Water and Soil Physico-Chemical Characteristics in Ibex Reserve: An Environmental Case Study of Houta Bani Tamim

Abstract

Protected areas are essential for conserving biodiversity and sustaining ecosystems, yet their effective management requires a clear understanding of soil and water quality, which underpin ecological processes. This study evaluated 15 soil and seven water samples to assess their physico-chemical properties, focusing on heavy metal concentrations. Results showed that soils were generally neutral to alkaline, with Hashwan-2 exhibiting the highest concentrations of calcium (26.5 meq/L), magnesium (11.2 meq/L), carbonates (0.32 meq/L), bicarbonates (3.66 meq/L), and chloride (35.43 meq/L). Heavy metal analysis indicated elevated nickel (51.628 mg/kg) and chromium (76.29 mg/kg) at Albuyitlar-2, and chromium (68.015 mg/kg) at Shabak-Mateam-1 1 1, exceeding US-EPA permissible limits of 45 mg/kg for nickel and 64 mg/kg for chromium. Water samples revealed high levels of aluminum (12.681 mg/L), manganese (0.146 mg/L), and iron (7.055 mg/L), also exceeding the US-EPA thresholds of 0.2, 0.1, and 0.5 mg/L, respectively. In contrast, more toxic metals such as arsenic, cadmium, lead, and mercury remained within safe limits. These findings highlight localized concerns regarding heavy metal contamination that warrant continued monitoring to ensure ecosystem health.

1. Introduction

The rising population poses inevitable pressure on the available natural resources, resulting in a significant disparity between the demand for resources and their availability [1]. At critical levels, this difference results in inequitable water utilization, leading to droughts and floods, and ultimately to water scarcity [2]. Similarly, soil is also at risk as a source of nutrients, a water-holding hub for plant growth, and an essential and complex integral part of the ecosystem. The unjustifiable use of soil is deteriorating the biological cycle. Due to impending concerns about soil and water resources, their preservation and sustainable management are crucial issues [3] for policymakers, ecologists, governments, and stakeholders, and predominantly for the well-being of life [4]. Soil and water chemical, biological, and physical properties are significant in contaminant transportation [5]. Pollutants disposed of in surface soils can migrate into groundwater, affecting water quality and ecosystem health [5,6]. Detailed investigations into soil-water interactions are necessary to understand the chemical composition of surface waters, particularly in areas with varying land use. The standard permissible doses of heavy metals (HMs) in soils and sediments for humans and animals are similar, as many studies have been conducted on laboratory animals and the potent impacts of HMs have been assessed. At the same time, the Environmental Protection Agency (EPA) has formulated varying standards for drinking water and aquatic life [7]. Furthermore, there are other available regulatory guidelines such as Saudi Standards, Metrology and Quality Organization (SASO), Gulf Standardization Organization (GSO) Gulf drinking/bottled water standards, and Ministry of Environment, Water & Agriculture (MEWA) Executive Regulations for Protection of Aqueous Media.

Protected or conservation areas are identified as nature reserves or national parks to help conserve and restore biodiversity [8,9,10] and supply ecosystem services to human societies [11]. Preserving the ecosystems in the central region of Tuwaiq’s mountains, without compromising their biodiversity and biological productivity, is the primary goal of the government for conservation areas. The Ibex Reserve Protected Area is primarily designed to preserve and ensure the reproduction of threatened and other key species, such as the Nubian ibex (Capra nubiana) and the mountain Gazelle (Gazella gazella). Other ecological aspects, such as groundwater recharge, rehabilitation of damaged habitats, and seed dispersal, are also important areas of interest. This reserve aims to enhance the welfare of local groups by providing nature-based recreation, eco-tourism, and scientific research opportunities. Adequate soil and water resources are a prerequisite for maintaining living groups of viable plant and animal species in vital regions of the Middle Tuwaiq Mountains.

Overgrazing, land-use transformations, resource extraction, and increasing urbanization are the environmental stressors in the Ibex Reserve that alter the natural water movement and recharge of groundwater [12]. Climate change also leads to such issues as intensifying the drought of the environment, shifting the pattern of precipitation, and reducing the resilience of the ecosystem [3]. The combination of these stresses and a growing human population leads to an unbalanced correlation between supply and demand, often leading to inequitable water distribution, water shortage, and ecosystem vulnerability [7,8].

The health and sustainability of an ecosystem revolve around soil and water physicochemical properties. They regulate contaminant flow, influence nutrient cycling, and determine water quality [11]. Ecological and health risks of heavy metals are acute because these substances settle in soils and sediments, move into groundwater, and biomagnify in flora and fauna [12,13]. Environmental policies like those set by the United States Environmental Protection Agency (EPA) give guidelines on safe exposure [14]. However, few studies have combined soil and water quality and health risk analyses in safeguarded arid areas.

The sustainable ongoing utilization of the Reserve for educational and recreational purposes will enable people to benefit from the sustainable use of natural resources. Among the top priorities, the reserve aims to save the Nubian ibex inhabiting the gorges of Wadi Hotat Bani Tamim. Wadi Hotat Bani Tamim is one of the most conspicuous natural valleys in the country, which is located in the Najd region of central Saudi Arabia, known for its spectacular limestone cliffs, seasonal streams, and desert vegetation, which offer the best shelter and pasture to wildlife. The topography and ecological diversity of the place render the environment a critical habitat to several endemic and rare species. However, the Nubian ibex population has decreased because of habitat destruction, excessive hunting, and human intrusion, which underscores the importance of the reserve in the conservation of the species and its rehabilitation to restore the ecosystem. The reserve is expected to safeguard the long-term existence of the Nubian ibex and the rest of the biodiversity in Wadi Hotat Bani Tamim through habitat conservation, anti-poaching programs, and ecological surveillance.

