Environmental factors controlling contamination and vulnerability of water alternative supply points in Lefock semi-urban watershed, West Cameroon

doi:10.21203/rs.3.rs-1885469/v1

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Environmental factors controlling contamination and vulnerability of water alternative supply points in Lefock semi-urban watershed, West Cameroon

https://doi.org/10.21203/rs.3.rs-1885469/v1

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Due to the poorly managed water network of the Dschang municipality (West Cameroun), the peri-urban population of the Lefock watershed, frequently, consumes doubtful quality water from alternative supply points (WASPs): spring, well, river, borehole. In this context, the present study aimed to explore the influence of close environment on the possible contamination of these resources. For this purpose, 22 WASPs were characterized (within a 10 m radius of the point) both from physiographic (nature of bedrock, water supply utility, soil type, land use) and anthropogenic (presence of pit latrines, domestic wastewater, domestic breeding, agricultural activities, wild garbage dump, washing clothes on-site). Then, chemical (NO₃⁻, NH₄⁺, PO₄³⁻) and bacteriological (faecal coliforms, faecal streptococci, total coliforms, and E. coli) contamination parameters were analyzed and compared with the World Health Organisation (WHO) standards. Multiple Factor Analysis (MFA) was done, using water quality variables as input combined with environmental data as supplementary data. It revealed that waters from WASPs were generally of very poor bacterial quality, due to proximity with pit latrines, domestic wastewaters, and/or agricultural plots. NO₃⁻ is exceptionally high where WASPs are close to agricultural plots and/or domestic wastewaters. The MFA showed that the chemical degradation of WASP mostly results from wider scale processes and is representative of diffuse (and likely long-term) impacts on the resource. In contrast, bacteriological contaminations were better governed by immediate contexts and appears to result from the combination of anthropogenic and physiographic constraints. Regarding vulnerability, the type of soil and the nature of the WASPs are the main influencing factors. The hydromorphic context accentuates the vulnerability, while the order of increasing vulnerability related to the type of WASPs is: spring - well and borehole - river. These results indicate that poor water management, combined with a limited consideration of local environmental specificities threatens the security and sustainability of this resource in semi-urbanized zones over heterogeneous aquifers, and argue for a twofold education effort for managers and end-users of the resource.

water quality

multivariate statistical methods

semi-urban watershed

alternative water supply point

west Cameroon

The availability of good water quality is a fundamental need that is still far from being met for a large part of the world's population (Tabué Youmbi et al. 2013; Akakuru et al. 2021). 2.1 billion people, representing 30% of the world's population still lack access to safe domestic water supply services, and 4.4 billion, or 60%, lack safely managed sanitation services (OMS/UNICEF 2017). This exposes water resources for various human needs to the susceptibility of anthropogenic contamination. It should be noted that this susceptibility to contamination can be enhanced or mitigated by natural environmental conditions (Riccioli et al. 2018; Njueya Kopa et al. 2021). However, water quality (both chemical and bacteriological) directly affects human health (WHO 2017). Hence the need to know the sources and causes of variation in the quality of water resources for human use. This enables effective strategic management measures to be taken to ensure a healthy, clean, and suitable quality condition for meeting various needs (Lenart-Boron et al. 2017; Scalize et al. 2021).

Almost half of sub-Saharan population are without access to improved drinking water sources, and 700 million people in the region lack access to proper sanitation. With the population almost doubling over the past 25 years in the region, access to sanitation has increased by only 6% and access to water by 20% over the same period (OMS/UNICEF 2017). Millions of people are therefore, left to fend for themselves (OMS/UNICEF 2017). Demographic growth in the cities of developing countries, coupled with precarious socio-economic conditions in these areas, lead to an anarchic occupation of land that uncontrolled by public authorities (Foster et al. 2020). This situation is at the origin of the birth and proliferation of informal settlements, which are almost the only way to occupy urban space in these countries (Eneke Takem et al. 2009).

