Effects of Freshwater Inflow on Water Quality in the Nueces Delta

1. Effects of Freshwater Inflow on Water Quality in the Nueces Delta Andrea Kopecky Marine Science Department CE 394K Term Project – Fall 2001

2. Where is the Nueces Delta? The Nueces Delta is upstream of Corpus Christi Bay on the coast of South Texas

3. One threat to the Nueces Delta • Decrease in freshwater • Population increase (more water usage) • Dams, reservoirs, diversions, etc. • Result = increase in salinity • Decrease in primary productivity and diversity • Causes stress, creates a harsh environment • Delta is now considered a reverse estuary

4. Fixing the inflow problem… • Rincon Bayou Demonstration Project • Included people from U.S. Bureau of Reclamation, UT Marine Science Institute, CRWR, TWDB • Project from 1994-1999 with purpose of increasing freshwater inflow to the Nueces Delta • 2 channels were created to divert water from the Nueces River Nueces River Overflow Channel Rincon Overflow Channel

5. Map of Nueces Delta • Made by David Eckhardt from the U.S. Bureau of Reclamation • It is a mosaic of eight color-infrared USGS DOQQ's (Digital Orthophoto Quarter Quadrangles) • The map is a raster image data set projected in UTM coordinates

6. Project objectives • Find out how an increase in freshwater influences water quality • Use salinity, ammonium, nitrate/nitrite, and silica concentrations at 10 stations in the area • Look for correlations between freshwater and the amount of each nutrient • Consider other factors that could influence the water quality

7. Water data used • Rincon gauge data • Precipitation • Freshwater inflow from the Nueces River • Station data for Nueces Delta • Monthly averages for salinity, ammonium (NH4+), nitrate (NO32-), nitrite (NO2-), and Silica at 10 stations for September 1998 to March 2001

8. Narrowing down the data set • I chose 3 months out of a possible 31 • Based on missing data and amount of inflow • Narrowed down to October 1998, April 1999, November 1999

9. Results • Salinity As freshwater inflow increases, salinity decreases

10. What else affects salinity (besides freshwater inflow)? • Temperature / Evaporation • As temp increases, evaporation increases, which increases salinity • Amount of tidal inflow • This could decrease or increase salinity, depending on the salinity of the estuary • Precipitation • Causes a decrease in salinity

11. Results • Ammonium • More variation • Trends not clear • Other factors are influencing the concentration

12. Factors that could influence [NH4+] • Uneven distribution of freshwater throughout the Delta • Amount of fertilizer in agricultural runoff varies • Sensitive ammonium test – error prone • Nitrifying bacteria – Cyanobacteria convert atmospheric nitrogen to NH4+ • Amount of phytoplankton and zooplankton

13. Results • Nitrate and Nitrite - At 8 of the stations, NO32- and NO2- were the highest during October ’98, which had highest inflow - At stations 50 and 54, April ’99 had the highest concentrations

14. What’s affecting nitrate & nitrite? • Nitrifying bacteria can convert NO32- to NO2- to NH4+ • Tidal inflow • Ground water inflow • Agricultural runoff • Seasonal fluctuations

15. Results • Silica • Highest silica levels during Oct ’98 at river stations (4, 4A, 4B) • April ’99 and November ’99 had similar concentrations • More freshwater = more silica

16. What influences silica concentrations? • Amount of runoff • Erosion of clays • Weathering of igneous rocks • Diatoms and other phytoplankton • Essential for their growth (used in cell walls) • Recycling of their cell walls

17. Conclusions • Freshwater inflow positively affects the water quality in the Nueces Delta • Causes a decrease in salinity • Increases the concentration of nutrients, including ammonium, nitrate, nitrite, and silica • An increase in nutrients can lead to an increase in biological productivity and diversity • There are other factors that also influence the concentration of nutrients

18. More Conclusions • GIS is helpful for… • Studying water quality • Visualizing data from multiple stations • Comparing data over time • Project expansion • Other water quality parameters • Other estuaries • Relationship between inflow & nutrients • Predict what effects dams/reservoirs will have • THE MORE WE KNOW ABOUT THE IMPACTS OF HUMAN ACTIVITIES ON WATER QUALITY, THE MORE WE CAN DO TO PROTECT OUR ESTUARIES!

19. Acknowledgements • Heather Alexander-Mahala and Dr. Kenneth Dunton, University of Texas Marine Science Institute • Dr. Maidment

20. Questions?