Latitudinal trends in the species richness of free-living marine nematode assemblages from exposed sandy beaches along the coast of Chile (18–42 °S)

The latitudinal pattern of species richness of free-living marine nematodes from exposed sandy beaches along the coast of Chile between 18 and 42° S was examined. Unlike many other examinations of latitudinal gradients, this study is not based on data mined from the literature, but on samples collected specifically to examine these themes. Five replicate quantitative 50 cm³ samples of sediment were taken from the zone of retention of 66 exposed sandy beaches. The free-living nematode fauna was identified and quantified to species level. The data were then examine using ordinary least squares and simultaneous autoregressive model (SAR_err) regression methods, examining the associations between species richness and latitude, coastline complexity, and sea surface temperature, primary productivity of the adjacent coastal waters and mean latitudinal range size. The species richness of free-living marine nematodes from exposed sandy beaches along the coast of Chile decreased with increasing latitude and was strongly associated with mean annual sea surface temperature. Mean latitudinal range size increased with increasing latitude, supporting Rapoport’s rule, and decreased with increasing species richness. The results suggest that the nematode fauna of exposed sandy beaches is derived from a low latitude fauna that has dispersed to higher latitudes, but that many species may be physiologically constrained, by temperature, from dispersing further south.     

Seasonal cycle of N2O vertical distribution and air-sea fluxes over the continental shelf waters off central Chile (∼36°S)

The continental shelf off central Chile is subject to strong seasonal coastal upwelling and has been recognized as an important outgassing area for, amongst others, N₂O, an important greenhouse gas. Several physical and biogeochemical variables, including N₂O, were measured in the water column from August 2002 to January 2007 at a time series station in order to characterize its temporal variability and elucidate the physical and biogeochemical mechanisms affecting N₂O levels. This 4-year time series of N₂O levels reveals seasonal variability associated basically with hydrographic and oceanographic regimes (i.e., upwelling and non-upwelling). However, a noteworthy temporal evolution of both the vertical distribution and N₂O levels was observed repeatedly throughout the entire study period, allowing us to distinguish three stages: winter/early spring (Stage I), mid-spring/mid-summer (Stage II), and late summer/early autumn (Stage III).Stage I presents low N₂O, the lowest surface saturation ever registered (from 64% saturation) in a period of high O₂, and a homogeneous column driven by strong wind; this distribution is explained by physical and thermodynamic mechanisms. Stage II, with increasing N₂O concentrations, agrees with the appearance of upwelling-favourable wind stress and a strong influence of oxygen-poor, nutrient-rich equatorial subsurface waters (ESSW). The N₂O build-up creates a “hotspot” (up to 2426% N₂O saturation) and enhanced concentrations of (up to 3.97 μM) and (up to 4.6 μM) at the oxycline (4-28 μM) (∼20-40 m depth). Although the dominant N₂O sources could not be determined, denitrification (mainly below the oxycline) appears to be the dominant process in N₂O accumulation. Stage III, with diminishing N₂O concentrations from mid-summer to early autumn, was accompanied by low N/P ratios. During this stage, strong bottom N₂O consumption (from 40% saturation) was suggested to be mainly driven by benthic denitrification.Consistent with the evolution of N₂O in the water column over time, the estimated air-sea N₂O fluxes were low or negative in winter (−9.8 to 20 μmol m⁻² d⁻¹, Stage I) and higher in spring and summer (up to 195 μmol m⁻² d⁻¹, Stage II), after which they declined (Stage III). In spite of the occurrence of ESSW and upwelling events throughout stages II and III, N₂O behaviour should be a response of the biogeochemical evolution associated with biological productivity and concomitant O₂ levels in the water and even in the sediments. The results presented herein confirm that the study area is an important source of N₂O to the atmosphere, with a mean annual N₂O flux of 30.2 μmol m⁻² d⁻¹; however, interannual variability could not yet be properly characterized.     