In the Lefock watershed area in West Cameroon, where the urban area directly borders the rural environment, the structural organization of land use varies from one area to another. Informal settlements characterize the urban area, while agricultural activities are much more present in the peri-urban area, which is less inhabited. The rate of access to the national distribution CAMWATER network is low, limited in the urban area, and very irregular. This forces the population to resort to alternative supply points such as wells, springs, boreholes, surface water, and sometimes even rainwater to meet their various water needs (Temgoua et al. 2010). Several studies conducted in some areas of the city of Dschang show that water from alternative supplies is of doubtful quality (Temgoua et al. 2010; Mba et al. 2019), induced by human practices. However, the potential sources of water contamination are multiplying with population growth.

Effective management of water resources is necessary to achieve the goals of sustainable development (United Nations 2021), which must meet the needs of current and future generations. It is in this context that the present study was conducted in the Lefock watershed area, in Cameroon. This area is representative of many semi-urban areas where self-access to water combined with weak socio-environmental conditions may cause contamination of the resource that in turn triggers adverse health and socio-environmental effects, as is well observed elsewhere such as in densely populated metropoles (Bertrand et al. 2022).

In this context, to propose management perspectives applicable in similar urbanized and semi-urbanized watersheds of the sub-Saharan area, this study aims at evaluating how surrounding physiographic and contamination source types may impact on these alternative water supplies used by the population. The specific objectives are (i) to provide a typology of alternative water sources regarding their environment, (ii) to investigate chemical and bacteriological contaminations, and (iii) evaluate, through statistical data processing how the environmental conditions near the water supply points may be related to the level and the type of contamination. This should allow delineating the main factors affecting the water quality of alternative points and on this basis proposing management’s ways to secure this alternative resource, especially in the perspective of a further in the framework of a future adapted management.

Study area

The Lefock watershed area is located between 2°24'15" and 2°27'00" North latitude and between 10°2'30" and 10°06'00" East longitude. Its outlet is located at the Caplamé Bridge, in the urban area. Administratively, this watershed is located to the east of the Dschang district; it partially overlaps the Nkong-Ni district (Fig. 1). A two-season subequatorial climate dominates the area (Kengni et al. 2019) characterized by a long rainy season (March-October) and a short dry season (November-February); the average annual rainfall is high with values reaching 1918.1 mm (Kengni et al. 2019). This watershed covers an area of about 20 Km².

The geological base is made up of granite-gneissic rocks, partially covered by volcanic rocks represented by basalts, ignimbrites and trachybasalts. These geological formations contain supperposed aquifers located on the one hand in the alterites and on the other hand in the cracks and fractures of the rocks (Kenzo-Tongnang et al. 2021). The soils found in the Watershed are Ferralsols and hydromorphic soils.

The Lefock watershed is very poorly covered by the national distribution network for the production and marketing of drinking water, which is also limited to the urban area. The peri-urban area is characterized by a predominance of non-functional standpipes and irregularly functioning standpipes, which forces the population of this area to rely on surface water (rivers), springs, wells, and boreholes for all its water needs.

Data collection and processing

Data collection was carried out in three stages: Firstly, preliminary work was carried out on a general and representative inventory of the alternative water points used in the Lefock Watershed coupled with an analysis of the different uses. Then, a mapping of the land use in the Lefock basin was performed. Secondly, water samples were taken at these points for chemical and bacteriological analyses. Finally, both environmental descriptions and analyses were processed through Multiple Factor Analysis (MFA) aimed at combining qualitative and quantitative dimensions of contamination risk over the studied area.

Physiographical and anthropogenic characterization of alternative sampling sites

An environmental survey was done through in-situ observation coupled with a description of the immediate environmental context within 10 m (minimum safety distance for a drinking water supply structure, prescribed by Djuikom et al. 2009; OMS 2017) around 22 water supply points. The environmental characteristics assessed were the physiographic settings (lithology, water supply structure, type of soil, land use class) and anthropogenic activities (pit latrines, domestic breeding, domestic wastewater, agricultural activities, illegal dumping of rubbish, cleaning of clothes).

Sampling and chemical /bacteriological analyses

For the water quality assessment, 22 samples were taken on May 21, 2021 (rainy season; April and May correspond to the period when fertilisers are mostly used in the area during ploughing) from different water supply points, in order to be spatially representative of the water uses at the watershed scale, according to the nature of the point, the geological context and the environmental context. This sampling comprised of 11 wells, 2 boreholes, 4 springs, and 5 points on watercourses (Fig. 2).

