Wetland Land Use/land Cover Changes, Paddy Farming Impacts on Soil Invertebrate Diversity, and Win-win Management Attributes in River Mpologoma Catchment, Uganda

Abstract

Land use/land cover (LULC) change, particularly the conversion of wetlands to agriculture, is a leading threat to freshwater wetlands with significant environmental and societal implications. In the River Mpologoma catchment, conversion of wetlands to agricultural land has eroded stream banks and reduced habitat quality, increasing flood incidences and biodiversity losses. Moreover, conversion of wetlands to agricultural land has persisted despite regulations prohibiting wetland farming; indicating that legal barriers alone may not be adequate to manage wetlands among wetland-dependent agrarian communities. This study examined the extent of wetland encroachment in River Mpologoma catchment to generate the management attributes that could possibly be incorporated into reconciliatory win-win wetland management to meet both human and environmental needs. Specifically, the study determined the past and future wetland LULC changes in the catchment, determined the impact of paddy farming on soil invertebrate diversity, and identified the wetland management attributes preferred by the people of River Mpologoma catchment for win-win management of the catchment’s wetlands. Wetland encroachment trends were determined through LULC change analysis using remote sensing and GIS techniques in ArcMap 10.7 and TerrSet Geospatial Monitoring and Modeling System while the impact of paddy farming on soil invertebrate biodiversity was determined by assessing the macro- and meso- invertebrate richness, density, and diversity among three sites of varying land use intensity in the catchment. For the preferred wetland management attributes, a survey using the Discrete Choice Experiment methodology was used on 400 respondents. Between 1986 and 2019, wetland area decreased by 603.73 km2; largely attributed to conversion to subsistence paddy farming (483.24 km2) and built-up (37.88 km2). Prediction by the Cellular Automata-Markov model revealed that subsistence paddy farming and built-up will continue to be the major land uses that will encroach on the wetlands in the River Mpologoma catchment by 2039. These should be a main focus for proper wetland management in the catchment. With regard to soil invertebrates, a total of 18 macro-invertebrate taxa dominated by Oligochaeta (53.7%) and Gastropoda (17.9%) and 24 meso-invertebrate taxa dominated by Oligochaeta (53.3%) and Nematoda (29.8%) were observed. Diplura, Ephemeroptera, Diptera, Odonata, and Trichoptera macrofauna and Isoptera, Gryllidae, Araneae, and Plecoptera mesofauna were only observed in the rice paddies, indicating that they are key invertebrate taxa in wetlands that have been converted for paddy rice farming in the River Mpologoma catchment. Macro-invertebrate richness and diversity and meso-invertebrate richness and density were higher in the large-scale commercial paddies than in the uncultivated natural wetland and smallholder paddies, indicating that, overall, large-scale commercial paddy farming could be more favorable to soil invertebrates than small-scale paddy farming and natural wetland. Soil pH, calcium, and phosphorus were the key soil environment parameters that correlated with the macro- and meso-invertebrate distribution. The preferred win-win wetland management attributes, in descending order, were:...............................................................