Soil Erosion by Wind and Dust Emission in Semi-Arid Soils Due to Agricultural Activities

Agricultural abandoned lands as emission sources of dust containing metals and pesticides in the Sonora-Arizona Desert

This investigation examines the transport of metal- and pesticide-polluted dust emitted by one of the most relevant agricultural areas of Northwestern Mexico. In the contaminated area, an excessive water extraction of the aquifer and seawater intrusion caused the abandonment of fields, which are pollutant-loaded dust emitters. We used air mass forward trajectories (HYSPLIT) model to obtain particle trajectories in the wind and the use of banned pesticides as geochemical tracers for dust transported by wind. Fifty dust samples from 10 agriculture fields and 26 roof dust of a city close to the agricultural area were analyzed for their contents of zirconium, lead, arsenic, zinc, copper, iron, manganese, vanadium, and titanium, by portable X-ray fluorescence. Nine pesticides were analyzed in the roof dust and agricultural soil samples by gas chromatography. Results show that the distribution of metals was significantly different between active and abandoned fields. Arsenic-lead-copper was mainly concentrated in abandoned fields, while zinc-iron-manganese-titanium was dominant in active fields. Two potential sources of metal contamination were found by principal component analysis (PCA): (I) a mixture of traffic and agricultural sources and (II) a group related to agricultural activities. The occurrence of banned pesticides in dust deposited on roofs collected at nearby cities confirms the atmospheric transport from the agricultural area. The HYSPLIT results indicated that the dust emitted from agricultural fields can reach up to the neighboring states of Sonora, Mexico, and the USA. The impacts that these emissions can have on human health should be studied in future research.

Coccidioides undetected in soils from agricultural land and uncorrelated with time or the greater soil fungal community on undeveloped land

Coccidioidomycosis is a typically respiratory fungal disease that, in the United States, occurs primarily in Arizona and California. In California, most coccidioidomycosis cases occur in the San Joaquin Valley, a primarily agricultural region where the disease poses a risk for outdoor workers. We collected 710 soil samples and 265 settled dust samples from nine sites in the San Joaquin Valley and examined how Coccidioides detection varied by month, site, and the presence and abundance of other fungal species. We detected Coccidioides in 89 of 238 (37.4%) rodent burrow soil samples at five undeveloped sites and were unable to detect Coccidioides in any of 472 surface and subsurface soil samples at four agricultural sites. In what is the largest sampling effort undertaken on agricultural land, our results provide no evidence that agricultural soils in the San Joaquin Valley harbor Coccidioides. We found no clear association between Coccidioides and the greater soil fungal community, but we identified 19 fungal indicator species that were significantly associated with Coccidioides detection in burrows. We also did not find a seasonal pattern in Coccidioides detection in the rodent burrow soils we sampled. These findings suggest both the presence of a spore bank and that coccidioidomycosis incidence may be more strongly associated with Coccidioides dispersal than Coccidioides growth. Finally, we were able to detect Coccidioides in only five of our 265 near-surface settled dust samples, one from agricultural land, where Coccidioides was undetected in soils, and four from undeveloped land, where Coccidioides was common in the rodent burrow soils we sampled. Our ability to detect Coccidioides in few settled dust samples indicates that improved methods are likely needed moving forward, though raises questions regarding aerial dispersal in Coccidioides, whose key transmission event likely occurs over short distances in rodent burrows from soil to naïve rodent lungs.

The role of soils in the regulation of air quality

Soils play a key role in meeting the UN Sustainable Development Goals (SDGs). In this study, we review the contribution of soils to the regulation of air quality, which is one of 'Nature's Contributions to People' identified by the Intergovernmental-Policy Platform on Biodiversity and Ecosystem Services (IPBES). This is particularly relevant for SDG3 (health and well-being) and 11 (sustainable cities and well-being) but also impacts other SDGs. Soils can act as both a source and a sink of air pollutants (and their precursors). In addition, soils support plant growth which plays a major role in regulating air quality. The scale of the soil impacts on air quality range from global (e.g. greenhouse gas fluxes, stratospheric ozone depletion) to local (e.g. odours, particulates, pathogen transport). Harmful emissions from soil can be increased or decreased by anthropogenic activity, while climate change is likely to modify future emissions patterns, both directly and in response to human mitigation and adaption actions. Although soils are not the only source of these pollutants, it is worthwhile managing them to reduce erosion and nutrient losses to maintain soil health so we may continue to benefit from the contributions to good quality of life they provide. This article is part of the theme issue 'The role of soils in delivering Nature's Contributions to People'.

