Analytical procedures more » have been developed to estimate this aspect of benthic-habitat quality. One aspect of benthic habitat quality is the relative amount of trophic support that a given benthic habitat provides demersal bottom-feeding fishes.
The quality of benthic habitats at proposed disposal sites was identified as a major topic of interest in the PSDDA study because of potential impacts to demersal fish feeding habitat. In 1985 a joint effort was initiated to examine long-term requirements and strategies for open-water disposal of dredged materials. Army Engineer District, Seattle is currently involved in a decision-making process regarding the designation of open-water dredged-material disposal sites in Puget Sound and adjacent waters. Concentrations of Ag, As, Cu, Hg, Sb, and Zn have declined significantly in the last 20 years, lending support to the hypothesis that the strengthening of environmental regulations since 1970 has influenced the water quality of Puget Sound. Significant decrease in PCB and DDT concentrations were also observed with a 2 to 4-fold decrease in surficial sediment concentrations. Hydrocarbon contamination appears to parallel that of heavy metals. The mean concentration of Pb, for example, has decreased upwards of 20% during this period, with an overall drop of about 30% since its maximum concentration in the 1950s and 1960s. The contaminant level of many metals has continued to decrease steadily in the last 10 years. Sedimentation rates were approximately 1 to 2 cm/yr and deposition rates ranged from 480 to 1000 mg/cm2/yr.
0 kommentar(er)
