Globally, aquatic systems face increasing challenges with respect to increased greenhouse gas (GHG) emissions, eutrophication and strongly altered fish community composition. Although it is known that benthivorous fish can influence sediment and water column biogeochemistry, studies showing causal relationships are largely lacking. Here, we used a mesocosm approach with Common carp (Cyprinus carpio) to unravel the effects of bioturbation on GHG and nutrient dynamics. We hypothesised that fish bioturbation decreases methane (CH4) emissions and increases carbon dioxide (CO2) emissions by increased sediment oxygenation. Additionally, lower phosphorus (P) mobilisation was expected due to increased binding to ferric iron (Fe3+). We found that benthivorous fish increased water turbidity, and reduced CH4 diffusion to the atmosphere by 33%, and ebullition by 67%, probably because of sediment oxygenation. Simultaneously, however, CO2 emissions increased due to higher aerobic decomposition, leading to higher overall GHG emissions. In contrast to our hypothesis, we did not find indications of bioturbation affecting P mobilisation from the sediment, probably because P binding was already high in the control treatment as a result of high porewater Fe:P ratios. We conclude that bioturbation by fish has strong effects on GHG emissions as a result of higher overall decomposition rates offsetting reduced CH4 emissions. Depending on porewater Fe:P ratios, benthivorous fish may additionally reduce P mobilisation.

Aim Anthropogenic modifications in the landscape are accelerating biogeochemical cycles and causing unbalances in terrestrial and aquatic ecosystems with still unknow impacts on biotic and abiotic processes. Therefore, there has been increasing scientific interest in the links between human activities and ecosystems functions. Methods Here we review the role of aquatic sediments in the carbon and pollutant cycle. Results We briefly explore the historical context, origin, and composition of the sediments, as well as the factors that influence the processes of carbon and contaminants cycling and the role of sediments in the greenhouse gases emissions in aquatic ecosystems. Conclusions Aquatic sediments can help to understand the terrestrial and aquatic ecosystem changes, once they are good sentinels, reflecting key biogeochemical processes over time.

O objetivo do trabalho é realizar uma análise da quantidade e da qualidade físico-química e biológica das águas de um trecho doribeirão Espírito Santo, bem como avaliar a densidade e a riqueza das espécies fitoplanctônicas nas águas e quais nutrientes são determinantes na sua limitação. Foram realizadas 10 coletas ao longo de 5 anos em 3 pontosao longo da baciahidrográfica do ribeirão Espírito Santo.O ponto 1 se encontra em ambiente rural. O ponto 2 está situado após a captação de água da Estação de Tratamento de Água. O ponto 3 transpassa o Distrito Industrial de Juiz de Fora. O ponto 1 apresentou maior influência nos parâmetros físicos e químicos com o aumento da vazão do que os pontos 2 e 3. Fato esse que pode ser explicado pela contribuição do carreamento de compostos pelas chuvas. Algumas vazões medidas apresentaramvalores menores do que a Q7,10, revelando a importância da continuidade do monitoramento.O ponto 2 e 3 são influenciados pelos despejos de efluentes. Isso faz com que suas águas sejam nutricionalmente mais ricas do que o ponto 1, formando um ambiente favorável para adominância fitoplantônica. Ainda assim, o ponto 3 é o mais degradado, possuindo mais parâmetros em desconformidade com as normas.

Small Hydroelectric Power Plants (SHPs) are considered hydroelectric plants of reduced size and power that modify the landscape in a lower degree. As they are generally built-in sequence along the course of a river, these reservoirs are subject to the Cascading Reservoir Continuum Concept (CRCC), which provides a gradient effect mainly observed on suspended particles and nutrients. These effects can reflect in the phytoplankton community, which respond in terms of changes in their structure and function to environmental changes. Here, we aimed to investigate whether spatial variation would be more explanatory than temporal variation for phytoplankton structure and composition in cascading SHPs reservoirs. Furthermore, we sought to understand the effect of the hydrodynamics of run-of-river and storage reservoirs for phytoplankton community composition. We assessed the predictive power of physical and chemical conditions of the water, and zooplankton density as explanatory variables for phytoplankton taxonomic and functional diversity. The study was carried out over 6 years in three SHPs located on the Paraibuna River, Brazil, totaling 24 campaigns. After counting and identification, the phytoplankton species were classified according to qualitative functional traits related to morphology, physiology, and behavior. The reservoirs had significant differences in nutrients and suspended solids, corroborating with the CRCC. Nonetheless, these variables alone were not able to explain the distribution of phytoplanktonic species. However, as significant coupling between phytoplankton and zooplankton was found, and zooplankton might have influenced the phytoplankton distribution along the longitudinal gradient of the river. Furthermore, changes in taxonomic and functional composition of phytoplankton were mainly related to reservoir hydrodynamics and temporal variation. The last reservoir in the cascade was the one with the greatest phytoplankton species and functional diversity. Taxonomic and functional diversity indices were positively correlated, but at a certain point, functional richness reached a plateau. Here we highlight the complexity of understanding the role of cascading reservoirs in the structure and function of phytoplanktonic communities, which are subject to large spatial and temporal variations, even within the same stretch of a river.