Impact of the different vehicle fleets on PM10 pollution: Comparison between the ten most populous Italian metropolitan cities for the year 2018

The main aim of this research effort is to assess the impact of the different circulating vehicle fleets on PM10 pollution, comparing the results from the ten most populated metropolitan cities in Italy. Circulating diesel vehicles have been categorized in different groups depending on the vehicle type (car or Light Commercial Vehicle - LCV) and European emission standard. The annual mileage and the total PM10 emission for each category has been determined based on several data sources. Estimated overall annual emissions of PM10 particles have been compared with PM10 concentration measurements from distributed ground monitoring stations. A new index, named SoP (Strength of Pollution), has been defined in order to quantify the contribution of each fleet category to the overall PM10 pollution. The index has been computed for the ten most populated Italian metropolitan cities, i.e. all cities with more than 300.000 inhabits: Rome, Milan, Naples, Turin, Palermo, Genoa, Bologna, Florence, Bari and Catania. Results in terms of SoP estimates for year 2018 reveal the presence in these Italian cities of emission clusters with heterogeneous characteristics, which impose the adoption of different PM10 pollution mitigation approaches in the different cities. For example, in Naples, Catania and Palermo, Euro 0 car fleets emit a total PM10 mass which is respectively 19, 10 and 5 times the mass emitted by Euro 6 vehicles, and consequently a reduction of this fleet is desirable for pollution mitigation purposes. Conversely, in Rome, Genoa and Bari, Euro 3 and 4 car fleets emit a total PM10 mass which is 3-6 times the one emitted by Euro 6 vehicles, which calls for a reduction of these fleets. Thus, the extension to the entire national territory of the results obtained in a specific metropolitan city may be strongly misleading and produce limited effects in terms of pollution mitigation.

The Road Map to Classify the Potential Risk of Wind Erosion

Environmental degradation, for example, by wind erosion, is a serious global problem. Despite the enormous research on this topic, complex methods considering all relevant factors remain unpublished. The main intent of our paper is to develop a methodological road map to identify key soil–climatic conditions that make soil vulnerable to wind and demonstrate the road map in a case study using a relevant data source. Potential wind erosion (PWE) results from soil erosivity and climate erosivity. Soil erosivity directly reflects the wind-erodible fraction and indirectly reflects the soil-crust factor, vegetation-cover factor and surface-roughness factor. The climatic erosivity directly reflects the drought in the surface layer, erosive wind occurrence and clay soil-specific winter regime, making these soils vulnerable to wind erosion. The novelty of our method lies in the following: (1) all relevant soil–climatic data of wind erosion are combined; (2) different soil types “sand” and “clay” are evaluated simultaneously with respect to the different mechanisms of wind erosion; and (3) a methodological road map enables its application for various conditions. Based on our method, it is possible to set threshold values that, when exceeded, trigger landscape adjustments, more detailed in situ measurements or indicate the need for specific management.

CMIP5 climate projections and RUSLE-based soil erosion assessment in the central part of Iran

Soil erosion (SE) and climate change are closely related to environmental challenges that influence human wellbeing. However, the potential impacts of both processes in semi-arid areas are difficult to be predicted because of atmospheric variations and non-sustainable land use management. Thus, models can be employed to estimate the potential effects of different climatic scenarios on environmental and human interactions. In this research, we present a novel study where changes in soil erosion by water in the central part of Iran under current and future climate scenarios are analyzed using the Climate Model Intercomparison Project-5 (CMIP5) under three Representative Concentration Pathway-RCP 2.6, 4.5 and 8.5 scenarios. Results showed that the estimated annual rate of SE in the study area in 2005, 2010, 2015 and 2019 averaged approximately 12.8 t ha^-1 y^-1. The rangeland areas registered the highest soil erosion values, especially in RCP2.6 and RCP8.5 for 2070 with overall values of 4.25 t ha^-1 y^-1 and 4.1 t ha^-1 y^-1, respectively. They were followed by agriculture fields with 1.31 t ha^-1 y^-1 and 1.33 t ha^-1 y^-1. The lowest results were located in the residential areas with 0.61 t ha^-1 y^-1 and 0.63 t ha^-1 y^-1 in RCP2.6 and RCP8.5 for 2070, respectively. In contrast, RCP4.5 showed that the total soil erosion could experience a decrease in rangelands by - 0.24 t ha^-1 y^-1 (2050), and - 0.18 t ha^-1 y^-1 (2070) or a slight increase in the other land uses. We conclude that this study provides new insights for policymakers and stakeholders to develop appropriate strategies to achieve sustainable land resources planning in semi-arid areas that could be affected by future and unforeseen climate change scenarios.

