Pulsed carbon export from mountains by earthquake-triggered landslides explored in a reduced-complexity model

Abstract. In mountain ranges, earthquakes can trigger widespread landsliding and mobilise large amounts of organic carbon by eroding soil and vegetation from hillslopes. Following a major earthquake, the landslide-mobilised organic carbon can be exported from river catchments by physical sediment transport processes, or stored within the landscape where it may be degraded by heterotrophic respiration. The competition between these physical and biogeochemical processes governs a net transfer of carbon between the atmosphere and sedimentary organic matter, yet their relative importance following a large landslide-triggering earthquake remains poorly constrained. Here, we propose a model framework to quantify the post-seismic redistribution of soil-derived organic carbon. The approach combines predictions based on empirical observations of co-seismic sediment mobilisation, with a description of the physical and biogeochemical processes involved after the earthquake. Earthquake-triggered landslide populations are generated by randomly sampling a landslide area distribution, a proportion of which is initially connected to the fluvial network. Initially disconnected landslide deposits are transported downslope and connected to rivers at a constant velocity in the post-seismic period. Disconnected landslide deposits lose organic carbon by heterotrophic oxidation, while connected deposits lose organic carbon synchronously by both oxidation and river export. The modelling approach is numerically efficient and allows us to explore a large range of parameter values that exert a control on the fate of organic carbon in the upland erosional system. We explore the role of the climatic context (in terms of mean annual runoff and runoff variability) and rates of organic matter degradation using single and multi-pool models. Our results highlight that the redistribution of organic carbon is strongly controlled by the annual runoff and the extent of landslide connection, but less so by the choice of organic matter degradation model. In the context of mountain ranges typical of the southwest Pacific region, we find that model configurations allow for more than 90 % of the landslide-mobilized carbon to be exported from mountain catchments. A simulation of earthquake cycles suggests efficient transfer of organic carbon out of a mountain range during the first decade of the post-seismic period. Pulsed erosion of organic matter by earthquake-triggered landslides therefore offers an effective process to promote carbon sequestration in sedimentary deposits over thousands of years.

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Pulsed carbon export from mountains by earthquake-triggered landslides explored in a reduced-complexity model

Earth Surface Dynamics ◽

10.5194/esurf-9-823-2021 ◽

2021 ◽

Vol 9 (4) ◽

pp. 823-844

Author(s):

Thomas Croissant ◽

Robert G. Hilton ◽

Gen K. Li ◽

Jamie Howarth ◽

Jin Wang ◽

...

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Annual Runoff ◽

Transport Processes ◽

Mountain Range ◽

Biogeochemical Processes ◽

Organic Matter Degradation ◽

Carbon Export ◽

Model Framework ◽

Mountain Ranges

Abstract. In mountain ranges, earthquakes can trigger widespread landsliding and mobilize large amounts of organic carbon by eroding soil and vegetation from hillslopes. Following a major earthquake, the landslide-mobilized organic carbon can be exported from river catchments by physical sediment transport processes or stored within the landscape where it may be degraded by heterotrophic respiration. The competition between these physical and biogeochemical processes governs a net transfer of carbon between the atmosphere and sedimentary organic matter, yet their relative importance following a large landslide-triggering earthquake remains poorly constrained. Here, we propose a model framework to quantify the post-seismic redistribution of soil-derived organic carbon. The approach combines predictions based on empirical observations of co-seismic sediment mobilization with a description of the physical and biogeochemical processes involved after an earthquake. Earthquake-triggered landslide populations are generated by randomly sampling a landslide area distribution, a proportion of which is initially connected to the fluvial network. Initially disconnected landslide deposits are transported downslope and connected to rivers at a constant velocity in the post-seismic period. Disconnected landslide deposits lose organic carbon by heterotrophic oxidation, while connected deposits lose organic carbon synchronously by both oxidation and river export. The modeling approach is numerically efficient and allows us to explore a large range of parameter values that exert a control on the fate of organic carbon in the upland erosional system. We explore the role of the climatic context (in terms of mean annual runoff and runoff variability) and rates of organic matter degradation using single pool and multi-pool models. Our results highlight the fact that the redistribution of organic carbon is strongly controlled by the annual runoff and the extent of landslide connection, but less so by the choice of organic matter degradation model. In the context of mountain ranges typical of the southwestern Pacific region, we find that model configurations allow more than 90 % of the landslide-mobilized carbon to be exported from mountain catchments. A simulation of earthquake cycles suggests efficient transfer of organic carbon out of a mountain range during the first decade of the post-seismic period. Pulsed erosion of organic matter by earthquake-triggered landslides is therefore an effective process to promote carbon sequestration in sedimentary deposits over thousands of years.

