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Vicente Marcano Javier Campins Cesyen Cedeño Ernesto Palacios-Prü 《Planetary and Space Science》2004,52(7):613-621
There is evidence that space energy sources could give place to the appearance of phosphorylated nucleosides outside of Earth. These compounds may have been delivered mainly by interplanetary dust particles due to the lower temperatures experienced during atmospheric deceleration and impacts to the terrestrial surface. In this report, we communicate the results of pyrolytic studies to simulate atmospheric survivability of adenosine-5′-diphosphates (ADP) (and adenosine-5′-monophosphate, adenosine and adenine as degradation products) at temperatures <500°C and at various time intervals. Our results revealed that phosphorylated and non-phosphorylated nucleosides transported by IDPs having sizes of 10−6- could resist temperatures up to 500°C generated during atmospheric entry. However, atmospheric passage should not exceed a time due to the thermal lability of these molecules. Because of the high half-life showed by ADP in the presence of meteoritic powder, it is thought that extraterrestrial delivery of very complex biomolecules is more suitable under such protected conditions. These data indicate that the formation of a Fe2+- and/or Ca2+-complex could increase the stability of the molecules in the presence of meteoritic matter. Therefore, if the synthesis of nucleosides, nucleotides or oligonucleotides could take place in icy bodies, then micron-sized dust could have contributed significantly to the availability of phosphorylated nucleosides in the early Earth or in extrasolar early Earth-like planets, and thereby could have allowed the arising of an early biological activity. 相似文献
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Blooms of macroalgal matting are increasingly common within temperate zones and are often comprised of opportunistic species such as Ulva lactuca. Where this algae forms a dense mat, a stressful environment is created in the sediment below, influencing the invertebrate infaunal assemblage. This study was conducted over a six month period during which a dense mat of U. lactuca developed and subsequently dispersed. The algal mat was found to have a significant negative impact on species richness, abundance and biomass of the macroinfauna. However, a faunal community developed within the algal mat which contained several species not previously observed. This community increased the abundance and diversity of the overall invertebrate assemblage. The results are discussed in relation to impacts on the ecosystem as a whole. 相似文献
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Juan A. Alfonso Helga Handt Abrahan Mora Yaneth Vásquez José Azocar Eunice Marcano 《Marine pollution bulletin》2013
The oyster Crassostrea rhizophorae is a bivalve abundant in Venezuelan estuaries and consumed by local populations. No known values have been reported on trace metals in oysters from the central Venezuelan coast. We report the concentrations of Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V and Zn in the soft parts of C. rhizophorae, which were collected bimonthly between March 2008 and March 2009, at two sampling areas from the Central Venezuelan Coast: Buche estuary and Mochima estuary. Our results show that for each metal there is a similar temporal variation pattern. The concentrations of the heavy metals reported in this work are useful as reliable baselines and can be used for comparison in future environment studies. Concentrations in C. rhizophorae from the Buche estuary can be interpreted to be high on a global scale for Cd, Cu, Ni and Mn, indicating atypically raised bioavailabilities. 相似文献
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Paul S. Davison Paul J.A. Withers Eunice I. Lord Mark J. Betson Johan Strmqvist 《Journal of Hydrology》2008,350(3-4):290-302
PSYCHIC is a process-based model of phosphorus (P) and suspended sediment (SS) mobilisation in land runoff and subsequent delivery to watercourses. Modelled transfer pathways include release of desorbable soil P, detachment of SS and associated particulate P, incidental losses from manure and fertiliser applications, losses from hard standings, the transport of all the above to watercourses in underdrainage (where present) and via surface pathways, and losses of dissolved P from point sources. The model can operate at two spatial scales, although the scientific core is the same in both cases. At catchment scale, the model uses easily available national scale datasets to infer all necessary input data whilst at field scale, the user is required to supply all necessary data. The model is sensitive to a number of crop and animal husbandry decisions, as well as to environmental factors such as soil type and field slope angle. It is envisaged that the catchment-scale model would provide the first tier of a catchment characterisation study, and would be used as a screening tool to identify areas within the catchment which may be at elevated risk of P loss. This would enable targeted data collection, involving farm visits and stakeholder discussion, which would then be followed up with detailed field-scale modelling. Both tiers allow the effects of possible mitigation options at catchment scale (Tier 1) and field scale (Tier 2) to be explored. The PSYCHIC model framework therefore provides a methodology for identifying critical source areas of sediment and P transfer in catchments and assessing what management changes are required to achieve environmental goals. 相似文献
