Wet deposition of atmospheric nitrogen contributes to nitrogen loading in the surface waters of Lake Tanganyika, East Africa: a case study of the Kigoma region.

Lake Tanganyika, an African Great Lake, is a complex tropical ecosystem that has been subjected to extreme climate-related changes in the last century, including seasonal changes in temperature and rainfall, decreased overall annual rainfall, and greater frequency of rainstorms. Atmospheric nitrogen (N) is an important component of the lake's N loading, but how long-term and seasonal changes in precipitation affect this loading still needs clarification. This study aimed to improve our understanding of the seasonal features of N deposition in the lake, by monitoring atmospheric N deposition concentrations and fluxes from March 2013 to February 2014. There was a significant temporal variation in wet N depositions in the study area. The distribution of the annual rainfall into major (March-May 299.8 mm) and minor (October-December 343.2 mm) rainy seasons translated into 20 and 30% of N deposition. In September and January-February, there was 10 and 12% precipitation, representing 43 and 7% of N deposition in the lake. Nitrogen deposition was highest in September due to farmlands' burning during the dry season (June-August), leading to N accumulation in the atmosphere. In conclusion, the pattern of N deposition appears to be driven by the unique climatic characteristics of the lake basin and to be closely associated with local anthropogenic activities.