Determining Plant Suitability Based on Agronomic Characteristics

Technical Note DOER-C3

May 1999

2-mm screen. For saltwater sediments, the process also includes a sediment washing

procedure to remove soluble salts. After drying and grinding, the material is placed in 22-L

buckets, and reverse osmosis water is added at a ratio of 1:3 sediment to water. The mixture

is stirred with an electric stirrer and then allowed to settle. The water is then decanted, and

the drying and washing process is repeated two more times. This process usually reduces

the soluble salts concentrations to within levels suitable for most freshwater plants and

microbes. Another more rapid process involving oven-drying and oxidation with hydrogen

peroxide has been developed for predicting the long-term effects of drying and oxidation on

surface runoff water quality (WES 1998b) and is being considered as a replacement to the

above procedure for the plant tests. High levels of iron sulfides in some dredged materials,

such as Blackrock Harbor (Brandon et al. 1991), may result in extremely low pH (<3.0) after

the material dries and sulfide is oxidized. Additional tests for these conditions are described

in Appendix H of Lee et al. (1985).

Determining Plant Suitability Based on Agronomic Characteristics. Soils and

their chemical/physical characteristics vary widely, and even in some of the harshest soil

medium, there is a plant that can be established and survive. Selecting the appropriate plant

species is the key to establishing plant cover on dredged material. A systematic approach to

characterizing problem soil materials and selecting appropriate plant species is provided in

an instruction report for problem soils at CE construction sites (Lee et al. 1985). This

approach was successfully applied to the revegetation of dredged material for the Field

Verification Program CPF at Bridgeport, Connecticut (Brandon et al. 1991). Figure 5

summarizes the various physical and chemical analyses that should be considered in a phased

testing approach for dredged material considered for vegetation establishment. Once a

dredged material has been fully characterized, the appropriate plant species can be selected

according to the characterization results and the geographic location and climate. The

vegetation selection guide is provided in Appendix E in Lee et al. (1985), which is available

from the authors of this technical note.

The contaminant characterization will determine the type of phytoreclamation process

(Table 2) and the possible plant groups needed for evaluation. Some examples of phytore-

clamation demonstrations using various plants to perform various processes are shown in

Table 3. Plant species capable of accumulating significant levels of some metals are provided

in Table 4. Since the phytoreclamation technology is new and recent developments have

focused on certain plant species, the list of plants shown to be successful is limited. However,

this information can serve as a guide to the selection of appropriate plant types for further

evaluation. Geographic and climatic conditions at the phytoreclamation project site must

also be considered to ensure that appropriate plants are selected for the local growing season

and climate.

Plant Growth in Dredged Material and Effects of Amendments. Phytoreclamation

requires that plants survive on the material in which they are planted. Although the dredged

material characterization tests and plant guides described in the previous two sections indicate

the potential for plant growth, the singular or combined effects of various contaminants and/or

the effects of various amendments may alter this potential. Some useful screening tests for

this assessment are described by Sturgis et al. (1999) for both seed germination and plant

growth. The tests are designed to compare the effects of various manufactured soil blends,

consisting of dredged material and organic waste amendments, on plant biomass yields. For