Fluorescence is an easily available analytical technique used to assess the optical characteristics of dissolved organic matter (DOM).
Ongoing and amplified climate change in the Arctic is leading to glacier retreat and to the exposure of an ever\uffe2\uff80\uff90larger portion of non\uffe2\uff80\uff90glaciated permafrost\uffe2\uff80\uff90dominated landscapes. Warming will also cause more precipitation to fall as rain, further enhancing the thaw of previously frozen ground. Yet, the impact of those perturbations on the geochemistry of Arctic rivers remains a subject of debate. Here, we determined the geochemical composition of waters from various contrasting non\uffe2\uff80\uff90glacial permafrost catchments and investigated their impact on a glacially dominated river, the Zackenberg River (Northeast Greenland), during late summer (August 2019). We also studied the effect of rainfall on the geochemistry of the Zackenberg River, its non\uffe2\uff80\uff90glacial tributaries, and a nearby independent non\uffe2\uff80\uff90glacial headwater stream Gr\uffc3\uffa6nse. We analyzed water properties, quantified and characterized dissolved organic matter (DOM) using absorbance and fluorescence spectroscopy and radiocarbon isotopes, and set this alongside analyses of the major cations (Ca, Mg, Na, and K), dissolved silicon (Si), and germanium/silicon ratios (Ge/Si). The glacier\uffe2\uff80\uff90fed Zackenberg River contained low concentrations of major cations, dissolved Si and dissolved organic carbon (DOC), and a Ge/Si ratio typical of bulk rock. Glacial DOM was enriched in protein\uffe2\uff80\uff90like fluorescent DOM and displayed relatively depleted radiocarbon values (i.e., old DOM). Non\uffe2\uff80\uff90glacial streams (i.e., tributaries and Gr\uffc3\uffa6nse) had higher concentrations of major cations and DOC and DOM enriched in aromatic compounds. They showed a wide range of values for radiocarbon, Si and Ge/Si ratios associated with variable contributions of surface runoff relative to deep active layer leaching. Before the rain event, Zackenberg tributaries did not contribute notably to the solute export of the Zackenberg River, and supra\uffe2\uff80\uff90permafrost ground waters governed the supply of solutes in Zackenberg tributaries and Gr\uffc3\uffa6nse stream. After the rain event, surface runoff modified the composition of Gr\uffc3\uffa6nse stream, and non\uffe2\uff80\uff90glacial tributaries strongly increased their contribution to the Zackenberg River solute export. Our results show that summer rainfall events provide an additional source of DOM and Si\uffe2\uff80\uff90rich waters from permafrost\uffe2\uff80\uff90underlain catchments to the discharge of glacially dominated rivers. This suggests that the magnitude and composition of solute exports from Arctic rivers are modulated by permafrost thaw and summer rain events. This event\uffe2\uff80\uff90driven solute supply will likely impact the carbon cycle in rivers, estuaries, and oceans and should be included into future predictions of carbon balance in these vulnerable Arctic systems.Photochemical degradation of dissolved organic matter (DOM) has been the subject of numerous studies; however, its regulation along the inland water continuum is still unclear. We aimed to unravel the DOM photoreactivity and concurrent DOM compositional changes across 30 boreal aquatic ecosystems including peat waters, streams, rivers, and lakes distributed along a water residence time (WRT) gradient. Samples were subjected to a standardized exposure of simulated sunlight. We measured the apparent quantum yield (AQY), which corresponds to DOM photomineralization per photon absorbed, and the compositional change in DOM at bulk and individual compound levels in the original samples and after irradiation. AQY increased with the abundance of terrestrially derived DOM and decreased at higher WRT. Additionally, the photochemical changes in both DOM optical properties and molecular composition resembled changes along the natural boreal WRT gradient at low WRT (<3\uffc2\uffa0years). Accordingly, mass spectrometry revealed that the abundance of photolabile and photoproduced molecules decreased with WRT along the boreal aquatic continuum. Our study highlights the tight link between DOM composition and DOM photodegradation. We suggest that photodegradation is an important driver of DOM composition change in waters with low WRT, where DOM is highly photoreactive. Fluorescence is an easily available analytical technique used to assess the optical characteristics of dissolved organic matter (DOM).
