Climate change induced permafrost thaw in the Arctic is mobilizing ancient dissolved organic carbon (DOC) into headwater streams; however, DOC exported from the mouth of major arctic rivers appears ...predominantly modern. Here we highlight that ancient (>20,000 years B.P.) permafrost DOC is rapidly utilized by microbes (~50% DOC loss in <7 days) and that permafrost DOC decay rates (0.12 to 0.19 day−1) exceed those for DOC in a major arctic river (Kolyma: 0.09 day−1). Permafrost DOC exhibited unique molecular signatures, including high levels of aliphatics that were rapidly utilized by microbes. As microbes processed permafrost DOC, its distinctive chemical signatures were degraded and converged toward those of DOC in the Kolyma River. The extreme biolability of permafrost DOC and the rapid loss of its distinct molecular signature may explain the apparent contradiction between observed permafrost DOC release to headwaters and the lack of a permafrost signal in DOC exported via major arctic rivers to the ocean.
Key Points
Permafrost DOC microbial utilization is greater than modern DOC in arctic rivers
Permafrost DOM has unique molecular signatures (high levels of aliphatics)
Unique molecular signature of permafrost DOM lost on biodegradation
Chromophoric dissolved organic matter (CDOM) fluxes and yields from 15 major U.S. rivers draining an assortment of terrestrial biomes are presented. A robust relationship between CDOM and dissolved ...organic carbon (DOC) loads is established (e.g., a350 versus DOC; r2 = 0.96, p < 0.001). Calculated CDOM yields are also correlated to watershed percent wetland (e.g. a350; r2 = 0.81, p < 0.001) providing a method for the estimation of CDOM export from ungauged watersheds. A large variation in CDOM yields was found across the rivers. The two rivers in the north‐eastern U.S. (Androscoggin and Penobscot), the Edisto draining into the South Atlantic Bight, and some rivers draining into the Gulf of Mexico (Atchafalaya and Mobile) exhibit the highest CDOM yields, linked to extensive wetlands in these watersheds. If the Edisto CDOM yield is representative of other rivers draining into the South Atlantic Bight, this would result in a CDOM load equivalent to that of the Mississippi from a region of approximately 10% of the Mississippi watershed, indicating the importance of certain regions with respect to the role of terrigenous CDOM in ocean color budgets.
Key points
Multisite CDOM load and DOC load relationship
Development of CDOM yields shows important regions for future study
First estimate of CDOM flux from major U.S. Rivers
The Congo and Amazon are the two largest rivers on Earth and serve as major sources of dissolved organic carbon to the ocean. We compared the dissolved organic matter (DOM) composition of both rivers ...using Fourier‐transform ion cyclotron resonance mass spectrometry to investigate seasonal and regional differences in DOM composition exported to the ocean. We found that over a 15‐month observational period in the Congo River, molecular aromaticity and oxygenation between the wet and dry periods varied slightly, but most of the relative abundance of DOM formulae (∼90%) were present in all samples, suggesting that Congo River DOM quality is stable across different hydrological conditions. In contrast, the multi‐year DOM composition in the Amazon River was highly susceptible to changes in hydrology, with clear differences in molecular aromaticity, oxygenation, and heteroatom (N, S, P) content between the wet and dry seasons. Overall, the DOM composition of the Congo River was more terrestrial than Amazon River DOM, which was more characteristic of aquatic DOM. Finally, we compared the relative contribution of island of stability (IOS) formulae between the rivers and found that both rivers export similar amounts of these formulae annually, more than several major rivers combined, and that the Congo is more than twice as efficient in exporting these IOS formulae. With changing precipitation and land use, the quantity and composition of exported DOM will likely reflect the mobilization of additional terrestrial and anthropogenic sources that will also be subjected to downstream land‐to‐ocean cycling.
Plain Language Summary
Almost 16% of the global riverine dissolved organic carbon (DOC) export is delivered by just two rivers: Amazon and Congo. Although both rivers drain immense tropical rainforests, differences in landscape, precipitation, and riverine discharge all contribute to the distinct molecular composition of their dissolved organic matter (DOM). We compared DOM composition of both rivers over several years and found that hydrology is an important driver for determining the DOM composition of both rivers; however, it is more important for the Amazon than Congo, which had DOM that was more similar across the wet and dry seasons. Overall, both rivers had more aromatic and oxygen‐rich DOM than temperate or arctic rivers, but DOM from the Congo had a more terrestrial signature than the Amazon River DOM. Finally, we found that DOM molecular formulae thought to be stable over long periods of time in marine systems were exported in similar amounts by both rivers, even though the Amazon exports about twice as much DOC annually compared to the Congo, suggesting that the Congo is more than twice as efficient per unit volume at exporting molecular formulae that is thought to be stable in the ocean for long periods of time.
