Enhanced bioavailability of dissolved organic matter (DOM) in human-disturbed streams in Alpine fluvial networks

[摘要] The influence of human activities on the role of inland waters in the global carbon ( C ) cycle is poorly constrained. In this study, weinvestigated the impact of human land use on the sources and biodegradation of dissolved organic matter (DOM) and its potential impact on bacterialrespiration in 10 independent catchments of the Lake Geneva basin. Sites were selected along a gradient of human disturbance (agriculture andurbanization) and were visited twice during the winter high-flow period. Bacterial respiration and DOM bioavailability were measured in the laboratorythrough standardized dark bioassays, and the influence of human land uses on DOM sources, composition and reactivity was assessed from fluorescencespectroscopy. Bacterial respiration was higher in agro-urban streams but was related to a short-term bioreactive pool (0–6  d ofincubation) of autochthonous origin, whose relative contribution to the total DOM pool increased with the degree of human disturbance. On the otherhand, the degradation of a long-term (6–28  d ) bioreactive pool related to terrestrial DOM was independent from the catchment land use anddid not contribute substantially to aquatic bacterial respiration. From a greenhouse gas emission perspective, our results suggest that humanactivities may have a limited impact on the net C exchanges between inland waters and the atmosphere, as most CO 2 fixed by aquaticproducers in agro-urban streams is cycled back to the atmosphere after biomineralization. Although seasonal and longitudinal changes in DOM sourcesmust be considered, the implications of our results likely apply more widely as a greater proportion of autochthonous-DOM signature is a commonfeature in human-impacted catchments. Yet, on a global scale, the influence of human activities remains to be determined given the large diversityof effects of agriculture and urbanization on freshwater DOM depending on the local environmental context.

[学科分类] 大气科学