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Traces of sunlight in the organic matter biogeochemistry of two shallow subarctic lakes

Biogeochemistry ◽

10.1007/s10533-021-00820-9 ◽

2021 ◽

Author(s):

Marttiina V. Rantala ◽

Carsten Meyer-Jacob ◽

E. Henriikka Kivilä ◽

Tomi P. Luoto ◽

Antti. E. K. Ojala ◽

...

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Lake Sediments ◽

Lake Water ◽

Human Impacts ◽

Global Environmental Change ◽

Carbon Export ◽

Subarctic Lakes ◽

Carbon Regulation ◽

In Situ Experiments

AbstractGlobal environmental change alters the production, terrestrial export, and photodegradation of organic carbon in northern lakes. Sedimentary biogeochemical records can provide a unique means to understand the nature of these changes over long time scales, where observational data fall short. We deployed in situ experiments on two shallow subarctic lakes with contrasting light regimes; a clear tundra lake and a dark woodland lake, to first investigate the photochemical transformation of carbon and nitrogen elemental (C/N ratio) and isotope (δ13C, δ15N) composition in lake water particulate organic matter (POM) for downcore inferences. We then explored elemental, isotopic, and spectral (inferred lake water total organic carbon [TOC] and sediment chlorophyll a [CHLa]) fingerprints in the lake sediments to trace changes in aquatic production, terrestrial inputs and photodegradation before and after profound human impacts on the global carbon cycle prompted by industrialization. POM pool in both lakes displayed tentative evidence of UV photoreactivity, reflected as increasing δ13C and decreasing C/N values. Through time, the tundra lake sediments traced subtle shifts in primary production, while the woodland lake carried signals of changing terrestrial contributions, indicating shifts in terrestrial carbon export but possibly also photodegradation rates. Under global human impact, both lakes irrespective of their distinct carbon regimes displayed evidence of increased productivity but no conspicuous signs of increased terrestrial influence. Overall, sediment biogeochemistry can integrate a wealth of information on carbon regulation in northern lakes, while our results also point to the importance of considering the entire spectrum of photobiogeochemical fingerprints in sedimentary studies.

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Consequences of nutrient load reductions for carbon and alkalinity dynamics within the region of freshwater influence of River Elbe

10.5194/egusphere-egu21-1716 ◽

2021 ◽

Author(s):

