The Effects of Dry-season Urban Runoff on Normalized Differential Vegetation Index by Riparian Vegetation in San Diego County, California

Southern California is a semi-arid ecosystem, in which a majority of streams are ephemeral and intermittent. By increasing water loads via anthropogenic water sources, these rivers may become perennial. Altering a river???s hydrological regime from an ephemeral or intermittent regime into a perennial regime can have a large effect on the riparian habitat existing within the semi-arid west region. This study focused on linking perennialized streams to dry-season urban runoff and examined how normalized differential vegetation index (NDVI) of riparian habitats are affected. This was completed by using Landsat Satellite imagery, a remote sensing method, to test if NDVI could be linked to the amount of irrigation within the watershed. Stream surface water, rain, and tap water were also sampled to test if the isotopic signature of the stream???s surface water could be linked to tap water. A positive correlation was found between the percentage of irrigated areas within the sub-watershed and dry-season NDVI, once the effects of impervious surface cover (ISC) were accounted for. Conversely, a negative correlation was found between the percentage of irrigated areas and the difference in NDVI between the two seasons (wet- minus dry-season), indicating that as irrigation increased the riparian NDVI became more consistent throughout the year. These results indicate that anthropogenic water is providing supplemental dry-season runoff to riparian habitats; however, the streams??? surface water isotopic signatures did not resemble tap water samples, nor was it a mixture of tap and rain water; therefore, I was not able to directly link dry-season irrigation water to streams in this study. However, stream surface water shifts further below the global meteoric water line and becomes more enriched in Deuterium and O18 , indicating that the streams??? surface water isotopes are subject to fractionation due to evaporation during the dry-season. Therefore future studies should focus on more comprehensive sampling of potential sources of anthropogenic water to determine the stream???s water source.Biological Science