Division of Spill Prevention and Response

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Tactic AM-5: Testing Soil and Water for Revegetation

This tactic describes procedures for conducting tests on soil and water to provide information to help select tundra rehabilitation tactics. Some of the procedures and protocols are similar to those used to test soil for contaminants. Sample soils and water in affected and unaffected (i.e, reference) tundra to:

  • Determine if salinity is suitable for germination and establishment of plants.
  • Determine whether pH conditions are suitable for plant growth and microbial activity, and
  • Determine baseline conditions that can be used to compare with conditions in the future
  • Determine if tundra affected by a spill is substantially different from undisturbed tundra

Collect at least 3 to 6 soil samples from a site to account for variability. For larger sites, it may be useful to collect 3 to 6 samples from the area with the highest concentration of contaminants, and 3 to 6 samples from areas with moderate or lower contaminant concentrations. In addition, collecting 3 to 6 soil samples from a nearby unaffected area with similar vegetation and soil will allow the affected tundra are to be compared with undisturbed tundra, which may be important for selecting tundra rehabilitation tactics. For example, tundra near the coast can have naturally saline soils, indicating that salt-tolerant species may be needed to revegetate a site. Tundra soils typically have a surface organic layer overlying a mineral soil layer with very different characteristics, and these differences must be accounted for when using soil characteristics to make decisions.

Collect soil samples from a pit dug using a clean shovel. If necessary, collect samples at different depths to represent the entire active layer (surface to frozen subsurface). Segregate the organic rooting mat, which typically has a high content of plant roots and partially decomposed organic matter, from lower layers of mineral soil. Place each sample in resealable plastic bags (e.g., Ziploc® brand), or in DuPont™Tyvek® bags typically used by geologists. Label each bag with the site name, date, unique sample identification, and the initials of the person collecting the sample. Request that the soils laboratory analyze the organic soil layer separately from the mineral soil layer. Refrigerate soil samples
4 ± 2°C (36–43°F) until analysis to minimize biological activity. Soil samples should be air dried or frozen if it is not possible to keep them refrigerated before delivery to the laboratory within 14 days of being collected. If samples are air dried, ensure they are not exposed to hot temperatures.

Testing for Salinity

The salinity of soil and water is important to tundra plants because high concentrations of salts, such as sodium chloride, can interfere with the absorption of water into the plants, even when a substantial amount of water is present in the soil. Salts may also interfere with the ability of plants to absorb mineral nutrients (e.g., nitrogen and phosphorus). Electrical conductivity (EC) is used as a measure of the concentration of water-soluble salts in soil and water; high EC values indicate high salinity.

Tundra soil is considered saline if EC is greater than 4 dS/m (deciSiemens per meter) which is equivalent to 4 mmhos/cm (millimhos per cm). EC can also be measured in water bodies that may have been affected by a spill. EC in natural tundra water bodies is typically <800 µS/cm (microSiemens/centimeter) which is equivalent to 800 µmhos/cm (micromhos/centimeter). In tundra that is naturally saline (e.g., salt marshes), EC can be much higher. See Table 13 for conversion factors for the most common EC units.

Table 13. Conversion factors for electrical conductivity units

From

To

Multiply by:

dS/m

µS/cm

1000

dS/m

mmhos/cm

1

mmhos/cm

µS/cm

1000

The standard method used by a laboratory to express salinity is to measure EC of a saturated extract at 25°C. A soil extract is prepared by mixing a known mass of soil with a known volume of deionized water, usually at a 1:1 ratio. The laboratory procedure used to measure electrical conductivity in soil is described in Soil Survey Investigations Report No. 42, Soil Survey Laboratory Methods Manual, Version 4.0, November 2004, USDA, NRCS. A similar method using a portable EC meter can be used in the field to rapidly assess soil salinity. A portable EC meter also can be used in the field to rapidly assess salinity of surface water. Because salinity is affected by temperature, field measurements of EC should be converted to specific conductance, which standardizes EC values to 25°C. EC results from a laboratory are reported at 25°C and do not need to be converted.

Field observations can also provide good evidence of salinity. Note the presence of free salt on the soil surface, the presence of bare ground when the surrounding tundra is vegetated, and the presence of salt-tolerant plant species. Using portable EC meters in the field to measure EC in soil and water is often helpful to aid in planning the location and number of samples to be collected for laboratory analysis.

Testing specifically for concentrations of sodium and chloride may be needed. Ion specific probes that are supported by portable field meters are available. Sodic soils have high concentrations of sodium and are a specific type of saline affected soil. If salinity is high and the pH is high (>8.5), the sodium adsorption ratio (SAR) should also be calculated. SAR takes into consideration that the adverse effect of sodium is moderated by the presence of calcium and magnesium ions.

