1. Introduction

2. Study Area

3. Material and Methods

4. Results and Discussion

Distribution of Heavy Metals

The summary statistics of heavy metals (metalloids) concentration in the study area is presented very well. For instance, Table 1 and Figure 6 illustrate that a high concentration of As above the permissible limits of WHO was observed in different stations (including GW1, GW2, GW3, GW5, & so on) in the groundwater samples. The high concentration of As was found in GW8 (near) 201 µg/L, which is 200 times higher than the permissible limit, which is 10 µg/L (WHO, 2011). Half (50%) of the samples revealed very high concentration of As (above 10 µg/L) recorded in stations GW7(11.1 µg/L) (Merti camp near Shibo-gebi), GW5(18.1 µg/L) (Merti Kera compound), GW3(34.3 µg/L) (Merti Beret house), GW6(41.9 µg/L) (Abadir 4th camp), GW2(83.1 µg/L) (Merti near Buret area), GW1(116.1 µg/L) (Addis Ketema Mosque), GW12(117.2 µg/L) (AIP-10.2) and GW8(210 µg/L) (AIP-41). About 6 sites are located around Lake Beseka. Almost all are deep wells, while, the remaining 2 sites are piezometers and were showing extremely high values. These stations are found in Amibera Irrigation (state) farms. Both are piezometer stations and their water levels at the time of sampling were 1232 cm (AIP-10.2) and 167 cm (AIP-41) meters. In fact, some researchers investigated the extent of As in the Rift Valley (MER), in which 50% of the samples exceeded the permissible limit of 10µg/L (WHO, 2011). Arsenic may also be present in some groundwater sites within the southern Rift where sodium-bicarbonate geothermal waters exert an influence on groundwater quality, although no data are available to substantiate this.

Aluminum (Al), Iron (Fe), and Manganese (Mn)

The concentration of Al varied from 20.3 to 2615.2 µg/L, a low concentration of Al was observed at site GW10 (20.3 µg/L), whereas the highest Al concentration was found at GW12 (2615.2 µg/L). The major source of Al in groundwater might be the volcanic ash, weathering of aluminum-containing rocks such as bauxite. The Al concentration of 2615.2 µg/L was found in groundwater samples collected below LB at station GW12 (AIP12). Aluminum ions in other compounds also hydrolyze, and this continues until the cationic charge has run out, ending the reaction by hydroxide formation. The beginning of the hydrolysis reaction is as follows:

Al³⁺(aq) + 6H₂O(l) [Al(H₂O)₆]³⁺ (aq)

Aluminum mainly occurs as Al³⁺ (aq) under acidic conditions and as Al(OH)₄^- (aq) under neutral to alkali conditions. Other forms include AlOH₂⁺ (aq) and Al(OH)₃ (aq). The regular aluminum concentration expected in groundwater is 4µg/L because it is present in soils as water-insoluble hydroxide. Depending on the variability of pH values the solubility of Al rapidly might increase, causing aluminum concentrations to rise above 5µg/L. However, elevated levels of aluminum (> 200µg/L) have an impact not only on fish but also on birds and other species that eat tainted fish and insects as well as on animals that inhale the metal through the air. When birds eat infected fish, their eggshells thin and their offspring are born with low birth weights. Animals that inhale aluminum through the air may experience respiratory issues, lose weight, and become less active. The effects of aluminum have drawn our attention, mainly due to the acidifying problems. Aluminum may accumulate in plants and cause health problems for animals that consume these plants.

Metals that are found naturally in rocks, minerals, and soils are iron (Fe) and manganese (Mn). When these solid materials enter the aquifer, groundwater in it starts to disintegrate them. This causes their contents, such as manganese and iron, to be released into the water. The concentration of Fe varied from 6.20 to 741.9 µg/L, the lowest concentration of Fe was observed at different sites including GW8 (6.20 µg/L), whereas the highest Fe concentration was found at GW12 (741.9 µg/L). As iron-bearing minerals and rocks weather, iron is naturally added to groundwater. The World Health Organization (WHO) establishes a 300 µg/L as the maximum permitted concentration of iron in drinking water. In the study high concentrations of iron above the maximum permitted limit were recorded in stations (Table 2).

