed by incubating intact sediment cores from a shallow eutrophic lake (Lake Taihu). We further evaluated the role of settling particles (SP) in the recovery of N cycle processes after dredging and its potential impact on the N budget. Our results demonstrated that dredging could help reduce organic matter and total N in sediments; improve the redox environment of the SWI; slow down N mineralization, N fixation, denitrification, and anaerobic ammonia oxidation (anammox); and alter the N budget at the SWI and the contribution of various N cycle processes. However, the input of SP enriched in fresh organic matter and N could accelerate the recovery of N cycle processes at the SWI, reducing the variation in the N budget and the contribution of each N cycle process caused by dredging. Dredging significantly reduced the N flux at the SWI, which was evident from the reduction of inorganic N release flux and N removal through denitrification and anammox. Therefore, sediment dredging has its advantages and disadvantages in managing internal N loading in lakes. To maintain a long-term control on the release of internal N through sediment dredging, measures should be taken based on the in-lake and watershed to inhibit the inflow and settlement of particulate matter.
... The sampling site is located to the north of Taihu Lake in the inner bay of Meiliang Bay (Fig. S1), which is the most eutrophic part of the lake, with an area of 129 km 2 and an average depth of 1.9 m (Chen et al., 2003). The site-specific environment is described in our previous study (Wen et al., 2020). ...
Article
Understanding the history of microcystins (MCs) pollution in large lakes can help inform future lake management. We collected sediment cores from Lake Taihu to: investigate the long-term record of MCs (MC-LR, MC-YR, and MC-RR), explore the main environmental drivers of MCs, and assess their public health and ecological risks. Results showed that MCs content in all cores increased over time. The core from north Taihu had the highest MC concentrations, with an average total MCs (sum of MC-LR, MC-YR, and MC-RR = TMCs) content of (74.31±328.55) ng/g. The core from eastern Taihu showed the lowest average TMCs content of (2.91±3.95) ng/g. PCA showed that sediment MCs at the three sites were positively correlated with sediment chlorophyll-a. MC-LR and MC-YR in northern and western Taihu negatively correlated with both the sediment total organic carbon/sediment total nitrogen ratio (STOC/STN) and water nitrate (NO3⁻-N) concentration, but three MC congeners at eastern Taihu showed positive correlations with water orthophosphate (PO4³⁻-P), NO3⁻-N, and STOC/STN. Generalized additive model analysis at each site revealed that NO3⁻-N was the main TMCs driver in northern and western Taihu where phytoplankton dominated, whereas PO4³⁻-P was the main TMCs driver in eastern Taihu where macrophytes dominated. At the whole lake scale, total phosphorus (TP) and PO4³⁻-P were the most important environmental drivers influencing MCs; TP explained 47.4%, 44.2%, and 47.6% while orthophosphate explained 34.8%, 31.2%, and 34.7% of the deviance on TMCs, MC-LR, and MC-YR, respectively. NO3⁻-N also showed a strong effect on MCs variation, especially on MC-YR. Risk assessment showed that both ecological and public health risk has increased in recent years. We conclude that while control of phosphorus and nitrogen input should be a major focus for future lake management, lake zone-specific management strategies may also be important.
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The cover image is based on the Original Article A trophic cascade triggers blooms of Asterionella formosa in subtropical eutrophic Lake Taihu, China, by Xia Liu et al. https://doi.org/10.1111/fwb.13986.
