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Effects of Mining on Terrestrial Ecosystems

Environmental Effects of Mining in the Anthracite Region: Problems and Possible Solutions

 

Kenneth M. Klemow, Ph.D.

Effects of Mining on Terrestrial Ecosystems

Anthracite mining has devastated tens of thousands of acres of terrestrial ecosystems in eastern Pennsylvania. Strip mining especially caused the removal of the original vegetation and all soils on the site. The result was a barren landscape covered by a coarse substrate, often with steep slopes. In some cases, those culm banks caught fire, producing even more hazardous and stressful conditions. Unlike unmined sites that can recover relatively quickly after clearing, revegetation on strip mined sites occurs slowly. It is not uncommon to see 50-80 year old culm banks that are essentially barren.

A combination of physical and biological factors interact to restrict the rate of natural revegetation on abandoned anthracite mines. Severe substrate conditions are perhaps the greatest problem, on both burned and unburned areas. Studies conducted over the past several decades have documented that sites underlain by culm, ash, and mine-wash have low concentrations of important nutrients like nitrate, phosphate, calcium, and potassium. Moreover, they often have toxic levels of iron and aluminum. The coarse substrate on culm banks does not retain water, resulting in drought-prone conditions that often rival the most severe deserts on the planet. The black substrate also absorbs solar energy and converts it to heat,resulting in summertime surface temperatures that exceed 150oF.

A variety on biological factors also limit revegetation on mined sites, and these act in subtle ways that are still being discovered by ongoing research. Certainly, fresh culm and mine-wash lack seeds or rootstocks that would serve as a source of new plants. Instead, vegetation development must depend on the fortuitous immigration of seeds from plants growing off-site. In the case of large culm banks, the nearest source of seeds might be a quarter of a mile away. Moreover, those seeds must successfully germinate and produce established seedlings, which is difficult in the highly unfavorable thermal, chemical, and moisture environments of culm and mine wash.

Research conducted in the past several decades has shown that mine-derived soils lack a healthy population of soil microbes, including fungi, bacteria, and invertebrates. Plants on strip mines cannot form associations with certain soil fungi that normally serve as a feeder system for critical nutrients and water. Moreover, the lack of fungi and many types of bacteria and invertebrates prevent normal recycling of nutrients within the soil, further impairing fertility.

The vegetation that does develop on mined sites in eastern Pennsylvania is very different from that on unmined sites. Culm banks especially bear a mix of scrubby growth having much lower stature than more favorable off-mine sites. Mineland vegetation rarely exceeds thirty feet in height, in sharp contrast to maturing forests that often exceed 100’. Species composition is also rather distinctive in that the dominant woody species on mined sites include invasive species that have low commercial value like gray birch, black locust, and trembling aspen. More valuable oaks, maples, hickories, ashes, and hemlocks are rare on mined sites. The understory of mined sites is also rather poorly developed, being composed of prickly shrubs like tall blackberry and multiflora rose, as well as weedy, alien herbs like spotted knapweed, switchgrass, and white sweet clover.

Functionally, the vegetation that develops on mined sites has several characteristics that are indicative of an unhealthy system. First, the level of species diversity is lower than that of unmined sites, making mineland vegetation relatively unstable. Second, the vegetation has low level of productivity, measured by the relative inability to capture energy and pass it to higher trophic levels. Third, the vegetation is composed of species that cannot generally reproduce in its own shade, and thus may not be sustainable. Fourth, the stressful physical conditions on mined sites make the component species more susceptible to disease. For example, trembling aspen trees on stressful sites are often damaged by hypoxylon canker while those on unstressed sites resist that fungal disease. Finally, mineland woods do not provide much soil stabilization, oxygen production, or water purification, which are important functions normally associated with natural forested ecosystems.

Animal populations, including both game and non-game species, are also severely restricted on mined sites. The scrubby vegetation characterized by high densities of prickly shrubs, confers poor habitat for species normally accustomed to shaded or grassland conditions in Pennsylvania. Also, the lack of moisture and extreme thermal conditions excludes most species except for a few snakes, spiders, and tolerant insect species. Mine-land vegetation is often unpalatable and has relatively low nutritive value for grazing animals.

 

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