Luciana Pena Mello Brandão

The Paraopeba River basin has been exposed to long-term anthropogenic pressures, including urbanization, wastewater discharge, land-use changes, and mining. These impacts were intensified by the Brumadinho tailings dam collapse in 2019, which released approximately 1.6 million m³ of iron-mining tailings into the Paraopeba River. This study evaluated spatial and temporal dynamics of zooplankton communities and their relationships with environmental gradients. Eighteen sampling campaigns were conducted at nineteen monitoring sites, integrating physicochemical variables, nutrients, and metals with biological indicators. Sampling began approximately one year after the collapse and therefore does not capture the acute response to the initial tailings pulse. During the monitoring period, zooplankton assemblages showed no marked differences between upstream and downstream areas. Community structure was more strongly associated with hydrological seasonality and ongoing anthropogenic pressures, particularly nutrient enrichment and urban effluents. Turbidity, metals, and nutrients were important environmental correlates of richness, diversity, and density. Rotifers and copepods dominated, while the invasive Kellicottia bostoniensis persisted across sites and seasons. Tributaries supported higher densities and more exclusive species, potentially reflecting differences in nutrient availability, hydrodynamic conditions, and habitat retention. Overall, hydrological dynamics and contemporary anthropogenic stressors were more closely associated with community patterns than the upstream–downstream spatial gradient.

Urban freshwater ecosystems are increasingly exposed to mixtures of pollutants, including per- and polyfluoroalkyl substances (PFAS). However, their ecological effects remain poorly understood, especially in tropical regions with limited sanitation infrastructure. This study investigated PFAS contamination, water quality, and microbial community structure in Pampulha Lake, a tropical urban reservoir in southeastern Brazil. Spatiotemporal patterns in prokaryotic and eukaryotic diversity were assessed over a year (2022–2023) using environmental DNA metabarcoding of 16S and 18S rRNA genes by integrating taxonomic data with PFAS concentrations and water quality. Physicochemical and multivariate analyses revealed strong seasonal and spatial heterogeneity, influenced by eutrophication, hydrological variability, and pollution gradients. Among the seven PFAS detected above quantification limits, PFBS and PFOA were the most common. Prokaryotic communities showed significant correlations with PFAS, especially with sulfonated forms, while eukaryotic communities were more stable. Diversity patterns highlighted microbial community sensitivity to environmental stress. Overall, results indicate that PFAS influenced microbial assemblages, supporting their inclusion in monitoring frameworks, and eDNA was proved effective for assessing ecological risks in tropical urban reservoirs.

In 2015, the collapse of the Fundão tailings dam released millions of cubic meters of mine waste into the Rio Doce Basin, causing profound and lasting environmental impacts. We analyzed 3 years of seasonal variation of water quality and metal concentrations across two middle Rio Doce sub-basins: one impacted by the tailings (Doce River) and a non-impacted reference system (Santo Antônio River). We hypothesized that tailings-associated variables (e.g., turbidity, Mn, As, Fe, Al) would differ in concentration and seasonality between the sub-basins, reflecting altered ecological responses nearly a decade after the collapse. Multivariate analyses (PCA, PERMANOVA) and mixed-effects models revealed significant spatial and temporal differences, with the impacted sub-basin showing persistently higher turbidity and metal loads, especially during the rainy season. Cluster analysis identified spatial groups corresponding to contamination gradients relative to the tailings source and confluence zones. Overall, our results demonstrate that the legacy of the tailings continues to shape water quality dynamics and suspended particulate matter in the Rio Doce system, highlighting the need for ongoing, spatially explicit monitoring to support ecosystem recovery and management.

There are several water treatments carried out in reservoirs worldwide, and evaluating their effect on water quality is essential for improving techniques. Pampulha reservoir, an urban eutrophic reservoir, is strongly impacted by domestic and industrial sewage. This study aimed to investigate its water quality using a spatial and temporal approach, discussing the effects of existing pollution control techniques in this system, such as Phoslock^®, Enzilimp^®, and waste retaining curtain. Monthly in situ spatial sampling was conducted at 30 points over a year, accompanied by a historical analysis of water quality using secondary data from 2013 to 2021. Results showed that water quality varied historically, with chlorophyll-a, cyanobacteria biovolume, and total phosphorus concentrations exceeding legal limits even after the application of the remediation treatments. Although these specific interventions led to a reduction in cyanobacterial biovolume, they were accompanied by an increase in chlorophyll-a and microcystin concentrations, while total phosphorus levels remained largely unchanged. The region near main tributaries (Ressaca and Sarandi streams) had the poorest water quality indices. The waste retaining curtain was effective in concentrating pollution in this area, leading to worse quality and shallower waters due to sediment accumulation. Thus, spatial variation in water quality was also observed. This study highlights the importance of temporal and spatial scale studies to aid recovery policies and water quality control in urban reservoirs.

