Identified wetland uses were grouped in six categories of unused, fallow, grazing, rice, upland food and high-value crops. Relating land uses with land use indicators revealed correlations between them, giving insights into key land use drivers. Spearman correlations between land use categories and the classificatory variables also revealed a weak relation of land use with wetland size (r = 0.17), wetland shape (r = 0.35), and hemeroby (r = 0.29). However, a significant (P < 0.001) negative relation with the steepness of valley slopes (r = -0.20), market proximity (r = -0.28), wetland accessibility (r = -0.33), and particularly the flooding regime (r = -0.46) was also observed.
Based on these land uses and identified key use drivers, redundancy analysis (RDA) explained land uses under different biophysical and socio-economic conditions. The six land use categories were further subdivided into: unused or extensively used under not drained and permanently flooded wetland areas and intensive uses in completely drained seasonally flooded areas using PCA.
The first two axes of the principal component analysis explained 33 (axis 1) and 31% (axis 2) of the total variance in land use. Axis 1 discriminated positively the unused or extensive use types and negatively the moderate to intensive use types, primarily based on wetland accessibility (r = 0.50), flooding regime (r = 0.46), fertiliser use (r = -0.72), and land use on uplands (r
= -0.59). Axis 2 differentiated land uses mainly based on area size (r = 0.40), hemeroby (r = 0.25), and wetland accessibility (r = -0.49). In general, the physical accessibility and the flooding regime of wetland partly determined the conversion of wetland areas for agricultural production (Figure 3).
Consequently, unused wetlands were associated with permanent flooding and difficult physical accessibility. Grazing and other extensive uses of wetlands were related to the steepness of upland slopes (wetlands with gentle slopes are easily accessible by livestock). Fallow areas or abandoned portions were explained by soil type, fertility indicators, and land use duration. Finally, continuous and intensive cropping was related to wetland drainage, intense use of adjacent areas for crop production, and application of fertiliser. Such relations were further reflected in differential land use patterns between derived wetland cluster groups (Figure 4). Most unused wetland sub-units (92%) occurred in extensively WCGs 1 and 2, whereas WCGs 4 and 5 embedded most of those drained (78%) under intensive food and high-value crop production.
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Figure 3: Redundancy analysis ordination diagrams of the major land use categories with the independent variables for small wetlands characteristics. Land use categories are represented by bold solid arrows and the explanatory variables are in dashed arrows.
Figure 4: Percentage of wetlands allocation to defined land uses per wetland typology in the study area. Colour and pattern gradients denote the intensity of land use intensity from unused (plain white) to intensive use (plain black).
1 2 3 4 5
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4. Discussion
The typology developed in this study combined rapid rural and participative approaches, wetland mapping, and multivariate analysis techniques to unravel the complexity in heterogeneous small wetland systems for better understanding of their agricultural use. The use of different approaches for data collection and analyses was important to relate the wetland systems to their use by the local people who live in these rural areas. The combination of social and environmental approaches for collecting data contributed to improve the understanding of wetland functioning critical for future management initiatives. For example, the use of the Rapid Rural Appraisal (RRA) approach, which emerged in the late 1970s in social sciences, helped to quickly collect, analyse, and evaluate information of the rural conditions of the study area (cf.
data collection section in materials and methods). The approach was efficient in collecting relevant information on the wetland uses at the different study sites (51 RRA sessions) within the short time period of the survey. This confirms the primary objective of the RRA development as a way to reduce the cost and the time consuming factors of other research procedures (Cernea, 1991). Furthermore, the local knowledge of wetland communities on the flooding behaviour of the wetland and changes in land use over time and space highly contributed to defining land use determinants.
The development of wetland typology is a step forward to identify key drivers of diversity of wetlands and uses and to understand the small wetland systems under different biophysical conditions and varying socio-economic environments. By combining environmental and socio-economic indicators of land use in the analysis, the typology allowed linking identified drivers, creating socio-ecological niches for specific wetland uses in the study area. The typology used various dimensions in geomorphology, agroecology, population density, markets, and management strategies to explain differences in land uses across sites. Agroecology, markets, and population density partly explain the diversity of rural livelihood strategies across and within locations in SSA, besides determining different land use patterns across areas. Furthermore, diversity of livelihood strategies represent to a large extent production orientation and objectives of rural farming households. The interaction of these factors influences farmers’ actions, land use decisions, and management options (Kobrich et al., 2003; Siebert et al., 2006; Tittonell et al., 2010; Giller et al., 2011). The variability in socio-economic attributes coupled with the biophysical differences leads to different intensities of land use and associated
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management practices. Different practices can in turn affect the hydrology of the wetland (i.e. drainage or irrigation infrastructure - IVC / WARDA, 1997) and soil characteristics (i.e. soil improvement by farmers’ investment in organic amendments or soil nutrient depletion (Roberts, 1988; Dixon and Wood, 2003). The wetland typology thus shows the scope for linking the heterogeneous wetland systems to land users (i.e. farmers) in order to explain the diversity observed in small wetland systems.