Geochemical fingerprinting and magnetic susceptibility to unravel the heterogeneous composition of urban soils.

The typically high heterogeneity of urban soil properties challenges their characterization and interpretation. The objective of this study was to investigate if proximally sensed volume-specific magnetic susceptibility and/or geochemical soil properties can uncover differences in anthropogenic, lithogenic and pedological contributions in, and between, urban soils. We also tested if volume-specific magnetic susceptibility can predict heavy metal enrichment. Data on 29 soil properties of 103 soil horizons from 16 soils from Ghent, Belgium, were analyzed by factor analysis. A correlation analysis, and in-depth analysis of five contrasting urban soils supplemented insights gained from the factor analysis. The factor analysis extracted four factors: 29.2 % of the soil property variability was attributed to fossil fuel combustion and industrial processes, with high (>0.80) loadings for S, organic carbon, magnetic susceptibility, and Zn. Furthermore, 26.0 % of the variability was linked to parent material differences, with high loadings (>0.80) for K, Rb and Ti. In absence of geogenic carbonates, increased soil alkalinity due to anthropogenic input of CaCO3 explained 17.0 % of the variability. Lastly, 4.7 % of the variability resulted from variable Zr contents by local geology. Elemental analysis by XRF, possibly combined with magnetic susceptibility measurements, helped to explain lateral or vertical differences related to (1) the nature of anthropogenic influence, for instance burning (e.g., by the S and Zn content) or the incorporation of building rubble (e.g., by the Ca content); (2) the particle size distribution (e.g., by the K, Rb or Ti content); (3) lithology (e.g., by the Zr content); or (4) pedology, such as organic matter build-up (e.g., by the S content) or leaching of alkalis (e.g., by the Ca content). Even though artifacts and soil translocation were common in the studied soils, volume-specific soil magnetic susceptibility measured on fine earth predicted the total heavy metal pollution loading index well (Pearson correlation = 0.85).

Effectiveness of terracing techniques for controlling soil erosion by water in Rwanda.

Despite long-standing efforts in terracing, limited field-based evidence of its effectiveness as implemented within rural farming systems of humid tropical regions, such as Rwanda, is available. This study aimed to reveal regional differences in effectiveness of two widely used terracing techniques. Traditional slope farming (NP) was compared to bench (BT) and farmers' based progressive terraces (PT) in terms of runoff, soil losses, and topsoil fertility in two contrasting agro-ecological zones, the Eastern Plateau (Murehe) and Buberuka Highlands (Tangata). During four consecutive rainy seasons, event-based data were collected using erosion plots (5 m width x 22.2 m length). Effectiveness indices of both terracing systems, as well as (R)USLE P-factor values, were calculated. The annual average soil losses under NP ranged from 4.71 ± 5.02 ton ha-1 to 46.01 ± 7.28 ton ha-1 in Murehe (14% slope gradient) and Tangata (43% slope gradient), respectively. Bench terracing clearly outperformed the farmer-based progressive terrace at both locations, leading to negligible soil losses. In terms of runoff reduction, an effectiveness of 70 and 85% respectively, was observed at Murehe and Tangata. The effectiveness of PT reached 52% for runoff control and 93% for soil loss control at Tangata, thereby confirming its huge potential as erosion control measure, even in mountainous areas. In the hilly landscape of Murehe, the runoff generated by PT - in some years - can exceed that under traditional farming, while the measure reduced soil losses by half on average. Associated USLE P-factors varied between seasons with an annual average values of 0.001-0.02 for BT, and 0.07 to 0.55 for PT at Tangata and Murehe, respectively. These variations in performance by site and terracing system also resulted in differences in topsoil chemical fertility, with BT generally outperforming both PT and NP at Tangata. At Murehe, PT showed a significantly lower chemical fertility compared to BT and NP. Poor quality risers explained the overall lower performance of PT at Murehe. The study thus confirmed the huge potential of (bench) terraces to sustainably reduce soil erosion rates when established within an integrated approach, paying attention to correct installation and fertility-supporting agronomic practices. More attention should be given to riser installation (e.g. distance) and maintenance of PT. Adoption of these erosion control measures can be recommended to similar agro-ecological zones for sustainably protecting the lands while mitigating or adapting the effects of climate change.

Estimation of aggregate stability of some soils in the loam belt of Belgium using mid-infrared spectroscopy.

