HS2.3.1 | Understanding the mechanisms of solute and particulate exports from catchments and options for minimizing agricultural impacts on water quality
EDI
Understanding the mechanisms of solute and particulate exports from catchments and options for minimizing agricultural impacts on water quality
Convener: Andreas Musolff | Co-conveners: Inge van Driezum, Carolin Winter, Daniel Graeber, Brian Kronvang, Camille Vautier
Orals
| Fri, 19 Apr, 08:30–12:30 (CEST)
 
Room 2.44
Posters on site
| Attendance Fri, 19 Apr, 16:15–18:00 (CEST) | Display Fri, 19 Apr, 14:00–18:00
 
Hall A
Orals |
Fri, 08:30
Fri, 16:15
Anthropogenic activities like agriculture and wastewater discharge have resulted in the degradation of groundwater and surface water quality with severe implications for both human and environmental health. There is an urgent need to mitigate these impacts on water quality crucial for maintaining the ecological, recreational, and industrial functions of water resources.
Water quality is typically monitored and assessed at the catchment scale. Understanding the underlying processes and causal relationships remains challenging due to the complex interplay of hydrologic, biogeochemical, and temporal factors. This large scale of monitoring does not always match the scale of mitigation measures to minimize anthropogenic impact on water quality.
Data-driven statistical analysis of discharge and concentration time series at catchment outlets offers valuable insights into the scaling of processes and the effectiveness of measures. Long-term, high-frequency, and multi-site data sets can inform experimental and modeling studies, enabling us to move from patterns to processes and gain a deeper understanding of solute and particulate mobilization, retention, and export mechanisms.
This session brings together contributions on the assessment of mitigation measures, analysis of solute and particulate export dynamics, and catchment modeling to optimize mitigation placement.

Orals: Fri, 19 Apr | Room 2.44

Chairpersons: Andreas Musolff, Carolin Winter, Camille Vautier
08:30–08:35
08:35–08:55
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EGU24-13731
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solicited
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Highlight
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On-site presentation
Kimberly Van Meter, Nandita Basu, and Danyka Byrnes

Excess nitrogen from intensive agricultural production, atmospheric N deposition, and urban point sources elevates stream nitrate concentrations, leading to problems of eutrophication and ecosystem degradation in coastal waters. A major emphasis of current US-scale analysis of water quality is to better our understanding of the relationship between changes in anthropogenic N inputs within watersheds and subsequent changes in riverine N loads. While most water quality modeling assumes a positive linear correlation between watershed N inputs and riverine N, many efforts to reduce riverine N through improved nutrient management practices result in little or no short-term improvements in water quality. Here, we use nitrate concentration and load data from 478 US watersheds, along with developed N input trajectories for these watersheds, to quantify time-varying relationships between N inputs and riverine N export. Our results show substantial variations in watershed N import-export relationships over time, with quantifiable hysteresis effects. Our results show that more population-dense urban watersheds in the northeastern U.S. more frequently show clockwise hysteresis relationships between N imports and riverine N export, with accelerated improvements in water quality being achieved through the implementation of point-source controls. In contrast, counterclockwise hysteresis dynamics are more common in agricultural watersheds, where time lags occur between the implementation of nutrient management practices and water-quality improvements. Finally, we find higher tile-drainage densities to be associated with more linear relationships between N inputs and riverine N. The empirical analysis in this study is bolstered by modeled simulations to reproduce and further explain drivers behind the hysteretic relationships commonly observed in the monitored watersheds.

How to cite: Van Meter, K., Basu, N., and Byrnes, D.: Memory and Management: Competing Controls on Long-Term Nitrate Trajectories in U.S. Rivers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13731, https://doi.org/10.5194/egusphere-egu24-13731, 2024.

08:55–09:05
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EGU24-9538
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On-site presentation
Jens Kiesel, Tobias Houska, Janosch Müller-Hillebrand, and Nicola Fohrer

High-frequency observations of solute and particulate concentrations (C) and associated discharge (Q) measurements allow the analysis of C-Q relationships on the event-scale. Together with catchment attributes and event properties, C-Q relationships can be used to disentangle the fine-grained dependencies between catchment properties, hydrologic processes and water quality.

We collected 72 high-frequency (sub-hourly), continuous C and Q time series across Germany in catchments ranging from 8 to 122.000km² (median of 6.051km²). Besides discharge at all 72 locations, the database contains water temperature (60 locations), turbidity (34), conductivity (59), oxygen (57), pH (53), ammonia (16), nitrate (22), phosphate (10) and chlorophyll (12) in varying lengths over a maximum period of 20 years. Event filters were used to extract single discharge events. Hysteresis indices and classes of each event were used to describe the C-Q relationships. Event properties such as season, magnitude, variability, length, antecedent conditions, rise- and fall characteristics and physical catchment characteristics were assigned to each C-Q relationship.

We used a Random Forest model to explain the hysteresis properties based on the event- and catchment characteristics. Particularly the variables turbidity and conductivity revealed spatio-temporal dependencies, which we relate to interplays of land use and soil characteristics. We further found that the C-Q patterns are significantly impacted by the identifiability and definition of the extracted discharge events across the heterogeneous catchments as well as the resolution and quality of the measurements of the different C variables.

How to cite: Kiesel, J., Houska, T., Müller-Hillebrand, J., and Fohrer, N.: German-wide analysis of high-frequency, continuous concentration-discharge relationships, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9538, https://doi.org/10.5194/egusphere-egu24-9538, 2024.