While, the concentration of Mn varied from 2.4 µg/L to 908.5 µg/L, a low concentration of Mn was observed at site GW1 (2.4 µg/L), whereas a high Mn concentration was found at GW3 (908.5 µg/L). As shown in Table 2, for a particular well, the amount of dissolved iron and manganese in the groundwater changes seasonally. For instance, high concentrations of Fe (14 stations, or 87.5%) and Mn (in 11 stations, or 69%) were recorded in partly wet season (Nov 10, 2021). This variance is typically linked to the surface bringing in oxygenated water during times of strong recharge. The oxygenated water will keep the iron and manganese from dissolving, resulting in low quantities of these metals in the water drawn from the well. Iron and manganese will dissolve once more in the recharge water when the oxygen has been used up, giving the water dissolved iron and manganese properties.

Arsenic (As), Molybdenum (Mo), and Vanadium (V)

Heavy metals enter groundwater through numerous anthropogenic activities, including mining, agriculture, landfills, and urban developments (Matthew S Schuler, Rick A Relyea, 2018). As shown in Table 1, a high concentration of chloride was observed. Accordingly, the presences of high concentrations of chloride affect the solubility and mobility of metals. As metals are desorbed and transformed into a soluble phase, chloride complexes can increase the solubility of the metals, increasing their persistence in soil and freshwater ecosystems (Warren and Zimmerman 1994). Depending on the Redox conditions, and microbiological environment, As species can be present in water in solution or in a precipitated form, and they can also adsorb or desorb from the existing precipitates (Issa et al., 2010; Issa et al., 2011). When As species are soluble in water, they can be present in both inorganic and organic forms. For As species both As(III), arsenite, and As(V), arsenate, can be present (Ljubinka and Vladana, 2017). For oAs species, MMA, and DMA are soluble forms of organic As species (Ljubinka and Vladana, 2017). Water-soluble arsenic species existing in natural water are inorganic As(iAs) and organic As(oAs) species. As species exhibit different toxicity (Issa et al., 2011). The investigation of As species and their behavior in various samples, especially in natural waters and the environment is important for chemistry and environmental protection (Ljubinka and Vladana, 2017). From the value of the chemical equilibrium constants for each molecular or ionic form of As in water, the present species can be recognized (Rajaković et al., 2013).

When choosing and analyzing the most dominant form of As in water, the most present is inorganic As as As(V). If As(III) is present, there are two important things that need to be taken into account, As(III) is more poisonous (even at low concentrations) than As(V) (Ljubinka and Vladana, 2017). Besides, the severe toxic effect, As(III) is easily oxidized. Due to different reasons, the formation of complex solutions between As oxyanions and other elements is limited, however, even such limited interactions still influence As speciation (Redman et al., 2002). Arsenic species can be transformed into insoluble compounds in combination with other elements, such as iron and sulfur (Mandal and Suzuki, 2002). The adsorption of arsenate As (V) and arsenite As (III) to mineral surfaces is reduced in the presence of natural organic matter (NOM) (Grafe et al., 2001; Grafe et al., 2002; Redman et al., 2002). Surface complexation models suggest that dissolved carbonate should interfere with As adsorption on mineral surfaces at carbonate concentrations typically measured in-ground and soil waters (Appelo et al., 2002).

Molybdenum is a Group VIB HMs, Mo(IV) and Mo(VI) are predominant states in nature. The most common oxidation states are 4⁺ and 6⁺ (Pauline and David, 2017). It occurs as molybdenite (MoS₂) and moly dates (MoO₄²) in igneous or sedimentary rocks. Even though most Mo compounds aren’t very soluble in water, the molybdate ion MoO₄^2- forms, when Mo-containing minerals come into contact with oxygen and water is soluble.

