Agriculture Reference
In-Depth Information
drainage water in agricultural areas (Broad-
meadow and Nisbet, 2004). Once the soil
system is disturbed by converting forest or
grassland to cultivated and managed soils,
soil structure is lost and macroaggregates
are mechanically broken down, exposing
protected organic matter to microbial deg-
radation and nutrient leaching. Within
5-10
years after the land-use conversion, signifi-
cant quantities of organic carbon and nitro-
gen of the soil are depleted (Mann, 1986;
Lal, 2004), decreasing the soil fertility and
decreasing the ability for water filtration
and transformation. Livestock grazing of
pastures exerts significant impact on soils
due to the decrease of aboveground bio-
diversity, soil compaction, increase in ero-
sion and soil loss, as well as increase in the
inputs of manure. Stamati
et al
. (2011) have
shown that a nearly linear relationship ex-
ists between dissolved organic nitrogen
(DON) export and livestock N load that op-
erates at regional scales. De-vegetation of
grazing lands coupled with increased car-
bon inputs in the form of manure caused de-
cline in the biochemical quality of soil and
leaching of soluble organic matter.
issues: treatment of preferential flow and
non-equilibrium (Kohne
et al
., 2009a,b),
pore-scale structures and pore heterogen-
eity (Gharasoo
et al
., 2012), as well as two
flow domain issues and microenvironments
(Steefel
et al
., 2005). Upscaling of processes
from the laboratory to the field has always
been an obstacle to model parameter estima-
tion. A critical review on upscaling sorption/
desorption processes in reactive transport
models concluded that inclusion of small-
scale processes might not always lead to
better prediction of the larger-scale behav-
iour of metal/radionuclide transport due to
conceptual model errors, geochemical heter-
ogeneities and incorrect model discretization
compared to the scale of the processes (Miller
et al
., 2010). Steefel and co-workers (2005)
have summarized the main challenges in
reactive transport as follows:
•
treatment of chemical microenviron-
ments and assessment of how they af-
fect the bulk geochemistry, including
C-N dynamics;
•
treatment of flow, chemistry and mech-
anical deformation of the matrix in a
unified way;
•
resolving the discrepancies between la-
boratory and field reaction rates; and
•
upscaling reactive transport processes.
Modelling of Soil Hydrology and
Coupled C-N Biogeochemical
Transport Across Scales
Strategies for Merging Scales and
Concepts to Advance Hydrologic and
C-N Reactive Transport
Reactive transport modelling has been used
as a way to gain better understanding of the
coupled biogeochemical process in soils
and groundwaters (Regnier
et al
., 2003) for
the past two decades. Several recent articles
are available that review the current state of
the art of reactive transport modelling in
fractured rock, investigating the design of
nuclear depository facility (MacQuarrie and
Mayer, 2005), contaminant transport in ground-
waters (Steefel
et al
., 2005), tracer and pesti-
cide transport in structure soils (Kohne
et al
.,
2009a,b) and organic matter and soil struc-
ture dynamics (Nikolaidis and Bidoglio, 2013).
Even though significant advancement
has been made, further improvement in our
understanding of reactive transport model-
ling will require addressing the following
A wide range of modelling strategies exists
for biogeochemical modelling with a range
of scales, processes, mechanisms and states.
These approaches range from bottom-up
approaches, where plot-scale studies use
intensive monitoring and detailed local
modelling to improve our understanding of
process-level biogeochemical cycles for C
and N, to regional- and continental-scale
approaches to simulating the C-N dynamics
in atmospheric models that by necessity
may neglect the details of processes under-
standing obtained in the plot-scale research.
Ecosystem approaches extend the plot-scale
models for C-N and water to landscape
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