Low-order streams are suggested to dominate the atmospheric CO 2 source of all inland waters. Yet, many large-scale stream estimates suffer from methods not designed for gas emission determination and rarely include other greenhouse gases such as CH 4 . Here, we present a compilation of directly measured CO 2 and CH 4 concentration data from Swedish low-order streams (> 1600 observations across > 500 streams) covering large climatological and land-use gradients. These data were combined with an empirically derived gas transfer model and the characteristics of a ca. 400,000 km stream network covering the entire country. The total *Correspondence: marcus.wallin@geo.uu.se Author Contribution Statement: MBW brought the idea and compiled the concentration data. MBW and TG designed the study, analyzed the data and conducted the modelling component. AC, JA, DB, KB, JK, HJ, EL, SL, SN, SB, CT and GAW provided data, ideas and catchment/region specific information. MBW wrote the manuscript with great support from all co-authors.Data Availability Statement: Data are available in the Uppsala University data repository at http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-332472.Additional Supporting Information may be found in the online version of this article.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. This article is part of the Special Issue: Carbon cycling in inland waters Edited by: Emily Stanley and Paul del Giorgio Scientific Significance StatementStreams have been identified as disproportional emitters of CO 2 to the atmosphere across all inland waters. Despite their suggested importance, reliable large-scale stream C emission data are often lacking which makes current estimates uncertain. Here, we show that Swedish low-order streams emit much higher amounts of C to the atmosphere than previously reported, corresponding to 21% of the estimated terrestrial C sequestration. We also show that local scale spatiotemporal variability in stream gas concentrations often exceeds variability across regions, and that stream surface area matters. Without such fundamental information, large-scale stream C emission estimates will always be associated with a large degree of uncertainty.1
We investigated the role of lake sediments as carbon (C) source and sink in the annual C budget of a small (0.07 km 2 ) and shallow (mean depth, 3.4 m), humic lake in boreal Sweden. Organic carbon (OC) burial and mineralization in the sediments were quantified from 210 Pb-dated sediment and laboratory sediment incubation experiments, respectively. Burial and mineralization rates were then upscaled to the entire basin and to one whole year using sediment thickness derived from sub-bottom profiling, basin morphometry, and water column monitoring data of temperature and oxygen concentration. Furthermore, catchment C import, open water metabolism, photochemical mineralization as well as carbon dioxide (CO 2 ) and methane (CH 4 ) emissions to the atmosphere were quantified to relate sediment processes to other lake C fluxes. We found that on a whole-basin and annual scale, sediment OC mineralization was three times larger than OC burial, and contributed about 16% to the annual CO 2 emission. Other contributions to CO 2 emission were water column metabolism (31%), photochemical mineralization (6%), and catchment imports via inlet streams and inflow of shallow groundwater (22%). The remainder (25%) could not be explained by our flux calculations, but was most likely attributed to an underestimation in groundwater inflow. We conclude that on an annual and whole-basin scale (1) sediment OC mineralization dominated over OC burial, (2) water column OC mineralization contributed more to lake CO 2 emission than sediment OC mineralization, and (3) catchment import of C to the lake was greater than lake-internal C cycling.
Inland waters are hotspots for carbon (C) cycling and therefore important for landscape C budgets. Small streams and lakes are particularly important; however, quantifying C fluxes is difficult and has rarely been done for the entire aquatic continuum, composed of connected streams and lakes within the same catchment. We investigated carbon dioxide (CO 2 ) evasion and fluvial fluxes of dissolved inorganic carbon and dissolved organic carbon (DIC and DOC) in stream and lake systems within the 2.3 km 2 catchment of a small boreal lake. Our results show pronounced spatial and temporal variability in C fluxes even at a small spatial scale. C loss from the catchment through CO 2 evasion from headwaters for the total open water-sampling period was 9.7 g C m À2 catchment, dominating the total catchment C loss (including CO 2 evasion, DIC, and DOC export from the lake, which were 2.7, 0.2, and 5.2 g C m À2 catchment, respectively).Aquatic CO 2 evasion was dominated by headwater streams that occupy~0.1% of the catchment but contributed 65% to the total aquatic CO 2 evasion from the catchment. The importance of streams was mainly an effect of the higher gas transfer velocities than compared to lakes (median, 67 and 2.2 cm h À1 , respectively). Accurately estimating the contribution of C fluxes from headwater streams, particularly the temporal and spatial dynamics in their gas transfer velocity, is key to landscape-scale C budgets. This study demonstrates that CO 2 evasion from headwaters can be the major pathway of C loss from boreal catchments, even at a small spatial scale.
Boreal lake sediments are important sites of organic carbon (OC) storage, which have accumulated substantial amounts of OC over the Holocene epoch; the temporal evolution and the strength of this Holocene carbon (C) sink is, however, not well constrained. In this study we investigated the temporal record of carbon mass accumulation rates (CMARs) and assessed qualitative changes of terrestrially derived OC in the sediment profiles of seven Swedish boreal lakes, in order to evaluate the variability of boreal lake sediments as a C sink over time. CMARs were resolved on a short-term (centennial) and long-term (i.e., over millennia of the Holocene) timescale, using radioactive lead ( 210 Pb) and carbon ( 14 C) isotope dating. Sources and degradation state of terrestrially derived OC were identified and characterized by molecular analyses of lignin phenols. We found that CMARs varied substantially on both short-term and long-term scales and that the variability was mostly attributed to sedimentation rates and uncoupled from the OC content in the sediment profiles. The lignin phenol analyses revealed that woody material from gymnosperms was a dominant and constant OC source to the sediments over the Holocene. Furthermore, lignin-based degradation indices, such as acid-to-aldehyde ratios, indicated that postdepositional degradation in the sediments was very limited on longer timescales, implying that terrestrial OC is stabilized in the sediments on a permanent basis.
Streams are major sources of carbon dioxide (CO 2) and methane (CH 4) to the atmosphere, but current large-scale estimates are associated with high uncertainties because knowledge concerning the spatiotemporal control on stream emissions is limited. One of the largest uncertainties derives from the choice of gas transfer velocity (k 600), which describes the physical efficiency of gas exchange across the water-atmosphere interface. This study therefore explored the variability in k 600 and subsequent CO 2 and CH 4 emission rates within and across streams of different stream order (SO). We conducted, for the first time in streams, direct turbulence measurements using an acoustic Doppler velocimeter (ADV) to determine the spatial variability in k 600 across a variety of scales with a consistent methodology. The results show high spatial variability in k 600 and corresponding CO 2 and CH 4 emissions at small spatial scales, both within stream reaches and across SO, especially during high discharge. The k 600 was positively related to current velocity and Reynolds number. By contrast, no clear relationship was found between k 600 and specific stream characteristics such as width and depth, which are parameters often used in empirical models of k 600. Improved understanding of the small-scale variability in the physical properties along streams, especially during high discharge, is therefore an important step to reduce the uncertainty in existing gas transfer models and emissions for stream systems. The ADV method was a useful tool for revealing spatial variability in this work, but it needs further development. We recommend that future studies conduct measurements over shorter time periods (e.g., 10-15 min instead of 40 min) and at more sites across the reach of interest, and thereby derive more reliable mean-reach k 600 as well as more information about controls on the spatial variability in k 600 .
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.