Unlocking the potential of conservation agriculture for soil carbon sequestration influenced by soil texture and climate: A worldwide systematic review

Conservation Agriculture (CA) systems have gained significant attention as a sustainable cropping approach that not only improves crop yields but also contributes to climate change adaptation and mitigation through enhanced soil organic carbon (SOC) sequestration. However, a comprehensive understanding of the influence of soil texture and climate conditions on SOC sequestration under CA remains limited. To address this knowledge gap, we conducted a systematic review using the PRISMA method, analyzing data from 35 peer-reviewed articles encompassing 71 field experiments and 451 observations worldwide. Our findings demonstrate the substantial positive impact of CA on SOC sequestration, with an overall increase of approximately 78%. Remarkably, only a mere 2% of observations reported neutral effects, while 20% indicated adverse outcomes. Notably, SOC sequestration rates were highest in tropical regions experiencing dry winters, reaching an impressive 2.50 Mg/ha/year in the topsoil layers. Moreover, fine and moderate textured soils, such as clay, clay loam, loam, and clay sandy, exhibited higher SOC sequestration rates (20-27%) compared to coarse-textured soils dominated by sandy proportions (9%). These findings emphasize the significance of climate conditions and soil texture in shaping the impact of CA on SOC sequestration

Oued Moulouya: vecteur de transport des métaux lourds (Maroc)