2MoS₂ + 7O₂ 2MoO₃ + 4SO₂

MoO₃ + 2NH₃ + H₂O (NH₂)₂(MoO₄)

Strong alkaline molybdates have a high solubility for Mo(VI) oxides (MoO₄^2-). Mo can exist in a wide variety of oxidation states, which are discussed in numerous Mo chlorides. Molybdenum (Mo) may be transformed in the LB catchment because of the hot weather and volcanic factors around the lake. In Lake Beseka, under physiological conditions (at pH > 6.5), the molybdate anion, [MoO4]^2-, is the sole molybdenum species in aqueous media (Cruywagen, 2000; Cruywagen et al., 2002). Molybdenum compounds including molybdenum trioxide and polymolybdates transform rapidly to the [MoO4]^2- ion under environmentally relevant test conditions. Protonated forms, such as [HMoO4]^- and H₂MoO4, are found at pH < 5 (Smedley and Kinniburgh, 2017). Molybdenum tends to be more mobile under alkaline conditions, but adsorption increases with decreasing pH (Goldberg et al., 2020). In the study we found that the highest concentration of Mo varied from 2.6 to 802.4 µg/L, a low concentration of Mo was observed at site GW15 (2.6 µg/L), whereas, the highest concentration was observed in GW11 (802.4 µg/L).

In water, V(IV) is commonly present as a vanadyl cation [VO²⁺, VO(OH)⁺], whereas V(V) exists as a vanadate oxyanion (H₂VO₄ ⁻, HVO₄ ²⁻) (Wanty and Goldhaber, 1992). VO²⁺ is strongly adsorbed on solid phases, including organic and oxyhydroxide phases (Wehrli and Stumm, 1989). Vanadium varies in concentration around the world, and it is usually found associated with iron-bearing water (Kohl and Medlar, 2006). Vanadium was found in groundwater samples (Winter, 2004). The minimum and maximum vanadium concentrations found were 1.7 µg/L and 528 µg/L, respectively. Vanadium (V) is significantly correlated with other trace elements such as arsenic, fluoride, and boron (Khosravi, et al. 2021). As seen in Table 4, it is mostly found associated with As (r=0.91).

Barium (Ba), lithium (Li), and Strontium

The concentration of barium in groundwater is regulated by barite (BaSO₄) solubility (Elena Gimenez-Forcada and Marisol Vega-Alegre, 2015). The relationship between strontium and barium in groundwater is controlled by the dissolution of sulfate salts containing strontium and the precipitation of barite (Elena Gimenez-Forcada and Marisol Vega-Alegre, 2015). Surprisingly, Groundwater with low SO₄^2- concentrations (or less than 10 mg/L) could be predicted to have high Ba contents (Reimann et al., 2002). As a result, only very low concentrations of Ba (ranging between 6.8 to 76.2 µg/L) were found in the investigated sites. This could be because the groundwater samples had significant concentrations of SO₄^2- (188.5 mg/L). Although barium compounds are utilized in many industrial applications and can be found as trace elements in both igneous and sedimentary rocks, the majority of Ba in water comes from natural sources. Barium may be a connection between cardiovascular illnesses (WHO, 1993). Nearly all (100%) of the samples in the research area had results (Ba) below the WHO standards (700 µg/L).

Like all alkali metals, lithium reacts easily in water and does not occur freely in nature due to its activity. Lithium compounds such as lithium chloride, lithium carbonate, lithium phosphate, lithium fluoride, and lithium hydroxide are more or less water soluble. In the study, the highest concentration of Li 68 µg/L was observed in GW8. Most sampling stations do not exceed the WHO standard (WHO, 2011). However, too much lithium may be toxic.

