Nutrient dynamics in Mediterranean temporary streams: A case study in Pardiela catchment (Degebe River, Portugal)

Most of the streams in the Mediterranean region are temporary, following predictable seasonal of flooding and drying, with a transition from lotic conditions to shallow lentic conditions. The goal of our study was to assess the nitrogen and phosphorus dynamics in channel-bed processes of temporary streams between floods. Results show that, during winter, temperatures ranged between 9.5 and 11.2 °C and oxygen concentration ranged from 8.0 to 9.5 mg L⁻¹, whereas, during summer, temperatures varied between 21.2 and 26.8 °C and oxygen between 1.2 and 5.3 mg L⁻¹, with oxygen depletion in the pools during the night. The nitrate concentrations were far more abundant during winter (February), while ammonium concentration increased after stream fragmentation into pools (especially in July when oxygen depletion conditions favoured ammonification). Results on sediment profiles showed that the most active sediment layers for NH₄-N are the top 2–3 cm, corresponding to the sediment depositional sites of the stream. Phosphate concentrations had larger variability, yet concentrations decreased from winter to spring and increased again in summer, when the shallow water pools were formed. Sediment profiles at the sediment depositional sites showed that PO₄-P was more dynamic in the first 6 cm.

In Mediterranean temporary streams, nutrient dynamics vary seasonally, as the system transits from lotic conditions to shallow lentic conditions, evidencing the regeneration of nutrients from organic and inorganic matter during the flow cessation period.     

Biochronology and biochron boundaries: A real dilemma or a false problem? An example based on the Pleistocene large mammalian faunas from Italy

Reconstructing the Neogene-Quaternary biostratigraphy in continental environments and recognising ‘boundaries’ between successive mammalian faunal complexes is a problematic task. The definition and application of biochronology has been often tainted by references to and inferences from biostratigraphy. Actually, the discontinuities in the continental sedimentary record, environmental conditions, taphonomic and sampling biases are responsible for the fact that the stratigraphical order of the lowest and highest occurrences of fossil remains (stratigraphic datum) does not necessarily reflect the temporal order of actual first/last appearances of taxa (palaeobiological events) in time. Nonetheless, the first/last appearance bioevents (recorded by lowest/highest occurrences of fossil remains in fossiliferous levels of different continental stratigraphical successions) have been the principal foundation for establishing the biochronological setting of continental mammal faunas. Therefore, from a theoretical point of view, ‘boundaries’ should be defined by the oldest and/or youngest ‘historical occurrence’ of one or more taxa. What about an operational approach?Some examples of the Italian faunas are presented, focusing on the transition from the Villafranchian to the Galerian and from the Galerian to the Aurelian Land-Mammal Ages. The results obtained indicate the difficulty of defining a stable scheme that can be applied for correlation by the international scientific community.     

Reddening of dune sands—evidence from southeast India

Thin section, SEM, and TEM analyses have indicated that the red ‘teri’ sands of southeast India have formed from weathering in situ of coastal dune sands. The data does not support a detrital origin for the red sands. C¹⁴ dates indicate that dune deposition and weathering, to a maximum depth of 10 m, leading to the formation of a hematite, koalinite and illite rich matrix has taken place rapidly over the past 25,000 years. It is postulated that garnet was a major source of hematite (ferric oxide).     

Isotopic ages and tectono-metamorphic history of the metamorphic basement of North-Eastern Sardinia

New Rb/Sr and K/Ar data on minerals and whole-rocks from the metamorphic basement of Northeastern Sardinia are presented. A formation of augen gneiss of volcano-sedimentary origin yields a Rb/Sr whole-rock age of 441±33 m.y.; a Rb/Sr isochron age of 306±10 m.y. is found for the minerals separated from one of these samples. K/Ar measurements on micas also yield ages of 319–284 m.y. A banded migmatite which originated through a process of metamorphic differentiation was analysed by the Rb/Sr method. Six bands, treated as whole-rock samples, fit an isochron of 344±7 m.y. Biotite and plagioclase from one of these bands yield an isochron age of about 300 m.y.The radiometric results reported in this paper and all those previously published are discussed in order to investigate the tectono-metamorphic history of this important segment of the ancient Mediterranean basement. It is argued that in this area there is only indirect evidence of a Caledonian orogenic event (late orogenetic acidic magmatites emplaced 458-441 m.y. ago) while the main features of the metamorphic basement must be related to the Hercynian orogeny the climax of which can be fixed at about 340 m.y. The concordance of the ages of the separated minerals (310-300 m.y.) suggests that the metamorphic succession stayed above the specific critical temperatures for about 40 m.y., after which it was suddenly uplifted contemporaneous with the emplacement of the, essentially post-kinematic, Hercynian granitoids.     

