Valley Soils Research Articles

Роль горнообогатительного комбината в образовании техногеохимических аномалий мышьяка в почвах Соймоновской долины (Южный Урал)

Introduction. The heterogeneity of soil cover of mountainous areas carries in itself the specific formation of technogeochemical anomalies in the areas of metallurgical combines, and the remoteness and inaccessibility of these areas requires detailed studies of the processes of pollutants in the soil and mechanisms of their behavior. The aim of the study was to investigate the influence of aero-industrial emissions from the copper smelter on the formation of techno-geochemical anomalies of arsenic in soils and its spatial distribution. Methods and materials of the research. Studies were conducted in the area of the Karabash copper smelter (KMC), located in the southern Urals (Russia), Chelyabinsk region, one of the main pollutants of soils is arsenic, which is formed in the Soymanovskaya Valley and adjacent landscapes techno-geochemical soil anomalies. In the course of works 25 soil sections were laid at different distances and directions from KMC, taking into account the specific geo-morphological features of the territory. In the selected soil samples we determined the acidity of the salt extract, the content of organic matter, granulometric composition, gross content of arsenic and its exchangeable form. Determination of arsenic was carried out by atomic adsorption spectrometry (AA-6800 Shimadzu). To identify the dependence of arsenic concentration in the upper 0-15 cm of the soil thickness with the distance from the CMC was carried out to calculate the Pearson coefficient and the concentration coefficient (Kc). Research results and discussion. The study area was divided into 5 zones depending on the distance from CMC. Excess concentrations of gross arsenic relative to the background content varies from 64 times in the 2 km zone to 3 times at a distance of more than 10 km. Maximum concentrations were recorded in the upper 0-15 cm of the soil thickness in the 2 km zone. The exchangeable form of arsenic has a specific accumulation near the combine, with a distance of more than 10 km from the combine, there is a tendency to reduce the content of this form, to a complete absence. In the intraprofile distribution there is a pattern of accumulation in the upper 0-15 cm of the soil layer, with depth significantly decreasing. Conclusions. Patterns in the spatial distribution of arsenic in soils based on the distance from the emission of aeroindustrial emissions were revealed. Maps of the spatial distribution of gross arsenic and exchange forms in the soils of the study area. It was determined that an important role in the formation of techno-geochemical anomalies plays pH of the environment. During the calculation of Ks revealed local areas that form anomalous halos dispersion, which are confined mainly to places near the CMC and the direction of the prevailing winds. Two local areas were identified for which the Kc values are more than 50. Pearson criterion calculations confirm the dependence of the spatial distribution of arsenic in soils on the wind rose. The results may be useful in the preparation of geochemical maps of arsenic distribution. In the prediction of local and radial differentiation of arsenic in other regions with similar activity of the combine, as well as in the correction of the regional geochemical background of arsenic in soils.

Purification and Characterization of Bioactive Metabolite from Streptomyces monomycini RVE129 Derived from the Rift Valley Soil of Hawassa, Ethiopia.

Streptomyces species have produced a variety of bioactive secondary metabolites with intriguing antimicrobial and anticancer properties. In this study, the bioactive compound obtained from the potent strain RVE129 was purified and characterized. Its bioactivity against various pathogens and its cytotoxicity toward the human cervical cancer (HeLa) cell were also examined. The strain was previously isolated from unexplored areas of the rift valley soil of Hawassa (Ethiopia) and identified by phenotypic characteristics and complete sequencing of the 16S rRNA gene and found to be closely related to Streptomyces monomycini strain NRRL B-24309 (99.65%); accession no. (ON786620). The active fraction undergoes bioassay-guided purification using the TLC method after being extracted by ethyl acetate. Then, it was subjected to physicochemical and structural characteristics using UV-Vis, FTIR, and NMR spectroscopic methods. A minimum inhibitory concentration of the purified antibiotic was achieved by the broth microdilution method. The cytotoxicity of HeLa cells was determined using the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The acquired data from spectroscopic studies was compared with that of the reported natural compounds in data bases and found to be the known antibiotic, setamycin. The antibiotic (RVE-02) showed a broad spectrum of bioactivity against both Gram-positive and Gram-negative bacteria, with MIC values that ranged from 1.97 to 125 μg/ml. The bioactivity results also demonstrated antiproliferation and morphological change in HeLa cells with an IC50 value of 24.30μg/ml of antibiotic. The antibiotic, obtained from S. monomycini RVE129, could be a potential candidate to combat pathogens including drug-resistant S. aureus. Further, the effect on HeLa cells suggests that it could be a prominent cancer chemotherapeutic agent.

