A cross-continental comparison of stream invertebrate community assembly to assess convergence in forested headwater streams     

Liliana García  Isabel Pardo  John S. Richardson 《Aquatic Sciences - Research Across Boundaries》2014,76(1):29-40

We studied two forested, headwater streams to compare patterns of invertebrate community structure and consequences for ecosystem functioning in two temperate locations, Galicia (NW Spain) and Vancouver (SW Canada). The two sites were selected due to the similar dominance of congeneric invertebrate species, as well as similarity in their hydromorphological and physico-chemical characteristics. Field experiments tested for similarities and dissimilarities in the invertebrate community assembly in leaf packs in streams. Our results indicated that alder leaves always decomposed faster than eucalyptus leaves, from threefold higher in Galicia to tenfold in Vancouver. At the species level, the biogeographic factor was the main source of variation on invertebrate assemblages (84.9 %), but this percentage quickly decreased at higher levels of taxonomic resolution, i.e. family. Moreover, there was a strong leaf species influence in both sites. There were more invertebrates colonizing leaves (per unit mass) in Vancouver than in Galicia (fourfold on average), though alder leaves seemed to be always the preferred resource (5.5-fold higher density on average). Regardless, a similar trophic structure was found between sites and leaf species. Brillia spp. and Corynoneura spp., a shredder and a collector-gatherer, respectively, seemed to be the most important species and showed similar colonization patterns in both sites with potential to strongly influence the leaf processing and nutrient cycling in these ecosystems. Even though our results are limited to the similarity found between only two sites, results from other studies, where the same species have been found coexisting during leaf pack processing, reinforces our results that common rules and mechanisms determine patterns of key ecological processes on a biogeographical scale.  相似文献   

A comparison between the Linear Regression Model with autocorrelated errors and the Partial Adjustment Model     

Helena Mouriño  Maria Isabel Barão 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(4):499-511

In this paper we consider a Linear Regression Model with a design matrix that fits the periodic structure of a time series. As a consequence, the residuals are very often autocorrelated. The main problem is that residual autocorrelation does not necessarily entail error autocorrelation. To analyse the effects of selecting different formulations to accommodate the autocorrelation in the residuals, we consider two seemingly different ways to deal with this problem: the Linear Regression Model with the error terms following an Autoregressive Stationary Process and the Partial Adjustment Model. We study the equivalence between the two formulations. We go over the problem of estimating the parameters and, especially, of making inferences in this framework. After parameter estimation, we analyse the adequacy of the models. We demonstrate that the issue of selecting the most appropriate model to capture the autocorrelation in the residuals is, in this context, a kind of an artefact since the main results concerning the fitted values and forecasting features are the same. These modelling procedures are applied to the Portuguese coastal upwelling data and we compare the estimated models.  相似文献   

Inorganic and methylmercury: do they transfer along a tropical coastal food web?     

Kehrig HA  Seixas TG  Baêta AP  Malm O  Moreira I 《Marine pollution bulletin》2010,60(12):2350-2356

Methylmercury (MeHg) and inorganic mercury (Hg_inorg) were evaluated in the water of a Brazilian estuary, with two size classes of plankton and seven fish species of different feeding habits. Water partition coefficients (PCs) in microplankton were fourfold higher for MeHg than for Hg_inorg; and water PCs in mesoplankton were 26 times higher for MeHg than Hg_inorg. Difference between microplankton and mesoplankton MeHg bioaccumulation factor (BAF) was higher (0.60 log units) than Hg_inorg BAF (0.24 log units), indicating that trophic transfer of MeHg between planktonic organisms is more efficient than Hg_inorg transference. MeHg concentrations, proportion of mercury as MeHg and its biotransference factors (BTFs) in the microplankton, mesoplankton and fish increased with increasing trophic level while biotic concentrations of Hg_inorg and proportion of mercury as Hg_inorg decreased thus indicating that MeHg was indeed the biomagnified species of mercury. MeHg reflected the vertical trophic guilds distribution, due to the fact that the top predator fish presented the highest concentration (0.77 μg g⁻¹ d.w.), followed by the less voracious species (0.43 μg g⁻¹ d.w.); while planktivorous fish presented the lowest concentrations (0.044 μg g⁻¹ d.w.). Hg_inorg did not present the same behavior. Results suggest that feeding habits and trophic guild are important parameters, influencing biotransference and biomagnification processes.  相似文献   

Late Pleistocene: Holocene record of environmental changes in Lake Zirahuen,Central Mexico     

Beatriz Ortega  Gabriel Vázquez  Margarita Caballero  Isabel Israde  Socorro Lozano-García  Peter Schaaf  Esperanza Torres 《Journal of Paleolimnology》2010,44(3):745-760