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The behavior and dynamics of arsenic at Ilha do Mel, Guaraque?aba, and Paranaguá, located in the Paranaguá Estuarine Complex, Brazil, were investigated in this work. Samples were collected in March, September, and December of 2005. With respect to arsenic behavior, the total concentrations were higher for Paranaguá (22.5?±?2.5?μg?L?1) on average, followed by the samples of Guaraque?aba (14.4?±?3.2?μg?L?1) and Ilha do Mel (8.7?±?1.1?μg?L?1). The concentrations found in this work were consistently greater when compared to other estuaries. The results can be attributed to geological factors. Nevertheless, it was also possible to realize that higher concentrations were found in Paranaguá, the more impacted environment. These results represent a strong indication that human activities in the area contribute to the enrichment of the estuary with this metalloid. Arsenic was mainly present in the dissolved phase, which corresponded to more than 70% of the total concentration. This behavior can represent a greater residence time of this metalloid in the water column. The marine phytoplankton presence was decisive in dictating the distribution of As in the waters of Paranaguá estuary. Organic species, which are considered the less toxic, were found in higher concentrations in the eutrophic areas such as Guaraque?aba and Paranaguá. This was a typical behavior during the summer probably due to higher biological activity. 相似文献
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Arne saltmarsh, an RSPB reserve, is situated in Poole Harbour on the English south coast. In recent years, there has been concern about possible changes in the suitability of the site for Redshank (Trigna totanus) due to sika deer (Cervus nippon) grazing. In order to assess these changes, 50 plots were established in three different locations: 20 in grazed areas, 20 in ungrazed areas and 10 fenced enclosures. Deer grazing was found to significantly affect structural and species diversity of the saltmarsh vegetation. Spartina anglica dominated in ungrazed areas whilst Salicornia ramosissima and, to a lesser extent, Puccinellia maritima dominated in grazed sites. In grazed areas the vegetation cover was significantly lower, as was vegetation height and volume. In addition, significant changes were observed in the root biomass, which was lower in grazed areas. Infaunal diversity was generally low throughout the survey area. However, significant variations were observed. Invertebrates abundance was more abundant in grazed plots than in ungrazed plots, and least abundant in fenced plots. The study indicated that in its current condition, localised areas of Arne saltmarsh do not provide adequate habitat requirements for Tringa totanus. 相似文献
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Byanka Damian Mizerkowski Karl-J. Hesse Norbert Ladwig Eunice da Costa Machado Rodrigo Rosa Taiana Araujo Daniela Koch 《Ocean Dynamics》2012,62(10-12):1409-1424
The present study focuses on the nutrient sources and gradients in Paranaguá Bay (Southern Brazil), where nutrient inputs are related to losses from fertilizer loading in Paranaguá harbour and the discharge of untreated waste water. The input of dissolved inorganic nutrients to the bay from the harbour and city, as well as from river and atmospheric deposition, amounted to 642?t?year?1 DIN-N and 92?t?year?1 PO4-P. Harbour losses accounted for 6?% of total DIN-N and 39?% of total PO4-P loads to the bay, whereas sewage inputs from the city were responsible for 21?% and 22?%, respectively. River inputs made up 68?% of DIN-N, mainly in the form of nitrate, and 35?% of PO4-P loads, while atmospheric wet deposition was estimated to be in the order of 5?% of DIN-N and 4?% of PO4-P loads. Local maxima in nutrient levels deriving from highly concentrated sewage discharge were observed in front of the harbour and city of Paranaguá, but the plumes are diluted rapidly due to short residence times. DIN concentrations are negatively correlated with salinity, indicating the importance of freshwater input as a main factor controlling nitrogen distribution. Elevated phosphate levels in the stratified middle section of the bay may result both from harbour emissions and phosphate remobilization from sediments. Generally lower DIN and PO4 concentrations during the warmer rainy season are supposed to be due to intensified assimilation rates especially in the middle section of the bay where dense phytoplankton blooms are observed. The bay as a whole cannot be classified as being seriously eutrophic, albeit eutrophication symptoms prevail in some restricted locations in front of Paranaguá harbour. 相似文献