Eutrophication Processes and Equations Implemented in WASP 7

Eutrophication Processes and Equations Implemented in WASP 7 Eutrophication Module

Watershed & Water Quality Modeling Technical Support Center DO Periphyton Phytoplankton Photosynthesis atmosphere Reaeration Respiration Death&Gazing Oxidation Detritus C P N CBOD 1 Dis. Org. P Dis. Org. N NH 3 Nitrification Adsorption Mineralization CBOD 2 CBOD 3 PO 4 NO 3 SSinorg Denitrification N 2 Settling

Watershed & Water Quality Modeling Technical Support Center Phytoplankton • The growth rate of a population of phytoplankton in a natural environment: – is a complicated function of the species of phytoplankton present – involves differing reactions to solar radiation, temperature, and the balance between nutrient availability and phytoplankton requirements • Due to the lack of information to specify the growth kinetics for individual algal species in a natural environment, – this model characterizes the population as a whole by the total biomass of the phytoplankton present

Watershed & Water Quality Modeling Technical Support Center Phytoplankton Kinetics Si NO 3 NH 3 Phyt Light O C: N: P PO 4 Where: Cp = phytoplankton carbon concentration (mg/L) RG = growth rate constant (per day) RD = death rate constant (per day) RS = settling rate constant (per day)

Watershed & Water Quality Modeling Technical Support Center Phytoplankton Growth NO 3 NH 3 Phyt Light O C: N: P Growth rate constant: PO 4 Gmax = maximum specific growth rate constant at 20 C, 0. 5 – 4. 0 day-1 XT = temperature growth multiplier , dimensionless XL = light growth multiplier, dimensionless XN = nutrient growth multiplier, dimensionless

Watershed & Water Quality Modeling Technical Support Center Temperature Effects on Phytoplankton Temperature multiplier: where G = temperature correction factor for growth (1. 0 – 1. 1) T = water temperature, C

Watershed & Water Quality Modeling Technical Support Center Light Effects on Phytoplankton

Watershed & Water Quality Modeling Technical Support Center Light Effects on Phytoplankton Integrated over depth: D = average depth of segment, m Ke = total light extinction coefficient , per meter I 0 = incident light intensity just below the surface, langleys/day (assumes 10% reflectance) Is = saturating light intensity of phytoplankton, langleys/day

Watershed & Water Quality Modeling Technical Support Center Light Effects on Phytoplankton

Watershed & Water Quality Modeling Technical Support Center Light

Watershed & Water Quality Modeling Technical Support Center Total Light Extinction • Ke back = background light extinction due to ligands, color, etc. • Ke shd = algal self shading, • Ke solid = solids light extinction • Ke DOC = DOC light extinction,

Watershed & Water Quality Modeling Technical Support Center Light Extinction Components Background: Solids: DOC:

Watershed & Water Quality Modeling Technical Support Center Light Extinction Formulation Algal Self Shading: Options: • Model Calculates (Default) Mult = 0. 0587, Exp= 0. 778 • User Specifies Mult & Exp • Switch Off Self Shading

Watershed & Water Quality Modeling Technical Support Center Phytoplankton Growth, reprise

Watershed & Water Quality Modeling Technical Support Center Nutrient Effect on Phytoplankton

Watershed & Water Quality Modeling Technical Support Center Nutrient Limitation on Growth

Watershed & Water Quality Modeling Technical Support Center Phytoplankton “Death” NO 3 NH 3 Death rate constant: Phyt Light O C: N: P PO 4 k 1 R = endogenous respiration rate constant, day-1 1 R = temperature correction factor, dimensionless k 1 D = mortality rate constant, day-1 k 1 G = grazing rate constant, day-1, or m 3/g. Z-day if Z(t) specified Z(t) = zooplankton biomass time function, g. Z/m 3 (defaults to 1. 0)

Watershed & Water Quality Modeling Technical Support Center Phytoplankton Settling NO 3 NH 3 Phyt Settling rate constant: v. S = settling velocity, m/day AS = surface area, m 2 V = segment volume, m 3 Light O C: N: P PO 4

Benthic Algae or periphyton

Watershed & Water Quality Modeling Technical Support Center Differences Fixed and Floating Plants Floating Attached Yes No Types Diatoms Greens Blue Greens Periphyton Filamentous Algae Rooted Macrophytes Units chl-a/m 3 g. D/m 2 or mg A/m 2 Transport mg Light Average Water Column Light at Bottom Predation Zooplankton Insect Larvae, Snails Substrate Not an Issue Rock vs. Mud

Watershed & Water Quality Modeling Technical Support Center Functional Groups • Periphyton: algae attached to and living upon submerged solid surfaces • Filamentous Algae – Cladophora • Macrophytes: Vascular, Rooted Plants – Myriophyllum, Elodea, Potamogeton

Watershed & Water Quality Modeling Technical Support Center Lakes versus Rivers load transport

Watershed & Water Quality Modeling Technical Support Center “Shallow Stream with Attached Plants” Fixed Plants 100 cf (g. C/m 2 ) 50 0 N, P 2 cn , cp (g. N/m 3 , g. P/m 3 ) 1 0 Organic or “Lost” Fraction co 20 (g. C/m 3 ) 10 0 0 2000 Downstream Distance, m 4000 x