The effects of atmospheric nitrogen (N) deposition on organic matter decomposition vary with the biochemical characteristics of plant litter. At the ecosystem\uffe2\uff80\uff90scale, net effects are difficult to predict because various soil organic matter (SOM) fractions may respond differentially. We investigated the relationship between SOM chemistry and microbial activity in three northern deciduous forest ecosystems that have been subjected to experimental N addition for 2 years. Extractable dissolved organic carbon (DOC), DOC aromaticity, C\uffe2\uff80\uff83:\uffe2\uff80\uff83N ratio, and functional group distribution, measured by Fourier transform infrared spectra (FTIR), were analyzed for litter and SOM. The largest biochemical changes were found in the sugar maple\uffe2\uff80\uff93basswood (SMBW) and black oak\uffe2\uff80\uff93white oak (BOWO) ecosystems. SMBW litter from the N addition treatment had less aromaticity, higher C\uffe2\uff80\uff83:\uffe2\uff80\uff83N ratios, and lower saturated carbon, lower carbonyl carbon, and higher carboxylates than controls; BOWO litter showed opposite trends, except for carbonyl and carboxylate contents. Litter from the sugar maple\uffe2\uff80\uff93red oak (SMRO) ecosystem had a lower C\uffe2\uff80\uff83:\uffe2\uff80\uff83N ratio, but no change in DOC aromaticity. For SOM, the C\uffe2\uff80\uff83:\uffe2\uff80\uff83N ratio increased with N addition in SMBW and SMRO ecosystems, but decreased in BOWO; N addition did not affect the aromaticity of DOC extracted from mineral soil. All ecosystems showed increases in extractable DOC from both litter and soil in response to N treatment. The biochemical changes are consistent with the divergent microbial responses observed in these systems. Extracellular oxidative enzyme activity has declined in the BOWO and SMRO ecosystems while activity in the SMBW ecosystem, particularly in the litter horizon, has increased. In all systems, enzyme activities associated with the hydrolysis and oxidation of polysaccharides have increased. At the ecosystem scale, the biochemical characteristics of the dominant litter appear to modulate the effects of N deposition on organic matter dynamics.
", "keywords": ["Litter Chemistry", "Geology and Earth Sciences", "13. Climate action", "Soil Organic Matter", "Science", "Ecology and Evolutionary Biology", "0401 agriculture", " forestry", " and fisheries", "Nitrogen Deposition", "04 agricultural and veterinary sciences", "15. Life on land", "Dissolved Organic Matter", "Extracellular Enzyme Activity"]}, "links": [{"href": "https://doi.org/10.1111/j.1365-2486.2005.01001.x"}, {"rel": "related", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/Global%20Change%20Biology", "name": "related record", "description": "related record", "type": "application/json"}, {"rel": "self", "type": "application/geo+json", "title": "10.1111/j.1365-2486.2005.01001.x", "name": "item", "description": "10.1111/j.1365-2486.2005.01001.x", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.1111/j.1365-2486.2005.01001.x"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2005-07-19T00:00:00Z"}}, {"id": "10.1111/j.1365-2486.2012.02749.x", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-25T16:18:56Z", "type": "Journal Article", "created": "2012-05-24", "title": "Experimental Litterfall Manipulation Drives Large And Rapid Changes In Soil Carbon Cycling In A Wet Tropical Forest", "description": "AbstractGlobal changes such as variations in plant net primary production are likely to drive shifts in leaf litterfall inputs to forest soils, but the effects of such changes on soil carbon (C) cycling and storage remain largely unknown, especially in C\uffe2\uff80\uff90rich tropical forest ecosystems. We initiated a leaf litterfall manipulation experiment in a tropical rain forest in Costa Rica to test the sensitivity of surface soil C pools and fluxes to different litter inputs. After only 2\uffc2\uffa0years of treatment, doubling litterfall inputs increased surface soil C concentrations by 31%, removing litter from the forest floor drove a 26% reduction over the same time period, and these changes in soil C concentrations were associated with variations in dissolved organic matter fluxes, fine root biomass, microbial biomass, soil moisture, and nutrient fluxes. However, the litter manipulations had only small effects on soil organic C (SOC) chemistry, suggesting that changes in C cycling, nutrient cycling, and microbial processes in response to litter manipulation reflect shifts in the quantity rather than quality of SOC. The manipulation also affected soil CO 2 fluxes; the relative decline in CO 2 production was greater in the litter removal plots (\uffe2\uff88\uff9222%) than the increase in the litter addition plots (+15%). Our analysis showed that variations in CO 2 fluxes were strongly correlated with microbial biomass pools, soil C and nitrogen (N) pools, soil inorganic P fluxes, dissolved organic C fluxes, and fine root biomass. Together, our data suggest that shifts in leaf litter inputs in response to localized human disturbances and global environmental change could have rapid and important consequences for belowground C storage and fluxes in tropical rain forests, and highlight differences between tropical and temperate ecosystems, where belowground C cycling responses to changes in litterfall are generally slower and more subtle.
