Mineralisation of nitrogen in a chronosequence of rehabilitated bauxite mines

Abstract

Mine site rehabilitation should aim to establish quickly and maintain the processes of nutrient cycling at rates comparable with, or approaching, those of native forests. Current management strategies for rehabilitating bauxite mines and other mine sites in Australia usually include planting fast-growing understorey species at high densities and applying fertiliser. We provide the first detailed study of nitrogen (N) availability and N transformations (mineralisation/immobilisation) in such rehabilitated mine sites. Mean concentrations of NO3– (0–5 cm) in a chronosequence (7, 13, 22, and 27 years old) of rehabilitated mine sites ranged from 0.5 to 1.3 kg/ha, and NH4+ from 4.0 to 9.5 kg/ha. In burnt and unburnt native jarrah (E. marginata Donn ex. Smith) forests adjacent to the mine site, mean NO3– concentrations in surface soil (0–5 cm) were 0.8 kg/ha (burnt) and 1.1 kg/ha (unburnt), and mean NH4+ concentrations were 6.8 kg/ha (burnt) and 7.8 kg/ha (unburnt). Concentration of NH4+ at 0–5 cm was strongly related to soil water content (R2 = 0.69, P < 0.05) in rehabilitation sites, but not at 5–10 cm depth. Rates of N mineralisation (0–5 cm) in rehabilitation sites ranged from 34 to 52 kg/ha.year, of the same order as rates in native forest soil. In all rehabilitation and native forest sites, rates of N mineralisation were significantly related to rates of N-uptake at both 0–5 and 5–10 cm depth (R2 > 0.63, P < 0.05). Soil C/N ratios (0–5 cm) in rehabilitation sites ranged from 22.4 to 38.8, and in native forests from 35.6 (burnt) to 40.3 (unburnt). Soil C/N ratios increased with depth in both rehabilitation and native forest sites (ranged from 31.2 to 51.6). Availability of water was the major determinant of nitrogen availability in this strongly Mediterranean climate.

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

“…By contrast, surface soil horizons were depleted in 15 N (1.4-2.3‰), probably as a result of N mineralisation (e.g. Todd et al 2000), and as predicted by theories advanced by Gebauer and Dietrich (1993), Högberg (1997), and Nadelhoffer and Fry (1988). Högberg et al (1996) have also suggested that the pathway for the development of δ 15 N signals of surface soils is: available pools of N → plant N → litter N The results of this study, and the homogenisation of soil caused by many procedures in mine site rehabilitation, provide some confirmation of this theory, particularly from the strong relationship between litter δ 15 N and soil δ 15 N (Fig.…”

Succession in Bird and Plant Communities over a 24-Year Chronosequence of Mine Rehabilitation in the Australian Monsoon Tropics

“…As such it represents a more extreme form of ecosystem disturbance than selective logging or clearing for agriculture, albeit typically affecting much smaller areas. Thus, mine rehabilitation programs generally attempt to establish plant productivity and nutrient cycling processes as soon as possible, a goal that has led in the past to applications of fertilizer and the seeding of fast growing, often exotic, and N‐fixing species at high densities (Parrotta & Knowles 1999; Todd et al 2000).…”

Hydraulic traits and water use of Eucalyptus on restored versus natural sites in a seasonally dry forest in southwestern Australia

“…Trees on restored sites grew in dense, single-age stands that intercepted radiation in full and were completely exposed to meteorological drivers of transpiration including temperature, humidity and wind speed (Koch, 2007a), and they were generously supplied with nutrients via additions of phosphatic fertilizers and a vigorous understorey of nitrogen-fixing Acacia spp. (Todd et al, 2000).…”