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Abstract Cyanobacterial blooms, which not only threaten the health and stability of aquatic ecosystems but also influence the microbial community within, emerges as one of the most concerning problems in China. However, how cyanobacterial blooms affect the spatiotemporal variation of aquatic microbial communities remains relatively unclear. In this study, we used high-throughput sequencing to investigate how the cyanobacterial and bacterial community spatiotemporally vary along with main cyanobacterial bloom phases in upstream rivers of a eutrophicated water source reservoir. Both cyanobacterial and bacterial diversities in each river were significantly lower (P
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1. The importance of trophic interactions for determining the distributions, abundances,and taxonomic compositions of organisms in ecosystems has long been studied and debated. Here we test the effect of a trophic cascade on diatom (Asterionella formosa) blooms in subtropical, eutrophic Lake Taihu, China. 2. A long-term data series (2005–2015) on planktivorous fish, zooplankton and diatoms has been analysed. Structural equation modelling is used to test our hypotheses about the influences of top-down and bottom-up forces on A. formosa. 3. Since 2009, a spring bloom of A. formosa has occurred in the lake, coinciding with reduction of Daphnia galeata biomass and of total cladoceran biomass following a marked increase in the stock of planktivorous fish (bighead carp and silver carp). Light, phosphorus (total and soluble reactive phosphate) and silica did not mact as limiting factors for the growth of A. formosa. 4. Structural equation modelling analysis showed that top-down effects of cladoceran on A. formosa biomass were more important than bottom-up effect (wind speed and soluble reactive phosphate). Although A. formosa was negatively correlated with total nitrogen, total with other inorganic nitrogen (NO3 and NH4) did not restrict the proliferation of diatom blooms after 2007. These results suggested that the substantial reduction of the Daphnia population caused a diatom bloom through a trophic cascade by planktivorous fish. 5. Our study provides new insight into the effects of trophic interactions on diatom bloom formation in natural freshwater ecosystems.
Article
Our study assessed the actual water situation in the estuarine area of Lake Wuli, Meiliang Bay, Lake Taihu, China, based on eutrophication levels and status of water quality using the trophic level index (TLI) and water quality index (WQI) methods. In the wet (August 2017) and dry (March 2018) seasons, 22 estuarine areas were tested at 69 sampling sites, which included lake and rivers. Five parameters—chlorophyll a (Chl-a), total phosphorus (TP), total nitrogen (TN), Secchi disk (SD) and permanganate index (CODMn)—were measured to calculate the TLI, and 15 parameters—temperature (T), pH, electrical conductivity (EC), dissolved oxygen (DO), total dissolved solids (TDS), TN, TP, ammonium (NH4-N), nitrate (NO3-N), nitrite (NO2-N), CODMn, calcium (Ca²⁺), magnesium (Mg²⁺), chloride (Cl⁻) and phosphate (PO4-P)—were measured to calculate the WQI. The average TLI and WQI values in the wet season were 61.69 and 60.70, respectively, and the eutrophication level and water quality status were worse than that in the dry season (TLI: 57.40, WQI: 65.74). Significant differences were observed between three parts of Lake Wuli (West, Middle and East). Regardless of wet or dry season, East Wuli had worse eutrophication levels and water quality status than the other parts, whereas West Wuli showed less severe levels. DO, TN and CODMn used in the minimum WQI (WQImin) were the most effective parameters in our study. WQImin had stricter standards than WQI when analyzing water quality in the estuarine area of Wulihu. Factor analysis from principal component analysis (PCA) indicated that N might be the main factor affecting water quality of the most eastern sites in the wet season, and P may be the main factor in the dry season. Our results provide a valuable contribution to inform decision-making for the management of water environments by providing the actual water situation of the estuarine area of Lake Wuli.
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In eutrophic lakes, the decay of settled algal biomass generates organic carbon and consumes oxygen, favoring sediment nitrogen loss via denitrification. However, persistent winds can cause algae to accumulate into dense mats, with uncertain impacts on sediment nitrogen removal. In this study, we investigated the effects of algal accumulation on sediment nitrogen removal in a shallow and eutrophic Chinese lake, Taihu. We found that experimental treatments of increased algal accumulation were associated with decreased sediment nitrogen losses, indicating the potential for a break in coupled nitrification-denitrification. Likewise, field measurements indicated similar decreases in sediment nitrogen losses when algal accumulation occurred. It is possibly caused by the decay of excess algal biomass, which likely depleted dissolved oxygen, and could have inhibited nitrification and thereby denitrification in sediments. We estimate that if such algal accumulations occurred over 20% or 10% of lake area in Taihu, sediment nitrogen removal rates decreased from 835.6 to 167.2 and 77.2 μmol N m-2h-1, respectively, during algal accumulation period. While nitrogen removal may recover later, the apparent nitrogen removal decrease may create a window for algal proliferation and intensification. This study advances our knowledge on the impacts of algal blooms on nitrogen removal in shallow eutrophic lakes.
