Itzhak Katra

Richness and Diversity in Dust Stormborne Biomes at the Southeast Mediterranean

Dust storms include particulate matter that is transported over land and sea with biota that could impact downwind ecosystems. In addition to the physico-chemical compositions, organismal diversities of dust from two storm events in southern Israel, December 2012 (Ev12) and January 2013 (Ev13), were determined by pyro-sequencing using primers universal to 16S and 18S rRNA genes and compared. The bio-assemblages in the collected dust samples were affiliated with scores of different taxa. Distinct patterns of richness and diversity of the two events were influenced by the origins of the air masses: Ev13 was rich with reads affiliated to Betaproteobacteria and Embryophyta, consistent with a European origin. Ev12, originated in north-Africa, contained significantly more of the Actinobacteria and fungi, without conifers. The abundance of bacterial and eukaryotic reads demonstrates dissemination of biological material in dust that may impose health hazards of pathogens and allergens, and influence vegetation migration throughout the world.

Contribution of dust storms to PM10 levels in an urban arid environment

Quantitative information on the contribution of dust storms to atmospheric PM10 (particulate matter with an aerodynamic diameter ≤10 µm) levels is still lacking, especially in urban environments with close proximity to dust sources. The main objective of this study was to quantify the contribution of dust storms to PM10 concentrations in a desert urban center, the city of Beer-Sheva, Negev, Israel, during the period of 2001–2012. Toward this end, a background value based on the “dust-free” season was used as a threshold value to identify potentially “dust days.” Subsequently, the net contribution of dust storms to PM10 was assessed. During the study period, daily PM10 concentrations ranged from 6 to over 2000 µg/m3. In each year, over 10% of the daily concentrations exceeded the calculated threshold (BVt) of 71 µg/m3. An average daily net contribution of dust to PM10 of 122 µg/m3 was calculated for the entire study period based on this background value. Furthermore, a dust storm intensity parameter (Ai) was used to analyze several storms with very high PM10 contributions (hourly averages of 1000–5197 μg/m3). This analysis revealed that the strongest storms occurred mainly in the last 3 yr of the study. Finally, these findings indicate that this arid urban environment experiences high PM10 levels whose origin lies in both local and regional dust events. Implications:The findings indicate that over time, the urban arid environment experiences high PM10 levels whose origin lies in local and regional dust events. It was noticed that the strongest storms have occurred mainly in the last 3 yr. It is believed that environmental changes such as global warming and desertification may lead to an increased air pollution and risk exposure to human health.

Discovery of fairy circles in Australia supports self-organization theory

Significance Pattern-formation theory predicts that vegetation gap patterns, such as the fairy circles of Namibia, emerge through the action of pattern-forming biomass–water feedbacks and that such patterns should be found elsewhere in water-limited systems around the world. We report here the exciting discovery of fairy-circle patterns in the remote outback of Australia. Using fieldwork, remote sensing, spatial pattern analysis, mathematical modeling, and pattern-formation theory we show that the Australian gap patterns share with their Namibian counterparts the same characteristics but are driven by a different biomass–water feedback. These observations are in line with a central universality principle of pattern-formation theory and support the applicability of this theory to wider contexts of spatial self-organization in ecology. Vegetation gap patterns in arid grasslands, such as the “fairy circles” of Namibia, are one of nature’s greatest mysteries and subject to a lively debate on their origin. They are characterized by small-scale hexagonal ordering of circular bare-soil gaps that persists uniformly in the landscape scale to form a homogeneous distribution. Pattern-formation theory predicts that such highly ordered gap patterns should be found also in other water-limited systems across the globe, even if the mechanisms of their formation are different. Here we report that so far unknown fairy circles with the same spatial structure exist 10,000 km away from Namibia in the remote outback of Australia. Combining fieldwork, remote sensing, spatial pattern analysis, and process-based mathematical modeling, we demonstrate that these patterns emerge by self-organization, with no correlation with termite activity; the driving mechanism is a positive biomass–water feedback associated with water runoff and biomass-dependent infiltration rates. The remarkable match between the patterns of Australian and Namibian fairy circles and model results indicate that both patterns emerge from a nonuniform stationary instability, supporting a central universality principle of pattern-formation theory. Applied to the context of dryland vegetation, this principle predicts that different systems that go through the same instability type will show similar vegetation patterns even if the feedback mechanisms and resulting soil–water distributions are different, as we indeed found by comparing the Australian and the Namibian fairy-circle ecosystems. These results suggest that biomass–water feedbacks and resultant vegetation gap patterns are likely more common in remote drylands than is currently known.

