Phytoplankton driven distribution of dissolved and particulate lipids in a semi-enclosed temperate sea (Mediterranean): Spring to summer situation

The relationship between changes in lipid classes and phytoplankton composition and abundance in the northern Adriatic was studied during spring and summer 2008 at two stations with different nutrient levels, i.e. at the western mesotrophic and eastern oligotrophic areas. Changes in the phytoplankton community depended on temporal surface nutrient depletion and bottom accumulation; that is, microphytoplankton, mainly diatoms Pseudo-nitzschia sp., developed at nutrient richer surface layers of the mesotrophic area in spring and at deeper layers of the oligotrophic site in late summer. In other periods nanophytoplankton dominated. Dissolved organic carbon (DOC) and lipid content were comparable for the two stations, while particulate organic carbon (POC) was richer at the mesotrophic side. Total lipid concentrations varied in the range from 8.0 to 92.2 μg l⁻¹ and from 16.9 to 76.9 μg l⁻¹ in the dissolved and particulate fractions, respectively. DOC and POC contents were in the ranges from 0.77 to 1.58 mg l⁻¹ and from 0.06 to 0.56 mg l⁻¹, respectively. Lipid and organic carbon distribution did not follow phytoplankton progression, indicating decoupling between organic matter production and decomposition throughout the investigation period. The main sources of lipids were marine phytoplankton and bacteria. Low nutrient conditions caused increased biosynthesis of lipids. Also, increasing oligotrophy led to an increasing number of phytoplankton taxa. The synthesis and accumulation of glycolipids by the developed taxa were enhanced during nutrient exhaustion, contributing in late summer, on average, 20.2 and 22.0% at the mesotrophic and oligotrophic stations, respectively, in the particulate fraction. The distribution of bacterial lipids and lipid breakdown products implies that bacterial lipid degradation was significant in spring, while very probably lipid abiotic degradation took place during summer.     

Social networks and trade of services: modelling interregional flows with spatial and network autocorrelation effects

Recent literature on border effect has fostered research on informal barriers to trade and the role played by network dependencies. In relation to social networks, it has been shown that intensity of trade in goods is positively correlated with migration flows between pairs of countries/regions. In this article, we investigate whether such a relation also holds for interregional trade of services. We also consider whether interregional trade flows in services linked with tourism exhibit spatial and/or social network dependence. Conventional empirical gravity models assume the magnitude of bilateral flows between regions is independent of flows to/from regions located nearby in space, or flows to/from regions related through social/cultural/ethic network connections. With this aim, we provide estimates from a set of gravity models showing evidence of statistically significant spatial and network (demographic) dependence in the bilateral flows of the trade of services considered. The analysis has been applied to the Spanish intra- and interregional monetary flows of services from the accommodation, restaurants and travel agencies for the period 2000–2009, using alternative datasets for the migration stocks and definitions of network effects.     

Luquillo Experimental Forest: Catchment science in the montane tropics

Catchments in the Luquillo Experimental Forest (LEF) of Puerto Rico are warm, wet and tropical with steep elevational relief creating gradients in temperature and rainfall. Long-term objectives of research at the site are to understand how changing climate and disturbance regimes alter hydrological and biogeochemical processes in the montane tropics and to provide information critical for managing and conserving tropical forest ecosystems globally. Measurements of hydrology and meteorology span decades, and currently include temperature, humidity, precipitation, cloud base level, throughfall, groundwater table elevation and stream discharge. The chemistry of rain, throughfall, and streams is measured weekly and lysimeters and wells are sampled monthly to quarterly. Multiple data sets document the effects of major hurricanes including Hugo (1989), Georges (1998) and Maria (2017) on vegetation, biota and catchment biogeochemistry and provide some of the longest available records of biogeochemical fluxes in tropical forests. Here we present an overview of the findings and the data sets that have been generated from the LEF, highlighting their importance for understanding montane tropical watersheds in the context of disturbance and global environmental change.     

More than a checkbox: engaging youth in disaster risk reduction and resilience in Canada

Fire has become one of the main disturbances in terrestrial ecosystems worldwide. It is known that elevation influences the occurrence of fire events; however, this variable has been poorly studied, although it is of particularly relevance to the Mexican topography. The objective of this research was to analyze the altitudinal distribution of forest fires in Mexico over a period of 11 years. Elevation gradients were defined based on a Digital Elevation Model and the main ecoregions of the country: (1) shrubland and tropical forests (0–1000 masl), (2) grasslands (1001–2000 masl) and (3) temperate forests (>?2000 masl). Each ecoregion was divided into Climate Research Units and the number of fires per unit was quantified. The G Getis–Ord statistic was applied in order to define the spatial patterns presented by the fire events. A relationship between the occurrence of fires and the El Niño Southern Oscillation phenomenon was also determined through a Pearson correlation. The results showed that the occurrence of fire events presented variability along elevation gradients, with elevation a determining factor in their occurrence. Gradient 3, with the highest elevation, had the greatest number of fires and also presented the largest area of fire event clustering. These results contribute to the knowledge of the spatial distribution of forest fires in Mexico and are of value to appropriate decision-making for effective fire management.