Chapter
Large-scale commercialization of the Haber-Bosch (HB) process is resulting in intensification of nitrogen (N) fertilizer use worldwide. Globally N fertilizer use is far outpacing that of phosphorus (P) fertilizer. Much of the increase in N fertilizers is also now in the form of urea, a reduced form of N. Incorporation of these fertilizers into agricultural products is inefficient leading to significant environmental pollution and aquatic eutrophication. Of particular concern is the increased occurrence of harmful algal blooms (HABs) in waters receiving nutrient enriched runoff. Many phytoplankton causing HABs have physiological adaptive strategies that make them favoured under conditions of elevated N:P and supply of chemically reduced N (ammonium, urea). We propose that the HB-HAB link is a function of (1) the inefficiency of incorporation of N fertilizers in the food supply chain, the leakiness of the N cycle from crop to table, and the fate of lost N relative to P to the environment; and (2) adaptive physiology of many harmful algae to thrive in environments in which there is excess N relative to classic nutrient stoichiometric proportions and where chemically reduced forms of N dominate. The rate of HAB expansion is particularly pronounced in China where N fertilizer use has escalated very rapidly, where soil retention is declining, and where blooms have had large economic and ecological impacts. There, in addition to increased use of urea and high N:P based fertilizers overall, escalating aquaculture production adds to the availability of reduced forms of N, as does atmospheric deposition of ammonia. Harmful algal blooms in both freshwaters and marginal seas in China are highly related to these overall changing N loads and ratios. Without more aggressive N control the future outlook in terms of HABs is likely to include more events, more often, and they may also become more toxic.
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Algal blooms (ABs) can affect the migration of phosphorus (P) among sediments, interstitial water and overlying water. It is important to analyze the characteristics of P and their interactions in the three media during ABs. A 5-month field study (June to October in 2016) was conducted in Zhushan Bay of Lake Taihu. P fractions, P adsorption characteristics and P diffusion fluxes at the sediment-water interface (SWI) were investigated. During the outbreak period of ABs from June to August, labile P concentrations in the sediment measured by diffusive gradients in thin films (DGT-labile P) and its diffusion fluxes across the SWI increased significantly. The equilibrium P concentration (EPC0) of the sediment was higher than the PO4³⁻-P concentration in the overlying water. During the period of decline of ABs from September to October, the concentrations and diffusion fluxes of DGT-labile P sharply decreased. However, the sediment total P (TP), overlying water TP, total dissolved P (TDP) and PO4³⁻-P concentrations increased. These results show that the ability of sediment solids to supplement interstitial water labile P was significantly enhanced by the outbreak of ABs. Labile P was then intensively released into the overlying water by interstitial water. Degraded algae became a crucial P source during the period of decline of ABs. P from the degraded algae was re-released to the sediment and overlying water. The observed DGT-labile P and DGT-labile Fe coupling in June, September and October confirmed the Fe redox-driven P release mechanism in sediment during these periods. The decoupling of DGT-labile P and DGT-labile Fe was observed in July and August and was probably caused by algal decomposition, labile organic P degradation and/or sulfate reduction in sediment stimulated by the ABs outbreak.
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The Chinese government has made a strong effort to solve pollution problems in the Taihu Basin, and scholars have also paid close attention to these issues. Based on 2094 valid studies on the Taihu Basin obtained from the Web of Science (WoS) core database from 1998 to 2019, this study conducted a systematic review of research and development trends using bibliometric methods. The results reveal that academic achievement has increased rapidly in recent years, especially after a severe blue-green algae bloom event in Taihu Lake in 2007. Taihu Basin related studies are becoming more interdisciplinary in nature with an integration of knowledge. Chinese Academies of Sciences and universities in Eastern China play key roles in academic output. Although hotspots of environmental topics vary at different time periods, the eutrophication issue at Taihu Lake has long been a focus. Eutrophication studies on Taihu Lake have evolved from “general causes of eutrophication” to “more detailed causes of eutrophication” to “long-term monitoring and management of water quality” to “risk assessment”. Future trends in Taihu Basin research should continue to emphasize risk assessment and long-term management. This bibliometric review presents a comprehensive analysis of Taihu Lake-related research, which can provide important insights into the potential direction for future studies.
