Soil and Revegetation Success in Response to Land Disturbances from Construction and Mining Activities

Written by Alex Zimmerman on . Posted in Mining

Soil and Revegetation Success in Response to Land Disturbances from Construction and Mining Activities"The good ground is gone" often refers to the challenging nature of construction sites these days. Building on steeper slopes, within tighter boundaries all the while accelerating construction schedules is adding to the challenge of construction managers. Often the revegetation and restoration is unfortunately not planned or timed for successful long-term vegetation success. Site soil conditions are frequently overlooked and the timing necessary for seed germination, expression, and establishment are rarely factors in determining the schedule of seeding applications for optimum results. All too often less than desired results or failure is the accepted outcome. This will increase the future maintenance costs and encourage the repeated “finger pointing” while seeking to blame one cause or another. Typically, this often-repeated process fails to address the fundamental causes and thereby rarely fixes the problems moving forward. In an effort to break out of this all too often repeated cycle lets break down the principle challenges and explore options for successful restoration of challenging sites.

Successful, long-term, revegetation starts with the soil. Without the quality soil that takes years to accumulate naturally revegetation efforts regularly fail or the outcomes are less than ideal. During construction, mining, and general land disturbing activities the soil will be degraded even while practicing the best topsoil harvesting and stockpiling management practices. Many areas where vegetation is desired are essentially mineral without any organic matter or biological activity. When available, stockpiled topsoil will also degrade, the environment within the pile will create conditions that microbes, essential for plant health, will be negatively affected. The longer the stripped soils are stockpiled the more living organisms are lost. Recommendations and even requirements for limiting the depth of the pile to reduce the loss of beneficial microbes is rarely possible given the tight boundaries of project limits facing site operators. When the stockpile depth is able to be minimized the pile must also be turned regularly to reduce the loss of the essential nutrient cycling microbiome present in healthy soils.

Given the challenges of harvesting, stockpiling, maintaining, and reusing the topsoil at many construction or mining sites, importing topsoil and or compost has become more common. The variety in quality and performance is as significant as the number of sources. The organic matter can be quite different among approved source suppliers of topsoil. Many times, the supplied topsoil is a blended product where harvested soil is mixed with sand improving drainage yet sacrificing water holding capacity and organic matter. Compost is a varied as the parent material used in the composting process. Typically providing a much higher amount organic matter, ideally compost should be incorporated into the parent material at the site however this added cost and the time it requires will usually result in a blanket or layer of compost applied at various depths. Consider where the results of this practice exist in nature and why the decision to incorporate the compost into the site soil is often made for monetary reasons above best practices. Weather spreading harvested and or, manufactured topsoil, or even compost other site challenges often will lead project designers and managers into less than ideal choices. Steep and remote locations can make the efficient and productive placement impossible. Equipment may not physically be able to get to difficult to reach site locations. Where options are available like tele-conveyers for remote soil placement the mobilization, erection, and equipment removal expenses in addition to the imported materials will quickly drive the costs of restoration to a level that project teams will be forced to question the expense. When imported soils or compost are placed on steep slopes there is always the risk of sloughing. As the organic matter retains moisture and the weight increases gravity may overcome the surface friction and result in the slippage of the layer, even after the desired vegetation has expressed. Compacted material, especially silty parent material, below the topsoil or compost layer will only increase the risk of surface movement during periods of saturation as the silty compacted material becomes slippery when the water soaks through the installed blanket layer of topsoil or compost.

When faced with all the potential problems of revegetation site managers and designers must work together to achieve the best outcomes. Often the site conditions and soil quality in areas where vegetation is desired are not completely known during the design phase. A second look at the site conditions during and after grading activities may reveal conditions that are very different from the assumptions that were made during the planning and design phase. With all the potential challenges facing revegetation the weather may be the biggest one of all. For seeds to germinate express and establish moisture will be necessary. Frequently restoration efforts are not timed to coincide with the optimum climate conditions but are simply initiated around production schedules. This lack of consideration to the timing of seeding for optimum moisture often can result in failed vegetation, plants that germinate and or express and then dry out and die. Weeds will also fare better and inadvertently many fertilizer specifications encourage weeds with increased nitrogen levels above what the desired native species require. With a high percentage of rapidly available nutrients many fertilizers have been consumed by weeds or even volatized before the typically slow germinating native species have begun to express. This common pitfall can be avoided with the information from a simple soil test and a comparison of the nutrients necessary for the desired plant species.

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