In fact, strontium (Sr) and barium (Ba) are alkaline-earth metals that are a common trace element in most rocks, soils, sediments, and waters. Both rock weathering and soil erosion can lead to strontium contamination of water supplies. Because many strontium compounds react violently with water, they can travel across the environment rather easily. The groundwater sites that were analyzed showed Sr concentrations ranging from 71.1µg/L to 1236 µg/L, with the lowest concentration being seen there. Some stations including GW recorded above the 700 µg/L or Canadian water requirements, (Health Canada, 2019). In general, carbonates have higher strontium contents than ultrabasic rocks and sandstones. There are many sedimentary basins (which frequently contain evaporites), and carbonates that could be sources of sulfur or are probably connected to sulfur minerals (Musgrove, M., 2021).

Chromium (Cr), cadmium (Cd), and Zinc (Zn)

Cadmium (Cd) is expected in high concentration at low pH, however, not valid for the Rift Valley groundwater (Reimann et al., 2002). For instance, high pH wells (piezometer stations) showed also high Cd at station GW11 at 210 cm (2.1m). In the study at GW11, partly in dry and wet seasons, 4.6 µg/L (pH=8.44) and 0.62 µg/L (pH=9.06) were recorded respectively. The highest mean concentration of Cd-values is found in the alkaline groundwater samples at very high pH-values (Cd=2.62 µg/L). The source might be anthropogenic (might be fertilizers and pesticides). Chromium (Cr) is a well-known cancer-causing element. Anthropogenic sources like the tanning industry pollute water bodies in the Awash Basin (Abebe et al., 2023). While, the concentration of Cr exhibited in all samples was below the maximum allowable limit (50 µg/L) noted by WHO (WHO, 2008, 2011). Arguably, the previous studies done in the Rift Valley found the highest value of Cr in GW was 21 µg/L (Reimann et al., 2002). Similarly, the highest concentration of Cr recorded in this study was 10.7 µg/L in GW1 (at Addis Ketma, near LB).

Zinc (Zn), across all sampling stations, ranged from 10 to 6060 µg/L. In groundwater, the concentration of zinc (Zn) is usually expected between 10 to 40 µg/L. However, the highest concentration of Zn, 6060 µg/L was recorded in the groundwater sample collected in the piezometer station (GW11). Even higher Zn concentration (up to µg/L) was recorded in the rift valley of Ethiopia. In the study, the concentration of Zn was recorded between 871 µg/L to 6000 µg/L in the Amibera irrigation fields, or piezometer stations. Surprisingly the highest concentration of Zn was recorded in all piezometer stations, this might be associated with the fertilizers and chemicals (pesticides, herbicides, or else) used for cotton production or sugar cane plantation.

Silver (Ag), Antimony (Sb), and Tin (Sn)

Silver (Ag) is considered to be less toxic to humans. The main natural source of Ag is sulphidic ores. Its mobility is very low under alkaline conditions. Silver (Ag) ranged from 0.1 to 0.2 µg/L. The concentration of antimony (Sb) varies between ND to 5.3 µg/L across all sampling stations. Tin (Sn), across all sampling stations, ranged from 0.1 to 3.5 µg/L. The highest concentrations of Sb and Sn were recorded in GW11 with the values of 5.3 µg/L and 3.5 µg/L, respectively. It might be from organo-tin compounds or chemicals used for biocides in the Amibera state farm. Of the various tin-bearing minerals, cassiterite is an oxide, while the remainder is complex sulfides. The concentration of Sb in GW is expected 0.001µg/L, however, in the study, above 5 µg/L was recorded in station GW11 (WHO, 1993), but less than 20 µg/L the limit improved by WHO (WHO, 2011).

