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Map of the Garonne River basin indicating the position of the sampling stations and the location of the major cities.
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Dissolved nutrient and chlorophyll-a concentrations were monitored on 17 occasions and at 16 sites in the Garonne River (France). Concentrations of dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) increased about threefold downstream of the urban area of Toulouse. Chlorophyll-a concentrations increased concomitantly with DIN...
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... a catchment of 57,000 km 2 , the Garonne River basin is the third largest river basin in France after the Rhone and Seine (Fig. 1). The Garonne River is a shal- low river (generally <2 m) and has a high flow velocity, even in its lower reaches (~0.4 m s -1 ). This high flow velocity prevents planktonic algae to attain a high bio- mass (Améziane et al. 2003). Due to an important frac- tion of hard substrates in the river bed, turbidity of the Garonne River is low ...
Context 2
... INTRODUCTION During the 20 th Century, N and P inputs into rivers around the world have increased dramatically as a result of intensive agriculture and industrial and municipal waste water discharges (Meybeck 1982). Increased concentrations of N and P are often accompanied by an increase in algal biomass or eutrophication. In rivers, the effects of eutrophication may be moderate because phytoplankton development is limited by short water retention times rather than inorganic nutrient concentrations. Nevertheless, many studies in different river basins have demonstrated a positive relation between N and P enrichment and algal biomass (e.g., Biggs & Close 1989; Basu & Pick 1996; Van Nieuwenhuyse & Jones 1996; Lohman et al . 1999). N and P have received much attention in eutrophication studies because they are essential nutrients for all phytoplankton groups and because their concentrations are strongly influenced by human activities. Si is only required by a few algal groups and Si concentrations are not directly influenced by human activities. Therefore, Si has historically received much less attention. The predominant source of dissolved silica (DSi) is the natural weathering of silicate minerals (Tréguer et al . 1995). The only significant human source of Si consists of metasilicates, of which small amounts are used in deter- gents and fertiliser. Nevertheless, recent estimates have shown that anthropogenic Si inputs may amount to 6% of total Si inputs in a river basin (Sferratore et al . 2006). The most important algal group that requires Si are the diatoms, who need large amounts of Si for the construc- tion of their cell wall. Compared to other algal groups, diatoms are adapted to low-light conditions (because of the pigment fucoxanthin) and to a turbulent water column (because of their high cell density). Therefore, diatoms are often a dominant component of the phytoplankton of the turbulent and turbid lower reaches of rivers (e.g., Garnier et al . 1995). They are also important primary producers in the shallower, upper reaches of rivers, where they are a dominant component of the phytobenthos. Because of the importance of diatoms in river ecosystems, primary producers have a potentially strong influence on Si concentrations. Due to anthropogenic inputs of N and P, Si:N and Si:P ratio's have decreased in many rivers worldwide (Turner et al . 2003; Billen & Garnier 2007). When Si:N and Si:P ratio's are low, diatom production becomes limited by Si and total consumption of Si increases (Conley et al . 1993). Diatoms convert dissolved Si to biogenic Si or opal, which has a low remineralisation rate and easily accumulates in sediments. Therefore, Si consumption in rivers by diatoms may result in an increased retention of Si and a reduced export of Si to coastal ecosystems. Lower Si inputs in coastal waters have been shown to have an adverse effect on diatom production and to favour nuisance algae over diatoms (Humborg et al . 1997; Ittekkot et al . 2000; Cugier et al . 2005). Most studies on Si retention in river basins have focused on retention of Si in lakes or reservoirs in river basins (e.g., Conley et al . 2000). These studies have shown that production of diatoms in reservoirs or lakes and subsequent burial of biogenic Si in sediments results in reduced dissolved Si transport to coastal sys- tems (e.g., Conley et al . 2000; Humborg et al . 2000), although some of these claims have been refuted by more recent studies (Teodoru et al. 2006). Few studies have investigated the consequences of eutrophication on Si consumption in the river itself. Using an ecosystem model, Billen et al . (2001) demonstrated that increased anthropogenic N and P inputs resulted in increased retention of Si in the Seine River basin over the last 50 years. Here we present monitoring data from the Garonne River that suggest that N and P inputs from the city of Toulouse result in increased consumption of dissolved Si by algae. 