Carbon Studies

Objective:

To determine the effect of sludge application on: soil CO2 flux; branch and needle expansion factors to quantify carbon sequestered in trees; CO2 sequestration in trees and soil; and vegetative growth 

Soil CO2 Flux

Closed chambers were used to measure CO2 flux near the ground surface at certain periods during the growing season in various sludge amended and control research plots. 

  • Meteorological instruments were used inside and outside the chambers to assess atmospheric conditions. 
  • Two plexiglass chambers measuring 0.5 m x 0.5 m x 1.0 m were equipped with an air sampling port connected to a gas chromatograph (GC) to measure CO2 concentrations. 
  • CO2 measurements were made continuously for 30 minutes under daylight conditions and again under covered conditions.
  • Vegetation from within each chamber was collected and dried in the laboratory to determine the above ground biomass. 
  • Field measurements for sludge amended plots were completed June 26 to 28, 2000 when vegetative growth was high and again on October 11, 2000 when vegetative growth rates were low.

Summer Study Locations

  • ANC Cut Block: de-ink pulp sludge applied (0 to 100 t/ha) and incorporated 8 years prior to monitoring.
  • Millar Western Thinned Forest:  mature, thinned forest area where 0 and 53 t/ha of MW sludge was applied 2 years before CO2 monitoring.  An understory cover of mainly grass was monitored and another test was made on an understory cover consisting mainly of herbaceous plants.
  • ANC Juvenile:  an area containing juvenile lodgepole pine where 0 and 58 t/ha of ANC de-ink sludge was applied 2 years before CO2 monitoring.  Each chamber contained one small (80 cm) lodgepole pine seedling.
  • ANC Spread without incorporation on a slope trial:  sludge application (0, 50 and 80 t/ha) applied without incorporation 3 years before the CO2  assessment.

Fall Study Locations

  • Operational Spreading (Vegetated): juvenile tree area where 0 and 50 t/ha ANC de-ink sludge was applied about 1 month before CO2 monitoring.  Each chamber was placed over vegetation including a small pine tree.
  • Operational Spreading (No Vegetation, Undisturbed):  the same area as above except one chamber was placed on bare soil with no sludge and the second chamber was placed on an area where 50 t/ha of sludge was applied but no vegetation was visible.  These chambers monitored the respiration of the sludge-applied area as compared to the surface of unamended soil where no photosynthesis was expected.
  • Operation Spreading (No Vegetation, Disturbed):  the same area as above however the surface of the sludge treatment and soil control was disturbed by mixing the top 5 cm before CO2 flux was measured. 

Expansion Factor Development

Branch and needle expansion factors to quantify carbon sequestered in trees were developed by selecting 3 trees in each of the control and sludge amended treatments on the basis of average size in that treatment for small, medium, and large and completing the following activities: 

  • Trees were cut down and the base diameter was measured.  
  • One branch was removed from the middle of each tree and left to dry, and then it was used to determine the ratio of branch wood weight to needle weight.  

CO2 Flux Results

Chamber Measurements

  • Sunny conditions decreased CO2 concentrations
  • CO2 concentrations remained unchanged or even increased under cloudy conditions

ANC Cut-Block Location (Summer)

  • Gross photosynthesis was more than 2 times greater for the sludge treatment than the control.
  • Respiration rate for the sludge treatment was also higher than the control. 
  • This indicates greater plant and soil organism activity in the sludge treatment. 
  • This may be due to the vegetation differences between the plots, and higher available nitrogen in the sludge treated plot which is directly related to higher rates of photosynthesis.

Millar Western Thinned Forest Site (Summer)

  • Plant photosynthesis both in sunny and cloudy conditions was greater in the sludge treatment than in the control for the grass and herbaceous covers, likely because of the higher nitrogen content of the sludge treated areas.

