Efecte de la granulometria i la profunditat en l’estructura del biofilm microbià en sediments fluvials de dos rius de capçalera

Abstract

The following study was carried out to determine the structural variations in fluvial biofilm depending on the depth and type of sediment (particle size) taken from headwaters of two tributaries. Biofilm parameters were analysed from sediment obtained at two different sampling points from Arbúcies and Gualba rivers, two different tributaries of the Tordera river. Both water and sediment samples were obtained through field work, and analysed at a laboratory in accordance to sampling location and sediment depth. The field samples were taken using a sediment sampler. In each sampling point, samples from surface and depth had been analysed separately, and physicochemical conditions of water had been analysed too. Samples of water had been taken in each point. On the laboratory on the one hand, the general parameters of each point were analysed, those include nutrients, particle size and organic matter analysis, and on the other hand the parameters of biofilm structure through chlorophyll, bacterial density and EPS analysis. Statistical analysis has been performed to see the relation between these parameters. The physicochemical analysis showed a similarity between the two streams sampled. The results from sediment revealed differences in biofilm structure depending on the depth of sediment, being the highest concentrations of organic matter, chlorophyll, bacterial density and EPS at surface layers. This can be related to the presence of high solar radiation and availability of oxygen and nutrients in the surface compared to deeper sediment layers. Particle size only affects significantly on organic matter concentration that is higher in fine sediment than coarse. A relation has been found between the parameters composing the biofilm structure. Thanks to a correlation matrix it has been observed that these relations may vary depending on the depth of the sediment. The results revelled that on the surface, algae have a more important role in the EPS matrix formation and in organic matter concentration, whilst at depth the concentration of organic matter is related to bacterial density