After samplings, waters were stored in polyethylene bottles previously washed 3 times with the water to be sampled (Rodier et al. 2009). A first aliquot was isolated for anion analysis. The second one was for cation analysis and was therefore acidified (with 3 drops of 0.1N HNO₃) to avoid any mineral precipitation. The third samples for bacteriological analysis was taken using a carefully washed 250 ml glass bottle. The bottle was previously rinsed with distilled water and autoclaved at 120°C for 30 minutes. Samples were transported to the laboratory in a refrigerated cabinet and analyzed within 24 hours after collection.

For each sampled site, 7 parameters, indicators of contamination were analyzed at the FASA Environmental Chemistry and Soil analysis Laboratory in Dschang University: Ammonium (NH₄⁺), nitrate (NO₃⁻), and phosphate (PO₄³⁻) ions were measured by titration. Bacteriological analyses were performed to assess faecal coliforms, total coliforms, faecal streptococci, and E. coli. These bacteria were identified and counted by filtering 100 ml of the water sample through a cellulose ester membrane with a porosity of 0.45 µm. The membranes were then placed on selective media for 24 h at 44°C. ENDO AGAR lactose medium, Slanetz medium, Slanetz, and Bartley medium were respectively used to select and growth faecal coliforms, E. coli, faecal streptococci and total coliforms (AFNOR 2006).

Data processing through statistical analysis

To highlight the possible causes of contamination, the hydrochemical, bacteriological, and environmental data were subjected to statistical analysis. Multivariate Statistical Analyses (MSA) including correlation matrix analysis, and Multiple Factor Analysis (MFA) using Microsoft Office Excel version 2013 and R version 4.1.1 were applied to the data. Given the high variability of the bacteriological data, they were reduced by applying the logarithm function (Tabué Youmbi et al. 2013) before being subjected to MSA processing.

Type of supply water utilities

The alternative water sources used by the population of the Lefock watershed are wells, springs, boreholes, and surface waters. These water collection points belong to a complex environment: from a geological point of view, the rocks are granites, gneisses, basalts, and ignimbrites. The soils are hydromorphic in the lowlands and ferrallitic on the hillsides and tops. Several anthropogenic activities (pit latrine, domestic wastewater, agricultural plot, domestic breeding, wild garbage dump, and washing clothes) around these supply points (about 5–30 m radius) constitute a risk of contamination for the water, a phenomenon that is common to suburban communities in Cameroon (Tanawa et al. 2002; Djuikom et al. 2009)

The environmental characteristics (within 10m) of the alternative water points sampled show that the water points used by the people in the Lefock Watershed are frequently close to many potential sources of contamination. This is a recurrent situation in small towns in sub-Saharan Africa, where the urban environment develops in an anarchic manner with spontaneous settlements and constitutes a significant contamination risk for the resources exploited by the population (Frédéric et al. 2015; Akakuru et al. 2021).

Focusing on community contamination sources, it revealed that 64% (14/22) of the points are potentially impacted by wastewater, while 68% (15/22) should be under influence of agricultural practices and 9% (2/22) at the proximity of wild garbage dump. Regarding individual practices, it appears that pit latrines, domestic breeding, and washing clothes are found near 50% (11/22), 9% (2/22), and 9% (2/22) of the water sampled points respectively. It is worth noting that some activities are logically associated with one type of water, i.g. washing clothes is found in near-surface waters.

Water quality

The values of the contamination indicator parameters are presented in Table 1. The comparison of the studied parameters with the international standard prescribed by the WHO shows that:

