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Mine Reclamation

By: Mariah Harrod

Healthy soil is essential for vegetation to grow and lock atmospheric carbon

dioxide into the ground. Mining processes tend to acidify, compact the top layer,

increase bulk density, disturb microbial populations, and lower organic pools of nitrogen,

carbon, and sometimes phosphorous within the soil. Acidity can limit certain kinds of

vegetation from establishing roots and growing. Compaction is almost always a

deterrent for new vegetative colonization as it prevents root spreading and water

percolation. Within one study, organic carbon and nitrogen pools in the top layer were

depleted 53-83% each due to mining. Nutrients are often the limiting factor for plant

growth, and so restoration must replenish these materials. Adding lime can reduce

acidity to a pH above 5.5 (as is recommended in Article 10), deep-ripping or chiseling

the soil can reverse compaction (Article 5), and applying cow manure can increase

nutrient pools to promote plant growth (Article 5). An application of 140 to 170 kg ha−1

actual N or of phosphorous can also be applied if these are shown to limit plant growth.

Current mining laws mandate that the land’s original contour be approximately

replicated, the removed top soil replaced, and some sort of vegetation planted. Yet no

guidelines currently exist mandating what use these compacted, depleted fields must

serve. Hay, pasture, and forests are common reclamation uses of mined fields in the

Ohio/Indiana/Illinois region. As of 2007, 3.2 Mha of reclaimed fields exist in the USA and

0.04 Mha in Ohio with the potential of sequestering C up to 8.19 Tg yr−1 under forest

land use (Article 10). Yet the potential of SOC accumulation (for 30-cm depth) in

grassland (hay and pasture) is about 62 Mg ha−1 over a period of 28 yr, which is 72%

more than it would have been under a forest land use. If 3.2 Mha RCMS are converted

to pasture in the USA, the potential C sequestration is 353.6 Tg in the USA after 50

years. Pastures produce the highest soil pool of carbon (and thus sequester it quite

quickly), whereas forests store carbon in biomass. Pastures also have the highest

amount of nitrogen (previously depleted by mining) due to cattle excretions. Hay

exhibited the highest electrical conductivity, which generally positively correlates with

vegetative yield, but agriculture most efficiently brought pH down to a desirable level.

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Article 10

In 2007, Lorenz and Lal confirmed there was great potential for carbon

sequestration in reclaimed mining soils, particularly pasture (Article 13). Compared to

forests, pastures sequestered the greatest amount of soil organic carbon and increased

bulk density at the greatest rate. Yet amongst pastures and hay, forests sequestered

the most methane with the least global warming potential (Article 6). In a study

comparing meadows and hay, researchers found that meadows exhibited great nitrogen

sequestration potential (Article 14). Reclaimed treatments even sequestered more

methane than undisturbed forests (Article 6). For cropland reclamation, researchers

found that for growing corn, no tilling proved most productive (in terms of biomass

production); for growing soy, moldboard plowing proved most productive (Article 8).

Reclaimed corn fields even produced equally as well as unmined corn fields while

sequestering more carbon (Article 8). Carbon sequestration rates were about 0.3 Mg C

ha−1 yr−1 greater in untilled agricultural soils (Article 8).

To improve the success of reclamation, researchers found that flue gas

desulfurization gypsum (FGD) best mitigated abnormally acidic soils (though lime was

not tested within this experiment) and encouraged vegetative growth. FGD should be

preferred over biosolids in this region (Article 7). Additionally, deep ripping of the soil

and manure vastly improve the carbon sequestration rates of the reclamation sites with

the latter being most crucial (Article 5). Compaction and nutrient deficits—such as

phosphorous within reclaimed forests—prove the most potent limiting factors within

these sites, and so reclamation practices must seek to remedy these. The type of

vegetation itself is significant—different plants grow and perish at different rates, and so

one’s goals for the site should be encompassed by the life cycle of the chosen

vegetation.

