EELGRASS SURVEYS IN EAGLE HARBOR, WA, FOLLOWING CAPPING OF ADJACENT CONTAMINATED SEDIMENTS.

Abstract

Between October 1993 and August 1995, the density of eelgrass (Zostera Marina L.) in three beds within or near Eagle Harbor, WA, was recorded as counts of stalks within 0.1 m2quadrats. The surveys were conducted by the EPA Region 10 Dive Team and were designed to document any changes in eelgrass density following capping of nearby contaminated sediments, since it was unknown whether cap sediments might migrate and affect nearby beds. During the surveys, 30 quadrats were placed randomly in a 100 m by 20 m rectangle in the middle of each bed. In some quadrats two divers made counts. Shoot density differed: the Wyckoff bed (nearest the sediment cap) consistently had the least amount of eelgrass and the Murden Cove bed (to the north of Eagle Harbor) the most. Changes within beds appeared to be related to the natural cycle of winter reduction rather than the movement and subsequent deposition of cap materials. Variability among divers in counting stalks was a function of stalk density. The highest difference in counts ([high-low1Ihigh) was 33% when the density was high and less than 14% (within 1 or 2 stalks) when density was low.