Experimental/Manipulative Studies

ERDC TN-DOER-C23

September 2001

nor were they intended as field validation efforts. However, the approaches used in these studies

are instructive and as such are included in this review. For example, studies by Tagatz and Ivey

(1981) and Tagatz et al. (1987) evaluated the effects of pesticide-spiked sediments on benthic

recruitment. Although these studies were not implicitly designed as field validation studies, they

did use an experimental/manipulative approach to compare laboratory and field colonization rates.

These studies examined the effects of the synthetic pyrethroid pesticide fenvalerate on benthic

recruitment. In their 1981 study Tagatz and Ivey placed aquaria in the environment to allow

"natural" colonization to occur while a second set of aquaria were allowed to colonize under an

unfiltered flowing seawater system in the laboratory. The laboratory-developed communities were

then dosed continuously via a flow-through aqueous exposure system for 8 weeks at concentrations

of 0.01, 0.1, and 1.0 g fenvalerate/L. For the field portion of the study, aquaria were retrieved

from the field after about 8 weeks and then dosed in the lab for 1 week at concentrations of 0.1, 1.0,

and 10.0 g fenvalerate/L. Results indicated that benthic community structure was significantly

altered in both laboratory- and field-derived communities at concentrations of 0.1 and 1.0 g

fenvalerate/L. In a 1987 study, Tagatz et al. modified their earlier approach by evaluating

recruitment in aquaria containing fenvalerate-spiked sediments. Sediments were spiked at concen-

trations of 0.1, 1.0, and 10 g/g. Six groups of four aquaria each were placed in the field. Each

group consisted of an unspiked control, 0.1, 1.0, and 10 g/g spiked sediment. Sediment cores were

obtained at 0, 7, 21, 35, 49, and 56 days for subsequent chemical analysis. After 8 weeks all aquaria

were removed from the sediments and returned to the laboratory for benthic community analysis.

Results indicated that the 10-g/g treatment showed significant changes in benthic community

structure.

A similar study by Kalke, Duke, and Flint (1982) studied the impact of weathered oil on benthic

communities colonized in the laboratory and in situ. Aquaria with clean bedded sediment were

established under both laboratory and field conditions and allowed to be colonized by planktonic

larvae for a period of 8 weeks. Weathered oil was distributed to both laboratory and field replicate

compartments; after 4 additional weeks, the experiments were terminated. Results indicated that no

significant effects from the oil treatment were observed for the laboratory-colonized communities,

whereas total density of macrobenthos, species composition, and numbers of species were signifi-

cantly reduced in the field-colonized systems. The authors suggested that the differences observed

between laboratory and in situ exposures were due to differences in mechanisms of colonization.

In the laboratory studies, colonizing organisms were supplied to the aquaria via a water pump

whereas in the in situ studies colonizing organisms settled naturally or moved into the compartments

from the surrounding environment. As a consequence, in the in situ studies, densities of colonizing

organisms were much higher than in the laboratory studies. Low oxidation-reduction potential

measurements in both field and lab samples suggested that the oil had reduced the depth of the

oxygenated layer by approximately half, which would adversely affect subsurface benthic produc-

tion and alter other processes such as nutrient regeneration. This reduction in the oxygenated layer

manifested effects in the higher density in situ studies but not in the lower density laboratory

colonization experiments.

The Field Verification Program (FVP) initiated by USACE and USEPA in the 1980's represents

the largest and most relevant (in terms of dredged material testing) field validation effort conducted

to date. The FVP followed an earlier and much larger research program conducted by USACE in