Key Points
Congo River dissolved organic matter (DOM) composition remains mostly stable across the year, while Amazon River DOM varies seasonally with discharge
Amazon River DOM is less aromatic, less oxygenated, and more heteroatom‐rich than Congo River DOM
Both rivers export similar amounts of island of stability molecular formulae but the Congo is over twice as efficient
The arctic freshwater system: Changes and impacts White, Daniel; Hinzman, Larry; Alessa, Lilian ...
Journal of Geophysical Research - Biogeosciences,
December 2007, Letnik:
112, Številka:
G4
Journal Article
Recenzirano
Odprti dostop
Dramatic changes have been observed in the Arctic over the last century. Many of these involve the storage and cycling of fresh water. On land, precipitation and river discharge, lake abundance and ...size, glacier area and volume, soil moisture, and a variety of permafrost characteristics have changed. In the ocean, sea ice thickness and areal coverage have decreased and water mass circulation patterns have shifted, changing freshwater pathways and sea ice cover dynamics. Precipitation onto the ocean surface has also changed. Such changes are expected to continue, and perhaps accelerate, in the coming century, enhanced by complex feedbacks between the oceanic, atmospheric, and terrestrial freshwater systems. Change to the arctic freshwater system heralds changes for our global physical and ecological environment as well as human activities in the Arctic. In this paper we review observed changes in the arctic freshwater system over the last century in terrestrial, atmospheric, and oceanic systems.
As climate‐driven El Niño Southern Oscillation (ENSO) events are projected to increase in frequency and severity, much attention has focused on impacts regarding ecosystem productivity and carbon ...balance in Amazonian rainforests, with comparatively little attention given to carbon dynamics in fluvial ecosystems. In this study, we compared the wet 2012 La Niña period to the following normal hydrologic period in the Amazon River. Elevated water flux during the La Niña period was accompanied by dilution of inorganic ion concentrations. Furthermore, the La Niña period exported 2.77 Tg C yr−1 more dissolved organic carbon (DOC) than the normal period, an increase greater than the annual amount of DOC exported by the Mississippi River. Using ultra‐high‐resolution mass spectrometry, we detected both intra‐ and interannual differences in dissolved organic matter (DOM) composition, revealing that DOM exported during the dry season and the normal period was more aliphatic, whereas compounds in the wet season and following the La Niña event were more aromatic, with ramifications for its environmental role. Furthermore, as this study has the highest temporal resolution DOM compositional data for the Amazon River to‐date we showed that compounds were highly correlated to a 6‐month lag in Pacific temperature and pressure anomalies, suggesting that ENSO events could impact DOM composition exported to the Atlantic Ocean. Therefore, as ENSO events increase in frequency and severity into the future it seems likely that there will be downstream consequences for the fate of Amazon Basin‐derived DOM concurrent with lag periods as described here.
Plain Language Summary
Increases in atmospheric carbon concentrations originate from many sources and pose a serious threat to global ecosystem health and humanity. The Amazon River delivers one‐fifth of global discharge and represents the largest single flux of dissolved organic carbon (DOC) from land to ocean. As climate change is projected to increase precipitation anomalies throughout the Amazon, flooding and droughts will become more frequent and severe, disrupting the natural seasonal rhythm of the Amazon River. We demonstrate that precipitation anomalies in South America (caused by La Niña) exported an additional amount of DOC from the Amazon River to the Atlantic Ocean than the Mississippi River exports annually. Organic compounds mobilized during the La Niña were more aromatic, presumably from terrestrial sources. These compositions, measured near the mouth of the Amazon River, arrived six months after Pacific sea‐surface temperature and pressure anomalies indicated the onset of La Niña, highlighting the lag time that events in the Pacific take to impact the Atlantic Ocean.