09:05–09:15
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EGU24-10390
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On-site presentation
Tobias Houska, Ingo Müller, Klaus Kaiser, Klaus-Holger Knorr, Maximilian Lau, Conrad Jackisch, and Karsten Kalbitz

Peatlands are an important natural terrestrial carbon sink. Any impact on the drivers of hydro-biogeochemical processes in these ecosystems can be particularly severe. Climate change and degradation by drainage and ditching are dramatically changing peatlands. Degraded peatlands turn from effective carbon sinks to emitters. They can also threaten drinking water supplies, as (heavy) metals can leach from degraded peatlands together with dissolved organic carbon (DOC). However, quantifying DOC fluxes from terrestrial to aquatic ecosystems is challenging. The hydro-biogeochemical processes at the soil-aquatic interface are not only complex but also occur at different spatial and temporal scales. These processes depend on a variety of constantly changing external conditions such as temperature, nutrient and oxygen availability. In addition, there is no sensor that can directly measure DOC concentrations in streams in situ.

Here we investigated the DOC concentration in two nested catchments of two adjacent streams in the Ore Mountains of southern Saxony, Germany. One stream is dominated by mineral soils, the other by (degraded) peat soils. Each of the four sites is equipped with YSI-EXO fDOM sensors. Other data include discharge, water temperature, turbidity and electrical conductivity. A machine learning algorithm (Random Forest) was trained to predict DOC concentration from the available data set (validation r² between 0.85 and 0.98). The 15-minute resolution DOC data were analysed for potential driving factors. Interestingly, the area-specific loads of the peat-dominated catchment with 3.4 g C m-2 a-1 were not significantly different from those of the mineral soil-dominated catchment with 1.8 g C m-2 a-1. However, the annual loads were almost twice as high as previously determined from monthly data. With the high-resolution DOC data, we can identify periods of extreme DOC concentrations (up to 40 mg l-1) after heavy rain events in summer and constant high DOC concentrations of 20 mg l-1 during snowmelt in winter. By applying the algorithm to DOC:DON ratios, we were also able to quantify the different sources contributing to streamwater DOM with plant-derived material from peat and microbially-derived material from the mineral soil.

Previous DOC measurements, mostly based on 2-week to monthly measurements, are likely to greatly underestimate the contribution of DOC to C fluxes in ecosystems. This is particularly important for C-rich ecosystems such as peatlands.

How to cite: Houska, T., Müller, I., Kaiser, K., Knorr, K.-H., Lau, M., Jackisch, C., and Kalbitz, K.: Increasing stream water DOC concentrations in peat-affected catchments: insights from high-resolution water quality analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10390, https://doi.org/10.5194/egusphere-egu24-10390, 2024.

09:15–09:25
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EGU24-15329
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On-site presentation
Benny Selle, Anja Hortmann, Klaus-Holger Knorr, and Hjalmar Laudon

Riparian wetlands are major sources of dissolved organic carbon (DOC) to streams. Increasing DOC concentrations were observed for many northern streams during the last decades, with potential implications for carbon (C) storages of wetland soils and streamwater quality. Drivers behind these trends, and particularly the significance of redox processes in wetland soils, are still incompletely understood. In soils, organic C is often associated with or bound to iron (oxy) hydroxides. These associations of iron (Fe) and organic C may immobilise and protect soil organic matter from mineralisation under oxic conditions. However, organic C can be remobilised if ferric Fe is reduced under anoxic conditions, a process which also increases pH further enhancing DOC solubility. Redox processes are therefore presumably important drivers of DOC dynamics in both wetland soils and the adjacent streams. We hypothesised that in-stream DOC concentrations are mainly driven by redox conditions within riparian organic soils, where DOC mobilisation is controlled by reduction of DOC associated Fe. We further propose that these DOC mobilising redox processes are particularly relevant for periods of rewetting of riparian soils, e.g. in autumn. In this study, were used monitoring data following a drought experiment conducted in summer 2017 in a sub-catchment of Krycklan in northern Sweden. For the experiment, a drought was simulated for a sub-catchment in Krycklan by damming a lake outlet that feeds a small stream. For the rewetting period after the drought experiment, daily time series of discharge, DOC and Fe feeding into the manipulated stream section were calculated from data measured at the top and the bottom of the stream section. Discharge was measured by flumes. From discharge time series, baseflow feeding into the stream section was computed using a baseflow separation filter. Time series of baseflow was assumed to represent average watertable dynamics in riparian wetlands. Both Fe and DOC concentrations were obtained from absorbances measured across different wavelength using a portable ultraviolet–visible probe. Adsorbances were converted into aquatic concentrations using a partial least-squares regression model calibrated on Fe and DOC concentrations measured in the laboratory. Furthermore, concentration time series were corrected for discharge and in-stream retention (for DOC only). We found that Fe increased with increasing baseflow with a time lag of 5d indicating delayed iron reduction in riparian areas in response to elevated watertables. Dynamics of DOC were weaker related to baseflow than to Fe, but DOC was significantly correlated to Fe. From rules to obtain directed acyclic graphs it can be inferred that changing baseflow - as a proxy of watertables in riparian wetlands - caused changing discharge corrected Fe concentrations in the stream, which can be understood as a proxy of Fe concentrations in riparian wetlands. Changing Fe concentrations caused changes of computed in-stream DOC concentrations, which can be seen to represent mobilised DOC pools in riparian wetlands. It is concluded that redox driven mobilisation of DOC is a plausible process for rainfall periods in autumn, when riparian soils are rewetted after summer.

