eutrophication processses

Eutrophication ProcessesProcesses and Equations Implemented in WASP7 Eutrophication Module

Watershed & Water Quality Modeling Technical Support Center


PhytoplanktonThe 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 requirementsDue 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


Phytoplankton KineticsPhytNO3PO4NH3SiO C:N:PLight


Phytoplankton Growth Gmax = maximum specific growth rate constant at 20 C, 0.5 4.0 day-1XT = temperature growth multiplier , dimensionlessXL = light growth multiplier, dimensionlessXN = nutrient growth multiplier, dimensionless


Temperature Effects on Phytoplanktonwhere

G = temperature correction factor for growth (1.0 1.1)

T = water temperature, CTemperature multiplier:


Light Effects on Phytoplankton


Light Effects on Phytoplankton D = average depth of segment, mKe = total light extinction coefficient , per meter I0 = incident light intensity just below the surface, langleys/day (assumes 10% reflectance) Is = saturating light intensity of phytoplankton, langleys/dayIntegrated over depth:


Light Effects on Phytoplankton


Light


Total Light ExtinctionKe back = background light extinction due to ligands, color, etc.Ke shd = algal self shading, Ke solid = solids light extinctionKe DOC = DOC light extinction,


Light Extinction ComponentsBackground:Solids:DOC:


Light Extinction FormulationAlgal Self Shading:Options:Model Calculates (Default)Mult = 0.0587, Exp= 0.778User Specifies Mult & ExpSwitch Off Self Shading

Chart1

0.0628

0.1033394645

0.201981689

0.3388382486

0.5742729097

1.1738490776

2.0451819809

3.6100385026

5.0645639122

6.4574316776

7.8088410627

Di Toro Formulation

WASP7 Fit to Di Toro

Chlorophyll a

Light Extinction

Analysis of Di Toro Self Shading Formulation

Sheet1

Di Toro:k_shd = 0.0088 a + 0.054 a^0.667

Wool:k_shd = 0.0587 a^0.7785

k_shd, 1/meter

chl a, ug/LDi ToroWool

10.0630.059

20.1030.101The Wool fit to the Di Toro self-shading formulation shows that a simpler power relationship can be used with little loss in accuracy.

50.2020.205

100.3390.352

200.5740.605

501.1741.234

1002.0452.117

2003.6103.631

3005.0654.978

4006.4576.228

5007.8097.409

Sheet1

0

0

0

0

0

0

0

0

0

0

0

Di Toro Formulation

WASP7 Fit to Di Toro

Analysis of Di Toro Self Shading Formulation

Sheet2

Sheet3


Phytoplankton Growth, reprise


Nutrient Effect on Phytoplankton


Nutrient Limitation on Growth


Phytoplankton Deathk1R = endogenous respiration rate constant, day-11R = temperature correction factor, dimensionlessk1D = mortality rate constant, day-1k1G = grazing rate constant, day-1, or m3/gZ-day if Z(t) specifiedZ(t) = zooplankton biomass time function, gZ/m3 (defaults to 1.0)


Phytoplankton SettlingSettling rate constant:vS = settling velocity, m/dayAS = surface area, m2 V = segment volume, m3

Benthic Algaeor periphyton


Differences Fixed and Floating Plants

FloatingAttachedTransportYesNoTypesDiatomsGreensBlue GreensPeriphytonFilamentous AlgaeRooted MacrophytesUnitsmg chl-a/m3gD/m2 or mg A/m2 LightAverage Water ColumnLight at BottomPredationZooplanktonInsect Larvae, SnailsSubstrateNot an IssueRock vs. Mud


Functional GroupsPeriphyton: algae attached to and living upon submerged solid surfacesFilamentous AlgaeCladophoraMacrophytes: Vascular, Rooted PlantsMyriophyllum, Elodea, Potamogeton



Shallow Stream with Attached PlantsFixedPlants

N, P

Organic orLostFraction


Typical RatesMaximum growth rate 30 g/m2/d (10-100)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


Phytoplankton:Based on Average LightPeriphyton:Based on Bottom LightPeriphyton Model


Effect of Light on Periphyton


Overview of Nutrient Cycling


The Phosphorus Cycle Inorganic PDIP taken up by algae (phytoplankton and periphyton) for growth DIP sorbs to solids to form particulate inorganic PParticulate inorganic P may settle with inorganic solidsOrganic Pduring 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 poolparticulate detrital P may settle out at the same velocity as organic matter (vs3)Particulate detrital P dissolves to DOPDOP mineralizes to DIP


Phosphorus CyclePhytoplankton 4PO43Org. P8KdissC15DpC4apc(1-fop)C8(1-fd8)C3(1-fd3)DpC4apcGpC4apcDetr. P15


Phosphorus EquationsPhytoplankton P

Detrital P


Phosphorus EquationsDissolved Organic P

Inorganic P


Phosphorus Reaction Terms


Nitrogen CycleInorganic N pool:ammonia and nitrate N are used by algae (phytoplankton and periphyton) for growthfor physiological reasons ammonia is preferredthe rate at which each form is taken up is proportional to its concentration relative to the total inorganic N (NH3+NO3) availableAmmonia is nitrified to nitrate at a temperature and oxygen dependent rateNitrate is denitrified to N2 gas at low DO levels at a temperature dependent rate


Nitrogen CycleOrganic N pool:

during algal respiration and death, a fraction of the cellular nitrogen is recycled to the inorganic pool in the form of ammonia nitrogenthe remaining fraction is recycled to the detrital N poolparticulate detrital N may settle out at the same velocity as organic matter (vs3)particulate detrital N dissolves to DONDON mineralizes to ammonia-N


Nitrogen CyclePhytoplankton4NO32NH31Detr. N14N2(1-PNH3)PNH3GpC4ancGpC4ancDpC4anc(1-fon)Org. N7fon


Summary of Nitrogen Equationorganic componentsPhyt N

Detrital N

DON


Summary of Nitrogen Equations inorganic componentsNH3 N

NO3 N


Ammonia Preference FactorkmN = 25 g/LNO3 , g/LPNH3


Nitrogen Reaction Terms


DO-BOD-Phytoplankton EquationsCBOD

DO


DO Production from Phytoplankton Growth using NO3 Two steps in synthesis of biomass (CNxOP) from NO3

(1) x NO3 x NH4 + (3/2) x O2 (2) CO2 + x NH4 CNxOP + O2

(net) CO2 + x NO3 CNxOP + ( 3/2 x + 1 ) O2

Synthesizing 1 mole of C produces ( 3/2 x + 1 ) moles of O2 Synthesizing 1 gram of C produces (32/12) [ 3/2 x + 1 ] grams of O2

Given aNC (g N / g C) in phytoplankton, x = (12/14) aNC moles

Synthesizing 1 gram of C, then, produces: (32/12) [ (3/2) (12/14) aNC + 1] grams of O2 = 32 [ (1.5/14) aNC + (1/12) ] grams of O2 (in Wasp6 code) = [ (48/14) aNC + (32/12) ] grams of O2 (in Wasp6 manual)


DO/BOD Reaction Terms

eutrophication processses

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