Special Report: Monitoring water quality
Fig. 1 Typical clear stream in Rwanda near the source of the Nile
Professor Eberhard Fischer from the University of Koblenz-Landau highlights the importance of freshwater algae and bryophytes for monitoring water quality in the tropics.
In the working group of Professor Fischer, different organisms are studied, e.g. lichens, fresh water red algae, bryophytes and various flowering plants such as Linderniaceae, gingers or orchids. Here the algae and bryophytes growing in streams and rivers of tropical Africa are addressed.
Freshwater algae and bryophytes – developing a monitoring system for water quality in tropical Africa – the case study of Rwanda
Aquatic ecosystems have been subject to anthropogenic impact on a worldwide scale. In rivers, contaminants from agricultural run-off or urban inputs are important in the Northern Hemisphere, but also increase in the tropics. Climate change has an impact on aquatic ecosystems as well. For an assessment of these impacts, a biological monitoring is applied. Currently, benthic macroinvertebrates are the most widely used bioindicators, but benthic algae, especially diatoms, are becoming more important.
Algae are thus widely used as bioindicators of water quality in Europe. Specially diatom-based indices of water quality, mainly using benthic diatoms, have been developed, but other algal groups, such as freshwater red algae, proved to be valuable indicators for running waters. In Europe, the ecological requirements of many diatom species are well known. The European Standard EN 13946 (2003) provides guidance for the sampling and pre-treatment of benthic diatoms from rivers. The majority of bioindication work has been done in Europe and North America, and the diatom-based indices have proved invaluable for water quality biomonitoring in European rivers. Despite an elaborated taxonomic framework, however, new species are discovered regularly within a routine monitoring (e.g. two Navicula species in France and Belgium, cf. Beauger et al. 2015, Phytotaxa 230: 172-182).
Recently, these methods have also been applied to South America (Southern Brazil, Lobo et al. 2004, Acta Limnol. Bras. 16: 15-40) and South Africa (e.g. Taylor et al. 2003, Hydrobiologia 592: 455-464). However, problems arose when the European-based methods were transferred to Africa, where endemic African taxa are dominant in the samples. It has become clear that the majority of species recorded form a special paleotropical flora with a high percentage of species new to science (see Cocquyt et al. 2014, Phytotaxa 158: 76-84).
This is also true for Rwanda, a small east African country which may serve as a model system for biomonitoring in the tropics. Here, only a few studies on diatoms are available and the knowledge of presumably rich flora is incomplete. The first study was that of Lemmermann (1914, Wissenschaftliche Ergebnisse der Deutschen Zentral-Afrika-Expedition 1907-1908, 2: 92-94), who listed 33 taxa in 27 species, mainly from the Rukarara in Nyungwe and Lake Mohasi. A thorough investigation of algae in the rapids of the Rusizi near Bugarama (Kufferath 1957, Acad. Royale Sciences Coloniales Classe des Sciences Naturelles et MedicalesMémoires in-8° Nouvelle série 5, 3: 1-70) at the border of Rwanda, Burundi and the Democratic Republic of Congo, revealed 54 taxa and 51 species of diatoms in 18 genera, with Nitzschia as the most species-rich genus. 11 species are described as new to science and considered as endemic to the Rusizi rapids. An ecological study, including some diatom species, is available for Lake Kivu (Sarmiento et al. 2006, Journal of Plankton Research 28: 815-829). Thus, fewer than 100 species of diatoms are actually known from Rwanda. First results from Rusumo Falls show that at least 30-40 species are present in this locality. The diatom flora is very rich but identification of species is still preliminary.
A planned project intends to use diatoms, freshwater red algae and bryophytes to evaluate and subsequently monitor the water quality of streams and rivers in Rwanda. Rwanda is of special hydrological importance as it has a very large diversity of aquatic habitats and harbours one of the sources of the Nile River, which is situated in a mountain rainforest (Nyungwe National Park). In Rwanda there is also the watershed between the Nile and the Congo River on the eastern crest of the Albertine Rift. All streams flowing westward to Lake Kivu end up in Lake Tanganyika and from there in the Congo River System. All streams flowing eastward go to the Akagera-Nile and Lake Victoria, and flow into the Blue Nile. Rwanda has undisturbed sources and clear, unpolluted streams, but also streams and rivers in anthropogenic disturbed landscape mainly polluted by soil erosion.
Industrial pollution does not actually play an important role. The aim of the planned study, together with colleagues from Rwanda and Belgium, is to first develop a taxonomic framework by an inventory of the diatom flora in different habitats with emphasis to rivers and streams. Thus, a suite of biomonitoring tools will be introduced that should enable an assessment and subsequent monitoring of benthic diatoms.
Other algae suitable for a biomonitoring are freshwater red algae. The advantage of this group is that it is comparatively species poor, but there exist major taxonomic problems. Actually, the taxonomic literature covers mainly Europe, North America, parts of South America (especially Brazil) and Australia. There is also a world monograph of freshwater red algae available (Kumano 2002, Biopress Limited, Bristol). While red algae are regularly used in the biomonitoring of European or North American Rivers, there are only few attempts to apply these methods in the tropics. Wanninee et al. (2015) studied the possibility of freshwater red algae as bioindicators for water quality of streams in parts of Thailand (Journal of Agricultural Technology 11: 1349-1358). In Rwanda, like in diatoms, a taxonomic framework has to be developed first. Observations indicate that freshwater red algae of the genera Batrachospermum, Kumanoa and Hildebrandtia are mainly present in the high mountain sources and clear streams.
A final plant group successfully used for monitoring water quality, but also for monitoring climate change, is the bryophyte group, e.g. liverworts and mosses (see Frahm 1998, Biologische Arbeitsbücher 57, Quelle & Meyer, Wiesbaden). For Rwanda, the liverworts are already well known (Fischer 2013, Abc taxa 14), but for mosses, a taxonomic framework has yet to be developed.
With the development of such a taxonomic framework of benthic diatoms, freshwater red algae and bryophytes for Rwanda, a regular biomonitoring similar to that applied in Europe will enable a continuous monitoring of water quality and of the effects of climate change in a tropical country undergoing numerous ecological changes.
Professor Dr Eberhard Fischer
Botany and Biodiversity
Department of Biology, Institute for Integrated Natural Sciences
University of Koblenz-Landau, Campus Koblenz
+49 (0)26 1287 2224
