Freshwater macroinvertebrate distribution in two basins with different salinity gradients (Guadalete and Guadaira river basins,south-western Spain)

This work reports the results of one year's sampling of aquatic macroinver-brates in various streams with different salinity gradients. The study area was the headwaters of the rivers Guadaíra and Guadalete, located in the same geographical area in south-western Spain. The most interesting feature of the Guadaíra basin is the natural salinity of its waters due to the abundance of gypsum in its headwaters. Lithologically, the headwaters of the Guadalete basin flow over marls, clay, sandstone and limestone. Salinity values in most streams do not reach 1 mS cm^–1. At least at the levels of salinity found in the Guadaíra basin headwaters, the existence of a well-structured community of macroinvertebrates can be claimed. Of the groups studied, Diptera and Coleoptera showed the highest species richness, being distributed preferentially at the ends of the conductivity spectrum. Groups including taxa inhabiting waters of low salinty and taxa inhabiting waters with high salinity could be reliable indicators of salinity.     

Effect of pillar reinforcement on long-term stability of an oil shale mine

Summary Stability in Exxon's Colony Pilot Mine in the Piceance Creek Basin, Colorado has been monitored by periodic pillar stress determinations and roof to floor convergence measurements since 1971. Pillar failure has caused marginal stability in some areas of the mine. Measurements taken during the process of failure provided valuable information on thein situ pillar strength and long-term behaviour of the mine structure. Four pillars were reinforced by 32 mm (1.25 in.) diameter tensioned grouted bolts to increase long-term stability in the northern area of the mine. Stability of this area is necessary because future plans envisage its use as an exit/access and ventilation exhaust.Computer analyses were performed to help evaluate the effect of pillar reinforcement on long-term stability. Results indicate that bolting is particularly useful in stabilizing failed pillars, but its effects are significant only in the immediate area of the pillar. The projected significant decrease in deformation of two extensively failed pillars near a main entry indicates that bolting reinforcement will assist the long-term stability of the opening.     

LONG VALID TIME ENERGY PERFECT CONSERVATIVE FIDELITY SPECTRAL SCHEMES OF BAROTROPIC PRIMITIVE EQUATIONS

In accordance with a new compensation principle of discrete computations,the traditional meteo-rological global (pseudo-) spectral schemes of barotropic primitive equation (s) are transformed intoperfect energy conservative fidelity schemes,thus resolving the problems of both nonlinear computa-tional instability and incomplete energy conservation,and raising the computational efficiency of thetraditional schemes.As the numerical tests of the new schemes demonstrate,in solving the problem of energy conser-vation in operational computations,the new schemes can eliminate the (nonlinear) computational in-stability and,to some extent even the (nonlinear) computational diverging as found in the traditionalschemes,Further contrasts between new and traditional schemes also indicate that,in discrete opera-tional computations,the new scheme in the case of nondivergence is capable of prolonging the valid in-tegral time of the corresponding traditional scheme,and eliminating certain kind of systematical com-putational“climate drift”,meanwhile increasing its computational accuracy and reducing its amount ofcomputation.The working principle of this paper is also applicable to the problem concerning baroclin-ic primitive equations.     

THE ROLES OF BOUNDARY-LAYER DYNAMICS ON THE DEVELOPMENT OF MADDEN-JULIAN OSCILLATION*

In this paper,a tropical atmospheric model of relevance to shorts-term climate variations(Wang and Li 1993) is utilized for study of the development of Madden-Julian oscillation.The model contains an interactive process of boundary-layer Ekman convergence and precipitation heating.The model is solved by expanding dependent variables in terms of parabolic cylindrical functions in the meridional direction and truncating three meridional modes n=0,2,4 for equatorial symmetric solutions.The free wave solutions obtained under long-wave approximation are induced as a Kelvin wave and two Rossby waves.After considering the effect of boundary-layer dynamic process,the modified Kelvin wave becomes unstable in long-wave bands with a typical growth rate on an order of 10^-6 s^-1and an eastward phase speed of 10 m s^-1;the most unstable mode is wavenumber one.These theoretical results are consistent with the observed Madden-Julian oscillation in equatorial area.For the two modified Rossby waves,one with a smaller meridional scale(n=4) decays except for extra long-waves;the other with a larger meridional scale(n=2) grows in short-wave bands.This may be relevant to explaining the westward propagation of super cloud clusters in the Madden-Julian oscillation.The theory suggests that the boundary-layer dynamic process is an important mechanism in the development of the Madden-Julian oscillation.     

Stakeholders’ perceptions of the impacts of invasive exotic plant species in the Mediterranean region

Invasive species pose an increasing environmental problem across the globe, but to date socio-economic perspectives on this problem have been limited. In this study stakeholder perceptions of the impacts of invasive exotic plant species on the islands of Mallorca, Sardinia and Crete are examined through the use of semi-structured interviews, Likert scales and Contingent Valuation. Results showed substantial concerns about the impact of invasive exotic plant species on the islands, particularly on Mallorca where awareness of the issue has increased in recent times due to campaigns to eradicate terrestrial and aquatic invasive plants. Not all perceptions are negative and several respondents suggest that a turnover in local species is an inherent part of the sense of the place in the region. If the management of invasive exotic plant species in the Mediterranean region is to improve then there is a need to raise awareness of the impact of invasive species amongst both the general public and professional stakeholders.     

