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Worldwide, freshwater environments are impacted by inputs of nutrients and dissolved organic matter from human activities. Yet, the recovery of aquatic systems is usually focused only on nutrient management. In our work, we presented the case of an urban and hypereutrophic environment (Pampulha reservoir, Belo Horizonte, Brazil) that receives discharges from several streams and was treated with lanthanum modified bentonite (Phoslock®) and microbial bioremediation (Enzilimp®). Our goals were to evaluate whether the treatment could improve the water quality and characterize the spatiotemporal variation of dissolved organic matter sources and indices according to absorbance and fluorescence measurements from the reservoir and streams post-application months (2018). In our results, the reservoir showed a relative decrease in its phosphorus concentration compared to data from before the treatment. On the other hand, carbon concentrations reached expressive values in the post-application months following a similar pattern found in the streams. Our data showed that the reservoir’s high resistance in its hypereutrophic condition was related to the elevated loading of external inputs coming from the streams. The parallel factor analysis (PARAFAC) identified four main carbon sources, two of them being potential tracers of organic pollution in the Pampulha reservoir and watershed, together with absorbance and fluorescence indices. Our findings suggest that carbon parameters can be essential tools to provide adequate monitoring and optimization of water recovery attempts in complex, polluted environments.

Synthesizing human motion through learning techniques is becoming an increasingly popular approach to alleviating the requirement of new data capture to produce animations. Learning to move naturally from music, i.e., to dance, is one of the more complex motions humans often perform effortlessly. Each dance movement is unique, yet such movements maintain the core characteristics of the dance style. Most approaches addressing this problem with classical convolutional and recursive neural models undergo training and variability issues due to the non-Euclidean geometry of the motion manifold structure.In this paper, we design a novel method based on graph convolutional networks to tackle the problem of automatic dance generation from audio information. Our method uses an adversarial learning scheme conditioned on the input music audios to create natural motions preserving the key movements of different music styles. We evaluate our method with three quantitative metrics of generative methods and a user study. The results suggest that the proposed GCN model outperforms the state-of-the-art dance generation method conditioned on music in different experiments. Moreover, our graph-convolutional approach is simpler, easier to be trained, and capable of generating more realistic motion styles regarding qualitative and different quantitative metrics. It also presented a visual movement perceptual quality comparable to real motion data., Comment: Accepted at the Elsevier Computers & Graphics (C&G) 2020

Controlling factors of CH4 ebullitive flux are still poorly understood within daily timescales in aquatic environments. Here, we explored if Chaoborus larvae bioturbation can influence the timing of daily CH4 ebullitive flux and how this emission pathway is affected considering direct observations in a tropical reservoir. For this, we collected CH4 bubbles on two different days and three sampling periods: 1–4 pm, 4–7 pm and 7–10 pm. In the middle of each period, we collected Chaoborus larvae, chemical, and environmental variables and acoustically surveyed the underwater environment. We found similar temporal patterns of CH4 emissions between the periods in both days. The intervals of higher CH4 ebullitive flux (1–4 pm and 4–7 pm) appeared to correspond with the exit period of Chaoborus larvae from sediment (2:30 pm to 5:30 pm). Furthermore, the density of benthic larvae, a proxy of the bioturbation intensity, was the only variable that significantly correlated with the ebullitive flux, presenting a high and positive relation. Our findings suggest that the stochastic nature of the CH4 ebullitive flux may not be absolute truth, and this emission pathway might be enhanced daily by a Chaoborus-driven physical disturbance.

Dissolved organic matter (DOM) is a central driver of many processes in aquatic environments. Here, we address the issue of spatial and temporal variations in DOM quantity and quality in a deep tropical lake (Brazil). We measure DOC, Chl-a, suspended solids, nutrients and CDOM metrics in surface water samples taken from 21 sampling sites during six campaigns, and we quantify their links with water depth and rainfall estimates. Temporal effects explain between 74.5 and 94.5% of the variance in DOC, SUVA254, aCDOM440, and Chl-a, and all those parameters were influenced by rainfall. In contrast, spatial variations affect more S275-295 and aCDOM254. The contributing drainage area varies spatially in morphology and geometry, and each portion affects a specific part of the lake, resulting in a spatial variation in DOM quantity and quality. Our findings demonstrate the importance of the input of allochthonous DOM (which depends on seasonal rainfall and drainage area shape) to DOM dynamics in a tropical lake. The study area is receiving lower rates of precipitation in recent times, and our results suggest that this may alter the seasonal patterns of input of DOM and nutrients in the lake, with possible impacts on water quality, aquatic biota and ecosystem functioning.

In the present study, we assessed the potential of dipterans as functional indicators of extreme drought. Dipteran assemblages were sampled four times in 2014 and 2015 at 141 sites, from six reservoirs located in two semi-arid watersheds. Our results showed that dipteran functional traits changed over an extreme drought period (p

Hydropower dams are touted as one of the cleanest forms of energy production, yet they are associated with severe environmental impacts on both the physical structure and functioning of river ecosystems. The threat is particularly acute in the Brazilian Cerrado—a biodiverse savanna region, spanning over 2 million km2, that concentrates the headwaters of several critical South American watersheds. Our study analyzed the current distribution of large and small hydroelectric plants in the Cerrado and focused on understanding their effect on land use changes. We also propose a Dam Saturation Index (DSI) to help spur more integrated planning for this region. Results indicate that the Cerrado river basins contains 116 (30%) of Brazil’s large hydroelectric plants and 352 (36%) of its small hydroelectric plants. Moreover, these plants spurred significant land use changes within a 5-km buffer of the dams, with over 2255 km2 of native vegetation cleared by 2000 and an additional 379 km2 in the ensuing 20 years, could reach ~1000 km2. Based on the historical anthropization process in the Brazilian savannas, we expect new crops, pastures, and urban equipment to be incorporated into this landscape, with different impact loads.

Worldwide, freshwater environments are impacted by inputs of nutrients and dissolved organic matter from human activities. Yet, the recovery of aquatic systems is usually focused only on nutrient management. In our work, we presented the case of an urban and hypereutrophic environment (Pampulha reservoir, Belo Horizonte, Brazil) that receives discharges from several streams and was treated with lanthanum modified bentonite (Phoslock®) and microbial bioremediation (Enzilimp®). Our goals were to evaluate whether the treatment could improve the water quality and characterize the spatiotemporal variation of dissolved organic matter sources and indices according to absorbance and fluorescence measurements from the reservoir and streams post-application months (2018). In our results, the reservoir showed a relative decrease in its phosphorus concentration compared to data from before the treatment. On the other hand, carbon concentrations reached expressive values in the post-application months following a similar pattern found in the streams. Our data showed that the reservoir's high resistance in its hypereutrophic condition was related to the elevated loading of external inputs coming from the streams. The parallel factor analysis (PARAFAC) identified four main carbon sources, two of them being potential tracers of organic pollution in the Pampulha reservoir and watershed, together with absorbance and fluorescence indices. Our findings suggest that carbon parameters can be essential tools to provide adequate monitoring and optimization of water recovery attempts in complex, polluted environments.