Table 1

Concentration of contamination indicators in water samples (Collected in May 2021, rainy season)
Sample name	PO₄⁻ (mg/l)	NO₃⁻ (mg/l)	NH₄⁺ (mg/l)	Faecal Coliforms (CFU/100 ml)	E. coli (CFU/100 ml)	Total coliforms (CFU/100 ml)	Faecal Streptococci (CFU/100 ml)
E1	0.74	56	140	290	160	1680	196
E2	0.74	0	0	480	50	1960	84
E3	0.75	3.92	0	10800	250	42530	3600
E4	0.74	11.20	0	6800	190	17400	284
E5	0.85	5.60	0	8450	770	32450	4320
F1	0.74	28	0	200	280	1280	26
F2	1.00	2	0	90	30	1250	4
P1	2.26	56	5.600	20	0	1800	2
P2	0.78	84	72.800	50	0	7200	10
P3	0.78	0	72.800	120	10	9300	180
P4	0.74	28	0	1300	60	8200	140
P5	0.74	0	16.800	300	0	10 800	32
P6	0.78	12	0.006	100	0	5400	260
P7	0.74	0	0	3400	9000	31180	2520
P8	1.00	8	0	130	80	870	74
P9	0.78	4	0.003	7200	190	29400	4300
P10	0.85	2	0.003	520	0	2090	0
P11	1.00	5.88	0	370	0	5400	240
S1	0.58	0	0.002	30	0	3600	0
S2	1.00	22	0.003	20	40	240	2
S3	0.50	25	0	40	0	190	14
S4	0.74	15.40	0	570	0	1750	2
Mean	0.86	16.77	14	1876	505	9817	740
SD	0.34	22.35	35.320	3260	1905	12528	1459
Min	0.50	0	0	20	0	190	0
Max	2.26	84	140	10800	9000	42530	4320
WHO standards	-	50	< 0.5	20	0	-	20
S: Surface water; F: Borehole; P: well; S: Spring; SD: Standard Deviation; Min: Minimum; Max: Maximum

- Chemically, the quality remains within the WHO standard range except for three supply points (E1, P1 and, P2) where the nitrate concentration is above the guide value (Table 1). In various regions, fertilizers and pit latrine are the most important sources of nitrate contamination, which is above the drinking water limit in groundwater (Temgoua et al. 2010; Riccioli et al. 2018). Although the maximum nitrate value is below the maximum permitted limit for the majority of samples, these values are expected to increase due to the increase in anthropogenic activities such as agriculture which is expected to evolve with the progressive expansion of the population (the population of Dschang is estimated at 63 838 inhabitants with a 4.7% growth rate; United Councils and Cities of Cameroun, 2021) and change lifestyle (use of personal care products, detergent, pharmaceutical drugs, etc.). Ammonium concentration is also high (above 0.2 mg/l) in five samples. According to WHO (2017), natural levels of ammonium in groundwater and surface water are usually below 0.2 mg/l and much higher concentrations in water are an indicator of possible bacterial contamination or contamination by sewage or animal waste.

- According to WHO standard (2017), the water taken through the alternative water supply points is bacteriologically polluted except P1 (Table 1).

Heterogeneity of water contaminations and link with the surrounding environment

The correlation matrix (Table 2) between the contamination indicator parameters shows 03 observations. Firstly, the existence of a positive and strong correlation of E. coli with faecal streptococci (0.661) and faecal coliforms (0.630). E.coli are positively but weakly correlated with total coliforms (0.318). This suggests that the bacteriological contamination of the water resource is not only faecal. Then, it shows the existence of a positive and average correlation between NO₃⁻ and NH₄⁺ (0.549). The correlation between NO₃ and PO₄³⁻ is positive but weak (0.322). This shows that fertilizers are not solely responsible for the nitrate pollution observed in 3 samples analyzed (E1, P2, and P9; Table 1). Finaly, A negative and weak correlation between bacteria content (faecal coliforms, E. coli, faecal and total streptococci) and nitrogen (respectively − 0.387; -0.198; -0.243 and − 0.253 with NO₃⁻ and − 0.174; -0.01; -0.005 and 0.051 with NH₄⁺).

Table 2

Pearson correlation matrix between contamination indicator parameters
	PO₄³⁻	NO₃⁻	NH₄⁺	Log FC	Log E. Coli	Log TC	Log FS
PO₄³⁻	1
NO₃⁻	0,322	1
NH₄⁺	-0,085	0,549	1
Log FC	-0,306	-0,387	-0,174	1
Log E. Coli	-0,170	-0,198	-0,010	0,630	1
Log TC	-0,139	-0,243	-0,005	0,760	0,381	1
Log FS	-0,252	-0,253	0,051	0,766	0,664	0,718	1
In bold, significant values; log FC: log faecal coliforms; log TC: log total coliforms; log FS: log faecal streptococci

Similar observations have been made for groundwater in Iganga district in Uganda (Barrett et al., 1999); Niamey in Niger (Ousmane et al. 2006); Douala in Cameroon (Eneke Takem et al. 2009) and Yaoundé in Cameroon (Tabué Youmbi et al. 2013) and suggests that contamination comes from multiple and distinct sources. This feature appears therefore, consistent with the environmental description (within a 10 m radius) of the water supply sites highlighting multiple sources of contamination around these sites.

