Spatial Distribution Of Organic Matter Research Articles

Spatial distribution of organic matter in the surface sediments of Ubatuba Bay (Southeastern - Brazil)

Analyses of organic matter content, organic carbon, nitrogen, sulfur and granulometric variables were performed on 101 surface sediment samples from Ubatuba Bay in order to investigate the spatial distribution of organic matter, its origin and the relationships among its components. The samples were obtained with a manual corer, from water depths between 1 and 15m during 5 cruises of the R/V "Veliger II'', two months apart. Pearson correlation, regression and Principal Component Analysis (PCA) statistical methods were used to analyze the data. Strong correlations between organic matter and fine sediment fractions were obtained. The PCA revealed at least two main sample groups that reflect the different environmental conditions prevalent in the bay. There is a simple linear relationship between organic carbon content and the organic matter content determined by the calcination technique. Taking into account that the analysis of organic matter content is less expensive and less time consuming than the analysis of organic carbon, the present method of estimation can be useful when fast evaluation of the organic carbon content is needed for samples from similar environments.

Spatial and temporal patterns of bacterial density and metabolic activity in a karst aquifer

Karst aquifers are heterotrophic ecosystems fueled by organic matter imported from the surface. The temporal pattern of floods influences organic matter import and the spatial distribution of organic matter and biofilms in aquifer structural zones. We investigated spatial and temporal patterns of bacterial density and activity as indicators of energy availability and microbial dynamics in a karst aquifer. During baseflow, bacterial density and microbial hydrolytic activity were similar in the upper and lower zones of the aquifer. Floods apparently scoured aquifer biofilms and transported soil bacteria into the aquifer, increasing inactive bacterial density in the water column. Respiring bacterial density did not respond to floods and changed little over time. The overall proportion of total bacteria that were respiring was very high on some dates, resulting from a reduction of inactive cell density during flood recession. Floods appear to be key events in scouring senescent microbial assemblages in karst aquifers and stimulating microbial recolonization of the aquifer matrix. We conclude that a conceptual model of karst aquifer structure and function should incorporate changes caused by alternation between flooding and drying in the aquifer.

Localization of oil in microstructures of source rocks. Application of a microspectrofluorimetric method

Understanding primary migration mechanisms requires the study of the dynamic behavior of the fluid phases in source rock microstructures. The expulsion of oil from source rocks is linked to microlithological characteristics such as microfracturing and the spatial distribution of organic matter. This work has been carried out on both natural and artificial (hydrous pyrolysis) diagenetic series. The rock microstructures have been studied using natural light reflexion and fluorescence. The results show that the distribution of oil in different sites is a function of the maturity of the organic matter. The kinetics of fluorescence alteration of organic sites (Tasmanaceae, organo-mineral groundmass) have provided a criterion for in situ oil-kerogen discrimination. In addition, the role of hydrocarbons in the organo-mineral groundmass fluorescence has been studied in situ under the microscope by thermovaporisation and by chloroform extraction.