Carbon sequestration and sediment accretion in Cowichan Bay … · 2020-06-28 · 2. Estimate sediment accretion rate of estuary (210Pb in cores from various locations) 3. Determine

Carbon sequestration and sediment accretion in Cowichan Bay mudflats, British Columbia.

Prepared and Presented by Tristan Douglas

CERCA 2017 AGM

Cowichan Estuary Overview

• 4th largest estuary on Vancouver Island (492 hectares); ranked among top 10 BC estuaries for conservation habitat restoration potential

• Formed by two rivers: Cowichan and Koksilah

• Consists of 285ha mudflats and 205ha vegetated intertidal land, including saltmarsh and eelgrass

• Important rearing habitat for 229 bird species, including thousands of waterfowl

• Critical rearing habitat for salmon & trout species

History of Habitat Degradation • 1850s: logging and log rafting;

diking for agriculture and flood protection

• 1920s – 1960s: railway in tidal flats to connect with inland logging with export terminal; sawmill built

• 1970s – 1990s: sewage discharge from urban development; non-point source pollution; ban on shellfish harvest; Downstream river water undrinkable.

• 2000s - present: urban sprawl in floodplain and increase in flood protection; daily log boom grounding

Impact of Grounding Log

Booms

• Loss of eelgrass

• Degradation of microphytobenthos biofilms 7 ha. of potential

daily carbon sequestration lost

• Reduction of ecosystem functioning by dredging and tugboat activity

Prime Eel Grass Habitat

Historic Distribution

Historical Eel Grass

Channels

Historic Eelgrass Distribution 2005 Eelgrass Distribution “Towed underwater video survey Cowichan

Estuary” Archipelago Marine Research Ltd.

Intertidal Mudflats and “Blue Carbon” storage

• Estuarine “Blue Carbon” storage garnering recognition Reservoir in the world-wide budget of greenhouse gases

• Most work focused on saltmarshes, eelgrass, mangroves

• 164 ha of rehabilitated eelgrass beds in Komoks estuary, North of Cowichan Estimated capacity of 58t C/yr

• Less known about carbon sequestration capacity of intertidal mudflats Reportedly important carbon sinks, comparable to vegetated intertidal habitats.

Research Questions

• How is current industrial activity in the Cowichan Estuary affecting its carbon storage capacity?

• What is the relative importance of the Cowichan Estuary mudflats as a carbon sink compared to adjacent eelgrass and saltmarsh habitats?

Experimental Approach

1. Collect series sediment cores from the Cowichan estuary

2. Estimate sediment accretion rate of estuary (210Pb in cores from various locations)

3. Determine bulk carbon storage in the Cowichan Bay mudflats, saltmarsh and eelgrass, and sediments in area of grounded log booms

4. Identify dominant sources of buried carbon

Cowichan Estuary Sediment Core Sampling Scheme, May 2017

Cowichan Estuary Sediment Core Sampling Scheme, May 2017

Cowichan Estuary Sediment Core Sampling Scheme, May 2017

Saltmarsh Log Boom Eelgrass

Sediment Core Extraction from Saltmarsh and Eelgrass Habitats

Sediment Core Extrusion

• Cores up to 40cm length

• Cores sectioned at intervals of: • 1cm for top 10cm

• 2cm for mid 20 cm

• 5cm for remainder

• Each section subsampled for various analyses

Sub-Sampling Sediment Core Sections: Physical Characteristics

• Grain size analysis

• Organic carbon content

• 210Pb radiometric dating

• Fatty acid analysis

• Stable isotope analysis

Possible Sources of Organic Carbon in the Cowichan Estuary Mudflats • Adjacent Ecosystems

“Outwelling” from saltmarshes and eelgrass beds Terrigenous organic material

• Benthic-Pelagic Coupling Phytodetritus consumed by suspension and deposit

feeding benthic invertebrates can be deposited in sediment

Phytoplankton direct sedimentation

• Microphytobenthos Can account for up to half of autochthonous primary

production Photosynthetic activity limited to the top millimetres

due to the attenuation of sunlight and sediment grain size

Sub-Sampling Sediment Core Sections: Micro- biology

• DAPI cell counts

• Microbial community composition from 16S rRNA genes

• Redox boundaries - microprofiling

• Metabolic activity Primary production

Denitrification

Current State of Project

• 210PB Processed and ready to send to MyCore Scientific Inc.

• In March, fatty acid biomarker and stable isotope analysis at the The Scottish Association for Marine Science.

Acknowledgements • Kim Juniper, PhD (Thesis supervisor)

• Goetz Schuerholz, PhD (Committee member, CERCA Chair)

• Catherine Stevens, PhD (Committee member)

• Vera Pospelova, PhD (Committee member)

• Sheryl Murdoch, PhD Candidate

• Brett Jameson, PhD Candidate

• Grant Douglas

• Cory Arnold