scholarly journals Fluvial Sediment Transit Time Regulates the Fate of Organic Carbon between Source and Sink

2020 ◽  
Author(s):  
Marisa Repasch ◽  
Joel Scheingross ◽  
Niels Hovius ◽  
Hella Wittmann ◽  
Maarten Lupker ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Transit Time ◽  
Fluvial Sediment ◽  
Source And Sink

Quantifying and characterising organic carbon in newly-developed soils following glacier retreat in northern latitudes

2020 ◽  
Author(s):  
Saule Akhmetkaliyeva ◽  
Robert Sparkes ◽  
Leon Clarke ◽  
Andrew Dean ◽  
Simon Cook
Keyword(s):  
Organic Carbon ◽  
Dna Sequencing ◽  
Soil Development ◽  
Glacier Retreat ◽  
The Arctic ◽  
Glacial Meltwater ◽  
Fluvial Sediment ◽  
Sediment Samples ◽  
Glacier Front ◽  
Soil And Sediment

<p>Arctic and sub-arctic regions contain a globally significant reservoir of easily degradable glacial organic carbon (GOC) held within glacier ice, subglacial sediments, and proglacial sediments and soils. 21st century warming will result in global glacier retreat with the potential to expose and release GOC, degradation of which can produce CO<sub>2</sub> and/or CH<sub>4</sub> through physical, chemical or biological processes. Newly-exposed nutrient rich glacial landscapes may develop soils and ecosystems. However, current understanding of the nature of glacial carbon cycling is very weak. In this study, sources and transformations of organic carbon (OC) within proglacial environments were determined using a combination of organic biomarkers, DNA sequencing and elemental concentrations.</p><p>Soil development was characterised in three contrasting glacial systems (Oræfajökull ice cap in Iceland, Tarfala in Sweden and Zackenberg in Greenland) in order to understand the main source of OC in soils exposed after glacier retreat and soil development along downstream transects from the glacier front. Water, soil and sediment samples were collected during four successful field campaigns (Iceland and Sweden in summer 2018, Greenland and Iceland in summer 2019). Soil and sediment samples were analysed for organic carbon and nitrogen concentrations, bacteriohopanepolyol biomarkers (BHPs), a group of membrane lipids that can be used to trace major microbial groups, DNA sequencing and major elements (using ICP-OES and IC).  </p><p>Soil samples from moraines showed highest OC concentrations (up to 5.5% in Iceland), while fluvial sediment samples from all study areas had low to no OC. BHPs were rare in fluvial sediments, observed in riverbank soils and most common in moraines. Both total BHP concentration and R’soil index (up to 50.5 µg/g ΣBHPs in a Little Ice Age and 0.41 R’soil in a 2500-year-old Icelandic moraines) show development of soils over time along the downstream transect from the glacier front. DNA concentrations in soil extracts are much higher than fluvial sediment samples. Particulate OC concentration in glacial meltwater streams and proglacial lakes was low (up to 0.03 mg/L), perhaps due to the high total suspended sediment concentrations (up to 0.96 mg/L) in most of the streams. Water chemistry analyses showed significant Ca, S, Na, Fe, Mg and Al concentrations, that potentially would fertilise the Arctic Ocean.</p><p>Based on these preliminary data, it can be concluded that direct glacial output of organic carbon is low, but soil and ecosystem development in front of retreating glaciers leads to the build-up of new terrestrial OC stores. Erosion of OC from these pro-glacial landscapes by glacial meltwater might highly affect estimates of GOC. Future glacier retreat in deglaciating systems in the Arctic (Greenland and Sweden) and sub-arctic (Iceland) regions might increase terrestrial OC productivity and carbon export, as well as seeding biological production downstream.</p>

Unraveling the groundwater transit time control of permafrost derived dissolved organic carbon processing in a hillslope headwater watershed of Qinghai-Tibetan Plateau

2021 ◽  
Author(s):  
Yuqin Sun ◽  
Kale Clauson ◽  
Min Zhou ◽  
Ziyong Sun ◽  
Chunmiao Zheng ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Transit Time ◽  
Mean Transit Time ◽  
Frozen Soil ◽  
Permafrost Region ◽  
Transport Pathways ◽  
Microbial Utilization ◽  
Time Control

<p>Climate warming leads to massive thaws of the northern permafrost that has increased the release of soil organic carbon (SOC) to streams and rivers partly as dissolved organic carbon (DOC). The transport pathways of SOC releasing into porewater and entering into stream are undergoing profound hydrological changes triggered by permafrost thawing, yet the role that the groundwater plays in processing the permafrost derived DOC is ambiguous. Unravelling how subsurface flow affects permafrost sourced DOC processing is important especially in alpine watersheds of high-altitude permafrost region with extensive surface – groundwater interaction. Here, eight types of water were sampled from a small (25 km<sup>2</sup>), alpine (elevation 2960 to 4820 m a.s.l) watershed named Hulugou watershed (HLGW) with variably degraded permafrost in the Qinghai-Tibetan Plateau (QTP) in July and September of 2012, 2013 and 2018. The three end-members (glacier-snow meltwater, precipitation, and frozen soil meltwater) analysis suggested contribution of frozen soil meltwater to all types of water with variable DOC levels (0.4 to 22.6 mg L<sup>-1</sup>, n = 113), as constrained by <em>δ</em><sup>18</sup>O and electrical conductivity (EC). Spatial patterns of DOC quantity and quality between stream and subsurface waters (groundwater, spring, and seepage-II) point to differences in surface – groundwater exchanges in the upper-, mid- and lower stretch of the watershed. To evaluate the extent of DOC loss (ΔDOC), ΔDOC is calculated using an initial DOC (DOC<sub>0</sub>) estimated from mixing of three endmembers, minus the measured DOC concentration. The significant correlations between ΔDOC with proportion of protein-like fluorophores (<em>r</em> = -0.69, <em>p</em> < 0.01) and relatively aromatic C levels (<em>r</em> = -0.62, <em>p</em> = 0.02) indicate ΔDOC corresponding to the extent of microbial utilization of DOC in subsurface environment. Using previously established DOC biodegradation kinetics of 0.25 d<sup>-1</sup> in headwaters of QTP, the mean transit time of groundwater is estimated to be 6 and 20 days based on changes in subsurface ΔDOC of 32% and 74% from the outlet of HLGW for July and September, respectively. The more rapid groundwater transit time corresponds to the higher concentration and more boilable DOC in July (3.5 mg L<sup>-1</sup>, protein-like: 98%) than in September (1.0 mg L<sup>-1</sup>, protein-like: 53±26%). Together with the mass balance of DOC input and export fluxes showing half loss of C in HLGW, our results indicate that rapid groundwater transit time is associated with permafrost derived DOC processing in alpine hillslope subject to warming.</p>