Johannes Paetsch ◽

Helmuth Thomas

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Sulfate Reduction ◽

Biogeochemical Model ◽

Time Interval ◽

Nutrient Loads ◽

Organic Matter Degradation ◽

Strong Decrease ◽

Nitrogen And Phosphorus ◽

River Elbe

Since the early eighties of the 20th century nitrogen and phosphorus loads of the River Elbe, a river entering the North European Shelf at the southeastern coast, have decreased by a factor of about four. This resulted in a reduction of the eutrophication status in the adjacent German Bight and the coastal waters west of Denmark. In addition, benthic carbon and alkalinity pools have changed due to 1- changed carbon loads and, 2- changed decay pathways of benthic organic carbon.We investigate the consequences of observed nutrient and organic loads by rivers with a 3D-biogeochemical model including a 3D-early diageneses model within the sediment for the time 1979 - 2014. &#160;&#160;The results show a strong decrease of benthic carbon rather due to decreasing nutrient loads and subsequent autochthonous biological production than changes in organic loads. The export of inorganic carbon from the sediment is related to the magnitude of benthic organic carbon and cannot explain the strong decrease of the benthic POC pool.&#160;During the time until the early nineties aerobic degradation increases, whereas denitrification and sulfate reduction as organic matter degradation pathway decreases.Alkalinity production due to benthic organic matter degradation decreases over the first half of the investigated time interval and keeps constant during the second half. Denitrification and sulfate reduction dominate the mechanisms decreasing the alkalinity export. Benthic nitrification consuming alkalinity strongly increases during the first half of the time dampening the decrease of alkalinity export.

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Biogeochemical processes and labile composition of settling particulate organic matter in the south-west Pacific Ocean

Marine and Freshwater Research ◽

10.1071/mf02051 ◽

2003 ◽

Vol 54 (3) ◽

pp. 259 ◽

Cited By ~ 5

Author(s):

Lallan Prasad Gupta ◽

Hodaka Kawahata

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Particulate Organic Matter ◽

Deep Trap ◽

Biogeochemical Processes ◽

Shallow Trap ◽

The South ◽

Coral Sea ◽

South West ◽

Tasman Sea

Settling particles collected by sediment traps deployed for approximately 1 year in the Coral Sea and Tasman Sea were analysed to understand the biogeochemical processes controlling the cycling and flux of particulate organic matter (POM) in the south-west Pacific. Samples were analysed for 20 amino acids (AA) and two hexosamines (HA) and the data were interpreted together with already published data on opal (biogenic silica), organic carbon and total nitrogen contents. Mean fluxes of labile carbon and nitrogen at one site were significantly different (P < 0.04, t-test; n = 14–18) from those at other sites. The southernmost trap recorded the highest concentrations of AA, HA and organic carbon normalized AA. At a site in the south, POM was more degraded in the deep trap than in the shallow trap. Occasionally, higher fluxes were also recorded at the deep trap relative to the shallow trap. The C/Natomic ratio coupled with AA- and HA-based parameters clearly suggested contribution of POM through resuspension as well as lateral advection at the more southern site, whereas a strong influence of zooplankton on total mass flux was revealed at the northern site during the period August–September 1995. It is evident from the data that higher flux of particles having higher labile contents (AA and HA) is more prevalent in the Tasman Sea than in the Coral Sea.

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Local simulations of snow redistribution by wind with an intermediate-complexity snow cover model driven by different wind downscaling methods

10.5194/egusphere-egu21-14629 ◽

2021 ◽

Author(s):

Louis Quéno ◽

Paul Morin ◽

Rebecca Mott ◽

Tobias Jonas

Keyword(s):

Snow Cover ◽

Transport Processes ◽

Swiss Alps ◽

Small Scale ◽

Mountain Range ◽

Model Framework ◽

Intermediate Complexity ◽

Operational Modelling ◽

Snow Transport ◽

Large Domains

In mountainous terrain, wind-driven transport of deposited snow affects the overall distribution of snow, and can have a significant effect on snowmelt patterns even at coarser resolution.&#160; In an operational modelling perspective, a compromise must be found to represent this complex small-scale process with enough accuracy while mitigating the computational costs of snow cover simulations over large domains. To achieve this compromise, we implemented the SNOWTRAN-3D snow transport module within the FSM intermediate complexity snow cover model. We included a new layering scheme and a historical variable of past snow wetting, but without resolving the snow microstructure. Simulations are run and evaluated over a small mountain range in the Swiss Alps at 25 to 100 m resolution. Being implemented in the model framework of the SLF operational snow hydrology service (OSHD), simulations further benefit from snow data assimilation techniques to provide improved estimates of solid precipitation fields. As complex wind patterns in mountains are the key processes driving snow transport, we tested statistical and dynamical methods to downscale 1 km resolution COSMO winds to better reflect topographically-induced flow patterns. These simulations are a first step working towards the integration of wind transport processes over large domains in an intermediate-complexity and -resolution operational modelling framework.

