Role of ephemeral vegetation of emerging river bottoms in modulating CO₂ exchanges across a temperate large lowland river stretch

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• 作者：Rossano Bolpagni ; Silvia Folegot ; Alex Laini ; Marco Bartoli
• 关键词：Parafluvial zones ; Large rivers ; Static closed chamber technique ; C metabolism ; Microphytobenthos ; Therophytes
• 刊名：Aquatic Sciences
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：79
• 期：1
• 页码：149-158
• 全文大小：
• 刊物类别：Biomedical and Life Sciences
• 刊物主题：Freshwater & Marine Ecology; Marine & Freshwater Sciences; Oceanography; Ecology; Life Sciences, general;
• 出版者：Springer International Publishing
• ISSN：1420-9055
• 卷排序：79

文摘

Rivers and marginal wetlands contribute significantly to the carbon (C) exchange rate per unit area compared to adjacent terrestrial ecosystems, due to high C inputs, metabolic activity and CO₂ supersaturation. Within riverscapes, the contribution of emerging bottoms (i.e. parafluvial zones) and ephemeral vegetation (i.e. microphytobenthos or annual vascular plant communities) to the C metabolism is understudied. The aim of this study was to evaluate the CO₂ exchange rates at the water- and emergent sand bar-atmosphere interfaces within a lowland large temperate river stretch. CO₂ fluxes were measured seasonally, in summer (August 2007) and winter (March 2008) via static closed chambers, together with the primary producers’ biomass (microphytobenthos and vascular macrophytes). Our results showed that the river was a CO₂ source (between 0.2 and 7.6 mmol CO₂ m−2 day−1), whilst the vegetated parafluvial zones acted as a net sink, with assimilation rates peaking at 623.4 mmol CO₂ m−2 day−1. Emerging bare sediments were on the contrary net emitting CO₂ systems (2.7–60.1 mmol CO₂ m−2 day−1). Within lotic environments, seasonally emergent vegetated sand bars may represent important C fixation hot spots, with summer primary production particularly contributing to offsetting CO₂ emissions and counterbalancing the heterotrophic metabolism of the saturated zones. Based on these outcomes, we suggest that studies addressing the strictly aquatic fluvial environment, which is generally a CO₂ emitter, should be linked to those from transitional areas in order to better integrate terrestrial and aquatic C budgets.