Delta-Flux: An Eddy Covariance Network for a Climate-Smart Lower Mississippi Basin Page: 2
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For example, Arkansas, Louisiana, and Mississippi have
collectively experienced a 64% increase in irrigated land
from 1998 to 2008 (Vories and Evett, 2014), contributing
to one of the highest aquifer depletions in the United States
(Konikow, 2015). These changes to the water budget may
have substantially altered soil carbon sequestration by reduc-
ing soil drought conditions and associated crop responses.
Modifications to energy and hydrologic cycling could affect
regional climate impacts in this region (Boucher et al.,
2004). Furthermore, channelization of the Mississippi River
system and concomitant floodplain hydrology has reduced
bottomland hardwoods by 80% since the 1930s (Faulkner
et al., 2011; De Steven et al., 2015); the resulting conserva-
tion efforts that include reforestation and floodplain restora-
tion may re-establish certain ecosystem services, including
The relevance of the LMRB for regional- to continental-
scale carbon and water cycling is highlighted by examining
the United States' distribution of actual evapotranspiration
(ET) and gross primary productivity (GPP). We used a new
global process-based approach to estimating these terms
from Moderate Resolution Imaging Spectroradiometer
(MODIS) satellite imagery, the Breathing Earth System
Simulator (BESS) (Ryu et al., 2011; Jiang and Ryu, 2016), to
demonstrate the magnitude of these fluxes from Arkansas,
Mississippi, and Louisiana (Fig. 1). These states rank within
the top five in terms of annual ET rates and have early spring
inception of GPP. Products such as BESS require "boots on-
the-ground" flux and landscape observations for validation
and support. Although GPP estimates can be derived from
satellite imagery, the net carbon balance requires an estimate
of ecosystem respiration. This term requires locally based
parameterizations (Phillips et al., 2016) that can be provided
in part through flux tower measurements.
Despite the great potential for regional carbon
sequestration in its soils and vegetation stocks, the LMRB
region lacks observations of its carbon and water fluxes. This
region has been historically underrepresented in national
carbon cycling monitoring projects such as the National
Ecological Observatory Network (NEON), the Critical Zone
Observatory (CZO), the Long-Term Ecological Research
(LTER) Network, and AmeriFlux, which is a USDOE network
of scientist-managed sites that measure ecosystem fluxes of
CO2, water (H2O), energy, and sometimes other scalars such
as methane (CH4). Experiment-based observation programs
are particularly necessary given the opportunity for human
management-agricultural intensification, irrigation water
use, and conservation incentive programs-to affect soil
Networked observations have demonstrated many ben-
efits-pioneered in flux research through AmeriFlux (since
1996) and similar networks. Networks create a "Big Data"
framework that can allow novel insights through data
mining and intersite comparison (e.g., Boyd and Crawford,
2012). For example, robust geographic comparisons between
sites enhance process-based knowledge and test best man-
agement strategies. The cross-disciplinary collaboration and
new large-scale datasets generated by research networks are
crucial to ecological discovery (Weathers et al., 2016), and
.:_ r-Other States
J F M A M J JA S ON D
Fig. 1. (A) Average actual monthly evapotranspiration (ET). (B)
Gross primary productivity (GPP) for each of the 50 US states,
with Mississippi, Louisiana, and Arkansas highlighted. Values
average 2001 to 2015 from the monthly, 0.5-degree gridded
Breathing Earth System Simulator (BESS) product aggregated
from 1 km MODIS pixels (Jiang and Ryu, 2016).
they help to scale observations from individual sites to pose
regional and continental ecological questions (Peters et al.,
2014). We describe here the potential for a newly created
network of flux towers in the LMRB to address some of the
key gaps in our knowledge of region's carbon and water cycle
fluxes. We identify specific research questions that can be
targeted with Delta-Flux data, discuss mechanisms by which
the individual network node activities will be coordinated,
and highlight areas in which additional collaboration is
Observation Network: Delta-Flux
A consortium of researchers, representing US government
agencies and state academic institutions, recently formed a
regional network of eddy covariance towers named Delta-
Flux with the goal to integrate site-level findings on carbon
and water fluxes to inform cohesive, regional science needs.
The towers provide continuous measurements of net land-
atmosphere exchange of energy, H20 vapor, CO2, and CH4
over multiyear to decadal time scales. Measuring CH4 fluxes,
with their significant global-warming potential (Etminan et
al., 2016), is an especially important task in this region given
the high rice production and other wetland environments.
The network includes 17 existing, active towers spread across
11 sites in the region and two recently running towers in the
AGRICULTURAL & ENVIRONMENTAL LETTERS'
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Runkle, Benjamin R. K.; Rigby, James R.; Reba, Michele L.; Anapalli, Saseendran S.; Bhattacharjee, Joydeep; Krauss, Ken W. et al. Delta-Flux: An Eddy Covariance Network for a Climate-Smart Lower Mississippi Basin, article, February 23, 2017; Madison, Wisconsin. (https://digital.library.unt.edu/ark:/67531/metadc1234363/m1/2/?rotate=270: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT College of Arts and Sciences.