Lachlan J. Ingram

Influence of Topsoil Depth on Plant and Soil Attributes of 24-Year Old Reclaimed Mined Lands

ABSTRACT Topsoil replacement on reclaimed mine lands is vital for improved infiltration, plant rooting media, enhanced nutrient cycling, and as a potential source of plant propagules to increase plant community diversity. Varying topsoil depth may influence reclamation success. This study assessed the long-term (24 years) effects of four topsoil replacement depths (0, 20, 40, and 60 cm) on plant community attributes (species richness, diversity, canopy cover, and production) and soil characteristics [organic carbon (C), total nitrogen (N), available phosphorus (P), pH, soluble cations, electrical conductivity (EC), and cumulative water infiltration]. Species richness and diversity were highest at the 0 cm topsoil depth and lowest at the 60 cm topsoil depth. Percent canopy cover of grasses was highest (25%) at 60 cm and lowest (15%) at 0 cm topsoil depth. Percent forb cover was highest (6%) at the 0 cm depth and lowest (2%) at 60 cm topsoil depth. Seeded species cover was highest (12%) at the 40 cm depth, but was not significantly different from the other depths. Aboveground biomass was similar between the 40 (727 kg ha−1) and 60 cm (787 kg ha−1) topsoil depths and higher than the 0 (512 kg ha−1) and 20 cm (506 kg ha−1) replacement depths. Plant species richness and diversity decreased with increasing topsoil depth, while biomass increased. Organic C mass in the soil profile (75 cm) was greatest in the 60 cm topsoil replacement (18.7 Mg C ha−1) and lowest in the 0 and 20 cm treatments (11.3 and 10.5 Mg C ha−1, respectively). N mass (75 cm profile) exhibited a similar pattern with 60 cm of topsoil having the highest (1.9 Mg N ha−1) and the 0 and 20 cm the lowest (0.8 Mg N ha−1and 0.9 Mg N ha−1, respectively). Cumulative water infiltration was highest (134 mm) for the 40 cm topsoil depth followed by 60 cm (116 mm), and lowest (61 mm) for the 0 cm treatment. Soil N, organic C, and infiltration data indicate topsoil replacement depths of 40 and 60 cm provide the best nutrient status and water storage potential for sustainable reclamation. Placement of shallow topsoil replacement depths should be carefully planned to ensure topsoil thickness is adequate to sustain a vegetative community capable of protecting the soil surface against erosion. Variable topsoil replacement depths can be used in reclamation to manipulate plant community characteristics and create a mosaic of vegetation types. However, the reduced vegetation cover observed at the shallower topsoil depths may not protect against soil erosion; therefore, using variable topsoil depth replacement as a reclamation practice will require careful planning and implementation.

Forage Production and Quality of a Mixed-Grass Rangeland Interseeded With Medicago sativa ssp. falcata

Abstract Interseeding alfalfa into rangelands has been assessed for decades as a method of range improvement to increase forage production and forage quality for livestock. Research was initiated in 2001 to examine the long term effects of interseeding yellow-flowered alfalfa (Medicago sativa ssp. falcata) on northern mixed-grass rangelands. Forage production and forage quality parameters were assessed on sites interseeded in 1965, 1987, and 1998 and compared to adjacent native rangelands. Live aboveground biomass for the 1965, 1987, and 1998 interseeded sites was 68, 143, and 42% higher, respectively, compared to their native control areas. Alfalfa aboveground biomass accounted for 1 489 of the 2 969 kg·ha−1 live biomass harvested from the 1965 interseeded site, 1 940 of the 2 744 kg·ha−1 on the 1987 interseeded site, and 796 of the 2 322 kg·ha−1 on the 1998 interseeded site. Increased soil N resulting from N fixation by the alfalfa significantly increased the crude protein (CP) content of several native species, whereas the alfalfa itself provided forage with 16 to 18% CP. Alfalfa had higher protein degradability and provided higher concentrations of calcium (Ca), potassium (K), and magnesium (Mg) than the native rangeland grasses. This research has shown that the practice of interseeding yellow-flowering alfalfa into rangelands is sustainable over decades and will increase forage production and improve nutritive value of forage in the northern Great Plains.

