Rates of and influences onPhosphorus Flux in the STAs

Long-Term Plan Meeting3 March 2017

Flux chambers at STA-2 Cell 3 mid region

Mike Jerauld, Senior ScientistDB Environmental, Inc.

/21

Provisional conceptual model

2

Water

Floc/soil

Underlying soil

Inflow Outflow

Release

Nutrition

Diffusion

wet/dry deposition

Nutrition

C*

Biota

Removal

Resuspension

Avian

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

Relevance to STA outflow concentrations

3

Juston and DeBusk, 2011. WRR 47:W01511

STA-2 Cell 3average of 26 measurements

over 6 years

Inflow Outflow

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

Relevance to STA outflow concentrations

4

Juston and DeBusk, 2011. WRR 47:W01511

STA-2 Cell 3average of 26 measurements

over 6 years

Water

Floc/soil

Underlying soil

Inflow Outflow

Release

Nutrition

Diffusion

wet/dry deposition

Nutrition

C*

Biota

Removal

Resuspension

Avian

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

From conceptual model to experimental design

• Net flux vs diffusive flux

Working hypothesesFlux rates affected by:

1. Vegetation2. Soil characteristics3. Antecedent loading

5

Water

Floc/soil

Underlying soil

Inflow Outflow

Release

Nutrition

Diffusion

wet/dry deposition

Nutrition

C*

Biota

Removal

Resuspension

Avian

Objective: quantify and apportion net flux rates, and identify controlling variables

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

Overview of DBE P Flux Project efforts

6

Task Effort StatusTask 4 Data mining analysis of historical DBE data

• Soils, porewater, and surface water P datasets• Modelling of internal P profiles

completed

Task 7 New P flux field measurements and related analyses

• P flux chambers• Porewater P gradients• Related soil conditions• Other related variables

ongoing

Data integration

P-Flux project data integration and synthesis• Discharge P patterns, long-term, monthly-scale• Cross-project data integration

ongoing

TODAY

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

Soil diffusive flux: Peepers

MID UNV

7

MID VEG 2

-25

-20

-15

-10

-5

0

5

0 250 500 750 1000

Dep

th (c

m)

SRP (μg/L)

21

34

5

6

7

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

25 m

MID VEG

MID UNV

Net flux: in situ flux chambers

STA-2 Cell 3 OUTGoogle Earth – Feb 2016

8

• 1.5 m diameter

• Open top, open bottom

• Installed in marsh“in situ”

• Large openings allow exchange with marsh

• Vegetated & unvegetated

/21

Net flux: in situ flux chambers

9

• Openings sealed during 2-wk monitoring events

• WQ sampled at t = 0, 1, 3, 7 & 14 days 0

50

0 7 14

TP (μ

g/L)

Days since chamber closure

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

Study area and experimental design

STA-3/4 STA-2

Flowway3

Cel

l 3

Three “well-performing” flow-ways:• STA-2 Cell 1• STA-2 Cell 3• STA-3/4 Flow-way 3

Three regions:• Inflow • Mid• Outflow

Vegetated Unvegetated

Vegetated chambers: Net P flux

Unvegetated chambers: Net flux, minusmacrophyte P cycling

Peepers: Flux due to diffusion

INF (C20)

MID (C128)

OUT (C200)

10

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

DBE P Flux Project field work

Activity to date:– Advance peeper deployments, Cell 1 (April 2015) & Cell 3 (July 2015)– Cell 1 chamber event (Sept 2015)– Lake O. release monitoring (Winter 2015/16)– Cell 3 “High flow” chamber event (March 2016)– Cell 3 “Low flow” chamber event (July/Aug 2016)– Cell 3 “High flow” chamber event (November 2016)– Cell 3 “Low flow” chamber event (Jan/Feb 2017)

Reporting period:STA-2 Cell 3 spring, summer & fall chamber monitoring events.

11

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

Monitoring event antecedent conditions

12

STA-2 Cell 3: Phosphorus loading rate

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

DIFFUSIVE FLUX MEASUREMENTS

13

/21

-30

-20

-10

0

0 200 400 600 800

Dep

th (c

m)

SRP (μg/L)

INFMIDOUT

Porewater P profiles

14

Example data set:November 2016: “High Flow”

General observations

• Inflow outflow trends

• No discernible effect of vegetation (SAV)

• Negligible gradients of DOP. SRP key porewater constituent.

• Porewater SRP concentrations at OUT always near or below detection limit.

21345

6

7

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

-10

10

30

50

70

90

INF MID OUT

SRP

flux

pot.

(ug/

L/cm

) 2010Summer'15 Adv. peepersSpring 2016, "High flow"Summer'16, "Low flow"Fall'16, "High flow"

Diffusive flux potential

Consistent, negligible diffusive flux potential at outflow region, even after 17 years of flow-through operation

15

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

CHAMBER RESPONSES

16

/21

0

50

100

150

0 7 14

TP (μ

g/L)

MID-V MID-UV

MID

0

10

20

30

40

0 7 14

TP (μ

g/L)

Days since chamber closure

OUT

Flux chamber TP

General observations

• Inflow outflow gradient

• Increasing TP concentration over closure period(i.e., positive net flux)

• Recent measurement events suggesting vegetation effect at MID and OUT

17

<< Example data set:November 2016: “High Flow”

VegetatedUnvegetated

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

Preliminary net flux rates

18

Example data set:November 2016: “High Flow”

0

2

4

6

8

10

MID OUT

Aver

age

flux

(mg/

m2 /d

)

VEG UNV

General observations

• Rates comparable to previous work in WCA-2A (Fisher and Reddy, 2001)

• Inflow outflow gradient

• Positive flux rates at outflow

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

Preliminary comparison of calculated flux rates

19

Example data set:November 2016: “High Flow”

0

2

4

6

8

10

MID OUT

Aver

age

flux

(mg/

m2 /d

)

VEG UNV

General observations

• Rates comparable to previous work in WCA-2A and STAs (Fisher and Reddy, 2001;Newman and Pietro, 2001)

• Net flux >> diff. flux0

2

4

6

8

10

MID OUT

Aver

age

flux

(mg/

m2 /d

)

VEG UNV

Net flux(chamber)

Diff. flux(peeper)

Not a typo…calculated diffusion rates of 0

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

Key findings to date

1. So far, no evidence of strong influence of diffusive fluxes on water TP in the outflow region

2. Yet, strong evidence of positive net fluxes in chambers

3. Net flux apparently insensitive to soil P

4. Effect of vegetation and antecedent load on net flux still under investigation

5. Interpretation of flux complicated by apparent rapid P transformations in the water column

20

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary

/21

Key question going forward

21

What sources contribute to net flux in STA outflow regions?

Water

Floc/soil

Underlying soil

Inflow Outflow

Release

Nutrition

Diffusion

wet/dry deposition

Nutrition

C*

Biota

Removal

Resuspension

Avian

Introduction Methods and Experimental Design Diffusive Flux Net Flux Summary