Comparison of three land evaluation systems in capability assessment of soils of coastal plains sand in Southeastern Nigeria

Land evaluation systems vary in approach and have not always produced good results outside regions where they were originally conceived. To test the extent of their agreement, Land Capability Classification (LCC), Fertility Capability Classification (FCC), and Suitability Rating were combined in physically evaluating soils of Coastal plains sand, Imo State, Nigeria, using data from 20 pedons. With respect to LCC, soils of inland valleys were limited mainly by wetness, which had 2 out of 6 profiles of the unit classified beyond the arable. The well-drained upland soils, all of which fell within the arable classes, were subject to sheet and rill erosion. By standards of FCC, soils were limited by ‘g’ - water logging; e - low ability to retain nutrients; i - potential fe - toxicity; k - low nutrient capital reserves. Based on suitability rating, soils potentials for agriculture varied from poor to good. Results of LCC and FCC correlated significantly (r = 0.771), but none of these correlated with suitability ratings of the soils. Use of the international systems should be augmented with further soil tests some of which may be got from other comparable systems so as to capture other locally important environmental details. Subjecting factors identified by FCC to suitability rating improved evaluation procedure. Land use in the location did not strictly consider the capability of the land. Cultivating rice to the wet soils or draining them, contour cultivation on slopes, adequate fertilization of soils are recommendations to improve land management.

Controls on vertical distribution of organic carbon in the intermontane valley soils (Barak, Northeast India)

The Intermontane valleys interspersed with rugged landscapes represent a unique ecosystem and are the barn of the eastern Himalayas (EH). Soil organic carbon (SOC) plays an important role in controlling cropland productivity in these valleys. Despite this, very little is known about SOC inventories (content and stocks) and their complex interplay with some of the major control factors such as climate, elevation, land use, parent materials, and soil properties. Therefore, the objective of this study was to assess the relative influence of heterogeneous control factors (PL: Parent materials and land use) on the vertical distribution of SOC inventories at a homogeneous climate and altitude. For the study, I choose one of the largest but largely unexplored intermontane valleys (Barak) of the eastern Himalayas. By exposing a total of 72 profiles to the C horizon or water table, a thorough analysis of the influence of PL on SOC inventories (Dichromate oxidizable) and key soil parameters controlling vertical distribution of SOC in valley soils were determined The measured SOC content in the surface soil (0.15–0.24 m deep) varied from 0.91% to 1.42%, while in the soil profile (up to a depth from 1.19 to 1.56 m), the SOC content (PWA: profile weighted average) ranged from 0.60% to 0.97%. The surface layer represented only 15% soil profile depth, while contributing 33% of the SOC content (Dichromate oxidizable). The variation in SOC content (PWA) was higher among soil parent materials (e.g. Alluvium, pebble bedded-sandstone, sandstone intercalated with shale, and pure shale, CV> 16.0%) than in land use systems (e.g. Paddy agriculture, forest, and plantation, CV <3.0%). The SOC stock on the soil profile (PWA) ranged from 19.4 to 36.0 Mg ha−1. The total (soil profile) SOC stock varied from 67.5 to 161.1 Mg ha−1. In general, the SOC inventories increased relative to the clay content (correlation, r = 0.38–0.75, p < 0.05) and parent materials controlled the variation in surface and subsurface soils while the effect of land use was mostly limited to surface soils only. Deep soils (>1.55 m) developed on shale with higher clay content had higher SOC inventories (p < 0.05) than coarse-textured sandstone soils. Parent materials contributed to greater heterogeneity (R2adj = 77.1%) in SOC inventories compared to land use systems (R2adj = 61.7%). Therefore, in addition to land use, parent materials should be considered an important control factor in the estimation of SOC inventories and future research on C- sequestration in the intermontane valleys.