How to cite: Selle, B., Hortmann, A., Knorr, K.-H., and Laudon, H.: Redox driven mobilisation of DOC from riparian wetlands in Krycklan (N Sweden) after a drought experiment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15329, https://doi.org/10.5194/egusphere-egu24-15329, 2024.

09:25–09:35
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EGU24-2137
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Highlight
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On-site presentation
Stefano Basso and Heleen de Wit

Sustained increments of organic carbon concentrations in northern freshwaters have triggered concerns about the impacts of water browning and raised questions on the underlying mechanisms causing this phenomenon. In addition to the key role played by reduced sulfate deposition, hydrologic mechanisms have been put forward as possible concurrent causes of the observed trends of organic carbon concentrations. How the suggested hydrologic controls act is however still unclear. In this study we analyze long data series (> 30 years) of daily discharge and weekly to biweekly Total Organic Carbon (TOC) concentration for four reference acid-sensitive rivers in Norway, whose locations span the entire length of the country, to clarify hydrologic changes which may be promoting freshwater browning. In all cases we observe stable values of the slopes of double logarithmic relations between concentration and discharge, as well as a steady growth along the years of the intercepts of these relations. These joint observations enable sorting out previously proposed biogeochemical mechanisms for the observed trends of TOC concentrations (i.e., less sulfate deposition versus higher soil temperature). Decreasing ratios of concentration and discharge variability along the years, observed in all watersheds during the autumn season, point at growing stores of organic carbon produced in summer and suggest that the spatial distribution of the sources is becoming more homogeneous. In detail, analyses of the runoff frequency, which is typically higher in wetter and more hydrologically connected watersheds, suggest that sources are more homogeneously connected to streams than before. In fact, increasing trends throughout the years of the runoff frequency, as well as strong relations between runoff frequency and increasing concentrations of aquatic organic carbon, are detected in all cases. More connected sources together with more frequent runoff events, which multiply the chances for the organic carbon to reach streams, may hence contribute to the observed rise of organic carbon concentrations in northern freshwaters.

How to cite: Basso, S. and de Wit, H.: Increasing hydrologic connectivity contributes to browning of northern freshwater, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2137, https://doi.org/10.5194/egusphere-egu24-2137, 2024.

09:35–09:45
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EGU24-6339
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ECS
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On-site presentation
Celia Aranda Reina, Julien Bouchez, Jon K. Golla, Pierre-Alain Ayral, and Jennifer L. Druhan

In upland watersheds, depletion of essential nutrients due to physical erosion and chemical weathering can be compensated by exogenous inputs such as aeolian dust deposition. The presence and chemical composition of exogenous dust arriving in natural environments is commonly analyzed in soil profiles using a suite of geochemical and isotopic tracers. However, it remains an outstanding challenge to describe the impacts of dust on the reaction rates that produce these profiles and how this cascades into ecosystem function and water chemistry. As increasingly intense and episodic periods of drought and aridity are promoted by a warming climate, the role of dust production and deposition in Critical Zone structure and function requires improved modeling techniques to facilitate rigorous quantification and prediction. Here we present a newly developed process-based reactive transport framework by modifying the open source CrunchTope software in order to quantitatively interpret the impacts of dust deposition and solubilization in stream water chemistry, regolith weathering rates, and ecosystem nutrient availability. We describe two simulations: (1) a generic model demonstrating a simplified system in which bedrock uplift and soil erosion occur in tandem with solid phase dust deposition at the land surface; (2) a case study based on a small (0.54 km2) upland Mediterranean watershed located on Mont Lozère in the National Park of Les Cévennes, France. In the absence of an exogenous dust input, long-term field observations of calcium in stream water, rain, bedrock, soil, and plant samples cannot be produced from reactive transport simulations of the weathering profile. By adding a carbonate-rich depositional input consistent with the composition of Saharan dust, both stream water chemistry and elemental mass-transfer coefficients in the soil profile better align with field observations, suggesting that dust has become a significant input to this field site in the last ~10 ka. Over this period, the deposition of exogenous carbonates has introduced far more calcium into the system than what could be supplied by the Ca-poor granitic bedrock. This highly soluble carbonate also limits the reactive potential of infiltrating precipitation, ultimately inhibiting chemical weathering rates and hence the component of elemental export fluxes derived from local bedrock. This is the first demonstration of solid-phase dust deposition incorporated into a multi-component reactive transport framework. Our update to the CrunchTope source code allows us to show how dust incorporation affects geochemical cycling across upland watersheds beyond the prohibitive limitations of simplified steady-state assumptions, a feature that will allow further research of a variety of Critical Zone systems subject to the effects of environmental change scenarios. 

How to cite: Aranda Reina, C., Bouchez, J., Golla, J. K., Ayral, P.-A., and Druhan, J. L.: Quantifying the impacts of an exogenous dust input to the soil and stream chemistry of an upland Mediterranean watershed using a reactive transport modeling framework, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6339, https://doi.org/10.5194/egusphere-egu24-6339, 2024.

