U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12, 1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigations Report 99-4018B

Trends in Sediment Quality in Response to Urbanization

By Peter C. Van Metre and Edward Callender

ABSTRACT

Trends in hydrophobic contaminants identified in reservoir and lake sediment cores in three watersheds dominated by post-1960 urbanization follow several consistent patterns. Since the 1970s, trends include decreases in lead, increases in arsenic and zine, decreases in PCBs (polychlorinated biphenyls) and organochlorine pesticides (with the occassional exception of chlordane), and large increases in PAHs (polycyclic aromatic hydrocarbons). Trends in PAHs in a core from a fourth lake, where development mostly occurred before 1940, indicate highest concentrations in about 1950, which contrasts with trends in the newer urban watersheds. In this paper, we attempt to answer the question, "Is the sediment quality (and water quality as influenced by hydrophobic contaminants) getting better or worse?" The approach used is to normalize sediment-core concentrations of these contaminants to toxicity-based sediment quality guidelines, then sum the normalized concentrations. The results of this approach indicate that overall sediment quality improved from about 1950 to 1970 in the lake in an older watershed, where improvements were driven by decreases in total PAH. In contrast, sediment quality is declining coincident with urbanization in the three lakes in newer urban watersheds. In the newer urban watersheds decreasing trends in normalized total DDT, PCBs, and lead are more than offset by increases in PAHs, arsenic, zinc, and (or) chlordane.