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Carlson DF, Vivó-Pons A, Treier UA, Mätzler E, Meire L, Sejr M, Krause-Jensen D. Mapping intertidal macrophytes in fjords in Southwest Greenland using Sentinel-2 imagery. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 865:161213. [PMID: 36584947 DOI: 10.1016/j.scitotenv.2022.161213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Revised: 12/20/2022] [Accepted: 12/23/2022] [Indexed: 06/17/2023]
Abstract
Changes in the distribution of coastal macrophytes in Greenland, and elsewhere in the Arctic are difficult to quantify as the region remains challenging to access and monitor. Satellite imagery, in particular Sentinel-2 (S2), may enable large-scale monitoring of coastal areas in Greenland but its use is impacted by the optically complex environments and the scarcity of supporting data in the region. Additionally, the canopies of the dominant macrophyte species in Greenland do not extend to the sea surface, limiting the use of indices that exploit the reflection of near-infrared radiation by vegetation due to its absorption by seawater. Three hypotheses are tested: I) 10-m S2 imagery and commonly used detection methods can identify intertidal macrophytes that are exposed at low tide in an optically complex fjord system in Greenland impacted by marine and land terminating glaciers; II) detached and floating macrophytes accumulate in patches that are sufficiently large to be detected by 10-m S2 images; III) iceberg scour and/or turbid meltwater runoff shape the spatial distribution of intertidal macroalgae in fjord systems with marine-terminating glaciers. The NDVI produced the best results in optically complex fjord systems in Greenland. 12 km2 of exposed intertidal macrophytes were identified in the study area at low tide. Floating mats of macrophytes ranged in area from 400 m2 to 326,800 m2 and were most common at the mouth of the fjord. Icebergs and turbidity appear to play a role in structuring the distribution of intertidal macrophytes and the retreat of marine terminating glaciers could allow macrophytes cover to expand. The challenges and solutions presented here apply to most fjords in Greenland and, therefore, the methodology may be extended to produce a Greenland-wide estimate of intertidal macrophytes.
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Affiliation(s)
- Daniel F Carlson
- Arctic Research Centre, Aarhus University, Ole Worms Allé 1, Aarhus 8000, Denmark; Optical Oceanography, Institute of Carbon Cycles, Helmholtz-Zentrum Hereon, Max-Planck Str. 1, 21502 Geesthacht, Germany.
| | - Antoni Vivó-Pons
- Arctic Research Centre, Aarhus University, Ole Worms Allé 1, Aarhus 8000, Denmark; Centre for Ocean Life, National Institute of Aquatic Resources, Technical University of Denmark, Kemitorvet, Lyngby 2800, Denmark
| | - Urs A Treier
- Department of Biology, Ecoinformatics and Biodiversity, Aarhus University, Ny Munkegade 116, Aarhus 8000, Denmark
| | | | - Lorenz Meire
- Greenland Climate Research Centre, Greenland Institute of Natural Resources, Kivioq 2, Nuuk 3900, Greenland; Department of Estuarine and Delta Systems, Royal Netherlands Institute for Sea Research, Yerseke, the Netherlands
| | - Mikael Sejr
- Arctic Research Centre, Aarhus University, Ole Worms Allé 1, Aarhus 8000, Denmark; Department of Ecoscience, Marine Ecology, Aarhus University, C.F. Møllers Allé, Building 1131, 8000 Aarhus C, Denmark
| | - Dorte Krause-Jensen
- Arctic Research Centre, Aarhus University, Ole Worms Allé 1, Aarhus 8000, Denmark; Department of Ecoscience, Marine Ecology, Aarhus University, C.F. Møllers Allé, Building 1131, 8000 Aarhus C, Denmark
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Kwan V, Fong J, Ng CSL, Huang D. Temporal and spatial dynamics of tropical macroalgal contributions to blue carbon. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 828:154369. [PMID: 35259389 DOI: 10.1016/j.scitotenv.2022.154369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Revised: 03/02/2022] [Accepted: 03/03/2022] [Indexed: 06/14/2023]
Abstract
Blue carbon ecosystems are a vital part of nature-based climate solutions due to their capacity to store and sequester carbon, but often exclude macroalgal beds even though they can form highly productive coastal ecosystems. Recent estimates of macroalgal contributions to global carbon sequestration are derived primarily from temperate kelp forests, while tropical macroalgal carbon stock in living biomass is still unclear. Here, using Singapore as a case study, we integrate field surveys and remote sensing data to estimate living macroalgal carbon stock. Results show that macroalgae in Singapore account for up to 650 Mg C biomass stock, which is greater than the aboveground carbon found in seagrass meadows but lower than that in mangrove forests. Ulva and Sargassum dominate macroalgal assemblages and biomass along the coast, with both genera exhibiting distinct spatio-temporal variation. The annual range of macroalgal biomass carbon is estimated to be 450 Mg C yr-1, or 0.77 Mg C ha-1 yr-1. Noting the uncertainties of the fate of macroalgal biomass carbon, we estimate the potential sequestration rate and find that it is comparable to mature terrestrial ecosystems such as tropical grasslands and temperate forests. This study demonstrates that macroalgal seasonality allows for a consistent amount of biomass carbon to either be exported and eventually sequestered, or harvested for utilization on an annual basis. These findings on macroalgal growth patterns and their considerable contributions to tropical coastal carbon pool add to the growing support for macroalgae to be formally included in blue carbon assessments.
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Affiliation(s)
- Valerie Kwan
- Department of Biological Sciences, National University of Singapore, Singapore 117558, Singapore; Centre for Nature-based Climate Solutions, National University of Singapore, Singapore 117558, Singapore.
| | - Jenny Fong
- Tropical Marine Science Institute, National University of Singapore, Singapore 119227, Singapore
| | - Chin Soon Lionel Ng
- Tropical Marine Science Institute, National University of Singapore, Singapore 119227, Singapore
| | - Danwei Huang
- Department of Biological Sciences, National University of Singapore, Singapore 117558, Singapore; Centre for Nature-based Climate Solutions, National University of Singapore, Singapore 117558, Singapore; Tropical Marine Science Institute, National University of Singapore, Singapore 119227, Singapore.
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How Far Can We Classify Macroalgae Remotely? An Example Using a New Spectral Library of Species from the South West Atlantic (Argentine Patagonia). REMOTE SENSING 2020. [DOI: 10.3390/rs12233870] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Macroalgae have attracted the interest of remote sensing as targets to study coastal marine ecosystems because of their key ecological role. The goal of this paper is to analyze a new spectral library, including 28 macroalgae from the South-West Atlantic coast, in order to assess its use in hyperspectral remote sensing. The library includes species collected in the Atlantic Patagonian coast (Argentina) with representatives of brown, red, and green algae, being 22 of the species included in a spectral library for the first time. The spectra of these main groups are described, and the intraspecific variability is also assessed, considering kelp differentiated tissues and depth range, discussing them from the point of view of their effects on spectral features. A classification and an independent component analysis using the spectral range and simulated bands of two state-of-the-art drone-borne hyperspectral sensors were performed. The results show spectral features and clusters identifying further algae taxonomic groups, showing the potential applications of this spectral library for drone-based mapping of this ecological and economical asset of our coastal marine ecosystems.
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