Occurrence of soil erosion after repeated experimental fires in a Mediterranean environment

In the Mediterranean area, forest fires have become a first-order environmental problem. Increased fire frequency progressively reduces ecosystem recovery periods. The fire season, usually followed by torrential rains in autumn, intensifies erosion processes and increases desertification risk. In this work, the effect of repeated experimental fires on soil response to water erosion is studied in the Permanent Field Station of La Concordia, Valencia, Spain. In nine 80 m² plots (20 m long × 4 m wide), all runoff and sediment produced were measured after each rainfall event. In 1995, two fire treatments with the addition of different biomass amounts were applied. Three plots were burned with high fire intensity, three with moderate intensity, and three were unburned to be used as control. In 2003, the plots with the fire treatments were burned again with low fire intensities. During the 8-year interval between fires, plots remained undisturbed, allowing regeneration of the vegetation–soil system. Results obtained during the first 5 months after both fire experiments show the high vulnerability of the soil to erosion after a repeated fire. For the burned plots, runoff rates increased three times more than those of 1995, and soil losses increased almost twice. The highest sediment yield (514 g m^− 2) was measured in 2003, in the plots of the moderate fire intensity treatment, which yielded only 231 g m^− 2 of sediment during the corresponding period in 1995. Runoff yield from the control plots did not show significant temporal changes, while soil losses decreased from 5 g m^− 2 in the first post-fire period to 0.7 g m^− 2 in the second one.     

Human Impact Since Medieval Times and Recent Ecological Restorationin a Mediterranean Lake: The Laguna Zoñar, Southern Spain

The multidisciplinary study of sediment cores from Laguna Zoñar (37°29′00′′ N, 4°41′22′′ W, 300 m a.s.l., Andalucía, Spain) provides a detailed record of environmental, climatic and anthropogenic changes in a Mediterranean watershed since Medieval times, and an opportunity to evaluate the lake restoration policies during the last decades. The paleohydrological reconstructions show fluctuating lake levels since the end of the Medieval Warm Period (ca. AD 1300) till the late 19th century and a more acute dry period during the late 19th century – early 20th century, after the end of the Little Ice Age. Human activities have played a significant role in Laguna Zoñar hydrological changes since the late 19th century, when the outlet was drained, and particularly in the mid-20th century (till 1982) when the spring waters feeding the lake were diverted for human use. Two main periods of increased human activities in the watershed are recorded in the sediments. The first started with the Christian conquest and colonization of the Guadalquivir River Valley (13th century) particularly after the fall of the Granada Kingdom (15th century). The second one corresponds to the late 19th century when more land was dedicated to olive cultivation. Intensification of soil erosion occurred in the mid-20th century, after the introduction of farm machinery. The lake was declared a protected area in the early 1980s, when some agricultural practices were restricted, and conservation measures implemented. As a consequence, the lake level increased, and some littoral zones were submerged. Pollen indicators reflect this limnological change during the last few decades. Geochemical indicators show a relative decrease in soil erosion, but not changes in the amount of chemical fertilizers reaching the lake. This study provides an opportunity to evaluate the relative significance of human vs. climatic factors in lake hydrology and watershed changes during historical times. Paleolimnological reconstructions should be taken into account by natural resources agencies to better define lake management policies, and to assess the results of restoration policies.     

一种时间分数阶扩散方程初边值问题的隐式有限差分格式

通过Caputo型与G runwald型的分数阶导数的转化关系以及利用G runwald型的标准数值近似公式对Caputo型分数阶导数进行离散,可构建时间分数阶扩散方程初边值问题的隐式有限差分格式。此差分格式是无条件稳定和无条件收敛的。     

Neotectonic aspects of the northern margin of the Adana-Cilicia submarine basin, NE Mediterranean

The sedimentary basins that dominate the north-eastern Mediterranean (Adana-Cilicia basins in the west and Iskenderun basin in the east) are located on the flanks of a partly submerged positive structure (a part of the Africa-Eurasia convergence zone) along which strike-slip faults are evident. This study summarizes the findings of two seismic surveys carried out in the Alanya-Mersin offshore region. Some 850 km of geophysical survey lines were compiled on these cruises. Based on the results determined from these surveys, the north and central part of Adana-Cilicia basin can be subdivided into eastern, central and western structural sub-basins separated by the Ecemiş fault complex in the east and the Anamur-Kormakiti structural high in the west at the same time. Results of this study also indicate that Ecemiş and Anamur-Kormakiti faults are active. Late Miocene regional compression was responsible for the compartmentation of this complex into the present arrangement and has initiated the rotational regime which has governed subsequent tectonic developments, notably the extensional behaviour of the NE-SW trending Ecemiş and Anamur-Kormakiti faults and the transpressive behaviour of the NNE-SSW trending border fault complex.