This study aims to evaluate the soil and water quality. Firstly, this research will determine the concentration of various elements in water and soil samples from the Ibex Reserve Protected Area, thereby comprehending the physicochemical properties of the reserve’s soil and water. Secondly, the health risk evaluation will be determined, which may occur when humans, animals, and plants are exposed to heavy metals or other toxins in the soil and water. There is a dire need to manage the rising problem of heavy metal pollution that is increasingly threatening the livelihood of the earth and water ecosystems in the region. Wadi Hotat Bani Tamim, with seasonal water streams and limestone-formed characteristics, is especially susceptible to pollution caused by the runoff of surrounding agricultural affairs, urban development, and industrial effluents. Lead, cadmium, and zinc are heavy metals that may find their way to soil and plant cover, thus getting into the food chain and ultimately impacting the health and reproductive success of sensitive species like the Nubian ibex. The need to tackle this environmental issue aligns with key research priorities in nature protection, restoration, and species conservation. Specific monitoring and remediation measures in this ecologically important valley are thus critical to preserving biodiversity and environmental resiliency in central Saudi Arabia.

This study is unique in combining a comprehensive assessment of soil and water physicochemical properties with a health risk evaluation of heavy metals in a protected arid ecosystem. By linking ecosystem quality with conservation management strategies, this research addresses an urgent gap in understanding how environmental stressors affect biodiversity and human well-being.

This study provides a novel contribution by integrating soil and water physico-chemical assessments with heavy metal risk evaluation in the Ibex Reserve. Specifically, it seeks to determine the current state of soil and water quality, evaluate heavy metal concentrations against international safety standards, and assess the associated ecological and human health risks. In doing so, the research asks: What are the key physico-chemical characteristics of soil and water in the Ibex Reserve? To what extent are heavy metals present and potentially hazardous? Moreover, how can the findings guide conservation policies and sustainable resource management in protected arid ecosystems?

2. Materials and Methods

The Ibex Reserve Protected Area spans an area of 1867 square kilometers, located 180 km south of Riyadh. This area has a heritage dating back to the Heritage Conservation Department, predating the National Center for Wildlife Development establishment. The reserve is located in the Emirate of Riyadh (Houta bin Tamim and Al Harik), at coordinates Latitude 23°27′ N and Longitude 46°30′ E. The general soil map indicates that the entire site is characterized by a rocky outcrop of ordinary desert crisp soil and ordinary dry limestone soil, with cliffs. A thin layer of deep Campanian sandy clay-skeletal soil lies under the cliff on the site’s western edge. The sampling strategy involved a stratified random sampling strategy to achieve a representative coverage of the environmental variations within the study area. The study area was initially subdivided into sub-regions (strata) according to topographical, land use, and underlying soil type visible differences using geological and soil maps (Figure 1). The stratum was further broken down into 1 km × 1 km grid cells, where individual sampling points were assigned randomly with the help of GIS-based random coordinate generation. This strategy ensured sites were data-rich regarding natural and anthropogenic gradients, e.g., distance to agricultural lands, urban settlements, and drainage networks, and reduced space bias.

To sample the soil, fifteen grid locations of the various strata were selected to cover the differences in soil texture and sources of contamination. Similarly, seven water sampling points were done on available surface-water bodies, drainage pathways crossing these strata. The random strata design gave a balanced spatial representation of the study area but retained the possibility of statistical comparisons of discrete geomorphological and land-use categories. This methodology is consistent with general environmental monitoring principles advised by the U.S. Environmental Protection Agency (EPA, 2002 [15]) and the World Health Organization (WHO, 2008 [16]), as it guarantees the representativeness and scientific rigor of the data.

2.1. Environmental Conditions

The two climatic seasons in the reserve are hot and dry summer, May–August, with temperatures reaching up to 40 °C, and cold winters, during which the temperatures on a night may sometimes reach freezing. Even though rainfall is low and there is a lack of precipitation, the region’s geomorphology allows water to be stored temporarily at the base of the valleys and in shallow depressions after seasonal rains. These micro-habitats are very important to the maintenance of the vegetation in the area, as the rainwater runs off the plateau and helps recharge the groundwater periodically. This moisture is favorable to a comparatively prosperous plant community of around 260–263 species, of which the prevalent ones are Acacia spp., perennial grasses, and other drought-resistant shrubs. The intermittent rainfall and groundwater recharge on this vegetation emphasize the sensitive nature of the hydrological processes and species of plants in the arid environment of the reserve.

2.2. Plant Species

Perennial species include many composite and cruciferous plants. Acacia tortilis predominates in the terraces and alluvial plains. Other plant species prevalent in the area are Panicum turgidum, Cenchrus ciliaris, Stipagrostis, Oropetium, Tripogon spp., and Haloxylon salicornicum. The reserve hosts over 260 plant species, with perennial shrubs, grasses, and Acacia species forming the dominant vegetation. In particular, Acacia tortilis plays a keystone role in stabilizing soils, providing shade, and supporting herbivore populations.

Table 1. Dominant Plant Species in the Ibex Reserve.

Species	Growth Form	Ecological Role	Habitat Preference
Acacia tortilis	Tree	Keystone species: soil stabilization, fodder, shade	Terraces, alluvial plains
Panicum turgidum	Perennial grass	Dune stabilizer; fodder resource	Sandy soils, dunes
Cenchrus ciliaris	Perennial grass	Drought-tolerant forage grass	Alluvial soils, plains
Stipagrostis spp.	Perennial grass	Soil binder; adapted to arid soils	Rocky slopes, sandy soils
Haloxylon salicornicum	Shrub	Salt-tolerant; prevents desertification	Saline/alkaline soils

summarizes the dominant species in the study area.