Pliocene extensional tectonics in the Eastern Central Patagonian Cordillera: geochronological constraints and new field evidence

Recent field work and review of radiometric data obtained from Neogene lavas and plutonic rocks exposed in the Eastern Central Patagonian Cordillera (46–48ºS), which overlie subducted segments of the South Chile Ridge, suggest important Late Miocene to Pleistocene morphological changes in relation to base level variations and/or tectonic events. We present new field observations from a region south of Lago General Carrera‐Buenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5–4 Ma and after 3 Ma. We also show that the 12 Ma basaltic flows of the Meseta del Lago Buenos Aires (∼2000 m a.s.l.) have been subjected to deep incision, with younger lavas dated at 1.2 Ma partially filling the valleys. These incisions are thought to reflect progressive eastward tilting of the entire meseta. Our new observations, together with additional features from Central Patagonia, strongly suggest that tectonic events led to a regional widespread morphological change after 5 Ma. The coincidence in time and space between the subduction of segments of the South Chile Ridge at 6 and 3 Ma causing opening of a slab window, and strong base level variations in the studied area, suggests a cause‐and‐effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. The uplift is purely tectonic in origin and occurred prior to the subduction of the South Chile Ridge. Extension should be a consequence of this subduction.     

Habitat provision of barnacle tests for overcrowded periwinkles

In habitats where competition for space is a shaping force of animal distribution such as in the intertidal rocky ecosystem, new habitats are readily taken by colonising species. We examined the importance of empty Chthamalus spp. tests as a habitat for the intertidal common periwinkle Melaraphe neritoides on Portuguese rocky shores. The role played by the space between neighbouring barnacles as a habitat for other species has been largely studied with regard to how an ecosystem functions, whereas the equivalent role of empty barnacle tests remains largely unknown. The small periwinkle is one of the most abundant snails in European rocky shores and is an important prey for key mobile predators. Biological facilitation is common in the rocky intertidal zone, where biological structures often potentiate the abundance of other species. The role played by barnacles as biological facilitators through habitat provision is not fully understood. In this study, the abundance and morphometric features of empty barnacle tests and their occupants were examined across shore levels and shores with differing exposures, as these are important gradients explaining barnacle distribution. The availability of empty barnacle tests was also experimentally manipulated to examine the percentage, time and length of occupation. Empty barnacles were more abundant on the midshore of sheltered shores and barnacle tests were wider on the upper shore but taller on the midshore. The minimum barnacle test occupation rate by the periwinkle was 70%. Barnacle shell height was an important factor determining snail occupation, where taller barnacles harboured significantly more, but not necessarily larger, snails. Snails outside the barnacle tests were significantly larger than those found within, suggesting that this crustacean group has an increased importance as a habitat for juvenile snails, thus potentially influencing the population dynamics of M. neritoides. We found that occupation of experimentally created empty barnacles was extremely high (70%) on the day after, and remained at 100% after 3 months of monitoring. Our study is the first of its kind to focus on the features of barnacle tests that snails occupy and their occupying snail traits. According to our results, it is clear that barnacles have an important role in providing additional habitat for young gastropods. The small periwinkle is an important grazer and prey for intertidal and subtidal foraging predators; hence, the potential refuge role of barnacle tests for juvenile M. neritoides may be important in the dynamics of intertidal communities.     

High connectivity and directional gene flow in European Atlantic and Mediterranean populations of Ciona intestinalis sp. A

Understanding the factors that cause population divergence has long been of interest to marine biologists in their attempts to interpret the effect of human‐mediated vectors. Broadcast‐spawning species with limited dispersal capability are excellent candidates to measure the present‐day patterns of genetic diversity. The tunicate Ciona intestinalis (Ascidiacea) is comprised of a complex of morphologically cryptic species that form vigorous aggregates in eutrophic habitats (harbors, gulfs and lagoons) where they can compete with the epibenthic community and cause biofouling problems. This study investigated biogeographic variability and migration patterns of C. intestinalis sp. A along Northeast Atlantic and Mediterranean coasts using microsatellite markers. Data presented here on 371 specimens collected from 17 populations reveal high genetic polymorphism, but with a deficit of heterozygote deficiency. Absence of evidence for isolation by distance suggests that the genetic patterns do not reflect the geographic distribution of sampled populations. Substantial gene flow and artificial potential for dispersal boost high levels of within‐population genetic variability and prevent genetic differentiation within and between seas. A predominant eastward migration pattern was revealed by the data set, with very limited opportunity for C. intestinalis sp. A to travel westward. This directional movement indicates that other properties (e.g. habitat quality, genetic traits, mating system, life cycle) may cause adaptive divergence at a large biogeographic scale.     

Synthetic Spectra of Long-Period Variables: A First Comparison with ISO Observations

Exploratory synthetic spectra were computed for carbon-rich long-period variables. We used dynamic model atmospheres of Höfner &; Dorfi (1997) and calculated partial pressures, absorption- and scattering coefficients as input for the spectral synthesis code of Jørgensen et al. (1992). First ISO SWS-observations of the carbon-Mira T Dra are compared with our synthetic spectra.