Development and application of a methodology to estimate regional natural conditions for trace metals in marine sediments of southcentral Alaska's coastal region.

摘要

Increasing levels of resource development and population growth along Alaska's relatively pristine coastline require responsible environmental stewardship that is based on scientifically defensible monitoring and assessment. This thesis develops a methodology to assess the spatial distribution of coastal sediment trace metals and estimate their natural condition along Alaska's coastline. Marine sediments provide a better integrated long-term signal for naturally occurring and anthropogenic chemicals than repeated water measurements. The first of three manuscripts reports on marine sediment trace metal concentrations from a probabilistic sampling survey of Alaska's Southcentral coastal region. Results are described on a proportional basis, i.e., percent of estuary area, for the distribution of As, Cd, Cr, Cu, Pb, Hg, Ni, Ag, and Zn in the sediments. With the exception of naturally elevated Cr and Ni at a site bounded by a chromite ore body, sediment trace metal concentrations measured represent non-analmous levels. The second manuscript develops natural conditions for fluvial trace metal inputs from two major Southeast Alaska coastal watersheds: Cook Inlet and Copper River. The stream sediment trace metal natural conditions place levels in the adjacent coastal sediments into context. Two exploratory data analysis techniques, the Tukey Box plot and Median + 2 Median Absolute Deviation, combined with geochemical mapping are used to develop stream sediment trace metal natural conditions. The third manuscript builds on the first two to develop a methodology to estimate coastal sediment natural conditions. Population estimates for the cumulative area 90% UCB 95% sediment trace metal of interest obtained from the sampling survey methodology and screened reference sites is used to establishing an upper threshold value for regional natural conditions. While this work establishes natural condition marine sediment trace metal levels for this region, the significance of these levels from an ecotoxciological perspective remains to be established. Additional studies are needed along other sections of Alaska's coastline, coupled with biological assessments, if Alaska is to develop relevant sediment quality guidelines.