Upload
brian-bovaird
View
701
Download
0
Embed Size (px)
DESCRIPTION
Agricultural Soil Science and the Remediation of Oil and Brine Spills
Citation preview
Agricultural Soil Science and the Remediation of Oil and Brine Spills
Kerry SubletteCenter for Applied Biogeosciences
University of Tulsa
Remediation of Oil and Brine Spills
• Typical bioremediation process for oil:– Fertilizer
• Provide N and P for hydrocarbon degraders– Bulking agent
• Increase O2 and water infiltration– Tilling
• Mixing• Aeration
– Control pH and moisture to the extent possible
Remediation of Oil and Brine Spills
• Typical elements of brine spill remediation:– Drainage control
• So the salt has somewhere to go– Organic matter
• Increases permeability to water and mobilize salt
– Tilling• Mixing• Improving permeability
– Gypsum• Combat sodicity
Remediation vs. Restoration• How do we define the remediation endpoint?
– Reduction in concentration of contaminants (hydrocarbons, brine)• Regulatory limit• Risk to human health or environmental receptors• Land use
• Remediation is not restoration– Both the original spill and the remediation process disrupt soil
ecology• Disruptions in N and P cycling• Reduced diversity of soil microbes and invertebrates• Loss of vegetation
– All levels of ecosystem affected• Producers (plants)• Consumers (bugs, worms, mites, nematodes, etc.)• Decomposers (microbes)
• What constitutes restoration?– It depends
• Land use• Landowner wishes (within reason)• Restoring ecosytems
Remediation vs. Restoration• We need to start thinking about remediation and
restoration together- what should we do differently?
Remediation vs. Restoration• Who can help us with this? Who else
– works to grow something in the soil– strives to maximize yield– is careful to maintain soil fertility so that the soil remains productive?
• When we do bioremediation– our crop is a functioning
community of hydrocarbon-degrading microbes
– our “yield” is rapid and efficient removal of hydrocarbon
– next season’s crop is a restored plant communityand functioning soil ecosystem
• Lessons learned will also have application in the remediation of brine spills
Some good advice from the ag industry
• Fertilizers and salinity• Surface crusting• Soil compaction• Gypsum and soil
nutrients• Letting the weeds talk
What the ag industry knows about fertilizers and salinity
• Fertilizers increase soil salinity• Excess fertilizer application reduces yield and
increases runoff of N and P• Practical limits to amount of fertilizer added to the
soil in a single application– Soil salinity prior to fertilizing– Tolerance of the crop– Form of the fertilizer
• Rule-of-thumb for N, maximum application of 3-4 lbs/1000 ft2
Fertilizer salt index
• The fertilizer salt index is a relative measure of the salinity produced by a fertilizer in soil water– Sodium nitrate is the standard against which all
other fertilizer are compared• Salt index (SI) for NaNO3 = 100
• The partial salt index is a relative salt index per unit weight of nutrient (one unit = 20 lbs of N, P2O5, or K2O)
• The SI cannot predict amount of fertilizer that will do injury to plants (or microbes); it is for comparison of fertilizers only
Salt indices of common fertilizers
Fertilizer SI Fertilizer SIAmmonium nitrate
(33% N)104 Gypsum 8
Urea(46%)
71 Calcium nitrate (15.5% N) 65
Ammonium sulfate(21% N)
88 Monoammonium phosphate (MAP) (11% N)
26
Diammonium phosphate (DAP) (18% N)
29 Triple super phosphate(45% P2O5)
10
Muriate of potash 32
Partial salt indices of common fertilizers per unit nutrient (20 lbs of nutrient)
Fertilizer Nutrient PSI Fertilizer Nutrient PSI
Ammonium nitrate
N 3.06 Gypsum 0.25
Urea N 1.62 Calcium nitrate N 4.20
Ammonium sulfate
N 3.25 Sodium nitrate N 6.08
Diammoniumphosphate
(DAP)
P2O5 0.46 Monoammoniumphosphate
(MAP)
P2O5 0.10
Muriate of potash
K2O 1.94 Triple super phosphate
P2O5 0.22
An illustration of the problem
Soil impacted with light crude is to be bioremediated. The total TPH inventory is found to be 5600 kg and the total spill area is 12,000 ft2 (about 2% TPH). How much N should be applied for effective in situbioremediation?