09:45–09:55
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EGU24-2921
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On-site presentation
Elias Getahun and Atticus Zavelle

Applying road salt to melt ice on urban roads and pavements has raised the chloride levels in streams and rivers in the U.S. over time, which can damage aquatic life. High chloride levels in the waterbodies of the Fox River watershed, where one-third of the land is urban, are mainly caused by road salt application for deicing. This study analyzed how the chloride levels changed over the years and seasons in the Fox River watershed – from Stratton Dam to Illinois River. The Seasonal Kendall Tau (SKT) method was used to estimate the annual and seasonal trends in chloride concentration at 44 monitoring sites on the Fox River and its tributaries for three time periods (2017–2021, 2012–2021, and 1997–2021), after conducting exploratory data analysis and assessing the data suitability. The chloride concentration in the watershed varied over time, space, and season. From 2012 to 2021, it declined or remained stable at most of the monitoring sites, but it rose slightly from 1997 to 2021. The 5-year trend from 2017 to 2021 was similar, except that some sites showed an increase in summer and fall. The chloride concentration along the Fox River and Tyler Creek showed a longitudinal pattern, decreasing from upstream to downstream in most seasons and periods, except for the 5-year annual and fall trends, which increased. Weighted Regression on Time Discharge and Season (WRTDS) models were developed to estimate the trends in flow-normalized chloride flux for one site on the Fox River and two sites on its tributaries with daily flow data. The resulting trends indicate that the chloride fluxes dropped significantly at the Fox River and Polar Creek sites, mainly in the winter of 2012–2021. However, the site on Blackberry Creek had an opposite trend of increasing chloride flux, except for the winter flux, which also declined. Trends in selected streamflow statistics including mean, 7-day minimum, and 1-day maximum flows were also analyzed for the three monitoring sites to provide insight into how hydrologic variability affects chloride trends. The trends in annual and seasonal flow statistics exhibited a steep slope for low flows but a gradual slope for high flows, indicating more variability in the low flow statistics during the periods of analysis. The changes in chloride concentration and flux were partly related to the changes in flow, but other factors affecting water quality, such as watershed conservation, may also play a role. Assessing trends over distinct periods provides a nuanced understanding of how mitigation strategies may influence water quality improvements through the years and serves as a crucial guide for initiatives aimed at enhancing the overall health of the Fox River ecosystem. Choosing deicing methods that balance cost, performance, and environmental impacts should be a vital part of a mitigation plan. Moreover, monitoring and evaluating trends can help assess the current status of chloride levels in the watershed and inform future actions.

How to cite: Getahun, E. and Zavelle, A.: Chloride Trends in the Fox River watershed: Stratton Dam to Illinois River , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2921, https://doi.org/10.5194/egusphere-egu24-2921, 2024.

09:55–10:05
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EGU24-3559
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ECS
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On-site presentation
Sheng Huang, Jun Xia, Yueling Wang, Gangsheng Wang, Dunxian She, and Jiarui Lei

Pollution control and environmental protection of the Yangtze River have received major attention in China. However, modeling the river’s pollution load remains challenging due to limited monitoring and unclear spatiotemporal distribution of pollution sources. Specifically, anthropogenic activities’ contribution to the pollution have been underestimated in previous research. Here, we coupled a hydrodynamic-based water quality (HWQ) model with a machine learning (ML) model, namely attention-based Gated Recurrent Unit, to decipher the daily pollution loads (i.e., chemical oxygen demand, COD; total phosphorus, TP) and their sources in the Middle-Lower Yangtze River from 2014 to 2018. The coupled HWQ-ML model outperformed the standalone ML model with KGE values ranging 0.77–0.91 for COD and 0.47–0.64 for TP, while also reducing parameter uncertainty. When examining the relative contributions at the Middle Yangtze River Hankou cross-section, we observed that the main stream and tributaries, lateral anthropogenic activities, and parameter uncertainty contributed 15%, 66%, and 19% to COD, and 58%, 35%, and 7% to TP, respectively. For the Lower Yangtze River Datong cross-section, the contributions were 6%, 69%, and 25% for COD and 41%, 42%, and 17% for TP. The primary drivers of the anthropogenic pollution sources, in decreasing order of importance, were temperature (reflecting seasonality), date, and precipitation. This study emphasizes the synergy between physical modeling and machine learning, offering new insights into pollution load dynamics in the Yangtze River.

How to cite: Huang, S., Xia, J., Wang, Y., Wang, G., She, D., and Lei, J.: Deciphering pollution loads in the Middle-Lower Yangtze River by coupling water quality models with machine learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3559, https://doi.org/10.5194/egusphere-egu24-3559, 2024.

10:05–10:15
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EGU24-4925
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Virtual presentation
Keming Mao and Xiankun Yang

China has been a traditional aquaculture powerhouse, contributing over one-third of the global production. The Guangdong-Hong Kong-Macao Greater Bay Area stands out as a primary region for aquaculture. Pond aquaculture is a significant method employed in this area, benefiting from its geographical advantages with a widespread and numerous distribution of fish ponds within the Greater Bay Area. The primary production units for aquaculture ponds are predominantly household-based, decentralized, and lack a significant intensive production effect. Aquaculture personnel often rely on experiential judgment to assess water quality. In recent years, increased human factors and a lack of effective management in the aquaculture pond industry have exacerbated water pollution issues. This has resulted in a growing severity of water pollution problems, with governmental departments unable to conduct large-scale monitoring of aquaculture pond water quality. Dissolved oxygen serves as a crucial indicator reflecting the water quality of these aquaculture ponds. Only dissolved oxygen concentrations within suitable ranges can facilitate the growth of aquatic products; concentrations that are either too high or too low can adversely affect aquatic product growth. This study utilized Landsat 8/9 OLI satellite images, employing atmospheric correction based on Rayleigh reflectance. It combined machine learning and water body index methods to establish a dissolved oxygen Support Vector Regression (SVR) inversion model (R2=0.67). This model determined the trends in dissolved oxygen concentration changes and spatial distribution patterns in aquaculture ponds within the Greater Bay Area over the past decade. The results indicate that from 2013 to 2023, there was a marginal decrease of 0.04% in dissolved oxygen concentration. Concentrations decreased during 2014-2016 and 2018-2020, while they increased in other years. Seasonally, concentrations were higher in spring and autumn and lower in summer and winter. Summer exhibited the lowest dissolved oxygen concentration throughout the year, with the smallest concentration difference and relatively concentrated numerical distribution. Dissolved oxygen concentrations varied significantly in other seasons. Aquaculture ponds in low latitude coastal areas generally had lower dissolved oxygen concentrations, while those in northern mountainous and upstream river regions had relatively higher dissolved oxygen concentrations.

