Enhanced stream greenhouse gas emissions at night and during flood events

Headwater streams play a large role in aquatic greenhouse gas emissions. Carbon dioxide (CO2) and dissolved oxygen in streams often undergo changes through diel cycles. However, methane (CH4) and nitrous oxide (N2O) have unknown diel dynamics. Here, we reveal consistent patterns in CO2, CH4, and N2O over diel cycles and during flood events using high-frequency continuous observations in a subtropical headwater stream. Diel cycles were most pronounced during baseflow. Increased nighttime discharge due to higher groundwater inputs enhanced gas transfer velocities and concentrations. Overall nocturnal emissions were 31%, 68%, and 32% greater than daytime for CO2, CH4, and N2O, respectively. Floods dampened diel signals. If both flood events and diel patterns are neglected, estimates of greenhouse gas emissions from headwaters may be greatly underestimated. Overall, CH4 and N2O emissions from headwater streams may be underestimated by similar to 20-40% due to a lack of observations during nighttime, floods, and in warmer climates

Carbon emission from Western Siberian inland waters

High-latitude regions play a key role in the carbon (C) cycle and climate system. An important question is the degree of mobilization and atmospheric release of vast soil C stocks, partly stored in permafrost, with amplified warming of these regions. A fraction of this C is exported to inland waters and emitted to the atmosphere, yet these losses are poorly constrained and seldom accounted for in assessments of high-latitude C balances. This is particularly relevant for Western Siberia, with its extensive peatland C stocks, which can be strongly sensitive to the ongoing changes in climate. Here we quantify C emission from inland waters, including the Ob' River (Arctic's largest watershed), across all permafrost zones of Western Siberia. We show that the inland water C emission is high (0.08-0.10 Pg C yr(-1)) and of major significance in the regional C cycle, largely exceeding (7-9 times) C export to the Arctic Ocean and reaching nearly half (35-50%) of the region's land C uptake. This important role of C emission from inland waters highlights the need for coupled land-water studies to understand the contemporary C cycle and its response to warming. Rivers and lakes are thought to be a major conduit of loss for the massive amounts of carbon locked away in high-latitude systems, but such losses are poorly constrained. Here the authors quantify carbon emissions from rivers and lakes across Western Siberia, finding that emissions are high and exceed carbon export to the Arctic Ocean

Groundwater discharge as a driver of methane emissions from Arctic lakes

Lateral CH4 inputs to Arctic lakes through groundwater discharge could be substantial and constitute an important pathway that links CH4 production in thawing permafrost to atmospheric emissions via lakes. Yet, groundwater CH4 inputs and associated drivers are hitherto poorly constrained because their dynamics and spatial variability are largely unknown. Here, we unravel the important role and drivers of groundwater discharge for CH4 emissions from Arctic lakes. Spatial patterns across lakes suggest groundwater inflows are primarily related to lake depth and wetland cover. Groundwater CH4 inputs to lakes are higher in summer than in autumn and are influenced by hydrological (groundwater recharge) and biological drivers (CH4 production). This information on the spatial and temporal patterns on groundwater discharge at high northern latitudes is critical for predicting lake CH4 emissions in the warming Arctic, as rising temperatures, increasing precipitation, and permafrost thawing may further exacerbate groundwater CH4 inputs to lakes

Global carbon dioxide efflux from rivers enhanced by high nocturnal emissions

Carbon dioxide (CO2) emissions to the atmosphere from running waters are estimated to be four times greater than the total carbon (C) flux to the oceans. However, these fluxes remain poorly constrained because of substantial spatial and temporal variability in dissolved CO2 concentrations. Using a global compilation of high-frequency CO2 measurements, we demonstrate that nocturnal CO2 emissions are on average 27% (0.9 gC m−2 d−1) greater than those estimated from diurnal concentrations alone. Constraints on light availability due to canopy shading or water colour are the principal controls on observed diel (24 hour) variation, suggesting this nocturnal increase arises from daytime fixation of CO2 by photosynthesis. Because current global estimates of CO2 emissions to the atmosphere from running waters (0.65–1.8 PgC yr−1) rely primarily on discrete measurements of dissolved CO2 obtained during the day, they substantially underestimate the magnitude of this flux. Accounting for night-time CO2 emissions may elevate global estimates from running waters to the atmosphere by 0.20–0.55 PgC yr−1

