Riparian wetland that act as a transitional buffer zone between aquatic and terrestrial ecosystems, play vital role in maintaining healthy ecosystems and modulating the biogeochemical cycles of carbon (C), nitrogen (N), and phosphorous (P) (Liu et al., 2016). Previous studies (Zhang et al., 2017; Zhao etal., 2019) were investigated carbon (C), nitrogen (N), and phosphorous (P) are an important elements recycled in wetland ecosystems. Besides major nutrients (C, N and P), wetland also regulates sulfur (S), calcium (Ca+ 2) and potassium (K+) recycling processes (Leal etal., 2017).
Ecological stoichiometry examines the balance and dynamics of multielement and their ecological interaction in ecological processes (Long et al., 2018). This discipline can help to better understand the different levels of biogeochemical cycling processes (Leal etal., 2017) in different ecosystems. This shows linkage among various research studies and biological groups by affecting ecological integrity in different land use systems in different scales (Gong et al., 2020a). Ecological stoichiometry is useful to establish the linkage between different ecosystem compartments primarily divided in to different land use types. This can affect surface vegetation, residual quantity, soil properties and nutrient supply (Liu et al., 2018). Wetland ecosystems have been severely degraded since the past decades due to population growth and lack of sound policy (Awulachew, 2006). These effects are primarily causing wetland changes to farmland, urbanization and overgrazing (Zhang et al., 2017). Thus, wetland soil nutrient heterogeneity has been driven by local disturbance including land use change, human pressures, regional scale difference, climatic factors and geological processes (Hilt et al., 2017; Liu et al., 2018). In addition to the major elements (C, N, P, and S), macronutrients (Mg+ 2, Ca+ 2, Na+ and K+) have been reported as essential biogenic elements in nutrient cycling and wetland ecosystems soil quality indicator (Li et al., 2017). Hence, better knowledge on the distribution trend and ecological stoichiometry of C, N, P, S, Ca+ 2 and K+ in relation to wetland degradation is a critical concerns. Previous studies suggested that nitrogen (N); phosphorus (P) and potassium (K) are valuable mineral elements and key focuses in ecolosysytems study that affect microbial activity and accumulation of soil nutrients (Li etal., 2018). Thus, these elemental concentration imbalances can influence soil structure and ecosystems integrity broadly (Liu etal., 2016; Zhao etal., 2019). Most previous studies pointed out nutrients accumulation and cycling processes are regulated by soil texture, pH, bulk density, moisture content and land use types greatly ( Iticha and Takele, 2019). The molar ratios of C: N, C: P and N: P can determine soil quality and influence soil organic carbon, nitrogen and phosphorus cycling by affecting microbial activity and rate of mineralization potential in different land use (Liu et al., 2016; Sun etal., 2019). Moreover, C: P and C: S often reflected plant residual quality resulted from either P and S immobilization or mineralization (Hu etal., 2017). Therefore, to better understand biogeochemical cycling and ecosystems functioning and the dynamic nature of C, N, P, S, Ca, and K concentration and their stoichiometry in different ecosystems are significant.
Riparian wetlands play significant role in maintaining ecosystems stability, biodiversity conservation and nutrient removal (Xiong et al., 2017; Lingfei etal., 2017). However, wetlands in developing countries are losing frequently (Zsuffa etal., 2014). Among the main associated factors for wetland degradation, overgrazing and extensive farming expansions are the major deriving forces (Svotwa et al., 2008). Previous studies (Symeonakis and Drake, 2010; Sakan et al., 2013) have reported that soil degradation and difference in rainfall distribution brought decline in agricultural production and productivity. These enforce the local community to shift from highland to wetland based for farming in Ethiopia (Giweta and Worku, 2018). Previous studies (Simane et al., 2013; Giweta and Worku, 2018) reported that chemical fertilizers input, siltation, intensive farmland expansion, lack of wetland policy and poor catchment management practices were the major deriving forces for wetland degradation in most part of Ethiopia. In the same trend Lake Chamo riparian wetland located within the Ethiopian Rift valley region has been severely threatened by anthropogenic pressures. In this area, the previous studies conducted were focused on natural conditions and water consumption modelling on sediment (Awulachew, 2006), ecosystem services-values and biophysical-geological changes (Assef and Bork, 2016), and Limnological changes (Teffera et al., 2017) within and around Lake Chamo basin. However, none of these studies considered the effect of riparian wetland conversion to farm and grazing land effect on soil their ecological stoichiometry of C, N, P, S, Ca, K in this area. Thus, this research gap enforced us to design the following objectives, (1) to determine the change in the distribution of C, N, P, S, K and Ca associated with wetland use change to farm and grazing land use types (2) to examine the relationship between environmental variables with C, N, P, S, K and Ca and their ecological stoichiometry in the study sites, (3) to determine spatial exchangeable bases variation in different land use types. We hope this study will benefit the local authorities and other policy makers to make reasonable decision on a series wetland restoration project to rehabilitate degraded wetland ecosystems in Chamo Lake basin.