Effect of seasonal changes in bottom water oxygenation on sediment N oxides and N2O cycling in the coastal upwelling regime off central Chile (36.5°S)

An intensive and seasonal coastal upwelling process, which attains maximal expression during late austral spring and summer, drives well-known changes in organic matter production and, therefore, in O₂ content in the water column. These variables have a concomitant effect on N sediment processes over the continental shelf off central Chile (36.5°S), which, in turn, can affect the , , and N₂O content in the bottom water. Hydrographic characteristics, benthic and fluxes, and denitrification rates were measured from 1998 to 2001 (with at least seasonal frequency). In order to elucidate how benthic N₂O recycling responds to different O₂ and nutrient levels and how it affects the bottom water N₂O content, net N₂O cycling was measured in December 2001 in sediment slurry incubations under different manipulated dissolved O₂ levels (anoxic: 0 μM; hypoxic: 22.3 μM; oxic: 44.6 μM) and without (natural) and with the addition of and (enriched experiments). Dissolved O₂ and contents (and also ) showed clear seasonal patterns according to the oceanographic regime, i.e., from hypoxic waters rich in nutrients during the upwelling season to oxic waters with less nutrient contents during the non-upwelling season. The bottom water, on the other hand, was influenced by benthic organic mineralization, which consumes O₂ as well as other electron acceptor N-species such as . Benthic fluxes (2.62-5.08 mmol m⁻² d⁻¹) were always directed into the sediments, whereas denitrification rates varied from 0.6 to 2.9 mmol m⁻² d⁻¹. N₂O was also consumed at rates of 5.53 and 4.56 μmol m⁻² d⁻¹ under anoxia and hypoxia, but N₂O consumption rates were reduced to almost half under oxic conditions in both natural and a -enriched experiments. With the -enriched experiments, however, N₂O consumption was very high (up to 24.25 μmol m⁻² d⁻¹) under anoxic and hypoxic conditions, suggesting that high levels induce more N₂O reduction to N₂ by denitrification. N₂O production rates were only measured when oxic conditions were observed in the -enriched experiment, suggesting some role of nitrification. Thus, N cycling in the sediments seems to affect the observed , NO²⁻, and N₂O content in the bottom water and, therefore, in the entire water column due to vertical advection associated with coastal upwelling.     

Copepod assemblages in a highly dynamic equatorial estuary on the Brazilian Amazon Coast

This study describes the spatial and temporal dynamics of the copepod fauna in the estuary of the Caeté River, a highly dynamic environment characterized by a unique set of hydrological and hydrodynamic attributes. This ecosystem is part of the Amazon Coastal Zone (ACZ), which sustains one of the world's largest continuous tracts of mangrove forest. In the present study, a predominance of high‐energy conditions characterized by macrotides and strong tidal currents was observed throughout the year. Salinity (0.03 ± 0.05–40.00 ± 0.84) and temperatures (26.43 ± 0.10–30.08 ± 0.43 °C) were higher than during the rainy season at all sampling stations. The highest chl‐a concentration (3.92 ± 1.47–17.63 ± 2.60 mg·m^?3) was recorded at the most oligohaline (innermost) station during the rainy season, while no spatial or seasonal pattern was found in dissolved nutrient concentrations, except for phosphates, which exhibited the highest concentrations during the dry season. A total of 22 copepod taxa was identified, of which the most abundant were Oithona hebes, Oithona oswaldocruzi, Acartia tonsa, Paracalanus quasimodo, Euterpina acutifrons and Pseudodiaptomus marshi. Copepodites and nauplii were also recorded. Mean total copepod abundance varied from 710.73 ± 897 individuals (ind.)·m^?3 at the inner station to 236,486 ± 398,360 ind.·m^?3 near the mouth of the estuary (outermost station). The results reflected rainfall‐influenced oscillations in hydrological variables, mainly salinity, which determined shifts in the distribution of copepods and their community structure within the study area. This pattern may be typical of estuaries in the ACZ with similar hydrodynamic and hydrological attributes that are not influenced by the Amazon River plume.     

