Jonathan D. Anderson

ACCUMULATION OF ORGANIC CARBON IN RECLAIMED COAL MINE SOILS OF WYOMING

The potential to sequester carbon and increase organic nutrient storage in disturbed soils, such as those reclaimed after surface coal mining, appears to be significant. Quantification of organic carbon accumulation is complicated, however, by the presence of coal and coal dust in these soils. Our preliminary data on organic matter content of reclaimed soils at surface coal mines in Wyoming suggest they are sequestering carbon at a rapid rate. Data from a surface mine reclamation site near Hanna, WY indicate that surface (0-15 cm) soil organic carbon content has increased from a low of 10.9 g C kg soil in 1983 to 18.6 g C kg soil in 1998 and to 20.5 g C kg soil in 2002. Undisturbed soil directly adjacent to the reclaimed site has a mean organic carbon content of 15.1 g kg soil. At a mine near Glenrock, WY, soil organic carbon at a site reclaimed in 1979 increased from an estimated low of 5.8 g C kg soil to a current level of 18.4 g C kg soil. Organic carbon content of undisturbed soils adjacent to the reclaimed area range from 9.9 to 15.7 g C kg soil. In contrast to the elevated organic carbon content, amounts of microbial biomass in reclaimed soils at both mines are lower than in nearby undisturbed soils (ca. 60% or less). We have collected similar data from a number of other surface coal mines in Wyoming. We hypothesize that decomposition rates are slow in reclaimed mine soils due to low microbial activity relative to that in undisturbed soils. Additional

Amending bauxite residue sands with residue fines to enhance growth potential

Long term success of rehabilitation on bauxite-processed residue storage areas is dependant on establishing a capping stratum which will satisfy water use and nutrient cycling requirements of the intended plant community. Bauxite residue sand is the primary growth media for rehabilitating residue disposal areas (RDAs) in Western Australia however; the sustainability of the vegetation cover can be compromised by the poor water-retention and nutrient cycling properties of the residue sand. This glasshouse study was conducted to determine if adding untreated or altered residue fines ( 150 µm) would improve the characteristics of the final storage capping layer for sustained plant growth. Residue sand was amended by adding increments (1, 2, 3, 5, 10, 20 % w/w) of untreated or treated (carbonated or seawater washed) residue fines to determine whether these materials affected the chemical and physical properties of the growth media, and their ability to support vegetative growth (Acacia saligna), compared with the current practice of using only residue sand. Addition of residue fines increased water retention and extractable nutrient concentrations relative to untreated residue sand. However, the addition of residue fines increased both the electrical conductivity and exchangeable sodium percentage. Vegetative growth over a 3-month growing period varied with rate of residue fines addition, and residue fines pre-treatment (seawater > carbonated = unaltered). However, the addition of residue fines did not yield greater growth when compared with unamended residue sand. The importance of differences found in water retention and nutrient concentrations among residue treatments for plant growth need to be investigated in a water-limited field environment.

Plant-available manganese in bauxite residue sand amended with compost and residue mud

Manganese (Mn) deficiency has been a constraint for revegetation on bauxite residue sand and there is still no effective strategy to remedy this problem. The effect of addition of organic amendments (piggery waste, biosolids, and commercial compost) and mineral amendments (unamended, seawater-neutralised residue mud, and carbonated bauxite residue mud) on Mn forms and availability in residue sand was studied. Incubation of residue sand with organic amendments (applied at rates of 0, 10, and 50t/ha) over a 30-day period found little change in DTPA-extractable Mn concentrations, which remained below the critical level of 1mg/kg. The DTPA-extractable Mn concentrations were comparable to those in the exchangeable fraction (DTPA-Mn=0.931 ×Exch-Mn+0.358, r 2=0.84) and, therefore, may provide an estimation of plant-available Mn. The highest Mn concentrations were consistently associated with the carbonate fraction, suggesting that Mn was either retained by surface adsorption reactions and/or co-precipitated with calcium carbonate. The addition of residue mud amendments generally reduced DTPA-extractable Mn, probably through adsorption by hydrous Fe and Al oxides. Leaching did not cause significant (P>0.05) movement of Mn in residue sand columns, possibly due to the alkaline pH and specific adsorption reactions. Given the difficulty of increasing plant-available Mn by organic amendments, residue mud additions, leaching, and/or fertilisers, overcoming Mn deficiency in vegetation on bauxite residue sand may depend on using Mn-efficient species that are able to efficiently extract Mn associated with carbonate and Fe/Al oxyhydroxide fractions.

The influence of management practices on microbial and total soil nitrogen

Nitrogen (N) is usually the nutrient most limiting production in semiarid ecosystems and at very low concentrations can seriously impact ecosystem processes. Soil from five mines, incorporating a number of commonly used land reclamation practices (grazing vs. un-grazed; stockpiled vs. direct hauled soil; shrub mosaic vs. grass seed mix; and stubble mulch vs. hay mulch), were sampled and analyzed for soil total N (TN) and microbial biomass N (MBN). All mines were located in semiarid Wyoming in either mixed-grass or sagebrush steppe ecosystems. The various management practices investigated appeared to have little influence on TN. Reclaimed soils averaged 30% less TN than undisturbed native soils, suggesting that N could potentially limit vegetation production. Only two reclaimed sites (grass and shrub) at Mine 1 contained a greater mass of TN than an undisturbed site, and while the reason is unclear, greater precipitation (20% higher relative to the other sites sampled) may be responsible. The microbial communities present in undisturbed soils appear to uptake N more efficiently than microbial communities present in reclaimed soil, relative to total soil N. As N fertilizer is only rarely used in Wyoming surface mines, N can only accumulate in a reclaimed soil via wet or dry deposition or by N-fixation by free-living micro-organisms or through symbiotic relationships. However, as legumes are typically only a small component of the vegetation, presumably deposition and/or microbial fixation of N are responsible for the majority of N accumulation in these ecosystems. Despite the low TN in reclaimed soils, high plant production on these reclaimed soils suggests that TN is not limiting production.

THE INFLUENCE OF MANAGEMENT ON MICROBIAL BIOMASS AND SOIL ORGANIC CARBON IN RECLAIMED SURFACE COAL MINES OF WYOMING 1

This study was conducted to determine the long-term influence (>11 years) of a number of reclamation management practices on the concentration microbial biomass carbon (MBC) and the concentration and mass of soil organic carbon (SOC) in reclaimed soils from a number of surface coal mines located in Wyoming. We compared a number of commonly used reclamation management practices (grazed vs. ungrazed; stockpiled topsoil vs. direct hauled topsoil; hay-crimp mulch vs. stubble mulch; grass seed mixture vs. shrub seed mixture) at five surface coal-mines. In addition, a native, undisturbed prairie soil was also sampled at each of the five coal-mines native sites. Reclamation management practices compared in this study, with the exception of stubble mulching, did not have significantly different long-term effects on SOC concentrations. Microbial biomass C was more influenced than SOC by the compared practices in the soils examined. In more than half of the sites analyzed, reclaimed soils had SOC concentrations similar to undisturbed soil reflecting the potential to accumulate C in reclaimed coal-mine soils.