", "keywords": ["2. Zero hunger", "soil biogeochemistry", "microbial biomass", "soil nitrogen", "carbon dioxide", "04 agricultural and veterinary sciences", "dissolved organic matter", "Biogeochemistry", "15. Life on land", "soil carbon chemistry", "root biomass", "13. Climate action", "soil phosphorus", "0401 agriculture", " forestry", " and fisheries", "net primary productivity"]}, "links": [{"href": "https://doi.org/10.1111/j.1365-2486.2012.02749.x"}, {"rel": "related", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/Global%20Change%20Biology", "name": "related record", "description": "related record", "type": "application/json"}, {"rel": "self", "type": "application/geo+json", "title": "10.1111/j.1365-2486.2012.02749.x", "name": "item", "description": "10.1111/j.1365-2486.2012.02749.x", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.1111/j.1365-2486.2012.02749.x"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2012-06-25T00:00:00Z"}}, {"id": "10.5061/dryad.c2fqz61cf", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-25T16:21:32Z", "type": "Dataset", "title": "Oxygen availability regulates the quality of soil dissolved organic matter by mediating microbial metabolism and iron oxidation", "description": "Dissolved organic matter (DOM) plays a vital role in biogeochemical processes and in determining the responses of soil organic matter (SOM) to global change. Although the quantity of soil DOM has been inventoried across diverse spatio-temporal scales, the underlying mechanisms accounting for variability in DOM dynamics remain unclear, especially in upland ecosystems. Here, a gradient of SOM storage across twelve croplands in northeast China was used to understand links between DOM dynamics, microbial metabolism, and abiotic conditions. We assessed the composition, biodegradability and key biodegradable components of DOM. In addition, SOM and mineral-associated organic matter (MAOM) composition, soil enzyme activities, oxygen availability, soil texture, iron (Fe), Fe-bound organic matter and nutrient concentrations were quantified to clarify the drivers of DOM quality (composition and biodegradability). The proportion of biodegradable DOM increased exponentially with decreasing initial DOM concentration due to larger fractions of depolymerized DOM that was rich in small-molecular phenols and proteinaceous components. Unexpectedly, the composition of DOM was decoupled from that of SOM or MAOM, but significantly related to enzymatic properties. These results indicate that microbial metabolism exhibited a dominant role in DOM generation. As DOM concentration declined, increased soil oxygen availability regulated DOM composition and enhanced its biodegradability mainly through mediating microbial metabolism and Fe oxidation. The oxygen-induced oxidation of Fe(II) to Fe(III) removed complex DOM compounds with large molecular weight. Moreover, increased oxygen availability stimulated oxidase-catalyzed depolymerization of aromatic substances, and promoted production of protein-like DOM components due to lower enzymatic C/N acquisition ratio. As global changes in temperature and moisture will have large impacts on soil oxygen availability, the role of oxygen in regulating DOM dynamics highlights the importance of integrating soil oxygen supply with microbial metabolism and Fe redox status to improve model predictions of soil carbon under climate change.", "keywords": ["2. Zero hunger", "soil organic carbon", "iron cycling", "13. Climate action", "FOS: Agricultural sciences", "Biodegradation", "oxygen availability", "enzymatic