Les mines qui sont abandonnées avec leurs installations minières et métallurgiques constituent un exemple représentatif du transfert des éléments métalliques dans l’écosystème. Au Maroc, le site minier d’Aouli est drainé par l’oued Moulouya (l’unique oued de la région) d’une longueur de 520 km avec un bassin versant d’une superficie d’environ 50.000 km2. A travers ce travail, nous avons déterminé un certain nombre de paramètres chimiques afin de voir la destinée de certains métaux (Pb, Zn, Cu et Cd) issue de ce district minier abandonné. Les résultats ont montré que dans l’eau, dans les matières en suspension et dans les sédiments, il y a une contamination métallique due à la mine d’Aouli situé au niveau de la Haute Moulouya ; tandis qu’au niveau de la Basse Moulouya, l’affluent oued Za contribue à cette contamination par un apport anthropique qui résulte en une augmentation des teneurs en cadmium, plomb et zinc. L’effet de cette contamination externe est également mis en évidence par les caractères géochimiques d’une station témoin situé en amont de l’oued loin de toute influence minière.L’examen des rapports des différents éléments (Cd, Pb et Cu) par rapport au Zn dans les sédiments montre qu’ils sont préservés dans les sédiments en aval (Basse Moulouya). Par contre, au niveau de la Haute et la Moyenne Moulouya, on assiste à une diminution des rapports Cu/Zn et Cd/Zn et une augmentation du rapport Pb/Zn au niveau de la station S3; ce qui reflète l’effet de la mine d’Aouli. L’augmentation des rapports au niveau des stations S1 et S4 sont en relation avec la présence d’algues et qui jouent un rôle important dans la modification des teneurs en Zn dans les sédiments.L’étude de ces rapports a permis de confirmer que dans notre cas aucun effet notable dû aux apports des affluents n’est mis en évidence sur le contrôle des concentrations des éléments dans les sédiments de l’oued Moulouya. Cette particularité permet de suggérer que dans la cas de l’oued Moulouya la dilution physique est plus importante que la mobilisation chimique et permet d’expliquer le déclin en aval des concentrations des éléments métalliques.Mining activity started in Morocco in the 9th century. Several metals were prospected for but lead was preferentially mined owing to its silver content. The mining history of Morocco can thus be summarized by the history of lead prospecting within the country. Strong mining activity resumed in the 1970s and has been maintained since that time, with lead still being the main metal produced. In 1980 its production reached about 170,000 tons of concentrated lead, which corresponds to 3.5% of the world's production (Wadjinni, 1998). In 1975, the Aouli and Mibladen mines were depleted and in 1986 the Zaida mine was closed. This resulted in large mining districts being abandoned with their mining and metallurgic equipment left on the surface together with all the accompanying waste materials, including tailings. This has created an important source of contamination, progressively releasing trace elements into the environment.The goal of the present study was to characterize the spatial distribution of the heavy metals (Cd, Cu, Pb and Zn) released from the Aouli mine into the Moulouya River. This river, which drains the Aouli, Mibladen and Zaida mines, is a good example of the pollution impact arising from abandoned mining sites. In order to understand the behaviour and the fate of these metals within the only permanent river in this region, contamination levels were measured in three components of this river, namely: water, suspended solids and sediments.Due to the presence of mountainous areas (Rif, Middle and High Atlas), the Moulouya River basin is characterized by variable relief. The river basin also contains high plateaus (the Horsts chain) and low plains (the Missour-Outat El Haj and the Taourirte-Guercif basins). This large area can thus be subdivided into three zones designated by the upper, middle and lower Moulouya basins (Fig.1).The Upper Moulouya basin corresponds to the southwest region of the Oranaise Meseta that is bounded by the High Atlas on the Southeast and by the Middle Atlas on the Northwest. They are composed of two separate Paleozoic massifs (the Bou-Mia and the Aouli). The Paleozoic substratum that outcrops into these massifs consist of pelletic and quartzitic rocks intruded by Hecynian granites and overlain non-uniformly by a Mesozoic cover consisting of Triassic evaporite/clastics and Jurassic and Cretaceous carbonates and shales.The Middle Moulouya basin is separated from the Lower Moulouya basin to the North by the Yacoubat paleo-high that corresponds to an East-West oriented topographic bulge where the river narrows considerably. The outcropped rock consists mainly of Jurassic carbonates and marls, Cretaceous carbonates, marls and sandstones and Tertiary and Quaternary conglomerates, marls and gypsum.The Lower Moulouya basin corresponds to a vast plain extending from the Yacoubat High in the South to the Jbel Mazgout and the Beni-Snassen in the North. This area is underlain by Paleozoic granites, Triassic marls and basalts, Jurassic and Cretaceous carbonates, marls and sandstones and Tertiary and Quaternary conglomerates, marls and carbonates. The Moulouya river basin is characterised by a variable climate, which changes from a Mediterranean type in its low portion to a sub-Saharian type in its median portion and to a continental type at higher elevations.Sampling was carried out during low water level periods. In order to obtain good representative sampling, three samples were taken from each station and were used to measure metal contaminant concentrations in water, suspended solids and sediments. The sediment samples were taken from approximately 5 cm below the surface within the river plain, which is characterized by fine-grained low-energy organic matter-rich sediments.We defined a certain number of pollution parameters within the Moulouya basin, based on the samples taken from eight representative sites. The areal distribution of metal concentrations in water and in suspended solids shows the existence of two main contamination sources: the abandoned Aouli mine and urban waters. Dissolved Zn concentrations varied from 3 to 30 µg·L-1 and the two highest concentrations occurred at station 3 near the Aouli mine and at station 8 located in oued Za near the town of Taourirt (Table 1). Cadmium, Cu and Pb concentrations showed similar trends with high concentrations occurring at stations S3 and S8 for Cd and Cu and at stations S3 and S5 for Pb (Fig. 2). These high levels were explained by the effect of Aouli mine for station S3, the Tindit mineralization area for station S5 and urban waters from Taourirt for station S8.Metal concentrations in sediments reflect the downstream attenuation of the Aouli mine effect (station S3). In fact this station is characterized by high metal concentrations, especially Pb and Zn and to a lesser degree Cd and Cu. For Cu, its concentration in sediments was found to be similar to its concentration in the suspended solids. This is explained by the precipitation of Cu(II) as oxides and hydroxides. The areal distribution of Pb and Cd was similar to that of Zn, suggesting that the Aouli mine is also a source of these metals.By comparing concentration ratios of different metals with respect to that of Zn, we found that all these ratios remain constant downstream from the Aouli mine, with the exception of the Pb/Zn ratio, which increased at station S3 (Fig. 3). This distribution indicates an effect of the Aouli mine (station S3) and to a lesser degree of the Tindit area (station S4). No notable effect of the Moulouya tributaries on the concentrations of metals was detected