How to cite: Mao, K. and Yang, X.: Remote Sensing Retriving of Dissolved Oxygen Concentration in Aquaculture Ponds in the Guangdong-Hong Kong-Macao Greater Bay Area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4925, https://doi.org/10.5194/egusphere-egu24-4925, 2024.

Coffee break
Chairpersons: Inge van Driezum, Brian Kronvang, Daniel Graeber
10:45–10:50
10:50–11:00
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EGU24-14984
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On-site presentation
Jørgen Windolf, Kristoffer Piil, Torben B. Jørgensen, Hans E. Andersen, Tommy Dalgaard, and Brian Kronvang

The Danish EPA has in the 3rd River Basin Management Plan (RBMP) under the Water Framework Directive set target nitrogen loads for each coastal water for how to reach the reduction needed from coastal catchments to be implemented in 2027. In this context four locally based pilotprojects have been initiated to engages stakeholders to find local solutions for the RBMP. One of these new pilots are focusing on the Hjarbæk estuary situated in Limfjorden being one of the coastal water bodies in Denmark that needs the highest reductions in nitrogen loadings to be achieved before 2027 (ca. 65 %). This new project involving a coastal water board with all main stakeholders in the region being represented was initiated in February 2023 and has delivered proposals for 2 scenarios by the end of 2023 that can assure that the Hjarbæk estuary reach the target of achieving good ecological conditions.

Because of the high reductions in nitrogen loadings needed it is necessary to reduce all sources and both nitrogen and phosphorus to reach the goal. Focus in the RBMP has so far been to reduce the total nitrogen (TN) loadings. In the locally based scenarios phosphorus has gained greater focus. Our calculations show that every ton of phosphorus that is removed corresponds to removing 22 tons of nitrogen in Hjarbæk Fjord.  To be most cost-effective the effort will be carried out based on the principle of achieving the greatest possible effect per area unit. For that a detailed mapping of nitrogen (N) attenuation in the catchment have been conducted at a scale of ca. 15 km2 (ID15 sub-catchments) including mapping of both N-retention in groundwater and surface waters as well as N-delays in groundwater in Karst sub-catchments. The mapping shows huge differences in N-retention in both groundwater and surface waters within the ID15 sub-catchment (<20 % to >80 %).

The local engagement of stakeholders representing all sectors in the catchment and estuary have worked together to set up two scenarios that includes: i) marine mitigation measures such as mussel farming and eelgrass planting; ii) reductions in point source loadings; iii) use of a new portfolio of N mitigation measures to be adopted at source (e.g. catch crops, early seeding, set a side, afforestation, etc.); iv) use of transport mitigation measures from field to surface water (several types of constructed wetlands, riparian buffers and restored wetlands); v) the possible use of different phosphorus mitigation strategies in the catchment (lowering bank erosional P-losses, buffer strips, afforestation, etc.).

How to cite: Windolf, J., Piil, K., Jørgensen, T. B., Andersen, H. E., Dalgaard, T., and Kronvang, B.: The establishment and use of local coastal water boards is tested in Denmark to find bottom-up solutions for RBMP 2027, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14984, https://doi.org/10.5194/egusphere-egu24-14984, 2024.

11:00–11:10
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EGU24-17087
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Highlight
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On-site presentation
Jeroen Geurts, Marelle Van der Snoek, Christian Fritz, and Gert-Jan Van Duinen

To counteract soil subsidence and greenhouse gas emissions, groundwater levels in agriculturally used peatlands are increased in summer (e.g. by subsurface irrigation). This rewetting could lead to increased nutrient mobilization under anaerobic conditions in nutrient-rich soils, which will lead to eutrophication in ditches and lakes. However, rewetted peatlands can also be used to purify surface water and utilize the available nutrients by cultivation of wet crops like Typha and Phragmites, which is called “paludiculture”. These wet crops can provide raw materials for fiber based products (e.g. insulation and building materials). Paludiculture can also be implemented in multifunctional buffer zones along streams in sandy landscapes.

This multifunctional land-use can create a win-win situation that combines biomass production of wet crops with the provision of ecosystem services, such as peat preservation and water purification. To underpin what the water purification potential of paludiculture is, measurements have been done in several mesocosm experiments and field-scale paludiculture pilots within national and European projects (e.g. VIP-NL, KLIMAP, Carbon Connects and CINDERELLA). These pilots and experiments were used to learn how to cultivate paludiculture crops under different hydrological circumstances (water level and fluctuations), nutrient loads, water quality, soil types and field configurations. We quantified the nutrient uptake by Typha and Phragmites and the change in water quality between inlet and outlet in different situations. The results are also used to investigate which combination of factors will give the most efficient combination of water purification, nutrient uptake and biomass production.  In the end, this contributes to developing new ways of sustainable and economical feasible farming on wet peat soils and in brook valleys.

