Sébastien Lamontagne

Goyder Forum 2017 – 4-5 July 2017

CSIRO Land and Water/Water for a Healthy Country

Sediments with hydrodynamically-driven flow: Significance for the nutrient budget of streams and coastal waters

Hyporheic exchange

Lamontagne – Goyder Forum 20172 |

Current - driven

Gravity-driven

Woessner 2000

Cranswick et al. 2014

Biogeochemical processes

Lamontagne – Goyder Forum 20173 |

POM

DOC

O2

NO3–

NH4+

PO43–

CO2

CH4

Redox

boundary

Denitrification potential in the Mississippi Basin

Lamontagne – Goyder Forum 20174 |

Gomez-Velez et al. 2015

…how about in the oceans?

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Precht and Huettel (2003)Tait et al. (2016)

Submarine groundwater discharge in the intertidal zone

1. Fresh groundwater discharge

2. Density-driven recirculation

3. Wave set-up and swash infiltration

4. Tide-induced recirculation

5. Seasonal sea-level variations

Lamontagne – Goyder Forum 20176 |

Heiss and Michael (2014)

Seawater recirculation >>Fresh groundwater

discharge

Lamontagne – Goyder Forum 20177 |

Piccaninnie Ponds Conservation Area

Recycling and

transformations

New inputs

Nutrient concentrations in ACWS porewater

Lamontagne – Goyder Forum 20178 |

0.5

0.6

0.6

<0.5

<0.5

1.4

0.8

2.0

2.2

1.8

4.9

4.3

8.7

3.1

2.8<0.5

TDN (mg N L–1)

Lamontagne et al. 2005

West Beach

Significance to ACWS area N budget (circa 2005)?

Source Annual Load (103 kg N year–1)

Bulk deposition ~720

Wastewater ~680

Penrice ~1460

Stormwater ~250

Regional groundwater ~50

Tidal pumping ~230

Total SGD ~10,000

Lamontagne – Goyder Forum 20179 |

Sources: Adelaide Coastal Waters Study;

Lamontagne et al. (2008)

Where are we at?

• Hydraulic exchanges in permeable sediments are a major biogeochemical process in rivers, lakes, estuaries and coastal waters

• Research in marine environments more recent:• Active at the coastline

• Can occur across the continental shelf

• Large shelf porewater displacement during storms?

Lamontagne – Goyder Forum 201710 |

Significance of exchanges with permeable sediments in SA coastal waters?

• Organic carbon and alkalinity export from mangroves

• Eutrophication • Adelaide’s coastline

• Aquaculture

• Sea level rise

• Ocean productivity

Lamontagne – Goyder Forum 201711 |

How do you measure exchange with permeable sediments?

Lamontagne – Goyder Forum 201712 |

Lamontagne – Goyder Forum 201713 |

Injected tracersFrom theory

𝐷𝑧 = 𝜑𝜅1

3+𝑓𝐺𝑥

2

15+𝑓𝐺𝑧

2

5

Natural tracers in porewater

Lamontagne – Goyder Forum 201714 |

Cranswick et al. (2014)

EC Radon Temperature

SOEST.Hawaii.edu

Mini-piezometer

Radium and Radon

Lamontagne – Goyder Forum 201715 |

Uranium-238

Thorium-232

Uranium-235

Th-234

Pa-234

U-234

Th-230

Radium-226

1600 years

Radon-222

3.83 days

Po-218Beta decay

Alpha decay

Beta decay

Alpha decay

Radium-228

5.75 years

Ac-228

Th-228

Radium-224

3.66 days

Rn-220

Po-216

Th-231

Pa-231

Ac-227

Th-227

Radium-223

11.4 days

Rn-219

Po-215

Time-series in tidally-influenced environments

Orica Workshop16 |Gleeson et al. (2013)

Synoptic surveys over the continental shelf (Limestone Coast Ra profiles)

Lamontagne – Goyder Forum 201717 |

Distance (km)

Conclusions

• We have underestimated nutrient recycling via hydraulically-mediated porewater exchange processes in coastal regions

• Many implications for carbon and nutrient cycling in South Australian coastal waters• Alkalinity and organic carbon export from tidal mangroves (‘blue

carbon initiative’)

• Nutrient budgets for ecosystems at risk of eutrophication (Gulf St Vincent)

• Sea level rise

• Link to ecosystem productivity

Lamontagne – Goyder Forum 201718 |

GROUNDWATER HYDROLOGY/WATER FOR A HEALTHY COUNTRY FLAGSHIP

Thank youCSIRO Land and WaterSébastien Lamontagne

t +61 8 8303-8713e sebastien.lamontagne@csiro.auw http://www.csiro.au/en/Organisation-

Structure/Divisions/Land-and-Water/SebastienLamontagne.aspx