Rachel L. Cook

Comparison of Trees and Grasses for Rhizoremediation of Petroleum Hydrocarbons

Rhizoremediation of petroleum contaminants is a phytoremediation process that depends on interactions among plants, microbes, and soils. Trees and grasses are commonly used for phytoremediation, with trees typically being chosen for remediation of BTEX while grasses are more commonly used for remediation of PAHs and total petroleum hydrocarbons. The objective of this review was to compare the effectiveness of trees and grasses for rhizoremediation of hydrocarbons and address the advantages of each vegetation type. Grasses were more heavily represented in the literature and therefore demonstrated a wider range of effectiveness. However, the greater biomass and depth of tree roots may have greater potential for promoting environmental conditions that can improve rhizoremediation, such as increased metabolizable organic carbon, oxygen, and water. Overall, we found little difference between grasses and trees with respect to average reduction of hydrocarbons for studies that compared planted treatments with a control. Additional detailed investigations into plant attributes that most influence hydrocarbon degradation rates should provide data needed to determine the potential for rhizoremediation with trees or grasses for a given site and identify which plant characteristics are most important.

Field Note: Successful Establishment of a Phytoremediation System at a Petroleum Hydrocarbon Contaminated Shallow Aquifer: Trends, Trials, and Tribulations

We report the establishment of a mixed hybrid poplar (Populus spp.) and willow (Salix spp.) phytoremediation system at a fuel-contaminated site. Several approaches were used to balance competing goals of cost-effectiveness yet successful tree establishment without artificial irrigation or trenching. Bare root and unrooted cuttings were installed using either: (1) 1.2 m deep holes excavated with an 8 cm diameter auger using a direct-push rig and backfilled with the excavated, in situ soil; (2) 1.2 m deep holes created with a 23 cm diameter auger attached to a Bobcat rig and backfilled with clean topsoil from offsite; and (3) shallow holes between 15–30 cm deep that were created with a 1.3 cm diameter rod and no backfill. Tree mortality from initial plantings indicated contaminated zones not quantified in prior site investigations and remedial actions. Aquifer heterogeneity, underground utilities, and prior remediation infrastructure hampered the ability of the site to support a traditional experimental design. Total stem length and mortality were measured for all planted trees and were incorporated into a geographic information system. Planting early in the growing season, augering a larger diameter hole, and backfilling with clean, uncontaminated topsoil was cost effective and allowed for greater tree cutting growth and survival.

Advances in Silviculture of Intensively Managed Plantations

Purpose of ReviewIntensive management of forest plantations has evolved significantly in recent decades because of advances in our understanding of environmental and silvicultural effects on forest productivity combined with improvements in information technologies. Our paper summarizes concepts that provide a basis for making strategic and operational silvicultural decisions that insure sustainability when applying intensive management of forest plantations. In addition, we include new information in areas where there are knowledge gaps in forest plantation management.Recent FindingsIntensive management of forest plantations increasingly incorporates large-scale precision silviculture to estimate silvicultural, biotic, and abiotic effects on site-specific forest productivity. Remote sensing measurements combined with strategically located ground information provide spatial modeling tools needed for this type of silviculture. Long-term field experiments, which are a part of this methodology, provide a mechanistic understanding of environmental and silvicultural effects on forest production that is required for the models driving silvicultural decisions. The focus on maximizing production will challenge scientific efforts to alleviate concerns about intensive land use and to provide solutions for water use conflicts while maintaining long-term productivity and sustainability. Future work will need to develop a better understanding of genetic × environment × silvicultural (G × E × S) interactions to improve productivity and simultaneously provide improved ecosystem services.SummaryNew silviculture technology combines remote sensing information with ground data to model resource availability and limitations to forest productivity. Understanding G × E × S permits successful implementation of these new silvicultural technologies. An improved understanding of G × E × S will provide practical tools that may be incorporated into our scientific and technical models while providing robust economic sustainability.

Deep soil carbon after 44 years of tillage and fertilizer management in southern Illinois compared to forest and restored prairie soils

No-till (NT) management can reduce soil erosion and increase soil carbon (C) in agricultural systems, but there is less certainty regarding deeper soil and how long-term tillage and fertilization practices compare to other land-use systems. The objective of this study was to quantify tillage and fertilizer management effects after 44 years (20 years in continuous corn [Zea mays L.] and 24 years in corn–soybean [Glycine max L.] rotation) on bulk density and soil C concentrations and stocks to a 1 m (3.3 ft) depth in a somewhat poorly drained Bethalto silt loam near Belleville, Illinois, and compare to nearby forest and restored prairie soils. Four tillage (moldboard plow, chisel tillage [ChT], alternate tillage, and NT) and five fertilizer (no fertilization control, nitrogen [N]-only, N + N-phosphorus-potassium [NPK] starter, NPK + NPKstarter, and NPK broadcast) treatments showed bulk density was lower in NT than moldboard plow treatments in 0 to 15 (0 to 6 in) and 25 to 50 cm (10 to 20 in) depths. Complete NPK treatments generally resulted in higher C stocks than N-only and control treatments from 0 to 25 cm (0 to 10 in), but no differences were detected from 25 to 100 cm (10 to 39 in) or 0 to 100 cm (0 to 39 in) due to fertilizer. No-till management increased C stocks compared to tillage treatments for 0 to 15 cm (0 to 6 in) and was greater than the ChT treatment for 0 to 100 cm (0 to 39 in). No-till/NPK maintained greater cumulative soil C stocks to 1 m than either undisturbed forest soils or restored prairie soils. Additionally, NT/NPK had the maximum soil C increase over time of 0.36 Mg C ha−1 y−1 (0.16 tn C ac−1 yr−1) for the top 15 cm (6 in) over 44 years.