the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Jun 2025
Identification of erosion hotspots and scale-dependent runoff controls on sediment transport in an agricultural catchment
Abstract. Understanding how agricultural land management influences sediment transport is crucial for identifying critical source areas (CSAs) and improving erosion mitigation strategies. While numerous studies focus on in-stream sediment concentrations, fewer investigate overland flow on the hillslopes. We monitored streamflow and sediment fluxes at an overland flow station (E2) and an in-stream station (MW) across 55 runoff events (2011–2022) in the Hydrological Open Air Laboratory (HOAL), Austria. The catchment was segmented into four distinct areas (A, B, GW9, C) based on topography, hydrological connectivity, and proximity to the stream, allowing a spatially explicit assessment of erosion hotspots. Temporal patterns of sediment transport were analysed to infer spatial variability, and differences in sediment transport dynamics among areas were quantified using Kruskal-Wallis tests and effect size analysis. Results suggest that at E2 (hillslope scale), non-erosive cultivation significantly reduced peak turbidity (~9.5 times) and sediment load (~3.8 times) in flat agricultural areas (7.2 % slope, <500 m from the stream) but had no measurable effect in steep (10–12 % slope) or distant (>1000 m) agricultural areas. Across all field types, conversion to non-erosive cultivation did not affect peak flow. At MW (catchment scale), compared to E2, peak turbidity at MW decreased (~5.4–7.7 times) due to dilution from subsurface flow contributions, while peak flow increased (~2.8–11 times) due to additional inputs from wetlands, springs, and subsurface flows. Sediment load at MW was ~2.4–5.4 times higher than at E2, likely due to unmonitored diffuse overland flow and sediment inputs from tile drainages. Our findings indicate that non-erosive cultivation alone in steep terrains or distant agricultural areas is insufficient to effectively mitigate sediment transport. Effective sediment management in agricultural catchments requires spatially targeted erosion control strategies that account for topography, hydrological connectivity, and field proximity to streams.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Hydrology and Earth System Sciences. The authors also have no other competing interests to declare.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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RC1: 'Comment on egusphere-2025-2541', Anonymous Referee #1, 24 Jul 2025
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General comments
The manuscript presents an experimental analysis of the factor contributing to runoff, erosion and sediment load, at the small (66 ha) headwater catchment scale. The results suggest that considering both catchment structural connectivity and crop type (erosive vs non-erosive) is needed to assess the effect of management pratices on sediment load and peak flow.
The assessment of sediment source and field-to-stream connectivity at the catchment scale is a current research question. The additional effects of agricultural conservation practices on water and sediment dynamics at the catchment scale is an additional interesting and relevant scientific question. The studied catchment presents a high-quality database of traditional hydrological gauging stations, including high-frequency rainfall, runoff, streamflow and tile drainage monitoring of water and sediment load.
However, the manuscript presents major issues that preclude publication.
First, calculations are hard or not possible to understand. Particularly, the assessment of sediment load values, a central point in this study, is unclear. Was the turbidity-sediment concentration rating curve of good quality? How was noise on turbidimeter values processed? The authors alternatively used turbidity and sediment load values in the analysis, but what is the point in analysing turbidity if sediment load values were available? Evaluating the robustness of the results is therefore not possible.
The methodology used for analysis is unclear. From my understanding, the authors chose to focus on peak values for flow and sediment/turbidity, which is surprising. To analyse the catchment dynamics, why not study the event-scale water volume and sediment load? How did the authors account for hysteresis effects? How was the noise on turbidity values processed? Both may have significant implications for the robustness of the results, particularly considering the significant scattering presented in the log-log plots (Figure 4).
The land use classification, which serves as a basis for analysis, is questionable. Defining winter wheat and winter barley as ‘non-erosive’ crops would require a strong justification, particularly in a study addressing the runoff event scale. What about the intra-annual variations of crops growing and agricultural practices, e.g. storm event occurring on ploughed fields vs crusted fields? It is questionable to propose general results such as those proposed in this manuscript without combining the analysis of both soil surface and rainfall dynamics.
Moreover, it is unclear how the authors labelled the different areas (A, B, C, GW9) as ‘erosive’ or ‘non-erosive’ (e.g. in Table 2 and 4), considering that these areas included a mix of erosive and non-erosive crops (e.g. Area A in Figure 2). It is therefore not possible to assess if the main results are supported by the data.
Last, the main message of the manuscript, as indicated in the abstract and conclusion, i.e. the need to consider both cultivation practices and catchment connectivity, lacks novelty, particularly considering that only part of the catchment structural connectivity was considered in the analysis.
As a conclusion, given the lack of novelty, the unclear analysis procedure, and the inability to assess whether the results support the claims presented, I would not recommend publication in HESS.
Specific comments
The title is misleading: ‘identifying erosion hotspots’ would require dedicated studies using e.g. sediment tracing and/or distributed modelling.
Figure 2 is hardly readable, please consider bringing monitoring stations to the foreground and / or to increase dots size. It may help readers to use intuitive names for the monitoring stations over the manuscript, i.e. what is the difference between ‘Sys’ and ‘Frau’? Would it be relevant to change these names for TD (Tile Drain) and other monitoring stations for e.g. S (Streamflow), R (Runoff)… ?
It is misleading to provides Pearson’s r on a scatterplot including regression lines. It is suggested to add correlation coefficients to the correlation matrices, and to indicate determination coefficients in the figures.
Table 3: It is surprising that the peak flow is not significantly affected by tile drainage. Literature underlines the importance of tile drainage in modulating peak flow.
l.493-497: It is not clear how a correlation coefficient can be used to deduce that ‘rainfall erosivity exerts a dominant control over hydrological and sediment transport mechanisms’. It is also surprising that the correlation between EI30 and the sediment dynamics is better at the catchment scale than at the plot scale, while increasing scale should results in a higher complexity.
Citation: https://doi.org/10.5194/egusphere-2025-2541-RC1 -
AC1: 'Reply on RC1', Christopher Thoma, 31 Jul 2025
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The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-2541/egusphere-2025-2541-AC1-supplement.pdf
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AC1: 'Reply on RC1', Christopher Thoma, 31 Jul 2025
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