Key Points
The Amazon River during a La Niña year exports an additional amount of dissolved organic carbon than the Mississippi exports annually
The Amazon River dissolved organic matter composition in a La Niña year was more oxidized and aromatic than during a non‐ENSO year
The dissolved organic matter composition in the Amazon River correlates to a 6‐month lag with La Niña indices
As the planet warms, widespread changes in Arctic hydrology and biogeochemistry have been documented and these changes are expected to accelerate in the future. Improved understanding of the behavior ...of water-borne constituents in Arctic rivers with varying hydrologic conditions, including seasonal variations in discharge–concentration relationships, will improve our ability to anticipate future changes in biogeochemical budgets due to changing hydrology. We studied the relationship between seasonal water discharge and dissolved organic carbon and nitrogen (DOC and DON) and nutrient concentrations in the upper Kuparuk River, Arctic Alaska. Fluxes of most constituents were highest during initial snowmelt runoff in spring, indicating that this historically under-studied period contributes significantly to total annual export. In particular, the initial snowmelt period (the stream is completely frozen during the winter) accounted for upwards of 35% of total export of DOC and DON estimated for the entire study period. DOC and DON concentrations were positively correlated with discharge whereas nitrate (NO
3
−
) and silicate were negatively correlated with discharge throughout the study. However, discharge-specific DOC and DON concentrations (i.e. concentrations compared at the same discharge level) decreased over the summer whereas discharge-specific concentrations of NO
3
−
and silicate increased. Soluble reactive phosphorus (SRP) and ammonium (NH
4
+
) were negatively correlated with discharge during the spring thaw, but were less predictable with respect to discharge thereafter. These data provide valuable information on how Arctic watershed biogeochemistry will be affected by future changes in temperature, snowfall, and rainfall in the Arctic. In particular, our results add to a growing body of research showing that nutrient export per unit of stream discharge, particularly NO
3
−
, is increasing in the Arctic.
INTRODUCTION: Exposure to low oxygen environments (hypoxia) can impair cognitive function; however, the time-course of the transient changes in cognitive function is unknown. In this study, we ...assessed cognitive function with a cognitive test before, during, and after exposure
to hypoxia.METHODS: Nine participants (28 4 yr, 7 women) completed Conners Continuous Performance Test (CCPT-II) during three sequential conditions: 1) baseline breathing room air (fraction of inspired oxygen, FIo2 0.21); 2) acute hypoxia (FIo2
0.118); and 3) recovery after exposure to hypoxia. End-tidal gas concentrations (waveform capnography), heart rate (electrocardiography), frontal lobe tissue oxygenation (near infrared spectroscopy), and mean arterial pressure (finger photoplethysmography) were continuously assessed.RESULTS:
Relative to baseline, during the hypoxia trial end-tidal (-30%) and cerebral (-9%) oxygen saturations were reduced. Additionally, the number of commission errors during the CCPT-II was greater during hypoxia trials than baseline trials (2.6 0.4 vs. 1.9 0.4 errors per block of CCPT-II). However,
the reaction time and omission errors did not differ during the hypoxia CCPT-II trials compared to baseline CCPT-II trials. During the recovery CCPT-II trials, physiological indices of tissue hypoxia all returned to baseline values and number of commission errors during the recovery CCPT-II
trials was not different from baseline CCPT-II trials.DISCUSSION: Oxygen concentrations were reduced (systemically and within the frontal lobe) and commission errors were increased during hypoxia compared to baseline. These data suggest that frontal lobe hypoxia may contribute to
transient impairments in cognitive function during short exposures to hypoxia.Uchida K, Baker SE, Wiggins CC, Senefeld JW, Shepherd JRA, Trenerry MR, Buchholtz ZA, Clifton HR, Holmes DR, Joyner MJ, Curry TB. A novel method to measure transient impairments in cognitive function during
acute bouts of hypoxia. Aerosp Med Hum Perform. 2020; 91(11):839844.
