Atmospheric deposition of nitrogen pollution is one of the major sources of nitrogen to many terrestrial and aquatic ecosystems, worldwide. This modeling study suggests that coastlines frequently experience disproportionally high dry deposition of reactive nitrogen. High concentrations of air pollution from coastal cities often accumulate over adjacent estuaries and coastal waters due to low dry deposition rates over the water and a shallow marine boundary layer trapping marine emissions. As high concentrations of pollutants over the water are transported inland, enhanced dry deposition occurs onshore along the coastlines. Large spatial gradients in air pollutants and deposition totals are simulated along the coastline with decreasing concentrations/deposition as the distance from the water increases. As pollutants are transported onshore, air pollution mixing ratios near the surface decrease due to removal by dry deposition, vertical dilution due to deeper mixing layer heights, and decrease in friction velocity as a function of distance inland from the coastline. Ammonium nitrate formation near agricultural ammonia sources, sodium nitrate formation near coastal areas with atmospheric sea‐salt loadings, and particulate growth via water uptake also contribute to large nitrate dry deposition totals at the coastline. Gradients in dry N deposition are evident over a monthly time scale and are enhanced during sea and bay breeze events. Current existing N‐deposition monitoring networks do not capture the large spatial gradients of ammonium, nitrate, and nitric acid concentrations near coastlines predicted by the model due to the coarse spatial density distribution of monitoring sites.
Military operations of the past two decades have used depleted uranium missiles and equipment, which have contaminated the soils of war‐torn areas. Once in the soil, the metal corrodes to oxidized forms whose solubility depends on soil conditions. This paper reviews the literature on the effects of depleted uranium contamination on bacteria, fungi, and plants to synthesize the research. This will enable soil microbiologists to understand the impact of uranium contamination on the ecosystem as a whole. Some bacteria thrive in high‐uranium environments, but many do not, so uranium contamination selects for the bacteria that can survive. Fungi can often tolerate it quite well, to the extent that some grow on depleted uranium chips and encourage faster corrosion. Some plants can accumulate uranium, but most can only tolerate it if the pH of the soil is high enough to keep the uranium insoluble and not bioavailable. Remediation techniques include natural attenuation, ex situ processing, and bioremediation, but none of these are perfect and the correct approach depends on the site. The negative human health effects associated with uranium contamination make further research and remediation work vitally important.
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