Litter cover as an index of nitrogen availability in rehabilitated mine sites

Abstract

The spatial heterogeneity of litter cover and bioavailability of nitrogen within a 9-year-old rehabilitated bauxite mine in south Western Australia was examined. Three replicate plots (6 m by 6 m) were each divided into 100 quadrats. Litter cover, vegetation distribution, and projected foliage cover were mapped, and litter (overstorey leaves, understorey leaves, and other assorted fractions) and soil (depth: 0–5, 5–10, and 10–30 cm) were sampled from within each quadrat. Litter distribution reflected projected foliage cover, and accumulated within microtopographic depressions. Distribution of soil nitrate (NO^3–) reflected the distribution of litter. The ¹⁵N natural abundance (d¹⁵N) values of soil (0–5 cm) and the understorey litter fraction were significantly correlated (R² = 0.529, P < 0.05), whereas carbon isotope composition (d¹³C) of soil (0–5 cm) was significantly correlated with the distribution of the assorted litter fraction (R² = 0.296, P < 0.05). It is concluded that site preparation practices that effect microtopography, such as contour ripping and revegetation along contours, will have a significant impact on nitrogen (N) distribution and bioavailability within rehabilitated mine sites.