The transformation and fate of sub-Arctic microphytobenthos carbon revealed through 13C-labeling

• Published in: Limnology and Oceanography
• Main Authors: Oakes, Joanne M., Rysgaard, Søren, Glud, Ronnie N., Eyre, Bradley D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: benthic microalgae; organic-matter; in-situ; nitrogen incorporation; intertidal sediments; microbial community; coastal sediments; sandy sediments; tracing carbon; salt-marsh; Arctic
• Online Access: https://pure.uhi.ac.uk/en/publications/58b01a7e-de75-4bc4-92ba-1dc66e041fc0; https://doi.org/10.1002/lno.10377

Microphytobenthos (MPB) at higher latitudes has been poorly studied. This study used pulse-chase 13C-labeling to investigate the production, processing, and fate of MPB-derived carbon (MPB-C) in sub-Arctic intertidal sediments over 31 d. Gross primary production (2.1 mmol C m−2 h−1 ± 0.4 mmol C m−2 h−1) was comparable to that reported for temperate regions. Some of the 13C fixed by sub-Arctic MPB was rapidly (within 0.5 d) transferred to deeper sediments (below 2 cm), but most was retained within surface sediments (>70.2% of the 13C present at any time during the study). At any time, MPB accounted for ≥ 49.8% of this 13C. The 13C content of sediment organic carbon declined over time, but > 31% of the 13C fixed within the first tidal cycle remained after 31 d, suggesting that sub-Arctic MPB may contribute to coastal carbon retention during the productive season. Over 21 d, 10.6% of the fixed 13C was removed via DIC fluxes and 0.3% via DOC fluxes from inundated sediment, and 0.6% as CO2 from exposed sediment. The greatest loss of 13C (38.2%) was via unmeasured pathways, including resuspension and/or removal by mobile consumers. The rates of MPB-C production and the relative importance of the pathways for MPB-C loss were similar to that observed for comparable lower latitude sediments, demonstrating that MPB at higher latitudes are not necessarily distinct from MPB at lower latitudes and probably play a similarly important role in ecosystem functioning. Apparently, local environmental conditions are more important than climate differences for determining the processing and fate of MPB-C.