Assessing the health of forested riverine systems in the Niger Delta area of Nigeria: a macroinvertebrate-based multimetric index approach.

Forested catchments surround most of the riverine systems in the Niger Delta area of Nigeria. Presently, there are no biomonitoring tools to assess the ecological health of forested rivers in the area. Hence, this study is aimed at developing a macroinvertebrate-based multimetric index for assessing the health forested riverine systems in the Niger Delta area of Nigeria. Physico-chemical variables and macroinvertebrates were sampled from 18 sites in 11 rivers. Physico-chemical variables were used to categorise river sites into three ecological classes, which include near natural sites (NNS), slightly disturbed sites (SDS) and moderately disturbed sites (MDS). Fifty-four(54) macroinvertebrate candidate metrics in four groups which include abundance, composition, richness and diversity were selected for the development of the Niger Delta forested rivers multimetric index (FoMIND). Of the 54 metrics selected, four were integrated into the FoMIND, and they include EPT/Chironomidae abundance, %ETOC, Diptera richness and evenness index. Correlation of integrated metrics with physico-chemical variables on redundancy analysis (RDA) ordination showed that EPT/Chironomidae abundance and evenness index positively associated with dissolved oxygen at NNS which confirmed the near-natural conditions of most of the forested riverine systems in the Niger Delta. Therefore, FoMIND is recommended as a rapid diagnostic tool for monitoring and assessing water quality conditions of rivers within forested catchments in Nigeria.