HR: 1330h
AN: H12B-0986    [PDF]
TI: Composition of Rainwater and its Impact on Regional Hydrologic Processes in the Midwestern United States
AU: * Iqbal, M Z
EM: m.iqbal@uni.edu
AF: Department of Earth Science, University of Northern Iowa, Cedar Falls, IA 50614-0335 United States
AB: This study was conducted in the Midwestern United States to determine the impact of rain composition on the regional hydrologic processes. It was hypothesized that a considerable amount of atmospheric aerosols in the region are derived from agricultural soil. These suspended soil particles include farm chemicals that contain nitrogen, phosphorus and sulfur compounds, which can dissolve in raindrops during condensation and change the rain composition leading to increased levels of acidity and nutrients to the surface water. In order to conduct this study, the predominant source of atmospheric moisture was determined by analyzing the isotope (oxygen and deuterium) composition of rainwater and surface water in the area. The observed ranges of Oxygen and Deuterium isotope values (in parts per thousands) are for Ames, delta-O: -30.1 to +1.3, delta-D: -233.0 to +10.1; for Cedar Falls, delta-O: -31.8 to -0.5, delta-D: -245 to -4.0; and for Iowa City, delta-O: -17.5 to -0.6, delta-D: -132.0 to +2.0. It was observed in this study that the isotopic relationships between delta-O and delta-D are generally well correlated with the Meteoric Water Line (MWL) suggested by Craig (1964) in all three sampling locations of the study area. On the contrary, approximately 50% of the samples in Ames, 61% in Cedar Falls, and 44% in Iowa City have d-excess values that are higher than +10 parts per thousand. Although the d-excess averages suggest a predominantly oceanic source of moisture (d-excess = +10 ppt), many condensation events were impacted by recycled (subjected to evaporation, transpiration, etc.) water from terrestrial sources. The results of chemical analysis of rainwater shows that the particulate materials from land sources, especially the agricultural chemicals considerably impacted the general composition of atmospheric moisture. The concentrations of chloride, nitrate, and sulfate, respectively are 3.0, 4.9, and 5.2 mg/L in Cedar Falls, and 4.0, 6.9, and 5.3 mg/L in Ames. This study indicates that the chemical as well as the isotopic composition of atmospheric vapor can be influenced by its interaction with the regional biospheric processes. Additionally, it is concluded that rainwater can transport land-derived aerosol particles to the area lakes and streams and thereby influence the general productivity in the aquatic ecosystem. More data are needed to quantify such productivity.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
DE: 1854 Precipitation (3354)
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2003 Fall Meeting