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Preserving a still high natural ecological value, the Lower Danube River System (LDRS) is a good example of a large ecological system in a critical unstable balance. The biodiversity changes along LDRS are discussed based on existing data from last four decades and on results of own research from the last seventeen years. The general methodological framework of data processing and interpretation is system identification. The paper addresses the following issues: structural heterogeneity of LDRS, diversity of local landscapes, ecosystems diversity in abiotic (hydrogeomorphic unit) and biotic (community) terms, species diversity of selected trophodynamic modules, functional diversity, and finally diversity of goods and services provided by LDRS as well as ethno-cultural diversity. Data analysis at landscape, ecosystem and species level has pointed out a large spectrum of biodiversity changes generated by local (within LDRS) and regional (catchment scale) social-economic factors. These changes had as consequence the reduction of the offer of goods and services provided to local and regional social-economic systems, which in turn generated changes in their management strategy. Sustainable management supposes the reduction of the human pressure at local and catchment level, the equitable sharing of benefits, as well as the mitigation, rehabilitation and restoration of altered structures and functions. This kind of management approaches needs appropriate scientific support and an unitary ecological network to integrate local and national efforts in the regional and European programs. An appropriate information system based on data and knowledge provided by long-term research and integrated monitoring programmes is the backbone of a decision support system for LDRS redesign and management in accordance with the principles of sustainable socio-economic development.
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Our concept of the 'balance of TN : TP : SRSi-ratios' attempts to determine whether the seasonal succession of phytoplankton communities is influenced by or res-ponds to nutrient stoichiometry. Because the molar average of TN : TP : SRSi = 20 : 1 : 17 for 118 measurements (7 lakes, 3 inflows, all seasons) was close to the marine optimum stoichiometric ratio, we used the ratio TN : TP : SRSi = 16 : 1 : 17 as a refer-ence point for ecological stoichiometry. Triangular diagrams of TN : TP : SRSi ratios scaled in physiological proportions of 16 : 1 : 17 were used to identify seasonal fluctua-tion patterns of major phytoplankton nutrients. In lakes with 'balanced nutrient ratios' TN : TP : SRSi ratios vary evenly around the stoichiometric optimum of 16 : 1 : 17 within a year. Lakes with balanced nutrient ratios, however, were more the exception than the rule and only occurred in 2 of 7 lakes studied. Lakes with constant concentrations of one nutrient element in relation to those of the other two were common. Unbalanced nutrient ratios were associated with relatively constant concentrations of either SRSi, or TN or TP. The relative change in availability of soluble reactive silica was more af-fected by differences in lake morphometry than that of TN or TP. Ratios of TN : TP : SRSi have the advantage of synoptically presenting the relative nutrient avail-ability for both diatoms and non-siliceous algae in phytoplankton communities. Shifts within the tripartite ratio correspond to successive substitution of phytoplankton groups, e.g. from diatoms to cyanobacteria.
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Mean zooplankter weight (W Zp) and the ratio of zooplankton to phytoplankton biomass (BZp/BPhyt) reflect adequately the trophic state of a body of water; they decrease with increasing trophy. In the moderately trophic Lake Peipsi, W Zp is 4.4g and in the strongly eutrophic Lake Vrtsjrv, 2.7g, while B Zp/B Phyt is 0.49 and 0.13, respectively. Mean cladoceran weight is 28 and 10g, mean copepod weight 10 and 6.7g, mean rotifer weight 0.9 and 0.6g, respectively. Interestingly, in winter, WZp and BZp/BPhyt are also significantly larger for L.Peipsi compared with L. Vrtsjrv: W Zp 1.2 and 0.7g, BZp/BPhyt 0.4 and 0.1, respectively. This difference is caused by E.gracilis (Sars) and Cyclops kolensis Lilljeborg which are still living in L.Peipsi, but have disappeared from L. Vrtsjrv. From the 1960s up to the present W Zp has decreased appreciably. Correlation analysis showed the weak relationship between the studied characteristics and nutrient content, while the relationship between mean weight and water nutrient content is more pronounced in the strongly eutrophic L. Vrtsjrv than in L.Peipsi. There was a positive correlation between W Zp and the biomass of the genus Daphnia in L. Peipsi, while in L. Vrtsjrv W Zp was positively correlated with the biomass of Chydorus sphaericus. In L.Vrtsjrv, W Zp was negatively correlated with the abundance and biomass of rotifers, as well as with the abundance of zooplankton comprised primarily of rotifers. A clear difference in both characteristics was revealed in the comparison of Lakes Peipsi and Vrtsjrv with ANOVA (p-level 0.002–W Zp and B Zp/B Phyt characterize both the trophy and the whole ecosystem of a body of water. Indirectly, they characterize dominating groups in phytoplankton and zooplankton, feeding relationships between phyto- and zooplankton and between zooplankton and fish, as well as the pressure of fish on zooplankton. The W Zp and B Zp/B Phyt can be used as marker characteristics in the evaluation of the trophy of a body of water and its ecosystem and, particularly, in permanent monitoring of bodies of water.
