3 research outputs found
Riverine Export of Aged Carbon Driven by Flow Path Depth and Residence Time
The flux of terrestrial C to rivers
has increased relative to preindustrial
levels, a fraction of which is aged dissolved organic C (DOC). In
rivers, C is stored in sediments, exported to the ocean, or (bio)Âchemically
processed and released as CO<sub>2</sub>. Disturbance changes land
cover and hydrology, shifting potential sources and processing of
DOC. To investigate the likely sources of aged DOC, we analyzed radiocarbon
ages, chemical, and spectral properties of DOC and major ions from
19 rivers draining the coterminous U.S. and Arctic. DOC optics indicated
that the majority is exported as aromatic, high molecular weight,
modern molecules while aged DOC tended to consist of smaller, microbial
degradation products. Aged DOC exports, observed regularly in arid
basins and during base flow in arctic rivers, are associated with
higher proportion of mineral weathering products, suggesting deeper
flows paths. These patterns also indicate potential for production
of microbial byproducts as DOC ages in soil and water with longer
periods of time between production and transport. Thus, changes in
hydrology associated with landscape alteration (e.g., tilling or shifting
climates) that can result in deeper flow paths or longer residence
times will likely lead to a greater proportion of aged carbon in riverine
exports
Fates of Terrigenous Dissolved Organic Carbon in the Gulf of Maine
A significant amount of organic carbon is transported
in dissolved
form from soils to coastal oceans via inland water systems, bridging
land and ocean carbon reservoirs. However, it has been discovered
that the presence of terrigenous dissolved organic carbon (tDOC) in
oceans is relatively limited. Therefore, understanding the fates of
tDOC in coastal oceans is essential to account for carbon sequestration
through land ecosystems and ensure accurate regional carbon budgeting.
In this study, we developed a state-of-the-art modeling approach by
coupling a land-to-ocean tDOC flux simulation model and a coastal
tDOC tracking model to determine the potential fates of tDOC exported
from three primary drainage basins in the Gulf of Maine (GoM). According
to our findings, over half a year in the GoM, 56.4% of tDOC was mineralized.
Biomineralization was responsible for 90% of that amount, with the
remainder attributed to photomineralization. Additionally, 37% of
the tDOC remained suspended in the GoM, and 6.6% was buried in the
marine sediment
Organic Carbon Burial in Lakes and Reservoirs of the Conterminous United States
Organic
carbon (OC) burial in lacustrine sediments represents an
important sink in the global carbon cycle; however, large-scale OC
burial rates are poorly constrained, primarily because of the sparseness
of available data sets. Here we present an analysis of OC burial rates
in water bodies of the conterminous U.S. (CONUS) that takes advantage
of recently developed national-scale data sets on reservoir sedimentation
rates, sediment OC concentrations, lake OC burial rates, and water
body distributions. We relate these data to basin characteristics
and land use in a geostatistical analysis to develop an empirical
model of OC burial in water bodies of the CONUS. Our results indicate
that CONUS water bodies sequester 20.8 (95% CI: 9.4–65.8) Tg
C yr<sup>–1</sup>, and spatial patterns in OC burial are strongly
influenced by water body type, size, and abundance; land use; and
soil and vegetation characteristics in surrounding areas. Carbon burial
is greatest in the central and southeastern regions of the CONUS,
where cultivation and an abundance of small water bodies enhance accumulation
of sediment and OC in aquatic environments