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Contamination Removal Success
After reclamation efforts have taken place, it is important to
determine: (i) whether tailings and waste rock are still exposed
to air and water, and (ii) whether waste material was treated and/or
contained effectively. Soil monitoring can determine if all the
contaminated material was removed and disposed of effectively. It
can also provide the reclamationist information on the success of
soil treatment processes as well as provide information on the success
of containment structures to contain waste material. A sampling
and analysis plan should be implemented that includes: (i) sampling
locations, (ii) the number of samples to be collected during each
sampling event, (iii) the parameters that the samples will be analyzed
for (i.e. pH, sulfate, metals), and (iv) the frequency of sampling
events (i.e. once a month, biannually). Once a sampling and analysis
event has been completed, the data should be reviewed and assessed.
If it is determined that contamination exists in areas where it
should have been removed or if the soil was inadequately treated
or contained, appropriate measures should be taken to solve the
problem.
Soil Health
In the process of mining for valuable ore bodies, soils are excavated
and, many times, left in stockpiles for a time period, often years,
until reclamation efforts take place. In the process, soil health
is compromised. The soils become depleted of organic matter, soil
structure becomes altered, essential macro- and micronutrients become
depleted, and as a result of these alterations, living communities
in the soil tend to die. Without these soil attributes, normal soil
functioning is compromised and as a consequence, plants will not
grow. For more information on these soil attributes and their function
in the soil environment, see the analytical methods section (link
to analytical methods section).
When reclaiming a site and using the stockpiled soil as topsoil
for plant growth, organic and nutrient amendments will be necessary
to bring the soil back to a healthy functioning state. If there
is not enough soil on-site, topsoil from other areas will be brought
in for reclamation purposes. Unlike stockpiled soils, recently excavated
soils generally retain most of their health properties. After reclamation
has taken place, monitoring for soil health properties indicates
whether efforts have been successful. The reclamationist can monitor
for various physical, chemical, and biological soil components to
assess soil health.
Physical properties that may be measured include: texture, depth
of soil and rooting, infiltration and soil bulk density, and water-holding
capacity. Texture will determine the soil's ability to retain and
transport water, nutrients, and contaminants. Measuring the depth
of soil and rooting zones will give an estimate of plant productivity
and erosion potential. Deeply rooted plants will help decrease soil
erosion. Infiltration and soil bulk density measurements will determine
the soil's leachability and its plant productivity and erosion potential.
Water-holding capacity gives information on water retention capabilities,
and nutrient/contaminant transport and erosion potential.
Chemical attributes that can be used to assess soil health include:
total soil organic matter content, active organic matter content,
pH, electrical conductivity, and extractable N, P, and K concentrations.
Total soil organic matter content defines a soil's carbon storage,
potential fertility (nutrient availability), and stability. Active
organic matter content defines a soil's structural stability and
the quantity of food available for microbes. Measurement of pH helps
the reclamationist define biological and chemical activity thresholds.
For example, most microbes cannot function at low pHs and high pHs.
Each microbe has a different pH range in which it functions most
successfully. The electrical conductivity (EC) of the soil can be
an indicator of plant and microbial activity thresholds. Above or
below different predetermined EC levels, specific plant and microbial
communities will not function successfully. Measurement of extractable
(easily solublized) macronutrients (N, P, and K) is important for
determining the quantity of plant-available nutrients and the potential
for N loss due to leaching.
Biological attributes that can be used to indicate soil health
include: microbial biomass C and N content, the content of potentially
mineralized N, specific microbial respiration rates, macroorganism
numbers, and the presence of mycorrhizae. Measuring the relative
masses of microbial C and N is important for determining microbial
health. For adequate soil function, a C:N ratio of 8:1 is necessary.
Soil microbes (heterotrophic) use carbon as a food source. Nitrogen
is also needed by microbes for synthesis of nitrogen-containing
cellular components, such as amino acids, enzymes, and DNA. Microbes
obtain their C and N requirements from organic matter. By measuring
the C:N ratio, it can be determined if the microbes are deficient
in either C or N and if the available organic matter is not providing
the microbes with the correct ratio of C:N . Measurement of potentially
mineralizable N content in the soil gives indication to soil productivity
and N supply potential. There may be a considerable amount of nitrogen
incorporated with the organic matter but how easily will this N
mineralize and become plant available? Measurement of the specific
microbial respiration rate generally entails measuring CO2 production
from a given mass of soil. CO2 is the byproduct of microbial respiration
and its production is an indicator of microbial activity. It is
also important to measure the number of macroorganisms found in
the soil. These macroorganisms can be split into three categories:
macrofauna, mesofauna, and microfauna. Macrofauna (> 2 mm) in soils
include moles, prairie dogs, snakes, earthworms, and millipedes.
Mesofauna (0.2 mm to 2 mm) include tiny springtails
and mites. Microfauna (< 0.2 mm) include nematodes
and single celled protozoans.
A typical, healthy soil might contain several species of vertebrate
animals, a half dozen species of earthworms, 20 to 30 species of
nematodes, hundreds of species of fungi, and perhaps thousands of
species of bacteria and actinomycetes.
Another group of are soil microorganisms are mycorrhizae, an important
symbiotic relationship between plant roots and specialized fungi.
This fungal-plant root symbioses occurs in members of more than
90% of vascular plant families. In general, the fungus benefits
from photosynthate (fixed carbon) supplied by the plant, while the
plant receives many benefits from the fungus. These benefits include
improved nutrient uptake (most recognized is phosphorus uptake),
improved water status, toxic metal resistance, root pathogen protection,
production of plant growth regulators, and improved soil structure.
Determining the presence of mycorrhizae in the soil is generally
achieved by sending soil to a lab for a mycorrhizae infectivity
potential assay. If mycorrhizae are absent, inoculating the soil
with mycorrhizae is an option. The most common forms of mycorrhizal
inoculums are: native topsoil, custom-produced native inoculum,
colonized transplants, and commercial inoculum.
Check out the following websites for more information on mycorrhizae:
For more information on soil health, see Brady
and Weil (1999). Also, check out the following websites.
Problem | Compliance
| Health & Safety | Sampling
| Analytical | Data
Quality
Site Assessment | Prediction
| Construction | GIS
| Monitoring & Assessment
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