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Fluxes of particulate matter, carbonates, organic carbon and nitrogen in the northern Adriatic continental shelf: A synthesis overview

Advances in Oceanography and Limnology ◽

10.4081/aiol.2018.7601 ◽

2018 ◽

Vol 9 (2) ◽

Author(s):

Michele Giani ◽

Juan Carlos Miquel ◽

Amelia De Lazzari ◽

Alfredo Boldrin

Keyword(s):

Organic Matter ◽

Particulate Matter ◽

Organic Carbon ◽

Primary Production ◽

Sediment Traps ◽

Transport Processes ◽

Advective Transport ◽

Northern Adriatic ◽

Benthic Respiration ◽

Time Space

Time series of composition and fluxes of settling particles in the marine environment, obtained by sediment traps, contribute to define the main processes driving the dynamics of particulate matter and of the time/space variability of benthic-pelagic exchanges. With this aim, the composition and seasonal and annual fluxes of settling matter, obtained from different projects and from published papers, at 8 sites of the Northern Adriatic shelf were estimated. The mean yearly particulate fluxes varied from 2763 to 14,447 g m-2 y-1, from 66 to 236 gC m-2y-1 for organic carbon (OC) flux, from 861 to 7525 g m-2y-1 for carbonates and from 12 to 42 gN m-2y-1 for nitrogen (N). The fluxes were characterized by high seasonal variations with marked increase in autumn or in winter with respect to spring or summer. The sink of particles occurs in relatively short episodes as about 50% of annual particle flux settles in less than 1-2 months in the western coastal area. This seasonality can be related to the riverine discharges, primary production and wind regimes of the basin. Utilizing the N/OC ratio as an index for discriminating the different origin of organic matter (i.e., resuspended/riverine and autochthonous), the primary marine carbon flux was estimated to range from 10 to 28% of the OC fluxes and accounted for 8-40% of the primary production, depending on the site. Then, due to the shallow waters of the basin and to the relevant riverine inputs, the total fluxes near the sea bottom were highly dependent on resuspension and advective transport processes. The important contribution of these last processes as source of organic matter is suggested also by the comparison between fluxes determined by sediment traps with mass accumulation rates (MAR) in sediments, derived from radionuclide measurements. Indeed, the fraction of OC fluxes which is not buried in the sediment is sufficient to support the benthic respiration processes.

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Dose-dependent regulation of microbial activity on sinking particles by polyunsaturated aldehydes: Implications for the carbon cycle

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1422664112 ◽

2015 ◽

Vol 112 (19) ◽

pp. 5909-5914 ◽

Cited By ~ 30

Author(s):

