Experimental Design, Plant Material, Culture Conditions, and Analyses

ERDC TN-DOER-C22

September 2001

Development Center, in drums, shipped in cooled overpacks. Upon arrival, the dredged material

was dried so that the moisture content was reduced to about 50 percent and the innate microbial

community could persist. Treatment included spreading and mixing the dredged material on plastic

sheets inside a greenhouse and turning it until it contained approximately 50 percent (by weight)

water. As a control substrate, two organic soils were chosen. Baccto R Lite potting soil (85-90

percent organic peatmoss), a highly organic, nutritious soil, Michigan Peat Company, Houston, TX,

was used for plants. For invertebrates, another highly organic soil was purchased from Carolina

Biological Supply Company, Burlington, NC. The test and both control soils were chemically and

physically characterized prior to testing (Table 2). The control soil for plants was nutritious (six

times more nitrogen and phosphorus than the test dredged material) and generally contained far

lower contaminant levels. However, it contained total vanadium and zinc levels that exceeded the

proposed plant CSCLs. The control soil for the invertebrates, on the other hand, contained a

relatively high total chromium concentration, that probably exceeded the proposed invertebrate

CSCL (CrVI is estimated to be about 10 percent of total chromium). A reference soil, in the sense

of an uncontaminated soil of similar composition to that of the test soil, was not included in the

plant and invertebrate tests.

PLANT TESTS

Experimental Design, Plant Material, Culture Conditions, and Analyses. A multifacto-

rial experimental design using a completely randomized design with four replicates per treatment

was used with the following treatments: (1) substrate type, (2) plant species, (3) pot size, and

(4) test duration. Two plant species were included, Cyperus esculentus (yellow nutsedge), a plant

species commonly used at the Environmental Laboratory as an index plant, and Cynodon dactylon

(bermudagrass). The latter species was selected for its wide geographical distribution, being

common in southern regions of North America, and rapid growth and profuse generative reproduc-

tion; and because most of its biomass is aboveground. The latter characteristic would facilitate

harvesting, and reduce sample number and analytical costs by a factor of two. Two pot types with

the same 2-L volume were tested, small pots with a 0.0167-m2 surface area and large pots with a

0.0238-m2 surface area. Three test durations were tested: for C. esculentus 21, 35, and 63 days;

and for C. dactylon 21, 63, and 77 days.

The experiment was started on 7 July 2000, with four pregerminated tubers of C. esculentus per pot

and 0.207 g C.dactylon seeds per 0.028-m2 pot surface, in a greenhouse at the Environmental

Laboratory. The plant propagules were purchased as follows: C. esculentus as tubers from Wildlife

Nurseries, Inc., Oshkosh, WI, and C. dactylon as common C. dactylon seeds from the Flower

Center, Vicksburg, MS. Pots were placed in saucers, with saucers daily replenished with deminer-

alized water. Test and control soils were kept at a soil moisture level of approximately 50 percent.

Soil moisture levels were monitored using irrometers (Irrometer Company, Riverside, CA). At

harvest time, each species was removed from its pot, C. esculentus was divided into aboveground

and belowground organs, and the plant material was manually freed from soil particles, rinsed with

demineralized water, blotted dry, weighed, and dried in a forced-air oven to constant weight

(70 oC). Growth response was expressed in g dry weight per m2. Metal concentrations were

determined in the plant material of the second and third harvests by acid-digesting 0.5 g dry plant

material in a microwave-oven for lead, vanadium, nickel, and zinc followed by measuring total