The impact of red mud on growth of wetland vegetation and substrate fertility

Abstract

Greenhouse experiments were conducted to evaluate the impact of “red mud”, the residue of the Bayer process for extracting alumina from bauxite, on wetland to investigate whether red mud can be used for wetland restoration. Two wetland species,Spartina alterniflora Loisel. andSagittaria lancifolia L., were used to test their response to the following substrate treatments: 100% marsh sediment, 100% red mud, a mixture of 50% marsh sediment and 50% red mud, a mixture of 50% red mud and 50% compost, and neutralized red mud. Each substrate treatment received two fertilization levels, fertilized (N−P−K) and unfertilized. Red mud could support the growth of the salt marsh species,Spartina alterniflora, but not the fresh marsh species.Sagittaria lancifolia. The high Na content and salinity of red mud, even when mixed with marsh sediment or compost, appeared to be the primary cause for the high mortality ofSagittaria in these substrates. Fertilization did not reduce the stress response ofSagittaria to red mud, but significantly increased the growth ofSpartina. Red mud is low in available N and P and required fertilizer or organic matter (e.g., compost) addition to increase fertility. In experiments with both fresh and salt marsh sediments, the concentrations of soluble heavy metals, with the exception of Mn, were not significantly greater for red mud than for marsh sediment. Thus, the release of heavy metals from red mud over the short-term may not pose an environmental concern. However, the mobilization of heavy metals over the long-term and the influence of plants in accumulating metals requires further investigation.