2.3. Sampling Mechanism

Soil samples were collected from 15 locations (Al-Faraa, Alzalaq-1, Hashwan-1, Hashwan-2, Shoaib Al-aswad, Aldakhil-1, Aldakhil-2, Shabak Mateam-1, Shabak Mateam-2, Albuyitlar-1, Albuyitlar-2, Hamit-1, Hamit-2, Ras-Alruhl, and Alwakf-1) from the surface layer (0–30 cm). A composite soil sample of the surface zone (0–30 cm) was taken at every sampling site. Three to five subsamples were collected in a radius of 5 m, at a depth of 0.30 cm, and extensively mixed to create a single representative sample of that site. This method reduces the variation in the area and offers a trustworthy forecast of the surface soils, particularly in contamination and nutrient distribution analyses.

One sample of water (around 1 L) was taken at each site location in a previously pre-cleaned polyethylene bottle and then divided in the laboratory according to measurements of physicochemical parameters (pH, electrical conductivity, total dissolved solids) and trace metals. The field did not acidify the samples since the sampling places were relatively near the laboratory and the samples could be processed immediately after they were taken, within a few hours of the collection period. Though it is generally advisable to in-field acidify using nitric acid to stabilize the dissolved metals, immediate transport and refrigeration were considered adequate to avoid substantial metal precipitation or adsorption before analysis.

Before ICP-OES analysis, the soil and water samples were ready according to the standardized procedures. In the case of soils, an accurate weight of air-dried, sieved (2 mm) material of soil (~1.00 g) was weighed into Teflon digestion vessels and subjected to closed-vessel microwave digestion with a 9 mL mix of concentrated HNO₃ and HCl (or HNO₃ HClO₄-HF in the event of complete digestion of silicates) using the manufacturer-provided microwave program (first ramp to 180 °C, then hold 15 min). Upon cooling, digests were diluted to 50 mL using the ultrapure deionized water and filtered using the 0.45 µm membranes if particulates were present. In the case of water samples, the samples were filtered (0.45 µm) and kept in the field by adding ultrapure HNO₃ to a pH of less than 2; an aliquot (usually 50 mL) was directly subjected to dissolved-metal analysis. In case of total (including particulate-bound) metals, unfiltered water aliquots were digested with HNO₃ using the hotplate or microwave digestion and adjusted to volume using deionized water.

The samples were taken only once in December 2023. About 500 g of soil was collected from each site, packed in a polythene bag, and transported to the laboratory for further analysis. The samples were air-dried (35 °C) for 72 h. After that, the samples were crushed and passed through a 2mm-sieve mesh. Water samples were collected from 07 (Aldakhil-1, Alfahili-2, Hashwan, Aldakhila-2, Alfahil-1, Tumir Hamayd-1, Tumir Hamayd-2) different points in plastic bottles, properly labeled, and transported to the laboratory for analysis.

2.4. Heavy Metals Determination Through Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES)

The analysis of heavy metals was done with the Inductively Coupled Plasma- Optical Emission Spectrometry analysis (ICP-OES) (PerkinElmer Optima 8000,Shelton, CT, USA). Acid-digestion of soil samples was done with a mixture of HNO₃-HClO4-HF 4-HF, and also water samples were filtered and acidified to a pH < 2. Calibration was done with certified multi-element standards, and the accuracy was checked using blanks, duplicates, and certified reference materials (ICP Multi-element standard solution certified reference material, Merck Life Science, Bayswater, Australia) ensures good quantitative results. The ICP-OES was calibrated in two complementary ways: external calibration, which was founded on multi-element standard solutions prepared using certified stock standards, and the standard addition method, used with selected samples to counter possible matrix interferences and confirm the consistency of external calibration results. Because we identified elements with varying concentration ranges, we used five multi-elemental acid-matched standards and one blank for calibration. All samples, blanks, and calibration standards were spiked with Yttrium (Y) at a 5 µg/L concentration. This internal standard (IS) was used to correct instrumental drift and matrix-induced signal variations during ICP-OES analysis [13].

2.5. Soil Analysis (pH, TDS, EC, Anions, Cations, and CaCO₃)

The soil pH was determined by preparing a 1:1 (w/v) soil-water suspension by mixing 10 g of air-dried soil with less than 2 mm deionized water (USDA Soil Survey Laboratory Methods Manual, 2014 [17]). The mixture was stirred and equilibrated at a standing position of 30 min, and pH was measured at a calibrated portable pH meter (buffers 4.00, 7.00, 10.00). Electrical conductivity (EC) was measured using a conductivity meter at 25 °C using the filtrate of the same suspension. The ISO 10390 [18] specifies a 1:5 ratio, but to take advantage of comparable procedures of the standard U.S. soil analysis and field-moisture condition, the 1:1 method was adopted. For this, soil samples were dried, crushed, and shaken with deionized water and filtered through a sieve. Next, the sample was loaded into the column, and ions were separated based on their retention rates. Finally, the conductivity reading was used to plot each ion, creating a chromatogram. The peaks under each ion are compared with calibrated standards.

The calcimeter method was used to measure CaCO₃ [14]. This method adds HCl to the sample in a pill vial, which is then sealed and placed in a pressure sensor. The sensor recorded the amount of CO₂ produced due to the reaction.

Soil organic matter (OM%) was determined by the method described by Walkley and Black [19]. 0.5 g of the soil sample was taken into a round-neck flask for this. Then 10 mL of potassium dichromate (1 N) was added, followed by concentrated sulfuric acid (20 mL). After that, the sample was allowed to stand for 30 min, and then 200 mL of distilled water, along with 3–4 drops of diphenylamine indicator, was added. Titration was carried out with a 0.5 M ferrous ammonium sulfate solution until the color changed from violet-blue to reddish-brown.

