Epipelon biomass responses to different restoration techniques in a eutrophic environment.

Eutrophication is a worldwide problem. In eutrophic lakes, phosphorus release from stored sediment hinders restoration processes. The epipelon is a community that grows attached to the sediment surface and has the potential to help phosphorus retention by autotrophic organisms. This study evaluated epipelon responses to four lake restoration techniques. The responses of abiotic variables and phytoplankton biomass were also evaluated. Four simultaneous mesocosm experiments were performed in a shallow eutrophic lake. The applied techniques were aeration, flocculant, floating macrophytes, and periphyton bioreactor. Water and epipelon samples were taken on days 3, 10, 17, 27, and 60. The aeration treatment and macrophytes decreased light availability in the epipelon, which had a predominance of heterotrophic components. Flocculant and periphyton bioreactor treatments favored epipelon growth with a higher contribution of autotrophic components. Therefore, some techniques may favor the epipelon growth, while others may harm the community, resulting in less efficient restoration processes. For the complete restoration of a lacustrine ecosystem, the choice of techniques to be applied must consider the restoration and maintenance of the benthic environment.

Nutrients and not temperature are the key drivers for cyanobacterial biomass in the Americas.

Cyanobacterial blooms imperil the use of freshwater around the globe and present challenges for water management. Studies have suggested that blooms are trigged by high temperatures and nutrient concentrations. While the roles of nitrogen and phosphorus have long been debated, cyanobacterial dominance in phytoplankton has widely been associated with climate warming. However, studies at large geographical scales, covering diverse climate regions and lake depths, are still needed to clarify the drivers of cyanobacterial success. Here, we analyzed data from 464 lakes covering a 14,000 km north-south gradient in the Americas and three lake depth categories. We show that there were no clear trends in cyanobacterial biomass (as biovolume) along latitude or climate gradients, with the exception of lower biomass in polar climates. Phosphorus was the primary resource explaining cyanobacterial biomass in the Americas, while nitrogen was also significant but particularly relevant in very shallow lakes (< 3 m depth). Despite the assessed climatic gradient water temperature was only weakly related to cyanobacterial biomass, suggesting it is overemphasized in current discussions. Depth was critical for predicting cyanobacterial biomass, and shallow lakes proved more vulnerable to eutrophication. Among other variables analyzed, only pH was significantly related to cyanobacteria biomass, likely due to a biologically mediated positive feedback under high nutrient conditions. Solutions toward managing harmful cyanobacteria should thus consider lake morphometric characteristics and emphasize nutrient control, independently of temperature gradients, since local factors are more critical - and more amenable to controls - than global external forces.

Simulating oligotrophication in a eutrophic shallow lake to assess the effect of periphyton bioreactor on phytoplankton and epipelon.

We evaluated the effects of a periphyton bioreactor on phytoplankton by experimentally simulating oligotrophication in a shallow eutrophic system. The experiment had two 50% diluted treatments with and without a periphyton bioreactor. Sampling was performed on days 6, 9, 12, 15, and 20 of the experimental period. The periphyton bioreactor accumulated biomass (chlorophyll-a, AFDM) and TP during the experimental period. Despite the biomass and TP loss due to periphyton detachment from the substrate after community reaching the algal biomass peak, the gains exceeded the losses, and the net rate was positive for all attributes in the bioreactor. Based on the average, our findings suggest that periphyton bioreactors negatively affected the phytoplankton total biovolume. Cyanobacteria were the most abundant phytoplankton group. However, the periphyton bioreactor caused the biomass loss of the Raphidiopsis raciborskii in phytoplankton. Our results suggest that bioreactor influenced the phytoplankton structure, reducing cyanobacterial biomass, especially Raphidiopsis raciborskii. However, the bioreactor did not reflect a significant increase in the epipelon biomass during the experimental period. We conclude that the periphyton bioreactor has the potential to assist in the maintenance of restored shallow lakes and reservoirs, especially in controlling phytoplankton growth.

