First exploration of the diatom diversity in lotic ecosystems in the Biosphere Reserve of Yangambi (DR Congo)

Diatom investigation of material from the 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, followed in 2012 and 2013 by a sampling from the Lobilo River in the South-Western part 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 on the diatom diversity are given for three 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 river is located at 5 km from its mouth, while the sampling site of the Isalowe and Bosambila rivers 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. The first results of the diatom investigation of these three acid rivers (pH 5.5-5.9) revealed a diversity of more than 80 species belonging to 31 genera. Eunotia, typical for acid waters, was the dominant genus and was represented by a large species diversity among which E. cf. rhomboidea, E. zygodon. E. fuseyi, E. leonardii, E. rudis. Besides a rather 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 and Eunotia rudis were sporadically observed in all samples taken near the bridges but were more frequent in the Isalowe source sample. The species composition and presence of numerous cosmopolitan species point to an organic pollution. However, an in-depth study of the cosmopolitan taxa is needed to confirm the identification. With exception of the Isalowe source, the three other samples were taken downstream close to the mouth 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:2018