Globally, inland waters emit over 2 Pg of carbon per year as carbon dioxide, of which the majorit... more Globally, inland waters emit over 2 Pg of carbon per year as carbon dioxide, of which the majority originates from streams and rivers. Despite the global significance of fluvial carbon dioxide emissions, little is known about their diel dynamics. Here we present a large-scale assessment of day- and night-time carbon dioxide fluxes at the water-air interface across 34 European streams. We directly measured fluxes four times between October 2016 and July 2017 using drifting chambers. Median fluxes are 1.4 and 2.1 mmol m−2 h−1 at midday and midnight, respectively, with night fluxes exceeding those during the day by 39%. We attribute diel carbon dioxide flux variability mainly to changes in the water partial pressure of carbon dioxide. However, no consistent drivers could be identified across sites. Our findings highlight widespread day-night changes in fluvial carbon dioxide fluxes and suggest that the time of day greatly influences measured carbon dioxide fluxes across European streams.
In many regions around the world, large populations of native wildlife have declined or been repl... more In many regions around the world, large populations of native wildlife have declined or been replaced by livestock grazing areas and farmlands, with consequences on terrestrial-aquatic ecosystems connectivity and trophic resources supporting food webs in aquatic ecosystems. The river continuum concept (RCC) and the riverine productivity model (RPM) predict a shift of carbon supplying aquatic food webs along the river: from terrestrial inputs in low-order streams to autochthonous production in mid-sized rivers. Here, we studied the influence of replacing large wildlife (mainly hippos) with livestock on the relative importance of C3 vegetation, C4 grasses and periphyton on macroinvertebrates in the Mara River, which is an African montane-savanna river known to receive large subsidy fluxes of terrestrial carbon and nutrients mediated by LMH, both wildlife and livestock. Using stable carbon (δ13C) and nitrogen (δ15N) isotopes, we identified spatial patterns of the relative importance of...
Metabolismus in Fliesgewassern integriert die Produktion und die Respiration von organischem Mate... more Metabolismus in Fliesgewassern integriert die Produktion und die Respiration von organischem Material auf der Ebene eines Okosystems. Gelostes organisches Material (dissolved organic matter, DOM) in aquatischen Lebensraumen ist ein komplexer, extrem diverser Mix aus in-situ produzierten und von terrestrischen Okosystemen stammenden chemischen Substanzen. Ich untersuchte Auswirkungen der Landnutzung auf die DOM-Zusammensetzung und Nahrstoff- und Kohlenstoffkonzentrationen im Fliesgewasser und stellte dies in Bezug zum Metabolismus des gesamten Fliesgewassers, d.h. Bruttoprimarproduktion (BPP) und Gesamtrespiration des Okosystems. Dafur untersuchte ich 33 Fliesgewasser im Norden Osterreichs, deren Einzugsgebiete einen Landnutzungsgradienten von landwirtschaftlich und urban gepragten zu bewaldeten und naturnahen Flachen umspannten. Zur Charakterisierung der DOM-Zusammensetzung wurden Absorptions- und Fluoreszenzindizes, sowie DOM-Komponenten identifiziert durch parallele Faktorenanalys...
Large-scale studies are needed to identify the drivers of total mercury (THg) and monomethyl-merc... more Large-scale studies are needed to identify the drivers of total mercury (THg) and monomethyl-mercury (MeHg) concentrations in aquatic ecosystems. Studies attempting to link dissolved organic matter (DOM) to levels of THg or MeHg are few and geographically constrained. Additionally, stream and river systems have been understudied as compared to lakes. Hence, the aim of this study was to examine the influence of DOM concentration and composition, morphological descriptors, land uses and water chemistry on THg and MeHg concentrations and the percentage of THg as MeHg (%MeHg) in 29 streams across Europe spanning from 41°N to 64 °N. THg concentrations (0.06-2.78 ng L) were highest in streams characterized by DOM with a high terrestrial soil signature and low nutrient content. MeHg concentrations (7.8-159 pg L) varied non-systematically across systems. Relationships between DOM bulk characteristics and THg and MeHg suggest that while soil derived DOM inputs control THg concentrations, aut...