Copper (Cu), Cobalt (Co), and Nickel (Ni)

Copper (Cu) is a trace metal. According to the result of Table 3, the minimum and maximum concentrations of Cu were recorded from 47.7 µg/L to 369.7 µg/L. The mobility of Co strongly depends on the geochemical conditions (Reimann et al., 2002). Cobalt concentrations observed in the Rift Valley drinking water range from less than 0.002 to 3.1 mg/L (Reimann et al., 2002). However, the highest Co value was recorded in station GW (1.6 µg/L). Studies indicate that Co-deficiency problems are more widespread than Co-toxicity (Reimann and Caritat, 1998).

Table 3. Correlations between heavy metals (metalloids) and statistical summary of heavy metals concentration in groundwater (in µg/L).

Table 3. Correlations between heavy metals (metalloids) and statistical summary of heavy metals concentration in groundwater (in µg/L).

HMs	Al	Li	Mo	Ti	V	Mn	Ba	Ni	Cu	Zn	Sr	As	Rb	Cr	Zr	Nb	Ge	Co	Fe	Ga	Ag	Cd	Sn	Sb
Al	1.00
Li	-0.22	1.00
Mo	0.18	0.56	1.00
Ti	1.00	-0.23	0.19	1.00
V	0.03	0.33	0.26	0.04	1.00
Mn	0.07	-0.09	-0.06	0.04	-0.08	1.00
Ba	0.17	-0.05	0.14	0.18	-0.19	0.15	1.00
Ni	0.94	-0.12	0.40	0.95	0.14	0.08	0.35	1.00
Cu	0.86	-0.16	0.19	0.83	0.03	0.38	0.17	0.84	1.00
Zn	0.54	0.27	0.85	0.54	-0.09	0.01	0.35	0.68	0.47	1.00
Sr	-0.29	0.15	0.06	-0.28	-0.36	0.03	0.78	-0.13	-0.31	0.13	1.00
As	0.31	0.33	0.32	0.33	0.91	-0.07	-0.16	0.40	0.25	0.08	-0.42	1.00
Rb	-0.24	0.36	-0.25	-0.26	0.01	-0.17	-0.26	-0.36	-0.23	-0.30	-0.03	-0.08	1.00
Cr	0.04	-0.04	-0.02	0.05	0.49	-0.22	-0.19	0.06	0.11	-0.11	-0.34	0.33	0.44	1.00
Zr	0.86	0.01	0.52	0.87	0.18	0.03	0.19	0.91	0.77	0.76	-0.23	0.37	-0.11	0.32	1.00
Nb	1.00	-0.22	0.21	1.00	0.09	0.03	0.17	0.95	0.84	0.55	-0.29	0.36	-0.23	0.12	0.89	1.00
Ge	0.01	0.02	-0.28	0.00	-0.34	-0.17	-0.44	-0.22	-0.19	-0.16	-0.29	-0.24	0.57	-0.11	-0.08	-0.01	1.00
Co	0.94	-0.35	0.29	0.94	-0.02	0.02	0.10	0.97	0.88	0.65	-0.46	0.28	-0.30	0.13	0.92	0.95	0.09	1.00
Fe	0.93	-0.26	0.06	0.91	-0.17	0.04	0.44	0.89	0.93	0.46	-0.37	0.14	-0.51	-0.05	0.73	0.90	-0.08	0.92	1.00
Ga	0.25	-0.11	0.06	0.26	-0.19	0.19	0.99	0.41	0.25	0.32	0.72	-0.13	-0.27	-0.18	0.23	0.26	-0.42	0.19	0.59	1.00
Ag	0.71	0.20	0.79	0.71	0.11	0.02	0.25	0.83	0.66	0.94	-0.10	0.29	-0.26	0.10	0.91	0.73	-0.19	0.82	0.64	0.25	1.00
Cd	0.32	0.48	0.97	0.33	0.06	-0.13	0.02	0.48	0.22	0.92	-0.03	0.18	-0.32	-0.14	0.60	0.34	-0.10	0.43	0.08	-0.05	0.86	1.00
Sn	0.85	-0.15	0.31	0.86	0.32	0.04	0.13	0.87	0.78	0.53	-0.35	0.47	-0.07	0.49	0.95	0.90	-0.11	0.89	0.72	0.19	0.76	0.35	1.00
Sb	0.83	-0.22	-0.08	0.83	-0.04	-0.08	0.06	0.73	0.82	0.27	-0.34	0.26	-0.09	0.07	0.65	0.83	0.17	0.75	0.99	0.17	0.47	0.12	0.69	1.00
Min	20	6.7	2.6	0.5	1.7	2.4	6.8	0.2	47.7	10	71.1	0.9	2.2	0.2	0.4	0.1	0.1	BD	BD	1.0	0.1	BD	0.1	BD
Max	2615	68	802	17.1	528	908	76.2	8.8	370	6060	1236	210	35	10.7	20.2	3.5	1.5	1.6	741.9	10.3	0.2	2.6	3.5	5.3
Mean	232	30.9	149	12.1	101	117	28	1.7	114	871	454	42.4	11.5	1.7	3.3	0.3	0.5	0.5	144.9	3.8	0.1	0.7	0.6	1.4
WHO	200	NG	70	NG	20	400	300	200	1300	5000	700	10	NG	50	NG	NG	NG	NG	300	NG	10	3	NG	5

