Access Matting Reduces Mixedgrass Prairie Soil and Vegetation Responses to Industrial Disturbance.

Substantial interest exists in understanding the role of low-disturbance construction methods in mitigating industrial impacts to native grassland soils and vegetation. We assessed soil and vegetation responses to conventional high-disturbance sod-stripping and revegetation on sandy soils, and the alternative practice of low-disturbance access matting to provide a temporary work surface on sandy and loamy soils. Treatments were associated with high-voltage transmission tower construction during 2014 within the Mixedgrass Prairie. High-disturbance sites were hydroseeded in May of 2015, while low-disturbance sites recovered naturally. We assessed soil physical (bulk density, water infiltration) and chemical properties (organic matter, pH, and electrical conductivity) after construction and herbage biomass for three growing seasons. Sod-stripping led to 53% greater soil bulk density and 51% less organic matter than nondisturbed controls, while water infiltration increased by 32% in these high-sand (>80%) soils. In contrast, access matting led to minimal soil property changes regardless of the texture. While total herbage biomass was unaffected by all construction treatments, sod-stripping reduced grass biomass by 80% during the first growing season, which coincided with a 119% increase in forb mass. Root biomass (0-15 cm) also declined 77% with sod-stripping. Vegetation biomass on sites with access matting remained largely unaffected by the disturbance. Overall, low-disturbance construction methods using access matting were more effective than sod-stripping in mitigating the negative impacts of industrial development on Mixedgrass soil properties, as well as vegetation biomass, and are recommended as a best management practice during industrial disturbance.

Ecophysiological response of aspen (Populus tremuloides) and jack pine (Pinus banksiana) to atmospheric nitrogen deposition on reconstructed boreal forest soils in the Athabasca oil sands region.

Oil and gas extraction in the Athabasca Oil Sands Region of northeastern Alberta, Canada has increased anthropogenic nitrous oxide (NOx) and ammonia (NH3) emissions over the past three decades, leading to a potential increase in N deposition. Deposition on reclaimed sites was hypothesized to be higher than in surrounding boreal forests, but had not been quantified. The objective of this study was to assess the implications of this potentially increased deposition on reclaimed aspen (Populus tremuloides Michx.) and pine (Pinus banksiana Lamb.) ecosystems through the use of several N status indicators, including N deposition, total and available concentrations in plants and soils, and δ15N values in deposition and plants and soils. Atmospheric N deposition, which was dominated by ammonium (NH4+), averaged 24 kg N ha-1 year-1 as bulk precipitation and 6 kg N ha-1 year-1 as throughfall. Increased N deposition influenced the N cycle in both aspen and pine stands. Aspen appeared to be actively biocycling N as indicated by a closed N cycle, resulting in minimal N losses. Whereas the N cycle in pine may be more open as indicated by the dominance of soil nitrate (NO3-), and enrichment of 15N in available soil NH4+, root and foliar N. Therefore, we suggest that pine stands on reclamation sites may be at kinetic N saturation where the rate of N inputs exceeds vegetation and soil N net sinks, and do not require additional N fertilizer inputs.

Recreating a functioning forest soil in reclaimed oil sands in northern alberta: an approach for measuring success in ecological restoration.

During oil-sands mining all vegetation, soil, overburden, and oil sand is removed, leaving pits several kilometers wide and up to 100 m deep. These pits are reclaimed through a variety of treatments using subsoil or a mixed peat-mineral soil cap. Using nonmetric multidimensional scaling and cluster analysis of measurements of ecosystem function, reclamation treatments of several age classes were compared with a range of natural forest ecotypes to discover which treatments had created ecosystems similar to natural forest ecotypes and at what age this occurred. Ecosystem function was estimated from bioavailable nutrients, plant community composition, litter decomposition rate, and development of a surface organic layer. On the reclamation treatments, availability of nitrate, calcium, magnesium, and sulfur were generally higher than in the natural forest ecotypes, while ammonium, P, K, and Mn were generally lower. Reclamation treatments tended to have more bare ground, grasses, and forbs but less moss, lichen, shrubs, trees, or woody debris than natural forests. Rates of litter decomposition were lower on all reclamation treatments. Development of an organic layer appeared to be facilitated by the presence of shrubs. With repeated applications of fertilizers, measured variables for the peat-mineral amendments fell within the range of natural variability at about 20 yr. An intermediate subsoil layer reduced the need for fertilizer and conditions resembling natural forests were reached about 15 yr after a single fertilizer application. Treatments over tailings sand receiving only one application of fertilizer appeared to be on a different trajectory to a novel ecosystem.

Nitrogen mineralization and microbial activity in oil sands reclaimed boreal forest soils.

Organic materials including a peat-mineral mix (PM), a forest floor-mineral mix (L/S), and a combination of the two (L/PM) were used to cap mineral soil materials at surface mine reclamation sites in the Athabasca oil sands region of northeastern Alberta, Canada. The objective of this study was to test whether LFH provided an advantage over peat by stimulating microbial activity and providing more available nitrogen for plant growth. Net nitrification, ammonification, and N mineralization rates were estimated from field incubations using buried bags. In situ gross nitrification and ammonification rates were determined using the 15N isotope pool dilution technique, and microbial biomass C (MBC) and N (MBN) were measured by the chloroform fumigation-extraction method. All reclaimed sites had lower MBC and MBN, and lower net ammonification and net mineralization rates than a natural forest site (NLFH) used as a control, but the reclamation treatment using LFH material by itself had higher gross and net nitrification rates. A positive correlation between in situ moisture content, dissolved organic N, MBC, and MBN was observed, which led us to conduct a moisture manipulation experiment in the laboratory. With the exception of the MBN for the L/S treatment, none of the reclamation treatments ever reached the levels of the natural site during this experiment. However, materials from reclamation treatments that incorporated LFH showed higher respiration rates, MBC, and MBN than the PM treatment, indicating that the addition of LFH as an organic amendment may stimulate microbial activity as compared to the use of peat alone.