Spatio-seasonal variation in wetland water quality, heavy metal pollution and macroinvertebrate communities in the Waterberg Mountain Complex

Wetlands in semi-arid southern Africa are increasingly threatened by combined climatic and anthropogenic stressors, yet seasonal data on water quality and biota remain scarce. We assessed 11 wetlands in the Waterberg Mountain Complex, Limpopo Province sampling during early rains and late rains. At each site we measured in-situ physico-chemical variables, quantified water-sediment heavy metals and collected benthic macroinvertebrates. Dissolved oxygen was the only physico-chemical variable showing a significant seasonal decline (11.7 mg/l early rains to 5.8 mg/l in late rains; p < 0.05). Iron exceeded Canadian guidelines in 64% of LR samples (max = 22 mg/l). Cadmium exhibited the greatest seasonal increase in sediments (p < 0.01). Diptera dominated macroinvertebrate assemblages particularly at the most metal-enriched site whereas Ephemeroptera, Trichoptera and Odonata were abundant in wetlands with higher oxygen and lower metal loads. Canonical correspondence analysis linked turbidity, conductivity and temperature with tolerant taxa (Hemiptera, Hydracarina), whereas redundancy analysis indicated zinc and cadmium strongly structured communities at polluted sites. These findings highlight oxygen limitation and localized Fe–Cr–Cd enrichment as key stressors influencing macroinvertebrate diversity. As the first integrated seasonal assessment for Waterberg wetlands, the study provides a baseline for monitoring systems facing intensifying land-use and climate pressures and underscores the need for continued multi-season biomonitoring to guide adaptive management.