Land use and cover changes in the Likangala catchment of the Lake Chilwa basin, Malawi: implications for managing a tropical wetland

Abstract

This study analyses land use and cover changes in the Likangala River catchment of Lake Chilwa, Malawi, an endorheic tropical African lake. It also examines how land use-related physico-chemical and hydrological parameters in two affluent rivers of the lake affect the migratory and reproductive behaviour of Barbus paludinosus and B. trimaculatus, which are migratory, ecologically and economically important fish species. Land use analysis indicated increasing deforestation and conversion of agricultural land to homestead development. High soil losses of 100t ha -1 yr -1 were estimated in the upper reaches of the catchment. High rainfall kinetic energy and poor vegetation cover were major determinants of soil loss. Sediment yield was high (374t km -2 yr -1 ) in the more degraded catchment of the Likangala River, compared to 315t km -2 yr -1 in the less degraded Domasi River catchment. A situation analysis for the Likangala River catchment showed that a marked reduction in soil loss occurred when a combined 20% increase of contour ridging, maize yield and tree canopy was assumed. Multiple regression analysis indicated that sediment yield, river flow rate, electrical conductivity and total suspended solids are significant predictors of the migration dynamics and reproductive status of both Barbus species. Our results suggest that the most critical soil loss factor should form an integral part of soil conservation measures in the catchment and that appropriate management actions that reduce fishing pressure on breeding Barbus females in the affluent rivers should be formulated to ensure the success of spawning migrations of breeding females into these rivers. The study further demonstrates how a combination of land use modelling, community outreach, river water quality analysis and fish population dynamics analysis can be used to identify factors useful for managing and monitoring the catchments of small tropical lakes.

The natural history and fisheries ecology of Lake Chilwa, southern Malawi

“…Results also showed that degraded rivers with reduced river discharge on the Malawi side were devoid of Labeo mesops, while the Mnembo River, which has significantly higher river discharge and a relatively undisturbed catchment, has higher fish biodiversity, including Labeo mesops. Recent studies (Jamu et al, 2003;Delaney et al, 2006;Macuiane et al, 2009) support results of earlier work (Furse et al, 1979b;Kalk et al, 1979) which showed that marshes serve a critical function as breeding and nursery areas and swamps as de facto closed areas or sanctuaries. However, burning of marshes, siltation and conversion of these marshes to rice fields threaten the sustainability of the fishery.…”

“…Although it appears to be resilient to heavy fishing pressure, environmental degradation may pose a greater threat to sustainability of the fishery and hence livelihoods dependent on the lake. For example, Jamu et al (2003) and Delaney et al (2006) showed that high river sediment yield and low river flow had negative impacts on recruitment and spawning migration of Barbus to influent rivers. Results also showed that degraded rivers with reduced river discharge on the Malawi side were devoid of Labeo mesops, while the Mnembo River, which has significantly higher river discharge and a relatively undisturbed catchment, has higher fish biodiversity, including Labeo mesops.…”

Riparian ecosystem resilience and livelihood strategies under test: lessons from Lake Chilwa in Malawi and other lakes in Africa

“…B 369: 20130052 Lake Chilwa supports the livelihood of over 1.5 million people in the basin through agriculture and natural resource goods and services. Low water levels have negative implications on people's livelihoods through loss of income and employment, reduced fish supply, increased conflicts from competition for resources and increased exploitation of birds [46,48]. Receding water exposes land to crop farming and livestock grazing which negatively impacts wetland vegetation and associated biodiversity [48].…”

“…Low water levels have negative implications on people's livelihoods through loss of income and employment, reduced fish supply, increased conflicts from competition for resources and increased exploitation of birds [46,48]. Receding water exposes land to crop farming and livestock grazing which negatively impacts wetland vegetation and associated biodiversity [48]. Crowding of fishing villages which remain with adequate water levels for fishing has also resulted in poor sanitation [49].…”

“…Agricultural production can also indirectly reduce the availability of other ecosystem services. Typically, increased irrigation and deforestation in the Lake Chilwa catchment has reduced suitable fish breeding habitat in the lake [48].…”