Impacts of land-use and land-cover change on stream hydrochemistry in the Cerrado and Amazon biomes.

Studies on the impacts of land-use and land-cover change on stream hydrochemistry in active deforestation zones of the Amazon agricultural frontier are limited and have often used low-temporal-resolution datasets. Moreover, these impacts are not concurrently assessed in well-established agricultural areas and new deforestations hotspots. We aimed to identify these impacts using an experimental setup to collect high-temporal-resolution hydrological and hydrochemical data in two pairs of low-order streams in catchments under contrasting land use and land cover (native vegetation vs. pasture) in the Amazon and Cerrado biomes. Our results indicate that the conversion of natural landscapes to pastures increases carbon and nutrient fluxes via streamflow in both biomes. These changes were the greatest in total inorganic carbon in the Amazon and in potassium in the Cerrado, representing a 5.0- and 5.5-fold increase in the fluxes of each biome, respectively. We found that stormflow, which is often neglected in studies on stream hydrochemistry in the tropics, plays a substantial role in the carbon and nutrient fluxes, especially in the Amazon biome, as its contributions to hydrochemical fluxes are mostly greater than the volumetric contribution to the total streamflow. These findings demonstrate that assessments of the impacts of deforestation in the Amazon and Cerrado biomes should also take into account rapid hydrological pathways; however, this can only be achieved through collection of high-temporal-resolution data.

Landscape cultivation alters δ³°Si signature in terrestrial ecosystems.

Despite increasing recognition of the relevance of biological cycling for Si cycling in ecosystems and for Si export from soils to fluvial systems, effects of human cultivation on the Si cycle are still relatively understudied. Here we examined stable Si isotope (δ(30)Si) signatures in soil water samples across a temperate land use gradient. We show that - independent of geological and climatological variation - there is a depletion in light isotopes in soil water of intensive croplands and managed grasslands relative to native forests. Furthermore, our data suggest a divergence in δ(30)Si signatures along the land use change gradient, highlighting the imprint of vegetation cover, human cultivation and intensity of disturbance on δ(30)Si patterns, on top of more conventionally acknowledged drivers (i.e. mineralogy and climate).

A clinical pilot study of the dimensional accuracy of double-arch and complete-arch impressions.

STATEMENT OF PROBLEM: It has been suggested that articulated casts fabricated with the double-arch impression technique may have superior occlusal accuracy than those fabricated with a single complete-arch impression. However, lack of tray rigidity may lead to flexure of the impression/tray complex, resulting in inaccurate dies in the bucco-lingual dimension. PURPOSE: This clinical pilot study compared the dimensions of dies fabricated with 3 types of double-arch impressions to dies fabricated with the conventional complete-arch, custom tray method. MATERIAL AND METHODS: Thirty-five addition silicone impressions were made of cast metal copings cemented onto natural teeth prepared as complete-crown abutments. Four combinations of tray types and impression material viscosity were used: (1) complete-arch, custom acrylic trays loaded with heavy-bodied material; (2) double-arch, disposable plastic trays loaded with heavy-bodied material; (3) double-arch, disposable plastic trays loaded with putty material; and (4) double-arch, reusable brass metal trays loaded with heavy-bodied material. Immediately prior to tray insertion, light-bodied impression material was syringed over all copings as a wash. The 4 copings were fabricated from cast gold and simulated metal-ceramic complete-crown thimbles with polished collars and had "projections" on the occlusal surfaces. The impressions were poured in type IV die-stone. Bucco-lingual and inter-abutment dimensions were measured. The differences between the stone dimensions and cast metal control dimensions were calculated and converted to percent dimensional change. The data were analyzed with 1-way analysis of variance, Student t tests, and Mann-Whitney tests (P<.05). RESULTS: The plastic double-arch tray loaded with heavy-viscosity addition silicone and a low-viscosity wash produced the least accurate combination inter- and intra-abutment dimensions. For this protocol, 1.17% mean dimensional change was recorded. This result was significantly different than that obtained for the other 3 impression methods tested. No significant differences were found between the complete-arch method and protocols in which putty was loaded in a plastic or metal tray. CONCLUSION: Within the limitations of this pilot study, the more rigid tray/impression material combinations more accurately replicated stone dies.