The soil samples’ total nitrogen (TN) and total phosphorus (TP) were analyzed according to the conventional wet-digestion protocols. A 0.5g of air-dried, sieved soil was digested with an H₂SO₄ H₂O₂ mixture. The Kjeldahl digestion method was used to determine TN, and the molybdenum blue method of colorimetry was used to determine TP. The concentration of nitrogen was assessed using an auto-Kjeldahl analyzer (e.g., Gerhardt Vapodest 500, C. Gerhardt GmbH & Co. KG, Königswinter, Germany). In contrast, phosphorus was assessed spectrophotometrically at 880 nm using a UV-Vis spectrophotometer (e.g., Shimadzu UV-1800, Shimadzu, Kyoto, Japan)—precision of the analysis. Procedural blanks, duplicates, and standard reference soils were analyzed with each batch to keep analytical precision.

2.6. Water Analysis (Physical Parameters pH, TDS, EC, and Turbidity)

The pH of the water was determined using the AHPA 4500-H+ B method, whereas the Total dissolved solids (TDS) in the water sample were determined by the standard procedure of the APHA 2540 C method. This method primarily assesses turbidity and is crucial for determining water quality [20]. The APHA 2510 B method was used to measure electrical conductivity; this method also establishes a relationship between electrical conductivity and temperature, essential for accurate solute identification [21].

2.7. Statistical Analysis

OriginPro 2023 and SPSS 27.0 were used to perform the statistical analyses. Measures of central tendency, such as mean, standard deviation, and coefficient of variation, were computed to assess the distribution of heavy metal contents and soil physicochemical characteristics. The difference in the mean concentrations of the metals in the sample sites was compared by one-way analysis of variance (ANOVA) followed by a post hoc test at 95% confidence (p < 0.05). Sampling locations were compared instead of with a reference (background) sample because there was no uncontaminated control site in the reserve. Spatial patterns were also determined by grouping landforms and determining the distance to the possible sources of contamination. Pearson’s correlation coefficients (r) were computed to test the associations between the heavy metals in soil and water and to determine the correlation between the metal concentrations and the soil properties, including the pH, EC, and organic matter.

3. Results & Discussion

3.1. Soil Properties (pH, TDS, EC, Anions and Cations)

The pH levels of the soil samples ranged from 6.72 to 7.92. The highest pH was measured in Shabak-mateam-2 (7.92), followed by Albuyitlar-1 (7.82). Among the 15 samples, seven showed a pH of ≥7.5, while eight showed a pH of <7.5. Overall, the soils were neutral to slightly alkaline; however, the lowest pH was recorded in Hashwan-2 (

Table 2. Soil properties (pH, TDS, EC, Anions and Cations).

Sample ID	${\mathit{N}\mathit{a}}^{1+}$ meq/L	EC ds/m	Cl− meq/L	${\mathit{S}\mathit{O}}_4^{2-}$ meq/L	${\mathit{H}\mathit{C}\mathit{O}}_3^{1-}$ meq/L	${\mathit{C}\mathit{O}}_3^{2-}$ meq/L	${\mathit{M}\mathit{g}}^{2+}$ meq/L	${\mathit{C}\mathit{a}}^{2+}$ meq/L	${\mathit{K}}^{1+}$ meq/L	${\mathit{N}\mathit{a}}^{1+}$ meq/L	EC ds/m
Al-Faraa	1.46	0.66	0.31	0	0.23	1.28	0.05	0.75	0.0319	159	7.1
Alzalaq-1	0.51	0.25	0.15	0	0.15	0.54	0.02	0.25	0.0124	66.3	7.75
Hashwan-1	3.62	2	0.93	0	1.06	3.7	0.21	2.14	0.1073	538	7.4
Hashwan-2	35.43	3.46	3.66	0.32	11.2	26.5	2.56	4.35	0.412	2060	6.72
Shoaib Al-aswad	2.97	1.32	0.5	0	0.95	2.26	0.16	1.37	0.0681	344	7.15
Aldakhil-1	0.51	0.25	0.15	0	0.15	0.54	0.02	0.25	0.0121	60.7	7.73
Aldakhil-2	33.06	3.81	2.77	0.28	5.92	16.4	7.62	12.96	0.4	2000	6.9
Shabak Mateam-1	0.49	0.29	0.13	0	0.11	0.49	0.02	0.3	0.0124	62.4	7.57
Shabak Mateam-2	0.84	0.39	0.19	0	0.18	0.78	0.03	0.42	0.0192	96	7.92
Albuyitlar-1	1.5	0.73	0.41	0	0.43	1.49	0.1	0.9	0.0377	189	7.82
Albuyitlar-2	4.12	2.21	0.95	0.01	1.3	3.83	0.24	2.28	0.0789	393	7.16
Hamit-1	0.76	0.35	0.16	0	0.16	0.62	0.03	0.41	0.016	80	7.81
Hamit-2	3.14	1.12	0.54	0	0.41	2.73	0.09	1.42	0.0658	329	7.5
Ras Alruhl	7.56	2.56	0.8	0	1.92	3.25	0.72	4.48	0.1454	728	7.05
Alwakf-1	1.98	0.95	0.51	0	0.65	1.63	0.11	0.9	0.0436	219	7.14
p value	0.011	0.292	0.058	0.001	0.017	0.022		0.037	0.021	0.021	0.595
Max	35.43	3.81	3.66	0.32	11.2	26.5	7.62	12.96	0.412	2060	7.92
Min	1.98	0.25	0.13	0	0.11	0.49	0.02	0.25	0.0121	60.7	6.72
Mean	6.53	1.357	0.811	0.041	1.655	4.403	0.799	2.212	0.098	488.293	7.381

). Total dissolved solids (TDS) comprise inorganic salts: calcium, magnesium, potassium, sodium, bicarbonates, chlorides, and sulfates. In our study, TDS varied from 60.7 mg/kg in Aldakhil-1 to 2060 mg/kg in Hashwan-2. A 2000 mg/kg TDS content was observed in Aldakhil-2, the second-highest (Table 2). Electrical conductivity of Hashwan-2 was highest (0.412 ds/m), followed by Aldakhil-2 (0.4 ds/m). Lowest EC was observed in Aldakhil-1 (0.0121 ds/m).

