Anthropogenically derived nitrogen (N) has a central role in global environmental changes, including climate change, biodiversity loss, air pollution, greenhouse gas emission, water pollution, as well as food production and human health. Current understanding of the biogeochemical processes that govern the N cycle in coupled human-ecological systems around the globe is drawn largely from the long-term ecological monitoring and experimental studies. Here, we review spatial and temporal patterns and trends in reactive N emissions, and the interactions between N and other important elements that dictate their delivery from terrestrial to aquatic ecosystems, and the impacts of N on biodiversity and human society. Integrated international and long-term collaborative studies covering research gaps will reduce uncertainties and promote further understanding of the nitrogen cycle in various ecosystems.

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ABSTRACT:The increasing influx of heavy metals into water bodies from industrial, agricultural, and domestic activities is of global concern because of their well documented negative effects on human and ecosystem health. A recent study of streams in Blantyre and Zomba, Malawi revealed lead levels of up 0.118 mg/L, exceeding the World Health Organisation acceptable level of 0.01 mg/L. Our ongoing study on low cost effective heavy metal remediation techniques in developing countries has already demonstrated that Moringa oleifera, the well known source of natural water clarifiers, is effective in heavy metal detoxification of water. This paper presents the first reported use of a related species, the African moringa, Moringa stenopetala for lead detoxification and preliminary investigation of the interaction of the metal with the polyelectrolytes of M. oleifera and stenopetala. The potential of M. stenopetala for lead removal was tested by means of jar tests. With an initial lead concentration of 7 ppm, M. stenopetala seed powder, at doses of 0.50, 1.00, 1.50, 2.00 and 2.50 g/100mL, reduced the concentration of lead by 20.00 ± 0.00, 46.19 ± 2.06, 71.19 ± 2.06 and 89.43 ± 0.60 and 96.23 ± 0.12 % respectively. M. stenopetala was more effective than M. oleifera in removing lead from water (p=0.001 at 95% confidence level). For oleifera, lead levels decreased exponentially during the first 5 h. of the reaction and then equilibrium was established; for stenopetala, a linear decrease was observed. The pH of the mixture rose from 2.30 to a maximum of 2.53 and 2.57 and then fell to an equilibrium value of 2.30 and 2.29 for oleifera and stenopetala respectively. Lead removal was also affected by pH, ionic strength, and water hardness. Our results show that M. stenopetala has potential in lead remediation of contaminated waters. Further studies are being carried out on remediation of other metals and the mechanism of the metal moringa interaction.

The objective of this study was to develop a rural domestic defluoridation technology for the removal of fluoride from groundwater using locally available raw bauxite. Drinking groundwater sample of high fluoride concentration (6.17 mg/L) was collected from a borehole in Machinga district of Southern Malawi where dental fluorosis is prevalent due to the high fluoride. Defluoridation of the water sample was done in a model domestic defluoridation unit in batch mode to optimize raw bauxite dosage and contact time. Sand and charcoal were used for water clarification. Optimum bauxite dosage and optimum contact time were determined as 0.150 kg/L and 15.0 min respectively. An optimum combined dosage of sand and charcoal for water clarification was found to be 0.720 kg/L. The specific safe water yield for this system was found to be 36.0 L/kg adsorbent. An empirical model of the form where Y is the specific safe water yield, x is the height/cross sectional area ratio of a defluoridator is developed to show the significance of defluoridator design in defluoridation.

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