scholarly journals Fluvial organic carbon cycling regulated by sediment transit time and mineral protection

2021 ◽  
Author(s):  
Marisa Repasch ◽  
Joel S. Scheingross ◽  
Niels Hovius ◽  
Maarten Lupker ◽  
Hella Wittmann ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Transit Time ◽  
Management Practices ◽  
River Channels ◽  
Channel Mobility ◽  
River Modelling ◽  
Organic Carbon Cycling ◽  
Lateral Erosion ◽  
Global Carbon

AbstractRivers transfer terrestrial organic carbon (OC) from mountains to ocean basins, playing a key role in the global carbon cycle. During fluvial transit, OC may be oxidized and emitted to the atmosphere as CO2 or preserved and transported to downstream depositional sinks. The balance between oxidation and preservation determines the amount of particulate OC (POC) that can be buried long term, but the factors regulating this balance are poorly constrained. Here, we quantify the effects of fluvial transit on POC fluxes along an ~1,300 km lowland channel with no tributaries. We show that sediment transit time and mineral protection regulate the magnitude and rate of POC oxidation, respectively. Using a simple turnover model, we estimate that annual POC oxidation is a small percentage of the POC delivered to the river. Modelling shows that lateral erosion into POC-rich floodplains can increase POC fluxes to downstream basins, thereby offsetting POC oxidation. Consequently, rivers with high channel mobility can enhance CO2 drawdown while management practices that stabilize river channels may reduce the potential for CO2 drawdown.

scholarly journals Impacts of anthropogenic inputs on hypoxia and oxygen dynamics in the Pearl River estuary

2018 ◽  
Vol 15 (20) ◽  
pp. 6105-6125 ◽  
Author(s):  
Bin Wang ◽  
Jiatang Hu ◽  
Shiyu Li ◽  
Liuqian Yu ◽  
Jia Huang
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
River Estuary ◽  
Pearl River Estuary ◽  
Pearl River ◽  
The Pearl River Estuary ◽  
Concentration Changes ◽  
The Pearl River ◽  
Oxygen Dynamics ◽  
Source And Sink

Abstract. In summer, the Pearl River estuary (PRE) experiences hypoxia, largely driven by the high input of fresh water with low dissolved oxygen (DO), abundant nutrients and particulate organic carbon from the Pearl River network. In this study, we used a well-validated physical–biogeochemical model together with a DO species-tracing method to study the responses of hypoxia and oxygen dynamics to the anthropogenic perturbations of riverine inputs (i.e. DO, nutrients, and particulate organic carbon) in July–August 2006. Model results showed that hypoxia in the PRE was most sensitive to riverine inputs of particulate organic carbon, followed by DO concentrations and nutrients. Specifically, a 50 % decrease (increase) in riverine input of particulate organic carbon led to a 47 % decrease (64 % increase) in hypoxic area, with the sediment oxygen demand and water column production being the two most important processes contributing to changes in DO concentration. Changes in the riverine inputs of DO and nutrients had little impact on the simulated hypoxia because of the buffering effects of re-aeration (DO fluxes across the air–sea interface); i.e. the re-aeration responded to the changes in surface apparent oxygen utilization (AOU) associated with river-induced variations of oxygen source and sink processes. The PRE features shallow waters (with averaged depth of 10 m) in which oxygen provided by the re-aeration could penetrate to bottom waters via vertical diffusion and largely offset the changes in DO contributed by other oxygen source and sink processes. This study highlights the importance of re-aeration in reducing hypoxia variability in shallow estuaries.

Cerebral vascular mean transit time determined by PET and DSC-MRI

2005 ◽  
Vol 25 (1_suppl) ◽  
pp. S676-S676
Author(s):  
Masanobu Ibaraki ◽  
Hiroshi Ito ◽  
Eku Shimosegawa ◽  
Hideto Toyoshima ◽  
Keiichi Ishigame ◽  
...  
Keyword(s):  
Transit Time ◽  
Mean Transit Time ◽  
Dsc Mri ◽  
Cerebral Vascular

Transit-time effects in saturated absorption resonances

1986 ◽  
Vol 47 (12) ◽  
pp. 2025-2039 ◽  
Author(s):  
A. Titov ◽  
Yu. Malyshev ◽  
Yu. Rastorguev
Keyword(s):  
Transit Time ◽  
Time Effects ◽  
Saturated Absorption
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