Watershed & Water Quality Modeling Technical Support Center Typical Rates • Maximum growth rate 30 g/m 2/d (10100) • Respiration rate 0. 1/d (0. 05 -0. 2) • Death rate 0. 05/d (0. 01 -0. 5) (During sloughing could be higher) • Nutrient half-saturation constants tend to be higher that phytoplankton by a factor of 10 to 100

Watershed & Water Quality Modeling Technical Support Center Periphyton Model Phytoplankton: Based on Average Light Periphyton: Based on Bottom Light

Watershed & Water Quality Modeling Technical Support Center Effect of Light on Periphyton (a) floating plants (b ) periphyton

Watershed & Water Quality Modeling Technical Support Center Overview of Nutrient Cycling Phytoplankton, C Periphyton, C-dw 1 adc NCRB anc/adc PCRB apc/adc 1 -fon 1 -fop Detr C kdiss OCRB CBODi fon Detr P Detr N kdiss 1 Diss. Org. P kdiss 1 Diss. Org. N Inorganic pool

Watershed & Water Quality Modeling Technical Support Center The Phosphorus Cycle • Inorganic P – DIP taken up by algae (phytoplankton and periphyton) for growth – DIP sorbs to solids to form particulate inorganic P – Particulate inorganic P may settle with inorganic solids • Organic P – during algal respiration and death, a fraction of the cellular phosphorus is recycled to the inorganic pool – the remaining fraction is recycled to the detrital P pool – particulate detrital P may settle out at the same velocity as organic matter (vs 3) – Particulate detrital P dissolves to DOP – DOP mineralizes to DIP

Watershed & Water Quality Modeling Technical Support Center Phosphorus Cycle Phytoplankton 4 Gp. C 4 apc Dp. C 4 apc(1 -fop) PO 4 3 C 3(1 -fd 3) Detr. P 15 Kdiss. C 15 Org. P 8 C 8(1 -fd 8)

Watershed & Water Quality Modeling Technical Support Center Phosphorus Equations • Phytoplankton P Growth Death Settling • Detrital P Death Dissolution Settling

Watershed & Water Quality Modeling Technical Support Center Phosphorus Equations • Dissolved Organic P Dissolution Mineralization • Inorganic P Death Mineralization Growth Settling

Watershed & Water Quality Modeling Technical Support Center Phosphorus Reaction Terms

Watershed & Water Quality Modeling Technical Support Center Nitrogen Cycle • Inorganic N pool: – ammonia and nitrate N are used by algae (phytoplankton and periphyton) for growth – for physiological reasons ammonia is preferred – the rate at which each form is taken up is proportional to its concentration relative to the total inorganic N (NH 3+NO 3) available – Ammonia is nitrified to nitrate at a temperature and oxygen dependent rate – Nitrate is denitrified to N 2 gas at low DO levels at a temperature dependent rate

Watershed & Water Quality Modeling Technical Support Center Nitrogen Cycle • Organic N pool: – during algal respiration and death, a fraction of the cellular nitrogen is recycled to the inorganic pool in the form of ammonia nitrogen – the remaining fraction is recycled to the detrital N pool – particulate detrital N may settle out at the same velocity as organic matter (vs 3) – particulate detrital N dissolves to DON – DON mineralizes to ammonia-N

Watershed & Water Quality Modeling Technical Support Center Nitrogen Cycle N 2 NO 3 2 Org. N 7 Gp. C 4 anc ×(1 -PNH 3) NH 3 1 Gp. C 4 anc ×PNH 3 Phytoplankton 4 Dp. C 4 anc ×fon ×(1 -fon) Detr. N 14

Watershed & Water Quality Modeling Technical Support Center Summary of Nitrogen Equation organic components • Phyt N • Detrital N • DON

Watershed & Water Quality Modeling Technical Support Center Summary of Nitrogen Equations inorganic components • NH 3 N • NO 3 N

Watershed & Water Quality Modeling Technical Support Center Ammonia Preference Factor PNH 3 km. N = 25 μg/L NO 3 , μg/L

Watershed & Water Quality Modeling Technical Support Center Nitrogen Reaction Terms

Watershed & Water Quality Modeling Technical Support Center DO-BOD-Phytoplankton Equations • CBOD • DO

Watershed & Water Quality Modeling Technical Support Center DO Production from Phytoplankton Growth using NO 3 Two steps in synthesis of biomass (CNx. OP) from NO 3 (1) x NO 3 → x NH 4 + (3/2) x O 2 (2) CO 2 + x NH 4 → CNx. OP + O 2 (net) CO 2 + x NO 3 → CNx. OP + ( 3/2 x + 1 ) O 2 Synthesizing 1 mole of C produces ( 3/2 x + 1 ) moles of O 2 Synthesizing 1 gram of C produces (32/12) [ 3/2 x + 1 ] grams of O 2 Given a. NC (g N / g C) in phytoplankton, x = (12/14) a. NC moles Synthesizing 1 gram of C, then, produces: (32/12) [ (3/2) (12/14) a. NC + 1] grams of O 2 = 32 [ (1. 5/14) a. NC + (1/12) ] grams of O 2 (in Wasp 6 code) = [ (48/14) a. NC + (32/12) ] grams of O 2 (in Wasp 6 manual)

Watershed & Water Quality Modeling Technical Support Center DO/BOD Reaction Terms