Development of macroinvertebrates-based multimetric index to assess the ecological health of a rural river in North-central Nigeria

Most inland water ecosystems in Africa have been subjected to different anthropogenic stresses which in turn affect their overall health and productivity. The ecological status of the Wanzum River, a tropical river in North central Nigeria was assessed by developing a multimetric index (MMI) using macroinvertebrates. Macroinvertebrates were sampled monthly from four sampling stations using standard methods for a period of 12 months (December 2021 - November 2022). A total of forty-five (45) candidate metrics in the measures of macroinvertebrates diversity, richness, composition and abundance were selected for the development of the MMI. Out of the forty-five (45) metrics selected, twenty-one (21) were sensitive as they showed discriminatory potential between station 1 and stations 2, 3 and 4. Of the twenty-one (21) candidate metrics that showed discriminatory potentials, only seven were deemed repeatable, and they were further processed for redundancy and repeatability tests. The metrics that were repeatable includes; Mollusca + Diptera abundance, %Ephemeroptera, %Mollusca, %Ephemeroptera Plecoptera Trichoptera, %Mollusca + Diptera, %Ephemeroptera + Trichoptera and Coleoptera + Hemiptera richness. Of the seven metrics that were repeatable, only %Mollusca was not redundant at r ≥ 0.78 while the remaining six redundant. We added three more metrics to %Mollusca based on their level of ecological significance, and the three metrics includes; Mollusca + Diptera abundance, %EPT and Coleoptera + Hemiptera richness. The final MMI score falls between 0 and 4, and were categorised into four ecological classes which are good, fair, poor and very poor.