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Carbon Cascades from Land to Ocean in the Anthropocene

Periodic Reporting for period 2 - C-CASCADES (Carbon Cascades from Land to Ocean in the Anthropocene)

Reporting period: 2017-01-01 to 2018-12-31

The Intergovernmental Panel on Climate Change Assessment Report (5th IPCC AR) includes the transport of carbon across the Land-Ocean Aquatic Continuum (LOAC) as a key component of the global carbon cycle but fails to quantify the historic changes of this transport due to human activities (land-use and climate change, hydraulic management, and agricultural, domestic and industrial activities). Earth System Models (ESMs) also do not account for the lateral flows of carbon and associated greenhouse gas (GHG) exchange with the atmosphere. This is a major knowledge gap because these fluxes have recently been demonstrated to contribute significantly to policy-relevant global and regional carbon budgets in high-profile research papers. In the absence of this assessment, large uncertainties remain concerning the fate of the anthropogenic CO2 emitted into the atmosphere and its potential impact on climate projections.
To make a breakthrough in this field, the ‘C-CASCADES – Carbon Cascades from Land to Ocean in the Anthropocene’ project was launched on January 1st, 2015. The ambition was to significantly advance the predictive capability of Earth System Models (ESMs) by integrating within them observations, analyses and mechanisms of the carbon transfer in the LOAC. The 3 science objectives were to:
• Understand the critical mechanisms that transport carbon in the LOAC from technical developments, observations and experiments (WP1)
• Assess carbon transfers in the LOAC for selected “hotspot” regions and river catchments (WP2)
• Model the LOAC at the global scale, for attribution of historical changes and future feedbacks on climate (WP3)
As further elaborated below, the 3 science objectives have been fully fulfilled. In particular, the LOAC carbon cycle is now integrated into three European ESMs. Simulations encompassing the historical period and 21st century projections have successfully been carried out in hotspot regions (e.g. Pan Arctic, Amazon, Congo) and at the global scale. In addition, C-CASCADES delivered policy-relevant tools and technological innovations to agencies responsible for environmental monitoring. C-CASCADES also trained 15 Early-Stage Researchers (ESRs) both as future scientists and scientifically skilled professionals, able to pursue a successful career in academia, industry or the policy-sector. It is anticipated that 14 ESRs will receive a PhD degree.
C-CASCADES has covered all key components of the LOAC, that is, terrestrial ecosystems, streams, rivers, lakes and reservoirs, estuaries and river plumes as well as the coastal and open oceans. These interconnected compartments of the LOAC have been studied across a wide-range of environments – from the Pan-Arctic down to the Tropics and from near-pristine systems in the boreal region to catchments in temperate regions heavily impacted by human activities. The dynamics of all major organic and inorganic carbon pools have also been investigated through the full range of methodological approaches, from field observations using cutting-edge sensor technology, to mesocosms experiments, and further to highly detailed process-based modeling, as well as statistical and Earth System modeling. In addition to regional scale studies, C-CASCADES has analyzed several major carbon fluxes and processes at the global scale. This includes, for instance, DOC leaching from terrestrial soils into inland waters, headwater, rivers, floodplains and lake CO2 evasion, the 20th century changes in the CO2 exchange at the air-sea interface of coastal and open ocean waters and present-day carbon fluxes for the LOAC, in the context of the global carbon budget.
Significant progress in LOAC science has been achieved, described below for each Work Package:
WP1 - Process understanding: Technical development, observations and experiments:
• Sensors able to continuously measure CO2, CH4 and O2 concentrations across the full river-ocean mixing regime are available
• Inland waters play a very important role in the lateral carbon flux along the LOAC and in GHG emissions. While mountain streams and boreal waters seem to receive large parts of their gas concentrations from catchment soils and via groundwater, urban waters show deviating patterns and sources
• Temporal trends in natural waters show presently no overall significant increases in greenhouse gas concentrations in the waters
WP2 – Regional scale applications: benchmark studies on hot-spot areas:
• The discovery of the complex space-time nature of the carbon dynamics in a river delta system
• Novel and improved quantification of the Arctic carbon fluxes
• First quantification of the role of the Amazon river supply of nutrients for the productivity of the entire Atlantic ocean
• A novel sedimentary model for the Arctic which includes many key processes
WP3 – Global scale modelling and feedbacks on Earth system processes:
• Assessment of past, present-day and future global-scale terrestrial DOM (tDOM) production, decomposition and leaching to aquatic ecosystems, and its imprint on the global coastal and open ocean C cycle. Quantification of organic matter recycling and burial in marine sediments, the ultimate C incinerator along the LOAC
• Assessment of past, present-day and future role of the LOAC for the carbon balance and CO2 emissions of Pan-Arctic, boreal and tropical catchments
Exploitation and dissemination of C-CASCADES results:
• 27 peer-reviewed articles published, about an additional 30 to come
• 31 posters and 22 oral communications at international conferences
• Outreach products were produced for Stakeholders and the general public: website, videos, factsheets, “LOAC emissions” module on the Global Carbon Atlas (http://www.globalcarbonatlas.org/).
• Inter-sectorial partners valorised our results in a context useful to improved environmental consulting and industrial/commercial development (modelling platform DELWAQ, sensors by KM Contros, wastewater treatment strategies at Veolia)
The strength of C-CASCADES was to integrate different system studies, processes and scales and to bring together scientists from different fields. This was a great added value and helped us to make a breakthrough in understanding the LOAC response to human-induced perturbations, to deliver more accurate carbon budgets and to assess the impact of greenhouse gas emissions on future climate.
In terms of strengthening European innovation capacity, C-CASCADES contributed to the generation of a dynamic, highly skilled, and scientifically excellent group of young scientists ready to address the future challenges of Earth system science, thanks to the structuring effect of a strong interdisciplinary network. The access of training events to other researchers broadened the impact of the project (68 for the whole project lifetime).
In terms of socio-economic impact, C-CASCADES contributed to construct well-founded policies and to translate scientific results into operational models supporting the decision making process, e.g. implementation of the scientific results into a modelling platform (D-WAQ) that is used worldwide by water managers and consultants (Deltares); innovation in sensor technology (KM Contros); implementation of new models in the context of wastewater treatment and discharge to the environment (Veolia); implementation of all C-CASCADES data in the Global Carbon Atlas of the Global Carbon Project.
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