stoichiometry", "15. Life on land", "dissolved organic matter", "6. Clean water"], "contacts": [{"organization": "Li, Ye, Chen, Zengming, Chen, Ji, Castellano, Michael J., Ye, Chenglong, Zhang, Nan, Miao, Yuncai, Zheng, Huijie, Li, Junjie, Ding, Weixin,", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/10.5061/dryad.c2fqz61cf"}, {"rel": "self", "type": "application/geo+json", "title": "10.5061/dryad.c2fqz61cf", "name": "item", "description": "10.5061/dryad.c2fqz61cf", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.5061/dryad.c2fqz61cf"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2022-10-23T00:00:00Z"}}, {"id": "10.3390/w12061722", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-25T16:21:13Z", "type": "Journal Article", "created": "2020-06-18", "title": "Influence of Dissolved Organic Matter Sources on In-Stream Net Dissolved Organic Carbon Uptake in a Mediterranean Stream", "description": "Studies exploring how different sources of dissolved organic matter (DOM) influence in-stream dissolved organic carbon (DOC) uptake at the ecosystem scale are scarce in the literature. To fill this knowledge gap, we examined the relationship between DOM sources and in-stream net DOC uptake (UDOC) in a sub-humid Mediterranean stream. We considered four reach-scale scenarios occurring under natural conditions that differed in predominant DOM sources (groundwater, leaf litter, and/or upstream water). Results showed that groundwater inputs favored in-stream net DOC uptake, while leaf litter inputs promoted in-stream net DOC release. However, there was no clear effect of DOM source mixing on the magnitude of UDOC. Further, the variability in UDOC within and among scenarios was mostly explained by stream DOC concentration, suggesting that DOC availability limits microbial activity in this stream. DOM composition became a controlling factor of UDOC variability only during the leaf litter period, when stream DOC concentration was the highest. Together, these results suggest that the capacity of headwater forested streams to process DOC is closely tied to the availability of different DOM sources and how they vary over time and along the river network.
Studies exploring how different sources of dissolved organic matter (DOM) influence in-stream dissolved organic carbon (DOC) uptake at the ecosystem scale are scarce in the literature. To fill this knowledge gap, we examined the relationship between DOM sources and in-stream net DOC uptake (UDOC) in a sub-humid Mediterranean stream. We considered four reach-scale scenarios occurring under natural conditions that differed in predominant DOM sources (groundwater, leaf litter, and/or upstream water). Results showed that groundwater inputs favored in-stream net DOC uptake, while leaf litter inputs promoted in-stream net DOC release. However, there was no clear effect of DOM source mixing on the magnitude of UDOC. Further, the variability in UDOC within and among scenarios was mostly explained by stream DOC concentration, suggesting that DOC availability limits microbial activity in this stream. DOM composition became a controlling factor of UDOC variability only during the leaf litter period, when stream DOC concentration was the highest. Together, these results suggest that the capacity of headwater forested streams to process DOC is closely tied to the availability of different DOM sources and how they vary over time and along the river network.
Fluorescence is an easily available analytical technique used to assess the optical characteristics of dissolved organic matter (DOM).
