Analysing nitrate losses from an artificially drained lowland catchment (North-Eastern Germany) with a mixing model
Introduction
Tile drainage is a common agricultural practice which is used to improve moisture and aeration conditions especially in lowland areas, but shortens the residence time of water in the soil and therefore aggravates diffuse pollution of adjacent surface water bodies with nutrients and pesticides (e.g. David et al., 1997, Heppell and Chapman, 2006, Tomer et al., 2003). For example, Behrendt and Bachor (1998) estimated that 47% of the nitrogen and 12% of the phosphorus emissions from the federal state Mecklenburg-Vorpommern (North-Eastern Germany) to the Baltic Sea originated from tile drainage.
However, given that the area contributing to the tile drain discharge can be defined and an impermeable layer underlies the tile drains, tile-drained fields can be considered as large lysimeters and are therefore ideal for the quantification of solute transport at the plot and field scale (Lennartz et al., 1999, Richard and Steenhuis, 1988). Numerous investigations (e.g. Heppell and Chapman, 2006, Kohler et al., 2003, Lennartz et al., 1999, Stamm et al., 1998) on tile drainage have been conducted at the field scale, from where the diffuse pollution originates. However, there are only a few catchment scale studies on this subject (Tomer et al., 2003) although this is frequently the relevant management scale, as, for example, for the European Water Framework Directive (European Parliament and European Council, 2000). To assess the environmental impacts of tile drainage on surface water bodies, it is therefore a matter of particular interest how the tile drain discharge and its solute signal translate from the field to higher scales.
Frequently, tile drainage is accompanied by flow anomalies causing a further acceleration of water and solute fluxes (Kohler et al., 2003, Lennartz et al., 1999). This combination of tile drainage and preferential flow may therefore create a ‘short circuit’ between contaminated topsoils and receiving water bodies (Laubel et al., 1999, Stamm et al., 1998). In catchment hydrology, hydrograph separation is carried out to split the total streamflow into a baseflow component and a surface runoff component. When transferring hydrograph separation methods to tile drain discharge data, it is generally assumed that the fast component originates from ‘preferential flow’ (Everts and Kanwar, 1990, Richard and Steenhuis, 1988), from ‘event water’ (Heppell and Chapman, 2006) or, more generally, from a ‘rapid flow component’ (Laubel et al., 1999), while the baseflow is thought to correspond to matrix flow. To our knowledge, only manual linear baseflow separation methods (Laubel et al., 1999), often combined with mixing models (Everts and Kanwar, 1990, Kohler et al., 2003, Richard and Steenhuis, 1988), have been applied for tile drain discharge data so far. For larger catchments, in contrast, automated methods are widespread (e.g. Arnold et al., 1995, Müller et al., 2003), which also do not have a real physical basis, but have a better reproducibility and are more objective than manual methods (Chapman, 1999, Müller et al., 2003). Another approach to split the hydrograph into different components or origins is the use of isotopic and tracer data for mixing models (Heppell and Chapman, 2006, Joerin et al., 2002, Ladouche et al., 2001, Uhlenbrook and Hoeg, 2003). A simple, yet frequently used method is the end-member mixing approach (EMMA, Hooper et al., 1990), which assumes that the solute concentrations in a stream are the result of the mixing of two or more constant sources (‘end members’) (e.g. Durand and Torres, 1996, Soulsby et al., 2003, Wade et al., 1999).
In this paper, we aim to quantify the role of different flow components and flow paths for the NO3-N losses at the different spatial scales using data of a hierarchical monitoring program. This program was set up in an agriculturally dominated lowland area in North-Eastern Germany, and high nutrient concentrations have been measured at a collector drain outlet, in ditches and in a brook (Tiemeyer et al., 2006). For this purpose, we utilise the automated hydrograph separation method ‘recursive digital filter’ (Nathan and McMahon, 1990) in combination with a simple two-component mixing model.
