Sediment Geochemistry and Benthic Ecological Quality in Coastal Waters of Rivers State, Nigeria

Abstract

Coastal sediments act as repositories and potential secondary sources of contaminants, while their physicochemical characteristics influence the retention, mobility, and bioavailability of heavy metals. In the Niger Delta, increasing anthropogenic pressures have raised concerns about sediment contamination and its effects on benthic communities. However, integrated assessments linking sediment geochemistry, metal contamination, ecological risk, and benthic ecological quality in coastal waters of Rivers State remain limited. This study evaluated sediment geochemistry and benthic ecological quality in selected coastal waters of Rivers State, Nigeria, with an emphasis on heavy metal contamination, ecological risk and benthic community responses. Surface sediments and benthic macroinvertebrates were collected from five sampling stations using standard procedures. Sediments were analysed for physicochemical characteristics, particle-size distribution and Fe, Zn, Pb, Cu, Ni, Cr and Cd. Contamination factor (CF), pollution load index (PLI) and potential ecological risk index (RI) were determined, while benthic ecological quality was assessed using abundance, Shannon–Wiener diversity, Simpson diversity, dominance and Pielou evenness. Sediment pH ranged from 5.86 to 6.78, while total organic carbon ranged from 1.62 to 3.82%. Station 4 recorded the highest concentrations of Zn (131.40 mg/kg), Pb (44.60 mg/kg), Cu (48.20 mg/kg), Ni (32.70 mg/kg), Cr (39.70 mg/kg) and Cd (1.28 mg/kg). PLI indicated comparatively greater contamination at Stations 3–5, with Station 4 recording the highest value. Ecological risk was dominated by Cd, although overall RI remained within the low-risk category. A total of 1,113 benthic macroinvertebrates were recorded, with abundance decreasing from 301 individuals at Station 1 to 134 at Station 4. Shannon diversity similarly declined from 2.87 to 1.58. PLI correlated negatively with benthic abundance and Shannon diversity, whereas fine sediment fractions and organic carbon correlated positively with metal burden. The findings indicate spatially variable sediment contamination associated with deterioration in benthic ecological quality and highlight the importance of integrated geochemical and biological monitoring of coastal ecosystems in Rivers State.