Abstract
The Rwenzori region in Uganda, a global biodiversity hotspot, is currently undergoing exponential economic and population growth, which puts continuous stress on its freshwater ecosystems. In Sub-Saharan Africa, biomonitoring campaigns using region-specific biotic indices is limited, particularly in Uganda. In this research, we present the Rwenzori Score (RS), a new macroinvertebrate-based biotic index developed to specifically assess the aquatic health of Rwenzori streams and rivers. We collected and measured both biological and physicochemical variables and identified 34,202 macroinvertebrates, belonging to 64 different taxa. The RS was developed in two steps. First, using canonical ordination, we identified chemical variables that correlated significantly with gradients in macroinvertebrate assemblage distribution and diversity. Second, based on selected variables and weighted averages, we determined specific family indicator values and assigned pollution tolerance values (varying from 1: tolerant; to 10: sensitive) to a family. Finally, we established four water quality classes: poor, fair, good, and excellent. The RS is highly correlated with the Average Score Per Taxon System (p < 0.05), a well-known and widely used biotic index. The RS has 5 unique taxa that are not included in other regional indices. In this regard, the development of the RS is a beneficial tool for tailor-made biomonitoring that can contribute to the sustainable development of the Rwenzori stream and river basins.
Highlights
Environmental stressors are increasingly putting global biodiversity under tremendous pressure in many locations in the world [1,2,3]
The development of the Rwenzori Score (RS) is a beneficial tool for tailor-made biomonitoring that can contribute to the sustainable development of the Rwenzori stream and river basins
Water samples were collected from 101 sites (Figure 1) that were randomly chosen to give a comprehensive assessment of the Rwenzori study area while making provision for the following: accessibility, presence and absence of pools and riffles, hydrogeology and altitudinal gradients, anthropogenic and natural disturbances that may impact the ecological status at each sampling site, namely mining, water abstraction, agriculture, roads/paths, and residential and urban areas
Summary
Environmental stressors are increasingly putting global biodiversity under tremendous pressure in many locations in the world [1,2,3]. One technique for deducing biomonitoring datasets is to combine taxa as per their perceived sensitivity or tolerance to environmental stressors [33] Once these tolerance scores are determined, the ecological health of newly monitored sites can be evaluated based on whether macroinvertebrate taxa from sensitive or tolerant groups are largely sampled [34,35,36]. Few macroinvertebrate-based indices formulated on the assignment of tolerance scores to benthic macroinvertebrate families have been developed for aquatic systems in montane regions in sub-Saharan Africa such as Ethiopian highlands [39]. Most tolerance scores (e.g., SASS5 and TARISS) have been estimated using data collected in the different South African and Tanzanian eco-regions. We focused in our study on sections between altitudes of 900–1700 m.a.s.l., as we wanted to investigate mountain conditions along sites that were most accessible
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