53 research outputs found
A framework for modelling soil structure dynamics induced by biological activity
Acknowledgments: This work was funded by the Swedish Research Council for Sustainable Development (FORMAS) in the project âSoil structure and soil degradation: improved model tools to meet sustainable development goals under climate and land use changeâ (grant no. 2018-02319). We would also like to thank Mikael Sasha Dooha for carrying out the measurements for the water retention curves shown in figure 4.Peer reviewedPublisher PD
Relations between macropore network characteristics and the degree of preferential solute transport
The characteristics of the soil macropore network determine the potential for
fast transport of agrochemicals and contaminants through the soil. The
objective of this study was to examine the relationships between macropore
network characteristics, hydraulic properties and state variables and
measures of preferential transport. Experiments were carried out under
near-saturated conditions on undisturbed columns sampled from four
agricultural topsoils of contrasting texture and structure. Macropore network
characteristics were computed from 3-D X-ray tomography images of
the soil pore system. Non-reactive solute transport experiments were carried
out at five steady-state water flow rates from 2 to 12 mm h<sup>â1</sup>. The
degree of preferential transport was evaluated by the normalised 5%
solute arrival time and the apparent dispersivity calculated from the
resulting breakthrough curves. Near-saturated hydraulic conductivities were
measured on the same samples using a tension disc infiltrometer placed on top
of the columns. Results showed that many of the macropore network
characteristics were inter-correlated. For example, large macroporosities
were associated with larger specific macropore surface areas and better local
connectivity of the macropore network. Generally, an increased flow rate
resulted in earlier solute breakthrough and a shifting of the arrival of peak
concentration towards smaller drained volumes. Columns with smaller
macroporosities, poorer local connectivity of the macropore network and
smaller near-saturated hydraulic conductivities exhibited a greater degree of
preferential transport. This can be explained by the fact that, with only two
exceptions, global (i.e. sample scale) continuity of the macropore network
was still preserved at low macroporosities. Thus, for any given flow rate,
pores of larger diameter were actively conducting solute in soils of smaller
near-saturated hydraulic conductivity. This was associated with larger local
transport velocities and, hence, less time for equilibration between the
macropores and the surrounding matrix which made the transport more
preferential. Conversely, the large specific macropore surface area and
well-connected macropore networks associated with columns with large
macroporosities limit the degree of preferential transport because they
increase the diffusive flux between macropores and the soil matrix and they
increase the near-saturated hydraulic conductivity. The normalised 5%
arrival times were most strongly correlated with the estimated hydraulic
state variables (e.g. with the degree of saturation in the macropores
<i>R</i><sup>2</sup> = 0.589), since these combine into one measure the effects of
irrigation rate and the near-saturated hydraulic conductivity function, which
in turn implicitly depends on the volume, size distribution, global
continuity, local connectivity and tortuosity of the macropore network
Modelling pesticide leaching under climate change : parameter vs. climate input uncertainty
Assessing climate change impacts on pesticide leaching requires careful consideration of different sources of uncertainty. We investigated the uncertainty related to climate scenario input and its importance relative to parameter uncertainty of the pesticide leaching model. The pesticide fate model MACRO was calibrated against a comprehensive one-year field data set for a well-structured clay soil in southwestern Sweden. We obtained an ensemble of 56 acceptable parameter sets that represented the parameter uncertainty. Nine different climate model projections of the regional climate model RCA3 were available as driven by different combinations of global climate models (GCM), greenhouse gas emission scenarios and initial states of the GCM. The future time series of weather data used to drive the MACRO model were generated by scaling a reference climate data set (1970-1999) for an important agricultural production area in south-western Sweden based on monthly change factors for 2070-2099. 30 yr simulations were performed for different combinations of pesticide properties and application seasons. Our analysis showed that both the magnitude and the direction of predicted change in pesticide leaching from present to future depended strongly on the particular climate scenario. The effect of parameter uncertainty was of major importance for simulating absolute pesticide losses, whereas the climate uncertainty was relatively more important for predictions of changes of pesticide losses from present to future. The climate uncertainty should be accounted for by applying an ensemble of different climate scenarios. The aggregated ensemble prediction based on both acceptable parameterizations and different climate scenarios has the potential to provide robust probabilistic estimates of future pesticide losses
Functional test of pedotransfer functions to predict water flow and solute transport with the dual-permeability model MACRO
Estimating pesticide leaching risks at the regional scale requires the ability to completely parameterise a pesticide fate model using only survey data, such as soil and land-use maps. Such parameterisations usually rely on a set of lookup tables and (pedo)transfer functions, relating elementary soil and site properties to model parameters. The aim of this paper is to describe and test a complete set of parameter estimation algorithms developed for the pesticide fate model MACRO, which accounts for preferential flow in soil macropores. We used tracer monitoring data from 16 lysimeter studies, carried out in three European countries, to evaluate the ability of MACRO and this "blind parameterisation" scheme to reproduce measured solute leaching at the base of each lysimeter. We focused on the prediction of early tracer breakthrough due to preferential flow, because this is critical for pesticide leaching. We then calibrated a selected number of parameters in order to assess to what extent the prediction of water and solute leaching could be improved. <br><br> Our results show that water flow was generally reasonably well predicted (median model efficiency, ME, of 0.42). Although the general pattern of solute leaching was reproduced well by the model, the overall model efficiency was low (median ME = â0.26) due to errors in the timing and magnitude of some peaks. Preferential solute leaching at early pore volumes was also systematically underestimated. Nonetheless, the ranking of soils according to solute loads at early pore volumes was reasonably well estimated (concordance correlation coefficient, CCC, between 0.54 and 0.72). Moreover, we also found that ignoring macropore flow leads to a significant deterioration in the ability of the model to reproduce the observed leaching pattern, and especially the early breakthrough in some soils. Finally, the calibration procedure showed that improving the estimation of solute transport parameters is probably more important than the estimation of water flow parameters. Overall, the results are encouraging for the use of this modelling set-up to estimate pesticide leaching risks at the regional-scale, especially where the objective is to identify vulnerable soils and "source" areas of contamination
Forcing MACRO pesticides fate model with STICS crop model to simulate pesticides flows in innovative cropping systems
Forcing MACRO pesticides fate model with STICS crop model to simulate pesticides flows in innovative cropping systems. XV Symposium in Pesticide Chemistry âEnvironmental risk assessment and managemen
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