We measured the concentration of four cations, namely Na⁺¹, K⁺¹, Ca⁺², and Mg⁺². The highest concentrations of Na⁺¹ and K⁺¹ were in Aldakhil-2, at 12.96 meq/L and 7.62 meq/L, respectively, while Ca⁺² and Mg⁺² were maximum in Hashwan-2, which also showed the highest TDS and EC (Refer to Table 2).

Soil and water conservation are significant in attaining sustainable development goals [22,23,24]. Soil and water chemical properties were analyzed in detail and compared against various internationally recognized guidelines. Soil pH is a key variable, as it controls various chemical and biochemical processes in the soil environment. Soil pH measures the soil’s acidity or alkalinity, which governs the availability of nutrients to plants. It controls the mobility, availability, and translocation capability of elements existing in various chemical forms in the soil. The Ibex Reserve Protected Area soil sample had a mean pH of 7.38, while the water sample had a pH of 7.66, indicating a neutral to slightly alkaline environment.

3.2. Soil Organic Matter (OM%), Total Phosphorus (TP), Total Nitrogen (TN), and Calcium Carbonate

In the Ibex Reserve Protected Area, the organic matter content ranges from 0.024% to 0.37%. The highest OM was present in Alfaraa and Alwakf-1, at 0.37%, followed by Albuyitlar-1 (0.34%) and Hamit-2 (0.32%). At the same time, many sites, such as Hashwan-1 (0.07%), Hashwan-2 (0.053%), Shueayb-Al-Aswad (0.03%), and Ras-alruhi (0.024%), showed OM < 1. Meanwhile, all other sites have OM > 1, as shown in

Table 3. Descriptive statistics for soil chemical elements.

Sample ID	Organic Matter (OM) %	Total Phosphorus (TP) mg/kg	Total Nitrogen (TN) %	Calcium Carbonate %
Al-Faraa	0.37	<LOD	0.16	<LOD
Alzalaq 1	0.15	0.29	<LOR	<LOD
Hashwan 1	0.07	0.43	0.24	<LOD
Hashwan 2	0.053	0.33	0.31	<LOD
Shoaib Al-aswad	0.03	0.37	<LOR	<LOD
Aldakhil 1	0.15	0.29	<LOR	<LOD
Aldakhil 2	0.145	0.52	0.37	<LOD
Shabak Mateam 1	0.25	0.26	0.07	<LOD
Shabak Mateam 2	0.15	0.04	0.05	<LOD
Albuyitlar 1	0.34	0.62	0.16	<LOD
Albuyitlar 2	0.17	0.83	<LOR	<LOD
Hamit 1	0.22	0.63	0.09	<LOD
Hamit 2	0.32	0.41	0.24	<LOD
Ras Alruhl	0.024	0.41	0.19	<LOD
Alwakf 1	0.37	0.13	0.17	<LOD
Maximum	0.37	0.83	0.37
Minimum	0.024	0.04	0.05
Average	0.187	0.397	0.186

.

Previous studies have reported that the water and soils of sites in SA fell within the range of 6.8 to 8.4 [25]. The average soil pH value is previously reported as 7.64 for the Riyadh region [26], while [27] reported pH as 7.7 and average EC values as 1.03 dS/m in Riyadh. The dissolved soil minerals and irrigation water are the primary sources of salts; moreover, the weathered limestone and arid climate prevalent in the Riyadh region result in more evaporation than precipitation. Refs. [26,27] attributed these factors to increased pH and alkalinity in the area.

In our study, the values were also within an acceptable range of 6.5–9 for water and 8.5 for the soil. pH also provides details about the cation mobility. Refs. [28,29] showed that the solubility of heavy metals is highly dependent on soil pH. Higher pH (in alkaline soils) is not favorable for the transfer of heavy metals in soils [30], and it prevents heavy metals from being taken up by plants through the soil [31]. On the other hand, acid soils tend to favor the translocation of heavy metals. Due to these factors, the soils of the Inex reserve, being alkaline in nature, ensure minimal transport of heavy metals. Electrical conductivity is a measure of dissociated ionic species, dissolved substances, and salts (organic and inorganic).

EC provides the mobility of ionic species due to the presence of dissociated ions, and it is dependent on the correlation between fixed residues in water. It also entailed precipitation, terrestrial vegetation, and geological substrate types [32]. We observed variable TDS in both soil and water. The mean TDS in the soil was 488 mg/kg, and 282.2 mg/L in the water. Previously, refs. [33,34] have highlighted TDS levels exceeding 1000 mg/L in cities of SA. Our results showed a concentration far below that of previous studies or the EPA permissible limits, because the Ibex Reserve Protected Area is not significantly influenced by anthropogenic activities, unlike cities, where pollution and industrialization are increasing. Soil’s physical and biological characteristics are influenced by organic matter in that area due to the native flora and fauna [35,36,37]. The presence of salts or the salinity behavior is a measure of the total dissolved solids in water. Reference [16] has outlined permissible limits for drinking water, and for TDS it should not be >500 mg/L. In our water samples, the TDS values ranged from 121.5 to 627 mL/L with a mean of 282.21 mg/L (Table 3). These values were far below the limits described by USEPA (5000 mg/L). Previously, studies have claimed that in Saudi Arabia, groundwater samples showed varied TDS from 130 to 6000 mg/L [25], which exceeded the guidelines of Saudi Standards Metrology and Quality Organization (SASO) (2000) [38] and Gulf Cooperation Council Standards-GCCS (1993) [38], while 50% of samples exceeded EPA limits 2012. A similar report was made by refs. [33,34,39], who reported that TDS in groundwater exceeded 1000 mg/L in Hail and other cities of Saudi Arabia. TDS showed a direct relationship to EC, as EC is a function of dissolved mineral matter content in the water. We observed the highest TDS in the sample collected from Tumir Hamayd2 at 627 mg/L, and a similar sample also showed the highest EC at 1246 µs/cm.