Water use patterns of mule deer (Odocoileus hemionus) and the effects of human disturbance

To aid the effectiveness of water developments, patterns of deer visiting water sources and the responses of deer to disturbance were examined. Deer visited water sources day and night, but not all deer at water sources drank. Thus, the assumption that radio-telemetry locations within arbitrary distances of water indicate drinking events may lead to overestimates of watering frequency. Human disturbance did not preclude or seriously impede use of water by deer. Deer reacted by adjusting the amount of time spent at water sources, moving away from water to return later and/or increasing the frequency with which they drank.     

Changes of electrical conductivity in the vicinity of the curie temperature of basaltic rocks — theoretical model

Summary Samples of basalts, haematites and magnetites display either temporary or permanent (magnetite) weakening of the increase of the electrical conductivity with increasing temperature in the vicinity of their Curie temperature. Using the second quantization, this paper explains the observed pattern of the electrical conductivity adequately for magnetite and approximately for the other rocks by means of a quantum theory model of ferromagnetic minerals. This theory describes only the electron component of the electrical conductivity, which is responsible for the Curie temperature effect.Dedicated to RNDr. Jan Pícha, CSc., on his 60th Birthday     

Thermal and electric conductivity of three basaltic rocks of the Bohemian Massif under high temperatures

Summary The thermal, temperature and electric conductivities of three alkaline basalts are compared for temperatures ranging from 20 to 900 °C.     

Laboratory measurements of electrical conductivity of biotites

Summary For the sake of helping to clarify the anisotropic behaviour of KTB borehole rock samples, AC (10³ Hz) and DC electrical conductivities of powdered biotites and flogopites (sheet silicates) were investigated in various atmospheres (air, argon) at temperatures of 20–1200°C.Contribution No. 106/90, Geophysical Institute, Czechosl. Acad. Sci., Prague.     

Diatom-based reconstruction of Holocene hydrological changes along the Colorado River floodplain (northern Patagonia,Argentina)

Diatom assemblages recovered from a Colorado River delta core in northern Patagonia, Argentina were analyzed in order to assess past environmental conditions. A total of 35 samples were selected from a 172-cm core extracted 37 km from the mouth (39°36′19.6″S; 62°29′26.1″W). One-hundred and thirty-eight taxa were recognized and grouped according to life forms. Two diatom zones were identified by cluster analysis. At the base of the sequence, the Diatom Zone I (DZI; 4132 ± 35 ??2919?±?27 ¹⁴C yr BP), consisted of clays, and was characterized by assemblages dominated by aerophilous and benthic taxa and chrysophyte stomatocysts, which led to inferences of a sedimentary environment corresponding to a pond experiencing dry periods. The upper section (DZII) was dominated by fine sands and silts encompassing the last ~?150 yr with abundant planktonic and tychoplanktonic diatoms. Benthic diatoms were abruptly replaced by planktonic forms in this zone indicating a shift to deeper waters. These results characterize the meandering dynamics of a deltaic system. During the Mid-Holocene, more arid periods would have favored the deactivation of meanders and the formation of riverine and oxbow wetlands. In Late-Holocene and historical times, more humid conditions and the hydrological system across the floodplain reactivated the paleochannel. Today, the dominant diatom species are brackish/freshwater fragilaroids. A non-multidimensional scaling analysis showed a lack of analogy between fossil and modern samples. The change in diatom floras in recent historical times was attributed to anthropogenic disturbances, a consequence of the regulation of the river flow. This regulation is evidenced by less discharge, morphological modifications in the floodplain and increased salinity in the last decade.     

The effect of estrogen on cadmium distribution in rainbow trout (Oncorhynchus mykiss)

The effects of injections of 17β-estradiol (E2) and Cd, on the distribution of Cd and the induction of metallothionein (MT) mRNA and vitellogenin mRNA was investigated. Bone and liver were the main organs accumulating Cd. However, E2 redirected the metal accumulation from the bone and liver to the gill, gut and muscle upon exposure to E2. Cd did not induce the hepatic MT mRNA levels in animals treated with E2. The VTG mRNA levels were also reduced following co-injection of E2 and Cd. However, the kidney responded to Cd exposure by upregulating MT mRNA even in the presence of E2 treatment. In the liver the reduced MT mRNA induction led to a redistribution of CD from MT to non-MT proteins. The toxicological significance of these alterations in Cd handling remains to be determined.