(Chapra, L24) David Reckhow CEE 577 #20 1 General Model - PowerPoint PPT Presentation

Updated: 6 November 2017 Print version Lecture #20 Streeter-Phelps: Photosynthesis/Respiration (Chapra, L24) David Reckhow CEE 577 #20 1

General Model Kinetics Atmosphere (K a ) K 2 K 4 σ 4 SOD Organic N K 1 (K s ) K 3 Dissolved Oxygen β 3 CBOD (K d ) σ 3 NH 3 β α β 1 5 1 NO 2 β 2 α 6 β 2 NO 3 2

Modeling procedures  Verify model calculations  using a simplified example, check computer vs. analytical  Identify inputs (loads, rate coefficients, transport)  reaction coefficients - general  all rate constants must be uniform in space and time unless variations are linked to system characteristics  rates and formulations should fall within the range reported in the literature (e.g., Rates, Constants, and Kinetics Formulations in Surface Water Quality Modeling, Bowie et al., US EPA, Athens Environmental Research Laboratory, EPA/600/3-85/040, June 1985., see: http://www.epa.gov/ORD/WebPubs/surfaceH2O/s urface.html) or course website David Reckhow CEE 577 #20 3

Identifying inputs (cont.)  k d , k r − 0 . 434    simplified method: H = <   - 1 k 0 . 3 d ; for H 8 ft d   8  in-stream assessment = - 1 k 0 . 3 d for H > 8 ft d − = k t L L e r o = − k r ln ln L L k t o r Ln(CBOD) Time of travel David Reckhow CEE 577 #20 4

Identifying inputs (cont.)  k d , k r (cont.)  Tierney & Young correction for bottle rates ft/s nU Stream slope N = + k k d b z (ft/mile) ft 2.5 0.1 5 0.15 10 0.25 25 0.4 50 0.6 David Reckhow CEE 577 #20 5

Identifying inputs (cont.)  Determining bottle rates from Lab data  Thomas Method β 1 (t/BOD t ) 0.33 β o Incubation time (t) ( ) 1 ≅ β β − − 1 2 L o 1 0 6 − − ≅ β 1 3 k L b o 0 David Reckhow CEE 577 #20 6

Identifying inputs (cont.)  Photosynthesis/Respiration (Chapra L24) +    → + light  chemistry 6 6 6 CO H O C H O O 2 2 6 12 6 2  two important issues  long term effect: net of P & R  short term effect: extent of DO drop during night  Three common methods  Light and Dark bottle method  expose aquatic biota to natural light conditions, with “control” in the dark  Estimation from Observed Chlorophyll levels  Measurement of Diurnal DO Range David Reckhow CEE 577 #20 7

Additional notes on WLA (cont.)  Algal modeling  Level I  measure P-R: diurnal swings in D.O.  Level II  measure chlorophyll a, light, light extinction, nutrients “in-situ”  calculate P-R  Level III  assess nutrient loadings, light extinction  model nutrient conc., chlorophyll a, P-R David Reckhow CEE 577 #20 8

Time variability of Photosynthesis  Assumed to be proportional to light intensity T P ∫ P t dt ( ) 2 f = = 0 P P π m T P fT P P m P(t) Time of day David Reckhow CEE 577 #20 9

Light and dark bottle method Float  Expose aquatic plants to natural light conditions  “control” in the dark Light Dark Bottle Bottle bottle − DO DO = lf li P net t Light Dark Bottle Bottle − DO DO = di df R cm t Light Dark = − Bottle Bottle R R k L b cm d of = − Anchor P P R b net cm David Reckhow CEE 577 #20 10

Estimation from observed chlorophyll levels  Under conditions where algal metabolism is not limited Light attenuation factor P s 20 φ = − ≈ T P r G max . 1066 a 0 25 . a oa l Oxygen generated per Maximum plant unit biomass Concentration of growth rate for produced (0.1- plant biomass optimal 0.3 mg-O 2 /µg- (µg-chla/L) conditions (1.5- chla) 3.0 d -1 ) David Reckhow CEE 577 #20 11

P-R method  Respiration is from rates and stoichiometry  Need chlorophyll level Plant respiration rate (0.05- − = 0.25 d -1 ) T 20 R r k 108 . a oa ra ≈ 0 025 . a David Reckhow CEE 577 #20 12

 To next lecture David Reckhow CEE 577 #20 13