Biophysical controls on CO2 evasion from Arctic inland waters

CO2 evasion to the atmosphere from inland waters is a major component of the global carbon (C) cycle. Yet spatial patterns of CO2 evasion and the sources of C that fuel evasion remain poorly understood. In this thesis, I use detailed measurements of biological and physical drivers of CO2 evasion to assess how C is transformed and evaded from inland waters in the Arctic (Northern Scandinavia and Alaska). I found that lake size was a master variable controlling lake CO2 evasion in an Arctic catchment and that large lakes play a major role at the landscape scale. In stream networks, I found that catchment topography shapes patterns of CO2 evasion by dictating unique domains with high lateral inputs of C, other domains where biological processes were dominant, and domains where physical forces promoted degassing to the atmosphere. Together, these topographically driven domains created a strong spatial heterogeneity that biases regional and global estimates of CO2 evasion. Further, I found that photosynthetic activity in Arctic streams can produce a large change in CO2 concentrations from night to day, and as a result CO2 evasion is up to 45% higher during night than day. The magnitude of the diel change in CO2 was also affected by the turbulence of the stream and photo-chemical production of CO2. Overall, this thesis offers important insights to better understand landscape patterns of CO2 evasion from inland waters, and suggests that stream metabolic processes largely determine the fate of the C delivered from Arctic soils

Biophysical controls on CO2 evasion from Arctic inland waters

CO2 evasion to the atmosphere from inland waters is a major component of the global carbon (C) cycle. Yet spatial patterns of CO2 evasion and the sources of C that fuel evasion remain poorly understood. In this thesis, I use detailed measurements of biological and physical drivers of CO2 evasion to assess how C is transformed and evaded from inland waters in the Arctic (Northern Scandinavia and Alaska). I found that lake size was a master variable controlling lake CO2 evasion in an Arctic catchment and that large lakes play a major role at the landscape scale. In stream networks, I found that catchment topography shapes patterns of CO2 evasion by dictating unique domains with high lateral inputs of C, other domains where biological processes were dominant, and domains where physical forces promoted degassing to the atmosphere. Together, these topographically driven domains created a strong spatial heterogeneity that biases regional and global estimates of CO2 evasion. Further, I found that photosynthetic activity in Arctic streams can produce a large change in CO2 concentrations from night to day, and as a result CO2 evasion is up to 45% higher during night than day. The magnitude of the diel change in CO2 was also affected by the turbulence of the stream and photo-chemical production of CO2. Overall, this thesis offers important insights to better understand landscape patterns of CO2 evasion from inland waters, and suggests that stream metabolic processes largely determine the fate of the C delivered from Arctic soils

Biophysical controls on CO2 evasion from Arctic inland waters

CO2 evasion to the atmosphere from inland waters is a major component of the global carbon (C) cycle. Yet spatial patterns of CO2 evasion and the sources of C that fuel evasion remain poorly understood. In this thesis, I use detailed measurements of biological and physical drivers of CO2 evasion to assess how C is transformed and evaded from inland waters in the Arctic (Northern Scandinavia and Alaska). I found that lake size was a master variable controlling lake CO2 evasion in an Arctic catchment and that large lakes play a major role at the landscape scale. In stream networks, I found that catchment topography shapes patterns of CO2 evasion by dictating unique domains with high lateral inputs of C, other domains where biological processes were dominant, and domains where physical forces promoted degassing to the atmosphere. Together, these topographically driven domains created a strong spatial heterogeneity that biases regional and global estimates of CO2 evasion. Further, I found that photosynthetic activity in Arctic streams can produce a large change in CO2 concentrations from night to day, and as a result CO2 evasion is up to 45% higher during night than day. The magnitude of the diel change in CO2 was also affected by the turbulence of the stream and photo-chemical production of CO2. Overall, this thesis offers important insights to better understand landscape patterns of CO2 evasion from inland waters, and suggests that stream metabolic processes largely determine the fate of the C delivered from Arctic soils

