Freshwater macroinvertebrates along the Nigeria-Cameroon border enhance the conservation value of the lower Guinea forest biodiversity hotspot.

In Nigeria and tropical Africa, the bias towards the protection of natural sites on account of terrestrial biodiversity or their resultant ecosystem services has led to a considerably low number of freshwater conservation studies in the region. To close this gap, six lotic freshwater systems in three different natural sites (Obudu Mountains, Agbokim Waterfalls, and Cross River National Park) along the Cameroon border of Nigeria were evaluated for the biodiversity of macroinvertebrates and some aspects of water quality in December 2021 and March 2022. Among other macroinvertebrate-related indices, the community conservation index (CCI), which considers the presence of threatened, rare, and notable species, was used for the conservation evaluation of the freshwater systems. The Ephemeroptera-Plecoptera-Trichoptera (EPT) species were notably rich at the sites, with over 12 species each at the Afundu Stream, Kwa River, Cataract Stream, and Agbokim River. All of the sites had a very high conservation value, according to the CCI, which was greater than 20. Some Obudu sites (Grotto and Becheve streams), despite having fewer EPT taxa, had higher CCI than the Kwa or Agbokim River. This was due to the presence of the endangered damselflies (Africocypha centripunctata and Allocnemis vicki) at the Obudu sites and a rare mayfly species in Nigeria (Tricorythus tinctus), which was reported at Agbokim and Kwa Rivers. The presence of a notable damselfly genus (Pentaphlebia) at the Afundu stream of the Obudu Mountains also raises some hope that the critically endangered damselfly (Pentaphlebia gamblesi), whose adult was last seen in 1973, could still be alive at the site. Canonical Correspondence Analysis revealed that the proportion of scrapers had a strong association with high BOD and EC in Agbokim River, while the Becheve and Grotto streams which had high vegetal cover was positively associated with shredders. Also, increasing DO in Afundu Stream, Kwa River and Cataract Stream was positively associated with EPT richness. This study revealed that more freshwater ecological studies need to be conducted at isolated natural sites and protected areas in Africa. Findings from such studies have implications for preserving freshwater ecosystems of high conservation value from the various threats that characterize the Anthropocene.

Gold mining impairs the biological water quality of a culturally important river and UNESCO World Heritage Site in Nigeria.

The UNESCO World Heritage Sites have special conservation regulations because they are recognized as having significant cultural and/or natural value. One of Nigeria's two UNESCO-designated World Heritage Sites is the Osun River. It has immense biodiversity values, which are currently being threatened due to gold mining activities within its catchment area. Thus, this study seeks to ascertain the current biological water quality of this culturally and internationally important river using ecological and ecotoxicological approaches. Samples were collected from three environmental compartments (i.e., water, benthic sediment, and macroinvertebrates) in both dry and wet seasons from the section of the river that flows through the UNESCO site. Findings revealed that the river's physiochemical water quality has immensely degraded on account of extremely high total suspended solids, extremely low water transparency, and low dissolved oxygen. Three heavy metals exceeded their permissible limits in drinking water; i.e., Cd (364-367 times higher), Pb (75-104 times higher), and As (35-67 times higher). The contamination factor indicated that the benthic sediments were contaminated with Cd and Au, while the geo-accumulation (Igeo) index only indicates contamination on account of Cd, though Au ranks second in order of Igeo. The composition of the river's macroinvertebrate fauna suggests that it has been severely impacted because there was almost no stress-sensitive Ephemeroptera-Plecoptera-Trichoptera taxon present (one taxon and one individual only). Almost all of the chosen heavy metals had bioaccumulated in the three functional feeding guilds of macroinvertebrates. The current levels of heavy metals in the three environmental compartments of the river pose a great risk to both freshwater biodiversity and human health. Thus, a re-channeling of the upstream effluents from the river or any other natural water is advised. Also, a periodic environmental audit of the river should be conducted until it recovers from the pollution stress.