Regional nitrogen budget of the Lake Victoria Basin, East Africa: syntheses, uncertainties and perspectives

Abstract

Using the net anthropogenic nitrogen input (NANI) approach we estimated the N budget for the Lake Victoria Basin in East Africa. The NANI of the basin ranged from 887 to 3008 kg N km −2 yr −1 (mean: 1827 kg N km −2 yr −1 ) for the period 1995-2000. The net nitrogen release at basin level is due primarily to livestock and human consumption of feed and foods, contributing between 69% and 85%. Atmospheric oxidized N deposition contributed approximately 14% to the NANI of the Lake Victoria Basin, while either synthetic N fertilizer imports or biological N fixations only contributed less than 6% to the regional NANI. Due to the low N imports of feed and food products (<20 kg N km −2 yr −1 ), nitrogen release to the watershed must be derived from the mining of soil N stocks. The fraction of riverine N export to Lake Victoria accounted for 16%, which is much lower than for watersheds located in Europe and USA (25%). A significant reduction of the uncertainty of our N budget estimate for Lake Victoria Basin would be possible if better data on livestock systems and riverine N export were available. Our study indicates that at present soil N mining is the main source of nitrogen in the Lake Victoria Basin. Thus, sustainable N management requires increasing agricultural N inputs to guarantee food security and rehabilitation and protection of soils to minimize environmental costs. Moreover, to reduce N pollution of the lake, improving management of human and animal wastes needs to be carefully considered in future.

Dilemma of nitrogen management for future food security in sub-Saharan Africa – a review

“…It however becomes a significant risk to the environment when it ends up in water bodies or other areas where it cannot be used for plant growth. From a study by Zhou et al (2014), atmospheric N deposition accounted for 67% (i.e. 102 Gg N year -1 ) of the total N loading (152 Gg N year -1 ) into Lake Victoria in East Africa.…”

“…In general, human choices in terms of food consumption drive N use, particularly for food production (Sutton et al 2013). Selected investigations in SSA have been made to improve AE N ; however, quantification of N flows in the whole food supply chain has been too scarce to be representative, which has resulted in many uncertainties in N budgets Zhou et al 2014). Consequently, key intervention areas to optimise AE N and minimise N losses to the environment are often not well understood, particularly at national, regional, and continental scales.…”

“…These processes continuously create the spatial paradox of 'too little' and 'too much' N respectively, perpetuating food insecurity quantitatively and qualitatively (Marler and Wallin 2006) and leading to environmental pollution. For example, in highly populated regions of SSA like the Lake Victoria catchment, inadequate systems for municipal wastewater treatment have resulted in excessive N load into water bodies leading to eutrophication of certain sections of the lake (LVBC 2012;Zhou et al 2014). Some other sources of N overload of the SSA environment come from (1) atmospheric deposition (GalyLacaux and Delon 2014), (2) N-rich runoff of organic wastes from municipal and industrial areas, (3) N leaching mainly from commercial farms, and (4) insufficient treatment of wastewater from industry (e.g.…”

Gender and inorganic nitrogen: what are the implications of moving towards a more balanced use of nitrogen fertilizer in the tropics?

“…In poorly managed, low-input as well as high-input systems, N and phosphorus from eroding soil can reach water bodies and contribute to eutrophication (TEEB, 2015;Zhou et al, 2014). In the Lake Victoria watershed, a large fraction of the N entering the lake is from eroded soil leading directly to negative, gendered health outcomes.…”

“…Nutrient inflows into Lake Victoria -particularly N and phosphorus, have led to a five-fold increase in algae growth since the 1960s (Kolding et al, 2008). Zhou et al (2014) show that net N release in Lake Victoria at basin level is due primarily to livestock and human sources (https://outlook.live.com/owa/? path=/mail/inbox/rp#x__msocom_1) which contribute between 69% and 85%.…”