3.3. Heavy Metals in Soil Samples

The soil analysis for heavy metal content determined the concentration of 12 elements. Their concentration was compared to their respective limits as outlined by USEPA. Our results showed that the soils of Awal-Reserve contained metal elements in the following order: Fe > Al > Mn > Cr > Zn > Ni > Cu > Co > Pb > As > Mo > Cd (

Table 4. Heavy metal concentration in soil collected from 15 different locations of Awal-Reserve.

Sample ID	Al mg/kg	As mg/kg	Mo mg/kg	Zn mg/kg	Pb mg/kg	Cd mg/kg	Co mg/kg	Ni mg/kg	Mn mg/kg	Fe mg/kg	Cr mg/kg	Cu mg/kg
Al-Faraa	3363	0.21	0.79	12.62	3.23	0.146	0.753	8.791	93.11	5604	15.898	5.258
Alzalaq 1	2480	0.48	1.2	12.61	1.74	0.281	0.247	6.001	77.52	4629	13.571	5.391
Hashwan 1	2743	1.24	1.05	13.77	1.9	0.1	0.441	6.066	83.98	5206	13.446	4.483
Hashwan 2	4548	2.61	0.55	19.55	2.69	0.09	1.942	13.672	112.24	6840	22.272	9.052
Shoaib Al-aswad	4849	2.04	1.03	17.08	3.1	0.096	2.166	15.423	148.58	9169	28.878	8.965
Aldakhil 1	5832	1.56	0.83	41.7	4.33	0.899	4.652	30.113	228.24	13648	43.821	13.502
Aldakhil 2	5941	3.13	0.97	24.97	4.62	0.138	3.847	26.383	170.73	10884	41.184	12.011
Shabak Mateam 1	6855	3.14	1.68	27.21	7.73	0.052	12.206	21.012	324.89	38808	68.015	14.689
Shabak Mateam 2	5126	3.08	1.19	34.83	5.3	0.161	1.973	14.385	146.03	8344	23.409	20.517
Albuyitlar 1	6898	4.34	1.09	28.69	8.52	0.02	10.96	18.583	435.86	41279	60.859	13.339
Albuyitlar 2	7283	4.94	0.8	58.93	8.26	0.111	9.812	51.628	413.03	24122	76.29	20.908
Hamit 1	6556	3.95	1.22	24.61	2.65	0.063	2.891	22.414	157.95	9936	35.9	9.413
Hamit 2	7882	3.3	0.05	57.46	2.84	0.038	16.855	27.145	711.07	28063	57.495	25.648
Ras Alruhl	20	2.53	0.15	2.48	0.56	0.045	0.757	0.136	0.761	11.68	1.033	0.515
Alwakf 1	2.36	2.75	0.2	0.09	0.05	0.023	0.82	0.111	0.001	1.79	0.143	0.153
p value	0.103	0.042	0.295	0.517	0.170	0.087	0.595	0.786	0.175	0.825	0.591	0.305
Limit	-	17	4	200	70	3.8	20	45	-	-	64	63
Maximum	7882	4.94	1.68	58.93	8.52	0.899	16.855	51.628	711.07	41279	76.29	25.648
Minimum	2.36	0.21	0.05	0.09	0.05	0.02	0.247	0.111	0.001	1.79	0.143	0.153
Average	4691.891	2.62	0.853333	25.10667	3.834667	0.150867	4.688133	17.45753	206.9328	13769.7	33.48093	10.92293

). The comparison between the observed heavy metals and permissible limits is shown in Figure 2 and Figure 3.

Both the samples were within safe limits as described by USEPA; however, previously, samples from Saudi Arabia had shown EC (2239 μS cm⁻¹) values exceeding the [38]. We also measured Ca, Mg, and Na in waters from the Ibex Reserve Protected Area. The order of cations was Na > Ca > Mg. The concentration of these ions is highly influenced by the lithology of the rocks rather than anthropogenic activities [40]. Overall, the mean organic matter content was lower than 0.5%. We observed a mean of 0.18% organic matter in the Ibex Reserve Protected Area, which is significantly lower than the limits set by the US EPA. Organic matter content is correlated with agricultural practices and the richness of microbes, for example, in the southwest of Saudi Arabia (Al-Baha Region, Baljurashi district), which has a high organic matter content of 0.13 to 2.56%, due to restoration practices in the area [41]. The concentration of heavy metals in soil was assessed, and the results are presented in the table. Our results showed that all soil samples contained heavy metals. The As concentration ranges from 0.21 to 4.94 mg/kg and is within the permissible range the US EPA gives (17 mg/kg). It is worth noting that higher arsenic contents in soils are associated with increased weathering of rocks, agricultural activities, and seawater inputs [42]. Meanwhile, [43] stated that high arsenic levels indicate metal contamination, mainly due to industrial releases near the area. Cadmium content ranged from 0.02 to 0.899 mg/kg, which was also very low compared to the limits described by the US EPA (3.8), thus affirming that the soils of the Ibex Reserve Protected Area are below toxicity levels. Similarly, the Pb concentration (3.83 mg/kg) was also lower and within the safe zone, as it lies below the limits described by the US EPA (70 mg/kg) Figure 2 and Figure 3.