This study aimed to evaluate the importance of physical, chemical and biological factors (e.g., chlorophyll-a, and carbon) in the regulation of the summer epilimnion thickness (Zmix) of the tropical lakes focusing on trends of the current environmental variability. We sampled a set of tropical lakes from the middle Rio Doce lacustrine system (Minas Gerais, Brazil) for two consecutive summers. Besides Zmix, we analyzed the visible light attenuation (KdPAR), dissolved organic carbon (DOC), chlorophyll-a (Chl-a), total suspended solids (TSS), and fetch. We also analyze the quality of the dissolved organic matter (DOM) through colored dissolved organic matter (CDOM), spectral slope (S), DOC-specific absorbance (SUVA) and the ratio between the absorbance at 250 nm and 365 nm (E250:365). Our results showed quite different results during the two years studied. In the summer of 2012, when there was higher rainfall, variations in Zmix were correlated to the optical factors associated with DOM quality, while in the drier summer of 2013 Chl-a, TSS and fetch were the variables that more explained Zmix. It suggests that DOM regulates the Zmix in the rainy periods in the studied tropical lakes and that control is determined by the balance between the DOM input (runoff) and output (such as photodegradation) of the aquatic systems. In reduced rain conditions (summer 2013), the factors responsible by chemistry photodegradation of DOM were predominant, and the organic matter was no longer controlling Zmix, which was driven by internal mixing, productivity, and the wind (Chl-a, TSS and fetch). In this study we showed how changes in precipitation might cause shifts in the factors that regulate the epilimnion thickness in tropical lakes.

Despite the increasing understanding about differences in carbon cycling between temperate and tropical freshwater systems, our knowledge on the importance of organic matter (OM) pools on light absorption properties in tropical lakes is very scarce. We performed a factorial mesocosm experiment in a tropical lake (Minas Gerais, Brazil) to evaluate the effects of increased concentrations of allochthonous and autochthonous OM, and differences in light availability on the light absorption characteristics of chromophoric dissolved organic matter (CDOM). Autochthonous OM deriving from phytoplankton ( ∼ Chl a) was stimulated by addition of nutrients, while OM from degradation of terrestrial leaves increased allochthonous OM, and neutral shading was used to manipulate light availability. Effects of the additions and shading on DOC, Chl a, nutrients, total suspended solid concentrations (TSM) and spectral CDOM absorption were monitored every 3 days. CDOM quality was characterized by spectral indices (S250–450, S275–295, S350–450, SR and SUVA254). Effects of carbon sources and shading on the spectral CDOM absorption was investigated through principal component (PCA) and redundancy (RDA) analyses. The two different OM sources affected CDOM quality very differently and shading had minor effects on OM levels, but significant effects on OM quality, especially in combination with nutrient additions. Spectral indices (S250–450 and SR) were mostly affected by allochthonous OM addition. The PCA showed that enrichment by allochthonous carbon had a strong effect on the CDOM spectra in the range between 300 and 400 nm, while the increase in autochthonous carbon increased absorption at wavelengths below 350 nm. Our study shows that small inputs of allochthonous OM can have large effects on the spectral light absorption compared to large production of autochthonous OM, with important implications for carbon cycling in tropical lakes.

Ecosystem-level metabolism is a good sentinel for human and natural disturbances in freshwater systems, responding from local changes (for example, land use) to regional and global changes (for example, climate). Despite the increasing understanding of metabolic processes in tropical lakes, our knowledge on how morphometric and catchment characteristics affect metabolic responses to those changes in tropical lakes is still very scarce. We investigated how metabolic rates in the upper mixed layer of twelve Brazilian tropical lakes responded to reduced rainfall, considering their lake area and drainage area ratio and the percentage of native forest cover in their drainage area. An 80% reduction in the 2013 rainy season rainfall, compared with 2012, resulted in a reduction of approximated 1 m in the water column depth, a 1–2 m deepening of the upper mixed layer, a 50% reduction in mean light availability, and a doubling in total phosphorus concentrations. These changes were associated with 38% increases in gross primary production (GPP), stimulated by higher nutrient concentrations and reduced photoinhibition. These effects of reduced rainfall were strongest in lakes with a small volume in relation to their catchment areas. Our results show that climatic-related reductions in precipitation in this tropical region will reduce lake volumes, affect temperature, water mixing, and nutrient supply with pronounced effects on lake metabolic processes and carbon cycling in this region.

Dissolved organic carbon (DOC) is one of the most abundant fractions of organic matter in aquatic systems and plays an important role in the dynamics of aquatic environments, controlling both the penetration and the underwater light radiation climate. DOC can be photodegraded by light, thus facilitating biodegradation, especially in regions where the incidence of solar radiation is high, such as higher altitudes and lower latitudes. This study quantified the photodegradation of dissolved organic material in a natural tropical lake surrounded by native forests (Brazilian Atlantic Forest) through two experiments: i) the first experiment exposed concentrated autochthonous, allochthonous, and lake water to in situ solar radiation; ii) this experiment also exposed the same organic material to artificial UV radiation in an incubator under controlled conditions. The quality and quantity of dissolved organic carbon were measured using indices based on carbon absorbance and fluorescence spectrum. In the in situ experiment, it was observed that the DOC degradation profile of the concentrated allochthonous and autochthonous organic material were distinct from each other in the absorbance indices, and the lake water mostly resembled the latter one. On the other hand, we did not see evidence of any significant difference among treatments in the laboratory experiment. An increase in the SR index and a concomitant decrease in the fluorescence of humic compounds and SUVA254 over time were observed. In both experiments, the amount of degraded organic material over time was low and some possible explanations are discussed.

Collectively, reservoirs created by dams are thought to be an important source of greenhouse gases (GHGs) to the atmosphere. So far, efforts to quantify, model, and manage these emissions have been limited by data availability and inconsistencies in methodological approach. Here, we synthesize reservoir CH4, CO2, and N2O emission data with three main objectives: (1) to generate a global estimate of GHG emissions from reservoirs, (2) to identify the best predictors of these emissions, and (3) to consider the effect of methodology on emission estimates. We estimate that GHG emissions from reservoir water surfaces account for 0.8 (0.5–1.2) Pg CO2 equivalents per year, with the majority of this forcing due to CH4. We then discuss the potential for several alternative pathways such as dam degassing and downstream emissions to contribute significantly to overall emissions. Although prior studies have linked reservoir GHG emissions to reservoir age and latitude, we find that factors related to reservoir productivity are better predictors of emission.

