Assessing the Effect of Intensive Agriculture and Sandy Soil Properties on Groundwater Contamination by Nitrate and Potential Improvement Using Olive Pomace Biomass Slag (OPBS)

Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/ 4.0/). -- (This article belongs to the Special Issue Biomass—a Renewable Resource for Carbon Materials)The relationship between agricultural activities, soil characteristics, and groundwater quality is critical, particularly in rural areas where groundwater directly supplies local people. In this paper, three agricultural sandy soils were sampled and analyzed for physicochemical parameters such as pH, water content, bulk density, electrical conductivity (EC), organic matter (OM), cation exchange capacity (CEC), and soil grain size distribution. Major and trace elements were analyzed by inductively coupled plasma-optical emission spectrometry (ICP/OES) to determine their concentrations in the fine fraction (FF) of the soils. Afterward, the elemental composition of the soils was identified by X-ray powder diffraction (XRD) and quantified by X-ray fluorescence (XRF). The surface soil characteristics were determined by the Brunauer–Emmett–Teller (BET) method, whereas the thermal decomposition of the soils was carried out using thermogravimetric analysis and differential scanning calorimetric (TGA-DSC) measurements. The morphological characteristics were obtained by scanning electron microscopy (SEM). Afterward, column-leaching experiments were conducted to investigate the soil’s retention capacity of nitrate (NO−3). Parallelly, a chemical and physical study of olive pomace biomass slag (OPBS) residue was carried out in order to explore its potential use as a soil additive and improver in the R’mel area. The OPBS was characterized by physicochemical analysis, assessed for heavy metals toxicity, and characterized using (XRD, XRF, SEM, and BET) techniques. The results show that the R’mel soils were slightly acidic to alkaline in nature. The soils had a sandy texture with low clay and silt percentage (<5% of the total fraction), low OM content, and weak CEC. The column experiments demonstrated that the R’mel irrigated soils have a higher tendency to release large amounts of nitrate due to their texture and a higher degree of mineralization which allows water to drain quickly. The OPBS chemical characterization indicates a higher alkaline pH (12.1), higher water content (7.18%), and higher unburned carbon portion (19.97%). The trace elements were present in low concentrations in OPBS. Macronutrients in OPBS showed composition rich in Ca, K, and Mg which represent 10.59, 8.24, and 1.56%, respectively. Those nutrients were quite low in soil samples. Both XRD and XRF characterization have shown a quasi-dominance of SiO2 in soil samples revealing that quartz was the main crystalline phase dominating the R’mel soils. Oppositely, OPBS showed a reduced SiO2 percentage of 26,29% while K, Ca, and P were present in significant amounts. These results were confirmed by XRF analysis of OPBS reporting the presence of dolomite (CaMg, (CO3)2), fairchildite (K2Ca (CO3)2), and free lime (CaO). Finally, the comparison between the surface characteristic of OPBS and soils by BET and SEM indicated that OPBS has a higher surface area and pore volume compared to soils. In this context, this study suggests a potential utilization of OPBS in order to (1) increase soil fertility by the input of organic carbon and macronutrients in soil; (2) increase the water-holding capacity of soil; (3) increase soil CEC; (4) stabilize trace elements; (5) enhance the soil adsorption capacity and porosity

Integrated assessment of groundwater quality beneath the rural area of R'mel, Northwest of Morocco

This study evaluates the effect of anthropogenic activities on the quality of groundwater beneath a rural area (R'mel area) located in the perimeter of Loukkos, Northwest Morocco. Ten public wells for drinking water were sampled and characterized for physicochemical parameters, heavy metals and pesticides occurrence. Multivariate Statistical Analysis (MSA), Water Quality Index (WQI) and geographic information system (GIS) were employed to identify the sources of groundwater pollution, the suitability for drinking purposes and the groundwater quality distribution within the R'mel aquifer. The results showed that almost all the samples had concentrations of NO3− and Ca2+ exceeding the WHO limits set at 50 mg/L and 75 mg/L, respectively. The heavy metal content was very low in the groundwater except for arsenic which exceeded the WHO threshold of 10 μg/L in four locations. Nine pesticides including Atrazine, Trietazine, Terbutryn, Chlorpyriphos ethyl, Endosulfan sulphate, Endosulfan alpha, Endosulfan beta, Metribuzin and Metolachlor were detected in four sites. However, no pesticides exceeded the standard of 0.1 μg/L set by the European Union. The Principal Component Analysis (PCA) demonstrated that the R'mel groundwater was exposed to two types of pollution that depend on groundwater redox conditions, the first being defined as the release of geogenic/anthropogenic As under reducing conditions (minor pollution), while the second represents the nonpoint source pollution from agriculture (major pollution). The Hierarchical Cluster Analysis (HCA) has classified the samples into four clusters reflecting the rate of groundwater mineralization in the study area. Differently to HCA, the WQI has generated three groups. The comparison between WQI and HCA showed that the combined use of the two methods may lead to a better classification of groundwater samples. The spatial distribution of NO3− and WQI indicated the areas affected by irrigated agriculture, and the impact of anthropogenic activities on the R'mel groundwater has been assessed. © 2021 Elsevier B.V.Oficina de Cooperación al Desarrollo, Universidad de Sevill

Gestions alternatives de la ressource en eau : Approches territoriales

Coordination éditoriale : Pierre-Gil Salvador Coordination éditoriale pour la rubrique varia : Philippe Deboud