Alternative landfill soil/vegetation covers at Rocky Mountain Arsenal: could difference in plant roots between covers contribute to differences in cover function?

Alternative Landfill Soil/Vegetation

Covers at Rocky Mountain Arsenal:

Could differences in plant roots between

covers contribute to differences in cover

function?

Outline

• Background • Methods

• Root washing • Root scanning

• Root drying & weighing • Statistical analysis

• Results • Discussion

• Study findings • Report content

Background

• In May 2015, the Army notified Regulatory Agencies that the amount of water collected by Lys 001 and Lys 002 on the Shell Disposal Trench RCRA-equivalent cover exceeded the compliance standard of 1.3

mm/yr (Navarro report, 17 Sep 2015).

The purpose of the project reported here is to

• Investigate root development as possible contribution to this excessive percolation

Background

NS

ICS

SDT

LYS015 LYS007 LYS004 LYS001 LYS002 LYS003 C E G B F G E F G B G D D E F A B D A C F NS33 • Shell Disposal Trench (SDT) • Integrated Cover Systems (ICS) • Natural grassland area (NS)

Methods: Soil washing

• Took pictures: before and during the soil washing process • Thawed soils at least 2 days before wash

• Labeled the plastic bags to put washed roots, free from soil • Placed the roots in pre-labeled plastic bags and added water • Stored the roots in the refrigerator until scanning (up to 7 days)

Methods: Root scanning

• Placed sample in clear plexiglass box with water • Arranged sample so that it is well spread out

• If we have crowded roots changed to the bigger size trays

• For bigger trays we used 2-3 repeated scanning measures and used their averages for the analysis

• Used 400 dpi for the best root imaging

• We can edit the image: erase and add roots • Saved image with and without analysis

• Look over the data and do quality check. • If necessary scan the roots again.

Methods: Root drying & weighing

• After scanning, we dried the roots in the oven at 60 °C (24-48 hours) • Weigh each sample on a top-loading balance. Recommended to use

four significant digits after comma.

• Placed each sample in a separate coin envelope labeled with the sample identification information for long-term storage.

Methods: Statistical analysis - Roots

• Repeated Measures One-Way ANOVA

• Cap Type as independent variable

• Shell Disposal Trenches (SDT) • Integrated Cover System (ICS) • Natural Site (NS)

• Depth as repeated measure (within factor) • Response variables

• Root length density (RLD) • Mass per volume (MPV) • Average diameter (AD)

• Coefficient of variation and residuals for each response variable

• Significant Cap Type by Depth interaction indicates that the response variable differs by depth among the cap types

Methods: Statistical analysis - Vegetation Cover

• One-Way ANOVA

• Cap Type as independent variable

• Response variable: Vegetation Cover in 2015

Results: RLD

RLD differed among cap types at some depths

-140 -120 -100 -80 -60 -40 -20 0

0.E+00 2.E+04 4.E+04 6.E+04 8.E+04 1.E+05 1.E+05

Soil

depth,

cm

Root length density, m/m3

ICS SDT NS Control b a b ab a ab b a ab

Results: RLD

0 50,000 100,000 150,000 200,000 250,000 300,000 ICS SDT NS R oo t l en gh t d en sity , m/ m3

Total Root Length Density

b a

Results: MPV

-140 -120 -100 -80 -60 -40 -20 0

0.E+00 5.E+02 1.E+03 2.E+03 2.E+03 3.E+03 3.E+03 4.E+03 4.E+03

Soil

depth,

cm

Mass per volume, gr/m3

ICS SDT NS

Results: Average diameter

-140 -120 -100 -80 -60 -40 -20 0 0 0.1 0.2 0.3 0.4 0.5 0.6 Soil depth, cm Average diameter, mm ICS SDT NS Control b c a a a ab b b c c b a

Results: Average Diameter

0 0.5 1 1.5 2 2.5 3 SDT ICS NS Average Diameter b a a

Results: Patterns of Variation

• Coefficient of variation (mean/SD) and residuals (observation – mean) for RLD, MVP and AD.

• Detected no differences in these metrics that would indicate greater heterogeneity in one cap type than another, or in caps compared to the natural site

Results: Vegetation cover

0 10 20 30 40 50 60 70 80

AveGrass AveForbs TotAve, %

Cov

er

, %

Total vegetation cover

SDT ICS NS

Discussion

• ICS had greater RLD than NS at the shallowest depth • At about 100 cm, SDT had greater RLD than NS

• ICS had greater RLD than SDT at the deepest depth • MPV did not differ among cap types across depth • Average diameter was greater in SDT than ICS & NS • Vegetation cover did not differ between SDT & ICS

Report Contents

• Format of the report… • Hard copies

• Report

• Electronic copies

• Raw data • Images