Key Research Questions Addressed by the Study

What controls concentrations of mercury in stream water, sediment, and fish?

How do biological, chemical, and other environmental characteristics govern the methylation, transport, and bioaccumulation of mercury in streams?

This study includes stream ecosystems in relatively undeveloped forested areas and in highly urbanized areas to allow comparisons among contrasting land uses. The study also covers a wide range of landscapes with varying geology, climate, hydrology, and wetland density to better understand environmental factors controlling methylation, mercury transport, and bioaccumulation. The selected stream ecosystems vary in food-web complexity, which can also influence mercury biomagnification.

Mercury levels in fish are determined by:

• the amount of mercury entering an aquatic ecosystem from natural and anthropogenic sources (source strength);
• the extent to which an ecosystem converts inorganic mercury to methylmercury (methylation efficiency); and
• food-web interactions—longer food chains—from algae to predatory fish—should result in higher mercury concentrations in predatory fish.