Bacterioplankton communities have a pivotal role in the global carbon cycle. Still the interaction between microbial community and dissolved organic matter (DOM) in freshwater ecosystems remains poorly understood. Here, we report results from a 12-day mesocosm study performed in the epilimnion of a tropical lake, in which inorganic nutrients and allochthonous DOM were supplemented under full light and shading. Although the production of autochthonous DOM triggered by nutrient addition was the dominant driver of changes in bacterial community structure, temporal covariations between DOM optical proxies and bacterial community structure revealed a strong influence of community shifts on DOM fate. Community shifts were coupled to a successional stepwise alteration of the DOM pool, with different fractions being selectively consumed by specific taxa Typical freshwater clades as Limnohabitans and Sporichthyaceae were associated with consumption of low molecular weight carbon, whereas Gammaproteobacteria and Flavobacteria utilized higher molecular weight carbon, indicating differences in DOM preference among Glades. Importantly. Verrucomicrobiaceae were important in the turnover of freshly produced autochthonous DOM, ultimately affecting light availability and dissolved organic carbon concentrations. Our findings suggest that taxonomically defined bacterial assemblages play definite roles when influencing DOM fate, either by changing specific fractions of the DOM pool or by regulating light availability and DOC levels. (C) 2019 Elsevier B.V. All rights reserved.

Las concentraciones de nitrógeno y de fósforo son importantes no solo para el monitoreo del estado trófico de los diferentes ecosistemas acuáticos sino también esos nutrientes se constituyen en parámetros esenciales para calcular la capacidad de soporte de esos sistemas para usos múltiples como la acuicultura practicada en jaulas. En este estudio hemos evaluado diferentes algoritmos de interpolación para determinar la variabilidad espacial de la concentración de nitratos en el embalse de Nova Ponte, Minas Gerais (MG), Brasil. Se trata de un embalse de cabecera, con características predominantemente oligotróficas y un alto tiempo de retención hidráulica. Los datos de concentración de nitratos se obtuvieron in situ por medio de una sonda multiparámetros YSI modelo 6920, en agosto de 2008, en un total de 59 puntos de muestreo distribuidos a lo largo de la represa. Para la verificación de la dependencia espacial se calculó la razón de dependencia (RD) obteniéndose un valor de 20.35 que mostró dependencia fuerte, por lo que se optó por Krigeaje. Fueron probados dos métodos de Krigeaje, el Krigeaje Ordinario y el Universal y evaluados por medio del error medio estandarizado de los valores predichos, del error cuadrático medio y del error cuadrático medio estandarizado. De los dos métodos probados el que presentó mejor desempeño estadístico fue el Krigeaje Ordinario. La concentración de nitrato fue espacializada para toda el área de estudio presentando una variación de 273 µg.l-1 a 13.28 µg.l-1 para la Krigeaje Univeral y de 277.76 µg.l-1 a 16,19 µg.l-1 para la Krigeaje Ordinario. Los resultados de ambos procedimientos de interpolación sugieren claramente la existencia de una “pluma” de contaminación por nitratos en las aguas subsuperficiales de la represa de Nova Ponte. El aporte de nitratos a la represa ocurre principalmente a través del Río Santo Antônio, donde es posible identificar un claro patrón espacial con concentraciones más elevadas de esa especie de nitrógeno inorgánico aguas arriba, en dirección a la ciudad de Patrocinio (MG). Ese patrón sugiere que tanto las fuentes difusas como la escorrentía de las actividades agrícolas y descargas puntuales de aguas negras aguas arriba de la ciudad, pueden estar impulsando esa contaminación por nitratos.

Lakes are important components in the carbon cycling and threatened by direct and indirect human activities, which ultimately affect metabolic processes. We analyzed the daily dynamics of the air-water CO2 and O2 fluxes over nine days in a mesocosm experiment to determine how the inputs of inorganic nutrients (+NUTRI) and allochthonous organic matter (+OM) affected the metabolic processes. The control, representing the original state of the lake, showed low coefficient of variability among the days sampled and a predominant FCO2 to the atmosphere, but with mean values close to zero (0.2 ± 0.3 mmol m−2 d−1). In +NUTRI and +NUTRI+OM treatments mesocosms, the FCO2 and FO2 showed similar response, where the FCO2 was negative during all days (mean −1.8 ± 1.1 and −1.9 ± 1.2 mmol m−2 d−1, respectively) and FO2 was initially negative, becoming positive after day 4, and decreasing again after day 6. The +OM treatment intensified the FCO2 to the atmosphere (mean 0.4 ± 0.9 mmol m−2 d−1) with highest values at day 7. The ecosystem in +NUTRI and +NUTRI+OM treatments showed a similar recovery (8 days), while +OM treatment mesocosm was similar to the control conditions. The models showed that nutrients promoted larger overall changes and higher daily variability in both FCO2 and FO2, leading to a CO2 influx, followed by organic matter addition. In conclusion, this mesocosm experiment showed the fast response of the lakes to even small disturbances (e.g organic matter addition), which can intensify the sink or the source of carbon to the atmosphere and change the role of the lakes in the global carbon cycling.

De Mello NAST, Brighenti LS, Barbosa FAR, Staehr PA, Bezarra Neto JF. 2017. Spatial variability of methane (CH4) ebullition in a tropical hypereutrophic reservoir: silted areas as a bubble hot spot. Lake Reserv Manage. 35:105—114.The concentration of methane (CH4) has doubled in the atmosphere over the last 200 yr, raising the need to understand emissions of this potent greenhouse gas from inland waters. CH4 ebullition is the dominant pathway in shallow aquatic environments and is difficult to quantify due to its episodic nature and heterogeneous spatial distribution. We investigated the temporal and spatial variability of CH4 ebullition during 2013 in a shallow hypereutrophic urban reservoir, in Belo Horizonte City, Brazil. The average emission measured during summer was 780 mg CH4/m2/d, ranging from 1 to 3070 (n = 75). During winter, the average emission was 316 mg CH4/m2/d, ranging from 4 to 1253 (n = 75). A strong spatial variation (P < 0.001) was observed across the reservoir in both seaso...