Sensitive indicators of soil nutrients from reservoir effects in the hot-dry valleys of China

The construction of giant reservoirs can affect the hydroclimatic cycles and related soil nutrient recycling. The current understanding of variations in soil nutrients driven by reservoir impoundment is limited because soil often reacts slowly to changes and the impoundment effects can be masked by various factors, making detection difficult. The soils in the hot-dry valleys suffer from a savanna-like hot and dry climate, making it an ideal area for studying the effect of reservoir impoundment on the soil. Here we collected 138 soil samples in April and November along the cascading reservoirs located in the hot-dry valleys of China, including Xiangjiaba, Xiluodu, Baihetan, and Wudongde reservoirs. Results showed that (1) the reservoir impoundment does alter the soil nutrients. The contribution of the impoundment to the variation of soil nutrients was 3.82% in April and 6.44% in November. (2) Compared to April, a relatively dry and cold November is preferred for revealing the reservoir impact on soil nutrients in the hot-dry valleys. (3) Available nitrogen and available phosphorus, followed by soil organic matter, are potential sensitive indicators that can be used to reflect the reservoir impoundment effects. Additionally, pH may be a potential indicator, particularly in the head reservoir area. It is important to note that the effect of reservoir impoundment on soil nutrients is easily masked. This study encourages dam operating agencies, policymakers, and researchers to regard reservoirs as integral parts of the forcings that modify soil nutrients and is an essential step in gaining an insight into the impact of hydropower development on surrounding terrestrial ecosystem services related to soil nutrients.

Status of Morphological and Physico-chemical Properties of Balh Valley Soils of Mandi District of Himachal Pradesh in North Western Himalayas India

Background: Himachal Pradesh (India) lying in North West Himalayas were studied for their morphological, physical and chemical properties. Himachal Pradesh, is a mountainous region spread over an area of 55,673 km² with elevation ranging from 350 to 6,500 meters above mean sea level noticeably increased from west to east and south to north. For agricultural planning, development and the sustainable use of natural resources. The state has been categorized into four agro-climatic situations viz. low hills, mid hills sub humid, high hills temperate and high hills dry temperate. However, considerable variations exist within each zone, owing to soil type and local preferences resulting into diversified farming situations. Methods: A six profile sites of soils were collected randomly from vegetable and cereals growing areas falling under midhill zone. After collecting soil samples, these were air dried and analyzed for physical and chemical properties. The study determined the level of availability of nutrients and know the fertility status of studied areas. Result: The results show that soils are deep, well drained, silty loam to silty clay loam with dark brown to brownish yellow in colour. No gravels were noticed upto 0.6 m depth and the soil consistency was firm to loose. Few to many black brown concretions were observed only in rice growing soils. Silty loam was the dominant texture of the soils irrespective of soil depth. Coarse sand fraction was more in all soil profiles. Macro and micronutrients contents were higher under the vegetable growing soils than paddy and maize growing soils. In none of the soils except Dhangu, illuviation of clay had been observed. The values of bulk density, particle density and porosity were variable depending upon organic carbon and other soil characteristics. The soils were slightly acidic to neutral in reaction, medium to high in organic carbon and moderate in available N, P and K status. The DTPA-extractable Fe, Zn, Cu and Mn were also high in these soils. Similarity in the colour and texture in most of the soils indicated the dominant influence of parent material.

Application of Geoinformation Technologies for Assessment of the Epizootiological and Epidemiological Situation on Anthrax in the Volgograd Region

Objective of the study was to assess the epizootiological and epidemiological situation on anthrax in the Volgograd Region in the period of 1920–2019, to zone the territory according to the degree of disadvantage as regards anthrax using geographic information technologies. Materials and methods. The reporting data of the Rospotrebnadzor Administration, Veterinary Committee in the Volgograd Region, and literature sources were studied. ESRI-ArcGIS 10 software was used as a GIS-platform. Epizootic index was applied in the zoning according to the degree of disadvantage regarding anthrax in the territories of the region. Results and discussion. Currently, 529 stationary potentially hazardous as regards anthrax areas have been registered in 33 districts of the Volgograd Region, 53 anthrax burial sites are accounted for in 20 districts. During the period of 1970–2019, 226 cases of infection of farm animals and 37 cases of anthrax among humans were detected. Most of the stationary potentially hazardous as regards anthrax areas (347 sites, 66 %) were formed in 1930–1949. Maximum activity was observed in 1930–1959. The zoning of the territory of the Volgograd Region was carried out using ESRI-ArcGIS 10 software, as a result of which the municipal districts were divided into four groups according to the degree of disadvantage regarding anthrax. The potential of different soil and landscape zones in the persistence of the anthrax microbe was studied. It has been found that chernozem, chestnut, dark-chestnut soil types, which occupying more than 50 % of the total region area and predominate in the zones of moderately arid and dry steppes, alongside alluvial meadow soils of river valleys, floodplains of rivers are very favorable for the persistence of the anthrax pathogen. The territory of the Volgograd Region is endemic for this infection and epizootiological and epidemiological well-being in the region largely depends on the completeness and timelines of preventive measures. The use of geographic information technologies provides a comprehensive analysis of the infection activity manifestations with reliable improvement of the anti-anthrax surveillance system and control in making differentiated managerial decisions.

