The mineralogy of dust and the solubility of phosphorus in dry particulate matter: ecosystem impacts to a large, shallow eutrophic lake

Utah Lake is a large (380 km 2 ) shallow (<4 m deep) eutrophic lake in the United States that experiences regular harmful algal blooms (HABs). West of the Mississippi River, only Flathead Lake, Montana and Lake Tahoe, Nevada/California have greater surface areas among fresh water lakes. Unlike these other lakes, it is adjacent to a large urban corridor and its water quality is of concern for aesthetics, recreation and irrigation diversions. HABs in Utah Lake can affect ecosystem health, including the production of cyanotoxins and profound anoxia. Active sampling of the Utah Lake airshed has shown that the mineralogy and phosphorus content and solubility of dust varies in time and space. Dust is comprised of varying proportions of quartz, calcite, dolomite, sodium feldspar, gypsum, halite, illite and kaolinite. The soluble phosphorus fraction of dust is bi-modally distributed with nodes at 10% and 50% releases to synthetic lake water. Active sampling also showed that there is little attenuation of >2 μ m particles as air blows across the lake. Soluble phosphorus appeared to be associated with calcium-rich phases and especially areas with high gypsum content. As much as 1/3 of phosphorus is delivered to the lake during June through August. High phosphorus deposition during the summer months exacerbates the tendency for HABs to form in warm weather. Monte Carlo simulations suggest that phosphorus associated with atmospheric deposition alone is sufficient to maintain a eutrophic state in the lake. Dust has become a large, non-point source of phosphorus, with external fluxes to the lake that equal or exceed point sources like waste-water treatment plants. It is also largely anthropogenic as dust movement has increased 500% since European settlement. This suggests that active ecosystem management is needed to maintain and improve water quality and ecosystem function as non-point source phosphorus fluxes may overwhelm point-source controls.