Reliability of the Tanzania river scoring system (TARISS) macroinvertebrate index of water quality: a case study of the river Mpanga system, Uganda

Abstract

Uganda does not have a biomonitoring system for assessing the water quality of its rivers basing on benthic macroinvertebrates. An alternative system has been suggested in Tanzania. Differences in characteristics between Tanzania and Uganda may contribute to differences in the physical and chemical characteristics of rivers between the two countries, resulting in variations in macroinvertebrate assemblages and sensitivity levels in relation to disturbance. River Mpanga lies along the equator in western Uganda and shows heterogeneity of impacted and non-impacted sites along its course. The disturbance gradient of River Mpanga was determined using habitat integrity scores. The ability of the Tanzania River Scoring System (TARISS) to distinguish test from reference sites using macroinvertebrate assemblages was validated. Both qualitative and quantitative data were obtained through purposive sampling in both the wet and dry seasons. Macroinvertebrates were sampled following a slightly modified TARISS protocol. Canonical analysis of principle coordinates (CAP) showed that macroinvertebrate assemblages vary along a disturbance gradient, grouping test sites distinct from reference sites. Of the TARISS metrics, average score per taxon was able to distinguish between test and reference sites (p ¼ .009) among the TARISS metrics. Five taxa not included in TARISS were found in river Mpanga and were assigned sensitivity scores based on CAP predictive model in PERMANOVA. It was concluded that TARISS could be reliable for eastern African river systems but should be updated and/or modified by users in different regions to include missing taxa.

Rapid Bioassessment Protocols Using Aquatic Macroinvertebrates in Africa–Considerations for Regional Adaptation of Existing Biotic Indices

“…Some taxa (Dicercomyzidae, Ephemerythidae, Machadorythidae, Sisyridae, Curculionidae, Sciomyzidae, Stratiomyidae, Ampulariidae, Bithyniidae, and Mutelidae) included in NASS, TARISS, and ZISS should ideally be included in future versions of SASS as these taxa have been recorded in the South Africa, and a further revision of SASS is likely. In addition, a recent study in Uganda noted five new taxa to be included in a modified TARISS, namely Chordodidae, Ptilodactylidae, Aspidytidae, Leptopodidae, and Paraecnomidae, which were not included in the TARISS (Tumusiime et al, 2019), although the latter is not a recognized family and is included in Ecnomidae. Importantly, prior to any new taxon being included in a RBP developed for a new region, it is recommended that all identifications be confirmed by a recognized institute and their taxonomic classification be verified on the taxonomic backbone of the Global Biodiversity Information Facility.…”

“…The relationships between metrics and disturbance can be evaluated for each biotope (Dallas et al, 2018) and for the site as a whole (Kaaya et al, 2015). Recently, Tumusiime et al (2019) showed that macroinvertebrate assemblages differed between test (= impacted) and reference sites, which provided confidence in the ability of the TARISS to distinguish impacted and reference sites, thus validating the efficacy of TARISS in Uganda.…”

“…It has also been adapted for non-wadeable, deltaic aquatic biotopes in the Okavango Delta in Botswana: Okavango Assessment System (OKASS; Dallas, 2009). TARISS has been used in Ugandan and Rwandan rivers to assess water quality (Dusabe et al, 2019;Tumusiime et al, 2019), although identifications of macroinvertebrates were done on preserved samples in the laboratory and not in the field, and in the case of Dusabe et al (2019), the TARISS sampling protocol was not followed as biotopes were combined.…”

Rwenzori Score (RS): A Benthic Macroinvertebrate Index for Biomonitoring Rivers and Streams in the Rwenzori Region, Uganda

“…Additionally, the North American Hilsenhoff Biotic Index [46] and the fifth iteration of the South African Scoring System (SASS5) [47] that was developed for South African rivers has also gained popularity in Sub-Saharan African biomonitoring campaigns [48,49]. Recently, a Tanzania River Scoring System (TARISS) for Tanzanian rivers [50] derived from the SASS5 has been tested on two Ugandan rivers [51,52].…”

“…For example, most tolerance scores (e.g., SASS5 and TARISS) have been estimated using data collected in the different South African and Tanzanian eco-regions. However, regional macroinvertebrate taxon assemblages differ considerably in different tropical regions, and as a result, some of the macroinvertebrate taxa collected outside and even within Southern Africa and Tanzania have not been given tolerance scores [50,51,53,57,58]. Furthermore, the stressor gradients commonly observed in tropical regions can differ from the pollution gradients for which the SASS5 tolerance values were originally designed [59].…”