Aim: The main objective of this study was to evaluate the presence of temporal coherence of limnological variables and pairs of lakes considering four tropical lakes of the Rio Doce State Park, using monthly data from the Long-Term Ecological Research Program (LTER) between the years of 2004 to 2009. Methods Subsurface data (0.5 meters) from the Carioca, Dom Helvécio, Gambazinho, and Jacaré Lakes were used in the analysis. We estimated the temporal coherence from the creation of time series for each of the variables. Through these series, we calculated the Pearson correlation coefficient between all pairs of lakes (N=6) and performed the average. We also analyzed the correlation between the temporal coherence found for the different pairs of lakes and two predictors of spatial patterns: proximity and exposure to climatic factors. The spatial proximity of the lake pairs was calculated in kilometers, and the exposure to climatic factors was estimated using two metrics: surface area and surface area/mean depth ratio. Results The largest temporal coherence levels were recorded for water temperature (0.97), pH (0.78), and dissolved organic carbon (DOC) (0.74). The lowest levels were found for chlorophyll-a (0.25) and phytoplankton richness (-0.02). The average temporal coherence was 0.58. Different from other studies, no significant correlation was found between the synchronicity of the lake pairs and the differences in their exposure to climatic factors. Also, no relation was found with the spatial proximity. Conclusions Our results demonstrate the existence of temporal coherence in tropical lakes to compatible levels with those found in temperate regions. Our work contributes to the knowledge of how synchronicity works at different set of lakes and climatic regions. Resumo Objetivo: Este estudo teve como objetivo principal avaliar a presença de coerência temporal de variáveis limnológicas e pares de lagos para quatro lagos tropicais da região do Parque Estadual do Rio Doce, utilizando dados mensais do Programa de Pesquisas Ecológicas de Longa Duração (PELD) entre os anos de 2004 a 2009. Metodologia Dados de sub-superfície (0,5 metro) das lagoas Carioca, Dom Helvécio, Gambazinho e Jacaré foram utilizados nas análises. Nós estimamos a coerência temporal a partir da criação de séries temporais para cada uma das variáveis. Por meio dessas séries, foi calculado o coeficiente de correlação de Pearson entre todos os pares de lagos (N=6) e realizado a média. Nós também analisamos a correlação entre a coerência temporal encontrada para os diferentes pares de lagos e dois preditores de padrões espaciais: proximidade e exposição a fatores climáticos. A proximidade espacial dos pares de lagos foi calculada em quilômetros e a exposição a fatores climáticos foi estimada utilizando duas métricas: área superficial e área superficial / profundidade média. Resultados Os maiores níveis de coerência temporal foram registrados para temperatura da água (0,97), pH (0,78) e carbono orgânico dissolvido (COD) (0,74). Já os menores níveis foram verificados para clorofila-a (0,25) e riqueza fitoplanctônica (-0,02). A coerência temporal média foi de 0,58. Diferente de outros estudos, não foi encontrado uma correlação significativa entre as sincronicidades dos pares de lagos e as diferenças de suas exposições a fatores climáticos. Além disso, nenhuma relação foi encontrada com a proximidade espacial. Conclusões Nossos resultados demonstram a existência de coerência temporal em lagos tropicais a níveis compatíveis com aquelas encontradas em regiões temperadas. Nosso trabalho contribui para o conhecimento de como a sincronicidade funciona em diferentes conjuntos de lagos e regiões climáticas.

We studied the effects of particulate and dissolved optically active components on the attenuation of photosynthetic active radiation (PAR) in a tropical lake. The temporal and spatial distribution of tripton, Chl-a and a CDOM (440) and their relative contribution to the diffuse PAR attenuation coefficient (Kd) was investigated at 21 sites (dry and wet seasons and two intermediate periods) and at monthly interval at 1 pelagic site. Higher values of Kd were observed during the mixing period, characterized by a higher concentration of tripton and Chl-a compared to the stratified rainy season. In the spatial sampling PAR attenuation was dominated by tripton absorption/scattering (average relative contribution of 79%), followed by Chl-a (average 11.6%). In the monthly sampling tripton and Chl-a accounted for most of the Kd with relative contributions of 47.8% and 35.6%, respectively. Multiple linear regression analysis showed that Chl-a and tripton in combination explained 97% of the monthly variation in Kd (p

AIM: To study the distribution, structure, size and density of fish in the karst lake: Lagoa Central (Lagoa Santa, MG - surface area: 1.7 km²; mean depth: 4.0 m; and maximum depth: 7.3 m). METHODS: The hydroacoustic method with vertical beaming was applied, using the echosounder Biosonics DT-X with a split-beam transducer of 200 kHz. The analysis of the acoustic data was performed with the software Visual Analyzer (Biosonics Inc.). Thematic maps of density echoes associated with fish, estimated by the technique of echo-integration, were made using the kriging interpolation. The density and vertical distribution of insonified fish were estimated using the technique of echo-counting. RESULTS: The lake had a mean density of 0.89 echoes associated with fish per m², showing large spatial variations in the density of fish. The size estimated for the echoes associated with fish range from 2.7 to 15.9 cm (mean = 5.3 cm). CONCLUSIONS: The use of hydroacoustic to obtain rapid and realistic estimates of fish abundance and vertical distribution of the fish stock was successful OBJETIVOS: Estudar a distribuição, densidade e estrutura de tamanho de peixes nas águas da Lagoa Central (Lagoa Santa, MG - área: 1,7 km²; profundidade média: 4,0 m; e profundidade máxima: 7,3 m). MÉTODOS: O estudo utilizou o método hidroacústico com orientação vertical. Uma sonda Biosonics DT-X, equipada com um transdutor split-beam de 200 kHz, foi utilizada. A análise dos dados acústicos foi feita com o programa Visual Analyser (Biosonics Inc.). Mapas temáticos de densidades dos ecos associados a peixes, estimadas através da técnica de eco-integração, foram confeccionados utilizando a interpolação kriging. Já o número e distribuição vertical dos peixes insonificados foram determinados utilizando a técnica de eco-contagem. RESULTADOS: A Lagoa Central apresentou uma densidade média de 0,89 ecos associados a peixes por m², indicando grandes variações na densidade dos peixes em áreas particulares do lago. A estimativa de tamanho dos ecos associados a peixes variou de 2,7 a 15,9 cm (média = 5,3 cm). CONCLUSÕES: O uso de hidroacústica para obter estimativas rápidas e realistas de abundância de peixes e distribuição vertical da população de peixes foi bem sucedida

We investigated how allochthonous and autochthonous sources of dissolved organic matter (DOM) affected the optical conditions and chemical characteristics of two contrasting tropical freshwater systems (Dom Helvécio-DH and Pampulha reservoir) in a dry and rainy period in 2013. We analyzed PAR (photosynthetically active radiation) and UV (ultraviolet) attenuation coefficients, nutrients, chlorophyll-a (Chl-a), dissolved organic matter (DOC) and spectral characteristics of CDOM (colored dissolved organic matter). Significant differences in CDOM sources and quantity were observed, with a dominantly terrestrial input in DH during the rainy period with approximately 50% higher DOC and Chl-a levels, and a doubling in total nitrogen (TN) and total phosphorus (TP) compared to the dry winter period. The eutrophic Pampulha had several fold higher levels of DOC, Chl-a, TN and TP, with organic matter of mostly originating from phytoplankton in both seasons. Differences in source and quantity had strong implications on water transparency, DOC concentrations, CDOM quality and its susceptibility to photo- and biodegradation. DH was several fold clearer in both the UV and PAR spectrum. In DH transparency to both UV and PAR radiation was highest during the summer, suggesting elevated photo- and biodegradation during stratification. Pampulha was most transparent in the dry period even during period of algal bloom. In both systems we observed seasonal variations in concentrations of nutrients and Chl-a, and in DH differences were also found in DOC concentrations as well as the specific UV absorbance (SUVA254) and molecular size (M). Our results documents that different sources of DOM and seasonal inputs reflect in the seasonality of apparent and inherent optical properties and nutrients availability with implications for water quality and aquatic community.

