Renata Zocatelli

Free fatty acids in Lake Aydat catchment soils (French Massif Central): sources, distributions and potential use as sediment biomarkers

PurposeEighteen soils were sampled in the Lake Aydat catchment in order to analyse free fatty acid (FA) content; FAs are considered to be among the most amenable biomarkers to mobilisation by runoff waters. The majority of the study area has soil cover consisting of grasslands or forest since the 2nd World War, although some covers having changed more recently.Material and methodsThe soil studied all developed on volcanic rocks (andisols). The bulk organic matter (OM) content of the samples was characterized by Rock-Eval (RE) pyrolysis. The FAs were determined by gas chromatography–mass spectrometry (GC-MS) analysis of isolated and derivatized (methylation and trimethylsilylation) FA fractions.Results and discussionFew low molecular weight compounds (LMW; i.e., <C20) were detected; FA distributions were dominated by even numbered-carbon high molecular weight (HMW; ≥C20) normal FAs and difunctionalized FAs that included: dicarboxylic acids (diFAs), n-alkylcarboxylic acids (nFAs), and α- and ω-hydroxycarboxylic acids (αHOFAs and ωHOFAs). The distributions and abundances of HMW terms of all families (which can be all considered as representative of terrestrial OM source) displayed only slight differences. These differences were rationalized by the following ratios: (C26:0 + C28:0)/ΣCeven nFAs, C22/C24 di-FAs, and C20−/C20+ω-HOFAs). Soils from areas that had changed use recently consistently displayed intermediate ratio values typical of their double inheritance. All grassland soils and some samples from intermediate areas contained notable amounts of the bile acid deoxycholic acid that testifies to their present or recent use for cattle breeding.ConclusionsDespite the variety and the abundance of all HMW FAs in soils, work done previously on Lake Aydat sediments found only nFAs (Stefanova, M. and Disnar, J. R. 2000. Composition and early diagenesis of FAs in lacustrine sediments, Lake Aydat (France). Org Geochem 31, 41–55). These results suggest we should question the importance of the watershed contribution, the source (plant or soil) and mode of transportation of the FAs to the lake sediments.

Uso dos fenóis da lignina no estudo da matéria orgânica na Várzea do Lago Grande Curuái, Pará e no Lago do Caçó, Maranhão, Brasil

Este estudo tem por objetivo caracterizar os sedimentos superficiais, quanto ao seu teor e qualidade dos fenois da lignina, em dois sistemas lacustres distintos: a Varzea do Lago Grande Curuai (PA) e o Lago do Caco (MA). A Varzea do Lago Grande Curuai e localizada na margem direita do Rio Amazonas, aproximadamente 850 km da foz e e caracterizada pela presenca de lagos de aguas brancas e pretas. O Lago do Caco esta localizado no Maranhao, na borda do ecossistema amazonico. Foram realizadas analises da concentracao de lignina (λ), carbono orgânico total (COT), nitrogenio e isotopos do carbono (δ13C). Os resultados indicam que os sedimentos superficias de lagos de aguas brancas apresentam baixos valores de COT (1,5 a 3,6%), baixa concentracao de λ (0,73 a 1,28 mg.100mg CO-1) e alto indice de degradacao (0,29 a 2,01). Os sedimentos superficiais de lagos de aguas pretas apresentam maiores valores de COT (6,0 a 12,1%) e de λ (1,44 a 1,93 mg.100mg CO-1) em relacao aos sedimentos de lagos de aguas brancas, porem baixos em comparacao com os sedimentos do Lago do Caco (7,2 ~ 15,3% e 1,83 ~ 4,64 mg .100mg CO-1, respectivamente). Atraves das analises realizadas foi possivel identificar diferentes contribuicoes de fontes assim como diferentes estados de preservacao da materia orgânica sedimentada nos dois sistemas apresentados.

Environmental responses of past and recent agropastoral activities on south Greenlandic ecosystems through molecular biomarkers

Paleoenvironmental studies previously performed on Lake Igaliku revealed two agropastoral phases in south Greenland: the Norse settlement from AD 986 to ca. AD 1450 and the recent installation of sheep farmers, since the 1920s. To improve the knowledge of the timing and magnitude of the Greenlandic agropastoral activities, a lipid inventory was realized and compared with biological and geochemical data. During the 12th century, a major increase in deoxycholic acid (DOC) and coprophilous fungal spores revealed a maximum of herbivores. Synchronously, a minimum of the n-C29/n-C31 alkane ratio and tree and shrub pollen and a maximum of triterpenyl acetates showed a reduction in the tree and shrub cover, because of grazing activities. Lupanone, produced by angiosperms, appeared simultaneously in the molecular content, probably revealing an introduction of plant species by the Norse, as it has been the case for Rumex spp. No major erosion was recorded by trimethyl-tetrahydrocrysenes (TTHCs) and titanium (Ti) fluxes. No massive algal production, identified by the n-C17/total n-alkane ratio and mesotrophic diatoms, was either revealed. After the Norse abandon (around AD 1450), a return of the vegetation to quasi-pristine conditions was observed in the molecular content. Finally, a re-introduction of sheep in the 1920s provoked major impacts between the 1970s and the 1990s. A major decrease in the n-C29/n-C31 alkane ratio and tree and shrub pollen associated with maxima of triterpenyl acetates, TTHCs, Ti fluxes, and mesotrophic diatoms highlighted a reduction in the tree and shrub cover, a strong soil mobilization, and algal blooms, probably linking to the recent mechanized creation of hay fields and the massive use of fertilizers. In this study, molecular biomarkers revealed two periods of major impacts: the 12th century and between the 1970s and the 1990s, separated by centuries without agropastoral practices, allowing a quasi-resilience of the vegetation.

Lake Pavin Paleolimnology and Event Stratigraphy

In this chapter we present an up-to-date database of sedimentary sequences retrieved from Lake Pavin during the last 50 years in both oxic and anoxic waters. The detailed history of this mid Holocene crater lake can be reconstructed from the correlation of radiocarbon dated sedimentary sequences retrieved from the deep central basin, a subaquatic plateau and littoral environments. High-resolution measurements of sediment composition (diffuse spectral refl ectance, XRF core scanning) combined with the analysis of organic matter composition and preliminary pollen and diatom assemblages investigations on selected sediment cores are used to reconstruct (i) the evolution since ca. 7000 cal BP of Lake Pavin limnology together with its radiocarbon reservoir effect and (ii) the impact of a wide range of subaquatic slope failure events. Such a multidisciplinary approach of Lake Pavin basin fi ll revealed contrasted sedimentation patterns just after the volcanic eruption and following the development of a dense vegetation cover along the slopes of the crater. Pavin sedimenta-tion is rapidly and largely dominated by organic rich and fi nely laminated diatomite formation , but several short periods of enhanced mineral inputs might refl ect the infl uence of wetter periods, such as the Little Ice Age. Over the last millennium two large subaquatic mass wasting events are also identifi ed and may have signifi cantly impacted its limnology.