Dust Emission Thresholds in Loess Soil Under Different Saltation Fluxes

Soil-derived dust particles produced by aeolian (wind) processes have significant impacts on humans and the Earth’s systems. The soil particle size distribution is a major soil characteristic in dust emission models. Yet empirical information on the dependence of dust emission thresholds on soil particle size distribution is still lacking. The main goal of this study was to explore the dust emission threshold from semi-arid loess soil samples by a targeted wind-tunnel experiment. The results clearly show that the dust emission threshold is associated with the saltation threshold with no distinct direct aerodynamic lifting of the loose dust particle. The dust flux depends on the amount of the clay-silt fraction in the soil, the shear velocity, and the saltation flux under certain shear velocity. The study aimed to advance our understating of the dust emission processes, and to provide empirical information for parametrization in dust emission models and for management strategy of soils in preventing dust emission.

Dependence of the Dust Emission on the Aggregate Sizes in Loess Soils

Dust emission resulted from soil erosion by wind with significant impacts of soil (nutrient) loss and air pollution of particulate matter (PM). The ejection of dust from soil aggregates due to saltation has been hypothesized to play a major role in dust emission. Yet empirical information on the role of different aggregate sizes in dust emission is still lacking. The main goal of this study was to explore the dust emission threshold in different aggregate sizes of a semiarid loess soil. To this end, we conducted targeted wind-tunnel experiment on dust emission. The results show that dust emission from aggregate at size of 63–250 µm, 250–500 µm, and 500–1000 µm is enabled only under the conditions of saltation. The dust-PM threshold at shear velocities of 0.24–0.52 m/s depends on the aggregates size. Aggregates at the size of saltators (125–500 µm) were the most productive in dust generation by the mechanism of aggregate disintegration. In our bulk sample, the aggregate group of 63–250 µm has the highest contribution to the total dust emission. The study aimed to advance our capability in soil resources management and for model parameterization in dust emission schemes.

Soil Erosion and Gaseous Emissions

Accelerated soil erosion by water and wind involves preferential removal of the light soil organic carbon (SOC) fraction along with the finer clay and silt particles. Thus, the SOC enrichment ratio in sediments, compared with that of the soil surface, may range from 1 to 12 for water and 1 to 41 for wind-blown dust. The latter may contain a high SOC concentration of 15% to 20% by weight. The global magnitude of SOC erosion may be 1.3 Pg C/yr. by water and 1.0 Pg C/yr. by wind erosion. However, risks of SOC erosion have been exacerbated by the expansion and intensification of agroecosystems. Such a large magnitude of annual SOC erosion by water and wind has severe adverse impacts on soil quality and functionality, and emission of multiple greenhouse gases (GHGs) such as CO2, CH4, and N2O into the atmosphere. SOC erosion by water and wind also has a strong impact on the global C budget (GCB). Despite the large and growing magnitude of global SOC erosion, its fate is neither adequately known nor properly understood. Only a few studies conducted have quantified the partitioning of SOC erosion by water into three components: (1) redistribution over land, (2) deposition in channels, and (3) transportation/burial under the ocean. Of the total SOC erosion by water, 40%–50% may be redistributed over the land, 20%–30% deposited in channels, and 5%–15% carried into the oceans. Even fewer studies have monitored or modeled emissions of multiple GHGs from these three locations. The cumulative gaseous emissions may decrease at the eroding site because of the depletion of its SOC stock but increase at the depositional site because of enrichment of SOC amount and the labile fraction. The SOC erosion by water and wind exacerbates climate change, decreases net primary productivity (NPP) and use efficiency of inputs, and reduces soils C sink capacity to mitigate global warming. Yet research information on global emissions of CH4 and N2O at different landscape positions is not available. Further, the GCB is incomplete and uncertain because SOC erosion is not accounted for. Multi-disciplinary and watershed-scale research is needed globally to measure and model the magnitude of SOC erosion by water and wind, multiple gaseous emissions at different landscape positions, and the attendant changes in NPP.

A Clay-Based Geopolymer in Loess Soil Stabilization

Soil erosion has environmental and socioeconomic significances. Loess soils cover about 10% of the global land area. Most of these soils are subjected to increased land uses such as unpaved roads, which increase soil destruction and dust emission to the atmosphere. There is a significant interest in applications for dust control and soil stabilization. Application of geopolymers may significantly reduce environmental impacts. This study examines the use of a metakaolin-based geopolymer for dust control and soil stabilization in a semi-arid loess soil. The application of the geopolymer for dust control in comparison with common products (brine, bitumen, polyvinyl acetate-PVA) resulted in no dust emission. As a soil stabilizer, the geopolymer tested in this study provides remarkably good results in the tensile test. The most successful composition of the geopolymer, which is activation solution of sodium silicate and sodium hydroxide (NaOH) together with an addition of 30% metakaolin, obtained soil strength of 23,900 N after 28 days. The attempt to replace NaOH with lime (CaO) in the activation solution was far inferior to the original composition. There is a strong potential to develop natural soil stabilizers from a mineral base that even surpass their capabilities over existing synthetic stabilizers.