ABSTRACT
Thermal gradient of a Central Amazonian lake was studied to establish a link between seasonal variations in the water level, temperature, suspended particulate matter (SPM) and thermal stratification. Bimonthly measurements of temperature and PAR radiation were made at 0.25 m intervals from the surface to bottom from February 2004 to July 2006. Daily occurs full vertical mixing of the water column, and classic thermal stratification was not observed in the period. The effect of the winds associated to flood-pulse and the penetrative convection, transported the turbulent kinetic energy (TKE) into the lake mixing the column of water. This phenomenon was more expressive in the rainfall seasons when is generally higher contributing to the circulation of the water. The limit of the euphotic zone ranged from 1.36 to 1.77 m in the period studied. The results of the transmission curves for the sampling sites showed that, in general, less than 0.01% of the surface light reached the bottom. The trend curve developed can facilitate the understanding of the limnological and ecological processes in lentic systems of whitewaters of the Central Amazonian.
Foi estudado o gradiente térmico de um lago da Amazônia Central para estabelecer associação entre variações sazonais no nível de água, temperatura, material em suspensão e estratificação térmica. Bimestralmente, foram medidas a temperatura e a radiação luminosa da superfície ao fundo do lago no período entre fevereiro de 2004 e julho de 2006. Ocorreu completa mistura vertical diária da coluna de água, não sendo observada estratificação térmica clássica no período. A energia cinética turbulenta (ECT) proveniente da ação dos ventos em associação com o pulso de inundação foi responsável pela mistura da coluna de água. Esse fenômeno foi mais expressivo no período chuvoso, quando a ECT é geralmente mais alta, contribuindo para a circulação da água. A extensão da zona eufótica variou de 1,36 a 1,77 m. Os resultados das curvas de transmissão para os pontos de amostragem mostraram que menos de 0,01% da luz de superfície alcançou o fundo do lago. A curva de tendência desenvolvida poderá facilitar a compreensão dos processos limnológicos e ecológicos em sistemas lênticos de águas brancas da Amazônia Central.
Subject(s)
Thermal Stratification , Water CycleABSTRACT
Se estudió el efecto de la radiación ultravioleta (RUV) sobre dos cepas bacterianas marinas antárticas (UVps y UVvi) en la columna de agua de la caleta Potter (Shetland del Sur, Antártida). Frascos de cuarzo con las cepas en estudio fueron expuestos a la radiación solar en superficie, a 1 m y a 3 m de profundidad. Se realizaron ensayos con exposición directa y con filtros interferenciales que discriminaron la radiación UVA y la UVB. En otros ensayos se simuló una mezcla vertical de 4 m/h. Ambas cepas mostraron una disminución significativa del número de unidades formadoras de colonias, tanto en superficie como a 1 m de profundidad, luego de exponerlas a dosis superficiales de UVB de 8,4 kJ m-2. El estudio con filtros interferenciales mostró una disminución significativa de la viabilidad en ambos tratamientos UV en superficie y a 1 m. La cepa UVps mostró mayor sensibilidad a la UVB que a la UVA. La mezcla vertical amortiguó el daño causado por la UVB cuando la dosis en superficie fue de 4,8 kJ m-2. Este efecto amortiguador no se observó cuando la dosis en superficie fue de 7,7 kJ m-2. Estos resultados muestran que el efecto negativo de la RUV sobre el bacterioplancton sería particularmente importante en el primer metro de profundidad de las aguas costeras antárticas con abundante material particulado en suspensión.
The effect of UV radiation on two Antarctic marine bacterial strains (UVps and UVvi) was studied in the water column of Potter Cove (South Shetland, Antarctica). Quartz flasks were filled with the bacterial suspensions and exposed to solar radiation at 0 m, 1 m and 3 m depth. Assays using flasks exposed to direct solar radiation and others using flasks covered with/by interferential filters which discriminate between UVA and UVB, were performed. In other assays, a vertical mixing of 4 m/h was simulated. Both strains showed a significant decrease in viability (expressed as colony - forming units) when exposed to a surface UVB dose of 8.4 kJ m-2. Studies with interferential filters showed a significant decrease at 0 and 1 m depth under both UV treatments. The UVps strain appeared to be more sensitive to UVB than to UVA. Damage produced by UVB was attenuated by the vertical mixing when the surface UVB dose was 4.8 kJ m-2. This effect was not observed when surface UVB dose was 7.7 kJ m-2. These results show that the negative effect caused by UVB radiation on the bacterioplankton would be significant only in the first meter of water column of the Antarctic coastal waters with high levels of suspended particulate material.