Liquefaction hazard assessment and ground failure probability analysis in the Kathmandu Valley of Nepal

During the 2015 Gorkha Earthquake (Mw7.8), extensive soil liquefaction was observed across the Kathmandu Valley. As a densely populated urban settlement, the assessment of liquefaction potential of the valley is crucial especially for ensuring the safety of engineering structures. In this study, we use borehole data including SPT-N values of 410 locations in the valley to assess the susceptibility, hazard, and risk of liquefaction of the valley soil considering three likely-to-recur scenario earthquakes. Some of the existing and frequently used analysis and computation methods are employed for the assessments, and the obtained results are presented in the form of liquefaction hazard maps indicating factor of safety, liquefaction potential index, and probability of ground failure (PG). The assessment results reveal that most of the areas have medium to very high liquefaction susceptibility, and that the central and southern parts of the valley are more susceptible to liquefaction and are at greater risk of liquefaction damage than the northern parts. The assessment outcomes are validated with the field manifestations during the 2015 Gorkha Earthquake. The target SPT-N values (Nimproved) at potentially liquefiable areas are determined using back analysis to ascertain no liquefaction during the aforesaid three scenario earthquakes.

Occurrence of entomopathogenic fungi in muck-glial soils of the Liwiec river valley

For the preservation of biological diversity of soil microorganisms, including entomopathogenic fungi which are natural enemies of pests, areas that are subject to anthropogenic transformation as little as possible are of great importance. River valleys may be such areas. The aim of the study was to identification of types of entomopathogenic fungi, as well as to investigate the intensity of their occurrence in the upper genetic levels of meadow muck-glial soils located in the Liwiec river valley. The material for the research was soil samples collected in October 2018 and May 2019, in the upper reaches of the Liwiec river. Insecticidal fungi were isolated from individual genetic levels of the soils under study using the selective substrate isolation method. In the course of the research, insecticidal fungi of the genus were isolated: Beauveria spp., Metarhizium spp., Isaria spp. and Lecanicillium spp., with only Beauveria spp. and Lecanicillium spp. being found in the autumn. The greatest number of infection units was formed by the fungus Beauveria spp. and the greatest intensity of its occurrence was found in the turf level of the soils studied.

Increasing the Efficiency of Chili Pepper Cultivation through an Effective Fertilization System

The irrigated brown meadow soils of the Ararat valley are poor in humus content and other important plant required nutrients; hence, the application of scientifically justified quantities of the fertilizers becomes a priority measure. Considering the afore stated fact, the effect of various fertilizers’ combinations (N; NP; NPK; NPK + complexon via foliar feeding, thrice) on the plant growth, yield capacity and its quality has been studied. The best result has been recorded in the option of N120P120K120+complexon. The fruit quality has also improved: the content of dry matters and sugars has increased, while the nitrate content has decreased.

Chemical composition and barrier functions of soils of the Utulik-Solzan valley (southern shore of Lake Baikal)

Chemical composition and barrier functions of soils of the Utulik-Solzan valley (southern shore of Lake Baikal)

Salinization and ilimerization processes in the soils of the river valleys of the north-western Black Sea coast

Salinization and ilimerization processes in the soils of the river valleys of the north-western Black Sea coast

Trace-elements evaluation of composted municipal solid wastes used in dry season production of tomato (Lycorpersicum esculentus) in an inland valley soils of Delta State, Nigeria

Trace-elements evaluation of composted municipal solid wastes used in dry season production of tomato (Lycorpersicum esculentus) in an inland valley soils of Delta State, Nigeria

