Figure 1. Percent survival of three benthic invertebrates to increasing overburden stress after 6 days of burial

ERDC TN-DOER-E19

March 2005

(Terrados et al. 1998). Effects of deposition may also be difficult to separate from associated

effects of increased sediment flux including light attenuation (Terrados et al. 1998).

Unfortunately, field assessments of effects of siltation or deposition on SAV in U.S. waters is

very limited.

Successful settlement of kelp and other algal species on hard bottom substrata is clearly inhibited

by very thin layers of sediment (0.008 mm). Fucus serratus embryos responded negatively to

thicker layers of sediment, with a stronger negative reaction to fine and organically enriched

sediments, and most strongly to the presence of sulfide (Chapman and Fletcher 2002).

Because SAV may have a very wide range of growth forms, sizes and phenotypic plasticity, the

effects of deposition could vary considerably depending on habitat, season, and water depth.

Deposition may affect growth and survival due to light limitation, accumulation of waste

products due to limited diffusion and sulfide poisoning depending on grain size, water content,

and organic content of sediments.

Methods for expressing levels of sedimentation (thickness, volume, dry/wt weight).

Measurements of sedimentation (i.e., bedded sediments) relevant to biological effects may

require several dimensional variables including thickness, density, percent fines, geometric mean

size, and Fredle number (Caux et al. 1997). Fredle number is an index of permeability that has

been correlated with survival to emergence of salmon and trout (Lotspeich and Everest 1981).

Hinchey et al. (in preparation) chose effective overburden stress (kPa: bulk density and depth of

burial as described in Richards et al. (1974) as a reliable measure of the force exerted on

organisms by sediment burial, because it combines burial thickness and porosity. Their

experiments with sediments from the Chesapeake Bay and York River were conducted to assess

survival at 6 days of burial for a range of overburden thickness (0-25 cm) representing

overburden stress from 0-16 kPa (Figure 1). Force may be most important to mobile organisms

attempting to escape from deposition events, but permeability may be more important to the

survival and growth of sessile organisms buried under very thin layers of sediment (<2 mm).

100

Figure 1.

Percent survival of three

benthic invertebrates to

Macoma

increasing overburden

Leptocheirus

y = 93.068e-0.6327x

stress after 6 days of

Streblospio

R2 = 0.8815

burial (from Hinchey

Expon. (Streblospio)

et al., in preparation)

Expon. (Leptocheirus)

Linear (Macoma)

y = 94.356e-0.26x

R2 = 0.9465

0.0

4.0

8.0

12.0

16.0

overburden stress (kPa) calculated at 24 hr