O presente estudo avaliou a precisão de dois protocolos usados para a confecção de uma carta batimétrica para a Lagoa Central (Lagoa Santa, Estado de Minas Gerais, Brasil). Numa segunda etapa, o estudo estimou todos os parâmetros morfométricos primários e secundários desse ambiente. Finalmente, o estudo avaliou a importância dessas informações na qualidade de água e na ecologia geral do sistema. Os protocolos foram baseados no uso de dois sistemas distintos, usados para o levantamento batimétrico: uma ecossonda Biosonics DT-X (Biosoncs Inc.) e um Ecobatímetro SonarLite (Ohmnex Ltda), ambos acoplados a um D-GPS (Differential Global Positioning System) para a obtenção das coordenadas geográficas de cada profundidade medida. A Lagoa Central de Lagoa Santa é um pequeno lago natural, raso (Zmax < 7,5 m), com profundidade relativa baixa (Zr = 0,5%) e formato côncavo. Essas características a tornam menos propensa à formação de estratificação térmica estável e, portanto, menos sensível à formação de gradientes químicos verticais na coluna de água. Essa configuração pode ser vista como um dos fatores principais que impedem o agravamento do processo de eutrofização verificado nesse sistema.The goal of this study was to verify the utility and accuracy of two tools to obtain a bathymetric chart for Lagoa Central (Lagoa Santa, State of Minas Gerais, Brazil) and also to assess the morphometric parameters of the lake and their implications in the ecology of this system. The tested tools were the Biosonics DT-X (Biosonics Inc.) echosounder and the SonarLite (Ohmnex Ltda) bathymeter, both coupled to a Differential Global Positioning System (DGPS) to obtain the geographic coordinates associated with the depth in each point. Lagoa Central is a small, shallow (Zmax < 7.5 m), with low relative depth values (Zr = 0.5%) and concave. This makes the water body less prone to thermal stratification and more susceptible to eutrophication. Both investigated equipments demonstrated to be suitable for the survey, user-friendly, low-cost and with sub-metric accuracy.

The present study deals with the ecological impacts of the introduction of two alien species of piscivorous fish in several lakes of the Middle Rio Doce lake district in Minas Gerais, Brazil. It was demonstrated that these effects were not restricted only to the fish community. The introduction of the predatory red piranha Pygocentrus nattereri and the tucunaré Cichla cf. ocellaris caused not only a sharp decrease in the number of native fish species, but also major shifts in other trophic levels. Just after the fish were introduced, most lakes began to show conspicuous changes in phytoplankton species composition, in which Cyanophyceae gradually came to dominate. The zooplankton community lost several species, and in some cases, such as Lake Carioca, all the cladoceran species disappeared. On the other hand, invertebrate predators, represented by the dipteran Chaoboridae, boomed in the lake, with higher densities of exotic species, probably as a result of the "ecological release" by reduction of the original fish fauna. There was a general trend of species loss in different trophic levels. All these changes are apparently associated with decreases in water quality. The present situation in these lakes demands new approaches to the management and conservation of these ecosystems.

A Lagoa da Pampulha é um reservatório artificial que integra o Complexo Arquitetônico da Pampulha, em Belo Horizonte – MG. Nas últimas décadas, o processo de assoreamento na represa intensificou-se, devido ao adensamento populacional e industrial em sua bacia hidrográfica. Nesse período, uma série de intervenções foram realizadas no reservatório, alterando-lhe aspectos morfométricos primários e secundários. Este trabalho tem por objetivo apresentar a morfometria atual da Lagoa da Pampulha. Fez-se para tanto um levantamento batimétrico detalhado da represa, possibilitando a confecção de sua carta batimétrica e o cálculo de parâmetros morfométricos primários e secundários. Os resultados obtidos foram comparados com trabalhos anteriores. Houve ganho de volume em relação a 1999, e outros índices morfométricos também sofreram alterações, reflexo de intervenções recentes. O conhecimento e a interpretação correta do conjunto de dados apresentados são de grande valia para o planejamento de ações que busquem a recuperação da Lagoa da Pampulha.

The effect of water transparency, dissolved oxygen concentration and the invertebrate predator Chaoborusbrasiliensis on the day–night vertical distribution of the copepod cyclopoid Thermocyclops inversus was investigated in a shallow tropical reservoir, Nado Reservoir, Belo Horizonte, Brazil. Diel cycles were carried out over a period of 12 consecutive months, between October 1999 and September 2000. The different developmental stages of T. inversus exhibited diel vertical migration (DVM) and displayed a clear ontogenetic trend, with the amplitude of DVM increasing with the age of the organism, and ranging from 0.4 m to 0.8 m for nauplii, 0.4 m to 1.2 m for copepodite, and 1.1 m to 2.1 m for adults. We observed that seasonal changes in dissolved oxygen and C. brasiliensis directly influenced the vertical distribution of the copepod population in this reservoir. Furthermore, it was showed that the diurnal vertical migration is an important predator avoidance behavior since it diminished the spatial overlap between prey and its potential predator. This finding supports the hypothesis that the vertical migration is a defense mechanism against predation. Thus, T. inversus is able to remain in the anoxic layers during day light hours, and at night they move upwards avoiding hypolimnetic waters to escape from predation by Chaoborus.

Inúmeros trabalhos têm mostrado que a larva de Chaoborus desenvolve migração vertical diária, buscando evitar a predação por peixes, e que a amplitude da migração vertical cresce com o estágio larval. Neste estudo, monitorou-se a distribuição vertical de Chaoborus brasiliensis durante o dia e à noite de outubro/99 a setembro/00, em um reservatório raso, a lagoa do Nado. A profundidade média em que cada estádio foi encontrado foi estimada durante o dia e à noite e comparada à amplitude da migração entre eles. Adicionalmente, buscou-se determinar se a distribuição vertical de C. brasiliensis estava relacionada com a concentração crítica de oxigênio, 1,0mg.l-1. Não foram encontradas diferenças significativas entre a amplitude da migração vertical diária entre os estádios. A profundidade média em que os estádios eram encontrados durante o dia e à noite mostrou-se positivamente correlacionada com a profundidade da concentração crítica de oxigênio. Tal fato suporta a hipótese de que a migração vertical seja um mecanismo de defesa contra a predação por peixes, considerando que as larvas desse díptero usam a camada anóxica como refúgio contra os peixes predadores.Many investigations have shown that Chaoborus larvae develop diel vertical migration (DVM) to avoid fish predation and that this migration's amplitude is often associated with the instar stage. In this study, the Chaoborus brasiliensis vertical distribution was monitored in a shallow reservoir (Nado Lagoon, Belo Horizonte, Brazil), during the diel cycle, from October 1999 to September 2000. The mean depth in which each stage was found was estimated day and night and compared to their migration amplitude. No association was found between instar phase and DVM amplitude. Nevertheless, a clear association was found between the dissolved oxygen critical concentration and the amplitude of Chaoborus DVM. 1.0 mg.1(-1) was considered the concentration below which fish cannot survive. This finding gives support to the hypothesis that vertical migration is a defense mechanism against predation, since the larvae use the anoxic layer as a refuge against fish predation.

