Simulating vegetation cover dynamics with regards to long-term climatic variations in sub-arctic landscapes

Iceland is facing severe land degradation in many parts of the country. This study aims to increase the understanding of the complex interactions and interconnectivity between the critical factors that help maintain the land degradation processes in sub-arctic environments. A holistic approach in the form of a causal loop diagram (CLD) is applied for diagnosing the influencing factors. To further study the relationship between vegetation cover and its degradation, a dynamic model that uses a long-term temperature data as the main indicator function is constructed to simulate potential vegetation cover during the Holocene. The results depict an oscillating vegetation cover. Gradual degradation in potential vegetation cover begins ca. 3000 BP and accelerates greatly after ca. 2500 BP. From the time of the Norse settlement in the latter halve of the 9th century to present time, the simulated vegetation cover retreats ca. 25% in relation to climatic cooling.     

Residual impact of biochar on cadmium uptake by rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) grown in Cd-contaminated soil

Cadmium (Cd) is the family member of toxic heavy metals, and its accumulation in food crops has become a global environmental constraint. Biochar potentially minimizes the metal contents in plants, but limited work has been reported on its residual effect on subsequent crops. The residual effect of various biochar levels (0, 1.5, 3.0, and 5.0% w/w) on Cd accumulation in rice has been investigated in this study. Biochar treatments enhanced the rice growth, photosynthesis, and antioxidant enzymes, whereas diminished the Cd contents and oxidative stress in rice. Cadmium concentration in shoots decreased by 24.4, 36.6, and 57.5% in 1.5, 3.0, and 5.0% biochar treatments over the control. Biochar supply enhanced the soil pH and electrical conductivity, whereas diminished the soil bioavailable Cd. Overall, the results depicted a significant residual impact of rice straw biochar on rice growth attributes and Cd uptake. However, studies are still needed to explore the long-term sustainability of biochars prepared from different feedstocks on bioavailability of toxic metals in soils and uptake by food crops under field conditions.     

Relationship between Akhüyük fissure ridge travertines and active tectonics: their neotecteonic significance (Ereğli-Konya,Central Anatolia)

Arabian Journal of Geosciences - The Akhüyük travertine mass crops out approximately 10&nbsp;km to the north of Ereğli (Konya, Central Anatolia). Its morphology and relationship...     

Activity levels of 210Po and 210Pb in some fish species of the Izmir Bay (Aegean Sea)

We investigated the spatial scales of variation of macrofauna in intertidal flats subjected to different levels of contamination from urban effluents in two areas sampled in the Paranaguá Estuarine Complex. The scales considered were: Conditions; Tidal flats and Plots. Although the numerically dominant taxa showed the greatest variability at a scale of Tidal flats, the variability at the Condition scale was also significant. Tubificinae sp. 1, Laeonereis culveri and Heteromastus sp. were the most abundant organisms in the Contaminated area, while Heleobia australis was most abundant in the Non-contaminated area. Our results, contrary to those frequently observed in the literature, showed that the variability was significant at the scale of hundreds of metres (Tidal flats). At this scale, the intrinsic characteristics of each tidal flat are more important in determining macrofaunal distribution, while the effects of the urban sewage contamination represent the primary forces acting at a greater spatial scale.     

Acetylcholinesterase,glutathione and hepatosomatic index as potential biomarkers of sewage pollution and depuration in fish

The current study was designed to validate the biomarkers of sewage pollution in Mozambique Tilapia (Tilapia mossambica, Peters) reared in sewage treatment plant (STP) effluent in Ras Al Khaimah, United Arab Emerates, before and following depuration/detoxification. Cellular biomarkers, cholinesterase activity using acetylcholine as a substrate (acetylcholinesterase AChE) and reduced glutathione (GSH) and hepatosomatic index (HSI) were investigated in fresh water fish, Tilapia, raised in a fish farm (Group I/Clean, as Control), treated sewage water/TSW (Group II/Sewage) and thereafter exposed to fresh water in an aquarium for 6 weeks (Group III/Depurated) for depuration. The results showed significantly lower levels of AChE activities in liver (26% p < 0.01) and muscle (30% p < 0.01) of the fish reared in the STP water (Group II/Sewage) as compared to those recorded in the fish from fish farm (Group I/Clean). The depressed AChE level was fully restored in the muscle but partially in the liver after depuration (Group III/Depurated). In contrast, GSH levels were significantly raised in both liver (1.3-fold p < 0.01) and muscle (4-fold) of Group II fish as compared to Group I (control) fish raised in fish farm and following depuration in fresh water (Group III/Depurated) elevated GSH level in liver restored to control values, while remained unchanged in muscle. The average hepatosomatic index (HSI = weight of liver × 100/total fish weight), an indicator of hepatomegaly, in the Group II fish reared in TSW was also significantly higher than that in the reference Group I fish, but decreased to control level in Group III fish following depuration. This study suggests the importance of cellular biomarkers, AChE, GSH and hepatosomatic index in monitoring the impact of sewage water pollution on fish caused by a complex mixture of chemico-biological contaminants and its mitigation following depuration, an effective mean of fish detoxification.     

