Anthropogenic‐induced shifts in salinity and nutrient status of two freshwater tropical lakes in India

An understanding of ongoing changes in salinity and nutrient status, as influenced by anthropogenic forcing factors, is important for integrated lake basin management (ILBM) and conservation of water resources in dry tropical regions. This study analysed a range of water quality attributes, including salinity, nitrate (NO₃^?), ammonia (NH₄ ⁺ ), phosphate (PO₄ ^{3 ?}) and dissolved organic carbon (DOC) in two freshwater lakes in Rajasthan, India for three consecutive years (2000–2002). Between‐lake comparisons indicated marked differences in most of the water quality variables. The pH in both study lakes remained above neutral. Water hardness, salinity and concentrations of total dissolved salts (TDS), chlorides, NO₃^?, NH₄⁺, PO₃^3? and DOC were high in Lake Udaisagar, which received inputs from agricultural drainage and urban–industrial releases. The DOC in Lake Baghdara, which drains a woodland catchment, was similar to that for Lake Udaisagar, indicating the role of allochtonous inputs in the build‐up of DOC. The results of this study indicated that increasing human interferences have increased the nutrient concentrations in Lake Udaisagar. This factor, coupled with extended periods of dryness, drives these two freshwater lakes towards a high salinity. This study provides evidence of a human‐induced salinity increase and has relevance for ILBM and for the conservation of freshwater resources in dry regions.     

Application of WASP model for assessment of water quality for eutrophication control for a reservoir in the Peruvian Andes

Water quality models are important tools for facilitating assessment of the main processes occurring in an aquatic system. To this end, a water quality analysis simulation programme (WASP8) was used to assess the eutrophication process in El Pañe Reservoir. The reservoir has a useful water volume of 99.6 hm³ and is connected to six other reservoirs located in the Chili Basin of the Arequipa Region. El Pañe Reservoir, which is the basin head, has exhibited eutrophication problems since 2014, causing water treatment problems for human consumption and a high probability of cyanotoxin releases from intensive algal blooms. Accordingly, the reservoir was divided into 11 segments, ammonia, nitrate, phosphate, total phosphate, dissolved oxygen, water temperature and chlorophyll‐a being the simulated water quality parameters. The simulations were set in a steady state condition for 3 years from October 2015 to October 2018, subsequently determining aquaculture activity and benthic flux as being meaningful nutrient sources impacting the phytoplankton community. The results of the present study provide necessary evidence of the need to exhaustively quantify both sources in future research, which will aid decision makers in identifying the best management option that can help guarantee the sustainable development of the involved human activities.     

浅水湖泊水生态数学模型研究及应用

该文针对珠三角感潮浅水湖泊水环境模拟问题,在二维水流-污染物输移耦合数学模型基础上,结合WASP(water quality analysis simulation program)水生态数学模型原理,考虑溶解氧、氨氮、硝酸盐氮、有机氮、无机磷、有机磷、碳生化需氧量和叶绿素a等8个水质变量及其相互作用的溶解氧平衡子系统、氮循环子系统、磷循环子系统和浮游植物动力学子系统,建立了浅水湖泊水生态数学模型。通过室内实验系统模拟了珠三角某典型感潮人工湖泊外江来水营养条件对蓝藻生长的影响,确定了蓝藻生长速率等关键模型参数,并模拟了湖泊不同换水方案下叶绿素a的时空分布规律,为控制湖泊水体富营养化、预防蓝藻水华爆发提供科学依据。     

Feasibility Assessment of Data-Driven Models in Predicting Pollution Trends of Omerli Lake,Turkey

Data-driven models are commonly used in a wide range of disciplines, including environmental engineering. To analyze Omerli Lake’s historic water pollution status, this study monitors data for dissolved oxygen, 5-day biochemical oxygen demand, ammonium nitrogen, nitrite nitrogen, nitrate nitrogen, and ortho phosphate. The quality of the lake water is assessed based on measurements of dissolved oxygen. The collected data are analyzed using regression analysis and artificial neural network models. The main goal of this paper is to reveal the best applicable data-driven model in order to gain forward-looking information regarding the dissolved oxygen level of the lake using other pollution parameters. In order to ascertain eutrophic status, total phosphorus loads for each year are represented on a Vollenweider diagram. Results designate an increasing risk of eutrophication for Omerli Lake in recent years. Results of the data-driven models show that the artificial neural networks model constitutes the best relationship between the dissolved oxygen and other parameters.     