To assess this possible multi-dimensional contamination impact, a Multiple Factor Analysis (MFA) was carried out on all the data, i.e. 22 individuals (sampling sites) and 18 variables represented by four groups of variables:

- Two quantitative groups (active variables), namely: chemical contamination indicators (NO₃⁻, NH₄⁺ and PO₄³⁻) and bacteriological contamination indicators (faecal coliforms, E. Coli, total coliforms and faecal streptococci);

- Two qualitative groups (supplementary variables), namely: physiographic factors (lithology, nature of soil, topographic level, land-use class, and water supply structure) and anthropogenic factors (pit latrines, domestic breeding, domestic wastewater, agricultural activities, illegal dumping of rubbish, cleaning of clothes)

According to the Kaiser criterion, two principal components were extracted, accounting for 65.90% of the total variance in the dataset from all 07 dimensions produced. The projection of the variables on the Dim 1 * Dim 2 factorial plane favors the grouping of the variables into three groups (Fig. 3a):

-The group constituted by the indicator parameters of bacteriological contamination (faecal coliforms, faecal streptococci, E. coli, and total coliforms) which is positively correlated with dimensions 1 and 2;

-The group of nitrogenous indicators of chemical contamination (NH₄ and NO₃) which is strongly and negatively correlated with Dimension 1, but positively correlated with Dimension 2;

-A group consisting of PO₄ is negatively correlated with dimensions 1 and 2.

This distribution of the contamination indicators in space (Dim 1 × Dim 2) confirms a multiple and heterogeneous origin of the contamination of the drinking water resource taken by the alternative points in the semi-urban watershed of Lefock. The detachment of PO₄³⁻ from the other chemical contamination indicator parameters shows a different source of this element. The highest PO₄³⁻ content is obtained in sample P1 (Table 1), this sample also has a NO₃⁻ concentration above the WHO potability limit and would indicate punctual chemical contamination in the Lefock watershed.

Hierarchical clustering favors grouping of alternative supply sites in the factorial map according to the nature of the contamination (Fig. 3b, Table 3):

Table 3

Distribution of contamination indicator parameters within the clusters formed in the factorial plane dim 1 * dim 2 (according to Table 1 and Fig. 3b)
Cluster	Range	PO₄⁻ (mg/l)	NO₃⁻ (mg/l)	NH₄⁺ (mg/l)	Faecal Coliforms (CFU/100 ml)	E. coli (CFU/100 ml)	Total coliforms (CFU/100 ml)	Faecal Streptococci (CFU/100 ml)
Cluster 1 (Nitrate pollution)	Min	0,74	56	5,6	20	0	1680	2
Cluster 1 (Nitrate pollution)	Max	2,26	84	140	290	160	7200	196
Cluster 2	Min	0,5	0	0	20	0	190	0
Cluster 2	Max	1	28	72,8	570	280	10800	260
Cluster 3 highest bacterial content	Min	0,74	0	0	1300	60	8200	140
Cluster 3 highest bacterial content	Max	0,85	28	0,003	10800	9000	42530	4320
WHO standards		-	50	0,5	20	0	-	20

- Cluster 1 (E1, P1 and P2) is made up of sites with poor chemical quality (nitrate content greater than 50 mg/L);

- Cluster 2 (E2, P3, P5, P6, P8, P10, P11, F1, F2, S1, S2, S3, and S4) is made up of sites with levels of elements indicative of chemical and bacteriological contamination that tend towards the average of the data set analysed;

- Cluster 3 (E3, E4, E5, P4, P7 and P9) is made up of sites with the highest bacterial content.

This spatially heterogeneous distribution of sites according to the type of contamination underlines once again the heterogeneous character of the contamination of the water resource in the Lefock watershed. This heterogeneity of contamination type needs therefore, to be investigated as it reveals that further management should account for multi-dimensional aspect of risks and vulnerability.

