Partitioning of the diffuse attenuation coefficient for photosynthetically available irradiance in a deep dendritic tropical lake

ABSTRACT 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 aCDOM(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<0.001), but Chl-a 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.

Effects of nutritional conditions on lipid production by cyanobacteria

ABSTRACT The present study evaluated the effects of the culturing media and the levels of nitrogen and phosphorus on the growth, biomass productivity and lipid production of four species of Microcystis (M. novacekii, M. aeruginosa, M panniformis and M. protocystis). The lipid extract was obtained by refluxing with dichloromethane (Soxhlet). The biomass and biomass productivity yields were maximized with ASM-1 medium treatment enriched with nitrogen and/or phosphorus (0.25-0.65 g/L and 25-50.7 mg/L d-1, respectively). The lipid extract yields from M. panniformis and M. novacekii were inversely correlated with the concentration of nitrogen and directly correlated with the concentration of phosphorus (35.8 % and 31.7 %). The lipid extract yield from M. aeruginosa was inversely correlated with the nutrient concentration (23.3 %). M. protocystis exhibited a higher lipid content in the control medium (41.5 %) than in the nitrogen-enriched media. The recorded results show that a nutrient-poor culture medium favours cell growth and stimulates lipid accumulation, which directly affects the cost of cultivation by reducing nutrient consumption. All studied species may serve as biomass sources for biodiesel production, although M. protocystis exhibited the highest lipid production. Further studies are necessary to determine the composition of the recorded lipid extract.

Water quality and diversity of yeasts from tropical lakes and rivers from the Rio Doce basin in Southeastern Brazil

Yeast communities were assessed in 14 rivers and four lakes from the Doce River basin in Brazil, during the rainy and dry seasons of the years 2000 and 2001. Water samples were collected at the subsurface in all sites. The following physical and chemical parameters were measured: temperature, dissolved oxygen, pH, electrical conductivity, total phosphorus, ortho-phosphate, ammonium, nitrate, nitrite and total nitrogen and the counts of faecal coliforms and heterotrophic bacteria were carried out to characterize the aquatic environmental sampled. The yeast counts were higher in aquatic environments with the highest counts of coliform and heterotrophic bacteria. These environments receive a high influx of domestic and industrial waste. A total of 317 isolates identified in forty eight yeast species were recorded in the sites sampled and the specie Aureobasidium pullulans were found in eleven out of eighteen sites sampled and some opportunistic pathogens such as the yeast species Candida krusei were isolated only in the polluted rivers with a positive correlation with the biotic and abiotic parameters that indicate sewage contamination.

Occurrence and diel distribution of yeast in a paleo-karstic lake of southeastern Brazil

Foram estudadas a distribuiçäo sazonal e diuturna de leveduras na coluna d`agua da Lagoa Santa, um lago paleocárstico de Minas Gerais. A possível influência de parâmetros ambientais nas populaçöes fúngicas e na ocorrência das espécies de leveduras foi examinada. O lago mostrou homogeneidade térmica e coluna d`agua oxigenada durante o mês de junho, e estratificaçäo da temperatura e oxigênio dissolvido durante o período de setembro a março. A diversidade de espécies de leveduras diminuiu de acordo com o aumento da profundidade, provavelmente devido ao metabolismo oxidativo predominante entre as leveduras que poderia limitar sua distribuiçäo às águas oxigenadas da superfície. As espécies mais frequentes foram Crypococcus flavus, Rhodotorula minuta, Trichosporum cutaneum. Tr. pullulans e Aureobasidum pullulans. As contagens de leveduras e a diversidade de espécies foram maiores nos meses chuvosos de dezembro e março, e menores na estaçäo seca. Trichosporon cutaneum mostrou populaçöes elevadas na estaçäo seca, e poderia ser considerada uma espécie indígena do lago. A predominância de espécies oxidativas politróficas e pigmentadas sugere que a micobiota da Lagoa Santa é originária de solos e superfícies foliares. As populaçöes de leveduras da Lagoa Santa säo provavelmente mantidas pelo efluxo constante de espécies transitórias nas águas da chuva e dos afluentes do lago