How to cite: Geurts, J., Van der Snoek, M., Fritz, C., and Van Duinen, G.-J.: Paludiculture: multifunctional land-use to decrease nutrient loading, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17087, https://doi.org/10.5194/egusphere-egu24-17087, 2024.

11:10–11:20
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EGU24-7171
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ECS
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On-site presentation
Cih-Jin Huang and Chihhao Fan

In recent years, intensive agricultural practices have been adopted to enhance crop yields for food production. Therefore, the issue of agricultural non-point source pollution attracts attention due to the increasing use of fertilizer. The non-point source pollution control is diverse and difficult to manage because of the physical landscape and agricultural practices (e.g., topography, soil texture, farming, and irrigation). In addition, excessive fertilizer used to enhance crop yields would lead to land degradation. During a rainfall event, nitrogen and phosphorus from fertilizers would be washed into surface water and infiltrated into groundwater, resulting in the degradation of the aquatic environment.

In this study, the use of slow-release fertilizer, compared to the reference of conventional chemical fertilizer, and a constructed wetland were adopted at a pilot-scale study. During a 40-day growing cycle, Brassica Chinensis L.(Pak-Choi) was chosen as the model crop, and two types (i.e., chemical fertilizer and slow-release fertilizer) of fertilizers were applied under pre-designed conditions. Two simulated intense rainfalls were operated on the 26th and 33rd days, and the surface runoff was introduced to the constructed wetland for further nutrient removal. The soil and water samples from the soil and wetland were analyzed for nutrient concentration variation, and the nutrient distribution and removal efficiency were assessed. The results showed that the chemical fertilizer has a higher nutrient loss rate. The nitrogen (N), phosphorus (P), and potassium (K) contents in the soil increased rapidly after top dressing and decreased significantly after the simulated rainfall. In contrast, slow-release fertilizer has a relatively steady nutrient loss rate during the growing cycle. Meanwhile, the chemical fertilizer has a higher total N, P, and K loss via infiltration and runoff than slow-release fertilizer. For the wetland treatment, the N removal for chemical fertilizer and slow-release fertilizer after 15 days was 24.4 % (i.e., from 19.99 ppm to 15.11 ppm) and 29.5 % (i.e., from 20.81 ppm to 14.68 ppm), the P removal amount was 38.1 % (i.e., from 0.21 ppm to 0.13 ppm) and 87.5 % (i.e., from 0.08 ppm to 0.01 ppm), respectively. Opposing to the conventional chemical fertilizers, the use of slow-release fertilizers could reduce nutrient loss. The constructed wetland demonstrated a positive effect on removing the nutrients in neighboring water, which reduced the impact of agricultural non-point source pollution.

Keywords: Conventional farming, Best management practices, Slow-release fertilizer, Constructed wetlands

How to cite: Huang, C.-J. and Fan, C.: Non-point source pollution control in farmland by source-reduction strategies coupled with wetland treatment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7171, https://doi.org/10.5194/egusphere-egu24-7171, 2024.

11:20–11:30
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EGU24-12746
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ECS
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On-site presentation
Linda Heerey, Owen Fenton, Fiona Regan, Blánaid White, Nigel Kent, and Karen Daly

The agricultural sector is a large contributor to poor water quality in our freshwater systems. One potential pathway for agriculturally sourced pollution to enter the freshwater environment is through drainage ditches, which can be either open surface drains or subsurface pipes, or a combination of both. While large scale tile-drainage systems with a central output point are common in some countries, Irish agricultural drainage networks tend to be comprised of a complex network of drains, each with varying levels of connectivity to freshwater systems. Recent research by Moloney et al. (2020) categorised these drains in terms of their connectivity, finding that those with a direct connection between a farmyard and river/stream were at the greatest risk for transporting the highest concentrations of nutrients (phosphorus and nitrogen). Therefore, to target the most ideal location to mitigate against nutrient transport through drainage ditches, drains with direct farmyard connectivity provide the most resource- and cost-effective option.

This study investigated the effectiveness of sediment ponds installed in drainage ditches which had a direct connection between a farmyard and a river. Three case study farms were selected, two in the south (Cork) and one in the south-east (Wexford) of Ireland. All ponds were installed by 2021, with sampling commencing in December 2022. Grab water samples were collected weekly (Wexford farm) and fortnightly (Cork farms) at multiple points upstream and downstream of the ponds, and were analysed for nitrogen, phosphorus and dissolved organic carbon. Sediment samples were extracted from within the drainage ditches in summer 2023 and analysed for Mehlich-3 P, pH, Morgan’s P and particle size distribution. Initial results suggest ponds provide limited attenuation of nutrients, with no significant decreases at the downstream sample points. While sediment phosphorus concentrations are marginally elevated downstream, suggesting potential accumulation in the soil, further sampling is needed to confirm this trend. This study provides valuable insights into nutrient dynamics within agricultural drainage ditches and contributes to a better understanding of the effectiveness of sediment ponds as a potential mitigation measure for nutrient retention.

How to cite: Heerey, L., Fenton, O., Regan, F., White, B., Kent, N., and Daly, K.: Sediment ponds; an effective mitigation measure for reducing nutrient export in agricultural drainage ditches? , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12746, https://doi.org/10.5194/egusphere-egu24-12746, 2024.