These results address the second objective by demonstrating that heavy metal concentrations, including arsenic, cadmium, and lead, remain below toxicity thresholds, minimizing environmental and health risks within the reserve. Hence, the potable water resources are surface water, groundwater, treated wastewater, and desalinated seawater [39]. Therefore, it is crucial to maintain water quality standards in the protected areas, too. Aly et al. [44] also reported Co, Cd, Cu, Cr, Mn, Fe, Pb, Ni, and Zn in 62 samples obtained from Riyadh and Al-Ahsa regions, and their concentration was 0.01–2.0 mg/L. In another study, 180 water samples were collected from Riyadh. The authors revealed the presence of Cu, Cr, Pb, Mn, and Fe in safe limits [31].

Arsenic (As) also showed different concentrations across 15 locations, with the highest concentration in Albuyitiar, followed by Albuyitiar 2, Hamit-1, Hamit-2, and Aldakhil. Alzalaq 1 and al-Faraa showed the lowest concentration; however, both were statistically comparable. Cd was highest in Aldakhil 1, at 0.89 mg/kg, while all the remaining locations showed lower concentrations and were statistically equivalent. Pb differed significantly, and the most exposed area to Pb pollution was Albuyitiar 1 (8.52 mg/kg), followed by Albuyitiar-2 (8.26 mg/kg). At the same time, all other locations showed a moderately significant difference in Pb concentration. Cr, Co, Cu, Fe, Mn, Mo, Ni, and Zn showed a non-significant difference across all the tested locations.

3.4. Water Analysis

Water quality parameters for seven samples across the Ibex Reserve Protected Area were measured. It was observed that the water pH ranged from 7.24 to 7.99, with a mean pH of 7.65, indicating that the water was neutral to alkaline in nature. Total soluble solids and EC were highest in Tumir-hamayd-2, at 627 mg/L and 1246 ds/m, respectively. In our study area, the average water turbidity was 3.88, which was significantly lower than the limits described by the USEPA; however, Alfahil-1 showed much higher turbidity (21.1) compared to all other sites (

Table 5. Physical and chemical properties of water samples.

Sample ID	pH	TDS	EC	Turb.	Ca	Mg	Na
Aldakhil 1	7.81	330	659	0.8	23.646	16.636	79.62
Alfahili2	7.57	121.5	243	2	21.284	7.357	13.552
Hashwan	7.64	181	362	1.3	21.903	12.672	51.802
Aldakhila2	7.99	162	322	1.2	18.695	9.518	22.619
Alfahil 1	7.53	133	265	21.1	21.449	6.316	9.993
Tumir Hamayd1	7.24	421	843	0.6	21.855	12.656	50.968
Tumir Hamayd2	7.81	627	1246	0.2	24.167	4.198	10.94
p Value	0.904	0.509	0.501	0.025	0.592	0.812	0.663
Maximum	7.99	627	1246	21.1	24.167	16.636	79.62
Minimum	7.24	121.5	243	0.2	18.695	4.198	9.993
Average	7.655714	282.2143	562.8571	3.885714	21.857	9.907571	34.21343

and

Table 6. Heavy metal concentration in water samples collected from seven different locations at Ibex Reserve Protected Area.

Sample ID	Al	S	As	Mo	Zn	Pb	Cd	Co	Ni	B	Mn	Fe	Cr	Cu
Aldakhil-1	0.019	242	0.012	0.001	0.004	0.002	0	0.004	0.001	0.923	0.001	0.008	0.001	0.001
Alfahili-2	0.07	30.02	0.013	0	0	0.001	0	0.003	0.003	1.121	0.074	0.062	0.002	0
Hashwan	0.029	100.39	0.014	0.002	0	0.001	0	0.004	0	0.856	0	0.007	0.001	0.001
Aldakhila-2	0.045	46.388	0.012	0.001	0	0.001	0	0.003	0.003	1.059	0.002	0.001	0.001	0.002
Alfahil 1	0.131	16.463	0.004	0	0.002	0.003	0	0.004	0.002	1.138	0.146	0.032	0.002	0.001
Tumir-hamayd-1	0.021	99.667	0.002	0.002	0.001	0.001	0	0.004	0	0.862	0	0.01	0	0.001
Tumir-Hamayd-2	12.681	2.797	0	0.002	0.014	0.005	0	0.002	0.018	0.001	0.09	7.055	0.033	0.008
p value	0.955	0.544	0.165	-	0.943		-	0.939	0.975	0.872	0.677	0.954	0.65	0.945
Limit	0.2		0.15		0.12	0.01	0.000025	0.05	0.05		0.1	0.5	0.05	0.05
Maximum	12.681	242	0.014	0.002	0.014	0.005	0	0.004	0.018	1.138	0.146	7.055	0.033	0.008
Average	1.856	76.81	0.008	0.0011	0.003	0.002	0	0.0034	0.0038	0.8514	0.0447	1.025	0.0057	0.002

), indicating that there might be higher concentrations of solid/suspended particles in the water.

The occurrence of heavy metals in soil and water is due to both natural and anthropogenic processes. Igneous and sedimentary rocks are the most common natural sources of HMs [45]. Industrial advancements, such as the burning of fossil fuels, industrial dust, and urban runoff, are the most common sources of increasing lead, nickel, chromium, and mercury [46]. Several studies indicate that natural sources of HMs in the environment are mostly of modest relevance [47].

Water quality is affected by the release of various elements, especially those from aquifers, which are influenced by their interaction with the surrounding rocks. Rock-water interaction is the primary cause of arsenic release. Arsenic is also known as the “king of poisons”; however, the soil and water in the Ibex Reserve Protected Area have less arsenic and are far below the limits of 4.94 mg/kg and 0.15 mg/L for soil and water, respectively. However, critical follow-up at regular intervals must be carried out, as arsenic is found in natural water bodies in two forms, arsenite and pentavalent arsenic [48], which may prevail in nature over time.