Water quality assessment of a recently refilled reservoir: The case of Bütgenbach Reservoir, Belgium

Bütgenbach Reservoir is situated in the High Ardennes plateau in eastern Belgium (50°25′N; 6°13′E). It is used principally for flood control and for production of hydroelectric energy. It has been subjected to a previous series of studies because of its eutrophication problems and their impacts on the local economy. Bütgenbach Reservoir was emptied during spring 2004 for dam restoration, being refilled in mid‐September of the same year. Selected physicochemical and biological parameters (temperature, dissolved oxygen, pH, inorganic and organic nutrients, chlorophyll‐a) were measured fortnightly during the lake's productive season (mid‐April to mid‐October 2005) at three sampling sites throughout the water column. The water quality conditions after refilling of the lake were compared to previous studies accomplished at the same sampling sites (prior to emptying the lake). The actual trophic status was mesotrophic to eutrophic, based on the combination of total phosphorous and chlorophyll‐a concentrations, as well as water transparency. Bütgenbach Reservoir generally exhibits good water quality, based on the French water quality system SEQ‐eau. A longitudinal decrease in water quality was observed from upstream to downstream, because mainly of the differences in lake bottom morphology and water residence time, and their impacts on nutrient distribution in the lake.     

Impact of damming the Mogi-Guaçu River (São Paulo State, Brazil) on reservoir limnological variables

This study examined the effects of the damming of the Mogi‐Guaçu River (São Paulo State, Brazil) on the surface current velocity, water temperature, Secchi disc transparency, turbidity, colour, conductivity, pH and concentrations of nutrients and pigments. Surface‐water samples were taken before, during and after the reservoir was filled. Three sampling sites were established, one in the upper reach of the reservoir, one in the central area of the reservoir and one downstream from the dam. An additional sampling site was established on the Peixe River, the major tributary of the Mogi‐Guaçu in the study area. After filling of the reservoir, the surface current velocity tended to decrease, excepting downstream of the dam. The pH, and the Kjeldahl nitrogen, ammonia and chlorophyll‐a concentrations, tended to increase. The nitrite concentrations increased mainly in the upper reach and central area of the reservoir. The Secchi disc transparency and colour tended to decrease. A decreasing trend in dissolved oxygen concentration was observed mainly at the central area of reservoir. The conductivity tended to decrease, later returning to levels observed prior to reservoir filling. The nitrate, total phosphorus and orthophosphate concentrations exhibited an increasing trend after reservoir filling, followed by a decreasing concentration, reaching lower levels than those found prior to reservoir filling. High phaeophytin concentrations were measured for the filling phase. The observed water quality changes for Mogi‐Guaçu Reservoir generally were not as extreme as those observed for other tropical reservoirs. This trend was related to the operation of the reservoir. As Mogi‐Guaçu Reservoir is a run‐of‐the‐river reservoir with a short water retention time, the flooded area is not extensive and the retention of material and sedimentation upstream from the dam is not remarkable. These facts explain the small water quality changes observed for most of the variables after reservoir filling. The water quality decreased at the in‐lake site in the central part of the reservoir, attaining a hypereutrophic condition. This fact was related to the ageing of the reservoir and to cultural eutrophication.     

Development and application of dissolved oxygen (DO) and biological oxygen demand (BOD) model for Panshet and Ujjani Reservoirs,Maharashtra, India

A model of dissolved oxygen (DO) and biological oxygen demand (BOD) was developed to assess the water quality of Panshet and Ujjani Reservoir in Maharashtra, India, to ascertain if their water was suitable for various beneficial and designated uses. The model was calibrated with observed data from these two reservoirs. Seasonal water quality variations were studied during 2010–2011 The pH of Panshet Reservoir water is almost neutral, whereas Ujjani Reservoir is marginally alkaline. A rapid decrease in DO with depth during the summer appeared to be a common phenomenon for both reservoirs. Although the mean phosphate concentrations of both reservoirs were comparable, biological growth was much higher in Ujjani Reservoir, being attributed to a higher dissolved salt concentration in Ujjani Reservoir. The nitrate (NO₃^?) concentrations in both reservoirs remained within a range close to the global average for unpolluted freshwater. Sewage contamination appears to be a major problem for Ujjani Reservoir, especially as it relates to domestic water uses. A two‐layer, two‐dimensional mathematical model also was developed to assess reservoir water quality. An explicit, second‐order‐accuracy finite‐volume technique was used to solve two‐dimensional shallow water equations. The governing equations were solved with a Mac Cormack predictor–corrector scheme. The Reynolds turbulence terms were modelled with a sub‐grid‐scale (SGS) model, using a large eddy simulation (LES) approach. An empirical relationship developed by Street and Phelps describing liquid–air phase demand and natural re‐aeration was used to determine water quality parameters. The model was validated with numerical results from the literature. The field investigations were satisfactorily applied for the simulation of hydrodynamics and the prediction of DO and BOD in Panshet and Ujjani Reservoir.     

