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NUTRIENTS IN TEXAS RESERVOIRS

NUTRIENTS IN TEXAS RESERVOIRS. Nutrient Database Statistically-based Nutrient Criteria for Reference Reservoirs Selection of Reference Reservoirs Reservoir-specific Trends and Correlations Approaches to Nutrient Criteria in non-Reference Reservoirs. Evan Hornig (cehornig@usgs.gov)

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NUTRIENTS IN TEXAS RESERVOIRS

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  1. NUTRIENTS IN TEXAS RESERVOIRS • Nutrient Database • Statistically-based Nutrient Criteria for Reference Reservoirs • Selection of Reference Reservoirs • Reservoir-specific Trends and Correlations • Approaches to Nutrient Criteria in non-Reference Reservoirs Evan Hornig (cehornig@usgs.gov) Richard Kiesling (kiesling@usgs.gov)

  2. TEXAS NUTRIENT DATABASE • Sources • TCEQ TRACS Database • USGS NWIS Database • Scope • 1/70 through 4/03 • Depths < 2 feet at main pool sites • Winter (Oct-April) and Summer (May-Sept.) • Data from databases combined at the parameter level (TP, TN, DN, Chla, Secchi, Turbidity)

  3. Development of Reference Reservoir Nutrient Criteria For each lake/constituent/season with at least 15 measures, apply a probability-based criterion: The criterion is the minimum value the mean nutrient would have to attain such that a Student’s t test would reject the null hypothesis that the mean and the mean of the baseline data were drawn from the same population with a probability (0.05, 0.1, 0.2) (one-tailed).

  4. Selection of Reference Reservoirs • Based on reservoir and upstream segment land uses, select reference reservoirs: • Less than 10% of land use urban and agricultural • No major municipal discharges • Additional considerations – feedback from Texas Nutrients Workgroup

  5. Chihuahuan Deserts Western High Plains Southwestern Tablelands Central Great Plains Central Oklahoma/Texas Plains Edwards Plateau Southern Texas Plains Texas Blackland Prairies East Central Texas Plains Western Gulf Coastal Plain South Central Plains Texas Designated Reservoirs 25 26 Cherokee 29 27 35 32 33 24 30 ECOREGIONS 24 25 26 27 29 31 34 30 31 32 Reference Lakes in Bold/Italic 33 34 35

  6. Annual Trends from Selected Reference Lakes May-September R2=.40, P<.05 NS R2 NS R2 NS R2

  7. Ecoregion 35 South Central Plains Reference Lakes May-September NS R2 R2=.19, P=.09 R2=.16, P=.11 R2=.50, P<.05

  8. Reservoir Grouping • Purpose: To investigate linking criteria for non-reference lakes to reference lake conditions • Considerations: • Regional (e.g. ecoregions) • Lake hydrology (residence time) • Preliminary Results • Total Basin Area • Basin Slope • Mean Depth

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