11:30–11:40
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EGU24-9606
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Highlight
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On-site presentation
Stefan Jansen, Inge Van Driezum, Joachim Rozemeijer, Arnaut Van Loon, and Frank Van Herpen

It is known from recent international research that woodchip bioreactors can be an effective measure to reduce emissions of nitrate from agricultural drainage water. In the Netherlands, up till now no experience was present with woodchip bioreactors. Therefore, a field pilot was started at an agricultural test location situated in a lowland catchment in the south of the Netherlands (Vredepeel). A woodchip bioreactor was installed to treat drainage water from 4 ha arable land on sandy soil. Nitrate was measured in the in- and effluent of the bioreactor to estimate nitrate removal efficiency over time. Also, water chemistry and discharge were monitored. 
With a series of sampling points in the woodchip bioreactor, biogeochemical processes in the reactor are investigated that can explain the performance of the reactor. The goal is to not only determine the removal efficiency, but also potential side effects and effects of temporarily limited flow rate (e.g. sulfide and ammonia production and oxygen demand). We aim to give practical guidelines for practical design and application for agricultural fields in sandy lowland catchments. In this contribution we will present the monitoring results of one drainage season.

How to cite: Jansen, S., Van Driezum, I., Rozemeijer, J., Van Loon, A., and Van Herpen, F.: Field scale optimization of woodchip bioreactors for nitrate removal from drainage water in the Netherlands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9606, https://doi.org/10.5194/egusphere-egu24-9606, 2024.

11:40–11:50
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EGU24-6444
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ECS
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On-site presentation
Abdul Hadi Al Nafi Khan, Jan Vanderborght, Erik Smolders, and Jan Diels

As in other areas with intensive agriculture in Europe, Flanders struggles with bringing surface water quality in line with the EU Nitrates Directive. At about 25% of the 874 surface water measurement locations in Flanders monitored by the Flanders Environment Agency (VMM), the 90th percentile from monthly measurements conducted during 2018-2023 exceeded a NO3- concentration of 50 mg/L.

A large fraction of the nitrate that leaches out of the root zone is denitrified in the groundwater. However the denitrification rate varies spatially, so mitigation measures are best targeted to zones from where NO3- is transported to the surface water without undergoing significant denitrification in the aquifer. We used a novel methodology to predict NO3- concentrations in the outlets of small catchments that explicitly considers hydrochemical variation within aquifers and is based on the thickness of oxidized and reduced zones in an aquifer.

The depth of the redoxcline, the boundary between the oxidized and reduced zone, was determined from the phreatic groundwater monitoring network of VMM consisting of 2089 multilevel groundwater wells in Flanders. Analysis of the time series of hydro-chemical data (redox potential and dissolved NO3-, O2, Fe, Mn) allowed us to classify the filters as being in oxidized or reduced zone. For each well, the depth of the first ‘reduced’ filter was taken as the depth of the redoxcline.

Assuming a spatially uniform nitrate concentration in the groundwater recharge, the nitrate concentration of the water reaching the catchment outlet can be estimated as:

NO3- at catchment outlet = (thickness of oxidized zone / equivalent aquifer thickness ) × NO3-   in recharge water        (1)

This simple approach assumes that all nitrate is denitrified once the groundwater flowline crosses the redoxcline. Instead of the true aquifer depth, we used the aquifer's equivalent thickness, utilizing the Hooghoudt equation based on the average distance between watercourses. The nitrate input in the recharge water for this calculation was taken from VMM’s NEMO model, which provides the nitrate leachate from agricultural fields to groundwater.

Our investigation covered 68 small agricultural catchments (0.4-20.4 km²). The ratio of oxidized to entire aquifer thickness varied from 0.03 to 1, averaging 0.33. Therefore, on average, 33% of the agricultural areas would show high nitrate vulnerabilities because flowlines originating from there do not cross the redoxcline. However, the ratio of the average observed NO3- concentration in surface water to that in recharge water is 0.46, indicating an overestimation of denitrification. The estimated nitrate concentrations in surface water, calculated using Equation (1), showed a reasonable agreement with observed values (R2 = 0.32). A much lower R2 (0.08) is observed when replacing the ratio of thicknesses in Equation (1) with the average thickness ratio of 0.33. This suggests that the variation in nitrate concentration at the catchment outlet is predominantly governed by the relative thickness of the oxidized zone.

This method identifies nitrate-vulnerable areas along water courses in a catchment that can be used to better target mitigation measures across Flanders.

How to cite: Khan, A. H. A. N., Vanderborght, J., Smolders, E., and Diels, J.: Identifying nitrate-vulnerable zones for surface water pollution in Flanders based on the depth of the redoxcline and aquifer thickness, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6444, https://doi.org/10.5194/egusphere-egu24-6444, 2024.

