restorationofeutrophiclakeusing ... · ol" olp" olpc lakewater ph* 8.2 8.2 8.3* 8.0...

Restoration of eutrophic lake using dolomite to immobilize the phosphorus in the water column and sediments

Presenter: Boris Constantin

April 26-‐28 2016, Montreal SUSTREM 2016

Presentation plan

•  Introduction

•  Project goal and objectives

•  Material and methods

•  Results and discussion

•  Conclusion and perspectives

•  Questions

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Introduction: Eutrophication

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Anthropogenic eutrophication Natural eutrophication

Ten years Thousands of years

Oligotrophic Oligotrophic

Eutrophic Mesotrophic

•  Change in the algal population to harmful invasive species; •  Loss of recreational uses; •  General reduction in biodiversity…

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Introduction: Eutrophication

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Source : MDDELCC

•  Phosphorus: nutrient involving eutrophication with N

Sources : exogenous and endogenous •  Chlorophyll a: a pigment present in all photosynthetic organisms Indicator of algal biomass suspended in water •  Transparency: diminishes as the quantity of algae in the lake increases

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Introduction: Contextualization and problematics

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Lake Saint-‐Augustin

Advanced state of eutrophication

Problematics Drastic changes since the 20th century; Internal contamination through sediments.

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Introduction: Transporting of sediment phosphorus towards the water column

P accu

mulation ov

er time

Recent sediments 900 to 1522 mg of P/kg

Old sediments 400 to 900 mg of P/kg

Lake Saint-‐Augustin Roberge & Piennitz 2002

Important parameters in the salting out of P •  Potential of oxidation-‐reduction

•  pH

hypoxic

Acid pH Basic pH

P release related to calcium

P release related to iron

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Introduction: Lake Saint-‐Augustin Restoration

!  In 2007, the city of Québec, in collaboration with Laval University, implemented a pilot project.

!  A new project has been implemented: absorption of dissolved phosphorus and active recovery of sediments with dolomite.

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1.  Coagulation of phosphorus dissolved with alum (aluminum sulfate) and active recovery of sediments by limestone (calcite);

2.  Sediment sludging.

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Introduction: Solution examined

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Principles •  Contamination retention; •  Physical isolation of contaminants; •  Bioturbation reduction.

Dolomite •  Good P absorption capacity; •  Non toxic for aquatic species

and the environment; •  Easily available material at a

reasonable price. CaMg(CO3)2 Carbonated sedimentary rock

•  Powder = 12 μm •  Crushed = 1.25 to 5 mm

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Goal and objectives

EVALUATING THE PERFORMANCE OF THE DOLOMITE BASED RESTORATION METHOD

!  Conducting small scale column tests to simulate treatment by dolomite

!  Ensure regular follow-‐up of phosphorus in the water column

!  Assess phosphorus removal (dissolved and total amounts) in the water column

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Material and methods

"  Field activities

"  Characterization of lake water

"  Laboratory water column tests

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Material and methods Field activities

Sampling points localization

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The lake water has been sampled at 3 depths: •  Surface •  Mid-‐depth •  Bottom

Based on previous studies, the 2 points should have different P concentrations in the sediments.

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Material and methods Field activities

Field measurements

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WTW field multimeter •  pH: Sentix sensor •  Conductivity: TetraCon sensor •  Oxygen: FDO sensor

YSI sensor Turbidity measurement

Secchi Disk Transparency measurement

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Material and methods Characterization of lake water

!  Alkalinity !  Calorimetric titration

!  Dissolved metals !  Heated atomic absorption spectroscopy

!  Chlorophyll a !  Acetone extraction and measurement using spectrophotometry

!  Suspended matter !  Gravimetric method: filtration and filter weight difference

!  Soluble phosphorus !  Ascorbic acid method with spectrophotometry

!  Total phosphorus !  Ammonium persulfate digestion and spectrophotometry

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After adequate treatments:

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Method and material Column tests

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25 cm of sediments Unaltered sample

25 cm of water

Oxic conditions

Hypoxic conditions

De-‐ionized water

Lake water

Lake water + Dolomite powder

Lake water + Dolomite powder + Crushed dolomite

= 24 / sampling point

!  Column preparation

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25 cm of sediments Unaltered sample

25 cm of water


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Oxic condition Hypoxic condition

# Permanent bubbling

# 3H/day

Bottle of N2

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!  Sampling schedule and parameters analyzed

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Days Analyses

0 Regular + Metals + Alkalinity

1 Regular

2 Regular


8 Regular

12 Regular

20 Regular

24 Regular



Regular analyses: •  Potential oxidation-‐reduction; •  pH; •  Dissolved O2; •  Conductivity; •  Turbidity; •  Soluble P; •  Total P.

