Quantifying Metal Contamination and Potential Uptake by Phragmites australis Adans. (Poaceae) Along a Subtropical River System

Abstract

<jats:p>: Metal pollution is pervasive across terrestrial and aquatic ecosystems owing to anthropogenic activities. Sediments can accrue high concentrations of metals and act as secondary sources, and thus may be valuable indicators of metal contamination across spatiotemporal scales. In aquatic systems, the extent of metal pollution may be further mediated by transference among sediments and living organisms, with plant metal contaminants potentially predictive of underlying sediment concentrations. The present study thus quantifies the extent of metal pollutants (Na, K, Ca, Mg, Cu, Zn, Mn, B, Fe) across multiple study sites and seasons (cool-dry, hot-wet, hot-dry) in a subtropical river system. Furthermore, uptake by a key macrophyte species, Phragmites australis, was examined and correlated with sediment pollution levels among different plant parts. Overall, sediment pollution load indices differed seasonally, being significantly highest during the cool-dry season irrespective of sampling location, suggesting that periods with reduced water flows can exacerbate metal pollution levels in riverine sediments. Also, metal concentrations were highest in upstream wetland sites, indicating a capacity for metal sink effects in these areas. Overall, macrophytes contained high concentrations of select metals, however composition and concentrations differed across plant parts, with roots containing particularly high concentrations of Fe and B. Correlations between sediment and macrophyte concentrations were mostly non-significant, whilst stem Mn and Fe concentrations correlated significantly negatively and positively to sediment concentrations, respectively. The present study identifies key spatiotemporal differences in multiple metal contaminants in an understudied subtropical aquatic system that align with hydrological regime differences. Whilst macrophytes were not found to be major accumulators, or predictors, of metal contaminants in this study, they may collectively play a central role in concentration regulation in aquatic systems.</jats:p>

Aquatic Macrophytes Metal and Nutrient Concentration Variations, with Implication for Phytoremediation Potential in a Subtropical River System

“…According to Emenike et al [46], high metal concentrations were observed during the hot-dry season; similarly, our study showed a similar finding where some metal concentrations peaked during the hotdry season, suggesting that accumulation and concentration occur as the river recedes and evaporation significantly increases, whereas the pollutants/contaminants entering the system remain constant. In support of our findings, Netshiongolwe et al [19] also observed similar patterns in metal concentrations. In contrast with this study findings, Edokpayi et al [33] found that metal concentrations were high during the hot-wet season in the Mvudi River, which was attributed to changes in human activities across different seasons.…”

“…Phragmites australis was the least effective in translocating metals, although it showed accumulation of metals during the hot-dry and hot-wet seasons. Similarly, studies by Kassaye et al [40] and Netshiongolwe et al [19] observed that P. australis has an absorptive ability for heavy metals and tends to accumulate these metals within the roots. Furthermore, Kassaye et al [40] highlighted that S. corymbosus has the potential to absorb heavy metals from soils, and they mostly accumulate in its leaves.…”

“…Metal removal using living organisms has recently received a lot of public interest and research and development funding [17][18][19]. Thus, several studies have recommended phytoremediation as an environmentally friendly and cost-effective method for removing pollutants from aquatic ecosystems [20,21].…”

Aquatic Ecological Risk of Heavy-Metal Pollution Associated with Degraded Mining Landscapes of the Southern Africa River Basins: A Review

“…Several macrophyte species, including Eichhornia, Ludwigia, Polygonum, Pistia, Cyperus, Lemna, Elodea, Typha, and Azolla, have been used to study HM contamination dynamics in tropical aquatic environments [135,160,207,208]. Macrophytes are appropriate bioagents for the long-term monitoring of aquatic ecosystem health due to their sedentary nature, high diversity, abundance, ease of identification and handling, and tolerance to HM pollution [105,209,210]. Changes in the macrophyte community structure and composition can also be a valuable indicator of pollution trends and alterations of the stream water quality [184,211].…”

Safe Management of E-Waste Disposal to Prevent Harmful Effects on Human Health and the Environment

“…Leachate poisoned surrounding soils and vegetables. Studies revealed that upstream heavy metal concentrations were higher than downstream due to the leaching process 11,24) . The heavy metal contents tested were lead, mercury, zinc, cadmium, chromium, arsenic, iron, nickel, cobalt, selenium, and copper.…”