Organic matter characteristics in a Mediterranean stream through amino acid composition: changes driven by intermittency

Amino acid composition (quality) and abundance (quantity) of organic matter (OM) in an intermittent Mediterranean stream were followed during transitions from wet to dry and dry to wet conditions. Amino acids were analyzed in benthic material (epilithic biofilms, sand sediments, leaf material) as well as in the flowing water (dissolved organic matter, DOM). A principal component analysis and the estimation of the amino acid degradation index (DI) elucidated differences in amino acid composition and quality among the wet–drought–wet cycle. Amino acid content and composition were dependent on the source of OM as well as on its diagenetic state. The highest-quality OM (high DI and high N content) occurred on epilithic biofilms and the most degraded and lowest-quality OM occurred in sandy sediments. Differences between the pre- and post-drought periods were evident in DOM quality; autochthonous-derived material was predominant during the pre-drought (wet period preceding drying), while allochthonous inputs dominated during the post-drought period (wet period following drying). In contrast, benthic OM compartments were more stable, but benthic OM quality decreased continuously throughout the drought period. This study revealed that wet–drought–wet cycles resulted in subtle changes in benthic OM quality, and degradation of DOM was related to flow intermittency.     

Cenozoic tectosedimentary evolution of Mallorca island

Abstract

The results of recent biostratigraphic, sedimentologic and structural work concerning the island of Mallorca have led us to elaborate a synthesis of the Cenozoic tectosedimentary evolution of this area. The recognition in the field of several unconformities enabled us to distinguish four Depositional Sequences embracing the pre and syntectonic deposits.

From Paleocene to part of Middle Eocene there was no sedimentation in the Mallorca area. This stratigraphie gap follows the onset of Africa-Europe convergence.

The area was stable during the first sequence (Upper Lutetian-Bartonian), which is trangressive towards the NW. Tectonic activity is recorded by the conglomeratic wedges of Depositional Sequence 11 (Priabonian-Lower Chattian). A dramatic paleogeographic change ocurred between Depositional Sequence II and III. Observed thrusts and unstable platform sediments of Depositional Sequence III (Upper Chattian-Lo-wermost Burdigalian) indicate the onset of thrust tectonics in the area. Turbiditic deposits of Depositional Sequence IV (Burdigalian-Langhian) are clearly syntectonic. Post-orogenic deposits range from Serravalian to recent and are not discussed in this paper.

Synthetic regional geological cross-sections have been constructed. They are used to restore the cartographic structural units to their relative pre-tectonic position and a palinspastic map for each Depositional Sequence has been obtained. These maps show both the sedimentary environment distribution and the active tectonic structures; hence they illustrate the tectosedimentary evolution of the Mallorca area through the Cenozoic.

This work has evident limitations arising from the small area studied in relation to the Cenozoic Betic basin and from the lacking subsurface data.     

Provenance-related characteristics of beach sediments around the island of Menorca, Balearic Islands (western Mediterranean)

The island of Menorca, one of the Balearic Islands (Spain) located in the western Mediterranean, is characterised by a contrasting geology and landscape with two major geographic domains: (1) a southern region called Migjorn, comprised of Late Miocene calcarenites and limestones, and (2) a northern region known as Tramuntana, which is composed of folded and faulted Palaeozoic, Mesozoic and Tertiary (Oligocene) siliceous and calcareous rocks. Both domains are lined by numerous pocket beaches exhibiting a high variety of surficial sediment assemblages. Grain-size and compositional analyses revealed that cliff erosion and nearshore Posidonia oceanica meadows are the main sources of sediments consisting mostly of medium- to coarse-grained carbonate sands of marine biogenic origin, with variable amounts of terrigenous rock fragments and quartz. Based on distinctly different contributions of bioclastic material, biogenic carbonates and quartz, 320 sediment samples from 64 beaches were grouped into different facies associations dominated by either (1) biogenic sands, (2) biogenic sands with terrigenous contributions or (3) terrigenous sands with quartz. Nevertheless, there is a marked regional variability in sediment texture and composition. Thus, variable mixtures of carbonate and siliciclastic sediments characterise the beaches of the northern region, whereas the beaches of the southern region are composed mostly of carbonate sands of marine biogenic origin. An exception is the central sector of the south coast, which is enriched in quartz sand (~10 %); this can be related to outcrops of quartz-rich basement rock and also to rocks exposed in some northern drainage basins captured by southern streams since the Plio-Quaternary.     