Seeding or transplanting salt-tolerant plants may be appropriate for salt-affected sites if no salt-tolerant plants are growing nearby to revegetate the area (Tactic TR-9). Soil amendments (Tactic TR-13) may be appropriate if the site is too saline for any plant growth (Tables 14 and 15). Flooding (Tactic CR-7) or flushing (Tactic CR-8) also may be appropriate.

Table 14. Electrical conductivity values in tundra surface water and vegetation tolerance

Range of EC in Natural Tundra Water Bodies

Description

Vegetation Tolerance

dS/m and mmhos/cm

mS/cm

< 0.8

< 800

Freshwater

All plants

0.8 – 2.0

800 – 2000

Brackish

Most plants (some growth limitation)

2.0 – 6.0

2000 – 6000

Saline

Some plants (growth limitation)

> 6.0

> 6000

Very saline

Salt-tolerant plants only

Table 15. Electrical conductivity ranges in soil for plants

Electrical Conductivity Ranges in Soil for Plants
(multiple units presented)

Normal Range
in Tundra Soil

Non salt-tolerant

Salt-tolerant

0.3 – 4.0 mmhos/cm

4.0 – 6.0 mmhos/cm

<2 mmhos/cm

300 – 4000 mmhos/cm

4000 – 6000 mmhos/cm

< 2000 mmhos/cm

0.3 – 4.0 dS/m

4.0 – 6.0 dS/m

<2 dS/m

Testing for pH

Use portable meters to measure pH in soil and water rapidly, and to help in the planning of the location and number of samples to be collected
for laboratory analysis. Compare results to back-ground levels near the site and to the normal range for tundra on the North Slope. If the pH in soil is above or below normal range (5.2 to 7.8) for tundra, a soil amendment may be appropriate. A pH range of 6.0 to 7.0 is optimal for availability of nutrients in soil. However, other pH values may be normal for that area. If sample results are similar to background levels, soil amendments are not necessary (Table 16).

Table 16. Normal pH in tundra

Normal pH Range in North Slope Tundra

Soils

Water bodies

5.2 – 7.8

6.5 – 8.5

Testing for Physical and Chemical Characteristics of Soil

Testing for physical and chemical characteristics of soil can provide important information for selecting tundra rehabilitation tactics. The relative amounts of gravel, sand, silt, and clay, and the amount of organic matter are physical characteristics important to plant growth. Laboratories first separate each sample into the coarse earth (particles > 2 mm in size) and fine earth fractions (particles < 2 mm in size). Gravel typically comprises the coarse earth fraction in tundra soils. The fine earth fraction includes sand, silt, and clay. Most laboratory tests are conducted using only the fine earth fraction. The amount of organic matter in soil is important because it enhances water and nutrient holding capacity and improves soil structure. Some laboratory tests may not be possible if the sample is mostly organic matter. If the soil is analyzed for soil nutrients, the pH of the sample also should be analyzed because plants growing in soil with extremely high or low pH may not be able to absorb soil nutrients. Compare results from the affected area with undisturbed tundra to determine the relative importance of soil characteristics for vegetation recovery in the affected area (Table 17).

Considerations and Limitations

  • Soil sampling is typically done when the active layer is thawed.
  • If more than one plant community or soil type is found on a site, additional sampling will be required.
  • Comparison of results between different soil horizons and tundra types on a site is not valid. Also, samples must be compared with background results from similar soils and plant communities, to determine the extent to which the area was affected by a spill.
  • Mechanical analysis for soil samples may be necessary for backfill material imported to a site.

Equipment and Personnel

  • Shovel (1 worker) – to collect soil samples.
  • Ziploc® or other plastic bags (1-gallon size) or DuPont™Tyvek® bags – to store samples.
  • Labels and notebook – for recording sample identifications bags and soil horizons.
  • Cooler and blue ice – to store and ship samples to the soils laboratory.

Table 17. Laboratory tests for physical and chemical soil properties

Soil Property

Normal Range in
Tundra Soila

Physical

Particle Size (%)

Gravel

15b

Sand

18–69

Silt

15–64

Clay

10–39

Organic Matter (%)

5.7–55.5

Chemical

pH

5.2–7.8

Salinity

Electrical Conductivity (dS/m)

<2

Sodium Adsorption Ratio

<13c

Available Nutrients (mg/kg)

Nitrogen, Ammonium

8.7–19.5

Nitrogen, Nitrate

5.5–15.2

Phosphorus

0.1–15

Exchangeable Cations (mg/kg)

Potassium

92–349

Calcium

1399–7381

Magnesium

93–627

Sodium

15–150b

a Reference values (except where noted) from Walker (1985).
b Reference values from unpublished ABR data.
c Reference value from Brady and Weil (1996).


Updated: 12/20/2010