Table 4. Functional piezometer stations in Amibera irrigation schemes (SCD: Sample collected at the depth of).

Table 4. Functional piezometer stations in Amibera irrigation schemes (SCD: Sample collected at the depth of).

No.	Location description	Piezometer	SID	SCD	Soil type	Field cover
1.	Shelko near new Asphalt Road	AIP-41	GW-8	167cm	Fluvisols	Sugarcane
2.	Ambash near new settlement DC	AIP-40	GW-9	135cm	Fluvisols	Sugarcane
3.	Near to Bolhamo village	AIP-62	GW-10	95cm	Fluvisols	Sugarcane
4.	Melka-Sedi farm near 4th camp	AIP-10-1	GW-11	210cm	Fluvisols	Trees & shrubs
5.	Melka-Sedi farm near 4th camp	AIP-10-2	GW-12	1232cm	Fluvisols	Trees & shrubs
6.	Melka-Sedi farm near 4th camp	AIP-10-4	GW-13	215cm	Fluvisols	Trees & shrubs

N.B: Amibera Irrigation Project (AIP); Sources: from field visits and study (Mamo et al., 2019).

Niobium (Nb), Gallium (Ga) and Germanium (Ge)

Niobium (Nb) is a member of the fifth group of the periodic table. Niobium typically forms compounds with an oxidation state of +5. Niobium is closely associated with titanium in ores. Niobium can best be dissolved in a mixture nitric acid and hydrofluoric acids, completely miscible with iron. Its most common oxide is Nb₂O₅, which is produced by heating the metal in an oxygen environment. In a study of groundwater samples from LB and Amibera irrigation farms, Middle Awash, the typical range for naturally occurring Nb concentrations in groundwater was measured to be from 0.1 to 3.5 µg/L. High-level interaction between Al and Nb (r=1.0) was found in studied groundwater, which might be predominantly of a natural origin (Sutliff-Johansson, S., et al., 2021). Gallium (Ga) is the 34th most abundant element found in Earth’s crust (Emsley, 2001), and it is widely distributed in low amounts in many rock types. The results of this study showed that the minimum and maximum level of Ga was observed at 0.1 µg/L and 10.3 µg/L, respectively. The ecological effects of gallium may be similar to those of aluminum given their similar behavior in the environment. Germanium (Ge) is a non-essential and non-harmful element. An increased germanium level is mainly associated with thermal waters, waters with either very low or very high pH, and saline waters (Rosenberg, 2009). The highest concentration (1.5 µg/L) of Ge was recorded in GW16. Ge was found in increased amounts in CO₂-rich thermal waters, and alkaline sodium-dominated thermal waters (Ivanov, 1996).

