ECOSYSTEM-ATMOSPHERE CO2 EXCHANGE IN SUB-ARCTIC LAKES; WHAT IS THE ROLE OF EMERGENT MACROPHYTES?

Northern lakes are important sources of carbon dioxide (CO₂) to the atmosphere, yet global estimates of lake CO₂ exchange remain uncertain. In particular, the contribution of emergent macrophyte vegetation to lakes’ greenhouse gas (GHG) exchange is poorly known. We hypothesized that in sub-arctic lakes, often poor in organic matter and nutrients, vegetated areas contribute substantially to lakes’ ecosystem-atmosphere net CO₂ and GHG exchange. To test this hypothesis, we studied three lakes in the Atmosphere-Ecosystem Supersite in Pallas, Finland (68°00'N 24°09'E). The lakes had low organic carbon and nutrient concentrations but differed in catchment properties and sediment organic content. We measured ecosystem-atmosphere CO₂ exchange for two years in open water and vegetated areas (Carex spp., Equisetum fluviatile and Nuphar lutea) with paired transparent and opaque chamber measurements using portable GHG analyzers. In addition, high-frequency water CO₂ concentration and eddy covariance measurements were conducted in one lake. Macrophyte abundances were modeled using field and Sentinel-1 and 2-data. We observed net uptake of CO₂ in the vegetated areas, ca. 100–500 g CO₂ m² y^-1, which counters the effect of the CO₂ emissions in the open water areas, ca. 100–200 g CO₂ m² y^-1. On the other hand, macrophyte production can fuel heterotrophic respiration due to relocation of dead plant material. Accounting for the vegetated areas in lakes’ GHG exchange is essential and assuming that they behave like terrestrial wetlands is not a valid approach.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Sari Juutinen, Finnish Meteorological Institution (sari.juutinen@fmi.fi)

Authors:

Sari Juutinen, Finnish Meteorological Institution  (sari.juutinen@fmi.fi)

Jack Chapman, Finnish Meteorological Institute  (jack.chapman@fmi.fi)

Samuel Haverinen, Finnish Meteorological Institute  (samuel.haverinen@fmi.fi)

Pauli Putkiranta, University of Helsinki  (pauli.putkiranta@helsinki.fi)

Tarmo Virtanen, University of Helsinki  (tarmo.virtanen@helsinki.fi)

Annalea Lohila, Finnish Meteorological Institute  (annalea.lohila@fmi.fi)

Mika Aurela, Finnish Meteorological Institute  (mika.aurela@fmi.fi)