Though mining does slow or altogether halt the bioproductivity and sequestration

of these sites, reclamation has proven effective in restoring and sometimes even

surpassing the potentials of undisturbed soils. The reclamation use (pasture, meadow,

forest, agriculture) will likely remain for quite some time up to the whim of the

corporation mining that land unless research and political fortitude can produce an

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algorithm for determining which may be most suitable for that region in terms of soil

acidity, atmospheric gases, terrain, local economy, and native vegetation.

Article 1 (2013)

Minesoils typically contain far more carbon (C) than native soils. As a result,

quantifying the carbon sequestering abilities of restored post-mining soil poses

difficulties pertaining to the limitation of C differentiation technology. In order to judge

how much and at what rate atmospheric carbon—as is most pertinent within the context

of climate change—is stored in revived soils and revegetated areas, distinguishing

between inorganic C (carbonates), C derived from geological processes (geogenic), and

organic carbon (OC) resulting from plant decomposition is necessary. Multiple

techniques exist to discern between geogenic organic carbon and plant mass organic

carbon, the most reliable of which is radiocarbon testing known for being labor-intensive

and costly. Authors conclude further research must be done to find the most cost-

effective method for distinguishing between and quantifying the sources of carbon within

mining soils.

Article 2 (2010)

High soil bulk density, low soil organic carbon and nitrogen pools, and low

nutrient and water retention all discourage plant productivity and thus carbon

sequestration. Shrestha and Lal studied three different soil series a year after mine

reclamation in Ohio. Comparing to nearby undisturbed soils, the researchers found that

mining and reclamation increased soil pH and electrical conductivity. Reclaiming soils

also seemed to increase bulk density at the top layer tested (0-15 cm), but not at the

two lower (15-30 cm and 30-45 cm). Mining reclamation generally appeared to increase

soil pH and electrical conductivity (EC) while depleting organic carbon (C) and nitrogen

(N) pools. Organic carbon was more prominent in reclaimed sites that had large

concentrations of clay, indicating that clay and carbon sequestration capacities might be

positively correlated for these locations. Lastly, researchers found that carbon and

nitrogen contents as well as EC were similar in all layers of the soil despite the addition

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of a top soil cover, suggesting that reclamation should extend better care in removing,

storing, and replacing this crucial component. Proper restoration—aimed at

sequestration—should minimize carbon loss and soil compaction and reclaim quickly

following mining. Adding fertilizer and highly productive plants allows these soils to

increase their sequestration capacities over time.

Article 3 (2009)

Shrestha and Lal research mining soils in Ohio, this time within the context of

forest versus pasture use after 1-25 years. For the plots studied, sequestration rates

were highest per site following 14 years of forest reclamation or 6 years for pasture.

Rates began to slow following this pivotal point. For forest conversion, carbon pools

were found majorly within both soils and biomass; whereas, for pastures most of these

pools were in soil. 25 years following reclamation, reclaimed mine forests sequester

about five times more carbon than similar pastures.

Article 4 (2009)

Compared to an 11 year old reclaimed forest site, 40 year old undisturbed forest

carried a significantly greater amount of soil organic carbon and soil nitrogen within the

top 20 cm. Indeed, these disturbed forest soils are severely depleted of nitrogen and

authors call for more extensive nitrogen management. This backs up the theory that

mining—even alongside restoration—diminishes the sequestration ability of soils for

years to come. Policymakers wary of the significant costs of climatic change would be

wise to prioritize minimizing new mining over restoring mining soils.

Article 5 (2009)

In four simultaneous five-year treatments of reclaimed mine sites in eastern Ohio,

researchers found that adding manure and chiseling (deep ripping the soil to undo

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compaction) to the normal reclamation practice (NRP) typically employed by mining

companies in the state increased plant productivity. Using NRP as the control,

researchers found adding one of these increased aboveground plant biomass. Adding

extra mulch to the NRP of grading the material above the coal seam removed during

mining and then replaced, adding 30 cm of topsoil, seeding with a grass–legume

mixture, and applying oat straw mulch at the rate of 7 Mg ha−1 did not manifest

significant increase in biomass production as compared to NRP. Mulching also led to

lower nitrogen uptake from the soil into vegetation. Of the two treatments, manure was

more successful at promoting biomass production than chiseling, which did not exhibit

an increased growth rate until after five years of treatment. Both proved effective at

increasing carbon pools in the soil.