Phytoremediation study of mining soils: case of the Mibladen and Zaida mine (High Moulouya, Morocco)

The Upper Moulouya region, including the Mibladen (M) and Zaïda (Z) mines, is one of the highest lead (Pb) deposit areas in Morocco. These mines, abandoned without any measure of rehabilitation, constitute the main source of soil pollution by Metallic Trace Elements (MTEs) accumulation in the region. In this study, two greenhouse phytoremediation experiments (for the Mibladen and Zaida sites) were set up using Italian ryegrass (Lolium multiflorum) specie to assess its capacity and ability to remediate soils contaminated by zinc (Zn), cadmium (Cd), copper (Cu), and Pb. For both experiments, various factors including (i) three substrates (waste treatment [Wt]; clay uncovering [Cun]; and unpolluted control soil [Ucs]) and (ii) three treatments (no treatment, treatment with organic matter, and treatment with chemical fertilizers) were studied. The results before planting indicated that Wt substrates had poorer physicochemical properties than those of Cun, thus they are the most exposed to the degradation phenomena. This is confirmed by pollution index (PI) results that revealed the trend of PI (Z Wt)> PI (M wt)> PI (M Cun)> PI (Z Cun)> PI (Z Ucs)> PI (M Ucs). The results of experiments indicated that ryegrass crops can grow on substrates contaminated with MTEs. Depending on the applied fertilizers, available metals, and the type of soil, the phytoremediation results showed that L. multiflorum can tolerate, hyperaccumulate, and translocate MTEs from polluted substrates. Our findings suggest that this plant can be a solution for remediating alkaline soils polluted by Cd, Pb, Zn, and Cu in Mediterranean conditions

Pb et As dans des eaux alcalines minières : contamination, comportement et risques (mine abandonnée de Zeïda, Maroc)