A modeling approach to simulate impact of climate change in lake water quality: Phytoplankton growth rate assessment

Global climate change induced by increased concentrations of greenhouse gases (especially CO₂) is expected to include changes in precipitation, wind speed, incoming solar radiation, and air temperature. These major climate variables directly influence water quality in lakes by altering changes in flow and water temperature balance. High concentration of nutrient enrichment and expected variability of climate can lead to periodic phytoplankton blooms and an alteration of the neutral trophic balance. As a result, dissolved oxygen levels, with low concentrations, can fluctuate widely and algal productivity may reach critical levels. In this work, we will present: 1) recent results of GCMs climate scenarios downscaling project that was held at the University of Derby, UK.; 2) current/future comparative results of a new mathematical lake eutrophication model (LEM) in which output of phytoplankton growth rate and dissolved oxygen will be presented for Suwa lake in Japan as a case study. The model parameters were calibrated for the period of 1973–1983 and validated for the period of 1983–1993. Meteorologic, hydrologic, and lake water quality data of 1990 were selected for the assessment analysis. Statistical relationships between seven daily meteorological time series and three airflow indices were used as a means for downscaling daily outputs of Hadley Centre Climate Model (HadCM2SUL) to the station sub-grid scale.     

Characterization of water quality in a small hydropower plant reservoir in southern Brazil

The construction of large reservoirs can cause profound environmental changes. Reduced water flow, increased water residence time, thermal stratification, increased sedimentation rates and decreased dissolved oxygen concentrations are examples of such changes. These changes can affect water quality and the biota in the environments adapted to the natural conditions of a river. Small reservoirs developed in conjunction with hydropower plants, however, could reduce the degraded water quality. This study focuses on characterizing water quality in a small hydroelectric reservoir. The study reservoir has an area of 1.4 km² and a short water retention time. The Monte Claro Hydroelectric Power Plant is part of a complex consisting of three plants on the Antas River in the north‐west of Rio Grande do Sul state, Brazil. The reservoirs associated with these plants are operated as run‐of‐the‐river facilities. Monitoring results obtained by CERAN, the Energetic Company of Antas River (Companhia Energética Rio das Antas), were used to evaluate the reservoir water quality. Three samples were collected seasonally (spring, summer, autumn and winter) in the area of influence of this plant following the filling of the reservoir (2005–2008). The examined water quality parameters were electrical conductivity, colour, turbidity, alkalinity, pH, biological oxygen demand (BOD), chemical oxygen demand (COD), total phosphorus, dissolved oxygen, sulphate, nitrate, nitrite, ammonia, suspended and dissolved solids, chlorophyll‐a, total and faecal coliforms, water temperature and Secchi depth transparency. The results were interpreted using an index of water quality, Trophic State Index, reservoir water quality and CONAMA Regulation 357/05 (Brazilian legislation). Based on these analyses, no significant changes were exhibited in the water quality of the reservoir from the hydroelectric plant operation.     

Seasonal and diel changes of dissolved oxygen in a hypertrophic prairie lake

Humboldt Lake, a hypertrophic prairie lake typical of many found on the Great Plains of North America, is usually ice‐covered from early November to about mid‐May. The lake is an important recreational fishery, now mainly stocked with walleye. It has a high potential risk of experiencing fish kills because of the very large cyanobacterial blooms that develop in it, the high rates of algal and bacterial production and the high concentrations of ammonia (NH₃‐N) and dissolved organic matter. Following the collapse of cyanobacterial blooms, shallow prairie lakes are known to undergo periods of anoxia that can lead to summer fish kills. In some of the lakes, anoxia forms during the long period of ice cover, causing winter fish kills. Two years of seasonal and diel data (total phosphorus, dissolved oxygen (DO), NH₃‐N and chlorophyll‐a concentrations, and bacterial production) were analysed in this study to assess why significant fish kills did not occur during this period or during the ≈ 30 years of records from Saskatchewan Environment. Humboldt Lake did not become anaerobic, either following the collapse of the cyanobacterial bloom or under ice cover, indicating that the oxygen (O₂) influx (strong mixing) and production processes were greater than the microbial and chemical O₂ demands, both over seasonal and diel time scales. Several published risk threshold criteria to predict the probability of summer and/or winter fish kills were applied in this study. The threshold criteria of maximum summer chlorophyll and maximum winter NH₃‐N concentrations indicated that a summer fish kill was unlikely to occur in this hypertrophic prairie lake, provided its water quality remained similar to that during this study. Similarly, the threshold criteria of initial DO storage before ice cover and the rate of O₂ depletion under ice cover also indicated a winter fish kill was unlikely. However, recent development in the watershed might have resulted in significant water quality deterioration and the winter fish kill that occurred in 2005.     