Rubidium (Rb), Titanium (Ti), and Zirconium (Zr)

The higher concentrations of Rb, Ti, and Zr were found in stations GW4, GW12, and GW12 with levels of 35 µg/L, 171.3 µg/L, and 20.2 µg/L, respectively. Titanium (Ti) is a chemical element and is found in nature only as an oxide. Titanium (Ti), across all sampling sites, ranged from 0.5 to 171.3 µg/L. Zirconium (Zr), ranged from 0.4 to 20.2 µg/L across all sampling stations. The concentration of Rb ranged from 2.2 to 35 µg/L. The concentrations of Ti do not exceed the standard limits of WHO.

Multivariate Statistical Analysis

Principal component analysis (PCA): PCA is a linear analytical technique used to reduce a data set’s dimensionality while trying to guarantee that associations remain within the original data. Speaking to a large data set in less estimation may be interesting in data representation and compression tasks, where it is frequently used. In this study, the PCA analysis (Figure 8) indicates that while the Amibera irrigation schemes (from GW9 – GW13) may be the result of anthropogenic factors such as excessive use of pesticides and agricultural inputs or groundwater salinization, the main reasons for the heavy metal pollution near the LB GW (from GW1- GW8) may be geogenic. Al, Ti, Ba, Ni, Cu, Zn, Zr, Nb, Ge, Co, Fe, and Ga, are included in Cluster 1; Mo, Li, Sr, and Cd are included in Cluster 2; V, As, Rb, and Cr are included in Cluster 3; and Mn is the solitary element in Cluster 4. The likelihood of a similar origin is demonstrated by these clusters, and associations between clustered samples were anticipated.

Figure 7. The similarity plot of heavy metals in the dendrogram.

Figure 7. The similarity plot of heavy metals in the dendrogram.

As illustrated in Figure 8, the correlation type of matrix was chosen to weigh all parameters equally. As a result, the plot displayed the quantity of main components, or uncorrelated variables, in the heavy metals data sample. A short distance indicates the closure of two chemical parameters, while a high distance shows the dissimilarity in the parameters. For example, the first component has substantial positive loadings for Co, Ni, Zr, Nb, Cu, Sn, Sb, Ti, Fe, and Al. Conversely, the second component has significant negative loadings for As and Cr. All things considered, the biplot and dendrogram plots show that variations in the concentration of heavy metals in the groundwater aquifer under study may be caused by both geogenic (such as rock water interactions) and anthropogenic (such as surface runoff and fertilizers used in agriculture).

Figure 8. The principal component analysis (PCA) biplot of heavy metals.

Figure 8. The principal component analysis (PCA) biplot of heavy metals.

In the study, the words wells, boreholes, and piezometers are used interchangeably, however, they are not the same in functions, for instance, the drilled specifically to measure water level is an observation borehole. The level of water in an observation borehole will be a composite of all aquifers that are penetrated by the borehole. If it is drilled to measure water in a particular horizon and other horizons are cased off, it is called a piezometer. A piezometer, also known as a tube well, is primarily used for measuring subsurface water pressure. Since 1970s (Kebebe et al., 2021), more than fifty piezometer stations have been installed in the study area, with at least 25 of these used to monitor subsurface water quality and water level changes in the Middle Awash irrigation schemes. According to Mamo et al. (2019), all piezometers monitored in their studies have shallow water tables (Kebebe et al., 2021) and piezometers are mostly used to monitor shallow wells (Sprecher, S. W., 1993). Currently, over half of these piezometer stations are non-functional, primarily due to damage from machinery, while others suffer from lack of maintenance. This presents significant challenges due to limited information on their functionality, compounded by inadequate regulation and monitoring. The neglect of these valuable resources is notable. For this study, six sites were selected to assess the water quality and water level changes in the subsurface waters of Middle Awash.