Table 4 shows that the clusters constituted in the plan are also a function of the nearby anthropic context and confirms the influence of the activities carried out around the water supply points on the water quality. Cluster 3 groups the most polluted samples (Table 3). This cluster is the only one to present within it the presence of the 06 human activities referenced. This tends to confirm the role of the multiplicity of sources in the contamination occurrence.

Main environmental factors controlling water contamination and vulnerability in Lefock watershed

In order to clarify which type of factors mainly constrain the chemical and bacteriological contaminations, we therefore projected the physiographic and anthropogenic factors (supplementary variables) on the two-dimensional (Dim 1 * Dim 2) plane (Fig. 4a). This shows that on Dimension 1 that Bacteriological and chemical indicators are tightly associated (loadings of 0.63 and 0.65), suggesting that both types of contamination occur preferentially together. Dimension 2 is mainly influenced by chemical contamination indicators (0.65) that however, remain distant from Bacteriological indicators closer to both Natural and anthropogenic factors (loadings respectively of 0.24, 0.27, and 0.12). This suggests that while occurring preferentially together, bacteriological contamination is more related to a combination of anthropogenic and physiographic conditions, while chemical contamination is relatively more sensitive to surrounding physiographic patterns.

Considering these complex patterns, each type of contamination and their most probable drivers are discussed in this article.

Role of anthropogenic and natural drivers for chemical contamination

All three samples, which exceeded the WHO standard for nitrate (E1, P1, and P2; Table 1), were collected in urban areas, with the exception of sample E1, which was collected in surface water in a peri-urban area on the campus of the University of Dschang (the water collected flows from the agricultural and fish farming experimental plots of the University's Faculty of Agronomy and Agricultural Sciences). Samples P3 and P5 were also collected in the urban environment; in this samples, ammonium (NH₄⁺) level well above the average of 0.2 mg/l expected in natural waters (WHO 2017). This shows that the urban environment is more likely to result in chemical contamination of the resource than the peri-urban environment. All of these sites (E1, P1, P2, P3, and P5) have two or three of the following four elements in their immediate environment (Table 2): agricultural plot, domestic wastewater, domestic livestock, and pit latrine. This shows that the urban environment is much more vulnerable to chemical contamination of the resource than the peri-urban environment. The load of pollutants produced is indeed much higher in urban areas due to the higher population density. This result is in agreement with the observation of Lapworth et al (2017) that in sub-Saharan urban environments, the quality status of groundwater resources is often very poor due to inadequate waste management and source protection. Yemeli et al (2021) obtained similar results and showed by geostatistical interpolation of alkaline and alkaline earth element concentrations in groundwater and surface water, the existence of a geochemical anomaly in the center of the city of Dschang (in Cameroon), which she attributed to the much higher anthropogenic pressures in this location. The low values obtained for nitrates can be explained by the fact that agricultural activities in the area are seasonal with the non-intensive use of fertilizers. Overall, the relative disconnection between surrounding physiographic and anthropogenic features (Fig. 4a) would be consistent with the fact that the chemical degradation of the water quality is more related to a general and diffuse infiltration and flowing of water impacted by anthropogenic (both agriculture and urban-related processes) activities.

Role of anthropogenic and natural drivers for bacteriological contaminations

Each sampled point is split in the factorial space into two partial points (Fig. 4b), one of which represents the partial projection of this point in relation to the concentration of chemical indicators (red colour) and the other, the partial projection of the same point in relation to the concentration of bacteriological indicators (green colour).

Considering that bacteriological indicators appear more tightly related with the assessed natural and anthropogenic factors in the surrounding environment, we evaluated how partial individuals (Fig. 4b) influenced by the group of bacteriological contamination indicator variables are oriented in the plane along the SW (least contaminated pole)-NE (most contaminated pole) direction.

In order to clarify which anthropogenic or natural factors would be more related to the bacteriological contamination, then we discriminated each factor to visualize the strongest influence over the bacteriological contamination.

Three anthropogenic factors were found to have the greatest influence on the bacterial concentration measured in the samples studied. They are located in the environment close to more than 50% of the catchment points that are bacteriologically the most contaminated (Table 4). These are the presence of pit latrine, domestic wastewater and agricultural plot. These results complement those reported by Temgoua et al 2010 who attributed the origin of the bacteria observed in the groundwater of Dschang to the proximity of pit latrines.