Section snippets
The field site ‘Dummerstorf’
The experimental field site ‘Dummerstorf’ (Fig. 1) in the federal state Mecklenburg-Vorpommern is located around 10 km southeast of the city of Rostock in a pleistocene lowland landscape (latitude 54°01′N, longitude 12°13′E). A hierarchical measurement program was initiated in November 2003 in the rural catchment of the brook Zarnow. Long-term mean annual precipitation, potential (reference crop) evapotranspiration and temperature are 665 mm, 490 mm and 8.2 °C, respectively. Due to a precipitation
Sensitivity analysis
Fig. 2 shows some examples of the sensitivity analysis: the baseflow concentration c-NO3-Nbase,II of the ditch in 2003 (Fig. 2a), the fast flow concentration c-NO3-Nfast,I of the collector drain in 2005 (Fig. 2b), the proportion Adrained,III of tile-drained fields in the brook catchment (Fig. 2c) and the recursive digital filter parameter β (Fig. 2d).
For c-NO3-Nbase,II, no clear distinction between the behavioural and non-behavioural model runs can be detected (Fig. 2a). Neither for the other
Conclusions
To quantify the role of the different flow components and flow paths for the NO3-N concentrations and losses at different scales, we utilised results from the automatic hydrograph separation method ‘recursive digital filter’ in combination with a stochastic two-component mixing model at the three spatial scales collector drain, ditch and brook. The application of a regional sensitivity analysis showed that most of the model parameters can be classified as ‘sensitive’. All in all, the modelling
Acknowledgements
We thank M. Kietzmann for the extensive chemical analysis and T. Hartwig for his assistance with the field work. The funding of B. Tiemeyer by the Landesgraduiertenförderung Mecklenburg-Vorpommern is gratefully acknowledged. Furthermore, we would like to thank three anonymous reviewers for their efforts and helpful comments.
References (48)
- et al.
Automated base flow separation and recession analysis techniques
Ground Water
(1995) - et al.
Point and diffuse load of nutrients to the Baltic Sea by river basins of North East Germany (Mecklenburg-Vorpommern)
Water Sci. Technol.
(1998) Changing ideas in hydrology—the case of physically-based models
J. Hydrol.
(1989)Rainfall-Runoff Modelling—The Primer
(2001)A manifesto for the equifinality thesis
J. Hydrol.
(2006)- et al.
The future of distributed models: model calibration and uncertainty prediction
Hydrol. Processes
(1992) - et al.
Comparison of infiltration models to simulate flood events at the field scale
J. Hydrol.
(2005) A comparison of algorithms for stream recession and baseflow separation
Hydrol. Processes
(1999)- et al.
The movement of nitrate fertiliser from the soil surface to drainage waters by preferential flow in weakly structured soils, Slapton, S. Devon
Agric. Ecosyst. Environ.
(1985) - et al.
Nitrogen balance in and export from an agricultural watershed
J. Environ. Qual.
(1997)
Solute transfer in agricultural catchments: the interest and limits of mixing models
J. Hydrol.
Estimating preferential flow to a subsurface drain with tracers
Trans. ASAE
Nutrient transfer from soil to surface waters: differences between nitrate and phosphate
Aquat. Sci.
Analysis of a two-component hydrograph separation model to predict herbicide runoff in drained soils
Agric. Water Manage.
Chemistry of subsurface drain discharge from an agricultural polder soil
Agric. Water Manage.
Modelling stream water chemistry as a mixture of soil water end members: an application to the Panola Mountain catchment, Georgia, USA
J. Hydrol.
Uncertainty in hydrograph separation based on geochemical mixing models
J. Hydrol.
Untersuchungen zum Stickstoffaustrag über Dränung in einem nordostdeutschen Tieflandeinzugsgebiet
WasserWirtschaft
Using simple bucket models to analyse solute export to subsurface drains by preferential flow
Vadose Zone J.
Hydrograph separation using isotopic, chemical and hydrological approaches (Strengbach catchment, France)
J. Hydrol.
Subsurface drainage loss of particles and phosphorus from field plot experiments and a tile-drained catchment
J. Environ. Qual.
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2018, Agricultural Water ManagementCitation Excerpt :This coherence implies that whenever nitrate concentrations are high, part of the contaminated groundwater is discharged directly to the ditch via the tile drains, thus bypassing the buffer strip. The higher nitrate concentrations observed in the tile-drain compared with the ditch at the study site (Tiemeyer et al., 2008) are the consequence. A long-term accumulation of nitrogen in the study site’s soil, which is available for leaching, is indicated by the field nitrogen balance (Tiemeyer et al., 2006).