Photochemical degradation of dissolved organic matter (DOM) has been the subject of numerous studies; however, its regulation along the inland water continuum is still unclear. We aimed to unravel the DOM photoreactivity and concurrent DOM compositional changes across 30 boreal aquatic ecosystems including peat waters, streams, rivers, and lakes distributed along a water residence time (WRT) gradient. Samples were subjected to a standardized exposure of simulated sunlight. We measured the apparent quantum yield (AQY), which corresponds to DOM photomineralization per photon absorbed, and the compositional change in DOM at bulk and individual compound levels in the original samples and after irradiation. AQY increased with the abundance of terrestrially derived DOM and decreased at higher WRT. Additionally, the photochemical changes in both DOM optical properties and molecular composition resembled changes along the natural boreal WRT gradient at low WRT (<3\uffc2\uffa0years). Accordingly, mass spectrometry revealed that the abundance of photolabile and photoproduced molecules decreased with WRT along the boreal aquatic continuum. Our study highlights the tight link between DOM composition and DOM photodegradation. We suggest that photodegradation is an important driver of DOM composition change in waters with low WRT, where DOM is highly photoreactive.Ongoing and amplified climate change in the Arctic is leading to glacier retreat and to the exposure of an ever\uffe2\uff80\uff90larger portion of non\uffe2\uff80\uff90glaciated permafrost\uffe2\uff80\uff90dominated landscapes. Warming will also cause more precipitation to fall as rain, further enhancing the thaw of previously frozen ground. Yet, the impact of those perturbations on the geochemistry of Arctic rivers remains a subject of debate. Here, we determined the geochemical composition of waters from various contrasting non\uffe2\uff80\uff90glacial permafrost catchments and investigated their impact on a glacially dominated river, the Zackenberg River (Northeast Greenland), during late summer (August 2019). We also studied the effect of rainfall on the geochemistry of the Zackenberg River, its non\uffe2\uff80\uff90glacial tributaries, and a nearby independent non\uffe2\uff80\uff90glacial headwater stream Gr\uffc3\uffa6nse. We analyzed water properties, quantified and characterized dissolved organic matter (DOM) using absorbance and fluorescence spectroscopy and radiocarbon isotopes, and set this alongside analyses of the major cations (Ca, Mg, Na, and K), dissolved silicon (Si), and germanium/silicon ratios (Ge/Si). The glacier\uffe2\uff80\uff90fed Zackenberg River contained low concentrations of major cations, dissolved Si and dissolved organic carbon (DOC), and a Ge/Si ratio typical of bulk rock. Glacial DOM was enriched in protein\uffe2\uff80\uff90like fluorescent DOM and displayed relatively depleted radiocarbon values (i.e., old DOM). Non\uffe2\uff80\uff90glacial streams (i.e., tributaries and Gr\uffc3\uffa6nse) had higher concentrations of major cations and DOC and DOM enriched in aromatic compounds. They showed a wide range of values for radiocarbon, Si and Ge/Si ratios associated with variable contributions of surface runoff relative to deep active layer leaching. Before the rain event, Zackenberg tributaries did not contribute notably to the solute export of the Zackenberg River, and supra\uffe2\uff80\uff90permafrost ground waters governed the supply of solutes in Zackenberg tributaries and Gr\uffc3\uffa6nse stream. After the rain event, surface runoff modified the composition of Gr\uffc3\uffa6nse stream, and non\uffe2\uff80\uff90glacial tributaries strongly increased their contribution to the Zackenberg River solute export. Our results show that summer rainfall events provide an additional source of DOM and Si\uffe2\uff80\uff90rich waters from permafrost\uffe2\uff80\uff90underlain catchments to the discharge of glacially dominated rivers. This suggests that the magnitude and composition of solute exports from Arctic rivers are modulated by permafrost thaw and summer rain events. This event\uffe2\uff80\uff90driven solute supply will likely impact the carbon cycle in rivers, estuaries, and oceans and should be included into future predictions of carbon balance in these vulnerable Arctic systems. Studies exploring how different sources of dissolved organic matter (DOM) influence in-stream dissolved organic carbon (DOC) uptake at the ecosystem scale are scarce in the literature. To fill this knowledge gap, we examined the relationship between DOM sources and in-stream net DOC uptake (UDOC) in a sub-humid Mediterranean stream. We considered four reach-scale scenarios occurring under natural conditions that differed in predominant DOM sources (groundwater, leaf litter, and/or upstream water). Results showed that groundwater inputs favored in-stream net DOC uptake, while leaf litter inputs promoted in-stream net DOC release. However, there was no clear effect of DOM source mixing on the magnitude of UDOC. Further, the variability in UDOC within and among scenarios was mostly explained by stream DOC concentration, suggesting that DOC availability limits microbial activity in this stream. DOM composition became a controlling factor of UDOC variability only during the leaf litter period, when stream DOC concentration was the highest. Together, these results suggest that the capacity of headwater forested streams to process DOC is closely tied to the availability of different DOM sources and how they vary over time and along the river network. Fluorescence is an easily available analytical technique used to assess the optical characteristics of dissolved organic matter (DOM).