Rapid assessment of soil aggregate stability (AS) is vital for a better understanding of the processes of soil aggregate breakdown, which is necessary for effective soil erosion control planning. This study explored the possibility of quantifying the mean weight diameter (MWD) of soil aggregates after applying the three disruptive treatments of fast wetting (FW), slow wetting (SW) and mechanical breakdown (MB), representing the dominant aggregate breakdown mechanisms, using a handheld mid-infrared (MIR) spectrophotometer on soils of the Belgian loam belt. Partial least squares regression (PLSR) was used to build calibration models for the three treatment methods, using a calibration set accounting for 70% (75% in the case of MB) of the samples, which were validated by using a validation set of 30% (25% in the case of MB) of the total samples. Results showed very good prediction accuracies with coefficient of determination (R2) values of 0.73, 0.85 and 0.79, root mean square error of prediction (RMSEP) values of 0.29, 0.46 and 0.26 mm, ratio of performance to interquartile range (RPIQ) values of 2.16, 4.98 and 3.64 and residual prediction deviation (RPD) values of 1.99, 2.60, and 2.22, for FW-MWD, SW-MWD, and MB-MWD, respectively. The best prediction was obtained for SW-MWD. The results of this study suggest that, for soils where soil organic carbon is a relevant indicator of aggregate strength, the three AS indices can be estimated to a high accuracy with spectra information in the MIR region of the electromagnetic spectrum.

Hot wings: thermal impacts of wing coloration on surface temperature during bird flight.

Recent studies on bird flight propose that hotter wing surfaces reduce skin friction drag, thereby improving flight efficiency (lift-to-drag ratio). Darker wings may in turn heat up faster under solar radiation than lighter wings. We used three methods to test the impact of colour on wing surface temperature. First, we modelled surface temperature based on reflectance measurements. Second, we used thermal imaging on live ospreys (Pandion haliaetus) to examine surface temperature changes with increasing solar irradiance. Third, we experimentally heated differently coloured wings in a wind tunnel and measured wing surface temperature at realistic flight speeds. Even under simulated flight conditions, darker wings consistently became hotter than pale wings. In white wings with black tips, the temperature differential produced convective currents towards the darker wing tips that could lead to an increase in lift. Additionally, a temperature differential between wing-spanning warm muscles and colder flight feathers could delay the flow separation above the wing, increasing flight efficiency. Together, these results suggest that wing coloration and muscle temperature both play important roles in modulating wing surface temperature and therefore potentially flight efficiency.

The TRAC-PS dual radius total knee arthroplasty : Disappointing medium and long terms results.

The TRAC prosthesis is a dual radius, mobile bearing, posterior stabilized prosthesis, to increase stability by optimizing contact area and control wear using a mobile polyethylene. Between February 1995 and January 2000, a single surgeon performed a continuous series of 85 TRAC-PS TKAs in 85 patients at the University Hospital Brussels. A retrospective review on patient charts was performed. Patients available were scored clinically using the Knee Society Score, WOMAC osteoarthritis index, SF 36 and a Visual Analogue Scale for pain. 43 patients had died at time of evaluation, three were unavailable for examination due to bad general health and five were lost to follow up. The remaining 35 patients were examined with a mean follow-up of 13 years. The mean age of the patients at follow up was 83 years. The mean WOMAC score was 78,4(SD 17,9). The mean Knee Society Score was 86.8(SD 8,4) clinical and 42,6(SD 28) functional. The mean range of flexion was 105°. The mean SF-36 score was 59,8(SD 15,4). The VAS for pain was 6(SD 9). With revision (8 cases) as endpoint, survival rate of the prosthesis was estimated to be 92% at 13 years. Twenty-three Serious Adverse Events (28%) in 17 patients, related to the prosthesis were registered in this patient group. Long term results of this prosthesis were satisfying but a large number of serious adverse events led to abandonment of the TRAC-prosthesis.

Spatial Patterns of Heavy Metal Contamination by Urbanization.

Spatial analysis of heavy metals (HMs) is an important step toward developing predictive models of urban HM contamination. This study assessed the spatial distribution of the enrichment of eight HMs (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in the city of Ghent, Belgium. A database with soil HM concentrations measured at 2194 point observations was collected from the Public Waste Agency of Flanders. The degree of anthropogenic HM enrichment was quantified using an urban pollution index (PI). Enrichment of HMs showed high variations throughout the study area. Observed concentrations of As, Cd, Cr, and Hg did not exceed expected background values for the majority of the sampling locations (PI ≤ 1 for 76% [As], 64% [Cd], 50% [Cr], and 74% [Hg] of sampling points). Accordingly, predicted PI values of these HMs in Ghent were on average <2. On the other hand, observed median PIs for Cu, Ni, Pb, and Zn surpassed expected background values (PI >1) in 66, 76, 68, and 66% of the cases. The predicted PI means for the entire study area were 3.46 (Cu), 2.06 (Ni), 3.26 (Pb), and 3.28 (Zn). Comparison between various land use types and times since development indicated that HM enrichment was generally highest in urban land uses built up before 1933. Results, however, suggested that spatial patterns of HM contamination are difficult to predict in cities with a long history of industrialization without knowledge on the spatial distribution of (potentially) contaminating historical industrial activities.