How inland and coastal waterways influence climate
Date:
March 16, 2022
Source:
Princeton University
Summary:
Most global carbon-budgeting efforts assume a linear flow
of water from the land to the sea, which ignores the complex
interplay between streams, rivers, lakes, groundwater, estuaries,
mangroves and more. Climate scientists now detail how carbon is
stored and transported through the intricacy of inland and coastal
waterways. The work has significant implications for enforcing the
carbon calculations that are part of international climate accords.
FULL STORY ========================================================================== "Streams to the river, river to the sea." If only it were that simple.
==========================================================================
Most global carbon-budgeting efforts assume a linear flow of water from
the land to the sea, which ignores the complex interplay between streams, rivers, lakes, groundwater, estuaries, mangroves and more. A study
co-led by climate scientist Laure Resplandy, an assistant professor
of geosciences and the High Meadows Environmental Institute (HMEI)
at Princeton University, details how carbon is stored and transported
through the intricacy of inland and coastal waterways. Published in the
current issue of the journal Nature, the work has significant implications
for enforcing the carbon calculations that are part of international
climate accords.
Terrestrial and marine ecosystems have a powerful influence on climate
by regulating the level of atmospheric carbon dioxide (CO2). These
ecosystems, however, are often viewed as disconnected from each other,
which ignores the transfer of carbon from land to the open ocean through
a complex network of water bodies -- the continuum of streams, rivers, estuaries and other bodies carrying water from land to the sea.
In a detailed analysis, the team of researchers from Belgium, the United
States and France discovered that this land-to-ocean aquatic continuum
(LOAC) carries a substantial amount of carbon of anthropogenic (e.g., fossil-fuel) origin.
Thus, the carbon removed from the atmosphere by terrestrial ecosystems is
not all stored locally, as is commonly assumed, which has implications
for global agreements that require countries to report their carbon inventories. The researchers also found that the land-to-ocean carbon
transfer of natural origin was larger than previously thought, with far-reaching implications for the assessment of the anthropogenic CO2
uptake by the ocean and the land.
"The complexity of the LOAC, which includes rivers, groundwater, lakes, reservoirs, estuaries, tidal marshes, mangroves, seagrasses, and waters
above continental shelves, has made it challenging to assess its influence
on the global carbon cycle," said Pierre Regnier, a professor at the
University of Brussels who co-led the study with Resplandy.
Because of that complexity, important global carbon-budgeting efforts,
such as those of the U.N. Intergovernmental Panel on Climate Change
and the Global Carbon Project, typically assume a direct "pipeline"
transfer of carbon from river mouths to the open ocean. Another common assumption is that all the transported carbon is natural, neglecting
the impacts of human perturbations on this aquatic continuum, such as
damming and the decimation of coastal vegetation.
==========================================================================
In this study, the researchers synthesized more than 100 individual
studies of the various components of the continuum. From this
synthesis, LOAC carbon budgets were developed for two time periods:
the pre-industrial period and the present day. Their results confirm the well-known pre-industrial carbon "loop" in which carbon is taken up from
the atmosphere by terrestrial ecosystems, transferred by rivers to the
ocean, and then outgassed back to the atmosphere.
"We find the amount of carbon carried by this natural land-to-ocean
loop, 0.65 billion tons per year, is roughly 50% greater than previously thought," Resplandy said.
Furthermore, this loop is comprised of two smaller loops, one that
transfers carbon from terrestrial ecosystems to inland waters and
another from coastal vegetation (so-called "blue carbon ecosystems")
to the open ocean.
"A larger pre-industrial land-to-ocean carbon transport implies that the
ocean uptake of anthropogenic CO2 previously inferred from observations
was underestimated," Resplandy said.
"The flip side is that the land uptake of anthropogenic CO2 was
overestimated," added Regnier.
The study demonstrates that anthropogenic carbon carried by rivers is
either outgassed back to the atmosphere or eventually stored in aquatic sediments and the open ocean.
Philippe Ciais, a research director at the Laboratoire des Sciences du
Climat et de l'Environnement and a co-author of the study explained:
"This new view of the anthropogenic CO2 budget may have a silver lining
because sediments and the ocean offer arguably more stable repositories
than terrestrial biomass and soil carbon, which are vulnerable to
droughts, fires and land-use change." The researchers also have shown
that humans have decreased the uptake of atmospheric CO2 from blue-carbon ecosystems by up to 50%. "If left unprotected from sea-level rise,
pollution and coastal development, blue-carbon uptake of atmospheric
CO2 will further decline and contribute to additional climate warming,"
said Raymond Najjar, a professor from the Pennsylvania State University
who also co-authored the study.
========================================================================== Story Source: Materials provided by Princeton_University. Note: Content
may be edited for style and length.
========================================================================== Journal Reference:
1. Regnier, P., Resplandy, L., Najjar, R.G. et al. The land-to-ocean
loops
of the global carbon cycle. Nature, 2022 DOI:
10.1038/s41586-021-04339-9 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/03/220316120818.htm
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