Drought in Northeast Brazil—past,present, and future

This study provides an overview of the drought situation in Northeast Brazil for the past, present, and future. Droughts affect more people than any other natural hazard owing to their large scale and long-lasting nature. They are recurrent in the region and while some measures have been taken by the governments to mitigate their impacts, there is still a perception that residents, mainly in rural areas, are not yet adapted to these hazards. The drought affecting the Northeast from 2012 to 2015, however, has had an intensity and impact not seen in several decades and has already destroyed large swaths of cropland, affecting hundreds of cities and towns across the region, and leaving ranchers struggling to feed and water cattle. Future climate projections for the area show large temperature increases and rainfall reductions, which, together with a tendency for longer periods with consecutive dry days, suggest the occurrence of more frequent/intense dry spells and droughts and a tendency toward aridification in the region. All these conditions lead to an increase in evaporation from reservoirs and lakes, affecting irrigation and agriculture as well as key water uses including hydropower and industry, and thus, the welfare of the residents. Integrating drought monitoring and seasonal forecasting provides efficient means of assessing impacts of climate variability and change, identifying vulnerabilities, and allowing for better adaptation measures not only for medium- and long-term climate change but also for extremes of the interannual climate variability, particularly droughts.

     

Meteoric diagenesis during sea-level lowstands: Evidence from modern hydrochemical studies on northern Guam

Hydrochemical data for meteoric waters of the uplifted carbonate platform of northern Guam show that, contrary to recent models of lowstand diagenesis, phreatic dissolution is active beneath a 60–180 m thick vadose zone. Overland flow during high intensity rainfall events is focussed into surface detention ponds, which drain very rapidly via the epikarst and vertical fissures to the freshwater lens. We estimate that these waters contribute 13% of dissolved calcium in samples from pumping wells but may also deliver aggressive and/or organic-rich waters to the lens. Fast-flow vadose waters mix with lens-top waters to form fresher cap that discharges rapidly coastwards via cavernous porosity. Slower vadose percolation, sampled as cave drips, equilibrates with bedrock within the upper 30 m of the vadose zone, accounting for some 46% of dissolved calcium in the lens waters. The remaining 41% calcium is generated by net dissolution within the lens.     

Micrometeorological study of an urban valley

Winds, temperatures, and carbon monoxide concentrations were measured in a cross-section of the North Saskatchewan River Valley in central Edmonton on a clear October evening with cross-valley winds. The evolution of a complex asymmetrical valley inversion with vertical temperature gradients up to 12C (100 m)^–1 on the north-facing slope and 6C (100 m)^–1 on the south-facing slope is described. The inversion is accompanied by downslope winds of about 0.4 m s^–1 and a reversal from upvalley to downvalley winds. Carbon monoxide concentrations on the south-facing slope exhibit a well-defined evening maximum and an immediate response to the reversal from upslope to downslope winds.     

Do spectrally inferred determinations of chlorophyll <Emphasis Type="Italic">a</Emphasis> reflect trends in lake trophic status?

Visible reflectance spectroscopy (VRS) has been used to reconstruct lake sediment chlorophyll a concentrations. Despite good concordance between inferred and measured chlorophyll a values, questions remain as to whether this spectral technique is tracking past changes in aquatic primary production, or simply recording a diagenetic signal. In this study, we critically evaluate how well VRS chlorophyll a determinations track past trends in aquatic primary production using sediment cores from several lake systems with well-known trophic histories. Our study sites include Arctic, boreal and prairie lakes that encompass a gradient of trophic states. In general, our spectrally inferred chlorophyll a values tracked past trends in lake trophic status consistent with historical measurements of production, or as inferred by independent proxies of primary production. We conclude that VRS chlorophyll a inferences indeed track histories of lake production trends and that this method is widely applicable as a rapid, inexpensive and non-destructive alternative to wet-chemical analyses of sediment chlorophyll a concentrations.     

Adaptations of microphytobenthos assemblages to sediment type and tidal position

Tagus intertidal microphytobenthos (MPB) assemblages were characterized over a wide range of sediment type and tidal height and the possible effects of these variables on MPB spatial distribution and photo-adaptation mechanisms were investigated. Two transects with six different sediment type and different tidal height sites were sampled once every two months from 2002 to 2004. Upper shore and sandy sites showed higher chlorophyll a (chl a) content, with sandy sediments showing a biomass peak in late winter–early spring, and muddy sites showing no obvious seasonal pattern. Stepwise multiple linear regressions showed that only SiO₂, tidal height and sediment particle size <63 μm were significant variables (p<0.05), explaining 50% of MPB biomass spatial–temporal variability. However, when data were separated by transect, only tidal height remained significant at both transects. Sandier sediments exhibited higher zeaxanthin/chl a and lower fucoxanthin/chl a ratios characteristic of a mixed cyanobacteria/diatom assemblages, showing an alternate seasonality with cyanobacteria increasing in summer and diatoms dominating in spring. Diatom biofilms showed contrasting features depending on the sediment type. Epipsammic diatoms were small with an average length of around 10 μm, while epipelic diatoms showed a wider size range with size distribution peaks at 10–15 μm, 25–35 μm and >60 μm. Epipelic biofilms showed evidence of being low light-acclimated (high fucoxanthin/chl a) and of photo-regulating by vertical migration movements (presence of endogenous vertical rhythms and lower diatoxanthin/diadinoxanthin). Epipsammic biofilms showed higher diatoxanthin/diadinoxanthin ratios and no vertical migration rhythms. Thus, the two diatom biofilm types had distinct strategies to photo-regulate: epipelic diatoms using vertical migration to position themselves at the sediment depth of optimum light conditions, and epipsammic diatoms using the xanthophyll cycle to photo-regulate. Further studies comparing epipsammic and epipelic assemblages are necessary to better understand MPB photo-regulation mechanisms.     

