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Proposed Revisions to the Wissahickon Nutrient TMDL

Proposed Revisions to the Wissahickon Nutrient TMDL. Modifications. Parameter changes C:N:P ratio Half-saturation constant Model change Carrying capacity and substrate availability relationship Endpoint Interpreted narrative standard for phosphorus endpoint. Model Updates.

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Proposed Revisions to the Wissahickon Nutrient TMDL

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  1. Proposed Revisions to the Wissahickon Nutrient TMDL

  2. Modifications • Parameter changes • C:N:P ratio • Half-saturation constant • Model change • Carrying capacity and substrate availability relationship • Endpoint • Interpreted narrative standard for phosphorus endpoint

  3. Model Updates • Parameter Adjustment • Phosphorus half-saturation constant • Adjusted to 125 ugP/L from 50 ugP/L • Better represents Cladophora, one of the most common types found in Wissahickon • C:N:P ratio • Adjusted to 10.1:1.3:1 from 33.3:7:1 • Based on review of data collected in 2005 and represents community ratios

  4. Model Updates • Code Modification • Enhanced to better predict influence of substrate availability on periphyton growth • Reflects physical composition of steam bottom • Changed to represent available substrate and impacts on carry capacity (max amount periphyton that can grow) • Based on 2002 study of sediment size

  5. Model Updates • Code Modification (cont) • Previous model – substrate availability and carrying capacity were independent and applied to entire reach • New model – carrying capacity and available substrate are related with carrying capacity applied only to available substrate. • Converts segment-wide periphyton density to the real density of the available substrate

  6. Phosphorus Endpoint • In-stream endpoint for phosphorus based on interpretation of state narrative standard • Carrick & Godwin study (2006) • Stream data collected and regression models applied to estimate TP to achieve certain biomass levels • Goal was to reduce algal standing crop biomass to 100 mg/m2 • Studies show this level at which periphyton biomass becomes excessive • Resulted in a TP of 248 ug/L

  7. Calibration Results DO PO4

  8. Allocation Results for the Wissahickon Main Stem for Trout Stocking Uses DO results TP and Chlorophyll ‘a’ Results

  9. Allocations for Trout Stocking (and Warm Water Fishes)Classification Period

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