Abrupt Climatic Changes during the Last Glaciation Based on Pollen Analysis of the Abric Romani, Catalonia, Spain

The Abric Romani continental pollen record provides evidence of abrupt climate variations during the last glaciation. The pollen record reveals a pattern of high-frequency variations similar to that in ice cores as shown by oxygen isotopes or dust content. Analyses of 14 travertine samples yield coherent U-series ages in correct stratigraphic order, ranging from 40,000 to 70,000 yr. According to changes in the composition and structure of the vegetation, five paleoclimatic phases have been differentiated; the oldest, ranging from 70,200 to 65,500 yr ago, records thermophilous taxa which correspond to the last warm events of isotopic stage 5. The next phase, from 65,500 to 56,800 yr, records a cold, humid climate that correlates with isotope stage 4. During the third phase, from 56,800 to 49,500 yr, relatively warm and cold events alternate. The fourth phase, from 49,500 to 46,200 yr, records a cold, dry climate. The fifth phase, ranging from 46,200 to 40,800 yr, records a milder phase that is similar in appearance to the beginning of the Holocene.     

Landscape and climatic changes during the end of the Late Prehistory in the Amblés Valley (Ávila, central Spain), from 1200 to 400 cal BC

Correlations between ecological and cultural changes occurred during a short period between the end of Subboreal and the beginning of Subatlantic in the Amblés Valley (Ávila, central Spain) are analyzed, taking into account palaeopalynological and archaeological data. Plant dynamics from pollen analyses, both from archaeological sites and peat bogs, have been interpreted in relation to human settlements and the transformation of economic practices. These provided a comprehensive hypothesis on human/climate interactions at the beginning of the 1st millennium cal BC. There was an ecological crisis in the region that lasted for a century (ca. 850–760 cal BC). This was especially sharp due to both the geographical constraints of the area and its previous agrarian history. This event implied a sudden and abrupt climatic change from xeric and warm conditions (Subboreal) to more humid and cooler ones (Subatlantic). Environmental stress derived from climatic crisis could be an important factor in the explanation of the historical process, whose main consequences were both the origin of the Iron Age peasant villages and the end of the ‘dehesa’ type landscape.     

Influence of transient storage on stream nutrient uptake based on substrata manipulation

Quantification of the transient storage zone (A_s) has become critical in stream biogeochemical studies addressed to examine factors controlling nutrient uptake. It is expected that higher A_s may enhance the interaction between nutrients and biota and thus, increase nutrient uptake. However, results from the literature are controversial. We hypothesized that besides of the size of A_s, the intrinsic physical and biological characteristics of stream structures that generate A_s are also relevant for nutrient uptake. We performed 24 additions of phosphate, ammonium, and chloride in four reaches of a man-made channel where we introduced three types of naturally colonized substrata packs (mud, sand and cobbles) to modify A_s. We estimated ammonium and phosphate uptake coefficients in both the main channel and A_s using a solute transport model (OTIS-P) and compared the results among reaches with different substrata types. The introduction of substrata packs decreased water velocity and increased A_s similarly among treatments. Nutrient uptake coefficients in the main channel were similar among reaches with different type substrata packs; however, nutrient uptake coefficients measured in A_s differed among them as well as the ratio between ammonium and phosphorus uptake coefficients in A_s, which were 1.6 in reaches with mud packs and 0.02 in reaches with sand or cobble packs. Results obtained in this study suggest that the contribution of A_s in nutrient uptake not only depends on the size of A_s but on the type of materials used to increase A_s, and thus, have biogeochemical implications on restoration projects aimed to modify channel morphology.