2. METHODS With a catchment of 57,000 km 2 , the Garonne River basin is the third largest river basin in France after the Rhone and Seine (Fig. 1). The Garonne River is a shallow river (generally <2 m) and has a high flow velocity, even in its lower reaches (~0.4 m s -1 ). This high flow velocity prevents planktonic algae to attain a high biomass (Améziane et al . 2003). Due to an important frac- tion of hard substrates in the river bed, turbidity of the Garonne River is low compared to other lowland rivers, with suspended matter concentrations usually being below 50 mg L -1 (Coynel et al . 2004). This low turbidity combined with a shallow depth allows diatom biofilms to develop on the river bed (Eulin & Le Cohu 1998; Teissier et al . 2002; Améziane et al . 2003; Boulêtreau et al . 2006). Diatom biofilms regularly detach when their biomass is high and are then mixed into the water column (Boulêtreau et al . 2006). Diatoms from these biofilms make up about half of the cell numbers in phytoplankton samples of the Garonne River (Améziane et al . 2003). Both planktonic and biofilm diatoms may consume Si in the Garonne River. The catchment of the Garonne River is predomi- nantly agricultural and contains only one major urban area, Toulouse. The urban area of Toulouse is situated at the confluence of the Garonne and Ariège rivers and has approximately 1 million inhabitants. The largest tributary of the Garonne River downstream of Toulouse is the Tarn River. In contrast to the Garonne River, the Tarn River has no major urban areas in its catchment. The reservoir of Malause is situated at the confluence of the Garonne and Tarn rivers. The Malause reservoir is a large reservoir with a relatively shallow depth (area: 420 ha, mean depth: 3.6 m). The main goal of this study was to evaluate eutrophication caused by the urban area of Toulouse and the resulting impact on dissolved Si concentrations. Water samples were collected at 16 sites upstream and downstream of the city of Toulouse on 17 occasions between July 1992 to September 1993. Sampling occasions were selected to cover high-discharge as well as low-discharge periods. Water was collected using a bucket from bridges or from the river bank, as close as possible to the centre of the main channel. Temperature was measured in the field using a WTW 96 probe. For determination of chlorophyll- a concentration, a known volume of water was filtered through a GF/C filter. Chlorophyll- a was extracted in boiling ethyl alcohol and quantified spectrophotometrically (Marker et al . 1980). For determination of dissolved nutrients, water was filtered through GF/F filters and stored at 4 °C until analy- sis (within 48 hours). Nitrate, nitrite and silica concentrations were measured with a Technicon autoanalyser. Nitrite was determined using the diazotation method, nitrate was determined by cadmium reduction into nitrite and dissolved silica (DSi) was determined by the ammonium molybdate method (APHA 1985). Ammo- nium was measured spectrophotometrically by the indophenol blue method according to Scheiner (1976). Solu- ble reactive phosphorus (SRP) was determined spectrophotometrically with the molybdate and malachite green method (Motomizu et al . 1983). Dissolved inorganic nitrogen (DIN) was calculated as the sum of ammonium, nitrate and nitrite. Determination of solid par- ticulate matter (SPM) concentrations was performed by filtration using dry pre-weighed filters (Whatman GF/F, 0.7 μm). Daily discharge data for the Garonne (at Ver- dun) and Tarn (at Moissac) rivers were provided by water authorities (DIREN Midi-Pyrenees and CA des Coteaux de Gascogne HYDRO-MEDD/DE). 3. RESULTS Discharge of the Garonne and Tarn rivers upstream of their confluence in the Malause reservoir is shown in figure 2. The Garonne River had a high discharge in late autumn to early winter as well as in spring. Discharge of the Tarn River was comparable to that of the Garonne River in summer and autumn but it was slightly higher than that of the Garonne River in winter and lower in spring. In winter, temperature was below 10 °C throughout the river section under investigation (Fig. 3). In summer, temperature was below 18 °C at the most upstream station sampled but increased up to 28 °C downstream of the confluence of the Garonne and Ariège rivers. SPM concentrations were generally low (<40 mg L -1 ) during the low flow periods in winter to early spring and summer (Fig. 3). Peaks in SPM concentrations were observed during the autumn floods along the entire river section and in late spring in the section downstream of the confluence of the Tarn with the Garonne River. DIN concentrations increased from <1 mg L -1 upstream of Toulouse to >2 mg L -1 downstream of Toulouse (Fig. 4) and concentrations were lower during high discharge periods in winter. SRP concentrations were usually <10 μg L -1 upstream of Toulouse (Fig. 4). Only in late summer 1993, higher SRP were measured upstream of Toulouse. Downstream of Toulouse, SRP increased to >20 μg L -1 . Downstream of the confluence between the Tarn and Garonne rivers, SRP decreased again by ...