• An often quoted EPA recommendation is C:N:P:K of 100:10:1:1 (weight ratio)– Predicts a N requirement of 450 kg – Equivalent to about 82 lbs/1000 ft2
– 27 times the rule-of-thumb
An illustration of the problem
• A more reasonable approach taken by most practioners has been split additions of N, like an initial C:N of 150:1 followed by monitoring– Predicts a N requirement of 5.5 lbs N/1000 ft2
which still may be too high• Lesson- be judicious in fertilizer application
and monitor soil salinity along with N, P concentrations
• Rule-of-thumb: 3- 4 lbs/1000 ft2
higher SI lower SI
What the ag industry knows about surface crusting
Effect of rain on soil infiltration and oxygen transfer
• Rain drops strike the soil surface at about 20 mph
• Soil aggregates are separated due to beating of rain drops
• Surface soil macropores fill with soil particles forming a surface crust and reducing infiltration
• Anaerobic zone produced under the surface crust
• Reduced soil infiltration also causes surface flow and erosion
Type of rainfall
Intensity(inches/hr)
Relative energy impacting the
soilDrizzle 0.001 1.0
Light rain 0.004 5.5
Moderate rain 0.15 28
Heavy rain 0.59 154
Excessive rain 1.7 1454
Cloudburst 3.9 1500
Energy transfer to soil during rainfall
What types of soils tend to form surface crusts?
• Tendency to form crusts– High silt or clay content– Low organic matter concentrations and
weak aggregates– Small aggregates more susceptible to rain
Preventing crusting
• High concentrations of decaying organic matter in the soil
• Light surface dressing or mulch of organic matter– Too much and you limit oxygen transfer
• Coordinate cultivation with rainfall events• Larger aggregates and greater surface
roughness (chisel plough for cultivation)
Choice of cultivation equipment can have a dramatic effect on surface crusting
0 10 20 30 40 50 60 70 80 90
Accumulated rainfall (mm)100 mm = 4 inches
Infiltra
tion
rat
e (m
m/h
)
0 1
0 2
0 30
40
50
60 7
0
Chisel plough
Mouldboard + diskDisk
harrow
Surface dressing of organic matter reduces erosion
What the ag industry knows about soil compaction
• Soil compaction causes– Poor aeration and
oxygen transfer– Waterlogging– Excessive runoff and
erosion– Excessive soil
strength limiting root growth during revegetation
Bulk soil density
Low Medium High
Effect of soil compaction plant roots
Soil that plant roots cannot effectively penetrate will not support significant biodegradation of hydrocarbon
The effects of soil compaction maypersist for decades
Historic bison wallow (from the 19th
century) in tallgrass prairie in Oklahoma
Field capacity
Soil-tire interface pressure for an 18.4R38 tire
Properly inflated
Excessive inflation; greater potential for compaction
Depth of soil compaction from tire loads
Radial tires perform better in terms of reducing load on soil
Preventing soil compaction
• Add organic matter• Limit vehicular traffic• Keep out livestock• Cultivate at proper soil
moisture content• Use wider tires with
minimum inflation• Distribute loads• Monitor soil impaction
with soil penetrometer
Facilitating the movement of salt in soil for brine spill remediation
• Increasing permeability to water in the spill area– Mechanical loosening of the soil– Soil amendments
• Organic matter• Gypsum
• What does gypsum do?– Improves soil structure by displacing Na+ from
clays and promoting aggregation of clay particles
– Improved soil structure results in better infiltration rates
What the ag industry knows about gypsum
• Gypsum is used in the ag industry as a source of calcium and sulfur for crops– Typical application rates 1-2 tons/acre but highly dependent on crop
• Gypsum applications for remediation of brine spills can be tens of tons/acre
• Large gypsum applications can reduce soil fertility– Increasing Ca+2 in soil solution decreases uptake of K+ and
Mg+2 by plants– Ca+2 causes release of K+ and Mg+2 from soil and loss by
leaching – effect is increased by irrigation– Sulfate reduces uptake of molybdenum– Gypsum interferes with the humification process (formation
of stable soil organic matter)– Gypsum increases immobilization of P (effect compounded if
CaCO3 present)• Applied P can induce Zn+2 deficiency by reducing Zn+2 uptake• Zn+2 application can reduce uptake of Cu+2 and Mn+2
What the ag industry knows about gypsum
• Presence of high gypsum concentrations in soil makes fertilizer additions less effective– Need management of both macro and
micronutrients in gypsum applied soils – soil and leaf analysis recommended
What the ag industry knows about biological indicators of the restorationof soil health and fertility
• During revegetation pay attention to the weeds that pop up
• The weeds that grow on your site can signal adverse growing conditions in the soil such as:– Too little water– Too much water– Low N– High N– Too much shade– Compaction– Low pH– General low fertility
Barnyard grass-
poor drainage
Birdsfoot trefoil-drought, low
nitrogen
Common chickweed-too shady
Prostrate knotweed-compaction
Conclusions
• Careful attention to bioremediation and brine remediation practices can not only increase the efficiency of the remediation process but also lead to successful restoration an impacted site– Being careful about fertilizer applications– Coordinating rain events with cultivation– Using chisel ploughs for cultivation– Incorporating lots of organic matter in the soil– Keeping livestock off the sites– Carefully monitoring soil nutrients when gypsum is used– Monitoring salinity and compaction– Topdressing with hay