The structure and density of plankton communities greatly influence carbon and nutrient cycling as well as the environmental status of lake ecosystems. This community can respond to a range of environmental drivers, including those influenced by human perturbations on local and regional scales, causing abrupt changes and imbalances. While the implications of climate and land-use changes are evident for a range of tropical lake conditions, their impacts on planktonic population dynamics are less understood. In this study, we aimed to investigate how distinctive levels of nutrients, allochthonous organic matter (OM), and sunlight availability change phytoplankton and zooplankton density and structure in a natural tropical lake. Using an in situ mesocosm facility, we manipulated the addition of nutrients and OM, in addition to sunlight availability and a combination of these treatments. We monitored limnological parameters, plankton count, and identification for 12 days. The mesocosms included eight different combinations in a 2 × 2 × 2 factorial design, each with two replicates. Inorganic nutrient addition reduced phytoplankton species richness, favoring the dominance of opportunistic species such as Chlorella sp. at much higher densities. Organic matter also increased light attenuation and caused the substitution of species and changes in dominance from Pseudanabaena catenata to Aphanocapsa elachista. On the other hand, physical shading had less influence on these communities, presenting densities similar to those found in the control mesocosms. Zooplankton presented a group dominance substitution in all mesocosms from copepod to rotifer species, and copepod growth seemed to be negatively affected by Chlorella sp. density increase. Furthermore, this community was associated with the light attenuation indices and bacterioplankton. These results indicate that tropical planktonic responses to environmental changes can effectively occur in just a few days, and the responses can be quite different depending on the nutritional source added. The punctual nutrient addition was sufficient to provide changes in this community, evidencing the strength of anthropic events associated with strong nutrient input. Understanding tropical plankton dynamics in response to environmental changes, such as those simulated in this work, is important for understanding the effects of climate and anthropogenic changes on tropical lake functioning. This knowledge can strengthen measures for the conservation of freshwater systems by allowing predictions of plankton community changes and the possible consequences for the aquatic food chain and water quality.

Aim Temperature and light have been recognized as important factors for ephippia hatching in temperate and tropical freshwater systems. Oddly some authors suggested that decapsulation of resting eggs would be a pro when it comes to ex situ hatching studies, exposing those eggs to a greater amount of light. This study aimed to compare the difference in the hatching rate between resting eggs decapsulated and intact ephippia of Daphnia laevis, a zooplankton that occurs at lakes, in tropical freshwaters (Cladocera). Methods The ephippia used in this work were collected at the sediment of a reservoir, in Belo Horizonte city (Minas Gerais, Brazil). We set up the laboratory experiment with two distinct groups: intact ephippia and decapsulated resting eggs. For that, we manually decapsulated 120 ephippia and kept 120 others intact (six replicas with 20 ephippia each), then incubated them all with culture water at 22ºC (12h photoperiod) for 30 days with daily monitoring. Results The results showed that decapsulation influenced negatively the hatching success, as the intact ephippia had a hatching rate of 22%, while those decapsulated only had 6%. In addition, Daphnia hatchlings were observed for intact ephippia group up to the twenty-seventh day, while for the decapsulated the last hatching occurred on the tenth day. Decapsulated eggs are subject to high exposure to light and it may jeopardize the embryo development. Conclusions In this context, we suggest that removing the protective capsule from the eggs needs to be done with caution, since in some species this can damage the resting eggs, which alters the viability and compromise the accuracy of the hatching rates studies.

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 (S_250–450, S_275–295, S_350–450, S_R 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 (S_250–450 and S_R) 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.

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 on the light absorption characteristics of colored dissolved organic matter (CDOM), in addition to differences in light availability. We added inorganic nutrients (to stimulate OM autochthonous production by phytoplankton growth) and allochthonous OM, and also introduced shading. Dissolved organic carbon (DOC), Chl-a, nutrients, total suspended solid concentrations (TSM) and spectral CDOM absorption were measured every three days to evaluate how they responded to these treatments. CDOM quality was characterized by spectral indices (S_250–450, S_275–295, S_350–450, S_R and SUVA₂₅₄). The effect of carbon sources on the spectral CDOM absorption was investigated through principal component (PCA) and redundancy (RDA) analyses. The two different OM sources affected CDOM quality differently. Spectral indices (S_250–450 and S_R) 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 of autochthonous carbon increased absorption at wavelengths below 350 nm. Our results show that small inputs of allochthonous OM have much larger effects on the spectral characteristics on the lake CDOM, compared to large production of autochthonous OM.

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 (pa had more influence (higher regression coefficient). Thus, although most of light attenuation was due to tripton, seasonal variations in phytoplankton abundance were responsible for most of the temporal fluctuations in Kd.