From the floristic study, semi aquatic and marshland plant species in the wetlands were mainly herbaceous and shrubby and showed discoloration in patches throughout the wetland. According to Tsala et al., (1993) and Halabowski et al., (2020), the presence of metal pollutants in wastewater and other anthropogenic influences constitute a stress factor for plants through their toxic effects on the photosynthetic process and membrane function. The decolouration of vegetation in this wetland could therefore be allied to excessive chemical elements from anthropogenic activities.
The study sites did not differ considerably from the rest as they clustered together as a community, probably due to high similarity in species composition that are affected by similar levels of environmental disturbances. Human activities involving cutting, of raffias and woody species resulted to an open vegetation with shrubs scattered all over the wetlands. Hyde and Wursten (2007) and Zelnik et al., (2021) have noted similar vegetation composition in the mining-impacted sites in wetlands along Lake Victoria in East Africa and Slovenian watercourses, respectively. This could be indicative that, the areas have suffered some degree of disturbance either from cultivation or other human activities with the exception of the control site, with a relatively higher number of trees.
Macrophytes constituted an important part of the wetland. According to Lindholm et al., (2020), macrophytes play a key role in the remediation of macro and micronutrients because they have the capacity to grow vigorously in nutrient rich environments especially emergent and floating species. The plants could absorb and sequester pollutants; or reduce erosion by damping wave actions and as such should be considered for proper management in order to contribute significantly to the wellbeing of other components of the dynamic aquatic system.
Quadrat studies revealed 50 plant (macrophytes) species (mainly emergent herbaceous plants: grasses) distributed in 28 families. Ahmad et al., (2009) reported that grasses which are represented by 10.000 species and about 610 genera are the most widespread family of flowering plants of the world. Just as any aquatic ecosystem, these grasses were dominated by monocots. In some ponded areas close to the main river course, floating macrophytes were observed. Tita et al., (2012) did not identify such plants in the urban segment of the Mezam River system nor made mention of them in ponded areas proxy to it. The latter reported that in 2007, the Nkoup River system was characterized by eutrophic species such as Potamogeton spp and Ceratophyllum demersum in the upstream segments considerably impacted by agriculture whereas the downstream and urban segments were dominated by floating and emergent species all of which accumulate and bio-concentrate significant amounts of metal pollutants. The fact that these plants were not reported in the agricultural wetlands in the Bamenda Municipality is an indication that this wetland is under stress activities and, thus continually degrading. Diverse urban amenities with some having considerably noxious activities have come to existence within the environs of this agricultural wetland of the municipality. These activities either impinge directly through physical alteration and development and/or indirectly through widespread diverse chemical inputs on the agricultural soils. Acho-Chi (1998) had commented on this alteration.
In the wetlands of Bamenda Municipality, Poaceae (26%) occurred as the most represented family, followed by Asteraceae (12%), Cyperaceae (8%), Acanthaceae (6%), Amaranthaceae (6%) with other species less represented. The marsh land from visual observation was dominated by Leersia hexandra growing in open water and covering large areas. In the area Pennicitum purpureum and or Tithonia diversifolia lined the main river course with doted spots of Sacharum sp., Coix sp, Ludwigia, sp, and Nesonia sp.
From the flora distribution, the control site at Mbelewa showed the greatest level of species diversity. Species biodiversity is used to indicate the ‘biological health’ of a particular habitat and is higher in less polluted areas. The control site at Mbelewa was represented by 39 species. Here, the dominant species ranked in abundance were as follows Raphia farinifera > Ludwigia hexandra > Coix spp.> Leersia hexandra > Ehchinochloa paramidelis.
The peri-urban site (Mile 4 to Below Foncha segment) which was represented by 40 species had the dominant species ranked in abundance as Commelina bengalensis > Leersia hexandra > Cyperus distance > Ehchinochloa pyramidalis. The dominance of Commelina benghalensis generally occurring in extensive uniform stands along the edge of the channel and in ponded and pond- like areas was similarly reported by Tita et el., (2012). These plants thrive well in seasonally flooded environments and as such their abundance and diversity is proof of their high tolerance for fluctuating water levels and anthropogenic disturbances in the area (Grosshans and Kenkel, 1997, Lindholm et al., 2020).
At the Ayaba to Ngomegham segment (at Mulang), Pennisetum purpureum > Echinochloa pyramidalis > Tithonia diversifolia > Leersia hexandra were the abundant species. Pennisetum purpureum, Echinochloa pyramidalis and Tithonia diversifolia lined the main river course. Amongst the plants found in the area, Coix sp, Poligonium sp, Ludwigia sp, Nesonia sp, Leersia sp, Echinochloa sp, Portulaca oleraceae are obligate wetland species and thus rarely occur on dry land, while Penicum sp and Pennisetum purpureum have the same likelihood of occurring in wetlands as on dry land. Portulaca oleracea is a weed in cultivated fields and waste moist marshy places. It is also used as a vegetable and medicinal herb (Sher et al., 2011; Marwat et al., 2011). Penniseteum purpureum amongst others is very effective in waste water treatment (Greenway, 2003; and Tita et al., 2012). Alternanthera sessilis is a common species, very widespread in waste and cultivated grounds, especially in damp or wet conditions (Townsend, 1974). It is an agricultural weed that invades disturbed wet areas in tropical and subtropical areas. Overrall, A. sessilis has a low significant ecological impact (Tomaino, 2006) and thus a good indicator species. Just as, A. sessilis, Rumex dentatus L., apart from its allelopathic activity (producing substances that inhibit the growth of other plants near it), it also grows in disturbed habitats, often in moist areas.