Distinguishing the sources, ages, and fate of various terrestrial organic carbon (OC) pools mobilized from heterogeneous Arctic landscapes is key to assessing climatic impacts on the fluvial release ...of carbon from permafrost. Through molecular 14C measurements, including novel analyses of suberin‐ and/or cutin‐derived diacids (DAs) and hydroxy fatty acids (FAs), we compared the radiocarbon characteristics of a comprehensive suite of terrestrial markers (including plant wax lipids, cutin, suberin, lignin, and hydroxy phenols) in the sedimentary particles from nine major arctic and subarctic rivers in order to establish a benchmark assessment of the mobilization patterns of terrestrial OC pools across the pan‐Arctic. Terrestrial lipids, including suberin‐derived longer‐chain DAs (C24,26,28), plant wax FAs (C24,26,28), and n‐alkanes (C27,29,31), incorporated significant inputs of aged carbon, presumably from deeper soil horizons. Mobilization and translocation of these “old” terrestrial carbon components was dependent on nonlinear processes associated with permafrost distributions. By contrast, shorter‐chain (C16,18) DAs and lignin phenols (as well as hydroxy phenols in rivers outside eastern Eurasian Arctic) were much more enriched in 14C, suggesting incorporation of relatively young carbon supplied by runoff processes from recent vegetation debris and surface layers. Furthermore, the radiocarbon content of terrestrial markers is heavily influenced by specific OC sources and degradation status. Overall, multitracer molecular 14C analysis sheds new light on the mobilization of terrestrial OC from arctic watersheds. Our findings of distinct ages for various terrestrial carbon components may aid in elucidating fate of different terrestrial OC pools in the face of increasing arctic permafrost thaw.
Key Points
Molecular 14C content of multiple terrestrial markers is compared in pan‐arctic sediments
Suberin‐ and cutin‐derived diacids trace old and young terrestrial carbon separately
New light is shed on terrestrial carbon sources and mobilization pathways in arctic basins
The primary purpose of this study was to examine how the type and magnitude of changes in running behavior, as a consequence of COVID-19 pandemic restrictions, influence running-related injuries. ...Secondarily, we aimed to examine how lifestyle and psychosocial well-being measures may influence running behavior change. An online survey was advertised to individuals over the age of 18 that currently run or have previously participated in running for exercise. The survey questions examined injury history and new injuries sustained during COVID-19 restrictions, as well as changes related to training behavior changes, training environment changes, social behaviors, and psychosocial well-being. Changes reflected differences in running behaviors prior to COVID-19 restrictions (1 month prior to COVID-19 restrictions being imposed) and during COVID-19 restrictions (May 5 to June 10, 2020). A total of 1,035 runners were included in the analysis. Current injuries sustained during COVID-19 occurred in 9.5% of the runners. Injured runners made a greater number of total changes (
p
= 0.031) as well as training-related (
p
= 0.042) and environment-related (
p
= 0.017) changes compared with uninjured runners. A significant relationship was found between injury and those that reported less time to exercise to changes in work environment (
p
= 0017). This study highlights the multi-dimensional nature of running-related injuries and the need to consider the interaction of multiple changes in running behavior, rather than isolating single factors. Greater understanding of the underlying causes of running-related injuries can help reduce the risk of future injury.
Wildfires have produced black carbon (BC) since land plants emerged. Condensed aromatic compounds, a form of BC, have accumulated to become a major component of the soil carbon pool. Condensed ...aromatics leach from soils into rivers, where they are termed dissolved black carbon (DBC). The transport of DBC by rivers to the sea is a major term in the global carbon and BC cycles. To estimate Arctic river DBC export, 25 samples collected from the six largest Arctic rivers (Kolyma, Lena, Mackenzie, Ob’, Yenisey and Yukon) were analyzed for dissolved organic carbon (DOC), colored dissolved organic matter (CDOM), and DBC. A simple, linear regression between DOC and DBC indicated that DBC accounted for 8.9 ± 0.3% DOC exported by Arctic rivers. To improve upon this estimate, an optical proxy for DBC was developed based upon the linear correlation between DBC concentrations and CDOM light absorption coefficients at 254 nm (a254). Relatively easy to measure a254 values were determined for 410 Arctic river samples between 2004 and 2010. Each of these a254 values was converted to a DBC concentration based upon the linear correlation, providing an extended record of DBC concentration. The extended DBC record was coupled with daily discharge data from the six rivers to estimate riverine DBC loads using the LOADEST modeling program. The six rivers studied cover 53% of the pan-Arctic watershed and exported 1.5 ± 0.1 million tons of DBC per year. Scaling up to the full area of the pan-Arctic watershed, we estimate that Arctic rivers carry 2.8 ± 0.3 million tons of DBC from land to the Arctic Ocean each year. This equates to ~8% of Arctic river DOC export, slightly less than indicated by the simpler DBC vs DOC correlation-based estimate. Riverine discharge is predicted to increase in a warmer Arctic. DBC export was positively correlated with river runoff, suggesting that the export of soil BC to the Arctic Ocean is likely to increase as the Arctic warms.
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