David Maidment & Lynn E. Katz & Imane Mrini Center for Research in Water Resources The University of Texas at Austin Total Maximum Daily Load for Zinc in Nueces Bay Project Managers Sandra Alvarado - TCEQ Blake Traudt - GLO

Texas Department of Health Guidelines : –Average zinc concentrations in oysters from Nueces Bay should be consistently below 700 mg Zn/kg edible tissue Data Observations –High concentrations (~ 2,389 mg/kg) were found in oysters resulting in acute adverse health effects (TDH, 1994); –No threat for fish or crabs Zinc Impairment / criteria

Zinc in Oyster Tissue Target value : 700 ppm

Outline Review of issues Study area : Nueces Bay –Zinc impairment Study objectives –Study of Zinc monitoring data –Estimation of watershed zinc loadings Next steps

Sources of Contamination ? ?

Water Quality: Pollution Loading Model DEM Precip. Runoff LandUse EMC Table Concentration Load Accumulated Load Load [Mass/Time] = Runoff [Vol/Time] x Concentration [Mass/Vol]

Expected Mean Concentration Land Use EMC Table derived from USGS water quality monitoring sites

Water Quality Analysis Salinity Concentration and Mass Fluxes in Corpus Christi Bay. Fluxes Flow of water Advection Dispersion Loads Transport of Constituents Finite Segment Analysis

Observed vs. Expected Zinc (µg/l)Chromium (µg/l)

Physicochemical Reactions Sediment-Water Exchange Photochemical Reactions Inorganic Reactions Organic/Biological Reactions Atmospheric Deposition Flux sunlight

Resuspension and Deposition Resuspension Deposition

Study Area : Nueces Bay Nueces bay TMDL segment 2482 Average area of Km2 Mean depth : 0.68 to 0.92m Relatively small average residence time (V/Q) = 30 days Uses : Aquatic life, contact recreation, fishing, production of edible oysters, clams and mussels, and shellfish harvesting (oyster water use ) TMDL for zinc in oyster tissue

Study Objectives Acquire existing data and information necessary to support modeling and assessment activities Determine current allowable loadings of the constituent (zinc) Allocate the total loadings to appropriate pollutant sources

Zinc Monitoring Stations TCEQ monitoring stations

Zn conc. ( ppm) Zinc Monitoring data Zinc in sediments

A C B Industries: A Centex Cement Corp. B Central Power and Light C PPG Industries Inner Harbor Zinc Monitoring data Zinc in sediments

Zinc conc. (  g/L) Zinc Monitoring data Zinc in water

Zinc Monitoring data Zinc in sediments vs zinc in water Sediment Water

Hydrodynamic Circulation Simulation by Dr Junji Matsumoto, TWDB Animation

Average Zn Conc. = 100 ppm Sediment Data for Nueces Bay

Sediment Data for the Inner Harbor Average Zinc Conc. = 440 ppm

Zinc Monitoring data Zinc partitioning in sediment/water/oyster tissue Zinc in water ppm Zinc in sediment 100 ppm Zinc in Oyster tissue 2400 ppm Ratio = 55,000 Ratio = 24 Ratio = 2300

Watershed delineation Procedure DEMFlow_dir Watershed procedure developed for delineating watersheds in coastal and low-lying regions with little to no slope.

Watershed delineation delineated watersheds for each segment

Watershed source loadings of zinc PrecipitationRunoffLand use EMC Table concentrations Total Zinc Loadings = g/day loadings

Total annual loadings of zinc from non point source pollution : 282 kg Volume of the bay : Mm 3 Annual concentration of Zinc from NPS :4.53  g/L Mean Measured concentration of zinc in water in Nueces bay : 42.1  g/L Current watershed sources of zinc Watershed sources are not the whole picture

10 cm sediment bed depth and surface area of 74.9 km 2  V = 7,490,000 m 3 Mass of sediments = x10 10 kg Average concentration of zinc in sediments = 440 ppm (mg/kg) Total mass of zinc in sediments = 8,730 metric tons Estimation of Mass of Zinc in Sediments in Nueces Bay

Total mass of zinc in sediments = 8,730 metric tons Based on 1 kg/day watershed loading it will take 24,000 years to accumulate this mass We must have point sources or legacy sources !! Pollution Sources in Nueces Bay

Estimate background levels of zinc in sediments Evaluate point sources Consider hydraulics between inner harbor and Nueces Bay Suggestions … Next Steps

Zinc Monitoring data Zinc in sediments at station Nueces river North of Viola Basin mg/kg

Zinc Monitoring data in Nueces bay Zinc in sediments at station mg/kg

Zinc Monitoring data in Nueces bay Zinc in sediments at station 13422

Zinc Monitoring data in Nueces bay Zinc in sediments at station mg/kg

Zinc Monitoring data Zinc in sediments at station ( Inner Harbor Nr nav bridge) 865 mg/kg

Zinc Monitoring data Zinc in sediments at station ( Inner Harbor in Avery basin)

Zinc Monitoring data Zinc in sediments and water at station 13439( Inner Harbor)

Zinc Monitoring data Zinc in sediments at station ( Inner Harbor Nr nav bridge)