Comparison of Surface Water and Groundwater HMs Data in the Lake Beseka Catchment

In arrange to examine at the imaginable source of heavy metals both within the groundwater and surface water of LB catchment. Water tests analyzed within the display consider and past consider (abebe et al., 2023) was computed as takes after in Table 5. In arrange to center around analyzing volcanic action crack and geography of the bowl influences the neighboring water bodies like Lake Beseka region was computed. The discoveries moreover uncovered that the tall concentration of HMs including As was watched in Table 5. It may well be from the same sources influences both water bodies. Over the HMs counting Fe, Mo, V, Mn, Al, and also As in groundwater and surface water is non-potable and carries wellbeing chance on the off chance that devoured. Hence, we have to be creating remediation procedures for superior water supportability and security.

Comparing the HMs content of the two types of water and their potential sources was the goal of the above Table 5 and the Figures below (Figure 9 and Figure 10). Moreover, to investigate the water chemistry of surface water interaction across catchments. Table 5 illustrates that similar sources led to significant quantities of heavy metals and arsenic in both surface water and groundwater samples. In few cases, such as GW4, elevated levels of arsenic were observed exceeding the WHO endorsed threshold of 10 µg/L. Conversely, comparatively low concentrations of iron and aluminum were found in the Beseka catchment, whereas extraordinarily high concentrations of both were found in the surface water of Lake Beseka. It could be caused by man-made sources or by the catchment’s rocks deteriorating. In both cases, molybdenum concentrations were found to be quite similar, which may be because of similar sources.

Comparison of Water Level Change and Some Physicochemical Change

Although the terms well, borehole, and piezometer are used interchangeably throughout the study, they have different purposes. For example, an observation borehole is one that is drilled especially to record water level (Table 4). An observation borehole’s water level is a combination of all the aquifers the drill has entered. It is referred to as a piezometer if it is drilled to measure the water in a certain horizon and other horizons are cased off. Where piezometric levels are greater than the lake stage area, groundwater flow is directed towards the lake (Kebede et al., 2021). Current piezometric values at Melka Worrer show that shallow groundwater flows mostly into the River Awash. In many areas of the irrigation area, groundwater levels are shallow typically less than three meters below the surface. The study by Kebede et al. (2021) indicates that the direction of GW flow is towards the Lake, suggesting that the groundwater surface interaction may be the source of the high concentration of heavy metals in the LB. Heavy metals from ground sources or water flows into the lake may pollute the water. Therefore, the interaction may be the cause of the change in water chemistry.

About six piezometers were used to compute the water quality of the groundwater in the Amibera irrigation farms in order to look at the patterns in changing water levels. The secondary data from the Awash Basin Administration Office, MoWE, the water level change, and the water quality were computed based on the study’s findings, as shown in Figs. 11i and 11ii. The results showed that the quality and level of the water had changed. For example, in 2009, a groundwater sample was taken at the following levels: 5.61 meters (GW10), 2.5 meters (GW11), and 2.75 meters (GW9). However, in 2021, the levels were 1.35 meters, 2.1 meters, and 0.95 meters, respectively. Electrical conductivity (EC) also changed in 2021, rising from 8850 µS/cm (GW9), 15390 µS/cm (GW10), and 9650 µS/cm (GW13) to 1702 µS/cm, 2074 µS/cm, and 4985 µS/cm, respectively.

Figure 11. Spatiotemporal variability of wells EC in µS/cm (Figure 11i) and water depth (in meter) increment (Figure 11ii). (N.B: The water depth, EC and pH raw data from 2009 to 2014 was took from the Awash Basin Administration office, MoWE)

Figure 11. Spatiotemporal variability of wells EC in µS/cm (Figure 11i) and water depth (in meter) increment (Figure 11ii). (N.B: The water depth, EC and pH raw data from 2009 to 2014 was took from the Awash Basin Administration office, MoWE)

5. Conclusions

6. Future Works and Interventions

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