This page explores the use of a Russian Peat Corer (Figure 0.1).

Russian peat corer. It has a sampling length of 50 cm and a spearhead. The corer is first pushed upright and spearheaded down into the ground. Once the correct depth is reached, the user twists the handle in a clockwise direction to gouge the substrate sample into the corer and simultaneously close the metal flap over the sampled soil. The corer can then be safely extracted from the ground to collect the cored substrate.

Figure 0.1: Russian peat corer. It has a sampling length of 50 cm and a spearhead. The corer is first pushed upright and spearheaded down into the ground. Once the correct depth is reached, the user twists the handle in a clockwise direction to gouge the substrate sample into the corer and simultaneously close the metal flap over the sampled soil. The corer can then be safely extracted from the ground to collect the cored substrate.

Subcoring or slicing the core is a common scientific approach as it gives a detailed vertical profile of the seabed substrate. In exchange, subcoring increases the required laboratory work in proportion to the number of the subcores/slices made. Furthermore, as part of a larger research goal to map the seagrass carbon in Europe, the cores are used in conjunction with optical remote sensing. The surficial nature of optical remote sensing renders the vertical profile moot, as the detailed benthic substrate information cannot be easily derived from optical remote sensing. Nonetheless, a simplified representation of the benthic substrate information could still be possible by proxy(ies). One possibility is to sample the core as a whole rather than as subcores.

This study inspects the difference between using the whole core and the aggregated results of the subcores as a representation for optical remote sensing.

All analyses were performed in R version 4.5.2 (R Core Team 2025). All work belong to the REWRITE project.

1 Method

1.1 Sample collection

The fieldwork was conducted in Bourgneuf Bay. Three replicates each were collected in the persistent seagrass meadow and a sandier area. All GPS positions were collected using the SW Maps version 3.0.14.3 (Malla 2025) on a Google Pixel 9.

For each replicate, a 1-metre whole core and 1-metre subcoring core was collected. As the Russian peat corer has a sampling length of 50 cm, the 1-metre core was further split into two 50 cm samples, one at the 0-50 cm depth and the other at the 50-100 cm depth. Due to the spearhead design of the Russian peat corer, the 50-100 cm depth was sampled next to the 0-50 cm depth, rather than immediately below since the spearhead would have disrupted the area below during the coring process (Figures 1.1 and 1.2). The subcoring core was sliced in the field at 10 cm per subcore and separated into different collection bags. Meanwhile, for the whole core approach, both top and bottom cores were mixed in a bucket and then transferred into a single, large collection bag. For the first and the second replicate in the sand area, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate (Figure 1.2).

The samples were then transported to back to the laboratory and preserved in a 4 °C fridge.

Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.

Figure 1.1: Sampled cores at the persistent seagrass meadow. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach.

Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.

Figure 1.2: Sampled cores at the sandier area. Each row shows a set of replicate. The first two photographs on the left depicts the 0-50 cm and 50-100 cm cores for the subcore approach. The last two photographs on the right depicts the 0-50 m and 50-100 cm cores for the whole core approach. For the first and the second replicate, the corer for the subcore could only go up to a depth of about 75 cm and 80 cm, respectively. As such, they were sampled to 70 cm and 80 cm, respectively, for both the subcore and whole core approaches to ensure consistency within a replicate.

1.2 Sample drying and weighing

Using a syringe, 20 ml of samples were obtained from each sample bag. The extracted samples were weighed before and after they were dried. For the drying process, the extracted samples were dried in an oven at 60 °C for 72 hours and left to cool in a dessicator for at least one hour . Based on equation (1.1), the dry bulk density was then calculated using the weight of the dried soil and the volume extracted by the syringe (Howard et al. 2014).

\[\begin{equation} Dry\,bulk\,density\,(g/cm^3) = \frac{Mass\,of\,dry\,soil\,(g)}{Orignal\,volume\,sampled\,(cm^3)} \tag{1.1} \end{equation}\]

1.3 Granulometry

This section will be updated when the work is completed.

1.4 TOC measurement

This section will be updated when the work is completed.

1.5 Spatial upscaling

This section will be updated when the mapping work is completed.

1.6 Uncertainty

This section will be updated when the work is completed.

2 Results

2.1 Dry Bulk Density

The difference in dry bulk density between the mixed whole core and the averaged slices ranged between 1.7% and 6.6% for the persistent seagrass meadow with muddy substrate and 1.1% and 19.7% for the sandy substrate. Notably, there was a huge difference in the ‘Sand 3’ replicate (Figure 2.1). When ‘Sand 3’ is excluded, the largest difference is 6.9%. The presence of shells in the slices did not cause any seemingly anomalous patterns to the vertical profile.

Benthic soil/substrate dry bulk density vertical profile at Bourgneuf Bay. The two different methods are represented by different colours and the averaged values of all the slices are represented by a dotted line. Any points with the presence of shells in the sample are highlighted with a solid dot.

Figure 2.1: Benthic soil/substrate dry bulk density vertical profile at Bourgneuf Bay. The two different methods are represented by different colours and the averaged values of all the slices are represented by a dotted line. Any points with the presence of shells in the sample are highlighted with a solid dot.

Boxplot of the dry bulk density at Bourgneuf Bay using the whole core (mixed) approach and the aggregated subcoring approach.

Figure 2.2: Boxplot of the dry bulk density at Bourgneuf Bay using the whole core (mixed) approach and the aggregated subcoring approach.

2.2 TOC measurement

2.3 Spatial upscaling

This section will be updated when the mapping work is completed.

References

Howard, Jennifer, Sarah Hoyt, Kirsten Isensee, Emily Pidgeon, and Maciej Telszewski, eds. 2014. “Coastal Blue Carbon: Methods for Assessing Carbon Stocks and Emissions Factors in Mangroves, Tidal Salt Marshes, and Seagrass Meadows.” Arlington, Virginia, USA: Conservation International; Intergovernmental Oceanographic Commission of UNESCO; International Union for Conservation of Nature. https://www.thebluecarboninitiative.org/manual.
Malla, Avinab. 2025. SW Maps. Kathmandu, Nepal: Aviyaan Tech (P) Ltd; Softwel (P) Ltd. https://play.google.com/store/apps/details?id=np.com.softwel.swmaps&hl=en-US&pli=1.
R Core Team. 2025. R: A Language and Environment for Statistical Computing. Vienna, Austria: R Foundation for Statistical Computing. https://www.R-project.org/.