Species-specific response of phytoplankton to zooplankton grazing in tropical eutrophic reservoirs

Aim To test the hypothesis that zooplankton changes the structure of phytoplankton in tropical reservoirs by reducing the biomass of algal species susceptible to herbivory. Methods We experimentally evaluated the species-specific responses of phytoplankton to zooplankton within eutrophic reservoirs with different phytoplankton community structure in northeastern of Brazil. Water samples were collected from the subsurface in coastal regions of the Apipucos and Mundaú reservoirs in January/2012 and November/2014, respectively, and transported to the laboratory. The experiments were performed in Erlenmeyer flasks (1 liter) filled with water from the sample sites and were maintained for five days in the laboratory conditions. Two treatments were maintained (1) with phytoplankton and the presence of the native zooplankton and (2) without native zooplankton. Results Zooplankton proved to be an important factor, modifying the structure of the phytoplankton community, especially in the Apipucos reservoir. In this reservoir, we observed a significant reduction of biomass in diatom Cyclotella meneghiniana, and the chlorophyte Chlamydomonas sp., and an increase in the biomass of Raphidiopsis raciborskii. In the Mundaú reservoir, we observed a significant reduction of C. meneghiniana and R. raciborskii, while cyanobacteria Microcystis aeruginosa increased their biomasses in the presence of zooplankton. Conclusions These results show the importance of the microalgae community structure in phytoplankton-zooplankton interactions for food webs in tropical environments, as well as support the role of zooplankton in fostering cyanobacterial growth and maintain algal blooms.

Quantitative Fluxes of the Greenhouse Gases CH4 and CO2 from the Surfaces of Selected Polish Reservoirs

Research carried out in the years 2009–2011 and 2018–2019 sought to determine the magnitudes of fluxes of methane (CH4) and carbon dioxide (CO2) from the surfaces of three eutrophic reservoirs in SE Poland. The “static chamber” method was deployed at five or six stations located along the reservoirs, where the water column at its deepest slightly exceeds 2 m. Obtained values for the fluxes of CH4 varied across a wide (0–2513.48 mmol·m−2·d−1) range, with many of these values therefore exceeding those characteristics for large tropical reservoirs. The reservoirs studied were not found to differ significantly in terms of average CH4 flux, however. Where obtained values for CO2 fluxes in the range from −10.96 to 621.69 mmol·m−2·d−1 were concerned, most fell within the range given for temperate-zone reservoirs, while differences between reservoirs were noted for average values in this case.

Phytoplankton, Trophic State and Ecological Potential in reservoirs in the State of São Paulo, Brazil

This study evaluated the ecological potential of reservoirs in the Brazilian state of São Paulo, having phytoplankton as a biological quality element. Integrated water column sampling was carried out in the dam, and in the intermediate and fluvial zones of the Igaratá, Atibainha, Paiva Castro, Rio Grande, Itupararanga, Broa, Barra Bonita, Guarapiranga and Salto Grande reservoirs in July 2015. Physico-chemical and biological parameters were analyzed in all environments. The phytoplankton was analyzed under an inverted microscope, and measurements of density, diversity, equitability and dominance were determined. The data was ordered using PCA and CCA analysis. The ecological potential of the reservoirs was determined through the evenness index. The electrical conductivity, nitrate, nitrite and orthophosphate were higher in the more eutrophic reservoirs: Salto Grande, Barra Bonita, Guarapiranga and Rio Grande. A trophic gradient was observed among the sampling points, suggesting a conservation spectrum. There was dominance of cyanobacteria in the eutrophic reservoirs associated with low diversity and high dominance. The total density was correlated with TP, TN, and pH. A divergent relationship between the trophic state index and the evenness index was observed. The Atibainha, Itupararanga, Broa, Barra Bonita and Salto Grande reservoirs were classified as water bodies of very poor ecological quality (Bad). The evenness index seems to be a good alternative to the biomonitoring of the studied reservoirs.

Diversity and Dominance in phytoplankton community during nycthemeral cycles at different thermal patterns in water body in semiarid region of Brazil

The vertical distribution of phytoplanktonic species in tropical regions responds quickly to the physicochemical factors of water with ecophysiological changes and biomass. Abiotic factors are responsible for the changes in the dominance of the different groups. The study analyzed the diversity and dominance of the phytoplankton community in a eutrophic reservoir localized in the semiarid region of Brazil. The samplings were conducted in nycthemeral cycles in different thermal regimes along a vertical profile. The biomass was determined by density and specific biovolume. Patterns of richness, diversity and specific dominance index were analyzed. The significant differences between the biotic data were analyzed by the ANOVA two-way and t-test. Similarity matrices were plotted using the Jaccard and Bray-Curtis indices with subsequent data ordination. 33 taxa were identified during the study. Differences in thermal patterns that are occurring in nycthemeral cycles showed changes in the structure of the phytoplankton community. The atelomictic event contributed to changing of the algal structure, especially in biomass, dominance, and diversity that shows significant differences between periods. The lowest diversity reported (<1.03 bits.L-1) were influenced by monospecific dominance of the cyanobacteria C. raciborskii, thus recording greater biomasses, forming blooms throughout the study period. In the tropical eutrophic reservoirs, an algal bloom of cyanobacteria has persisted throughout the year, regardless of variations in the thermal regime, thereby reducing the phytoplankton diversity.

Challenges Regarding Water Quality of Eutrophic Reservoirs in Urban Landscapes: A Mapping Literature Review

Urbanized river basins usually suffer from anthropogenic pressure, compromising the quality of water. Unsafe water is a risk to public health, especially when there are occurrences of HABs (Harmful Algae Blooms) as in the case of cyanobacteria, which cause different human health problems. In this paper, we aimed to review the scientific literature documenting what has been studied in the scope of the stratified reservoirs of urbanized basins. The mapping review method was used to categorize existing literature on urbanized watersheds and eutrophic reservoirs. Using the keywords “Eutrophic Reservoir” and “Urban” and selecting all the years of open publication on the Science web page, we obtained 69 results, 53 of them meeting the requirements established for the search. Many of the studies mention as the most important determinant for eutrophication of reservoirs and the proliferation of algae, the anthropogenic influence through the diffuse load of streets, domestic and industrial sewage, and even drainage water from agricultural areas in the basin. The results of this study reinforce that informal settlements without sanitary infrastructure are aggravating the deterioration of water quality in urban water sources and therefore posing many risks to public health.