Day 4: addition of dolomite powder Day 8: addition of crushed dolomite

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Results and discussion Characterization of the lakewater column

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Point 1

[P]dissolved < 10 ppb [P]total = 27.3 ppb Conductivity = 719 μS/cm

19.3°C 103%

19.3°C 105%

18.3°C 73%

[P]dissolved < 10 ppb [P]total = 26.4 ppb Conductivity = 716 μS/cm

[P]dissolved < 10 ppb [P]total < 10 ppb Conductivity= 638 μS/cm

Point 2

23.6°C 91%

22.3°C 82%

22.1°C 53%

[P]dissolved = 20.7 ppb [P]total = 115.5 ppb Conductivity= 746 μS/cm

[P]dissolved = 21.9 ppb [P]total = 139.7 ppb Conductivity = 691 μS/cm

[P]dissolved = 31.3 ppb [P]total = 231.8 ppb Conductivity = 574 μS/cm

10 cm

265 cm

500 cm 235 cm

125 cm

15 cm

Spectrophotometer: P detection limit = 10 ppb % = % in dissolved

O2

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Results and discussion Tests during incubation

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•  pH •  Conductivity •  Alkalinity •  Soluble

phosphorus •  Total phosphorus

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Abbreviations

Contents of incubation core Oxic Hypoxic

De-‐ionized water O-‐N A-‐N

Lake water O-‐L A-‐L

Lake water + Dolomite powder O-‐LP A-‐LP

Lake water + Dolomite powder + Crushed dolomite

O-‐LPC A-‐LPC

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!  Point 1 : Dissolved phosphorus

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OXIC HYPOXIC


Final concentrations

ON OL OLP OLPC

[P]dissolved (ppb) < 10 < 10 17 15


AN AL ALP ALPC

[P]dissolved (ppb) 25 240 70 < 10

Spectrophotometer: P detection limit = 10 ppb

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[P]total (ppb)

Day 4 Final day

O-‐N 9 18

O-‐L 23 26

O-‐LP 102 44

O-‐LPC 94 47

[P]total (ppb)

Day 4 Final day

A-‐N 21 62

A-‐L 24 338

A-‐LP 83 127

A-‐LPC 147 28

!  Point 1: Total phosphorus

OXIC HYPOXIC


Eutrophication threshold [P]total set by the MDDELCC: 30 ppb

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!  Point 1: average values


OL OLP OLPC Lake water

pH 8.4 8.0 8.3 7.9

Conductivity (μS/cm) 811 823 799 679

Alkalinity (mg/L of CaCO3) 149 132 137 113

AL ALP ALPC Lake water

pH 7.8 8.2 8.2 7.9



The addition of dolomite did not affect these parameters

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!  Point 2 : Dissolved phosphorus

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OXIC HYPOXIC



ON OL OLP OLPC

[P]dissolved (ppb) 14 13 26 < 10


AN AL ALP ALPC

[P]dissolved (ppb) 362 677 151 < 10

Spectrophotometer: P detection limit = 10 ppb

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!  Point 2: Total phosphorus

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[P]total (ppb)

Day 4 Final day

O-‐N 24 60

O-‐L 30 44

O-‐LP 60 38

O-‐LPC 68 23

[P]total (ppb)

Day 4 Final day

A-‐N 166 565

A-‐L 140 879

A-‐LP 175 246

A-‐LPC 155 25

OXIC HYPOXIC

Eutrophication threshold [P]total set by the MDDELCC: 30 ppb

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!  Point 2: average values


The addition of dolomite did not affect these parameters

OL OLP OLPC Lake water

pH 8.2 8.2 8.3 8.0



AL ALP ALPC Lake water

pH 7.1 7.4 8.2 8.0



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!  Total phosphorus: Percentage removed*

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Oxic Hypoxic

Point 1 Point 2 Point 1 Point 2

LP 57% 37% -‐ 53% -‐ 40%

LPC 50% 66% 81% 84%

*Percentage removed calculated between day 4 and the final day of incubation

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Conclusion and perspectives

$  There is more P salted-‐out in hypoxic conditions

$  The best removal was obtained from the cores that received powdered and crushed dolomite in a hypoxic condition

$  Dolomite has good potential to retain contaminants $  Without the addition of crushed dolomite: the P concentrations

increase $  With the addition of crushed dolomite: the P concentrations are

stabilized $  With an adequate dosage, dolomite may bring the [P]total under

the eutrophication threshold

$  Larger scale tests (in situ) to confirm dolomite’s potential

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Thank you for your attention

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restorationofeutrophiclakeusing ... · ol" olp" olpc lakewater ph* 8.2 8.2 8.3* 8.0...

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