Des échantillons d’eau et de matière en suspension ont été prélevés le long de l’oued Moulouya et dans des lacs de carrière au niveau de l’ancien centre minier de Zeïda (Haute Moulouya, Maroc) en vue d’en évaluer la salubrité. Il est en effet important d’établir le degré et les causes éventuelles de dégradation de la qualité de ces eaux, compte tenu de leur usage à des fins tant domestiques qu’agricoles. Des résidus de traitement ont également été échantillonnés dans les haldes abandonnées.L’analyse des distributions et des variations spatio-temporelles des concentrations de Pb et As a permis de mettre en évidence que le centre minier a véritablement un impact sur la qualité des eaux de surface environnantes, malgré le caractère neutre à alcalin du drainage. Aucune ne rejoint les critères de l’Organisation mondiale de la santé en matière de Pb et As dans l’eau potable (10 µg/L), mais près de la moitié souscrit aux normes marocaines (50 µg/L). L’importance de la dégradation varie selon la saison et la localité, et le contraste entre sites a priori non dégradés et sites dégradés n’est pas toujours très prononcé. On observe même des variations à l’inverse des tendances attendues. Les résultats peuvent cependant être réconciliés en tenant compte de l’importance du transport particulaire par rapport au transport dissous au moment et au lieu de l’échantillonnage.Il appert que les minéralisations et les résidus miniers restés sur place peuvent constituer la principale source de pollution des eaux de surface de la région de Zeïda.The Upper Moulouya Basin was the location of extensive lead mining between 1930 and 1985, with three major operations near Aouli, Mibladen and Zeïda. The Moulouya drains about 7.5% of the Moroccan territory and provides drinking and irrigation water to many communities over its more than 500 km path. It is thus important to determine the impact of past mining activities on its water quality, since the mining sites were abandoned with little or no rehabilitation. This paper focuses on the Zeïda area, the uppermost of these mining centres on the Moulouya.About 630,172 t of lead concentrates (40‑70% Pb) were produced between 1972 and 1985 at Zeïda. Lead was mined from carbonate and sulphide mineral deposits (cerussite, 70%; galena, 30%) mixed with barite in stratiform ore bodies hosted by Permo-Triassic arkoses. Mining left 12 Mt and 70 Mt of tailings and wastes in fully exposed piles on each side of the Moulouya, as well as a dozen water-filled open-stopes. Mine drainage is of neutral pH, thanks to the low content of residual sulphide minerals and the availability of carbonate in the tailings and host rock. The river and some quarry-lakes are tapped to fulfill domestic, agricultural and stock-breeding needs. One lake is used to directly feed Zeïda’s water network (pop. 3,000), without any water treatment.The Moulouya, upstream and downstream of Zeïda, and four lakes were sampled twice in 2002 (dry period: February; wet period: April). Temperature, electric conductivity (EC), Eh and pH were measured in the field. Samples were filtered through 0.45 µm membranes. The filtrates were preserved with 4% HNO3 and kept at 4°C until analysis. The filters and their particulate fraction, as well as a composite sample of the tailings, were dried and kept dry until dissolution and analysis. All measurements were performed by ICP-MS and capillary electrophoresis analyses.Lead and arsenic are well above « normal » concentrations in the tailings, at 5,547 g/t and 192 g/t, respectively. These elements are clear threats to population health, since dust from unstabilized tailings can be dispersed by wind and rain waters, contaminating agricultural soils and surface waters, and eventually leading to cases of saturnism or arsenical intoxication in the population. All Pb and As concentrations measured in the waters sampled are above the World Health Organisation criteria for drinking water (10 µg/L for Pb and As). Nevertheless, about half of these measurements meet the Moroccan criteria (50 µg/L). All samples show near neutral or slightly basic pH values (7.2-8.9). EC is also high (> 1,000 µS/cm).As and Pb are largely associated with the particulate fraction (> 80% of total As and Pb), except for As in two lakes (< 40%). Overall, their concentrations are higher in the Zeïda area than upstream in the Moulouya. However, this is a tendency rather than a rule, because the differences are often small (< 50%) and suffer exceptions. For instance, Pb concentrations are 60% lower than the so-called uncontaminated reference station, in two quarry-lakes sampled during the wet period. The occasional lack of significant and consistent contrast between an obviously degraded environment and a pristine site was unexpected. The results were therefore further investigated, in order to identify possible explanations for the apparent discrepancies.Coherency in the data set emerges when one considers the relative importance of dissolved and particulate transport in the various types of environments sampled. Using this interpretation scheme, EC is considered as an indicator of solute transportation, since EC is a function of dissolved ionic components. Total Pb is regarded as an indicator of particulate transportation, since Pb is strongly adsorbed to particulate substrates at the pH observed. Following these assumptions, particulate transport appears to dominate over dissolved transportation in the Moulouya. Total Pb increases by factors of 3.4 and 9.8 from dry to wet periods, whereas EC decreases by 0.7-0.8, as a result of rain dilution. In two of the four lakes, dissolved transport is comparatively more important, since EC does not change significantly and total Pb shows only a small increase from the dry to the wet period. In these lakes, the dissolved input during the rainy period appears to be large enough to keep EC at its previous value, without significant dilution, as opposed to what is going on in the Moulouya. In the two other lakes, both EC and total Pb decrease from the dry to the wet period, pointing to dilution effects greater than either dissolved or particulate mobilization.Apparent discrepancies in the intensity and direction of variations are explained when prevailing modes of dispersion are taken into account. For instance, the enrichment factor of total Pb in the Moulouya, downstream of Zeïda, jumps from 1.1 (dry) to 3.2 (wet), with respect to the reference station. Meanwhile, EC increases only from 1.2 (dry) to 1.5 (wet). The greater increase of total Pb over EC is explained by prevalent particulate transport. In another case, the enrichment of EC with respect to the reference station, in two lakes, increases from 14.2 and 20.4 (dry) to 20.1 and 27.9 (wet) while total Pb enrichment decreases from 2.0 and 2.0 (dry) to 1.6 and 1.3 (wet). Here, the prevalence of dissolved transport in these two lakes, combined with particulate transport at the reference station, allow for a strong increase in the EC parameter, concurrent with a weak increase in total Pb. Finally, in the lakes where both dissolved and particulate transport are presumably minor, total Pb undergoes enrichment with respect to the reference station, in the dry period (by 3.4 and 1.8), whereas depletion characterizes the wet period (0.6 in both lakes). In this case, enrichment is likely the result of evaporation during the dry season, and depletion the result of dilution by rain during the wet period. These two types of lake behave differently because they are located next to residual mineral deposits (likely with more soluble phases), have short travel distances and thus fewer contacts with adsorbing substrates, which is not the case for the other two lakes