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Within the Danube River delta's lakes the Oligochaeta communities comprise between 7.9% and 36.2% of the total biomass of benthic fauna. Their importance in energy flow at the ecosystem level changed in relation to fast trophic transition of all shallow lakes to the hypertrophic state. The parameters of the energy budget of the dominant populations and the potential production of benthivorous fish species assessed during 1976–1994 interval support this conclusion. P/B ratio, K 1 and K 2 coefficients assessed for both the 1976–1980 and 1991–1994 intervals revealed different functional patterns of response of Potamothrix hammoniensis (Michaelsen, 1901) and Limnodrilus hoffmeisteri (Claparede, 1862) to varying trophic conditions. Changes in communities structure, size of the constituent populations and their age distribution, as well as the quantity and quality of food supply and level of hypoxia at the sediment/water interface were the main factors that affected the role of these populations as energy carrier from the huge energy pool represented by sedimented organic carbon to benthivorous fish species.
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Lake Taihu is in the meso-eutrophication stage, following the development of local industries, agriculture and an increase in the living standard of people. The main eutrophication part of this lake is Meiliang Bay. The COD was 4.63 mg/l (1993), T-N and T-P were 3.93 mg/l and 0.107 mg/l respectively in 1995. The dominant phytoplankton species are Microcystis, Anabaena, Melosira, Cyclotella and Cryptomonas. In summer, Microcystis spp. occupies 85% of algae biomass and forms a water bloom. This causes trouble for the people living around the lake, especially for the drinking water of Wuxi city. This paper introduces several methodological strategies of eutrophication control. These are to cut the exogenic loading, to suck and dredge the sediments, to collect and treat the harvested water bloom, to recover the aquatic plants in suitable places, and to properly culture the fishes. After that, Lake Taihu will be restored.
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In large and deep Lake Constance, total phosphorus concentrations during winter mixing (TPmix) were reduced by a factor of three (> 80 to ca. 30 ;g/l) from about 1979 to 1993. This resulted in an amplification and lengthening of phosphorus (P) depleted conditions throughout the season and water column. The response of the phytoplankton community depended on the time of the year and the level of aggregation under consideration. Total phytoplankton biomass quantified in terms of algal biovolume or chlorophyll concentrations decreased in summer, i. e. during the period of most severe P depletion, to about half of the original values during the first decade. In subsequent years, summer chlorophyll concentrations remained at this lower level whereas total biovolume increased again despite further decreases of TPmix. Average algal biomass in spring and autumn fluctuated without a distinct relationship to TPmix although P was depleted below the detection level during parts of these time intervals in recent years. This moderate response by community level parameters is attributed to changes in the temporal and internal organization of the algal community. Population dynamics and the relative importance of various taxonomical and functional groups such as mixotrophs and less-edible forms clearly changed in spring and summer. The renewed increase in algal biovolume in summer is mostly caused by species which are able to exploit additional P sources. For example, Dinobryon is an evidently mixotrophic organism which ingests P rich bacteria, its strongest competitors for soluble reactive phosphorus (SRP). Ceratium hirundinella might be migrating between the euphotic zone and deeper, P enriched water layers under suitable hydrodynamical conditions. At the level of genera and higher taxa, consistent trends in respect to TPmix were observed in spring and summer mostly indicating an adaptation to more oligotrophic conditions. In contrast, the functional group of well-edible algae showed little interannual variability and did not change in absolute numbers. This suggests that, in contrast to less-edible algae, well-edible forms are more strongly under top-down than bottom-up control, and that the nutritional basis of most herbivores changed less than it would be expected from the decrease in total algal biomass.