ANC Juvenile Area (Summer)

  • Sludge treatment and control assessment included a small lodgepole pine tree with an understory of moss and some fireweed.  The experiments were conducted under sunny conditions. 
    • The photosynthetic activity was lower for the sludge treatment than the control. 
    • Respiration was slightly higher in the sludge treatment than in the control. 
    • NEP for the sludge treatment was positive and negative for the control. 
    • Photosynthetic efficiencies were similar.
  • It appears from the data that the effect of sludge application to a juvenile pine stand was to increase the amount of CO2 emitted.
  Control Sludge Amended
Mean Height 259 cm 297 cm
Mean Base Diameter 47.6 mm 62.86 mm

Mean needle/branch

weight ratio

2.27 2.82

ANC Spread w/out Incorporation (Summer)

  • Compared 80 t/ha and 50 t/ha sludge treatments and also another 50 t/ha sludge treatment with a control.
    • All treatments were a CO2 sink except under cloudy conditions.
    • The NEP was similar for the 50 t/ha treatment and the control. 
    • The NEP was higher for the 80 t/ha treatment than the 50 t/ha treatment.
    • Respiration from the 80 t/ha treatment was less than half the rate from the 50 t/ha treatment. 
    • The control was the most photosynthetically efficient and 50 t/ha treatment plot was more photosynthetically efficient than the 80 t/ha treatment.

 

Operational Spreading (Vegetated, Fall)

  • The sludge treatment was a greater emitter of CO2 than the control even when vegetation was present in both chambers. 
    • The sludge treatment area was a source while the control area was a sink.

 

Operation Spreading (No Vegetation, Fall)

  • One chamber was placed on a sludge amended area and the other on a control area where vegetation was not present.
    • The increase in CO2 concentration was slightly higher for the sludge amended area.
  • CO2 flux increased only slightly when the sludge amended area was disturbed. 
    • These results indicate the importance of managing cut blocks in ways that would minimize surface soil disturbance.
  • A small amount of photosynthesis was observed in the control chamber even though there was no visible vegetation. 
    • Upon closer examination, green algae was observed present in the sludge which may have caused this.

Tree Measurement Results

Height and diameter measurements were completed for trees obtained from the juvenile stand experimental area.

  • Trees from the sludge amended treatments demonstrated twice the volume and therefore the carbon in the stem wood compared to the control treatment
  • Data indicates that needles sequester about the same amount of CO2 as the stem wood and somewhat more than the branches.  The roots sequester slightly less than the branches.

Carbon Storage Results

Cutblock Experimental Site

A linear fit of the yearly rate of CO2 sequestration per hectare was determined for each treatment. 

Pine carbon storage potentials:

  • D0 storage potential = 2.5 t CO2 /ha/yr
  • D3 storage potential = 7.5 t CO2 /ha/yr
  • D5 storage potential = 6.7 t CO2 /ha/yr
  • D10 storage potential = 6.5 t CO2 /ha/yr

Juvenile Stand Site

Control storage potential = 5.1 t CO2 /ha/yr

Operational Spreading Cut-block Sites

The data indicate that the 50 t/ha treatment has the potential to store 3 times the amount stored by the control treatment.

Conclusions

Based on the results achieved some preliminary and general conclusions are presented.  However, it must be noted that the work was a limited assessment that did not include replication of measurements or an assessment of variability at any of the monitoring locations.  The measurements were conducted at only two times during the growing season and continuous day-time and night-time CO2 flux data were not collected.

  • The CO2 flux varied with the weather conditions during measurements.  With sunny conditions, the microecosystem monitored was generally a CO2 sink while under cloudy conditions, the same sites became sources of CO2.
  • Soil, when disturbed by scraping the surface to remove vegetation, is a tremendous source of CO2 emissions into the atmosphere.  About 3.5 times more CO2 was emitted into the atmosphere from a disturbed surface soil than a relatively undisturbed soil.
  • Photosynthetic efficiency (CO2 uptake per gram biomass) was generally higher in sludge-amended sites over control sites.  Higher photosynthetic efficiency means that plants in the sludge treatment were more actively absorbing CO2.  
  • With the exception of the juvenile stand area, it was found that the understory in the sludge amended treatments resulted in higher net ecosystem productivity (NEP) than the control and could therefore, under certain conditions, improve the CO2 balance in boreal forest ecosystems.

Cumulative Wood Volume for Three Control and Three Sludge Amended Trees From the Juvenile Stand Site

Cumulative Wood Volume for the Control and Sludge Amended Pine and Spruce at the Cut-Block Site