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

Themeda triandra: a keystone grass species

Themeda triandra is a perennial tussock grass endemic to Africa, Australia and Asia. Within these regions it is found across a broad range of climates, geological substrates and ecosystems. Because it is widespread across these areas it has great economic and ecological value, as it is a relatively palatable species across most of its range. It is of critical importance in supporting local populations of both native and introduced herbivores, and is thus central to wildlife and livestock production, and consequently rural livelihoods. It is an important climax or subclimax species that is well adapted to fire, a common element of many areas where it is found. Inappropriate grazing management, however, can result in a decline of Themeda, as it is not well adapted to an uninterrupted, selective grazing regime. A decline in abundance of Themeda in a grassland is usually coupled to a decline in grazing value, species richness, cover and ecosystem function. In spite of its significant ecological and economic importance, there has been no attempt to review and synthesise the considerable body of research undertaken on this grass. Our aim is to summarise and synthesis work previously undertaken and identify areas where further research is required.

INFLUENCE OF RECLAMATION MANAGEMENT PRACTICES ON SOIL BULK DENSITY AND INFILTRATION RATES ON SURFACE COAL MINE LANDS IN WYOMING 1

A study was conducted to examine the impacts of land reclamation and management practices on the saturated infiltration rates (Ks) and bulk densities (BD) of soils in reclaimed surface coal mines of Wyoming. The use of direct- hauled topsoil vs. stockpiled topsoil, hay mulch vs. stubble mulch, grazing vs. no- grazing, and standard seed mixes (grass seeding) vs. shrub mosaic seed mixes as surface coal mineland reclamation practices were studied in five coal mines of the Powder River Basin, the Green River Coal Region and the Hanna Coal Field in Wyoming. Results from the reclaimed sites with the above listed management practices were compared to each other and with representative soils from adjacent native undisturbed sites. In all the study sites, native undisturbed soils had the lowest BD and the highest Ks compared to reclaimed soils. At Jim Bridger mine, results indicated no differences in BD and Ks between stockpiled and directly hauled soils. At the Belle Ayre mine, there was no significant difference in Ks between reclaimed soils and native undisturbed soil. At Seminoe mine, reclaimed stubble mulched soil had greater Ks (9.208 mm/min) than native undisturbed soil Ks (6.042 mm/min). At Jacobs Ranch, ungrazed soils had greater Ks (6.958 mm/min) than grazed soils Ks (3.350 mm/min) and native undisturbed soils (3.833 mm/min). BD at 0-5 cm for grazed soils was also greater (1.462 g/cm 3 ) than for ungrazed soils (1.255 g/cm 3 ) . Native undisturbed soils had the lowest BD (1.116 g/cm 3 ) averaged over all depths. Although native undisturbed BDs were generally lower, their Ks were not always greater. These results suggest that removal and manipulation of soil during mining accompanied by heavy machinery traffic over reapplied topsoil during reclamation may cause some degree of soil compaction relative to undisturbed sites. However, it can be concluded that land reclamation and management measures taken during and after mining may help to improve infiltration rates.

LONG-TERM PLANT COMMUNITY RESPONSES TO TOPSOIL REPLACEMENT DEPTH ON RECLAIMED MINED LAND 1

The use of topsoil on reclaimed mine lands may enhance plant community development and influence reclamation success. This study assessed the long-term (after 24 years) effects of different topsoil replacement depths (0, 200, 400, and 600 mm) on plant community cover, production, and diversity at a research site established in 1977 in south-central Wyoming. Plant species richness (number of species), canopy cover, aboveground biomass, and diversity were evaluated at the four topsoil depths in 2001. Plants were clipped, by species, to obtain mean biomass and to calculate importance values. Shannon-Weiner diversity indices were calculated for each topsoil depth. Species richness was highest (7.5) at the zero topsoil depth and lowest (5.6) at the 600 mm topsoil depth. Total canopy cover was greatest (average 26.7%) at 400 and 600 mm of topsoil and least (21.5%) at the zero topsoil depth. Seeded species canopy cover and seeded species biomass were also greatest at the 400 mm topsoil depth. Total biomass was similar for the 400 (734 kg/ha) and 600 mm (727 kg/ha) topsoil depths and lower but similar at the 200 mm depth (506 kg/ha) and 0 mm depth (513 kg/ha). Plant species richness and diversity index were highest at 0 mm (7.5 and 2.36, respectively) and lowest at 600 mm (5.6 and 1.87, respectively) of topsoil. Number of species and diversity decreased as topsoil depth increased. Increased plant biomass at the 400 and 600 mm depths and increased diversity at the 0 and 200 mm topsoil depths, indicate that variable replacement depths of topsoil can enhance reclamation success through greater species diversity and by creating a greater mosaic of vegetation. However, the reduced cover observed at these shallower topsoil depths may not be adequate to protect the soil from erosion.