Lower Simpson indices of diversity (0.94) recorded at the urban and peri-urban indicates that species diversity at the control site is higher than that at the urban and peri-urban sites that show no differences. The urban site had lower species abundances in certain areas, indicating worse environmental conditions such as from toxic chemical inputs from the urban catchment. Similar findings due to worse environmental conditions have been reported by Germ et al., (2021) in a study to assess the diversity of macrophytes and environment of the Ljubljanica River (Slovenia).
Variability of Surface Soil Properties in the Wetlands of Bamenda Municipality and the relationship with macrophyte diversity
The soils were slightly acidic with a lower pH (1:2.5) water value of 5.35 recorded at the urban site at Mulang (that receives drains from the urban zone) than that of 6.04 pH value recorded at the Mbelewa site (the control site). Soil pH plays a primordial role in nutrient availability to plants and therefore their growth, development and diversity. Low pH reduces the mineralization of soil organic matter and other nutrient reserves, inhibiting root growth and consequently, adsorption of nutrients. The soils of the Mulang site had the lowest pH and the least diversity of plants. The acidic nature of the soil at this site can also be attributed to various anthropogenic factors. The soils of the urban wetland site (Mulang) site registered the highest EC of 309 uS/cm while the lowest EC value (120 uS/cm) was obtained at the Peri-urban site of Mile four. The highest pH recorded in the urban site could be associated to additional inputs ions from industrial urban activities. Soil organic carbon was in the order of 14.38% > 13.88% > 13.30% for the Mulang, Mbelewa and Mile Four site, respectively. Soil organic matter is a good indicator of soil fertility and one of the most important soil components, along with stabilization soil structure and improving infiltration rate. Nowadays, soil organic matter stabilization is perceived as a mechanism for organic carbon storage in the soil. Organic matter supplies energy and cell building constituents for most microorganisms and is a critical factor in soil fertility. Organic carbon however showed moderate variation at the control and pri-urban site but was highly variable at the urban site with a lower diversity of species. Just like the SOM the soils of the urban zone had the best C/N ratio of 14.9. This means that the mineralisation rate of the SOM is good. The sum of the exchangeable bases across the study sites were similar (0.97, 1.09, 1.00 for the Mbelewa site, Mile Four site and Mulang site, respectively). Exchangeable acidity stood in the order of 0.378 > 0.300 > 0.223 for the control site, peri urban and urban site respectively. However, the concentration of exchangeable Al3+ was highest at the urban site, and a probable indication of inputs from industrial inputs from the urban site.
From the results, Sand, pH-H2O, pH-KCl, Na were consistently least variable across the three sites. Tabi and Ogunkunle (2007) had similarly reported least variability of soil pH for vertisols under rice cultivation in the Logone flood plain of Northern Cameroon. A very important parameter that influences many physico-chemical properties of soils including the availability of nutrients, plants richness and diversity is soil pH. In this study, though the pH variability reported is small, minor changes in pH units have significant effects on nutrient availability. Moderately variable Mg2+ and ΣBases were observed across the three zones of the study area which could be attributed to variation in levels of alluvial materials received. Also, variation in chrono sequences of materials that have been subjected to different intensities of weathering could have a significant effect on these physical parameters. All these factors have significant implications on nutrient availability to plants of the wetlands. The moderate variability of these bases implies that, for proper management of the wetlands, a unique policy for the area is insufficient to conserve the wetlands. C/N, and Exch. Acidity, were highly variable. These parameters owe a lot of their origin to organic materials, urban swept off, and farm inputs that could have also influenced the vegetation diversity across the zones.
Clustering of the variables
From the hierarchical dendrograms for the classification of the chemical variables of the surface soils from the wetlands, two significant clusters were formed. The clusters correspond to the geographical location of the sampling sites and possible sources defining the soil quality like agricultural activity, industrial impact and fertilizing, which influences the diversity of macroflora in the area. Amongst the two major clusters, one cluster combined rural environment (control site,) and the peri-urban site where urbanization inputs are minimal. The other cluster represented the urban environment with varying human activities. In the urban zone. Alternanthera sessilis which was widespread in this cluster is a common species, very extensive in waste and cultivated grounds, especially in damp or wet conditions (Townsend, 1974). According to Lazzaro et al. (2020), it impacts native plant species. The cluster on the lower part of the dendrogram represents dominantly rural and peri-urban areas with natural origins. Here, the dominant species were ranked in abundance as Commelina bengalensis > Leersia hexandra > Cyperus distance > Ehchinochloa pyramidalis. The dominance of Commelina benghalensis generally occurred in extensive uniform stands. The Mann-Whitney U test, revealed a significant lower (P < 0.05) concentration of the chemical constituents of the control site and the urban sites indicating contamination, warranting monitoring.