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... Concrete corrosion: It is intended to deteriorate the constituent material of concrete as a result of influencing factors that may be internal or external, with the presence of what helps corrosion, which is heat and moisture that occurs between the components of concrete such as calcium oxide, iron oxide, or silicon oxide with water components such as chlorides, sulfates, or silica. These materials, whose source may be from living organisms present in the water, such as algae and others, as a result of their death overtime and the decomposition of their bodies in the water, in addition to the entry of gases into the concrete cracks or the entry of the resulting salts after the evaporation of water during the high temperature Also, the pouring of concrete at high temperatures leads to the formation of air gaps inside the concrete and thus the cracking of the concrete [13]. The research aims to follow up on the seasonal changes of blue-green algae attached to the concrete abutments of some bridges within the city of Baghdad. ...
he attached Cyanophyta community is a model for monitoring aquatic systems and interpreting environmental change in aquatic systems. The present study aims to conduct a seasonal study on Cyanophyta attached to the concrete abutments of three bridges (Al-Jadriya Bridge, Bab Al-Moadam Bridge, and Al-Muthanna Bridge) in the Tigris River within the city of Baghdad, central Iraq (from October 2021 to June 2022). The study included the quality of Cyanophyta and, the eleven environmental parameters (water temperature, electric conductivity, salinity, pH, total alkalinity, Calcium, Magnesium, dissolved oxygen, total dissolved solids, total phosphorus, and total nitrogen). Monthly samples were taken from the water under each bridge from three sampling sites in the river, and the results were presented as four seasons. A total of 45 Cyanophyta taxa were identified in the three orders. Order: Chroococcales 11%; Order: Oscillatoriales 64%; Order: Nostocales 25% dominance of Oscillatoriales from the second site, and the highest number of species recorded in the autumn. The study showed clear differences in the total number of algal species attached to different sites. The study was able to add a new record species to the Iraqi algae flora, which is Lyngbya sordida Gomont.
... Concrete corrosion: It is intended to deteriorate the constituent material of concrete as a result of influencing factors that may be internal or external, with the presence of what helps corrosion, which is heat and moisture that occurs between the components of concrete such as calcium oxide, iron oxide, or silicon oxide with water components such as chlorides, sulfates, or silica. These materials, whose source may be from living organisms present in the water, such as algae and others, as a result of their death overtime and the decomposition of their bodies in the water, in addition to the entry of gases into the concrete cracks or the entry of the resulting salts after the evaporation of water during the high temperature Also, the pouring of concrete at high temperatures leads to the formation of air gaps inside the concrete and thus the cracking of the concrete [13]. The research aims to follow up on the seasonal changes of blue-green algae attached to the concrete abutments of some bridges within the city of Baghdad. ...
The attached Cyanophyta community is a model for monitoring aquatic systems and interpreting environmental change in aquatic systems. The present study aims to conduct a seasonal study on Cyanophyta attached to the concrete abutments of three bridges (Al-Jadriya Bridge, Bab Al-Moadam Bridge, and Al-Muthanna Bridge) in the Tigris River within the city of Baghdad, central Iraq (from October 2021 to June 2022). The study included the quality of Cyanophyta and, the eleven environmental parameters (water temperature, electric conductivity, salinity, pH, total alkalinity, Calcium, Magnesium, dissolved oxygen, total dissolved solids, total phosphorus, and total nitrogen). Monthly samples were taken from the water under each bridge from three sampling sites in the river, and the results were presented as four seasons. A total of 45 Cyanophyta taxa were identified in the three orders. Order: Chroococcales 11%; Order: Oscillatoriales 64%; Order: Nostocales 25% dominance of Oscillatoriales from the second site, and the highest number of species recorded in the autumn. The study showed clear differences in the total number of algal species attached to different sites. The study was able to add a new record species to the Iraqi algae flora, which is Lyngbya sordida Gomont.
... Ambient temperature influences many aquatic activities including chemical compositions in river and stream bodies. Higher temperatures and nutrient loads, the latter derived from the anthropogenic activities, promote higher nitrogen and phosphorus concentrations in the rivers [4][5][6], resulting in an increase in eutrophic vulnerability and a reduction in ambient levels of dissolved silica and dissolved oxygen (DO) [7,8] and ultimately a myriad of interacting toxicants such as ammonia [9]. Many aquatic organisms including fishes, therefore, are more sensitive to ammonia when their habitats have higher river temperatures with a low DO. ...