The effects of Chaoborus brasiliensis (Diptera, Chaoboridae), an invertebrate predator, on the zooplankton spatial distribution in a shallow tropical reservoir, Nado Lagoon, were investigated in this work. The habitat overlap degree, i.e., the overlap in the vertical distribution of predator and potential preys was measured during diel vertical migration (DVM). The study focused the reservoir predominant taxa (defined as the most frequent and abundant species). Several organisms showed DVM (Brachionus falcatus, B. caudatus, B. angularis, Moina micrura and Thermocyclops minutus), while in others this behavior was not clear, or even not detected (Keratella cochlearis, K. tropica, K. bostoniensis and T minutus nauplii). The conclusion was that C. brasiliensis influenced directly most zooplankters spatial distribution in this reservoir, and DVM was important to reduce spatial overlapping with the predator. Furthermore, the study showed that such behaviors change significantly along the season cycle.Foi analisado o efeito do predador invertebrado, Chaoborus brasiliensis (Diptera, Chaoboridae), sobre a distribuição espacial dos táxons predominantes da comunidade zooplanctônica de um reservatório tropical raso, lagoa do Nado, explorando as mudanças na sobreposição espacial entre predador e presas durante a migração vertical diária. A comunidade zooplanctônica apresentou uma variada gama de respostas à pressão de predação exercida pelas larvas de Chaoborus. Diversos táxons exibiram MVD (Brachionus falcatus, B. caudatus, B. angularis, Moina micrura, Thermocyclops minutus) e outros em que esse comportamento não foi tão nítido ou não foi detectado (K. cochlearis, K. tropica, K. bostoniensis e náuplios de T. minutus). A maioria dos táxons estudados tiveram a sua distribuição vertical associada à presença desse predador invertebrado, e a migração vertical diária dessas espécies foi importante na redução da sobreposição espacial com o predador. Além disso, o estudo demonstrou que esses padrões experimentam consideráveis mudanças ao longo do ciclo sazonal.

São descritas as características morfométricas de um pequeno reservatório, a lagoa do Nado. Trata-se de lago artificial raso, com 2,7 m e 7,6 m de profundidades média e máxima, respectivamente. A localização, no fundo de um pequeno vale, rodeado por vegetação de grande porte, elevada profundidade relativa (5,5%) e bacia de acumulação de formato cônico (Dv = 1,07), indica uma alta estabilidade física da coluna de água. O tempo de retenção da água no reservatório, no período seco, foi de 78 dias e, no período chuvoso, de 2,1 dias. O presente estudo ainda apresenta a primeira carta batimétrica do reservatório. Finalmente, o estado trófico foi avaliado mensalmente, de setembro/99 a setembro/00, utilizando-se o índice de estado trófico (IET) de Carlson. O reservatório foi considerado como meso-eutrófico ao longo do período de amostragem.This study presents the morphometric characteristics of a small urban reservoir: Nado Lagoon. It is an artificial, shallow lake with 2.7 m. mean depth and 7.6 m. maximum depth. It is located at the bottom of a relatively large valley, surrounded by tall trees, with high relative depth (5.5%) and conical accumulation basin (Dv = 1.07), with a high water column physical stability. The reservoir mean retention time was 78 days during the dry season and 2.1 days during the rainy season. This study also presents the first bathymetric map of the reservoir. The reservoir trophic state was monthly evaluated from September 1999 to September 2000, through Carlson trophic state index (TSI). The results classify the reservoir as meso-eutrophic throughout the sampling period.

AIM: This study aims to demonstrate the potential of hydroacoustics in the study of behavior of the invertebrate Chaoborus and fish in neotropical water environments; METHODS: Synoptic campaigns were conducted in May and June-2008 in Dom Helvécio and Carioca lakes, at the Parque Estadual do Rio Doce (MG), and Nado reservoir, Belo Horizonte (MG). The acoustic scattering of targets was studied using a downward-oriented split-beam 200 kHz echosounder; RESULTS: We detected clear echo signals from fish and Chaoborus larvae, which can be viewed in high density in all environments studied. The normal migratory behavior of the larvae of Chaoborus could be easily monitored in the Dom Helvécio Lake and the Nado reservoir. However, this behavior was not seen in Carioca Lake; CONCLUSIONS: This study revealed the potential application of acoustic approaches to study the behavior of fish and zooplankton organisms in freshwater aquatic systems. OBJETIVOS: O presente estudo tem como objetivo demonstrar as potencialidades da hidroacústica no estudo do comportamento do predador invertebrado Chaoborus e de peixes em ambientes aquáticos tropicais; MÉTODOS: Foram realizadas campanhas diurnas e noturnas em maio e junho/2008 nas lagoas Dom Helvécio e Carioca, no Parque Estadual do Rio Doce e no reservatório do Nado em Belo Horizonte (MG). O espalhamento acústico dos alvos foi estudado utilizando-se uma ecossonda com transdutor digital "split-beam" de 200 kHz direcionado verticalmente para o fundo do lago; RESULTADOS: A ecossondagem nos permitiu detectar eco-sinais claros provenientes de peixes e das larvas de Chaoborus, que estavam presentes grande densidade em todos os ambientes estudados. O comportamento migratório normal das larvas de Chaoborus pôde ser acompanhado facilmente na Lagoa Dom Helvécio e no reservatório do Nado. Entretanto, tal comportamento não foi visualizado na Lagoa Carioca. CONCLUSÕES: Os resultados mostrados neste estudo revelaram o potencial de aplicação da abordagem acústica no estudo do comportamento de peixes e organismos zooplanctônicos em sistemas aquáticos de água doce.

Foi analisado o efeito do predador invertebrado, Chaoborus brasiliensis (Diptera, Chaoboridae), sobre a distribuição espacial dos táxons predominantes da comunidade zooplanctônica de um reservatório tropical raso, lagoa do Nado, explorando as mudanças na sobreposição espacial entre predador e presas durante a migração vertical diária. A comunidade zooplanctônica apresentou uma variada gama de respostas à pressão de predação exercida pelas larvas de Chaoborus. Diversos táxons exibiram MVD (Brachionus falcatus, B. caudatus, B. angularis, Moina micrura, Thermocyclops minutus) e outros em que esse comportamento não foi tão nítido ou não foi detectado (K. cochlearis, K. tropica, K. bostoniensis e náuplios de T. minutus). A maioria dos táxons estudados tiveram a sua distribuição vertical associada à presença desse predador invertebrado, e a migração vertical diária dessas espécies foi importante na redução da sobreposição espacial com o predador. Além disso, o estudo demonstrou que esses padrões experimentam consideráveis mudanças ao longo do ciclo sazonal.

