Lotic eocsystems in the MAB Reserve of Yangambi (DR Congo): exploration of the diatom biodiversity

Diatom diversity from the Man and Biosphere Reserve of Yangambi, located in Tshopo Province (part of the formerly Oriental Province) and bordering the Congo River, have never been the subject of any investigation till recently. The first samples for diatom analyses were taken in the North-Western part of the Reserve during the Belgian-Congolese Boyekoli Ebale Congo 2010 expedition. Sampling from the Lobilo River in the South Western part was done in 2012 and 2013 in the frame of a Belgian research project (COBAFISH) financed by the Belgian Science Policy. In 2015 a more detailed sampling plan and monitoring was established covering nine rivers and streams as PhD thesis topic of the second author (VLIR-UOS project). Preliminary results of the diatom analyses are given for a selected number of rivers: Lobilo, Isalowe and Bosambila. The studied samples were all taken near the bridges over the rivers on road R408 Kisangani-Isangi. The sampling site of the Lobilo is located at 5 km from its mouth, while the sampling site of the Isalowe and Bosambila was within about ten meters from their entrance into the Congo River. Additionally a sample taken near the source of the Isalowe was also investigated. First results of the diatom flora in these three acid rivers (pH 5.5-5.9) revealed a diversity of more than 80 species belonging to 31 genera. Eunotia was the dominant genus and represented by large species diversity among which E. cf. rhomboidea, E. zygodon and several taxa described new to science (e.g. E. fuseyi, E. leonardii, E. rudis). Besides a large number of cosmopolitan species (e.g. Encyonema silesiacum, Eolimna minima, Frustulia crassinervia, F. saxonica, Gomphonema affine var. rhombicum, Navicula cryptocephala) pantropical species such as Encyonopsis frequentissimum and Tropical African species such as Cavinula lilandae were sporadically observed in all samples with exception of the Isalowe source. The species composition and presence of numerous cosmopolitan species point to an organic pollution. Indeed, the studied samples, with exception of the Isalowe source, were all taken downstream close to the month into the Congo River and have been exposed to human impact. Notwithstanding the rivers flow in a Reserve, they are running through small villages and are subject to the impact of local artisanal palm oil production.

Publication year:2017