Stream degradation increases with high anthropogenic activity and climate variability, while declines occur in biodiversity. However, few studies have been undertaken on tropical waterways, a major impediment to biodiversity conservation. The present study was conducted on 95 relatively pristine small streams in Eastern Thailand with 10 reasonably uncommon species of balitorid fishes. Measurements were made of 21 physical and chemical factors and the substrate particle size. Stepwise regression identified the direct importance of substrate particle size and nitrate on the species’ richness of balitorids, whereas its abundance was negatively related with iron concentrations. A Canonical Correspondence Analysis identified three fish groups: the 1st group was negatively correlated with ammonia and positively correlated with dissolved silica, the 2nd group was positively correlated with substrate particle size and negatively correlated with stream ambient temperature and ammonia concentration, and the 3rd group was negatively correlated with low dissolved silica, respectively. The results of this study may indicate the vulnerability of balitorids under climate warming and anthropogenic pressure that alter the water physicochemical factors and river degradation including the substrate type. Thus, a conservation framework should be provided regarding the limits for water temperature, ammonia, and iron in Thailand’s Water Quality Criteria to better protect its freshwater ecosystem. Balitorid is a potential bioindicator for evaluating the river temperature effect in combination with ammonia nutrient stressors as long as the way-of-life habits of the species are taken into account.
... Accordingly, numerous studies have documented DSi limitations in aquatic ecosystems; for example, in Solina-Myczkowce mountain reservoirs of San River, SE Poland (Koszelnik and Tomaszek, 2008), the Garonne river in France (Pandey et al., 2016;Yadav and Pandey, 2018), and the Upper Mississippi River System (UMRS) (Carey et al., 2019). Moreover, a negative correlation between limitation of DSi and chlorophyll-a concentrations was also revealed (Koszelnik and Tomaszek, 2008), suggesting that eutrophication enhances phytoplankton growth, accelerating DSi uptake, which results in depletion (Muylaert et al., 2009). Thus, depletion of DSi can also be caused by eutrophication, resulting in toxic algal blooms and subsequent changes to the ecosystem dynamics (Conley et al., 1993). ...
Dissolved silicon (DSi) is essential for aquatic primary production and its limitation relative to nitrogen (N) and phosphorus (P) facilitates cyanobacterial dominance. However, the effects of DSi on phytoplankton growth and community structure have yet to be fully determined in tropical lakes, particularly in relation to N and P. Therefore, this study investigated the role of DSi in Tonlé Sap Lake, Cambodia, a tropical floodplain system well known for its flood-pulse characteristics and high productivity. To that end, seasonal water sampling and in situ water quality measurements were performed around the floating villages of Chhnok Tru region. The concentration of DSi was significantly higher in the dry season than in the wet season at 16.3–22.1 versus 7.2–14.0 mg/L, respectively; however, both sets of measurements were comparable with lakes in other parts of the world. Meanwhile, the average molar ratio of TN:TP:DSi was 69:1:33 in the dry season and 39:1:24 in the wet season, which compared with the Redfield ratio of 16:1:16, suggested limitation of TP and DSi in both seasons. In addition, phytoplankton biomass in terms of chlorophyll-a was found to be a collective function of DSi, TN:TP, dissolved oxygen, and water temperature in both seasons. Taken together, these results suggest that DSi is affected by the annual hydrological cycle in the Tonlé Sap Lake flood-pulse ecosystem, serving as a secondary limiting nutrient of primary production during both the dry and wet seasons.
... DIN acts as a reactive tracer and captures shallow and surface flow pathways and anthropogenic sources of nutrient enrichment whereas dissolved inorganic silica (DSi) acts as a more conservative tracer and captures the governing dynamics of long-term background sources of the lithological substrata. DSi forms part of terrestrial biological silica cycles and is acritical nutrient for the aquatic ecosystem (Jansen et al., 2010;Muylaert et al., 2009;Wang et al., 2010). DSi cpmes into the ecosystem from weathering of soils and gets transported by fluvial networks to interact with surface water bodies. ...
... The biological cycling of silica in association with topographical characteristics of the watershed (West et al., 2005), significantly influences the concentration of silica (Moulton et al., 2000;Fulweiler and Nixon, 2005). The utilisation of silica by diatoms for its growth, reduces the DSi concentration Muylaert et al., 2009). ...
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... This may be due to its ability to reproduce and grow in different environmental conditions. As for the difference in numbers and percentages of algae studied, this is due to the difference in the aquatic environment in which it is located or infected with different] 17 ...