Bethanie R. Edwards ◽

Kay D. Bidle ◽

Benjamin A. S. Van Mooy

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Carbon Cycle ◽

Bacterial Community Composition ◽

Bioactive Molecules ◽

Nutrient Regeneration ◽

Carbon Export ◽

Sinking Particles ◽

Polyunsaturated Aldehydes ◽

Open Question

Diatoms and other phytoplankton play a crucial role in the global carbon cycle, fixing CO2into organic carbon, which may then be exported to depth via sinking particles. The molecular diversity of this organic carbon is vast and many highly bioactive molecules have been identified. Polyunsaturated aldehydes (PUAs) are bioactive on various levels of the marine food web, and yet the potential for these molecules to affect the fate of organic carbon produced by diatoms remains an open question. In this study, the effects of PUAs on the natural microbial assemblages associated with sinking particles were investigated. Sinking particles were collected from 150 m in the water column and exposed to varying concentrations of PUAs in dark incubations over 24 h. PUA doses ranging from 1 to 10 µM stimulated respiration, organic matter hydrolysis, and cell growth by bacteria associated with sinking particles. PUA dosages near 100 µM appeared to be toxic, resulting in decreased bacterial cell abundance and metabolism, as well as pronounced shifts in bacterial community composition. Sinking particles were hot spots for PUA production that contained concentrations within the stimulatory micromolar range in contrast to previously reported picomolar concentrations of these compounds in bulk seawater. This suggests PUAs produced in situ stimulate the remineralization of phytoplankton-derived sinking organic matter, decreasing carbon export efficiency, and shoaling the average depths of nutrient regeneration. Our results are consistent with a “bioactivity hypothesis” for explaining variations in carbon export efficiency in the oceans.

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Characteristics of Sediment and Organic Carbon Export from Pristine Boreal Forest Watersheds

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f82-226 ◽

1982 ◽

Vol 39 (12) ◽

pp. 1699-1718 ◽

Cited By ~ 83

Author(s):

Robert J. Naiman

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Boreal Forest ◽

Particulate Organic Matter ◽

Terrestrial Ecosystems ◽

Dry Weight ◽

Carbon Export ◽

Watershed Area ◽

First Choice ◽

Spring Freshet

Estimates of the amount of material moving annually from terrestrial ecosystems to the ocean are largely based on an incomplete understanding of events occurring throughout the hydrologic year, and only a vague comprehension of in-stream processes controlling that export. Discharge, suspended sediment, particulate organic matter (POM; > 0.5 μm), dissolved organic carbon (DOC; <0.5 μm diameter), and the percentage of organic matter were measured from 1979 to 1981 in five pristine Quebec streams: First Choice Creek (1st order; watershed area: 0.25 km2), Beaver Creek (2nd order; 1.83 km2), Muskrat River (5th order; 204 km2), Matamek River (6th order; 673 km2), and the Moisie River (9th order; 19 871 km2). All streams, with the exception of First Choice Creek, have a strong spring freshet when 43–55% of the annual discharge occurs. By describing sediment and organic carbon export throughout the annual hydrologic cycle, 1 showed that during the 2-mo spring freshet 71–92% of the annual sediment load is exported but only 59–65% of the annual POM load, and only 47–51% of the annual DOC load. Sediment yield is relatively constant between watersheds (1.5–7.6 g∙m−2∙yr−1), as is POM export (1.0–6.7 g ash-free dry-weight [AFDW]∙m−2∙yr−1); however, export DOC varies from 3.1 g C∙m−2∙yr−1 in First Choice Creek to 48.4 g C∙m−2∙yr−1 in Beaver Creek. There appears to be rapid loading of carbon between 1st- and 2nd-order streams in boreal forests, followed by biological and physical processing as watershed area increases. Thus, for the Moisie River watershed, export of total organic carbon (TOC) is reduced to only 4.7 g C∙m−2∙yr−1. Export of coarse particulate organic matter (> 1 mm) is negligible (normally < 0.1 mg∙L−1), as is oxidation of the suspended load (< 0.5%∙d−1). Effects of summer storms, natural diel variations, and depth of sample from the water column are shown to have a minimal influence on concentrations. Rating curves (kg∙d−1 vs. discharge) are developed to estimate the annual yield of sediment, POM, and DOC, and to evaluate long-term variations. From the results I suggest that in-stream processing and retention devices exert considerable control over the quantity and nature of suspended organic material. Physical processes such as the discharge regime and stream power are relatively less important in determining organic concentrations, but more important in determining sediment concentrations.Key words: seston, carbon, sediment, boreal forest, watershed, river, stream, export

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Carbon sources supporting benthic mineralization in mangrove and adjacent seagrass sediments (Gazi Bay, Kenya)