According to Akhtar et al. 2019, water supply points (wells, boreholes, springs, and surface water) are fed by rainfall through infiltration for groundwater and runoff for surface water carrying pollutants from the soil surface with limited attenuation of contamination. This process would be responsible for the bacteriological contamination of the waters collected by alternative means in the Lefock watershed.

From a physiographic point of view, the hydromorphic or ferrallitic nature of soils (water supply sites on hydromorphic soils are the most vulnerable to anthropogenic contamination) and the nature of the water supply (surface water is the most vulnerable to contamination, followed by wells. springs are the least vulnerable to contamination, while boreholes have a degree of vulnerability shared between springs and wells) are the elements of the nearby natural environment that best discriminate individuals in the factorial design (Fig. 4c).

According to Curmi et al. (1997); landscapes with a hydromorphic domain are characterized by an upstream, homogeneous, and highly permeable domain where water and solute transfers are mainly vertical; and a downstream, multilayered, low-permeability domain with two levels of water tables. This last domain features lateral transfers in the soil and of surface runoff, whose importance depends on the spatial and temporal extension of the saturated surfaces and their connectivity. This process could explain the high concentration of bacteria found in hydromorphic zones in the Lefock catchment.

On the other hand, Curmi et al. (1997) also show that in these areas denitrification is very high, which would justify the fact that these areas are not characterized by high nitrate concentrations although the sampling points are located close to nitrate-generating anthropogenic activities (see paragraph 4.1). Furthermore, the type of pit latrines used in the Lefock watershed is such that they reach the water table in hydromorphic areas. At this level, the groundwater table does not benefit from the vertical protection of the soil that exists in a ferralitic context.

According to the WHO drinking water standard, the water from the alternative water sources in the semi-urban watershed of Lefock is not suitable for human consumption as drinking water. The contamination of these water resources is strongly influenced by the environmental context near the water supply point. In addition, the lack of direct correlation between nitrate and faecal indicator bacteria in these waters suggests multiple and heterogeneous sources of contamination. The environmental description of the water supply points confirms this and the multiple factor analysis coupled with the hierarchical clustering on the main components highlights the characteristics that best contribute to the contamination of these sources (water supply point). Chemically, it is; agricultural plot, domestic wastewater, domestic breeding, pit latrine; bacteriologically, it is the presence of domestic breeding, pit latrines and wild garbage dumps. These latter impacts are stronger in surface waters and in wells than in boreholes and springs. In addition, some natural patterns seem to favour bacteriological contamination i.e. the hydromorphic nature of soils. In particular, this work showed that chemical and bacteriological contaminations, although being observed conjointly in various cases, have to be considered as the result of distinct processes. These results, therefore, argue for a two-scale management approach to limit environmental and health risks in using these alternative water supplies. At first, a watershed-scale management plan of nitrogen loadings should be considered, likely considering agricultural practices (their extent and location in relation to alternative water supply zones) in priority. Second, at the scale of the alternative water supply, special attention on individual practices should be carried out.

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Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Competing Interests

The authors have no relevant financial or non-financial interests to disclose.

Author Contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Lauric TONTSA, Emile TEMGOUA, Guillaume BERTRAND, Lucas KENGNI, Mike Castane MAKAYA MVOUBOU, Adoua NJUEYA KOPA, and Franck Fabrice MBA. The first draft of the manuscript was written by TONTSA Lauric and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Availability of data and materials

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Acknowledgements

The authors thank Dr. Obinna Chigoziem AKAKURU of the Department of Geology, Federal University of Technology, Owerri, Nigeria, for reviewing and improving the quality of the manuscript before submission to a scientific journal.

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Environmental factors controlling contamination and vulnerability of water alternative supply points in Lefock semi-urban watershed, West Cameroon

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Abstract

Figures

Introduction

Methodology

Study area

Data collection and processing

Physiographical and anthropogenic characterization of alternative sampling sites

Sampling and chemical /bacteriological analyses

Data processing through statistical analysis

Results And Discussion

Type of supply water utilities

Water quality

Heterogeneity of water contaminations and link with the surrounding environment

Main environmental factors controlling water contamination and vulnerability in Lefock watershed

Role of anthropogenic and natural drivers for chemical contamination

Role of anthropogenic and natural drivers for bacteriological contaminations

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1