Garças Reservoir trophic state dynamics: a 20-year synthesis / Dinâmica do estado trófico do Lago das Garças: 20 anos de síntese

The Garças Reservoir history reveals a remarkable case of human impacts resulting from the urbanization pressure over the 20th century. It is a shallow tropical system located in the Parque Estadual das Fontes do Ipiranga, a protected area within the city of São Paulo, São Paulo State, Brazil. Based on a comprehensive dataset (1997-2017), we evaluated the water quality temporal change using a trophic state index (TSI); in addition, we also verified whether the management procedures improved the water quality. Mechanical removal of macrophytes (1999) triggered an abrupt change from eutrophic-supereutrophic to the hypereutrophic state with feedback mechanisms. After five years (2005), a slowdown in the internal P loading process occurred, followed by the installation of the secondary wastewater treatment in the city zoo two years later (2007). Both processes promoted the beginning of water quality improvement. In 2011, TSI first dropped to supereutrophic state with the temporary diversion of the sewage effluent from the São Paulo State Department of Agriculture. This effluent was finally inactivated (2014) and the system sustained the supereutrophic state. TSI responded well to the historical key events related to the control of sewage effluents. After 11 years from the permanent impact of macrophytes removal, current results have demonstrated improved health of the system. It is absolutely necessary to improve the sewage treatment from the city zoo to continue the reservoir recovery considering that since 2014 it has been the only external phosphorous loading to Garças Reservoir. The history of Garças Reservoir can offer a better understanding of wrong management strategies and the vulnerability of tropical shallow systems to eutrophication.

A história do Lago das Garças é um caso notável dos impactos humanos devidos à pressão da urbanização do século 20. Trata-se de uma represa tropical rasa localizada no Parque Estadual das Fontes do Ipiranga, área protegida situada na cidade de São Paulo, SP, Brasil. Com base em um banco de dados abrangente (1997-2017), nós avaliamos as alterações temporais da qualidade da água utilizando o índice de estado trófico (IET) e se as medidas adotadas de manejo melhoraram a qualidade da água. Em 1999, a remoção mecânica das macrófitas foi o gatilho para a mudança abrupta da represa do estado eutrófico-supereutrófico para hipertrófico, com mecanismos de retroalimentação. Após cinco anos (2005), ocorreu a desaceleração do aporte interno de P. Após dois anos (2007), houve a instalação da estação de tratamento secundário de esgoto na Fundação Parque Zoológico (2007). Ambos os eventos promoveram o início de uma melhora da qualidade da água. Em 2011, o IET passou para supereutrófico com a desativação temporária do efluente de esgotos provenientes da Secretaria de Agricultura e Abastecimento do Estado de São Paulo. Em 2014, este efluente foi totalmente desativado e o sistema manteve seu estado supereutrófico. Assim, o IET respondeu coerentemente aos eventos-chave relacionados com o controle dos efluentes de esgoto. Após 11 anos do impacto permanente da remoção das macrófitas, os resultados demonstraram a melhoria da qualidade da água da represa. Para prosseguir com a recuperação do Lago das Garças há necessidade absoluta de aperfeiçoar o sistema de tratamento secundário de esgoto proveniente do Zoológico, considerando que desde 2014 é o único efluente com aporte externo de fósforo para a represa. A história do Lago das Garças contribui para um melhor entendimento de estratégias errôneas de manejo e da vulnerabilidade de sistemas tropicais rasos à eutrofização.

Epipelon, phytoplankton and zooplankton responses to the experimental oligotrophication in a eutrophic shallow reservoir.

Epipelon can contribute to the maintenance of shallow lake oligotrophication. Herein, we simulated oligotrophication by diluting eutrophic water and evaluated epipelon biomass and structure and potential relationships with phytoplankton and zooplankton communities. Dilutions of 25-75% negatively impacted phytoplankton biomass and zooplankton diversity and increased Rotifera density. Additionally, the 25% dilution increased Copepoda density, but had no effect on Cladocera. On both experimental days, epipelon chlorophyll-a and algal density responded to oligotrophication, but the algal biomass response was less pronounced after 14 days. Ceratium furcoides was dominant in the phytoplankton, while diatom species were dominant in the epipelon. We observed that experimental oligotrophication can influence both the biomass and taxonomic structure of the algal and zooplankton communities. Overall, we concluded that experimental oligotrophication negatively impacted the phytoplankton biomass and favored the development of the phototrophic epipelon; however, a large reduction in eutrophication (>50%) is required for a significant algal response in the benthic environment of a shallow tropical reservoir.

