Macroinvertebrates

ERDC TN-DOER-C22

September 2001

Macroinvertebrates. At each CDF, three surface litter samples, approximately 2 cm deep in an

area of 930 cm2, were collected concurrent with the dredged material samples. First large macroin-

vertebrates, such as earthworms and large arthropods, were removed from the samples within 4 days

after collection, and stored in 95 percent isopropanol until genera were determined. Subsequently,

a portion of the dredged material was placed in a Berlese funnel apparatus (15-cm funnel diameter)

for extraction of the smaller invertebrates (Borror and DeLong 1964). The extraction procedure

was allowed to proceed for 14 days to provide sufficient time for animals to move through the

dredged material column and into the alcohol. Identifications were made to the taxa levels, with

nomenclature following Chu (1949), Kaston and Kaston (1953), Borradaile et al. (1961), and Borror

and DeLong (1964).

The Monroe CDF was inhabited by relatively few invertebrates (Table 3) with small population

sizes. Soft-bodied invertebrates, such as gastropods and annelids, were absent. Most of the groups

identified were insects, foraging on the surface (beetles, flies including larvae, beetle larvae, spiders)

and living in the dredged material (collembola or springtails). Progressing upland along a transect

to the drier sites, the taxa remained the same but numbers of individuals per sample were smaller.

At the wet Manitowoc site a large and diverse Collembola (springtail) population occurred, but few

members of other taxa that were found at relatively higher diversities (at the class level) at both

drier Manitowoc sites. At the driest Manitowoc site, two earthworm species, centipedes, and

millipedes were identified. Dredged material sampled at the Manitowoc CDF had remained

undisturbed for a long time (several years) relative to that at the Monroe and Bayport Cell 6 sites.

Both driest Manitowoc locations, which were covered with herbaceous vegetation, supported large

and diverse invertebrate populations of earthworms, isopods, chilopods, diplopods, and insects. The

animals present, especially the large number of isopods, tend to illustrate the typical "boom and

bust" population dynamics of highly disturbed ecosystems. Species composition and population

density of the major taxa may be expected to fluctuate from year to year with the vegetation.

At the Bayport sites, soil-dwelling invertebrates were very sparse, with only a few surface foraging

animals. This may have been because the dredged material was recently placed in the site, the site

was wet and unconsolidated, and time was insufficient to allow normal soil processes to develop

and provide the microhabitats necessary for colonizing soil invertebrates.

Summarizing, invertebrate diversity and abundance varied per site, both being highest at sites where

the dredged material had become consolidated, the water table had decreased, and vegetation had

been established providing organic matter and microhabitats required for colonization by the

animals. In general, the time elapsed since the additions of dredged material to the CDFs has been

insufficient for the development of a stable vegetation cover, and the organic material and root

structure of the plants have been insufficient for the development of soil depth profiles. As a

consequence, the dredged materials in these CDFs is depauperate in soil macrofauna and meiofauna.

Among the taxa identified, springtails were present at six out of nine sites, and earthworms at one

out of nine sites. Based on their relevance for these toxicity tests, springtails and earthworms would

be suitable test organisms.

INITIAL TOXICOLOGIAL TESTING: Based on the recent chemical information on the dredged

material of the three CDFs, the Monroe CDF dredged material was selected for toxicological testing