Model-based estimation of pesticides and transformation products and their export pathways in a headwater catchment

Abstract. Pesticides applied onto agricultural fields are frequently found in adjacent rivers. To what extent and along which pathways they are transported is influenced by intrinsic pesticide properties such as sorption and degradation. In the environment, incomplete degradation of pesticides leads to the formation of transformation products (TPs), which may differ from the parent compounds regarding their intrinsic fate characteristics. Thus, the export processes of TPs in catchments and streams may also be different. In order to test this hypothesis, we extended a distributed hydrological model by the fate and behaviour of pesticides and transformation products and applied it to a small, well-monitored headwater catchment in Switzerland. The successful model evaluation of three pesticides and their TPs at three sampling locations in the catchment enabled us to estimate the quantity of contributing processes for pollutant export. Since all TPs were more mobile than their parent compounds (PCs), they exhibited larger fractions of export via subsurface pathways. However, besides freshly applied pesticides, subsurface export was found to be influenced by residues of former applications. Export along preferential flow pathways was less dependent on substance fate characteristics than soil matrix export, but total soil water flow to tile drains increased more due to preferential flow for stronger sorbing substances. Our results indicate that runoff generation by matrix flow to tile drains gained importance towards the end of the modelling period whereas the contributions from fast surface runoff and preferential flow decreased. Accordingly, TPs were to a large extent exported under different hydrological conditions than their PCs, due to their delayed formation and longer half-lives. Thus, not only their different intrinsic characteristics but also their delayed formation could be responsible for the fact that TPs generally took different pathways than their PCs. We suggest that these results should be considered in risk assessment for the export of agricultural chemicals to adjacent rivers and that models should be extended to include both PCs and TPs.

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Phosphorus fractions in preferential flow pathways and soil matrix in hillslope soils in the Thuringian Forest (Central Germany)

Journal of Plant Nutrition and Soil Science ◽

10.1002/jpln.201600305 ◽

2017 ◽

Vol 180 (3) ◽

pp. 407-417 ◽

Cited By ~ 11

Author(s):

Dorit Julich ◽

Stefan Julich ◽

Karl-Heinz Feger

Keyword(s):

Preferential Flow ◽

Phosphorus Fractions ◽

Soil Matrix ◽

Central Germany ◽

Flow Pathways ◽

Preferential Flow Pathways

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Quantifying the Importance of Preferential Flow in a Riparian Buffer

Transactions of the ASABE ◽

10.13031/trans.14286 ◽

2021 ◽

Vol 64 (3) ◽

pp. 937-947

Author(s):

Lucie Guertault ◽

Garey A. Fox ◽

Todd Halihan ◽

Rafael Muñoz-Carpena

Keyword(s):

Preferential Flow ◽

Riparian Buffers ◽

Riparian Buffer ◽

Design Tools ◽

Soil Matrix ◽

Innovative Method ◽

Matrix Flow ◽

Buffer Design ◽

Flow Pathways ◽

Preferential Flow Pathways

HighlightsRiparian buffers and vegetative filter strips are uniquely susceptible to preferential flow.An innovative method is proposed to partition infiltration into matrix and macropore domains.Riparian buffer matrix and plot-scale infiltration experiments were simulated with HYDRUS-1D and VFSMOD.Preferential flow accounted for 32% to 47% of infiltration depending on hydrologic conditions.Preferential flow mechanisms should be incorporated into riparian buffer design tools and models.Abstract. Riparian buffers are uniquely susceptible to preferential flow due to the abundance of root channels, biological activity, and frequent wetting and drying cycles. Previous research has indicated such susceptibility and even measured the connectivity of preferential flow pathways with adjacent streams and rivers. However, limited research has attempted to partition the riparian buffer infiltration between matrix and preferential flow domains. The objectives of this research were to develop an innovative method to quantify soil matrix infiltration at the plot scale, develop a method to partition infiltration into matrix and macropore infiltration at the plot scale, and then use these methods to quantify the significance of macropore infiltration at a riparian buffer site. This research further demonstrated the importance of considering preferential flow processes in design tools and models to evaluate riparian buffer effectiveness. Sprinkler and runon field experiments were conducted at an established riparian buffer site with sandy loam soil. Trenches were installed and instrumented with soil moisture sensors along the width of the riparian buffer (i.e., along the flow path toward the stream) for detecting non-uniform flow patterns due to preferential flow. Riparian buffer parameters, including soil hydraulic parameters, were estimated using HYDRUS-1D for the sprinkler experiments and VFSMOD for the runon experiments. This research partitioned the infiltration into matrix and preferential flow domains by assuming negligible exchange of water between the soil matrix and preferential flow pathways in comparison to the magnitude of soil matrix flow. For these experimental conditions with 0.20 to 0.48 L s-1 of runon and initial soil water contents of 0.29 to 0.32 cm3 cm-3, preferential flow accounted for at least 27% to 32% of the total runon water entering the riparian buffer. This corresponded to approximately 32% to 47% of the total infiltration. While increasing the riparian buffer plot soil hydraulic conductivity in single-porosity models can adequately predict the total infiltration and therefore the surface outflow from the buffer, design tools and models should specifically consider preferential flow processes to improve predictive power regarding the actual infiltration processes and correspondingly the non-equilibrium flow and solute transport mechanisms. Keywords: Flow partitioning, HYDRUS, Matrix flow, Preferential flow, Riparian buffer, VFSMOD.