Water Quality Changes in Lake Erie, 1968–1980

Data on chlorophyll a, total phosphorus, and hypolimnetic dissolved oxygen concentration, which were collected by Canada Centre for Inland Waters during the period 1968 to 1980, are statistically analyzed to evaluate the changes in the water quality of Lake Erie. There are strong evidences of a decreasing trend in the value of chlorophyll a and total phosphorus in the western, central, and eastern basins of the lake between 1970 and 1980. Furthermore, a statistical model is developed for the hypolimnetic dissolved oxygen concentration in the central basin. The model shows that the increase in depletion is related to the increase in the level of total phosphorus. Hence, it is possible to improve the anoxic conditions in the lake by controlling total phosphorus loadings.     

Spatio‐temporal trends of nutrients and physico‐chemical parameters on lake ecosystem and fisheries prior to onset of cage farming and re‐opening of the Mbita passage in the Nyanza Gulf of Lake Victoria

Many large lake ecosystems are experiencing increasing eutrophication and persistent cyanobacteria‐dominated algal blooms affecting their water quality and ecosystem productivity because of widespread non‐point and point nutrient sources. Accordingly, the present study utilized data of July 2003 and January–February 2004, as well as previous measurements of nutrients and physico‐chemical variables (electrical conductivity, dissolved oxygen, temperature, pH, turbidity and chlorophyll‐a), to characterize the spatial and temporal trends, as a means of better understanding the factors influencing lake environmental conditions, as support tools for long‐term ecosystem management and for better understanding the long‐term trends and effects. Inshore gulf areas were found to represent zones of maximum nutrient concentrations, compared to the deep main lake zones, with significant inter‐parameter correlations. Phosphorus, silicon and chlorophyll‐a concentrations were significantly correlated. Water electrical conductivity was also significantly and positively correlated with soluble reactive silicon (SRSi), alkalinity hardness DO, while exhibiting a negative association with water transparency. Water turbidity and transparency, electrical conductivity, and SRSi concentrations clearly describe a gradient from the gulf into the main lake. For such a shallow gulf, these findings suggest primary productivity is influenced mainly by the availability of nutrients, light transparency and the extent of availability of resuspended nutrients. The increasing eutrophic state of Lake Victoria is a serious concern since it contributes to an increased potential of more frequent occurrences of cyanobacterial blooms, a potential public health risk to both humans and wildlife. Improved understanding of influences from previous fish species introductions and concomitant changes in indigenous fish species, increased lake basin population and anthropogenic activities, water hyacinth resurgences, sustainability of biodiversity, and current interests in cage farming, are among the major concerns and challenges facing the contemporary Lake Victoria. The trends regarding nutrients and physico‐chemical characteristics are intended to support better monitoring efforts and data to promote the lake's ecosystem services and the sustainable management of the lake ecosystem.     

Dynamics of photosynthetic pigments in an Andean lake in Colombia

Guatavita Lake is a small, sheltered tropical high mountain lake located in the Colombian Andes, with a closed watershed and a maximum depth of 25 m. It is the freshwater source for human consumption in nearby small towns, as well as being a site of cultural value for the country, as it was a sacred place to indigenous peoples until about five centuries ago. As the structure and function of this aquatic ecosystem is poorly understood, this study provides initial knowledge on its phytoplankton biomass dynamics, which should be useful in designing efficient management plans with environmental baseline information for similar lakes elsewhere. Physical and chemical data, and photosynthetic pigment concentrations, were measured for the period November 1999–November 2000 at the central vertical axis of Guatavita Lake. The vertical profile of the chlorophyll‐a concentration was closely related to the dissolved inorganic nitrogen concentrations and the thermal stratification characteristics. The maximum chlorophyll‐a concentration in the metalimnion was recorded for the thermal stratification period (November 1999–June 2000). Deepening of the maximum chlorophyll‐a concentration began in February, continuing to June, when it reached its lowest value at the 15 m depth. The phytoplankton biomass values showed an increment within the entire water column at the beginning of the mixing period (July). The relation between the metalimnetic peak of chlorophyll‐a and the dissolved inorganic nitrogen concentration suggests the growth of the phytoplankton community is limited mainly by the availability of nitrogen.     