Transverse instability of megaripples

As a result of their inherent differences in stability, sand ripples and megaripples exhibit variations in terms of their wavelengths and grain-size distributions (unimodal for sand ripples and bimodal for megaripples). While sand ripples form almost straight lines, megaripples have greater sinuosity due to their transverse instability, a property that causes small megaripple undulations to grow with time. The origin of the instability is due to variations in megaripple height, variations that do not diminish over time, and due to the inverse dependence of ripple drift velocity on the height. Thus, the taller regions of ripples will move more slowly than the adjacent, shorter portions, an outcome that promotes further perturbation growth. We show an example based on fi eld work of the transverse instability of megaripples. The instability growth rate depends on the difference between the heights of the different segments of the megaripple. In contrast to the underlying instability of megaripples, normal sand ripples are essentially stable and are not affected by transverse perturbations, instead reacting quickly to the wind, which tends to smooth ripple height irregularities. The transverse instability of megaripples derives from the composition of their crests, which comprise coarse particles that allow initial perturbations in ripple height to grow further. The results suggest a physical mechanism for the transverse instability of megaripples and new insight into the spatial patterns of sand ripples.

Non-anthropogenic dust exposure and asthma medication purchase in children

Air pollution has been shown to increase frequency of asthma attacks, as usually measured by hospitalisation rates. We hypothesise that purchase of asthma reliever medications will reflect a broader association between the environmental exposure and asthma exacerbations. In a time series analysis, we estimated the association of dust storms with mild asthma manifestations, as indicated by medication purchases, during 2005–2011. We compared our results with the estimation of the association of dust storms with hospitalisations due to asthma and asthma-like symptoms. We detected 289 dust storms characterised by high levels of particulate matter <10 μm in diameter. We identified 42 920 children with asthma, wheezing or asthma-like symptoms, of whom 2418 were hospitalised. We observed a higher risk of asthma medication purchase on the day of a mild dust storm (relative risk 1.05, 95% CI 1.00–1.10). The next peak in drug purchases was 3 days later and was more pronounced among Bedouin-Arab children. Stratified analyses showed higher risks for hospitalisation among Bedouin-Arab children; especially among children living in temporary houses (relative risk 1.33, 95% CI 1.04–1.71). We observed an increased risk of asthma medication purchase associated with mild dust storms. The risk observed for hospitalisation was more pronounced among the rural Bedouin-Arab population. Air pollution during dust storms is associated with increased risk for asthma hospitalisation and medication purchase http://ow.ly/BBvKp

Mechanisms limiting the growth of aeolian megaripples

Megaripples are distinguished from regular ripples by their larger size and bimodal sediment distribution. The interplay between wind, grain size, and morphology controls their development, but the exact mechanisms that limit the size of megaripples have been unclear. Using wind tunnel experiments, we found two main mechanisms that limit the height of megaripples. The first mechanism is megaripple flattening due to strong enough winds that drive the coarse grains into saltation; the second mechanism is megaripple deflation by impacts of faster saltation grains. In this latter mechanism, the coarse grains are propelled by the impacts of fine saltating grains. The occurrence of both these mechanisms depends on the grain size distribution and increases with both megaripple height and wind speed. Thus, for a given wind environment and grain size distribution, there exists a limit on the size of megaripples, which is determined by these two mechanisms.

Particle-size fractionation of eolian sand along the Sinai-Negev erg of Egypt and Israel