Structural and successional variability of periphytic algal community in a Amazonian lake during the dry and rainy season (Rio Branco, Acre) / Variação estrutural e sucessional da comunidade de algas perifíticas em lago amazônico durante o período seco e chuvoso

The colonization process and successional patterns of a periphytic algal community were evaluated in a Amazonian Viveiro Lake (Rio Branco, Acre, Brazil). Sampling was performed over a period of 35 days; at four-day intervals for 20 days, and then at five-day intervals. Water sampling for physical, chemical and biological analyses was done during the dry and rainy season. Glass slides were used as artificial substrates for periphyton colonization. The structural community was evaluated through population density, algae class, diversity indices and descriptive species. Species richness, diversity and evenness increased as succession progressed. While density of Bacillariophyceae, Euglenophyceae and Zygnemaphyceae increased with succession, Cyanobacteria remained dominant. Synechocystis aquatilis, Synechocystis diplococcus and Navicula pseudolanceolata were the main descriptive species in both the dry and rainy season. Cymbela tumida, Frustulia rhomboides, Trachelomonas lacustris and Closterium acicularis was correlated with an increase in hydrologic level during the rainy season. Conversely, the density of Chlamydomonas sp., Chroomonas nordstedtii, Trachelomonas volvocinopsis, Trachelomonas volvocina and Synechococcus linearis was correlated with an increase in water transparency during the dry season. In general, the periphytic algal community showed high diversity and species richness independent of season. Season also had little influence on representation of algae class and main descriptive species. However, successional patterns varied by season, and changes in hydrologic levels acted directly on the succession path of periphytic algae. More research on periphyton dynamics is needed to improve our understanding of tropical lake ecosystems, especially in Amazonian.

A colonização e o modelo sucessional da comunidade de algas perifíticas foram avaliados no amazônico Lago do Viveiro (Rio Branco, Acre, Brasil). Amostragens foram realizadas no período de 35 dias com intervalos de quatro dias nos primeiros 20 dias e cinco dias no final. Foram realizadas amostragens da água para a determinação das variáveis físicas, químicas e biológicas no período seco e chuvoso. Lâminas de vidro foram usadas para a colonização do perifíton. A estrutura da comunidade foi avaliada através da densidade populacional, classes algais, índices de diversidade e espécies descritoras. A riqueza de espécies, diversidade e equitabilidade aumentaram com o avanço da sucessão. A densidade de Bacillariophyceae, Euglenophyceae e Zygnemaphyceae aumentaram com o avanço da sucessão, mas Cyanobacteria permaneceu dominante. Synechocystis aquatilis, Synechocystis diplococcus e Navicula pseudolanceolata foram descritoras da comunidade no período seco e chuvoso. Cymbela tumida, Frustulia rhomboides, Trachelomonas lacustris e Closterium acicularis foram correlacionadas com o aumento do nível hidrológico no período seco e chuvoso. Contrapondo, a densidade de Chlamydomonas sp., Chroomonas nordstedtii, Trachelomonas volvocinopsis, Trachelomonas volvocina e Synechococcus linearis foram correlacionadas com o aumento da transparência da água durante o período seco. De modo geral, a comunidade de algas perifíticas apresentou elevada diversidade e riqueza de espécies independentemente do período climático. O período climático apresentou pouca influência sobre a representatividade das classes algais e espécies descritoras. Contudo, os modelos sucessionais foram diferentes em cada período climático e as mudanças no nível hidrológico atuaram diretamente sobre a sucessão das algas perifíticas. Mais pesquisas sobre a dinâmica do perifíton são necessárias para melhorar a compreensão dos ecossistemas lacustres tropicais, especialmente na Amazônia.