Compreender os padrões de distribuição de espécies no ambiente e qual o papel que elas desempenham no ecossistema constitui um dos grandes desafios da ecologia. As comunidades planctônicas podem ser utilizadas como indicadores biológicos no monitoramento de ambientes aquáticos, uma vez que sinalizam mudanças nos ecossistemas através de alterações em sua estrutura, composição e metabolismo A abordagem funcional, baseada no uso de traços funcionais das espécies como descritores, sinaliza de forma mais abrangente alterações nas funções ecossistêmicas, como produção primária e transferência de energia para demais níveis tróficos. Assim, o objetivo desse estudo foi explorar como as mudanças na composição taxonômica da comunidade fitoplanctônica se refletem em mudanças nos traços funcionais das comunidades em reservatórios em cascata. A principal hipótese era de que a diversidade taxonômica e funcional da comunidade fitoplanctônica seria diferente entre os três reservatórios, sendo a variação espacial mais explicativa que a variação temporal para as mudanças na estrutura e composição do fitoplâncton. O estudo foi realizado ao longo de 6 anos (2013-2018) em três reservatórios em cascata ao longo do Rio Paraibuna, bacia do Rio Paraíba do Sul. Não houve uma separação na distribuição dos pontos por reservatórios em termos de variáveis ambientais, de forma que esses se mantiveram sobrepostos durante todo o período amostrado. No entanto, foi observado variação sazonal ao longo dos 6 anos estudados. Os dois reservatórios mais à montante apresentaram características muito semelhantes em termos de composição taxonômica do fitoplâncton e zooplâncton. O último reservatório da cascata, no entanto, apresentou maior diversidade para ambos os grupos. O traço arranjo unicelular foi aquele com maior contribuição em todos os reservatórios. No entanto presença de estrutura de sílica e mixotrofia tiveram uma considerável representatividade. A riqueza funcional também variou entre os reservatórios. Da mesma forma, a relação entre o índice de Shannon e o CWM se mostrou positiva para os reservatórios à montante, indicando uma tendência entre o aumento da diversidade e o CWM. Por outro lado, não foi possível observar uma tendência no reservatório à jusante. Os resultados mostraram que mudanças na estrutura da comunidade fitoplanctônica alteraram a contribuição dos traços funcionais desta comunidade nos ecossistemas, com potenciais impactos para os níveis tróficos superiores (zooplâncton) e funções ecossistêmicas associadas. Ainda, houve mudanças na estrutura e composição da comunidade zooplanctônica, indicando que a qualidade do recurso alimentar pode ser um fator direcionante para essa comunidade. Por fim, características espaciais dos sistemas, como sua posição no sistema em cascata foi um fator determinante para estrutura da comunidade fitoplanctônica.

Inorganic turbidity can limit light penetration in water and reduce phytoplankton photosynthesis. Anthropogenic activities such as mining can produce or augment the amount of suspended inorganic particles in water. Recent mining disasters in Brazil have released tons of mine tailings into aquatic ecosystems, with known and unknown negative consequences for aquatic life, biodiversity, and ecosystem services beyond the human and material losses. Here, we investigated the effects of inorganic turbidity on phytoplankton chlorophyll content and composition caused by sediments from two areas in Lake Batata, one natural and the other impacted by bauxite tailings. We experimentally compared the effects of different levels of turbidity (12, 50, and 300 NTU) caused by the addition of sediments from the two lake areas on a chlorophyll-a gradient (5, 15, and 25 μg/L). Inorganic turbidity did not consistently reduce chlorophyll-a concentrations. In treatments with high chlorophyll-a, high turbidity was associated with lower chlorophyll-a concentrations at the end of the experiment. On the other hand, in low-chlorophyll treatments, high turbidity was associated with higher chlorophyll-a concentrations. In treatments with sediments from the natural area, overall chlorophyll-a levels were higher than in treatments with sediments from the impacted area. Phagotrophic algae dominated both in treatments with sediments from the impacted area (Chrysophyceae 34%, Chlorophyceae 26%, and Cyanobacteria 22% of total density) and in treatments with sediment from the natural area (Euglenophyceae 26%, Chrysophyceae 23%, and Chlorophyceae 20%). We conclude that high turbidity does not lead to a reduction in chlorophyll-a concentrations and sediment from the natural area allowed higher chlorophyll-a levels, indicating that impacted area sediment affected more phytoplankton.

Aim Long-term ecological research often integrates many research groups and subjects in one or few sites sampled systematically along the time. In the Amazon, there is a tradition of long-term research in terrestrial habitats, but this has been less common in floodplain lakes. This study systematically reviews 35 years of research (1988-2022) in Batata Lake, a clear water flood plain lake impacted by bauxite mining tailings for ten years (1979-1989) and discuss some research opportunities and challenges for the future. Methods The review covered 99 scientific reports (78 papers and 21 book chapters) comprising a large spectrum of data from snapshot observations and experiments to enduring quarterly observational and hypothesis-testing studies. Soil, sediments, and the water column were consistently sampled in natural and impacted areas. Results Research topics were quite diverse and covered biological communities from aquatic virus to igapó flooded forests and provided an overview of ecological processes such as primary and secondary production. Ecological variables monitored along the project were constrained by a strong seasonality of the flood pulse and the effect of sampling areas (natural and impacted), which was performed by very connected research groups. Conclusions Despite the extensive information, long-term ecosystem function trends are still incomplete.