Soil Bulk Density, Total Pore Space, and Compaction

Due to Human Foot Traffic

Jessie Meeks and Ali Theuer, 2001

Contents:

ïPurpose and ObjectivesïSitesïMethodsïDataïDiscussionïWrapping up

We explored the relationship between calculated soil bulk density (g/cc) and estimated amounts

of human foot traffic.

ïSoil compaction increases bulk density and decreases pore space.ïA decrease in pore space leads to increased erosion and decreased soil productivity.ïLogging trucks are a known hazard, what can feet do?

Site 1: located on the Brook Trail, visited by less than 1,000 people annually (thatís 2,000 feet every year)

Site 2: located along the river trail, visited by just over a thousand people annually

Site 1Site 2

Site 3: located along the main loop trail, over 10,000 visitors per year

Site 4: located along aside trail with about 10,000 visitors per year

What did we do?

Soil samples were obtained by hammering a can of known volume into the ground,

both on and off trail at all four sites.

We took keen and meticulous notes and observations.

Samples were taken back to the lab and weighed.

The shape of some of the cans was compromised while hammering them into the soil.

The new volume of each can was determined using a graduated cylinder.

What did we find?

Bulk Density Data

Site 1 Site 2 Site 3 Site 4 Averages

bulk density=hydrated weight(g)/volume(cm3)on trail BD

265.92g/190.00cm3=1.400g/cm3

677.71g/350.00cm3=1.936g/cm3

218.75g/160.00cm3=1.367g/cm3

881.85g/500.00cm3=1.764g/cm3 1.617g/cm3

off trail BD549.42g/530.00cm3

=1.037g/cm3676.35g/460.00cm3

=1.470g/cm3645.01g/570.00cm3

=1.132g/cm3622.41g/550.00cm3=

1.132g/cm3 1.193g/cm3

difference .363g/cm3 .466g/cm3 .235g/cm3 .632g/cm3 .424g/cm3

% difference 25.93% 24.07% 17.19% 35.83% 25.76%

Bulk Density On and Off Trail

1.400

1.936

1.367

1.764

1.037

1.470

1.132 1.132

0.000

0.500

1.000

1.500

2.000

2.500

0 1 1 2 2 3 3 4 4 5

Site

Bulk Density (g/cm3)

on

off

What does it mean?

ïAn average difference in bulk densities of 25.76% between on trail and off trail was calculated

ïAs bulk density increases, pore space decreases

ïBulk density was greater on trail than off trail, therefore pore space is less on trail

ïSoil bulk density reaches a maximum, leveling off (i.e most of the pore space is compacted)

ïLess pore space results in increased soil erosion and decreased soil productivity

ïRelationships among the number of hammer blows, crumpling of cans, and the calculated bulk density were observed

SummaryHigher bulk densities on trails suggest that their soils areless productive and more susceptible to erosion than their offtrail counterparts

Error: a loss of soil mass may have ensued in the Transporting of samples from container to container

Study Improvements: continue the study over several years, varying the levels of foot traffic at the sample locations,and tracking the bulk density and total pore space over time.

Thanks!