|Document Type:||Technical Memorandum|
|Title:||Benthic invertebrates and sediment characteristics in freshwater, beach habitats of the lower Columbia River, 1994-95|
|Author/Editor:||George T. McCabe, Susan A. Hinton|
|Tech Memo Number:||NMFS-NWFSC-26|
In 1994 and 1995, we studied benthic invertebrates and sediment characteristics in freshwater, beach habitats (i.e., intertidal beaches and adjacent shallow subtidal habitats) at l0 areas of the lower Columbia River between river kilometer 53 and 122. All 10 areas had been used in the past for the disposal of dredged material pumped from the bottom of the navigational channel.
Disposal of dredged material in a narrow band (about 30 m wide) onto beaches in the lower Columbia River is commonly referred to as beach nourishment. The main goals of the study were to describe the benthic invertebrate communities at the beach nourishment areas and examine the relationship between sediment median grain size and standing crops of the amphipods Corophium spp., which are seasonally important in the diet of juvenile salmonids.
Benthic invertebrate and sediment samples were collected at the 10 beach nourishment areas in July and October 1994 and January and April 1995 with polyvinyl chloride (PVC) coring devices. The 10 areas were designated Beach Nourishment Areas O-34.0, W-40.9, W-43.8, O-44.0, W-45.0, O-45.1, O-47.8, O-57.0, W-70.1, and O-75.8. The "O" and "W" refer to Oregon and Washington, and the succeeding number refers to the approximate location in river miles from the mouth of the river. Mean numbers of taxa/categories (by month) collected in the beach nourishment areas were generally low, ranging from 2 to 8.
Major benthic invertebrate taxa collected in the 10 beach nourishment areas included nemerteans, oligochaetes, Fluminicola virens, Corbicula jluminea, Corophium salmonis, Corophium spinicorne, Chironomidae larvae, and Ceratopogonidae larvae. With the exceptions of Beach Nourishment Areas O-47.8 and O-75.8, total densities (i.e., standing crops) of benthic invertebrates in the beach nourishment areas were not significantly different (P > 0.05) between the 4 months. Densities of Corophium spp., most of which were C. salmonis, were not significantly different (P > 0.05) between months, except at Area O-75.8. In all areas except Area O-45.1, total benthic invertebrate and Corophium spp. densities were significantly higher (P < 0.05) at sampling stations 30 m from the high tide mark on the beach than at stations 15 m from the high tide mark. Densities of Corophium spp. varied widely within and between areas, with densities at individual stations ranging from 0 to more than 82,000 organisms/m2. The regression relationship for median grain size and Corophium spp. density was significant (P < 0.05); however, median grain size was a poor predictor of Corophium spp. density, explaining only 5% of the variation in Corophium spp. density (transformed)
All 10 beach nourishment areas supported substantial standing crops of Corophium spp. at times, particularly at stations along the 30-m transects. Since Corophium spp. are important prey for juvenile salmonids, and juvenile salmonids migrate along the beach nourishment areas, it is important to ensure that Corophium spp. populations in these areas are not adversely impacted.