苏格兰阿伯丁城市土壤的微生物特性研究

在重金属的胁迫下,阿伯丁城市土壤中微生物特征发生了显著的变化,与农村土相比,微生物基底呼吸作用明显增强,但微生物生物量却显著降低,微生物生理参数Ｃｍｉｎ／Ｃｏｒｇ、ｑＣＯ２值明显升高,Ｂｉｏｌｏｇ数据显示城市土壤对能源碳的消耗量和速度显著升高,而且对能源碳的利用方式发生了改变,但利用效率却明显降低,反映出微生物特性可作为城市土壤环境质量变异的有效指标。     

Sustainable development, sustainable decisions and the precautionary principle

One of the key foundations of sustainable development is the precautionary principle, a concept that has given rise to a considerable amount of controversy. For some, it is a barrier to technological progress and development, for others a means of preventing potentially harmful applications of science. What does this principle actually mean? What is its contribution to sustainable development in general and to decision-making in response to natural hazards in particular? How should it be applied? This paper will consider whether an examination of the relationship between science and law can assist in answering questions such as these, and thus provide some greater clarity about this important principle.     

Extent of the late-wisconsin glaciation in northwest Greenland and northern Ellesmere island: A review of the glaciological and geological evidence

In the Camp Century core, the difference in oxygen isotope ratio between Wisconsin and Holocene ice seems too large to be purely a climatic effect. A more likely interpretation is that the Wisconsin ice originated at an elevation of at least 500 m above the present station. Total gas content measurements on the core suggest that the elevation difference was about 1300 m. These results are inconsistent with the present ice flow pattern. Three hypotheses are considered: (1) The Wisconsin ice originated near the crest of a high ridge connecting the Greenland ice sheet with an ice sheet on Ellesmere Island. (2) The Wisconsin flow pattern was similar to the present one but ice was much thicker and the ice margin considerably in advance of its present position. (3) The Wisconsin ice originated near the main Greenland ice divide whereas the Holocene ice originates within 50 km of the station. Glacial-geological data are sparse but do not appear to support the first hypothesis, while the uplift data have been interpreted in two widely different ways. The second hypothesis might explain the oxygen isotope values but not the gas content measurements. The third hypothesis is thus considered the most likely one. Differences between Wisconsin and Holocene flow patterns might result from changes in positions of the ice margins as a consequence of lowered sea level in the Wisconsin.     

The Late Quaternary sediment successions of Llangorse Lake,south Wales

The last British-Irish Ice Sheet (BIIS) created a landscape with many sedimentary basins that preserve archives of paleoenvironmental and paleoclimatic change during the Last Glacial-Interglacial Transition (LGIT; ~ 18-8 ka BP). The typical lithostratigraphic succession of these archives is composed of minerogenic/allogenic sediments formed during cold climatic conditions and organic-rich/authigenic sediments during warmer climates. This paper presents a multi-core lithostratigraphy compiled from the extant lake and surrounding basin at Llangorse Lake, south Wales, a basin lying within the southernmost limits of the last BIIS. This lake contains one of the longest continuous terrestrial sediment successions in the UK. Uncertainty previously existed concerning the presence and distribution of sediments at the site related to the Windermere Interstadial (~ 14.7 to ~ 12.9 ka BP) and Loch Lomond Stadial (~ 12.9 to 11.7 ka BP). A new borehole survey demonstrates that LGIT-age sediments are present at the site with nekron mud (gyttja), corresponding to the Lateglacial Interstadial, deposited in the deeper part of the lake waters and that these deposits are equivalent in age to marl deposits found at shallower depths at the margins of the basin. These deposits are associated with warmer conditions experienced during the Windermere Interstadial and Holocene, whilst minerogenic-rich sediments were deposited during the colder climatic conditions of the Dimlington Stadial and the Loch Lomond Stadial with rangefinder radiocarbon dates confirming this attribution. A model of lake level changes shows that drainage of the Dimlington Stadial glacial lake caused the largest fall, but there was also a further, smaller lake level fall at the end of the Windermere Interstadial and/or the start of the Loch Lomond Stadial, before the level rose in the early Holocene. The lithostratigraphic results presented here form the framework for further paleoenvironmental and paleoclimatic research at Llangorse Lake.