Geochemical data obtained from X-ray fluorescence, physical properties, total organic and inorganic carbon content (TOC/TIC), and diatom analysis from a 6.61-m-long sedimentary sequence near the modern northern shore of Lake Zirahuen (101° 44′ W, 19° 26′ N, 2000 m asl) provide a reconstruction of lacustrine sedimentation during the last approximately 17 cal kyr BP. A time scale is based on ten AMS ¹⁴C dates and by tephra layers from Jorullo (AD 1759-1764) and Paricutin (AD 1943-1952) volcanoes. The multiproxy analyses presented in this study reveal abrupt changes in environmental and climatic conditions. The results are compared to the paleo-record from nearby Lake Patzcuaro. Dry conditions and low lake level are inferred in the late Pleistocene until ca. 15 cal kyr BP, followed by a slight but sustained increase in lake level, as well as a higher productivity, peaking at ca. 12.1 cal kyr BP. This interpretation is consistent with several regional climatic reconstructions in central Mexico, but it is in opposition to record from Lake Patzcuaro. A sediment hiatus bracketed between 12.1 and 7.2 cal kyr BP suggests a drop in lake level in response to a dry early Holocene. A deeper, more eutrophic and turbid lake is recorded after 7.2 cal kyr BP. Lake level at the coring site during the mid Holocene is considered the highest for the past 17 cal kyr BP. The emplacement of the La Magueyera lava flows (LMLF), dated by thermoluminiscence at 6560 ± 950 year, may have reduced basin volume and contributed to the relative deepening of the lake after 7.2 cal kyr BP. The late Holocene (after 3.9 cal kyr BP) climate is characterized by high instability. Extensive erosion, lower lake levels, dry conditions and pulses of high sediment influx due to high rainfall are inferred for this time. Further decrease in lake level and increased erosion are recorded after ca. AD 1050, at the peak of Purepechas occupation (AD 1300–1521), and until the eighteenth century. Few lacustrine records extend back to the late Pleistocene—early Holocene in central Mexico; this paper contributes to the understanding of late Pleistocene-Holocene paleoclimates in this region.  相似文献   

From locational fundamentals to increasing returns: the spatial concentration of population in Spain, 1787–2000     

María Isabel Ayuda  Fernando Collantes  Vicente Pinilla 《Journal of Geographical Systems》2010,12(1):25-50

Why is population not evenly distributed throughout a country’s territory? This paper focuses on the case of Spain, in order to empirically test two complementary theoretical explanations: (a) first nature advantages or locational fundamentals; and (b) second nature advantages or increasing returns. We estimate population density and population growth equations for the case of Spain between 1787 and 2000. Our results suggest that locational fundamentals explain the distribution of population prior to industrialization and that industrialization reinforced the pre-existing regional population disparities, especially as the share of increasing-returns sectors in the Spanish economy became significant. Finally, we perform an ANOVA analysis which shows that although in the pre-industrial economy first nature advantages were the most important in explaining the growth in provincial population densities, these were progressively superseded by the influence of first via second nature effects.  相似文献   

Natural responses of Neoproterozoic dynamic karst springs to rainfall events,São Miguel Watershed,Minas Gerais,Brazil     

Tássia Marques  Paulo Galvão  Pedro Assunção  Bruno Pandolf  Peter Marshall  Isabel Paiva 《水文研究》2024,38(3):e15107

Karst aquifers consist of complex networks of conduits in which groundwater flows and recharge/discharge processes are generally more dynamic than in other types of aquifers. Due to their intrinsic heterogeneity and anisotropy, monitoring, quantifying, and analysing natural responses of karst springs is an efficient tool. Unlike Cenozoic and Mesozoic rocks, in Neoproterozoic karst systems, groundwater circulates and stores generally in dissolution features known as tertiary porosity, as the rock's primary porosity is recrystallized, considered negligible. This article studies the hydrodynamics of a karst portion of the São Miguel River basin, southwest of the state of Minas Gerais, Brazil. The region is predominantly composed of Neoproterozoic carbonate rocks, dating from about 570 to 540 million years ago. During a hydrological year (2019–2020), three karst springs (S1, S2, and S3) were daily monitored through their natural responses (variations of electrical conductivity, EC, temperature, T, and discharge, Q) to rainfall episodes. The data were interpreted based on the analysis of spring hydrographs, time series, recession curves (seasonal and intra-annual), and statistics of EC, T, and Q variations. The results show the three springs generally exhibit quick flow, typically karstic, in the case of hydrosystems with a well-structured and functional underground drainage network. The time series indicate the hydrosystem drained by S1 presents slower circulation and a lower degree of linearity, resulting from the higher sinuosity of the system, while the hydrosystems of S2 and S3 have similar behaviours, of quick water circulations immediately after a rainy episode. The degrees of karstification classify S1 and S2 as complex and extensive karst systems consisting of several subsystems, and S3 as a system in which the conduit network is more developed at the upper epiphreatic zone than near the outlet.  相似文献   

Determination of Rare Earth Elements in Geological Reference Materials: A Comparative Study by INAA and ICP-MS   总被引：3，自引：0，他引：3  

Fung Dai Kin  M. Isabel Prudêncio  M. Ângela Gouveia  Erik Magnusson 《Geostandards and Geoanalytical Research》1999,23(1):47-58