The current study was conducted to identify the algae present in the project of irrigation AL-Alam within the province of Salah al-Din and diagnosis.and knowledge of the extent and the impact on environmental factors surrounding at four station. The first was Arab region of China within the perimeter of the project area while the last station was Awejelah area. The other stations lie in between the previous two stations. The ecological characteristics (physical, chemical and biological factors) where included during the study period started from November 2016 till June 2017. The study included measurements of some physical factors as air and water temperature, Turbidity and electrical conductivity, as well as some chemical factors as pH, dissolved oxygen, biological oxygen demand, total alkalinity, salinity, and chloride. Plant nutrition as silicate, nitrite and phosphates were also included and the study covered the types of algae in the study area Diatoms formed the majority types of phytoplankton available at the station followed by green algae and blue-green algae and euglena and Chrysophyta finally comes the peridian algae.and The results of the algae diagnosis showed 119 species of algae, which were divided into 6 2 populations divided into 7 species, 12 cultivars and 22 families comprising 54 species.
... This may be due to its ability to reproduce and grow in different environmental conditions. As for the difference in numbers and percentages of algae studied, this is due to the difference in the aquatic environment in which it is located or infected with different] 17 ...
The current study was conducted to identify the algae present in the project of irrigation AL-Alam within the province of Salah al-Din and diagnosis.and knowledge of the extent and the impact on environmental factors surrounding at four station. The first was Arab region of China within the perimeter of the project area while the last station was Awejelah area. The other stations lie in between the previous two stations. The ecological characteristics (physical, chemical and biological factors) where included during the study period started from November 2016 till June 2017. The study included measurements of some physical factors as air and water temperature, Turbidity and electrical conductivity, as well as some chemical factors as pH, dissolved oxygen, biological oxygen demand, total alkalinity, salinity, and chloride. Plant nutrition as silicate, nitrite and phosphates were also included and the study covered the types of algae in the study area Diatoms formed the majority types of phytoplankton available at the station followed by green algae and blue-green algae and euglena and Chrysophyta finally comes the peridian algae.and The results of the algae diagnosis showed 119 species of algae, which were divided into 6 2 populations divided into 7 species, 12 cultivars and 22 families comprising 54 species.
... Like bacterial biofilms, algal biofilm development can also be divided into four stages ( Fig. 1-7): 1) initial attachment 2) micro-colonies formation and active growth, 3) maturation, and 4) and dispersion (Achinas et al., 2019;Guzmán-Soto et al., 2021;Irving and Allen, 2011;Tolker-Nielsen, 2015). At the latter stage, cells detachment occurs linked to nutrients, light depletion (Matthiessen et al., 2010;Muylaert et al., 2009;Tesson et al., 2016). The dispersal cells enter into the floating water phase and can further attach to the biofilm. ...
Microalgae biofilm-based technology has been pointed out as a promising alternative to suspended cells cultivation. However, a better understanding of the impact of process operational factors on biofilm development and productivity is actually needed to fully confirm the potential of biofilm-based processes for biomass/compounds production at large-scale. This will help identifying stressful factors and optimizing this kind of processes, and it will also provide new knowledge on immobilized cell behavior, which remains poorly understood.The aim of this thesis is to assess the effect of operational factors like light, support and inoculum on growth, productivity, and physiological properties of sessile cells during biofilm development. To do so, C. vulgaris was immobilized on porous materials including fabric supports and membranes. Immobilized cell behavior (growth, composition, photosynthetic activity) was investigated under different conditions of light intensity, supports and inoculum density /physiology. In a continuously submerged reactor, cells acclimated within only 3 days to the new biofilm lifestyle. Low productivities were though obtained, which may be related to high detachment or support properties. Consequently, cell retention capability on five fabrics was tested afterwards in order to find promising supports. Accordingly, Terrazzo with the smallest pore size and mesh density exhibited the highest cell retention capability, representing thus a potential support for large-scale biofilm cultivation. Immobilized cells distribution on fabrics, biofilm development and activity were found to be strongly affected by the support material. Another biofilm-based system (perfused system) where cells are immobilized on a membrane was then used to study the combined effect of light intensity and inoculum density on biofilm developpement under more controlled conditions. Results showed that high cell density affects negatively the productivity on fabrics and membranes which may be linked to limitation in light and nutrients. Combined conditions of light and cell density which promote either biomass or lipids production were also identified. Inoculum acclimation to 350 and 500 µmol m-2 s-1 benefited biomass production and avoided photo-inhibition, respectively, suggesting the importance of considering photo-acclimation on biofilm-based systems set-up. For the first time, the acclimation process of cells switching from planktonic to the immobilized state was lastly studied. Unexpectedly, within the first hours, cells increased their size, accumulating carbohydrates, and decreasing the Chl a content. It is likely that changes in environmental conditions trigger this behavior, allowing the cells to acclimate to the new lifestyle.