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Comparative analysis of the biodiversity changes along the lower Danube riverine-riparian system is based on published data of the last four decades and specific studies during the last 15 yr. Structural changes in the Romanian Danube reach of 986 km upstream the Danube Delta, both in the aquatic environment within the river channel and in the adjacent aquatic, wetland and terrestrial systems, are reflected in the ecological structures at different levels: 1) percent distribution of different ecosystem types in the landscape structure, including functional connections, 2) changes in communities complexity, and 3) changes in the state of some plant and animal species in transition zones. Origins and impact of these anthropogenic changes on the dynamics and productivity of fish and wildlife are also considered. An attempt is made to argue, at least partially, the decline of anadromous fish species, like sturgeons as a result of these changes such as dams and river margin dikes. Needs for protection and rehabilitation measures for the Danube River and Floodplain biodiversity are discussed in a holistic manner. The role of floodplain wetlands as feeding, nesting and spawning habitats and as a source of biological components of the Danube River and Delta, is emphasized in the background of the continuous decline of biodiversity and productivity decline of fish and other species.
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China contains 28 of the world's large lakes (> 500 km2). Information on these lakes is considerably limited. This paper describes in greater detail the origin, location, and the physical, chemical, and biological characteristics of the Chinese lakes and discusses the prevalant lake fish management methods in China. Elements which have influenced changes in Chinese large lakes are discussed. Climatic condition and tectonic uplift have strongly influenced the large lakes in the Tibet-Qinghai-Sinkiang region while sediment loading and human impacts continue to be the major concern for the large lakes in the Pacific basin.
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The objective of this study is to summarise limnological effects of cultural eutrophication in some Chinese lakes. Detailed data are shown for Lake Tai Hu as an example for a very large shallow lake affected by anthropogenic impacts. Urban and industrial waste water discharged to the lake result in high nutrient concentrations, large algal blooms dominated by cyanobacteria, mainly species of Microcystis and strong horizontal gradients. Algal growth in this lake is mainly ligh and/or phosphorus limited. This situation is typical for most of the lakes included in this review although some of the large deep lakes seem to be nitrogen deficient. In some cases toxicological effects may be the reason for observed discrepancies. Lakes are of vital importance for populations in China as drinking water and nutritional resources. To prevent water shortage because of conflicting usage, anticipation, control and management of water pollution is urgently needed. Moreover, efforts must be taken to rehabilitate deteriorated freshwater ecosystems.
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Nutrient, phytoplankton and zooplankton dynamics have been monitored intensively at Loch Leven for 34 years. The data collected reveal a decline in phosphorus concentrations, following major reductions in external nutrient loading, and large changes in its seasonal availability, particularly in recent years. More striking has been an increasing trend in water temperatures, annual means increasing by about 1 C over the 34 years, with even greater increases observed for winter and spring periods. In response to these changes, there has been a general pattern of decline in measures of phytoplankton biomass (chlorophylla concentrations). Closer inspection reveals that the detailed response is, however, not so consistent with the environmental trends. A significant decline in chlorophylla concentrations occurred early on in the time series, before major reductions in nutrient availability. Correlation analysis revealed that this decline was associated with the re-appearance of Daphnia grazers. Further declines are only apparent in very recent years; correlation analysis and comparison of trends suggest that these were associated with the observed decline in nutrient concentrations. There was little correlation and no consistent relationship between annual measures of chlorophylla and water temperature, but winter mean values did show a consistent positive relationship. Spring Daphnia densities showed an even stronger, and significant, positive relationship with spring water temperatures. It is clear from this that the scale of climate change predicted in the future will significantly alter the functioning of shallow lakes and seasonal patterns in water quality. This is a particular concern in Europe with the implementation of the EC Water Framework Directive, as if the net effect of global warming on annual measures of water quality is negative, the principle aim of `good status' in all surface waters by 2016 will become even more difficult to achieve.