Globally, inland waters emit over 2 Pg of carbon per year as carbon dioxide, of which the majorit... more Globally, inland waters emit over 2 Pg of carbon per year as carbon dioxide, of which the majority originates from streams and rivers. Despite the global significance of fluvial carbon dioxide emissions, little is known about their diel dynamics. Here we present a large-scale assessment of day- and night-time carbon dioxide fluxes at the water-air interface across 34 European streams. We directly measured fluxes four times between October 2016 and July 2017 using drifting chambers. Median fluxes are 1.4 and 2.1 mmol m−2 h−1 at midday and midnight, respectively, with night fluxes exceeding those during the day by 39%. We attribute diel carbon dioxide flux variability mainly to changes in the water partial pressure of carbon dioxide. However, no consistent drivers could be identified across sites. Our findings highlight widespread day-night changes in fluvial carbon dioxide fluxes and suggest that the time of day greatly influences measured carbon dioxide fluxes across European streams.
In many regions around the world, large populations of native wildlife have declined or been repl... more In many regions around the world, large populations of native wildlife have declined or been replaced by livestock grazing areas and farmlands, with consequences on terrestrial-aquatic ecosystems connectivity and trophic resources supporting food webs in aquatic ecosystems. The river continuum concept (RCC) and the riverine productivity model (RPM) predict a shift of carbon supplying aquatic food webs along the river: from terrestrial inputs in low-order streams to autochthonous production in mid-sized rivers. Here, we studied the influence of replacing large wildlife (mainly hippos) with livestock on the relative importance of C3 vegetation, C4 grasses and periphyton on macroinvertebrates in the Mara River, which is an African montane-savanna river known to receive large subsidy fluxes of terrestrial carbon and nutrients mediated by LMH, both wildlife and livestock. Using stable carbon (δ13C) and nitrogen (δ15N) isotopes, we identified spatial patterns of the relative importance of...
Metabolismus in Fliesgewassern integriert die Produktion und die Respiration von organischem Mate... more Metabolismus in Fliesgewassern integriert die Produktion und die Respiration von organischem Material auf der Ebene eines Okosystems. Gelostes organisches Material (dissolved organic matter, DOM) in aquatischen Lebensraumen ist ein komplexer, extrem diverser Mix aus in-situ produzierten und von terrestrischen Okosystemen stammenden chemischen Substanzen. Ich untersuchte Auswirkungen der Landnutzung auf die DOM-Zusammensetzung und Nahrstoff- und Kohlenstoffkonzentrationen im Fliesgewasser und stellte dies in Bezug zum Metabolismus des gesamten Fliesgewassers, d.h. Bruttoprimarproduktion (BPP) und Gesamtrespiration des Okosystems. Dafur untersuchte ich 33 Fliesgewasser im Norden Osterreichs, deren Einzugsgebiete einen Landnutzungsgradienten von landwirtschaftlich und urban gepragten zu bewaldeten und naturnahen Flachen umspannten. Zur Charakterisierung der DOM-Zusammensetzung wurden Absorptions- und Fluoreszenzindizes, sowie DOM-Komponenten identifiziert durch parallele Faktorenanalys...
Large-scale studies are needed to identify the drivers of total mercury (THg) and monomethyl-merc... more Large-scale studies are needed to identify the drivers of total mercury (THg) and monomethyl-mercury (MeHg) concentrations in aquatic ecosystems. Studies attempting to link dissolved organic matter (DOM) to levels of THg or MeHg are few and geographically constrained. Additionally, stream and river systems have been understudied as compared to lakes. Hence, the aim of this study was to examine the influence of DOM concentration and composition, morphological descriptors, land uses and water chemistry on THg and MeHg concentrations and the percentage of THg as MeHg (%MeHg) in 29 streams across Europe spanning from 41°N to 64 °N. THg concentrations (0.06-2.78 ng L) were highest in streams characterized by DOM with a high terrestrial soil signature and low nutrient content. MeHg concentrations (7.8-159 pg L) varied non-systematically across systems. Relationships between DOM bulk characteristics and THg and MeHg suggest that while soil derived DOM inputs control THg concentrations, aut...
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