Heavy metals determined in the Ibex Reserve Protected Area water were subjected to Pearson’s correlation, and a scatter matrix was generated (Figure 4). The results showed that some metals were highly correlated with each other. As depicted in Figure 4 a strong and positive correlation existed between Co and S (r = 0.58), B and As (r = 0.58), Cu and Zn (r = 0.93), Cr and Zn (r = 0.95) Fe and Zn (r = r = 0.95) Pb and Zn (r = 0.92), Ni and Pb (r = 0.85), Pb and Fe (r = 0.86), Pb and Cr (r = 0.87), Pb and Cu (r = 0.84), similarly a strong and negative correlation existed between B and Zn (r = −0.92), Co and Ni (r = −0.88), Bo and Cu (r = −0.94).

The water quality assessment is of significant importance, especially in areas where water resources are scarce, such as Saudi Arabia, which is considered one of the world’s poorest water countries due to its annual rainfall of less than 100 mm. Hence, the potable water resources include surface water, groundwater, treated wastewater, and desalinated seawater [44]. Therefore, it is crucial to maintain water quality standards in the protected areas. Previously, it has been reported that water from aquifers is of good quality, apart from a few areas [49]. In a report, the total dissolved solids were estimated as 1000 mg/L, dominated by Ca²⁺ and HCO³⁻ [50].

Also reported were Co, Cd, Cu, Cr, Mn, Fe, Pb, Ni, and Zn in 62 samples obtained from the Riyadh and Al-Ahsa regions, with concentrations ranging from 0.01 to 2.0 mg/L. In another study, 180 water samples were collected from Riyadh. The authors revealed the presence of Cu, Cr, Pb, Mn, and Fe in safe limits [51].

The overall soil condition of the Ibex Reserve Protected Area is in a safer zone; however, a few areas are prone to heavy metal stress, as their concentration exceeds the permissible limits (Table 4). At sites where the heavy metal content is increasing over time, plant species with high bioaccumulation characteristics can be planted to safely extract pollutants. To conserve water quality, the governing authorities of the Ibex Reserve Protected Area must formulate strict regulations to restrict industrialization near the reserve.

Correlation coefficients are essential for estimating the relationship between the sources of heavy metals and their strength of relationship with each other [52]. Our results align with those of ref. [53], who stated a strong positive correlation between Cr and Ni, Cr and Zn, Cr and Mn, and Cu and Mn. However, in our case, we observed a strong negative correlation between Co and Ni, but ref. [53] showed a strong and positive correlation between the two metals. The positive relationship suggests that these metals originate from natural crystal sources, occurring through the natural weathering process [54]. Negative correlations were also observed, as depicted in Figure 4. The difference suggested that negatively correlated elements may have different origins.

4. Conclusions

Ibex Reserve National Park has maintained its diversity, and species preservation can be successful if the governing agencies implement proper management strategies. No doubt the soil and waters of the reserve are in safe zones and not polluted to a great extent, but careful considerations are still required, especially in the vicinity of Tumir Hamayd-2 because the water samples showed ample concentrations of aluminum and iron, along with high TDS and EC. Albuyitlar-2 soils had the highest nickel and chromium contents. As other toxic heavy metals can bioaccumulate, government agencies must make efforts to reduce their levels in soil and water.

This study on the Ibex Reserve Protected Area has several limitations that should be acknowledged. Firstly, the study was conducted during a single season (December 2023), which may not fully capture seasonal variations in soil and water properties. Secondly, the sample size, though representative, was limited to 15 soil sampling locations and seven water sampling points. A larger dataset with more extensive spatial coverage could provide a more comprehensive understanding of the area’s environmental conditions. Additionally, only surface soil samples (0–30 cm) were analyzed, which may not accurately reflect deeper soil layers where contaminants or nutrients could vary.

This research provides some implications for conservation management in the Ibex Reserve. The near-neutral to slightly alkaline pH of soils and waters affects the ecological balance. However, the low organic matter content suggests low soil fertility and microorganism activity. Management methods that should be promoted focus on organic enrichment, including mulching with vegetation remains, controlled use of compost, and promotion of native cover vegetation to improve soil health.

Even though the concentration of heavy metals was lower than international toxicity limits, the probability of accumulating heavy metals in the food chain makes it necessary to establish a long-term monitoring program. A program like this must feature seasonal sampling, multi-depth soil profiles, and increased spatial coverage to represent variability through the 1867 km² reserve. Early contamination warnings through bioindicators, like lichens, small mammals, or vital forage plants, would help to increase resilience to future pollution.

The water quality was determined to be within safe ranges, but the arid environment and the high rate of evapotranspiration increase the chances of salt build-up. Thus, management should adopt water-harvesting buildings, groundwater replenishment schemes, and efficacious irrigation techniques for local neighborhoods. Management of sustainable grazing in the form of rotational grazing and establishing exclusion areas would also mitigate the strain on weak soils and plants.

Moreover, conservation efforts must proactively reestablish habitats with the help of key species like Acacia tortilis and grass species that are resistant to drought (Panicum turgidum, Cenchrus ciliaris). Such species stabilize soils and provide fodder and shelter to herbivores, which enhances ecosystem services. Local communities can also be involved in conservation activities through eco-tourism projects or community education programs, and by enabling them to participate in land management to ensure that their livelihoods comply with the overall sustainability of the ecosystem.

This study provides the first integrated physico-chemical and heavy metal assessment of soils and waters in the Ibex Reserve, offering a baseline against which future changes can be monitored. Implementing the recommendations outlined above will help ensure that the reserve continues to function as a safe refuge for biodiversity and a model for sustainable resource management in arid protected areas.