Thursday, 13 July 2006

Permanent Vegetation Establishment on a Former Slag Disposal Pile in Pittsburgh, Pennsylvania, USA.

David Cremeens1, Jeffery A. Parobek1, Charles Miller2, and Sally Flinn3. (1) GAI Consultants, Inc., 385 E. Waterfront Dr., Homestead, PA 15120-5005, (2) Urban Redevelopment Authority of Pittsburgh, Pittsburgh, PA 15222, (3) Summerset Land Development Associates, Pittsburgh, PA 15212

Summerset at Frick Park in Pittsburgh, Pennsylvania, a joint project between the Urban Redevelopment Authority (URA) of Pittsburgh, Pennsylvania and Summerset Land Developers, is the development of a residential community on a former disposal area for slag from steel making. As part of this development, permanent vegetation is being established on a 2.06 km long, steep slope off of the slag plateau. The slope has a range of 30-100% with an elevation difference of 30-45 m between the plateau and the valley floor. Following grading of the slag, the slopes were covered with a compacted soil blend of soil materials, granulated slag and wood chips designed to optimize plant available water holding capacity (PAWC). In Phase 1 the soil blend was created from a 4:4:1 ratio of soil materials, slag, and chips. Soil materials were from on-site waste soil deposits, wood chips were imported and from on-site trees. On the Phase 2 slopes the 7:2:1 soil blend included imported soil materials and wood chips, and the inclusion of slope stabilization coir logs. Soil materials brought onto the site had to meet Pennsylvania State Department of Environmental Protection Act 2 guidelines for clean fill. Fertilizer (N-P-K-S) and seeding specifications were designed for the establishment of warm-season grasses and legumes as a dense groundcover, followed by planting deciduous and coniferous trees and shrubs. Fertilizers were added in bulk form to the soil blend, and applied in liquid form as part of the hydroseed mixture. Mycorrhizal fungi and legume inoculants were also added to the hydroseed mixture, and mycorrhizal fungi were applied to bare root seedlings as a dip. Warm-season grasses were chosen for their tolerance of the adverse site conditions and legumes for their ability to fix and supply nitrogen. Trees and shrubs were chosen for their tolerance of high pH and compaction, in addition to being native to the region. Challenges at the site include the high pH of the soil blend resulting from the use of slag, compaction resulting from construction, and exposure to solar radiation and wind resulting from the topography of the site. The establishment of a dense ground cover with its self-mulching effects has been foremost to the success of the project. The self-mulching layer provides shade, insulation, and increases infiltration of rainwater into the surface. Organic matter additions from the decaying plant residues are increasing the development of granular soil structure at the surface, reducing compaction at the surface, and initiating a surface soil ecosystem. The pH of the Phase I soil blend decreased by as much as 2.5 units, aided by applications of ammonium sulfate at 220 kg/ha in 1999 to 2001. As the pH decreases phosphorus and many micronutrients will become more plant available. The warm-season grasses and legumes have been observed self-seeding, while seedlings and saplings have been observed sprouting new growth. Some bare-root seedlings in dense stands of ground cover have shown new growth. This project has provided us with experience in reclaiming a difficult brownfield site for residential and municipal applications. The soil created for the slopes can be classified as Udorthents in the USDA system with a loamy-skeletal over cindery particle-size family and a carbonatic or calcareous mineralogy family, or as Technosols or Technic Anthrosols in the FAO/IUSS system. The slopes will probably not achieve a mature forest stand for a few centuries and compaction in the root zone will undoubtedly slow or even limit the growth of trees. However, the slopes will be a green landscape interfacing with the forested stream valley leading from one of Pittsburgh's large public parks to the last open stretch of shoreline on the Monongahela River.

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