Diversity and structural characteristics of soil microbial communities in different habitats of wild Lilium regale Wilson in Wenchuan area

ABSTRACT Lilium regale Wilson (L.regale), originated in the Minjiang River basin in Sichuan, China, has different phenotypic characteristics in different environments. To analyze the correlation between the phenotypes of L.regale and its soil micro-ecological environment, wild habitat soil of L.regale at the two altitudes were selected to analyze the diversity and community structure of microorganisms in soil, and measure the soil physicochemical factors and enzyme activities. The structural composition and diversity of fungal and bacterial communities in hillside and valley soils were significantly different (p< 0.01). Soil available potassium (AK) and soil enzyme activities such as urease (S_UE), sucrase (S_SC), and catalase (S_CAT) differed significantly different between hillsides and valleys (p < 0.01), while organic matter (OM), total phosphorus (TP), and polyphenol oxidase (S_PPO) had no great variances. Correlation analysis was conducted between the common and differential microorganisms and the morphological characteristics, soil physicochemical factors and soil enzyme activities of L.regale in both hillside and valley. The results showed that both of the fungal and bacterial could be clustered into two distinct groups by positive and negative correlations, suggesting that the representative microorganism may have structural characteristics that are directly related to soil physicochemical properties and enzyme activities, which conversely affect the phenotype of Lily. Therefore, the study on the native species of horticultural plants and the local soil microhabitat environment will benefit the conservation of wild Lily and provide theoretical guidance for the domestication and breeding of horticultural plants.

Profile distribution of soil organic carbon fractions under different landforms in the Meghalaya plateau of India

Assessment of organic carbon fractions in soil provides the basis to ascertain vulnerability of an ecosystem to climate change. In the present study, we assessed SOC fractions in four pedons under contrasting landforms i.e., denudational low hill, upper plateau, lower plateau and valley in the Meghalaya plateau, India. Results indicated that soils of the studied pedons were acidic in nature, low in cation exchange capacity and base saturation. Further, surface (0-30 cm) soils were high in Walkley Black C (WBC) content (0.83-1.13%) in the studied pedons located under different landforms. The density of very labile carbon (VLC) fraction up to a depth of 150 cm was highest (49.22 Mg ha?1) in pedon 2 (P2) located in the upper plateau under shifting cultivation while that of less labile carbon (LLC) was highest (50.25 Mg ha?1) in pedon 4 (P4) in the valley under paddy cultivation. Higher densities of WBC and LLC in the valley (P4) as compared to other landforms in the study area indicate higher carbon sequestration potential of valley soil.

Spatial variability and delineation of management zones based on soil micronutrient status in apple orchard soils of Kashmir valley, India.

Knowledge and up-scaling of status, availability, and distribution of soil micronutrients are hugely significant for enhancing crop productivity and profitability. However, regional database entailing spatial variability of key micronutrients for a major apple-producing region like the Kashmir Himalayan Region (KHR) is missing. We investigated 588 topsoil samples between 2016 and 2017 (to 30cm depth) to estimate spatial variability of extractable Zn, Cu, Mn, and Fe; develop spatial maps; and delineate potential management zones (MZs) in apple orchards using geo-statistical methods. Soil sampling was performed post-harvest season. Principal component analysis and fuzzy c-mean clustering were performed to develop MZs. Results exhibited wide variation, with high coefficient of variation (%) for Mn and Cu (123.9 and 114.4, respectively) and low (71.6) and medium (104) variability for Fe and Zn. Mean concentrations followed the order: Fe > Mn > Cu > Zn, with deficiencies evident towards central and northern regions of the study area. The best-fitted model was exponential. The nugget/sill ratio values were 0.41, 0.08, 0.37, and 0.38 for Zn, Cu, Mn, and Fe, respectively, indicating strong spatial dependence for Cu and moderate dependence for Fe, Zn, and Mn. Correlations between elevation, slope, and soil pH with micronutrients were negative, whereas with soil organic carbon and electrical conductivity positive relationships were identified. Three principal components accounted for 67·18% data variance. Based on the fuzzy performance index and modified partition entropy, five MZs were delineated, which exhibited variations from each other. These MZs highlighted the need for specific supplemental provisions in increasing soil fertility and apple productivity.