... Species richness and diversity are among the most intensively discussed concepts in the fields of theoretical ecology and conservation, Species Richness is the primary measurement for community and local diversity, the index describe the species composition and the range of its diffusion, and represent, the identified taxonomic units inside the sample and its diversity, the measure of taxonomic unit richness covers the changes in studied biological community (Al-Hassany et al., 2012) the result of Richness Index ranged from 9.38 in summer at site 2 and 29.57 in spring at site 1 (Figure 2.B), The statistical analysis showed that there were no significant differences between the seasons at Site 1 and Site 3, but with regard to the Site 2, the statistical analysis showed that there were significant differences (p < 0.05) between spring and summer, and for Site 4, there were significant The result revels that the station 1 shows increase in richness index, and these results belonged to variability of environmental factors that impacted the growth of epipelic algae, moreover the impact of substrate (sediment) on epipelic algae growth (Muylaert et al., 2009 andHassan et al.,2014) and there was a similar species composition at all studied sites with some differences due to the nature of each site and type of macrophytes in each on the bank of river such as Phragmitus australis, Typhah domingensis and Ceratophyllum demersum, These macrophytes lead to suitable condition of algal growth (Hassan and Shaawiat, 2015). The Eveness Index ranged between 0.18 in Autumn at site 2 and 0.28 in summer at site 1, where the statistical analysis showed that there were significant differences between sites along the study period (Figure 2. C).The recorded low values of the index indicates the dominance of a particular species over the rest of the other species or the prevalence of a few species with high densities. ...
The algal samples were collected monthly, from selected four sampling stations of Al-Diwanyia river at Al-Diwanyia City from September 2015 to June 2016. A total of 145 species belong to 44 genera of epipelic algae were recorded from four sampling stations throughout the study period. In the present study, Four biodiversity indices (Richness index, Shannon-Wiener index, Evenness index and Jaccard Similarity index) and one pollution index (Diatomic index) were employed to study the water quality of Al-Diwanyia river. The score of Diatomic Index ranged from 1.71 to 3.56. The score of each site confirmed moderate to high pollution. Considering all the water parameters, biodiversity indices and pollution index, it was clearly shown from the results of the present study that the water quality of Al-Diwanyia river was affected from anthropogenic actitivies at the river. Thus, algal communities were used as bioindicator of pollution of river.
... Diatoms need Si to produce their frustules, and DSi concentration constrained the contribution of Bacillariophyta to the total phytoplankton (Fig. 6a). Biogenic Si has a much lower remineralization rate than organic N and P during organism decay (Muylaert et al. 2009). Thus, the recycling rates of N, P, and Si vary greatly (Koszelnik andTomaszek 2008, Howarth et al. 2011), and eutrophication can enhance Si limitation and induce a shift from Bacillariophyta to Cyanophyta. ...
Cascade reservoir-river systems evolve to become a new ecological region produced by anthropogenic disturbances. Systematic studies of spatial–temporal patterns of phytoplankton community structure are still lacking in these systems, and thus we investigated phytoplankton composition and related environmental factors in the impounded Wujiang River, southwest China. The results showed that the dominant groups were Chlorophyta, Bacillariophyta, and Cyanophyta, whereas Pyrrhophyta and Cryptophyta mainly appeared from May to August. Bacillariophyta were dominant algae in the river water, Cyanophyta in the eutrophic reservoirs, and Chlorophyta, Bacillariophyta, and Cyanophyta were dominant in the mesotrophic reservoirs. Water temperature was an important limiting factor for algal growth, and algal biomass produced 2 peak values in May and in August. Backpropagation artificial neural networks (BPANNs) have accurately predicted time-series variation of dominant algal abundance. The sensitivity analyses indicated that water temperature, dissolved CO2, and silicon were the main factors influencing phytoplankton community structure, suggesting algal succession is constrained by carbon and silicon biogeochemical cycles. Results suggested that Cyanophyta used HCO3⁻ as an inorganic carbon source when the CO2 concentration was less than ~10 μmol L⁻¹, leading to the species succession from Bacillariophyta to Cyanophyta.
