Impacts of dredged material disposal on estuarine benthic macrofaunal communities in Coos Bay, Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2z10ws523

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  • Hopper dredge disposal of coarse grained sediment was investigated between May and September, 1986, at a designated disposal area, Site G, in Coos Bay, Oregon. The objectives of the study were to: (a) identify and describe the benthic macrofaunal community structure at Site G during May and September, 1986; (b) analyze May and September sediments at the site to determine possible differences in percent organics, sediment grain size, and volatile solids; and (c) determine if there were correlations between sediment parameters and the macrofaunal community structure. Three stations were located within the disposal site and eight stations were located within the surrounding area. Differences in sediment physical characteristics were not significant between seasons, although median grain size tended to be slightly finer in September. Furthermore, Stations 4,7, and 2 contained a higher percentage of gravels in May than at other stations or in September. Differences in sediment parameters among stations were few. There was no apparent relationship between depth and other sediment parameters. Differences in grain size distribution, organic content, percent fines, and depth were thus not sufficient to account for differences in community structure among stations or between cruises. Diversity, taxa richness, and numbers of individuals increased significantly in September. There was no significant difference in evenness between May and September. There were no significant correlations of community composition parameters and depth. Stations contained within Site G did not show consistent patterns or differences in diversity, richness, overall abundance, or evenness from other stations or between cruises. Organisms obtained at Site G were those typically found in high energy, coarse grained environments. Two of these species, Mediomastus californiensis and Spiophanes bombyx, increased in abundance in September. Increases in several species were consistent with seasonal variations that have been described in other studies. Many juveniles were obtained in the September samples. This finding could be indicative of seasonal recruitment or recolonization following a disturbance. Based on the information and data collected, it is unclear as to whether or not changes in community structure and composition were due to disturbance by disposal activities or to seasonal environmental and biological influences. Since increases in species abundance, richness and diversity occurred, detrimental effects related to disposal of 11,632 m3 of coarse grained sediment at Site G were not apparent.
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