Discipline: Ecology Environmental and Earth Sciences
Room: Exhibit Hall A
Francine Alejandra Robles - California State University, Los Angeles
Co-Author(s): Jwan Amin, California State University, Los Angeles; Gloria R. Gonzalez, California State University, Los Angeles; Kyung-Soon Richardson, California State University, Los Angeles; Samuel Rosales, California State University, Los Angeles; Andrew Sunda, California State University, Los Angeles; Cindy Zhan, California State University, Los Angeles.
The goals of this investigation are to study the major ion geochemistry of the Upper and Urban sections of San Gabriel River (SGR) in Southern California and to determine how storm water run-off influences water chemistry. The sampling region for the Upper SGR is located within the rural San Gabriel Mountains, and the Middle section is further downstream within the Los Angeles basin and is urbanized. The importance of understanding the controls of water chemistry in the SGR is that the river provides about one third of the water used in southeast Los Angeles County, apart from section of the river being used for recreation. The hypothesis is that the water chemistry in the upper portion of the San Gabriel River is influenced by the geology, while water chemistry in the middle section portion of the San Gabriel River is predominantly influenced by anthropogenic activities. Furthermore, stormwater run-off will result in a larger change in water chemistry in the urbanized section site as opposed to the Upper San Gabriel River. Water samples were collected over Fall and Winter. All samples we filtered. Part of the filtered sample was acidified to pH=2. In the field we measured the pH, temperature, conductivity and dissolved oxygen using a YSI or HACH multi-parameter probe. While in the lab the concentrations of the major anions were measured using the Ion Chromatograph (IC) and cations via ICP-OES. The temperature recorded in the Upper San Gabriel River ranged from 5.11-14.8?, whereas in the middle region it was higher as expected and ranged from 8.64-23.94?. The total dissolved solids in the Upper San Gabriel River was lower and ranged from 140.70-284.08 mg/L, compared to the middle section which ranged from 185.88-712.88 mg/L. The major ions in the Upper SGR are dominated by Ca and HCO3- with the middle section higher in Na and Cl. Nitrate was also higher in the middle section of the river. The TDS and chemistry of the upper section is consistent with our hypothesis that the major ions reflect the mountainous region and dominated by precipitation and local silicate geology while the higher Na-Cl type water in the middle section reflects urbanization as there is no geological source for the Na-Cl. No rain event One rain event captured during this sampling round generally showed lower TDS and major ions but no change was observed for nitrate in the middle section. The lower TDS is expected as precipitation is typically of very low TDS. The lack of decrease of nitrate could be attributed to excess nitrate of run-off in the urbanized are but is in need of further investigation. The preliminary conclusion is that, as hypothesized, water chemistry differentiated between the two sites on the San Gabriel River where the upper SGR is consistent with source waters in a relatively pristine region with silicate geology, while the middle section has higher TDS and impacted by urbanization. The influence of storm water run-off is less conclusive. While generally TDS decrease as expected the relative impact is yet to be determined and in need of further research. A more detailed sampling is planned for Fall 2019/Winter 2020 with sampling before and after the first major rain event and another later in the season. This follow up investigation will likely provide a better understanding of rain events on water chemistry between first rain events and subsequent events in the during the same season
Funder Acknowledgement(s): This project has been partially funded by the Center of Energy and Sustainability at Cal State LA (NSF-CREST HRD-0932421) via a graduate fellowship to Gloria Gonzales and NSF-LSAMP (HRD-# 1826490) research training support to Francine Robles, Samuel Rosales, and Cindy Zhang
Faculty Advisor: Andre Ellis, firstname.lastname@example.org
Role: This project was inspired by the research provided from Jwan Amin and Gloria R. Gonzalez. My involvement in this project was to study their provided data and expand it in comparison to the information that we had gathered to continue their research. I would collect field samples and proceed with a chemical analysis, which would then be studied and compared to the previous findings.