Conserving and managing seagrass ecosystems for their sedimentary organic carbon (SOC) stock in climate change mitigation and other ecosystem services is an increasingly important strategy in the face of increasing anthropogenic threats. In South Africa, there is limited data on how seagrass SOC stocks vary spatially and temporally. Langebaan Lagoon, South Africa’s only estuarine lagoon and a marine protected area (MPA), provides a unique natural laboratory for addressing knowledge gaps, while contributing to regional and global seagrass SOC data. To measure SOC to a depth of 50 cm, we collected 70 sediment cores across continuous and patchy (as well as some cores from unvegetated sediments) mono-specific meadows of the seagrass Zostera capensis across five sites, spanning the extent of the lagoon system and its seagrass cover. Cores were collected using a stainless steel Russian peat corer (5 cm diameter x 50 cm length). Cores were sub-sectioned into five depth intervals (0–5, 5–10, 10–20, 20–30 and 30–50 cm) in the field using a metal ruler and spatula. These sub-samples were acidified with 1N hydrochloric acid and rinsed to remove the inorganic carbon before the organic carbon content was quantified using an Elementar Vario EL Cube CHNS analyzer.

This dataset contains sediment organic carbon (%SOC) for salt marsh and intertidal seagrass, Zostera capensis, in the Olifants River Estuary on the west coast of South Africa. A total number of 81 sediment cores were collected in May 2023, across three sampling sites, along triplicate transects ~10 m in length (~50 m apart) to depths between 20 and 50 cm. A Russian peat corer (~50 cm length, 5 cm diameter) was used to collect cores. Included in this dataset is the %SOC for 27 cores to a depth of 50 cm collected in May 2024, at one of the sampling sites (upper site) from the previous sampling effort. All samples were acidified with 1N hydrochloric acid and rinsed to remove the inorganic carbon. The organic carbon content was quantified using an Elementar Vario EL Cube CHNS analyzer.

This dataset comprises sediment organic samples from seagrass meadows of the Cape dwarf-eelgrass (Zostera capensis), collected from six South African estuaries—Olifants, Berg, Breede, Knysna, Swartkops, and Mngazana—spanning approximately 1,800 km of coastline. At each estuary, two plots were sampled, and four sediment cores were collected using a Russian peat corer (50 cm depth, 5 cm diameter). Each core was sectioned into five intervals: 0–5 cm, 5–10 cm, 10–20 cm, 20–30 cm, and 30–50 cm. Samples were acidified with hydrochloric acid to remove inorganic carbon, and organic carbon content was measured using an Elementar Vario EL Cube CHNS analyzer.

Understanding the drivers of organic carbon (Corg) stock variability is key to improving the accuracy of seagrass blue carbon assessments and emphasizing their role as nature-based solutions to mitigate climate change. Using sediment coring (15 cm depth), we investigated Corg variability at fine spatial scales (< 110 m) and large spatial scales (~17 km) between the distributional limits of Zostera capensis at the upper and lower extents of South Africa’s Berg and Breede River Estuaries. Sediment cores were extracted by manually inserting an open-barrel PVC pipe (30 cm in length and 5 cm in diameter) into the seagrass meadow sediments to a depth of 20 cm and subsequently using natural vacuum-induced suction to draw out the sediment, where compaction was minimal (< 10%), and, as such, no compaction correction was conducted. Sediment cores were longitudinally sliced with a Bosch (230 mm) angle grinder. Once the halves were split, a permanent marker and ruler were used to mark the depth intervals (0–3 cm, 3–6 cm, 6–10 cm, and 10–15 cm), a small trowel (cleaned between use) was used to slice and extract the sediment depth interval samples. These sub-samples were acidified with 1N hydrochloric acid and rinsed to remove the inorganic carbon before the organic carbon content was quantified using an Elementar Vario EL Cube CHNS analyzer.

Conserving and managing seagrass ecosystems for their sedimentary organic carbon (SOC) stock in climate change mitigation and other ecosystem services is an increasingly important strategy in the face of increasing anthropogenic threats. In South Africa, there is limited data on how seagrass SOC stocks vary spatially and temporally. Langebaan Lagoon, South Africa’s only estuarine lagoon and a marine protected area (MPA), provides a unique natural laboratory for addressing knowledge gaps, while contributing to regional and global seagrass SOC data. To measure SOC to a depth of 50 cm, we collected 70 sediment cores across continuous and patchy (as well as some cores from unvegetated sediments) mono-specific meadows of the seagrass Zostera capensis across five sites, spanning the extent of the lagoon system and its seagrass cover. Cores were collected using a stainless steel Russian peat corer (5 cm diameter x 50 cm length). Cores were sub-sectioned into five depth intervals (0–5, 5–10, 10–20, 20–30 and 30–50 cm) in the field using a metal ruler and spatula. These sub-samples were acidified with 1N hydrochloric acid and rinsed to remove the inorganic carbon before the organic carbon content was quantified using an Elementar Vario EL Cube CHNS analyzer.