Assessment of heavy metal contamination in coastal lake sediments associated with urbanization: Southern Kerala,India

The study of the spatiotemporal variation of heavy metals in lake sediments is of great importance because heavy metals can result in toxic effects on aquatic biota through bioaccumulation. This study was undertaken to evaluate the degree of heavy metal contamination in the lacustrine sediments and the corresponding environmental deterioration in a tropical, urban, coastal lake (Akkulam–Veli), located in Kerala, India. The spatiotemporal variations of the cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn) concentrations in the lake sediments, as well as various indices of anthropogenic contamination, including Contamination Factor (CF), Pollution Load Index and Geoaccumulation Index (Igeo), were used to assess the degree of contamination. This study indicated contamination of the lake sediments with Cu, Pb and Zn. Urban domestic sewage and land run‐off are the major drivers of the heavy metal loads to the lake. During the pre‐monsoon, sediment contamination occurs in the upstream portion of Akkulam Lake because of a high clay content in the sediments. During the monsoon period, Akkulam Lake and the upstream portion of Veli Lake exhibit sediment contamination owing to high silt content. Domestic sewage is the main source of copper and zinc to the lake. Sewage bypass into the drains in the lake basin is largely responsible for the copper and zinc sediment contamination. High traffic levels and wastewater discharges from service stations/workshops are the main cause of the Pb loads entering the lake. Rubber particles of vehicle tires contain zinc and copper pigments that can accumulate on the surface of busy streets, entering the drains during rainfall events. Based on these study results, the accumulation of copper, zinc and lead in lake sediment can be controlled to a great extent by restricting the above‐noted activities. As the sediment content of lead, zinc and copper is confined to the clay fraction during the non‐rainy season and to the silt fraction during other seasons, lake restoration work should largely incorporate treating the clay and silt fractions, respectively, during both the non‐rainy season and rainy season.     

Multivariate analysis of the sediment quality of a tropical coastal lake system

Accurate knowledge of sediment quality is essential because it affects the magnitude and trends of water quality constituents. There are only a few analyses of sediment quality characteristics using multivariate analysis tools. This study utilizes hierarchical cluster analysis (HCA), factor analysis (FA) and multiple regression analysis (MRA) to demonstrate the usefulness of these techniques to analyse sediment quality for Akkulam–Veli Lake, a tropical coastal lake system in Kerala, India. The variation of sediment quality patterns during the premonsoon (PRM), monsoon (MON) and postmonsoon (POM) periods were assessed with cluster analysis. Factor analysis was used to identify prominent factors influencing sediment quality, while the factors influencing heavy metal partitioning in the sediment and overlying water were identified using multiple regression analysis. The study results indicated the sediment in the upstream portion of the lake was polluted during PRM, with the prominent factors being the ‘heavy metal factor’ and the ‘organic pollution factor’, followed by the ‘phosphorus pollution factor’ and the ‘cadmium pollution factor’. The ‘heavy metal factor’ and the ‘organic pollution factor’ are the prominent factors during MON, whereas the ‘heavy metal factor’, ‘organic pollution factor’ and ‘salinity factor’ were prominent POM factors. The salinity of the overlying water above the sediments plays an important role during PRM and POM, whereas the dissolved oxygen content was important during MON.     

Evaluation of performance of water quality models for a tropical lake system

The ability to predict water quality is a major requirement for planning and execution of developmental projects. It helps entrepreneurs to effectively plan and implement pollution control measures. This study evaluates the ability of different water quality models (statistical; remote sensing; mathematical) to predict salinity in Akkulam–Veli Lake, a tropical lake system. The performance of these three water quality models was evaluated. Prediction of salinity was made accurately with the mathematical model (WASP), compared to the other models. WASP facilitates prediction of daily water quality variations, which is not possible with the other models. A limitation of this model, however, was its ability to predict only a few water quality parameters. The statistical methods are reliable when the number of sampling sites and frequency of sample collection are high, making this method exhaustive and expensive. Remote sensing techniques proved to be less tedious, but are suitable only under specific situations, and not able to produce a high level of accuracy. Nevertheless, this method provides a continuous picture of spatial variations of different water quality parameters to a reasonable level of accuracy. The choice of the ‘best’ model varies on the basis of climatic and field conditions of the lake system of concern. Thus, a combination of water quality models was found to be the most ideal approach for analysing water quality data.     

