Water quality and presence of pesticides in a tropical coastal wetland in southern Mexico

The water quality of the Pozuelos-Murillo lagoon system in southern Mexico was evaluated during three periods between March and October 2002, with particular emphasis on the detection of organochlorine and organophosphorous pesticide residues in water and sediments. Physicochemical and microbiological parameters of water were also measured and integrated in a water quality index (WQI). Multivariate analysis was used to regionalise the lagoon system as a function of the behaviour of all measured parameters. Solid phase micro-extraction followed by gas chromatography (SPME-GC) was used for pesticide analysis. The concentration of phosphorous was found to be higher than that of nitrogenous compounds. This, besides a deficiency in dissolved oxygen and a high organic matter concentration (as COD), reflects eutrophication processes in some areas of the system. Measured levels of faecal coliforms and oils and greases were above the limits established by Mexican law and comparable to the concentrations reported for other highly polluted systems in Mexico. Residues of DDD (2.0 microg L(-1)) in water and DDE (247 ng g(-1)) and endosulfan I (814 ng g(-1)) sediments were detected by SPME-GC. The spatial distribution of these contaminants implies major potential risks because the most polluted sites were found to be those with the highest fishing activity. Although in general the WQI is on acceptable levels (65-80%), some contamination problems are evident.     

Biomarkers of exposure and effect in the Brazilian flounder Paralichthys orbignyanus (Teleostei: Paralichthyidae) from the Patos Lagoon estuary (Southern Brazil)

Biomarkers of exposure (liver metallothionein-like proteins content and catalase and glutathione S-transferase activities) and effect (liver lipoperoxidation and blood cell DNA damage) of contaminants were analyzed in the Brazilian flounder Paralichthys orbignyanus from the Patos Lagoon estuary (Southern Brazil). Flounders were collected for a year in two sites: "Coroa do Boi" (polluted site) and "Saco do Justino" (non-polluted site). Results indicated that micronucleated cells frequency was the best biomarker to distinguish flounders from the two sites. Taken together, data from DNA damage analyses (micronucleus test and comet assay) indicated that flounders from the non-polluted site efficiently repaired the DNA breaks, contrary to those from the polluted site, which probably had their DNA repair system inhibited or exhausted. Furthermore, data from enzyme activities (catalase and GST) and lipid peroxidation indicated that flounders from the polluted site were under oxidative stress in summer and autumn.     

An exotic Cretaceous kimberlite linked to metasomatized lithospheric mantle beneath the southwestern margin of the Francisco Craton,Brazil

We present major and trace element compositions of mineral concentrates comprising garnet xenocrysts,ilmenite,phlogopite,spinel,zircon,and uncommon minerals (ti...     

Spatial and temporal changes in dry-snow line altitude on the Antarctic Peninsula

Drastic changes were detected in glacial systems of the Antarctic Peninsula in the last decades. The observed phenomena comprise the disintegration of ice shelves, acceleration and thinning of glaciers, and retreat of glacier fronts. However, due to the lack of consistent systematic observations in particular of the higher parts of the glacial systems, it is difficult to predict further responses of the Antarctic Peninsula glaciers to climatic change. The present paper analyses spatial and temporal variations of changes in the dry-snow line altitude on the Antarctic Peninsula as extracted from a time series (1992–2005) of ERS-1/2 SAR and Envisat ASAR data. Upward changes in dry-snow line altitude were observed in general, and are attributed to extreme high-temperature events impacting the central plateaus of the Antarctic Peninsula and the increasing duration of warming periods. A mean decrease in dry-snow line altitude was detected on the west side of the peninsula and is identified as a response to recorded increase in precipitation and accumulation. These results validate the capability of SAR data for deriving superficial parameters of glaciers to be used as indicators of climatic changes in high-latitude regions where operational restrictions limit conventional meteorological observations.     

