Reducing salinity and organic
contaminants
in the Pearl Harbor sediment
using soil amendments and plants
N. V. Hue, S. Campbell, Q. X. Li, C. Lee†,
and J. Fong
Univ. of Hawaii and † US Army Corps of Engineers
Abstract
Phytoremediation is an emerging technology that can be used economically to clean-up sites moderately contaminated with trace elements and/or man-made organics. Thus, the technique was tried on the Pearl Harbor (Hawaii) dredged material (PHDM), which requires remedial actions on polycyclic aromatic hydrocarbons (PAHs) and perhaps some heavy metals. The PHDM was first amended with a high Ca soil (Mollisol) and a biosolids-based compost at different proportions to yield different salinity levels. A mixture that yields an electrical conductivity (EC) of the saturated paste extract of 15 - 20 dS m-1 was identified and used to evaluate the salt tolerance of five plant species. Germination and 1-mo-old biomass indicated that common bermudagrass (Cynodon dactylon), seashore paspalum (Paspalum vaginatum), cowpea (Vigna unguiculata), and beach pea (Vigna marina) can produce at least 40% biomass of the control at an EC of approximately 18 dS m-1, suggesting they are relatively salt tolerant. In contrast, Desmodium intortum either did not germinate or died within 2 wk of germination at the same salinity level. A subsequent greenhouse experiment, using mixtures of the PHDM (0 or 25% dry weight), organic amendments (10% leucaena green manure or biosolids-based compost), and a Mollisol in 6-L pots containing 4 kg material, yielded the following results. (i) A combination of transplanted seashore paspalum, seeded bermudagrass, and seeded Vigna marina was effective in taking up sodium and reducing salinity. (ii) Total PAH concentration was reduced by about 30% after 3 mo of active plant growth; however, degradation of individual PAH members varied significantly. (iii) Soil amendment with leguminous green manure was more effective than compost for use in bio- and/or phyto-remediations.