This is a long-term study (1993-1998) on the effects of increasing eutrophication on the crustacean zooplankton structure in a eutrophic reservoir. The study first demonstrates that the eutrophication increase verified is a phenomenon well described by a single abiotic variable: total phosphorus. During the study period, zooplankton suffered extensive qualitative and quantitative changes. Significant size and biomass responses of certain zooplankton groups to the temporal variations of total phosphorus were found. These findings suggest that the variables size and biomass of major zooplankton groups should always be considered simultaneously in order to assess impacts caused by eutrophication on the structure of zooplankton.

The temporal variability of energetic reserves of zooplankton in the eutrophic Pampulha reservoir was investigated during two successive annual cycles. The effects of dominance of large filter-feeding cladocerans (Daphnia) and the occurrence of massive blooms of the cyanobacteria Microcystis on the energetic reserves of zooplankton were tested. This study showed that phytoplankton composition has a greater effect on energetic reserves of zooplankton. Some associations between lipid levels and the specific composition of zooplankton were also found. This study also demonstrated that the elementary composition of phosphorus in zooplankton can be used as an estimator of the nutritional status of zooplankton. A variabilidade temporal de reservas energéticas do zooplâncton no reservatório eutrófico da Pampulha foi investigada durante dois ciclos anuais sucessivos. Foram testados os efeitos da presença dos grandes cladóceros (Daphnia) e a ocorrência de florações maciças da cianobactéria Microcystis sobre as reservas energéticas do zooplâncton. Este estudo mostrou evidências de que a composição do fitoplâncton apresentou efeito intenso sobre as reservas energéticas do zooplâncton. Foram também encontradas associações entre o nível de lipídeos e a composição específica do zooplâncton. Demonstrou-se ainda que a composição elementar do fósforo no zooplâncton pode ser usada como indicador do status nutricional do zooplâncton.

We investigated the effects of increase in sampling effort (30–1043 sampling points) on the accuracy of assessment of the spatial patterns of surface-water quality in a eutrophic tropical reservoir. The investigation was carried out during the dry season, when previous investigations showed that the spatial heterogeneity is more stable. A multi-parameter Yellow Springs Instruments probe coupled to a TechGeo D-GPS was used. This system is equipped to measure and store in a continuous recording mode, several physical and chemical parameters linked to geographical coordinates obtained with a precision of less than 1 m. We used different geostatistical approaches to determine the optimal number of sampling points required to reflect the real spatial patterns of water quality in the system. This approach was tested in a small tropical reservoir (Ibirite) that receives effluents from an oil refinery (the state-owned REGAP oil refinery, PETROBRAS) located near the city of Belo Horizonte. The study showed not only that the spatial patterns of water quality are significantly affected by sampling effort but also it was demonstrated that the establishment of an adequate sampling program is a critical point for the precise identification of source points of pollution. The results of this investigation enabled us to demonstrate the potential uses and limits of this method for rapid assessment of the water quality of lakes and reservoirs that receive external inputs of water contaminants or nutrients.

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Lagos são importantes centros de transformação de carbono e devido a isso, estão sujeitos aos efeitos das mudanças climáticas enquanto também são capazes de regulá-las. O metabolismo aquático é amplamente utilizado para monitorar os efeitos do clima nesses ecossistemas, uma vez que responde rapidamente a diversas alterações induzidas ou provocadas pelo clima. Sabendo disso, identificar e compreender as alterações na dinâmica da produção primária bruta (PPB), da respiração (R) e da produção líquida ecossistêmica (PLE) é crucial para melhor caracterizar as vulnerabilidades desses ambientes frente a diferentes distúrbios. O objetivo deste estudo foi comparar as mudanças físico-químicas, e nas taxas metabólicas de um lago tropical que perdeu cerca de 60% de volume nos últimos 10 anos. Acredita-se que a diminuição de volume pode levar a um aumento nas concentrações de nutrientes e de carbono, reduzindo a transparência e a disponibilidade de luz, influenciando as taxas metabólicas direta e indiretamente. Sendo assim, foram testadas as predições de que: i) as taxas de PPB e de R epilimnéticas aumentariam; e ii) o papel da sazonalidade no metabolismo epilimnético enfraqueceria devido as alterações físico-químicas induzidas pela perda de volume. Dois períodos distintos e duas estações (seca e chuva) foram utilizadas. O primeiro compreendeu os anos de 2011 e 2012 (P1) e o segundo compreendeu os anos entre 2017-2019 (P2), quando o lago apresentou um volume 60% menor que durante o P1. As taxas metabólicas foram estimadas utilizando dados de alta frequência e a técnica da modelagem inversa. Além disso, o fluxo atmosférico foi estimado utilizando 10 equações para entender o papel dos processos físicos nas estimativas do metabolismo. De uma forma geral, no P2 as concentrações de nitrogênio e fósforo total, clorofila-a, carbono orgânico dissolvido, sólidos totais em suspensão aumentaram e houve uma redução da disponibilidade de luz na camada de mistura. Tanto a PPB quanto a R aumentaram durante o P2 (40% e 38%, respectivamente). Enquanto a R variou sazonalmente e registrou os maiores valores na estação seca, a PBB foi semelhante na seca e na chuva, em contraste com o P1, onde ambas as taxas variaram de acordo com a estação, sendo maiores na estação seca. Com relação a PLE, enquanto durante o P1 o lago esteve próximo ao equilíbrio com a atmosfera (-0.18 ± 0.29 mmol O2 m-3 d-1; média ± erro padrão), no P2 houve uma troca entre autotrofia na chuva e heterotrofia na seca (6.44 ± 0.51 mmol O2 m-3 d-1 e -18.98 ± 1.81 mmol O2 m-3 d-1, respectivamente). Além disso, a diminuição do volume do lago no P2 tornou o tamanho da camada de mistura mais variável durante todo o período. Uma vez que processos físicos também afetam a oscilação do OD na água, a mudança na estabilidade da estratificação também contribuiu para as mudanças observadas nas taxas metabólicas. O metabolismo ecossistêmico mudou durante o período de seca hidrológica persistente e é provável que continue mudando em resposta às variações atuais e futuras no padrão pluviométrico e de temperatura. Lakes are important centers of carbon transformation, and due to that, are subjected to the effects of climate change, while they are also capable of regulating these changes. Aquatic metabolism is considered a good sentinel of climate, once the metabolic rates respond quickly to a series of alterations induced or caused by climate change. Therefore, identifying and understanding the alterations in lake gross primary production (GPP), respiration (R), and net ecosystem production (NEP) dynamics is vital to better characterize the vulnerabilities of these environments to natural and to human-induced disturbances. The study aimed at comparing the changes in physical, chemical, and, especially, in the dynamic and in the magnitude of metabolic rates of a tropical lake that lost about 60% of its volume in the last 10 years. It is believed that the decrease in volume can lead to an overall increase in nutrient and dissolved organic matter concentrations, reducing water transparency and light availability. These changes may influence metabolic rates directly and indirectly. Therefore, two predictions were assessed: i) epilimnetic PPB and R would increase; and ii) the role of seasonality in epilimnetic metabolism would diminish due to the physicochemical changes induced by water loss. Two distinct periods were sampled, the first one, between 2011-2012 (P1), and the second one, between 2017-2019 (P2), when the lake volume was ca. 60% lower than during P1. Each period was also evaluated between seasons (rainy and dry season). The metabolic rates were estimated using high-frequency measurements and the inversing modeling approach. Moreover, the atmospheric flux was calculated using 10 different equations to understand the role of physical processes in metabolic rates estimates. In general, during P2 there was an increase in concentrations of total nitrogen, total phosphorus, chlorophyll-a, dissolved organic carbon, total suspended solids, and a decrease in light availability in the upper mixed layer. Both GPP and R increased during P2 (40% and 38%, respectively). While R rates were different between seasons, with the highest rates registered during the dry season, GPP was similar in both dry and rainy seasons, contrasting with P1, when both rates responded to seasonality. In relation with NEP, during P1 the lake was close to atmosphere equilibrium (-0.18 ± 0.29 mmol O2 m-3 d-1; mean ± standard error), however, in P2 there was a switching between autotrophy during the rainy season and heterotrophy in the dry season (6.44 ± 0.51 mmol O2 m-3 d-1 e -18.98 ± 1.81 mmol O2 m-3 d-1, respectively). Moreover, the decrease in lake volume during P2 turned the mixed layer depth more variable during the entire period. Since the physical processes also affect the DO oscillation in the water column, the change in the stability of stratification also contributed to the changes observed in metabolic rates. The results of this study showed that ecosystem metabolism changed during the period of persistent hydrological drought, and it may continue to change in response to the ongoing variation in rainfall and temperature patterns.

CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Outra Agência Grande parte dos ambientes de água doce tropicais já enfrentaram algum tipo de distúrbio causado por ações antrópicas, como a eutrofização e a exploração desses recursos hídricos para captação de água utilizada na agricultura e pecuária, entre outros. Atualmente estes distúrbios estão sendo amplificados a medida que os efeitos das mudanças climáticas se fazem mais presentes, como as alterações nos padrões de chuva e na intensidade da luz solar incidente sobre o planeta, especialmente em ambientes tropicais. Tais alterações provocam consequências em todo o metabolismo e funcionamento aquático, assim como na estrutura das comunidades aquáticas. Neste contexto, é essencial o entendimento das alterações nos ciclos biogeoquímicos e nas comunidades planctônicas frente a estas mudanças ambientais. Desta forma, este trabalho teve como objetivos: 1) investigar, através de um experimento de mesocosmos in situ, a resposta das comunidades planctônicas frente a adição de nutrientes, matéria orgânica alóctone e sombreamento, e a interação destas adições, em um lago tropical (Lagoa Carioca, Médio Rio Doce, MG) circundado por Mata Atlântica; e 2) avaliar as mudanças em diferentes parâmetros da qualidade de água da lagoa Carioca após uma considerável perda de volume ocasionada por recentes mudanças nos padrões regionais de chuva. Nos mesocosmos, observamos respostas na composição do plâncton em poucos dias de experimento, com alterações na estrutura e densidade desta comunidade. A adição de nutrientes favoreceu a dominância de espécies fitoplanctônicas oportunistas, como Chlorella sp. e a adição de matéria orgânica ocasionou a substituição na dominância de Pseudanabaena catenata por Aphanocapsa elachista. Para o zooplâncton, houve a substituição da dominância do grupo Copepoda para Rotifera em todos os mesocosmos, e os grupos zooplanctônicos foram associados à transparência da água (coeficientes de atenuação difusa da radiação solar) e bacterioplâncton. A perda de volume do lago, por sua vez, causou impactos severos em muitos dos parâmetros observados. O lago se tornou menos transparente e com maiores concentrações de nutrientes na coluna d’água. Observou-se um aumento significativo na concentração de nitrogênio, nutriente essencial no processo de eutrofização. As propriedades ópticas indicaram que o escurecimento da lagoa parece ter ocorrido devido ao aumento na concentração de carbono orgânico dissolvido e pela entrada de matéria orgânica alóctone principalmente durante o verão, quando ocorre a entrada de grande quantidade de água nas fortes chuvas desta estação. Ainda assim, estas chuvas aconteceram sem periodicidade demarcada, e não foram suficientes para elevar os níveis de água perdidos pela lagoa durante a estação seca. Este estudo apresenta as modificações na qualidade da água e na estrutura e composição do plâncton frente a impactos frequentemente observados em lagos tropicais, como eutrofização, alterações no uso do solo (que alteram a qualidade e quantidade da matéria orgânica alóctone que entra nos ecossistemas aquáticos), e variabilidade na pluviosidade regional, que pode ser extrapolado para outros ambientes aquáticos e servir de subsídio para estratégias de conservação. The majority of freshwater ecosystems in the tropics have already faced disturbances caused by direct or indirect human actions, as eutrophication and exploitation of hydric resources to using water in agriculture or pasture, for example. Nowadays, those disturbances are becoming amplified with the increase of climate change effects, as changes in rain patterns, and the intensity of sunlight incident on the planet. Such modifications cause consequences in the metabolism and functioning of the lake. In this context, it is crucial the understanding of biogeochemical cycles alterations and plankton communities. Thus, this work aimed to: 1) investigate the response of planktonic communities through a mesocosms experiment with the addition of nutrients, allochthonous organic matter and shading, and the interaction of these additions in a tropical lake (Carioca Lake, Middle Rio Doce), surrounded by Atlantic forest; and 2) evaluate changes in different parameters of water quality of Carioca Lake after a considerable volume loss caused by recent changes in regional rain patterns. In mesocosms experiment, we observed responses in plankton composition after a few days of experiment, with alterations on structure and density of this community. The nutrients addition favored the dominance of phytoplankton opportunistic species, as Chlorella sp., and the organic matter addition provoked a substitution in dominance of Pseudanabaena catenata to Aphanocapsa elachista. In zooplankton, we observed the dominance substitution of Copepoda to Rotifera in all mesocosms, and the groups were associated with water transparency (diffuse attenuation coefficients of solar radiation) and bacterioplankton. On the other hand, the volume loss in the lake caused strong impacts in many of the observed parameters. The lake became less transparent and with higher nutrients concentrations in water column. We observed a significant increase in nitrogen concentration, essential nutrient in eutrophication process. The optical properties indicate that the lake darkening seems to occurred due to increasing on dissolved organic carbon concentration through the allochthonous organic matter input especially during summer, when the strong rains, common at this season, causes a massive water entrance, that also carries the organic material. Still, the rain events did not present a delimited frequency, and it was not enough to increase water levels that were lost by the lake during the dry season. This study presents the modifications in water quality and in structure and composition of planktonic community. The answers obtained in this work through simulation of eutrophication, land-use changes (that alters the quality and quantity of allochthonous organic matter in the system) and through observation on regional rainfall, can be extrapolated to development of aquatic environment conservation politics.