Extreme rainfalls in SE South America

Heavy rainfall trends in a region of south-eastern South America during 1959–2002 were discussed using daily data of 52 meteorological stations of Argentina, Brazil and Uruguay. Changes in intensity and frequency were both studied with different statistical tests and approaches to check the significance of trends of single and regional aggregated rainfall series. There were predominant positive trends in the annual maximum rainfalls, as well as a remarkable increment in the frequency of heavy rainfalls over thresholds ranging from 50 to 150 mm. However, significant positive trends were not shown in the series of annual maximums and shown only in 15% to 30% of the series of frequencies over thresholds. This lack of significance is due to the high variability of heavy rainfalls in space and time, which makes difficult their capture by single rain gauges. Thus, when the assessment of the heavy rainfall indicators of intensity and frequency were conducted at the regional and sub-regional level, it showed significant trends, both in intensity and frequency over thresholds, with a clearer signal in central and eastern Argentina between 30° and 40° S.     

Single subduction zone for the generation of Devonian ophiolites and high‐P metamorphic belts of the Variscan Orogen (NW Iberia)

Within the Variscan Orogen, Early Devonian and Late Devonian high‐P belts separated by mid‐Devonian ophiolites can be interpreted as having formed in a single subduction zone. Early Devonian convergence nucleated a Laurussia‐dipping subduction zone from an inherited lithospheric neck (peri‐Gondwanan Cambrian back‐arc). Slab‐retreat induced upper plate extension, mantle incursion and lower plate thermal softening, favouring slab‐detachment within the lower plate and diapiric exhumation of deep‐seated rocks through the overlying mantle up to relaminate the upper plate. Upper plate extension produced mid‐Devonian suprasubduction ocean floor spreading (Devonian ophiolites), while further convergence resulted in plate coupling and intraoceanic ophiolite imbrication. Accretion of the remaining Cambrian ocean heralded Late Devonian subduction of inner sections of Gondwana across the same subduction zone and the underthrusting of mainland Gondwana (culmination of NW Iberian allochthonous pile). Oblique convergence favoured lateral plate sliding, and explained the different lateral positions along Gondwana of terranes separated by Palaeozoic ophiolites.     

Spatially distributed tracer‐aided modelling to explore water and isotope transport,storage and mixing in a pristine,humid tropical catchment

Rapidly transforming headwater catchments in the humid tropics provide important resources for drinking water, irrigation, hydropower, and ecosystem connectivity. However, such resources for downstream use remain unstudied. To improve understanding of the behaviour and influence of pristine rainforests on water and tracer fluxes, we adapted the relatively parsimonious, spatially distributed tracer‐aided rainfall–runoff (STARR) model using event‐based stable isotope data for the 3.2‐km² San Lorencito catchment in Costa Rica. STARR was used to simulate rainforest interception of water and stable isotopes, which showed a significant isotopic enrichment in throughfall compared with gross rainfall. Acceptable concurrent simulations of discharge (Kling–Gupta efficiency [KGE] ~0.8) and stable isotopes in stream water (KGE ~0.6) at high spatial (10 m) and temporal (hourly) resolution indicated a rapidly responding system. Around 90% of average annual streamflow (2,099 mm) was composed of quick, near‐surface runoff components, whereas only ~10% originated from groundwater in deeper layers. Simulated actual evapotranspiration (ET) from interception and soil storage were low (~420 mm/year) due to high relative humidity (average 96%) and cloud cover limiting radiation inputs. Modelling suggested a highly variable groundwater storage (~10 to 500 mm) in this steep, fractured volcanic catchment that sustains dry season baseflows. This groundwater is concentrated in riparian areas as an alluvial–colluvial aquifer connected to the stream. This was supported by rainfall–runoff isotope simulations, showing a “flashy” stream response to rainfall with only a moderate damping effect and a constant isotope signature from deeper groundwater (~400‐mm additional mixing volume) during baseflow. The work serves as a first attempt to apply a spatially distributed tracer‐aided model to a tropical rainforest environment exploring the hydrological functioning of a steep, fractured‐volcanic catchment. We also highlight limitations and propose a roadmap for future data collection and spatially distributed tracer‐aided model development in tropical headwater catchments.