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Phosphite (P) is of emerging chemical interest due to its importance within the global phosphorus cycle. Yet, to date, precise/accurate measurements of P are still lacking due to the inherent analytical challenges linked to its instability/ease of oxidation and ultra-trace concentration. Here, we present the first in-situ sampling and speciation analysis method, for dissolved P, using the diffusive-gradients-in-thin-films (DGT) technique, combined with capillary-column-configured-dual-ion-chromatography (CC-DIC). Method optimization of the DGT elution regime, to simultaneously maximize desorption efficiency and CC-DIC sensitivity, along with the characterization of diffusion coefficients for P, were undertaken before full method validation. Laboratory-performance testing confirmed DGT-P acquisition to be independent of pH (3.0-10.0) and ionic strength (0-500 mM). The capacity for P was 45.8 μg cm, while neither P (up to 10 mg L) nor As (up to 1 mg L) impacted the DGT-P measurement. This novel method's functionality stems from the herein confirmed speciation preservation and double pre-concentration of P, resulting in quantification limits as low as 7.44 ng L for a 3-day deployment. Applications of this method in various terrestrial/aquatic environments were demonstrated and simultaneous profiles of P and P across a sediment-water interface were captured at mm resolution in two contrasting redox-mesocosm systems.

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.

Sources of pollution at the northern end of Lake Tanganyika are concentrated around Bujumbura, Burundi. This article studied the water quality characteristics of seven inflowing rivers emptying into Lake Tanganyika. Chemical analyses were carried out during rainy and dry seasons. The nutrients and suspended solids at some sites were above the critical level for healthy river water. Contamination was concentrated mainly around urban areas which have been newly developed to accommodate the rapidly growing population in the country. Compared to previous studies, the concentrations of nutrients in the river water were relatively high, indicating increasing pollution in Bujumbura's rivers. The mean values of physico-chemical parameters, with the exception of suspended solids, were found to be higher in the dry season than in the rainy season. This result is consistent with previous studies. Principal components analysis and factor analysis were employed for numerical analyses, and proven to be useful to assess the source of pollution in specific river sites, where monitoring data is missing. Routine monitoring of basic physical and chemical indicators of water quality is recommended for all urban lakes and rivers in order to protect both the aquatic ecosystem and health of the local residents living near the lake.

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