This dataset comprises sediment organic samples from seagrass meadows of the Cape dwarf-eelgrass (Zostera capensis), collected from six South African estuaries—Olifants, Berg, Breede, Knysna, Swartkops, and Mngazana—spanning approximately 1,800 km of coastline. At each estuary, two plots were sampled, and four sediment cores were collected using a Russian peat corer (50 cm depth, 5 cm diameter). Each core was sectioned into five intervals: 0–5 cm, 5–10 cm, 10–20 cm, 20–30 cm, and 30–50 cm. Samples were acidified with hydrochloric acid to remove inorganic carbon, and organic carbon content was measured using an Elementar Vario EL Cube CHNS analyzer.

Understanding the drivers of organic carbon (Corg) stock variability is key to improving the accuracy of seagrass blue carbon assessments and emphasizing their role as nature-based solutions to mitigate climate change. Using sediment coring (15 cm depth), we investigated Corg variability at fine spatial scales (< 110 m) and large spatial scales (~17 km) between the distributional limits of Zostera capensis at the upper and lower extents of South Africa’s Berg and Breede River Estuaries. Sediment cores were extracted by manually inserting an open-barrel PVC pipe (30 cm in length and 5 cm in diameter) into the seagrass meadow sediments to a depth of 20 cm and subsequently using natural vacuum-induced suction to draw out the sediment, where compaction was minimal (< 10%), and, as such, no compaction correction was conducted. Sediment cores were longitudinally sliced with a Bosch (230 mm) angle grinder. Once the halves were split, a permanent marker and ruler were used to mark the depth intervals (0–3 cm, 3–6 cm, 6–10 cm, and 10–15 cm), a small trowel (cleaned between use) was used to slice and extract the sediment depth interval samples. These sub-samples were acidified with 1N hydrochloric acid and rinsed to remove the inorganic carbon before the organic carbon content was quantified using an Elementar Vario EL Cube CHNS analyzer.

This dataset contains sediment organic carbon (%SOC) for subtidal seagrasses (Zostera capensis) in the Olifants River Estuary on the west coast of South Africa. A total number of 36 sediment cores were collected during May 2023, along triplicate transects (~50m apart) across three sampling sites. PVC pipes were used to collect cores up to a mean depth of 27 cm. Included in this dataset is the %SOC for 12 cores collected in May 2024 from one of the sampling sites from the previous sampling effort. All samples were acidifies with 1N hydrochloric acid and rinsed to remove inorganic carbon. Organic carbon content was quantified using an Elemental Vario EL Cub CHNS Analyzer.

This dataset contains sediment organic carbon (%SOC) for subtidal seagrasses (Zostera capensis) in the Olifants River Estuary on the west coast of South Africa. A total number of 36 sediment cores were collected during May 2023, along triplicate transects (~50m apart) across three sampling sites. PVC pipes were used to collect cores up to a mean depth of 27 cm. Included in this dataset is the %SOC for 12 cores collected in May 2024 from one of the sampling sites from the previous sampling effort. All samples were acidifies with 1N hydrochloric acid and rinsed to remove inorganic carbon. Organic carbon content was quantified using an Elemental Vario EL Cub CHNS Analyzer.

This dataset contains sediment organic carbon (%SOC) for salt marsh and intertidal seagrass, Zostera capensis, in the Olifants River Estuary on the west coast of South Africa. A total number of 81 sediment cores were collected in May 2023, across three sampling sites, along triplicate transects ~10 m in length (~50 m apart) to depths between 20 and 50 cm. A Russian peat corer (~50 cm length, 5 cm diameter) was used to collect cores. Included in this dataset is the %SOC for 27 cores to a depth of 50 cm collected in May 2024, at one of the sampling sites (upper site) from the previous sampling effort. All samples were acidified with 1N hydrochloric acid and rinsed to remove the inorganic carbon. The organic carbon content was quantified using an Elementar Vario EL Cube CHNS analyzer.