Abstract
Biogenic volatile organic compounds (BVOCs) affect atmospheric chemistry, climate and regional air quality in terrestrial and marine atmospheres. Although isoprene is a major BVOC produced in vascular plants, and marine phototrophs release dimethyl sulfide (DMS), lakes have been widely ignored for their production. Here we demonstrate that oligotrophic Lake Constance, a model for north temperate deep lakes, emits both volatiles to the atmosphere. Depth profiles indicated that highest concentrations of isoprene and DMS were associated with the chlorophyll maximum, suggesting that their production is closely linked to phototrophic processes. Significant correlations of the concentration patterns with taxon-specific fluorescence data, and measurements from algal cultures confirmed the phototrophic production of isoprene and DMS. Diurnal fluctuations in lake isoprene suggested an unrecognised physiological role in environmental acclimation similar to the antioxidant function of isoprene that has been suggested for marine biota. Flux estimations demonstrated that lakes are a currently undocumented source of DMS and isoprene to the atmosphere. Lakes may be of increasing importance for their contribution of isoprene and DMS to the atmosphere in the arctic zone where lake area coverage is high but terrestrial sources of BVOCs are small.
Highlights
Surface-to-atmosphere emissions of reactive Biogenic volatile organic compounds (BVOCs) control the atmosphere’s oxidation capacity and secondary aerosol formation
Marine environments are a predominant source of DMS10 and various physiological and ecological functions have been attributed to the production of this BVOC from its cellular precursor dimethylsulfoniopropionate (DMSP) in algae and bacteria[11]
Concentrations and production rates of isoprene and dimethyl sulfide (DMS) have previously been reported for estuarine and marine environments[18,19,20,21,22,23] and such information has facilitated the estimation of the source strength of these climate-active BVOCs to the atmosphere[24,25]
Summary
Surface-to-atmosphere emissions of reactive BVOCs control the atmosphere’s oxidation capacity and secondary aerosol formation. Isoprene comprises about a third of all BVOCs in the terrestrial atmosphere and is recognised for its function in the physiological acclimation in vascular plants[4,5,6] This gas is unreported in lakes despite the demonstration that heterotrophic bacteria[7], marine cyanobacteria, phytoplankton and seaweeds produce isoprene[8]. Marine environments are a predominant source of DMS10 and various physiological and ecological functions have been attributed to the production of this BVOC from its cellular precursor dimethylsulfoniopropionate (DMSP) in algae and bacteria[11] These include cryoprotection, an overflow mechanism under unbalanced algal growth, as grazing deterrents, an antioxidant system that quenches reactive oxygen species[10] or as chemical cues[12]. This shortage of ecosystem observations precludes the accurate estimation of global gas fluxes[15]
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