再生水回用于景观水体磷营养盐对叶绿素a和藻密度的影响研究

以北京市某再生水厂出水为研究对象,人工配制各浓度梯度的营养盐,试验研究补给再生水后景观水体水质指标的变化,重点考察磷对叶绿素a和藻密度的影响情况.试验结果表明叶绿素a和藻密度主要受水体中氮磷比和磷酸盐浓度的影响.在磷酸盐保持在1 mg/L以下,氨氮在2 mg/L以下,硝酸盐氮在8 mg/L以下,将再生水一次性补给景观水体是完全可行的,不会产生藻类暴发;当磷酸盐浓度增加至1.5 mg/L,藻密度将显著增加.     

Limnological features of Funil Reservoir (R.J., Brazil) and indicator properties of rotifers and cladocerans of the zooplankton community

Funil Reservoir receives inflow from a highly industrialized region and acts as a natural sink to pollutants. Among the consequences of the uncontrolled nutrient loading is the constant presence and periodic heavy blooms of Microcystis aeruginosa . This study verified limnological features and zooplankton assemblage of the Funil Reservoir focusing on the environmental-indicator properties of rotifers and cladocerans. The summer bloom of M. aeruginosa caused reductions in water transparency, nitrate and orthophosphate concentrations and raises in chlorophyll a , pH, dissolved oxygen and chemical oxygen demand values. All zooplankton species presented spatial and temporal variations with the exception of the copepods, which were present in all samples. According to canonical correspondence analysis, ammonium was the variable most related to zooplankton variability and different Rotifera and Cladocera assemblages indicated distinct environment conditions. Rotifer taxa associated with increases of water temperature and chlorophyll a concentration were found with high densities during M. aeruginosa blooms. Species of rotifer and cladocerans are suggested as indicators that can be used to identify different physical and chemical gradients or eutrophic increases in Funil Reservoir.     

A Post Audit of a Lake Erie Eutrophication Model

A post audit of a eutrophication-dissolved oxygen model of Lake Erie is presented. The model had been calibrated using data from 1970 and 1975. Projections were then made for use in establishing the IJC target loadings for phosphorus that would essentially eliminate the anoxia in the central basin. In the latter 1970s the phosphorus discharges to Lake Erie dropped substantially due to increased removal from point sources. The observed response of the lake to this change in loading is compared to the predicted response. A 10-year computation from 1970 to 1980 is made using measured lake loadings. Concentrations of total and dissolved phosphorus, nitrate, chlorophyll, dissolved oxygen, and anoxic area are compared to observations. Both agreements and deviations are examined. It is concluded that the IJC target loadings were reasonably accurate forecasts of the loadings required to achieve the goal of elimination of anoxia.     

Relationships between environmental factors,periphyton biomass and nutrient content in Garças Reservoir,a hypereutrophic tropical reservoir in southeastern Brazil

This study focused on evaluating the factors related to seasonal variations of periphyton biomass and nutrient content (N, P) in Garças Reservoir, a tropical, shallow hypereutrophic tropical reservoir in southeastern Brazil that exhibits a permanent cyanobacteria bloom. Artificial substrata were placed in the subsurface water (20 cm) of the lake on a monthly basis (incubation time of 28 days) over a 1‐year period. Two limnological periods were characterized, including: (i) a period of decreased water clarity, higher levels of soluble reactive phosphorus and higher phytoplankton biomass; and (ii) a period of relatively higher water clarity (as measured by Secchi depth), higher nitrate concentration and lower phytoplankton biomass. The periphyton chlorophyll‐a levels were lower during the first period, being negatively correlated with phytoplankton biomass. The results of this study suggest that during the period of decreased water clarity, periphyton was primarily light‐limited. In contrast, the periphyton biomass was higher during the second period, regardless of P limitation of periphyton growth. Rehabilitation of this highly degraded tropical reservoir must consider the light regime, which is controlled by phytoplankton abundance. Thus, a reduction in the P loading to the lake should be considered to suppress its cyanobacterial blooms, thereby improving conditions for submerged macrophytes and the re‐establishment of periphyton.