Data was obtained for the rare earth elements (REE) by instrumental neutron activation analysis (INAA) and inductively coupled plasma-mass spectrometry (ICP-MS) in twenty geological reference materials. In general, the precision obtained by ICP-MS is better for the light REE, decreasing with increasing atomic number. This is partly a result of the occurrence of the heavy REE at low concentrations. The precision of the data obtained by INAA is good (5% RSD). The data obtained also showed that for the elements determined by both methods, the accuracy is similar for the light REE and better for the middle and heavy REEs by INAA. Higher uncertainty is achieved by ICP-MS mainly for elements at very low concentrations, occurring at about ten times the chondritic values.  相似文献   

Effects of Paracentrotus lividus (Lamark, 1816) harvesting on benthic assemblages. An experimental approach     

Ana Catarina Torres  Marcos Rubal  Isabel Sousa‐Pinto  Puri Veiga 《Marine Ecology》2019,40(6)

The effect of harvesting on the diversity and structure of benthic assemblages is nowadays a relevant component of fishery management. Invertebrate harvesting is increasing worldwide and sea urchins are one of the main invertebrate target species. However, current knowledge about the effects of sea urchin harvesting on benthic assemblages is still poor. The aim of this study is to evaluate the influence of Paracentrotus lividus (Lamark, 1816) harvesting on tide pool assemblages from intertidal rocky shores. To achieve this objective, a field removal experiment was done for 10 months. Results of univariate and multivariate analyses showed that P. lividus harvesting had a significant effect on the number of taxa and structure of the benthic assemblage. Assemblages from pools where P. lividus were removed showed significant differences against controls; namely, where P. lividus were eliminated, pools showed higher number of taxa than control pools. This result contrasts with previous studies assessing effects of invertebrate harvesting that generally have found a biodiversity reduction in the exploited habitat. Despite this apparently positive effect of P. lividus harvesting, we should be cautious because effects of P. lividus harvesting on higher trophic levels or during long periods of time remain unexplored.  相似文献   

Geophysical investigation of the Colônia structure,Brazil     

Renato L. Prado  Isabel C. Espin Fenoll  Irfan Ullah  Gianna C. Maciel Miura  Alvaro P. Crsta  Roberto P. Zanon dos Santos  Wolf Uwe Reimold  Vagner R. Elis  Erico Imbernon  Claudio Riccomini  Liliana Alcazar Diogo 《Meteoritics & planetary science》2019,54(10):2357-2372

The origin of the nearly circular Colônia structure, located at the southwestern edge of the city of São Paulo, Brazil, has been the subject of a long‐standing debate, ever since the 1960s when the structure was first investigated by geophysical methods. The structure still raises interest for geological research, as its sedimentary infill holds important paleoclimatic information about the evolution of the tropical rainforest, as well as the interplay between the South American summer monsoon, the Intertropical Convergence Zone, and the southern Westerly wind belt—for possibly as long as several million years. In addition, the search for evidence to conclusively establish the origin of this structure continues, and the answer most likely lies in the lower portions of the basin's sedimentary infill, which also holds a significant potential for underground water resources. Here, we present the results from recent seismic (reflection and HVSR), gravimetric, and geoelectrical surveys. They have provided a reliable image of the sedimentary infill, and the maximum depth to basement within the structure has been constrained consistently by the different methods to approximately ?400 m. The geophysical data have also allowed to map the lateral contact between the crystalline basement rocks and the sedimentary infill, which indicates a diameter of approximately 2.8 km for the sedimentary basin, with 3.6 km being the diameter of the outermost limit of the structure. A total of six seismic stratigraphic boundaries were identified within the sedimentary infill, providing a framework for the planning of a deep drilling campaign and subsequent sampling program aimed at geological and paleoclimatology studies.  相似文献   

Stock and losses of trace metals from salt marsh plants     

Isabel Caçador  Miguel Caetano  Bernardo Duarte  Carlos Vale 《Marine environmental research》2009,67(2):75-82

Pools of Zn, Cu, Cd and Co in the leaf, stem and root tissues of Sarcocornia fruticosa, Sarcocornia perennis, Halimione portulacoides and Spartina maritima were analysed for a Tagus estuary (Portugal) salt marsh. Pools of Cu and Cd in the salt marsh were higher in spring/summer, indicating a net uptake of these metals during the growing season. Standing stocks of Zn, Cu, Cd and Co in the leaf and stem biomass of S. fruticosa, S. perennis and H. portulacoides showed a strong seasonal variation, with higher values recorded in autumn. The metal-containing leaves and stems that shed in the autumn become metal-containing detritus. The amount of this material washed out from the total marsh area (200 ha) was estimated as 68 kg of Zn, 8.2 kg of Cu, 13 kg of Co and 0.35 kg of Cd. The high tidal amplitude, a branched system of channels and semi-diurnal tidal cycle greatly favour the export of the organic detritus to adjoining marsh areas.  相似文献