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Field method for separating the contribution of surface-connected preferential flow pathways from flow through the soil matrix

Water Resources Research ◽

10.1029/2011wr011103 ◽

2012 ◽

Vol 48 (4) ◽

Cited By ~ 15

Author(s):

Emily C. Sanders ◽

Majdi R. Abou Najm ◽

Rabi H. Mohtar ◽

Eileen Kladivko ◽

Darrell Schulze

Keyword(s):

Preferential Flow ◽

Field Method ◽

Soil Matrix ◽

Flow Through ◽

Flow Pathways ◽

Preferential Flow Pathways

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Leaching of dissolved and particulate phosphorus via preferential flow pathways in a forest soil: An approach using zero-tension lysimeters

Journal of Plant Nutrition and Soil Science ◽

10.1002/jpln.201900216 ◽

2020 ◽

Vol 183 (2) ◽

pp. 238-247 ◽

Cited By ~ 2

Author(s):

Vera Makowski ◽

Stefan Julich ◽

Karl-Heinz Feger ◽

Lutz Breuer ◽

Dorit Julich

Keyword(s):

Forest Soil ◽

Preferential Flow ◽

Particulate Phosphorus ◽

Flow Pathways ◽

Preferential Flow Pathways

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Effects of preferential flow on snowmelt partitioning and groundwater recharge in frozen soils

Hydrology and Earth System Sciences ◽

10.5194/hess-23-5017-2019 ◽

2019 ◽

Vol 23 (12) ◽

pp. 5017-5031 ◽

Cited By ~ 4

Author(s):

Aaron A. Mohammed ◽

Igor Pavlovskii ◽

Edwin E. Cey ◽

Masaki Hayashi

Keyword(s):

Soil Moisture ◽

Groundwater Recharge ◽

Preferential Flow ◽

Frozen Soil ◽

Time Lags ◽

Runoff Generation ◽

Frozen Ground ◽

Soil Matrix ◽

Frozen Soils ◽

Flow Through

Abstract. Snowmelt is a major source of groundwater recharge in cold regions. Throughout many landscapes snowmelt occurs when the ground is still frozen; thus frozen soil processes play an important role in snowmelt routing, and, by extension, the timing and magnitude of recharge. This study investigated the vadose zone dynamics governing snowmelt infiltration and groundwater recharge at three grassland sites in the Canadian Prairies over the winter and spring of 2017. The region is characterized by numerous topographic depressions where the ponding of snowmelt runoff results in focused infiltration and recharge. Water balance estimates showed infiltration was the dominant sink (35 %–85 %) of snowmelt under uplands (i.e. areas outside of depressions), even when the ground was frozen, with soil moisture responses indicating flow through the frozen layer. The refreezing of infiltrated meltwater during winter melt events enhanced runoff generation in subsequent melt events. At one site, time lags of up to 3 d between snow cover depletion on uplands and ponding in depressions demonstrated the role of a shallow subsurface transmission pathway or interflow through frozen soil in routing snowmelt from uplands to depressions. At all sites, depression-focused infiltration and recharge began before complete ground thaw and a significant portion (45 %–100 %) occurred while the ground was partially frozen. Relatively rapid infiltration rates and non-sequential soil moisture and groundwater responses, observed prior to ground thaw, indicated preferential flow through frozen soils. The preferential flow dynamics are attributed to macropore networks within the grassland soils, which allow infiltrated meltwater to bypass portions of the frozen soil matrix and facilitate both the lateral transport of meltwater between topographic positions and groundwater recharge through frozen ground. Both of these flow paths may facilitate preferential mass transport to groundwater.

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Dye staining and excavation of a lateral preferential flow network

Hydrology and Earth System Sciences ◽

10.5194/hess-13-935-2009 ◽

2009 ◽

Vol 13 (6) ◽

pp. 935-944 ◽

Cited By ~ 77

Author(s):

A. E. Anderson ◽

M. Weiler ◽

Y. Alila ◽

R. O. Hudson

Keyword(s):

Slope Stability ◽

Solute Transport ◽

Preferential Flow ◽

Runoff Generation ◽

Flow Paths ◽

Soil Matrix ◽

Preferential Flow Paths ◽

Dye Staining ◽

Hillslope Scale ◽

Surrounding Soil

Abstract. Preferential flow paths have been found to be important for runoff generation, solute transport, and slope stability in many areas around the world. Although many studies have identified the particular characteristics of individual features and measured the runoff generation and solute transport within hillslopes, very few studies have determined how individual features are hydraulically connected at a hillslope scale. In this study, we used dye staining and excavation to determine the morphology and spatial pattern of a preferential flow network over a large scale (30 m). We explore the feasibility of extending small-scale dye staining techniques to the hillslope scale. We determine the lateral preferential flow paths that are active during the steady-state flow conditions and their interaction with the surrounding soil matrix. We also calculate the velocities of the flow through each cross-section of the hillslope and compare them to hillslope scale applied tracer measurements. Finally, we investigate the relationship between the contributing area and the characteristics of the preferential flow paths. The experiment revealed that larger contributing areas coincided with highly developed and hydraulically connected preferential flow paths that had flow with little interaction with the surrounding soil matrix. We found evidence of subsurface erosion and deposition of soil and organic material laterally and vertically within the soil. These results are important because they add to the understanding of the runoff generation, solute transport, and slope stability of preferential flow-dominated hillslopes.

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