ECOSYSTEM RECOVERY ON RECLAIMED SURFACE MINELANDS 1

The ultimate goal of mineland reclamation is reestablishment of a productive, functional, and sustainable ecosystem suitable for postmining land use. Evaluation of reclamation success for bond release, however, is limited to examination of the reestablished plant community with emphasis also placed on soil erosion protection and landscape hydrologic function. Most ecosystem components and processes of the reclaimed site are not examined but are crucial to ecosystem function and sustainability. The objective of this paper is to present data from our work on recovery of ecosystem structure (e.g. organisms, soils, mycorrhiza) and function (e.g. biomass production, carbon cycling, nitrogen cycling) on reclaimed surface coal mines in Wyoming. Our studies of chronosequences of reclaimed sites indicate increasing productivity through time in all groups of organisms monitored (plants, bacteria, fungi, nematodes and arthropods) as well as increasing concentrations of soil organic matter, rapid incorporation of organic carbon into soil aggregates, redevelopment of mycorrhizae, and reformation of carbon and nitrogen pools. Although the precise trajectory of the restored ecosystems are very difficult to predict because of changing control variables such as potential biota (invasive species) and climate, our data indicates ecosystem structure and function is recovering on reclaimed surface minelands.

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.

AGGREGATE SIZE DISTRIBUTION AND STABILITY UNDER A COOL SEASON GRASS COMMUNITY CHRONOSEQUENCE ON RECLAIMED COAL MINE LANDS IN WYOMING 1

Evaluation of mine reclamation success is based on examination of aboveground ecosystem components. Recovery of belowground constituents and processes, such as soil structure and nutrient cycling, is crucial to successful reclamation of disturbed lands. Inadequate recovery of belowground ecosystem structure and function during reclamation can lead to future site degradation. Our objective in this study was to test the hypothesis that recovery of plant community properties on reclaimed surface mine land accurately reflect recovery of soil structure, more specifically aggregate size distribution. In this study, above- and belowground constituents were sampled on reclaimed mine sites representing various ages (native rangeland, a 4 month old topsoil stockpile, 14, 26, and 29 year old reclamation) located in northeastern Wyoming. Cool-season grass (native and reclaimed) communities were sampled for aboveground biomass production, cover and species diversity according to Wyoming Department of Environmental Quality standards. Soil samples were analyzed for water stable aggregate size distribution with wet sieving. Soil structure appears to be recovering through time. An increase in macroaggregates (250-2000µm) on a weight basis and a decrease in free microaggregates (53-250 µm) and free silt and clay (<53 µm) on reclaimed sites with time was observed, indicating incorporation of free silt and clay and free microaggregates into macroaggregates. Aboveground biomass production and macroaggregate formation showed a significant relationship (R 2 = 0.457); however, no relationship was evident for microaggregate formation. No significant relationship existed among total cover and species diversity with respect to macro- and microaggregate formation. These preliminary results suggest that soil structural recovery is most closely related to plant biomass production, while other plant community properties do not necessarily reflect this recovery.

SHORT-TERM MICROBIAL RESPIRATION AS AN INDICATOR OF SOIL QUALITY FOR RECLAIMED COAL MINE SOILS OF NORTHEASTERN WYOMING

Soil quality and the ability of soil to sustain nutrient cycling in reclaimed soils will influence the subsequent establishment and maintenance of a permanent and stable plant community. We undertook an experiment using a recently developed “three-day CO2 flush method” to compare a range of soil biological indicators across a series of reclaimed, surface coal-mined sites in the Powder River Basin of northeastern Wyoming. In addition, we were interested in estimating the amount of soil organic carbon (SOC) required to sustain nutrient cycling. Soils were sampled from each of two different reclaimed sites on four different mines in 2000. In 2001 we sampled soils from three sites on three mines two reclaimed and a native, undisturbed prairie control site. For both years, soils were dried, rewetted, and microbial respiration measured at three and 21 days, using base trap methods. In addition, microbial biomass, nitrogen (N)mineralization, organic carbon (C) and total N were measured. Regression analyses were accomplished by regressing three-day microbial respiration against the other soil parameters measured. Correlations between three-day microbial respiration and all of the measured soil parameters were generally strong (r ≥ 0.55) and highly significant (P < 0.0001). There were differences between the reclaimed and native sites; the native sites exhibited more variability (although still significantly correlated), probably due to either differences in the relative lability of the substrates present or differences in the structure of the microbial communities present in the native versus reclaimed soils. We believe this method is of use as a relatively fast, accurate, and economical means by which soil quality can be ascertained. Estimates of SOC required to sustain nutrient cycling appears to be in the upper range of 0.1-0.7% C. Additional