Article 6 (2009)

Left unrepaired, post-mining soils return to a similar rate of productivity quite

slowly—about 200 years. Most common reclamation uses include forest, pasture, and

hay. This study evaluated these land uses after 28 years to find which had the lowest

emissions of CO2, CH4, and N2O. Researchers found that reclaimed pastures had the

largest soil organic carbon pool while emitting superlatively high amounts of CO2,

equating to a net gain in sequestered soil carbon. Global warming potential (GWP) was

highest for reclaimed pasture, second highest for reclaimed hay soils, and third highest

for reclaimed forests marking reclaimed forests the lowest GHG emitter. All uses

sequestered more methane than produced, with reclaimed mining soils absorbing even

greater proportions than lower GWP undisturbed forests. Forest reclamation should be

preferred over hay or pastures due to lower CO2 and N20 emissions and relatively high

methane intake.

Article 7 (2013)

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Researchers experimentally applied zeolite, fly ash, flue gas desulfurization

gypsum (FGD), and biosolids at 10% by weight to mining soils in Ohio. Of these

materials, FGD was found to be the best solution to abnormally acidic mining soils,

increasing pH from 3.1 to 5.0 and 4.2 to 7.0 at the two sites. This in turn increased seed

germination of the lettuce Lactuca sativa. For the aim of increasing soil aggregate

stability and saturated-water-holding capacity, biosolids proved best, though they did

not significantly improve plant-available-soil-holding capacity or encourage lettuce seed

germination. From these results and the researchers’ conclusion that soil acidity in the

absence of toxic metals—as in the case here in Ohio—is highly influential in preventing

vegetative growth, FGD is likely the ideal addition among studied materials.

Article 8 (2009)

In southwestern Indiana and southeastern Illinois, a large proportion of mined

lands are converted to cropland—often corn-soy rotations. Thus, researchers studied

the effects of moldboard plowing tilling on reclaimed agricultural mining soils in Indiana,

measuring recent soil organic carbon, total microbial biomass carbon, and active

microbial biomass carbon. Within the two-decade period, their main finding was that

restored croplands are equally—and occasionally more—valuable at carbon

sequestration as unmined croplands. For growing corn, no tilling proved most

productive; for growing soy, moldboard plowing proved most productive. Reclaimed

corn fields even produced equally as well as unmined soils. Carbon sequestration rates

were about 0.3 Mg C ha−1 yr−1 greater in untilled soils.

Article 9 (2008)

Among hay, pasture, and forest, the reclamation of mine soils with forest and hay

improved surface soil bulk density and cone index, and enhanced water infiltration

capacity and water-stable aggregates at the lower depths. These distinctions are more

similar to undisturbed forest than mining soils and so better promote vegetative growth

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for carbon sequestration. Therefore, establishment of forest and hay should be

encouraged in the RMS.

Article 12

Treatments included topsoil (graded overburden [OV] and standard [ST] and ripped

topsoil [RT]) and P fertilization (0 and 2.24 Mg ha−1 of rock phosphate)

-sequestration rate depends upon the vegetation type (green ash grows more slowly

than Austrian pine)

-P fertilization proven to be a limiting factor in most reforestation reclamation (improved

tree survival & growth)

-compaction also proven to prevent tree survival

Article 14 (2006)

-unfertilized/ungrazed meadow or hay field

-meadow with high Nitrogen storing potential, hay with high Carbon storing potential

-compaction great threat to successful reclamation

-more macroporosity and less soil moisture means more CH4 remains in soil