| Atmospheric mercury concentrations are increasing due to both anthropogenic and natural sources. This mercury is subsequently being deposited, and appearing at toxic levels in fish, and animals that prey on them (including humans). There is much uncertainty about the relative importance of various mercury sources to the atmosphere. Point sources of mercury pollution (e.g. volcanoes, coal fired power plants) are relatively easy to quantify, but are thought to contribute as little as half of the mercury to the atmosphere. Diffuse sources, while significant, have to this point been difficult to quantify, and knowledge of mercury cycling processes in these systems has remained elusive. I describe in this dissertation the development and testing of conditional sampling, a superior method for measuring surface-atmosphere mercury exchange from diffuse sources, and the utilization of this method to quantify mercury fluxes from several soil surfaces. It was determined through extended sampling periods that low mercury bio-solids (sewage sludge), when land applied as a fertilizer are not a significant source of mercury to the atmosphere, in contrast with previously published data from land applied bio-solids containing higher levels of mercury. Measurements over two similar cattle pastures in northern Minnesota showed that vegetated surfaces exhibit bi-directional mercury vapor exchange, and can under certain conditions be major sinks of atmospheric mercury. |