Eolian sand fractions along the west-east transport system of the northern Sinai Peninsula–northwestern Negev erg of Egypt and Israel were analyzed in this study with regard to source, dune geomorphology, eolian transport, and paleoclimate. The studied erg is composed of active linear (seif) dunes in northern Sinai (western part), and stabilized vegetated linear dunes in the NW Negev dune field (eastern part). Linear seif dunes differ from vegetated linear dunes in their vegetation cover, linearity, internal structure, and dynamics. Sand samples were analyzed for sand-grain morphology and particle-size distribution. Although both dune types are continuous landforms with similar orientations and sand-grain roundness values, the linear dunes of Sinai are coarser grained than the Negev vegetated linear dunes. The vegetated linear dunes have a variable but higher proportion of very fine sand (50–125 μm) content and a varying but lower sand fining ratio (defined as the ratio of fine sand percentage to very fine sand percentage). From these observations, we infer that fractionation of sand occurred along the studied eolian transport path during periods of enhanced windiness. Very fine sands are suggested to have been transported by saltation and low suspension from source deposits and sand sheets. We suggest that a significant proportion of the very fine sand fraction of Nile Delta sands has been transported downwind through northern Sinai during the late Pleistocene, especially when linear dunes reached the NW Negev due to last-glacial period windiness and probably larger sediment supply. Generally decreasing wind velocities and increasing precipitation along the west-east dune transport path enhanced vegetative cover in the northern Negev and enabled deposition of the very fine sand component within the dunes and probably further downwind. Our results suggest that particle-size distribution can elucidate much about erg history over time scales of a glacial-interglacial cycle, especially in cases where the sand provenance is of a single dominant source.

Air Pollution and Serum Glucose Levels: A Population-Based Study

AbstractRecent studies demonstrated an adverse effect of chronic exposure to air pollution (AP) on metabolic syndrome and its components. In a population-based study, we investigated the association between exposure to ambient AP and serum glucose (SG), among subjects with normal glucose, impaired fasting glucose (IFG), and diabetes mellitus (DM).We included 1,063,887 SG tests performed in 131,882 subjects (years 2001–2012). Exposure data included daily levels of SO2, NO2 and other pollutants of industrial, traffic, and nonanthropogenic sources. Demographical, clinical, and medications purchase data were assessed. Log-transformed SG levels were analyzed by linear mixed models adjusted for seasonal variables and personal characteristics.SG increases (%increase [95% CI]), among subjects with normal glucose, IFG, and DM, respectively, were associated with 6.36 ppb increase of NO2 measured 24 to 72 hours before the test (0.40% [0.31%; 0.50%], 0.56% [0.40%; 0.71%], and 1.08% [0.86%; 1.29%]); and with 1.17 ppb increase of SO2 measured 24 hours before the test (0.29% [0.22%; 0.36%], 0.20% [0.10%; 0.31%], and 0.33% [0.14%; 0.52%]). Among DM population, weakest association was observed among patients treated with Metformin (0.56% increase in SG [0.18%; 0.95%]).In conclusion, NO2 and SO2 exposure is associated with small but significantly increased levels of SG. Although DM patients were found to be more susceptible to the AP induced SG variations, Metformin treatment seem to have a protective effect. Given the chronic lifetime exposure to AP and the broad coverage of the population, even small associations such as those found in our study can be associated with detrimental health effects and may have profound public health implications.

Substantial dust loss of bioavailable phosphorus from agricultural soils.

Phosphorus (P) is an essential element in terrestrial ecosystems. Knowledge on the role of dust in the biogeochemical cycling of phosphorus is very limited with no quantitative information on aeolian (by wind) P fluxes from soils. The aim of this study is to focus on P cycling via dust emissions under common land-use practices in an arid environment by integration of sample analyses and aeolian experiments. The experiments indicate significant P fluxes by PM10 dust due to agricultural land use. Even in a single wind-dust event at moderate velocity (7.0 m s−1), P flux in conventional agricultural fields can reach 1.83 kg km−2, that accumulates to a considerable amount per year at a regional scale. The results highlight a negative yearly balance in P content (up to hundreds kg km−2) in all agricultural soils, and thus more P nutrition is required to maintain efficient yield production. In grazing areas where no P nutrition is applied, the soil degradation process can lead to desertification. Emission of P from soil dust sources has significant implications for soil nutrient resources and management strategies in agricultural regions as well as for loading to the atmosphere and global biogeochemical cycles.

A method for estimating the spatial distribution of soil moisture of arid microenvironments by close range thermal infrared imaging

The topsoil moisture content, its spatial distribution and dynamics, are important variables in understanding the response of arid eco‐geomorphic hill slope systems to rainfall. This study presents a method of measuring the soil moisture within a shrubs microenvironment by employing thermal infrared (TIR) imaging. A model for converting soil moisture (SMCM) is based on multi‐temporal TIR images. The method incorporates data from in situ measurements of soil temperature, moisture content and local meteorological variables collected simultaneously with TIR imaging. The results obtained, together with the high spatial resolution of the TIR images, demonstrated the efficacy of this method for mapping soil moisture on micro‐scale and also the potential for spatial analysis and change detection over time.