Search Results (5)

Soil erosion is a selective process which removes the light fraction comprised of soil organic carbon (SOC) and colloidal particles of clay and fine silt. Thus, a large amount of carbon (C) is transported by erosional processes, and its fate (i.e., emission, redistribution, burial, and translocation into aquatic ecosystems) has a strong impact on the global carbon cycle. The processes affecting the dynamics of soil C emission as greenhouse gases (i.e., CO_2, CH₄, N₂O), or its deposition and burial, vary among different stages of soil erosion: detachment, transport, redistribution, deposition or burial, and aquatic ecosystems. Specific biogeochemical and biogeophysical transformative processes which make erosion-transported carbon a source of C emission are determined by the type of erosion (rill vs. inter-rill in hydric and saltation erosion vs. air-borne dust in aeolian erosion), soil temperature and moisture regimes, initial SOC content, texture, raindrop-stable aggregates and water repellency, crusting, slope gradient, physiography and the slope-based flow patterns, landscape position, and the attendant aerobic vs. anaerobic conditions within the landscape where the sediment-laden C is being carried by alluvial and aeolian processes. As much as 20–40% of eroded SOC may be oxidized after erosion, and erosion-induced redistribution may be a large source of C. In addition, human activities (e.g., land use and management) have altered—and are altering—the redistribution pattern of sediments and C being transported. In addition to O₂ availability, other factors affecting emissions from aquatic ecosystems include sub-surface currents and high winds, which may also affect CH₄ efflux. The transport by aeolian processes is affected by wind speed, soil texture and structure, vegetation cover, etc. Lighter fractions (SOC, clay, and fine silt) are also selectively removed in the wind-blown dust. The SOC-ER of dust originating from sand-rich soil may range from 2 to 41. A majority of the C (and nutrients) lost by aeolian erosion may be removed by saltation. Even over a short period of three seasons, wind erosion can remove up to 25% of total organic C (TOC) and total N (TN) from the top 5 cm of soil. A large proportion of C being transported by hydric and aeolian erosional processes is emitted into the atmosphere as CO₂ and CH₄, along with N₂O. While some of the C buried at the depositional site or transported deep into the aquatic ecosystems may be encapsulated within reformed soil aggregates or protected against microbial processes, even the buried SOC may be vulnerable to future loss by land use, management, alkalinity or pH, the time lag between burial and subsequent loss, mineralogical properties, and global warming. Full article

Dust aerosols persistently affect nearly all landscapes worldwide, and the saltation activity caused by dusty weather (e.g., dust days) releases considerable amounts of aerosol into the atmosphere. Nevertheless, dust-induced saltation activity may also occur on non-dust days. To date, few studies have investigated the saltation activity characteristics on non-dust days. Moreover, the contribution of non-dust days to the total saltation activity remains ambiguous. This study comprehensively investigates the characteristics of saltation activity on non-dust days. Specifically, we analyze the influence of the saltation activity of non-dust days on dust aerosols by utilizing saltation, atmospheric, soil, dust aerosol (i.e., PM₁₀ and aerosol optical depth), and weather record data obtained from the Taklimakan Desert, China, between 2008 and 2010. Our results show that lower temperature, vapor pressure, and soil moisture on non-dust days reduces the saltation threshold velocity (5.9 m/s) more compared to on dust days (6.5 m/s). Furthermore, regarding wind speed, relatively strong monthly saltation activity occurs from March to August, and daily saltation activity occurs from 9:00 to 16:00. Although non-dust days only contribute 18.5% and 7.7% to saltation time and saltation count, respectively, both significantly influence the dust aerosols. Therefore, the effect of saltation activity on non-dust days cannot be undervalued, particularly while performing dust aerosol studies. Full article

The unmixing of grain-size distribution (GSD) with multivariate statistical analysis provides insight into sediment provenance, transport processes and environment conditions. In this article, we performed hierarchical clustering endmember modeling analysis (CEMMA) to identify the sedimentary environment of fluvial deposits at core HDZ04 drilled in the paleofloodplain on the north bank of the upper Yellow River. The CEMMA results show that four end members can effectively explain the variance in the dataset. End-Member 1 and End-Member 2 are polymodal and dominated by silty clay, and they are associated with the suspended load. End-Member 3 is composed of fine sand and silt, and medium-coarse sand makes up the majority of End-Member 4, corresponding to a mixed saltation load and bed load, respectively. Combined with the end-member scores, we constructed energy values to further divide the core samples into different depositional environments. Unit 2 and unit 5 have a high proportion of coarser end-member components, presenting a shallow channel and a high-energy channel environment, respectively. Unit 1 and unit 3 are composed of fine-grained silt and clay and are dominated by finer end-member components, which can be interpreted as a floodplain situation. Unit 4 is characterized by frequent fluctuations in grain-size composition and energy values, indicating the transition from a high-energy river channel to floodplain deposits. For the channel sedimentary environment, the accumulation rate was relatively low (0.32 mm/yr) due to the frequency migration of the channel. A high accumulation rate of the fluvial deposits had occurred in unit 1 during 1.6 Ka (4.35 mm/yr), which was a response to the influence of increased fluvial instability and human activity during the late Holocene. Full article

An accidental radiological release or the operation of a radiological dispersal device (RDD) may lead to the contamination of a large area. Such scenarios may lead to health and safety risks associated with the resuspension of contaminated particles due to aeolian (wind-induced) soil erosion and tracking activities. Stabilization technologies limiting resuspension are therefore needed to avoid spreading contamination and to reduce exposures to first responders and decontamination workers. Resuspension testing was performed on soils from two sites of the Negev Desert following treatment with three different stabilization materials: calcium chloride, magnesium chloride, and saltwater from the Dead Sea in Israel. Two and six weeks post-treatment, resuspension was examined by inducing wind-driven resuspension and quantitatively measuring particle emission from the soils using a boundary-layer wind tunnel system. Experiments were conducted under typical wind velocities of this region. Treating the soils reduced resuspension fluxes of particulate matter < 10 µm (PM₁₀) and saltating (sand-sized) particles to around background levels. Resuspension suppression efficiencies from the treated soils were a minimum of 94% for all three stabilizers, and the Dead Sea salt solution yielded 100% efficiency over all wind velocities tested. The impact of the salt solutions (brine) was directly related to the salt treatment rather than the wetting of the soils. Stabilization was still observed six weeks post-treatment, supporting that this technique can effectively limit resuspension for a prolonged duration, allowing sufficient time for decision making and management of further actions. Full article

Sand collectors are important for quantitatively monitoring aeolian sand activities. In this paper, an automatic high-precision sand collector was designed. Based on the measured data of aeolian transport performed with a piezoelectric saltation sensor (H11-Sensit) and a 10 m high meteorological tower, the sampling efficiency of the automatic sand sampler and the horizontal dust flux of the near surface were analyzed based on observed data. The results were as follows: the best-fitting function between the number of impacting sand particles and the amount of collected sand was a linear relationship. The average value of R² was 0.7702, and the average sand collection efficiency of the sand collector at a height of 5 cm was 94.3%, indicating good sand collection performance. From all field tests conducted so far, it appeared that a high-precision sand sampler was a useful device for making field measurements of horizontal dust fluxes and ascertaining the relationship between transition particles and wind speed. In the future, the equipment costs and wind drive will continue to be optimized. Full article