A quantitative assessment of nutrient flows in an integrated agriculture-aquaculture farming system at the shores of Lake Victoria, Kenya

The rural farming systems around Lake Victoria are predominantly subsistence with integrated crop and livestock production. The results presented here are based on integrated experimental smallholder aquaculture systems (Fingerponds) at the Lake Victoria wetlands. The overall objective was to increase fish protein supply to the households and the diversity in farming activities. The rural farming system was characterized using natural transect mapping alongside identification of bioresource flows between the system components. Nutrient flows were analyzed using Ecopath with Ecosim 5.1 software using nitrogen as the model currency. The model result scenario with and without the wetland demonstrated the importance of the natural wetland in the overall agroecosystem nutrient flows. The farming system is characterized by low nutrient throughput associated with low productivity. Nutrient balance at the Fingerponds sub-system level was highly positive compared to maize production, which is the dominant activity in the terrestrial ecosystem. Diversification of the farming system through integration of Fingerponds increases the nutrient flow pathways and functional diversity. However, Fingerponds had minimal impact on the agroecosystem performance indicators such as Biomass to throughput (B/E) and production to biomass (P/B) ratios, which are usually used to gauge ecosystem maturity and hence sustainability potential. This is probably because the overall farming systems productivity is low and Fingerponds is a small component of a larger agroecosystem. Nevertheless, modelling such systems with Ecopath provided a better insight to the agroecosystem nutrient flows.