Atmospheric deposition : testing methods of measurement and measuring rates in Iowa, U.S.A.
Eutrophication of aquatic systems by nutrients is a growing problem. Anthropogenic use of the nutrients nitrogen and phosphorus has increased in recent years, impacting many water bodies. Nutrients enter aquatic ecosystems through point source and nonpoint source pollution. One important nonpoint source pathway is atmospheric deposition. Atmospheric deposition of nutrients includes both dry and wet deposition. Dry deposition of nutrients occurs from particles or gas in the atmosphere being deposited to a surface in the absence of precipitation. Wet deposition of nutrients occurs in the form of rain or snow. These pathways of atmospheric transport may have increased rates of nutrient deposition in recent times from anthropogenic disturbances. Despite the importance of atmospheric deposition the literature on atmospheric deposition contains several unanswered methodological problems. Studies often use different methods in measuring atmospheric deposition. Contamination by insects falling into samplers is a frequent problem. There is also debate on whether temporal trends exist. This study investigates some of the different methods of measuring atmospheric deposition, explores the problem of contamination and whether it can be excluded or quantified, and tracks yearly trends and rates of deposition in one of the most agriculturally disturbed regions in the world.