RESEARCH ARTICLE 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 Qun Gao 1 & Shuang Chen 1 & Ismael Aaron Kimirei 1,2 & Lu Zhang 3 & Huruma Mgana 2 & Prisca Mziray 2 & Zhaode Wang 3 & Cheng Yu 1 & Qiushi Shen 3 Received: 26 May 2017 /Accepted: 25 January 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract 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. Keywords Atmospheric nitrogen deposition . Deposition flux . Seasonal difference . Lake Tanganyika . Climate change . Africa Introduction Lake Tanganyika is a complex tropical ecosystem. It is the deepest lake in Africa, with a maximum water depth of 1470 m (Coulter 1991; Cohen et al. 1993) (Fig. 1). Due to its hydrological and nutrient chemistry characteristics, Lake Tanganyika has a permanently stratified water column, which causes severe nutrient depletion in the surface waters (Edmond et al. 1993). Consequently, the upper epilimnion layer (0–20 m) is extremely nutrient-poor (Järvinen et al. 1999). Compared to other tropical lakes, Lake Tanganyika has an anoxic hypolimnion at depths around 100 m in the north and 240–250 m in the south (Coulter and Spigel 1991) and very low phytoplankton concentrations (Bootsma and Hecky 2003). Thus, the surface waters of the lake require nitrogen (N) from external sources to sustain primary produc- tion (Brion et al. 2006). Langenberg et al. (2003) indicated that wet atmospheric deposition provides approximately 83% of dissolved inorganic nitrogen (DIN) through an external source loading, with N from the atmosphere representing an important component of the N loaded into Lake Tanganyika. Climatic records from Africa have shown that temperature and rainfall patterns, as well as rainfall levels, have changed over the last millennium (Hulme et al. 2001; Holmgren and Öberg 2006), and climate change is significantly altering the environment of Lake Tanganyika (Verburg et al. 2003; Responsible editor: Philippe Garrigues * Qun Gao qgao@niglas.ac.cn 1 Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography & Limnology, Chinese Academy of Sciences (NIGLAS), Nanjing, Jiangsu 210008, China 2 Kigoma Center, Tanzania Fisheries Research Institute (TAFIRI), P.O. Box 90, Kigoma, Tanzania 3 State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography & Limnology, Chinese Academy of Sciences (NIGLAS), Nanjing 210008, China Environmental Science and Pollution Research https://doi.org/10.1007/s11356-018-1389-4