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The dynamics are presented of the main primary producers in seven representative Danube Delta lakes. Generally, the primary productivity developed from the macrophyte-epiphyte complex towards the phytoplankton. Species changes occurred in the two main compartments with increasing relative abundance of colonial blue-green algae in the phytoplankton and in submerged macrophytes of species with a vertical growth strategy. These changes are linked to accelerated eutrophication of the lakes, with increased phosphorus loading and a reduction in N:P ratio.
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Shallow polymictic lakes are very abundant in many regions of the world, they are more numerous than deep lakes and are of great importance especially in densely populated areas even when small. Their ecology differs from stratified lakes in many ways. During the eutrophication process, lakes may change from a clear water, macrophyte dominated state to an algal dominated state, a process known as the concept of `alternative stable equilibria'. The usefulness of this concept as a descriptor for the eutrophication process and as the basis for rehabilitation of lakes is tested on long-term data from two contrasting case study sites using a novel multivariate bubble-plot technique. In one case the concept proved to be useful and successful while it could not be applied to a large shallow turbid lake. The equilibrium concept is then generalised using further examples. Shallow lakes which are either macrophyte dominated or light limited because of high inorganic background turbidity have ratios of total phosphorus (TP) to algal Chlorophyll-a at or below 3:1. Deep oligotrophic or algal dominated lakes in contrast exhibit ratios between 3:1 and 1:1. Alternative stable equilibria of macrophyte or algal domination can occur within the same water-body at various locations, at different times of the year or during trophic development.
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An analysis of data from 49 shallow lakes showed, that the parameters of empirical models between phosphorus loading and concentration in the lake (e.g. Vollenweider type of relations) differ significantly for lakes without or with a reduced external loading. For lakes without a reduction of the external loading the summer phosphorus concentration is determined by the external phosphorus loading and the hydraulic loading. For these lakes the ‘classical’ models suffice; deviations between calculations and measurements are partly due to errors made in the determination of the loading. In contrast, for lakes where the external loading was reduced, the measured internal loading explains most of the variation in the summer lake concentration. The external loading is of minor importance and the ‘classical’ models cannot be applied. The internal loading measured before reduction of the external loading is not useful in predicting the concentration afterwards. Instead of the internal loading, the sediment composition can be used. The advantage of using sediment composition is that these variables are easier to determine and vary less in time. The most promising variable is the ratio between total P and total Fe in the sediment.
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The concept of limiting nutrients is a cornerstone of theories concerning the control of production, structure and dynamics of freshwater and marine plankton. The current dogma is that nitrogen is limiting in most marine environments while freshwater ecosystems are mostly phosphorus-limited, although evidence of phytoplankton limitation by either N or P has been found in both environments.However, the same considerations apply to the availability of phosphorus in freshwater as to nitrogen in oceans. In resource-limited environments the plankton dynamics depend mostly on the internal mechanisms which act to recycle the limiting nutrient many times over within the surface waters. As the overall productivity increases, this dependence on nutrient regeneration decreases.The relationship between the stock of limiting nutrient, rates of supply and plankton dynamics must therefore be seen in the light of the processes operating within the entire food chain over quite different time scales. There is strong evidence that process-rates are mostly size-dependent and that food web interactions at the microbial level (picophytoplankton, bacteria, microheterotrophs) strongly effect the production of carbon and the regeneration of nutrients in the pelagic zone.
Article
The seasonality of nutrients and chlorophyll a in Lake Erken (Sweden) was monitored during 1994 to 2001 (warm period) and compared to the time period 1975 to 1979 (cold period). The coupling to weather conditions and potentially influencing factors, such as water temperature, light conditions, and stratification were evaluated. During the warm period the ice cover period was considerably shorter and the ice breakup about one month earlier than in the cold period. The decrease in thickness and duration of snow cover resulted in considerably better light conditions during winter, favouring phytoplankton growth under the ice. The nitrate concentrations were much lower in late winter during the warm period. There were elevated phosphate and ammonium concentrations in the hypolimnion during August. Significantly higher phosphate and chlorophyll a levels were noticed in autumn during the warm period, compared to the cold period.
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