     

Experimental rare-earth-element partitioning in oldhamite: Implications for the igneous origin of aubritic oldhamite

Abstract— Aubritic oldhamite (CaS) has been the subject of intense study recently because it is the major rare-earth-element (REE) carrier in aubrites, has a variety of REE patterns comparable to those in unequilibrated enstatite chondrites and has an extraordinarily high melting point as a pure substance (2525 °C). These latter two facts have caused some authors to assert that much of the aubritic oldhamite is an unmelted nebular relict, rather than of igneous origin. We have conducted REE partitioning experiments between oldhamite and silicate melt using an aubritic bulk composition at 1200 °C and 1300 °C and subsolidus annealing experiments. All experiments produced crystalline oldhamite, with a range of compositions, glass and Fe metal, as well as enstatite, SiO₂, diopside and troilite in some charges. Rare-earth-element partitioning is strongly dependent on oldhamite composition and temperature. Subsolidus annealing results in larger partition coefficients for some oldhamite grains, particularly those in contact with troilite. All experimental oldhamite/silicate melt partition coefficients are <20 and the vast majority are <5, which is similar to those reported in the literature and is two orders of magnitude less than those inferred for natural aubritic oldhamite. These partition coefficients preclude a simple igneous model, since REE abundances in aubritic oldhamite are greater than would be predicted on the basis of the experimental partition coefficients. Our experimental partition coefficients are consistent with a relict nebular origin for aubritic oldhamite, although experimental evidence that suggests melting of oldhamite at temperatures lower than that reached on the aubrite parent body are clearly inconsistent with the nebular model. Our experiments are consistent also with a complex igneous history. Oldhamite REE patterns may reflect a complex process of partial melting, melt removal, fractional crystallization and subsolidus annealing and exsolution. These mechanisms (primarily fractional crystallization and subsolidus annealing) can produce a wide range of REE patterns in aubritic oldhamite, as well as elevated (100–1000 × CI) REE abundances observed in aubritic oldhamite.     

On Motion of Wind Waves

Parameters of wind waves in a deep-water zone of a reservoir is studied in the context of wave influence on shore stability. Data from measurements of wave parameters in reservoirs of Czech Republic are used. The relationship between the period and phase velocity of wind waves is discussed.     

Use of Plant Bioassays for the Detection of Genotoxins in the Aquatic Environment

The present article describes the use of plant bioassays for the detection of genotoxins in the aquatic environment and gives an overview of test methods, their detection spectrum for environmental mutagens and carcinogens and their limitations and pitfalls. The most widely used test systems are micronucleus assays with meiotic cells of Tradescantia and with meristematic root tip cells of Allium and Vicia. In the last years, protocols for single cell gel electrophoresis assays have been developed, which can be conducted with a variety of species. Also various gene mutation test procedures have been developed with plants but they have hardly ever been used in environmental studies. Plants detect a broad variety of environmentally relevant genotoxins, in particular directly acting compounds. Many pesticides and industrial chemicals caused positive results; plant assays are also a unique tool for the detection of DNA‐reactive carcinogenic heavy metals in the environment. In many studies with complex mixtures, positive results were obtained which indicates that plants are sufficiently sensitive to detect effects without concentration of water samples. One of the shortcomings of the use of plants as indicators is their lack of sensitivity towards certain classes of promutagens such as nitrosamines, heterocyclic amines, and polycyclic aromatic hydrocarbons (PAHs). However, the former compounds are hardly encountered in the environment and PAHs can easily be detected chemically and in other mutagenicity tests. Taken together, the currently available data show that plant bioassays are a useful component of test batteries for environmental monitoring.     

Global warming and the growth of ice sheets

Recent research has suggested that warmer conditions, that may result from increased levels of CO₂ in the atmosphere, may induce the growth of the Northern Hemisphere ice sheets (Miller and de Vernal 1992) through the impact of warmer temperature on the water carrying capacity of the atmosphere and thus on precipitation. In this study we examine this possibility by using a coupled energy balance climate-thermo-dynamic sea ice model. Results indicate that if summer ice albedo is high enough, and there is some mechanism for initially maintaining ice through the summer season, then it may be possible to have ice sheet growth under the conditions of CO₂ induced warming.This paper was presented at the Second International Conference on Modelling of Global Climate Variability, held in Hamburg 7–11 September 1992 under the auspices of the Max Planck Institute for Meteorology. Guest Editor for these papers is L. Dümenil