Environmental Assessment of EL Paso's Upper and Lower Valley Canal Systems Using Tree Ring Analysis

Dendrochronology, or tree-ring dating, is the science of dating of past environmental events or climatic changes utilizing tree ring growth patterns. The width of the rings of certain species of trees (i.e. Populus fremontii) are dependent on regional precipitation levels or the abundance of local water sources. Therefore thick rings are produced during wet years and, inversely, narrow rings during dry years. This growth can also be affected by, and date, such factors as slope gradient, soil properties, temperature and snow accumulation. The more a tree's rate of growth has been limited by such environmental factors, the more variation in ring to ring growth will be present and the higher probability of dating such factors. Trees showing a lack of ring width variability rings have generally constant environmental or climatic conditions and indicate that no environmental or climatic changes have occurred. Our study will examine the tree ring of the Rio Grande Cottonwood (Populus fremontii), due to its short life span, rapid growth, and wide spread occurrence in our proposed study area. Our study area will encompass sites along the Rio Grande, canals and residential areas in El Paso County. Our first goal will be to investigate the possibility of identifying environmental contaminants stored within various xylem tissue members of the tree rings and ascertaining dates and regional concentrations of heavy metals and therefore identifying possible sources of contamination. The second goal will be to use dendrochronology to identify and date any growth stress or impedance due to the effects of over pumping, canal lining, and flood control methods in the study area.