Etude petrologique et geochimique des lamprophyres et roches associees de la region de Tamazert (Haut-Atlas de Midelt, Maroc)

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Perspectives de phytostabilisation par Jatropha curcas L. des résidus miniers de la mine de Zaida (Haute Moulouya, Maroc)

Growth performance of Jatropha curcas were investigated on various substrates of abandoned lead mine of Zaida (High Moulouya, Morocco). Jatropha curcas shows proper installation despite elevated levels of trace metals and metalloids precisely Pb, Cu, Zn and As in experimental substrates. The accumulation of trace metals and metalloids (TMM) in the different compartments of Jatropha curcas depends on the type of substrate (clay uncovering, tailings, control soil). The low rate of translocation of TMM in J. curcas gives great power of phytostabilization.Les performances de croissance de Jatropha curcas L. ont été étudiées sur divers substrats de la mine de plomb abandonnée de Zaida (Haute Moulouya, Maroc). Jatropha curcas montre une bonne installation malgré les teneurs élevées en Pb, Cu, Zn et As dans les substrats expérimentaux. L’accumulation des éléments traces métalliques (ETM) dans les différents compartiments de Jatropha curcas dépend du type du substrat sur lequel elle est plantée (argile de découvrement, résidus miniers, sol témoin). Le faible taux de translocation des ETM confère à Jatropha curcas un grand pouvoir de phytostabilisation.El Himer Sarah, Bouabdli Abdelhak, Baghdad Bouamar, Saidi Naima. Perspectives de phytostabilisation par Jatropha curcas L. des résidus miniers de la mine de Zaida (Haute Moulouya, Maroc). In: Ecologia mediterranea, tome 39 n°2, 2013. pp. 19-30

Les rejets miniers de traitement : caractérisation, capacité polluante et impacts environnementaux, mine Zeïda, mine Mibladen, Haute Moulouya (Maroc)