CO2 evasion and carbon budget of Lake Torneträsk, a large, subarctic lake in northern Sweden (BSc Thesis)

<p> ABSTRACT</p> <p>Freshwater systems play an important role in the carbon cycle, but there are still large uncertainties, which must be solved in order to make climate change predictions more accurate. This study quantifies the annual flux of CO2 in lake Torneträsk, a large (345 km2) subarctic lake in northern Sweden, an area of a special interest as global warming is expected to be more severe in polar regions. Torneträsk catchment has been very well studied for decades, but until now not a single study focused on the main component of the landscape, lake Torneträsk. The results of this study are relevant in the carbon budget of the region, as the CO2 evasion from lake Torneträsk to the atmosphere is higher than previously considered. Due to its large surface, the amount of carbon released comprises 25% of the total amount of carbon (C) emitted from all lakes in the catchment (3 231 lakes). Temporal high resolution measurements of CO2 in lake surface water also show interesting daily and seasonal patterns, possibly related to water temperature and photosynthetic activity.</p> <p>Furthermore, I elaborate a first attempt of the lake carbon budget, the evasion of CO2 to the atmosphere comprises 16% of C entered from the catchment. The amount of C buried in the sediment is around 14%, and the rest flows downstream, 50% as dissolved inorganic carbon (DIC) and 20% as dissolved organic carbon (DOC).</p> <p>Torneträsk catchment is a unique environment in order to understand the biogeochemical cycles at a landscape scale, due to its large amount of studies carried out and its situation in a sensible area as the subarctic region. This study contributes unveiling the role of the most important lake in the region, in order to develop an accurate carbon budget for the whole catchment.</p

Fysikalisk-kemiska parametrar mätt vid en stor rumslig upplösning i Miellajokka-avrinningen, Sverige - Paired values of CO2 and k600 from the GLORICH database

High spatial resolution dataset of CO2 evasion in a stream network in northern Sweden (52.5 km2; Miellajokka catchment). We measured key hydrological parameters to estimate k600, directly determined the pCO2, and estimated stream CO2 evasion across 168 sites in the stream network. The publication of this data is currently ongoing. Please contact the main author for further details ([email protected]) Comparison of pCO2 values from a global compilation of river chemistry (GLORICH; Hartmann et al., 2014) with calculated site-specific k600 and CO2 evasion. .Dataset med hög rumlig upplösning för CO2-avflyttning i ett strömnätverk i norra Sverige (52,5 km2; Miellajokka upptag). Viktiga hydrologiska parametrar mätades för att uppskatta k600, direkt bestämd pCO2 och beräknad strömavlopp CO2-undvikning över 168 platser i strömnätet

Fysikalisk-kemiska parametrar mätt vid en stor rumslig upplösning i Miellajokka-avrinningen, Sverige

High spatial resolution dataset of CO2 evasion in a stream network in northern Sweden (52.5 km2; Miellajokka catchment). We measured key hydrological parameters to estimate k600, directly determined the pCO2, and estimated stream CO2 evasion across 168 sites in the stream network. The publication of this data is currently ongoing. Please contact the main author for further details ([email protected])Dataset med hög rumlig upplösning för CO2-avflyttning i ett strömnätverk i norra Sverige (52,5 km2; Miellajokka upptag). Viktiga hydrologiska parametrar mätades för att uppskatta k600, direkt bestämd pCO2 och beräknad strömavlopp CO2-undvikning över 168 platser i strömnätet