Biogeosciences Discussions ◽

10.5194/bgd-1-311-2004 ◽

2004 ◽

Vol 1 (1) ◽

pp. 311-333 ◽

Cited By ~ 5

Author(s):

S. Bouillon ◽

T. Moens ◽

F. Dehairs

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Bacterial Communities ◽

Carbon Sources ◽

Mangrove Ecosystem ◽

Community Respiration ◽

Seagrass Beds ◽

Carbon Export ◽

Organic Matter Pool ◽

Gazi Bay

Abstract. The origin of carbon substrates used by in situ sedimentary bacterial communities was investigated in an intertidal mangrove ecosystem and in adjacent seagrass beds in Gazi bay (Kenya) by δ13C analysis of bacteria-specific PLFA (phospholipid fatty acids) and bulk organic carbon. Export of mangrove-derived organic matter to the adjacent seagrass-covered bay was evident from sedimentary total organic carbon (TOC) and δ13CTOC data. PLFA δ13C data indicate that the substrate used by bacterial communities varied strongly and that exported mangrove carbon was a significant source for bacteria in the adjacent seagrass beds. Within the intertidal mangrove forest, bacterial PLFA at the surface layer (0-1 cm) typically showed more enriched δ13C values than deeper (up to 10 cm) sediment layers, suggesting a contribution from microphytobenthos and/or inwelled seagrass material. Under the assumption that seagrasses and mangroves are the dominant potential end-members, the estimated contribution of mangrove-derived carbon to benthic mineralization in the seagrass beds (16-74%) corresponds fairly well to the estimated contribution of mangrove C to the sedimentary organic matter pool (21-71%) across different seagrass sites. Based on these results and a compilation of literature data, we suggest that allochtonous carbon trapped in seagrass beds may often represent a significant fraction of the substrate for benthic mineralization - both in cases where seagrass C dominates the sediment TOC pool and in cases where external inputs are significant. Hence, it is likely that community respiration data systematically overestimate the role of mineralization in the overall seagrass C budget.

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Thermocline mixing and vertical oxygen fluxes in the stratified central North Sea

Biogeosciences Discussions ◽

10.5194/bgd-12-9905-2015 ◽

2015 ◽

Vol 12 (13) ◽

pp. 9905-9934 ◽

Cited By ~ 2

Author(s):

L. Rovelli ◽

M. Dengler ◽

M. Schmidt ◽

S. Sommer ◽

P. Linke ◽

...

Keyword(s):

Organic Carbon ◽

North Sea ◽

Bottom Water ◽

Algal Species ◽

Transport Processes ◽

Carbon Export ◽

High O2 ◽

Key Drivers ◽

Tidally Driven ◽

Central North Sea

Abstract. In recent decades, the central North Sea has been experiencing a general trend of decreasing dissolved oxygen (O2) levels during summer. To understand the potential causes driving lower O2, we investigated summertime turbulence and O2 dynamics in the thermocline and bottom boundary layer (BBL). The study focuses on coupling biogeochemical processes with physical transport processes to identify key drivers of the O2 and organic carbon turnover within the BBL. Combining our flux observations with an analytical process-oriented approach, we resolve the key drivers that ultimately determine the BBL O2 levels. We report substantial tidally-driven turbulent O2 fluxes from the thermocline into the otherwise isolated bottom water. This contribution to the local bottom water O2 and carbon budgets has been largely overlooked and might be a central factor maintaining relatively high O2 levels in the bottom water throughout the stratification period. With the current climate warming projections, we propose that higher water temperature and reduced turbulence could favour migrating algal species that could out-compete other species for light and nutrients, and shift the oxygen production zone higher up within the thermocline while maintaining similar organic carbon export to the bottom water. Due to the substantially lower turbulence levels in the central region of the thermocline as compared to the higher turbulence observed at the thermocline-BBL interface, such a shift in the production layer could lead to further isolation of the bottom water and promote the seasonal occurrence of lower O2 concentrations.

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