MS Thesis Defense - Cheyanne Olson

Subject: WILL SMALL DIVERSIONS TO FRESHWATER INFLOW AFFECT WATER QUALITY?

Speaker: Cheyanne Marie Olson

Chair: Dr. Paul Montagna

Committee: Dr. Dorina Murgulet, Dr. Michael Wetz

Date: March 23rd, 2017 (Thursday)

Time: 9:00 AM

Location: HRI 127

Freshwater inflow is a vital component of an estuary, as several ecological relationships exist between the level of inflow and aspects of estuary function. For future management, it is necessary to know how small diversions of freshwater inflow may impact both water quality and ecosystem function within estuaries. The purpose of this study was to examine effects of variation in freshwater inflow to make inference about water quality variables and estuary function during low inflow periods. This study focused on three bays: Carancahua Bay, San Antonio Bay (including Guadalupe Bay), and Tres Palacios Bay. Data was collected monthly via water quality sampling, in-situ and discrete datasondes, Nortek AquaPro Acoustic Doppler Current Profilers (ADCPs), precipitation and wind data collected from the National Climatic Data Center (NCDC), and two USGS flow gages. Freshwater inflow is responsible for driving nutrient concentrations and salinity ranges, as demonstrated by a principal component analysis. Based on results of the study, San Antonio Bay requires a larger amount of freshwater inflow change (above 10,000 ac-ft/mo) to yield corresponding changes in water quality response, because it typically receives large volumes of inflow. Conversely, Carancahua Bay Bay and Tres-Palacios Bay both require smaller volumes of freshwater inflow (less than 10,000 ac-ft/mo) to have large impacts on water quality response because these bays receive lesser amounts of inflow. Freshwater inflow can also alter net ecosystem metabolism (NEM) of an estuary. Freshwater inflow and salinity both had a significant but weak correlation to NEM when lagged, due to a time lag experienced between drivers and estuary response. The flow-to-water-quality concept created in this study provides a generic framework that can be applied by managers and policy-makers to analyze how specific amounts of flow diverted from, or added to, specific bays may alter water quality conditions.