Plant–metal interactions in contaminated freshwater sediments of the Fly River Flood Plain, Papua New Guinea: Copper

Sediments, water and 23 species of rooted, emergent and submerged aquatic macrophytes were sampled from eight different off‐river water‐bodies and flood plains (raunwaras) in the lower middle Fly River to examine the plant‐metal interaction in this mining impacted region. Plant samples obtained from contaminated sites generally showed increased metal concentration compared with the same species from uncontaminated sites. Mean copper concentrations observed for monocots were 7.56±6.05, 11.9±10.5, 15.0±10.7 mg kg−1 Cu (dry weight), corresponding to 0–70, 70–500 and 500–1000 mg kg−1 Cu in sediments. Similarly, dicot copper concentrations were 10.8±7.8, 26.6±15.2, 34.2±24.1 for 0–70, 70–500 and 500–1000 mg kg−1 Cu, respectively. The plants were distinctly grouped into monocots and dicots, with copper concentration in dicots significantly (P < 0.005) higher than in monocots. Copper concentrations in various plant parts appeared to be different from each other, however this trend was not significant. The following general trend was evident only for Nelumbo nucifera (significant at P < 0.01); seeds > fruits > flowers > petioles > stems > leaves. Species differences in copper content were observed to be significant for both monocots (P < 0.0005) and dicots (P < 0.05). Sediment copper concentrations, 266±120 mg kg−1 Cu (moderate impact) and 889±136 mg kg−1 Cu (severe impact) reflect the magnitude of copper‐rich sediment deposition, with sites closer to the main channel with higher concentrations than sites further away. Other sediment variables such as pH (r = 0.13 P < 0.05), Eh (r = 0.13 P < 0.05) and sediment organic matter (r = −0.13, P < 0.05) correlate with plant copper, confirming the various roles these variables play in the speciation, mobilization and availability of copper to aquatic macrophytes. Dissolved copper correlated poorly with plant copper. However, dissolved copper was found to correlate well with organic matter and particulate sulphur, confirming the existence of organic matter‐Cu and CuS complexes.