The aim of this study is to characterize the wastes of treatment abandoned at the mine sites Zeida and Mibladen (Upper Moulouya, eastern of Morocco).highlight the polluting capacity of these wastes and determine their environmental impacts taking into account climate semi-arid and geological context carbonate and silicate in the region. The results showed that the mining wastes at Zeida (RZ) and at Mibladen (RM) consist of fine particle size, have low geotechnical stability, highly mobile and exhibit high levels of toxic trace metals (MTE) (Pb: 5547ppm for RZ//10520ppm for RM). These wastes with alkaline pH are affected by intense water erosion and in particular wind erosion and they create multiple environmental impacts. lndeed, in addition to the negative impact on the landscape that they generate, MTE contained in these wastes are transported, spread and contaminate surface water resources and soil around: (water: Pb: 13-430g/1//Sediments Pb:33-2415ppm //Soils: Pb:71-566 ppm). However, we note that the risk of contamination related to chemical weathering from the studied wastes is reduced sequel on the one hand to the Jack of moisture in semi-arid climate favoring chemical reactions within the waste and second/y due to the abundance of carbonates and 1 or silicates in wastes and into the geological terrain of the region. Phenomena of acid mine drainage (AMD), in particular acidification of surface water and leachate, most remarkable phenomenon of AMD were detected anywhere in mining districts. This is the contaminated neutral drainage (CND) for mining wastes of Zeïda and Mibladen at upper Moulouya. Mechanical wind erosion is the main vector of the dispersion of suspended particles of contaminants from wastes studied.L'objectif de cette étude est de caractériser les rejets miniers de traitement abandonnés aux centres miniers Zeïda et Mibladen (Haute Moulouya, oriental du Maroc), de mettre en exergue la capacité polluante de ces rejets et déterminer leurs impacts environnementaux tenant compte du climat semi-aride et du contexte géologique dans la région. Les résultats ont révélé que les verses à rejets miniers à Zeïda (RZ) et à Mibladen (RM) sont constituées de particules de taille fine, de stabilité géotechnique faible, très mobiles et présentent des teneurs élevées en éléments traces métalliques toxiques (ETM) (Pb : 5547ppm pour RZ//10520ppm pour RM).Ces rejets à pH alcalin (8,4) subissent l'effet d'une intense érosion hydrique et en particulier éolienne et créent de multiples impacts environnementaux. En effet, en plus de l'impact paysager négatif qu'ils génèrent, les ETM contenus dans ces rejets sont transportés, disséminés et contaminent les ressources en eaux de surface et les sols aux alentours : (Eaux : Pb : 13-430µg/l//Sédiments : Pb : 33-2415ppm//Sols : Pb : 71-566 ppm). Toutefois, on note que le risque de contamination lié à l'altération chimique à partir des rejets miniers étudiés est réduit suite d'une part au manque d'humidité en climat semi aride favorisant les réactions chimiques au sein des rejets et d'autre part suite à l'abondance des carbonates et/ou des silicates dans les rejets et dans les terrains géologiques de la région. Les phénomènes du drainage minier acide (DMA), en particulier l'acidification des eaux de surface et des lixiviats, phénomène le plus remarquable du DMA n'ont été décelés nulle part au niveau des districts miniers. Il s'agit du drainage neutre contaminé (DNC) pour les rejets des mines Zeïda et Mibladen de la Haute Moulouya. L'érosion mécanique éolienne est le vecteur principal de la dispersion, à partir des rejets miniers étudiés, de particules en suspension contaminants

Heavy Metals in Tailings,Soils and Vegetation of an Abandoned Lead Mine Land in Morocco

The High Moulouya is a region where mining industry has been developed at the beginning of the 20th century. Residues generated from past mining activities have been dumped over the years as tailing ponds. The goal of this research was to determine the concentrations of three metal trace elements (MTE) in the tailings, in two plant species (Stipa tenacissima and Artemisia herba-alba) and soils surrounding these deposits. Lead, copper, and zinc have been specifically considered. Chemical analyses have been achieved using ICP-AES. Results showed significant concentration of Pb in mining residues and vegetation that colonize the surrounding area. Concentrations of the three heavy metals in soil and plant samples were minimal at 1 km from the piles of tailings. The maximum accumulation of metals within the 50-200 m zone suggests that the surrounding vegetation forms a wind erosion obstacle resulting in metal dust deposition.La Haute Moulouya est une région où l’exploitation minière a été développée depuis le début du XXe siècle. De ce fait, les résidus miniers générés par l’activité minière ont été disposés en haldes. Le but de cette recherche est de déterminer la quantité de trois éléments traces métalliques (ETM) dans les haldes, dans la végétation steppique et les sols avoisinant ces dépôts. Le plomb (Pb), le cuivre (Cu) et le zinc (Zn) ont été spécifiquement considérés. Les analyses chimiques ont été faites par ICP-AES. Les résultats d’analyse ont montré la présence de Pb en concentrations élevées dans les résidus miniers et dans la végétation qui colonise les sols avoisinants. Les concentrations en Cu, Pb et Zn dans les échantillons de sols et de plantes sont minimales à 1 km des haldes. L’accumulation maximale des métaux dans la zone 50-200 m suggère que la végétation environnante forme un obstacle à l’érosion éolienne qui provoque le dépôt de la poussière métallique.Baghdad Bouamar, Naimi Mustapha, Bouabdli Abdelhak, Sonnet Philippe, Lutts Stanley. Heavy Metals in Tailings,Soils and Vegetation of an Abandoned Lead Mine Land in Morocco. In: Ecologia mediterranea, tome 32,2006. pp. 85-91