Effects of 4-inch (10.16 cm) suction dredge mining on benthic macroinvertebrates in 3rd to 4th order streams were investigated in 1996 by evaluating four mining claim operations in Althouse Creek, Sucker Creek, and Taylor Creek in southwestern Oregon's Rogue River basin. The effects were site-specific. The study showed no significant (p>0.05) differences between treatment and control areas in density and species diversity of benthic macroinvertebrates. However, mean taxa richness significantly (p<0.05) increased thirty days following the end of the mining period. Collector-filterers were significantly (p<0.05) lower in dredged areas thirty days after the mining season. Because of constraints in sampling design, sample sizes and relatively small treatment areas, the results from this study are tenuous at best. There were apparent inherent differences in species dominance among sites possibly a result of differences in stream size and riparian conditions. This further confounds results of this study. / Graduation date: 2000

No description available.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Thesis (M.A.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references (leaves 74-82). / xi, 82 leaves, bound ill., maps 29 cm

Measuring the impact of physical disturbance on macrofaunal communities and sediment composition is important given the increased demand for the exploitation and disturbance of marine ecosystems. The aim of the present investigation was to provide a comprehensive study about the extent to which the disturbance (especially aggregate dredging) may affect benthic ecosystem function. The first part of the thesis concerns a field investigation of the impacts of dredging on the benthic community and related ecosystem function which was measured by different approaches including traditional methods based on benthic community structure and a more novel approach based on the functional traits of benthic organisms. The assessment was done by comparing dredged sites (Area 222, southeast England) with nearby undisturbed reference sites from the years 2001 to 2004 and in 2007. In general, low dredging intensity did not appear to impose great impacts on the benthic community and related ecosystem function compared to the higher intensity activity. Most of the analyses suggested that the community at the high dredging intensity site had yet to recover at the end of this study period. Among many factors related to the recovery of the benthic community was sediment composition where gravel deposits appeared to support a faster biological recovery. Meanwhile, the recovery of species with specific traits, such as tube-building and filter feeding also indicate a faster recovery for the whole community. The experimental work to determine different impacts of Hediste diversicolor on its surrounding depending on its relative size is discussed in Appendix 1.

The state of Georgia has two large ports that are accessed by way of navigable entrance channels. One of these ports is located in Brunswick, Georgia, and is maintained by the United States Army Corps of Engineers via periodic dredging. Sediments removed from the channel are typically pumped several miles offshore of Brunswick and placed in dredged material mounds, thus removing the sediment from the littoral cycle. This offshore placement, while being the most economically viable method, often negatively impacts the sediment budget of the coastal region and causes erosion downdrift of the channel, specifically along Jekyll Island. Onshore placement of the dredged material is not feasible due to increased associated costs and the high fraction of fines present in the material; thus, nearshore placement is a potentially viable alternative. Nearshore placement could possibly reduce erosion rates and provide protection to property from waves and storms. The USACE initiated a thorough field data collection campaign in 2002 to study the possibility of beneficial placement of dredged material. The author analyzed the existing data to predict the rate and direction of sediment movement away from an existing dredge mound. These predictions are then compared to bathymetric survey data in an effort to validate the results and methodologies used for sediment transport predictions. The ultimate goal is to use the results of this study along with numerical models currently being developed by the Corps to assess the possibility of sediments being transported toward the shore thus re-entering the littoral cycle and providing a benefit to the coast of Georgia.