Midbroken reinforced concrete shear frames due to earthquakes. A hysteretic model to quantify damage at the storey level

A nonlinear hysteretic model for the response and local damage analyses of reinforced concrete shear frames subject to earthquake excitation is proposed, and, the model is applied to analyse midbroken reinforced concrete (RC) structures due to earthquake loads. Each storey of the shear frame is represented by a Clough and Johnston hysteretic oscillator with degrading elastic fraction of the restoring force. The local damage is numerically quantified in the domain [0,1] using the maximum softening damage indicators which are defined in closed form based on the variation of the eigenfrequency of the local oscillators due to the local stiffness and strength deterioration. The proposed method of response and damage analyses is illustrated using a sample 5 storey shear frame with a weak third storey in stiffness and/or strength subject to sinusoidal and simulated earthquake excitations for which the horizontal component of the ground motion is modeled as a stationary Gaussian stochastic process with Kanai-Tajimi spectrum, multiplied by an envelope function.     

Contents to Volume 5

Volume Contents

Contents to Volume 5     

Rapid releases of metal salts and nutrients following the deposition of volcanic ash into aqueous environments

Deposition of volcanic ash into aqueous environments leads to dissolution of adsorbed metal salts and aerosols, increasing the bioavailability of key nutrients. Volcanogenic fertilization events could increase marine primary productivity, leading to a drawdown of atmospheric CO₂. Here we conduct flow-through experiments on unhydrated volcanic ash samples from a variety of locations and sources, measuring the concentrations and fluxes of elements into de-ionized water and two contrasting ocean surface waters. Comparisons of element fluxes show that dissolution of adsorbed surface salts and aerosols dominates over glass dissolution, even in sustained low pH conditions. These surface ash-leachates appear unstable, decaying in situ even if kept unhydrated. Volcanic ash from recent eruptions is shown to have a large fertilization potential in both fresh and saline water. Fluorine concentrations are integral to bulk dissolution rates and samples with high F concentrations display elevated fluxes of some nutrients, particularly Fe, Si, and P. Bio-limiting micronutrients are released in large quantities, suggesting that subsequent biological growth will be limited by macronutrient availability. Importantly, acidification of surface waters and high fluxes of toxic elements highlights the potential of volcanic ash-leachates to poison aqueous environments. In particular, large pH changes can cause undersaturation of CaCO₃ polymorphs, damaging populations of calcifying organisms. Deposition of volcanic ash can both fertilize and/or poison aqueous environments, causing significant changes to surface water chemistry and biogeochemical cycles.     

Soil erosion determinations by using 137Cs technique in the agricultural regions of Gediz Basin, Western Turkey

Gediz Basin is one of the regions where intense agricultural activities take place in Western Turkey. Erosion and soil degradation have long been causing serious problems to cultivated fields in the basin. This work describes the application of two different ¹³⁷Cs models for estimating soil erosion rates in cultivated sites of the region. Soil samples were collected from five distinct cultivated regions subject to soil erosion. The variations of ¹³⁷Cs concentrations with depth in soil profiles were investigated. Soil loss rates were calculated from ¹³⁷Cs inventories of the samples using both proportional model (PM) and simplified mass balance model (SMBM). When PM was used, erosion and deposition rates varied from −15 to −28 t ha⁻¹ year⁻¹ and from +5 to +41 t ha⁻¹ year⁻¹, respectively; they varied from −16 to −33 t ha⁻¹ year⁻¹ and from +5 to +55 t ha⁻¹ year⁻¹ with SMBM. A good agreement was observed between the results of two models up to 30 t ha⁻¹ year⁻¹ soil loss and gain in the study area. Ulukent, a small representative agricultural field, was selected to compare the present data of ¹³⁷Cs techniques with the results obtained by universal soil loss equation (USLE) applied in the area before.