Below‐ground plant–soil interactions affecting adaptations of rice to iron toxicity

Iron toxicity is a major constraint to rice production, particularly in highly weathered soils of inland valleys in sub-Saharan Africa where the rice growing area is rapidly expanding. There is a wide variation in tolerance of iron toxicity in the rice germplasm. However, the introgression of tolerance traits into high-yielding germplasm has been slow owing to the complexity of the tolerance mechanisms and large genotype-by-environment effects. We review current understanding of tolerance mechanisms, particularly those involving below-ground plant-soil interactions. Until now these have been less studied than above-ground mechanisms. We cover processes in the rhizosphere linked to exclusion of toxic ferrous iron by oxidation, and resulting effects on the mobility of nutrient ions. We also cover the molecular physiology of below-ground processes controlling iron retention in roots and root-shoot transport, and also plant iron sensing. We conclude that future breeding programmes should be based on well-characterized molecular markers for iron toxicity tolerance traits. To successfully identify such markers, the complex tolerance response should be broken down into its components based on understanding of tolerance mechanisms, and tailored screening methods should be developed for individual mechanisms.

Characterization and Land Suitability Evaluation for Cocoyam in Southern Nigeria

The soils on diverse landforms in Ikot Esidem, Southern Nigeria were characterized and their suitability evaluated for three varieties of cocoyam. The study area was stratified into flood plains, inland valleys, gentle slopes and crest. The results indicate that sand (30-78%) dominated pedons of gentle slopes and crest while silt (25-55%) and clay (19-51%) dominated the pedons of flood plains and inland valleys. The soils of flood plains and inland valleys were moderately acid (pH 5.0-5.7), medium to high in organic carbon (6.3-20.5 g/kg) and medium to high in base saturation (BS) (46-90%). The gentle slopes and crest units were strongly acid (pH 4.0-5.1), low in organic carbon (4.0-11.3 g/kg) and base saturation (20.5-34.7%). The land suitability evaluated the flood plains and inland valleys as moderately suitable and the gentle slopes and crest as not suitable for Dasheen Type Taro. The flood plains and inland valleys were also evaluated moderately suitable, whereas gentle slopes and crest were marginally suitable for Eddoe Type Taro. Efficient water control drainage and erosion control will enhance cocoyam cultivation depending on terrain type.

Carbon and Nitrogen Sourcing in High Elevation Landscapes of Mustang in Central Nepal

Mustang valley in the central Himalaya of Nepal is a unique landscape formed by massive soil mass during a glacial period, which is attributed to a mix of vegetations and long agricultural history. Soil nutrients and their sourcing is highly important to understand the vegetation assemblage and land productivity in this arid zone. Twenty soil samples (from 0 to 20 cm depth) were collected from three landscape positions in Mustang district: valley, ridge, and midslope. We explored nutrient sourcing using natural abundance carbon (δ13C) and nitrogen isotope (δ15N) employing isotope ratio mass spectrophotometry. The results showed that the total soil carbon (TC) and total nitrogen (TN) ranged from 0.3 to 10.5% and 0.3 to 0.7%, respectively. Similarly, the CN ratio ranged from 0.75 to 15.6, whereas soil pH ranged from 6.5 to 7.5. Valley soil showed higher values of TN, CN, and soil pH than the ridge and midslope soils. The valleys had more positive δ15N signatures than ridge and midslope, which indicates higher inorganic and organic N fertilizer inputs in the valley bottom than in the midslope and ridge. This suggests that a higher nutrient content in the valley bottom likely results from agro-inputs management and the transport of nutrients from the ridge and midslope. Soil pH and CN ratio were a non-limiting factor of nutrient availability in the study regions. These findings are crucial in understanding the nutrient dynamics and management in relation to vegetation and agricultural farming in this unique topography of the Trans-Himalayan zone of Mustang in central Nepal.

Role of the climate changez in soils salinization

The imformation about the changes occuring in the Kur-Araz valley soils has been given in the article. The investigations showed that the irrigated. Soils of the Mughan plain in the Kur-Araz valley exposed to salinization and solonetrification, the soils fertility decreased, the productivity obtaining from agricultural plants reduced as a result of the floods and mudslides. The same floods seriously damaged 70012 h of the zone and the meliorative measures were realized for their prevention.