# Presentation: 439897

## Eutrophication Processes

- Processes and Equations Implemented in WASP7 Eutrophication Module

## Slide 2

## 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

## Phytoplankton Kinetics

**Phyt**

**NO3**

**PO****4**

**NH3**

- Si

**O   C:N:P**

- Light

| 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) |

## Phytoplankton Growth

*          **G**max**  *=  maximum specific growth rate constant at 20 C, 0.5 – 4.0 day-1
*	**X**T**  *=  temperature growth multiplier , dimensionless
*	**X**L**  *=  light growth multiplier, dimensionless
*	**X**N**  *=  nutrient growth multiplier, dimensionless

## Temperature Effects on Phytoplankton

- where
-  ***G*  =   temperature correction factor for growth (1.0 – 1.1)
-   *T*   =   water temperature, C

- Temperature multiplier:

## Light Effects on Phytoplankton

## Light Effects on Phytoplankton

*              **D  *=  average depth of segment, m
*	**K**e**  *=  total light extinction coefficient , per meter
*	** **I**0**  *=  incident light intensity just below the surface, langleys/day 		          (assumes 10% reflectance)
*	** **I**s**  *=  saturating light intensity of phytoplankton, langleys/day

- Integrated over depth:

## Light Effects on Phytoplankton

## Light

## Total Light Extinction

*K**e back*  =  background light extinction due to 			ligands, color, etc.
*K**e shd*   =  algal self shading,
*K**e solid*  =  solids light extinction
*K**e DOC*  =  DOC light extinction,

## Light Extinction Components

- _Background:_

- _Solids:_

- _DOC:_

## Light Extinction Formulation

- _Algal Self Shading:_

- Options:
- Model Calculates (Default)
- Mult = 0.0587, Exp= 0.778
- User Specifies Mult & Exp
- Switch Off Self Shading

## Phytoplankton Growth, reprise

## Nutrient Effect on Phytoplankton

## Nutrient Limitation on Growth

## Phytoplankton “Death”

*k**1R*  =  endogenous respiration rate constant, day-1
***1R*  =  temperature correction factor, dimensionless
*k**1D*  =  mortality rate constant, day-1
*k**1G*  =  grazing rate constant, day-1, or m3/gZ-day if Z(t) specified
- Z(t) =  zooplankton biomass time function, gZ/m3 (defaults to 1.0)

## Phytoplankton Settling

*Settling rate constant:*

*v**S*   =  settling velocity, m/day
*A**S*  =  surface area, m2
* **V*  =  segment volume, m3

## Benthic Algae

- or periphyton

## Differences Fixed and Floating Plants

|  | Floating | Attached |
| --- | --- | --- |
| Transport | Yes | No |
| Types | Diatoms
Greens
Blue Greens | Periphyton
Filamentous Algae
Rooted Macrophytes |
| Units | mg chl-a/m3 | gD/m2 or mg A/m2  |
| Light | Average Water Column | Light at Bottom |
| Predation | Zooplankton | Insect Larvae, Snails |
| Substrate | Not an Issue | Rock vs. Mud |

## Functional Groups

- Periphyton: algae attached to and living upon submerged solid surfaces
- Filamentous Algae
- Cladophora
- Macrophytes: Vascular, Rooted Plants
- Myriophyllum, Elodea, Potamogeton

## Slide 22

## “Shallow Stream with Attached Plants”

***“******Shallow Stream with Attached Plants”***

**Fixed**
**Plants**
**N, P**
**Organic or**
**“****Lost”**
**Fraction**

## Typical Rates

**Maximum growth rate ******** 30 g/m****2****/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 Light**

**Periphyton:**

**Based on Bottom Light**

***Periphyton Model***

## Effect of Light on Periphyton

***Effect of Light on Periphyton***

## Overview of Nutrient Cycling

## 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 (vs3)
- Particulate detrital P dissolves to DOP
- DOP mineralizes to DIP

## Phosphorus Cycle

- Phytoplankton
-  4

- PO4
- 3

- Org. P
- 8

**KdissC15**

**DpC4apc(1-fop)**

**C8(1-fd8)**

**C3(1-fd3)**

**DpC4apc**

**GpC4apc**

- Detr. P
- 15

## Phosphorus Equations

- Phytoplankton P
- Detrital P

## Phosphorus Equations

- Dissolved Organic P
- Inorganic P

## Phosphorus Reaction Terms

## 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 (NH3+NO3) available
- Ammonia is nitrified to nitrate at a temperature and oxygen dependent rate
- Nitrate is denitrified to N2 gas at low DO levels at a temperature dependent rate

## 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 (vs3)
- particulate detrital N dissolves to DON
- DON mineralizes to ammonia-N

## Nitrogen Cycle

- Phytoplankton
- 4

- NO3
- 2

- NH3
- 1

- Detr. N
- 14

- N2

- ×(1-PNH3)

- ×PNH3

- GpC4anc

- GpC4anc

- DpC4anc

- ×(1-fon)

- Org. N
- 7

- ×fon

## Summary of Nitrogen Equationorganic components

- Phyt N
- Detrital N
- DON

## Summary of Nitrogen Equations inorganic components

- NH3 N
- NO3 N

## Ammonia Preference Factor

- kmN = 25 μg/L

- NO3 ,  μg/L

- PNH3

## Nitrogen Reaction Terms

## DO-BOD-Phytoplankton Equations

- CBOD
- 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