11:50–12:00
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EGU24-14010
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ECS
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On-site presentation
Qinghui Zeng

 Cascade reservoirs construction has modified the nutrients dynamics and biogeochemical cycles, consequently affecting the composition and productivity of river ecosystems. Cascade reservoirs in different rivers typically exhibit distinct variabilities in the retention characteristics of different nutrients. The Jinsha River, as the predominant contributor to runoff, suspended sediment (SS), and nutrients production within the Yangtze River, is a typical cascade reservoir region with unclear transport patterns and retention mechanisms of nutrients (nitrogen and phosphorus). Therefore, we monitored monthly variations in nitrogen and phosphorus concentrations from November 2021 to October 2022. The results demonstrated that the concentrations and fluxes of total phosphorus (TP) and particulate phosphorus (PP) significantly decreased as they moved downstream along the cascade of reservoirs, primarily due to PP deposited with SS, while total nitrogen (TN) and dissolved total nitrogen exhibited opposing trends. Moreover, the positive average annual retention rates for TP and PP were 9.64% and 15.64%, respectively, in contrast to the negative averages of -8.38% for TN and -10.51% for particulate nitrogen. A higher proportion of TP and PP was retained by the reservoirs in the flood season compared to the non-flood season. Additionally, the variability in runoff-sediment and hydraulic retention time (HRT) of cascade reservoirs played crucial roles in the retention of TP and PP. A stronger relationship between HRT and TP retention rate during the flood season suggested that the cascade reservoirs could effectively transport or intercept TP downstream when HRT was either less than or greater than 5.3 days. Consequently, the HRT of these reservoirs could be managed to control nutrients delivery, which was of particular significance for watershed government institutions. This study enhances our comprehension of how cascade reservoirs influence the distribution and transport patterns of nutrients, offering a fresh perspective on nutrients delivery regulation. 

How to cite: Zeng, Q.: Impact of cascade reservoirs on nutrients transported downstream and regulation method based on hydraulic retention time, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14010, https://doi.org/10.5194/egusphere-egu24-14010, 2024.

12:00–12:10
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EGU24-20251
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ECS
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On-site presentation
Alexandra Hockin, Bas van der Grift, and Damaris Scheper

Diffuse pollution of shallow groundwater as a result of leaching of substances from agricultural soils has a negative impact on groundwater quality. In the drinking water sector, the focus has traditionally been on nitrogen (nitrate) and crop protection products, which are subject to strict standards. Geochemical buffering processes in the subsurface convert a large part of the nitrate load that leaches to groundwater from agricultural soils. However, these processes can often lead to an increase in the hardness (sum of the calcium and magnesium concentrations) of groundwater, which is undesirable for drinking water and domestic use.

Recent research shows that 70% of phreatic groundwater extraction locations in the Netherlands show a significant increasing trend in hardness. However, quantitative insight into the relationship between spatial characteristics (land use, soil type and geochemical composition of the subsoil) and hardness has so far been lacking. In this research we analyzed a long time series of data (since 1900) from shallow (< 25 m below ground surface) phreatic and semi-confined groundwater extraction locations in the Netherlands. The trends in hardness and partial pressure of CO2 (PCO2) and relationship with spatial characteristics of the extractions is presented.

A clear influence of agriculture activities in groundwater protection areas was observed; the hardness in agricultural-dominated extraction sites was 2.5 times higher compared to nature-dominated extraction sites, while the trend in the increase in hardness was almost 3 times higher. The trend is observed in both calcium carbonate-rich and calcium carbonate-poor soils. In carbonate-rich areas, the hardness of groundwater is determined by the addition of acid, from atmospheric deposition, agricultural activities such as fertilization and crop harvesting and by weak acid (CO2) contributions from root respiration and mineralization of organic matter. In carbonate-poor soils hardness sources are the use of calcium and magnesium salts and the application of manure on agricultural land. 

In carbonate-rich systems, slightly less than half of the groundwater hardness was found to be due to limescale weathering due to strong acid input, while slightly more than half of the hardness was due to weathering from CO2. Higher PCO2 levels and trends in agricultural-dominated extraction sites comparted to nature-dominated sites reveals an impact of intensive agricultural production on the CO2 production is soils, and thereby on groundwater quality, that have not been considered so far.

To minimize hardness as a result of soil acidification it is recommended to reduce nitrogen deposition, limiting nitrate leaching and limit the use of fertilizers that acidify the soil. To minimize hardness as a result of weak acid (CO2) weathering, more extensive agricultural practices to reduce root respiration should be adopted, and the degradation of soil organic matter can be limited by preventing (short-term) lowering of groundwater levels in organic rich soils. The results indicate that land use has a significant effect on the hardness and PCO2 in groundwater. Mitigating measures should consider an area-based approach, taking into account the land-use, soil type and geochemical characteristics of the subsurface to limit the impacts of increased hardness and PCO2 as a result of agricultural activities.

How to cite: Hockin, A., van der Grift, B., and Scheper, D.: Unexpected impact of agricultural land-use practices on the concentration and trend in hardness of groundwater abstracted for drinking water supply, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20251, https://doi.org/10.5194/egusphere-egu24-20251, 2024.

12:10–12:20
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EGU24-17979
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Highlight
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On-site presentation
Marieke Oosterwoud, Harm Wismans, Astrid Vrijhoef, Richard van Duijnen, and Susanne Wuijts

Since the introduction of the EU Nitrates Directive (91/676/EEC), nitrogen concentrations have gradually declined. The recent summer droughts (2018-2020) in the Netherlands, have caused an increase in nitrogen concentrations in water leaching from agricultural soils, exceeding standards. It is expected that with increasing numbers of climate extremes, summer droughts will occur more often in the Netherlands. In order to develop possible strategies, it is important to better understand the underlying mechanisms and consequent impact of droughts on water quality. 


In rural areas of the Netherlands the water quality of shallow groundwater and surface water (leaching water) is strongly influenced by agricultural land use. The EU Nitrates Directive aims to protect waters against pollution caused by nitrates from agricultural sources. In the Netherlands, leaching of nitrogen to shallow groundwater and surface water is monitored for over 30 years by the Dutch Mineral Policy Monitoring Programme (LMM). Within the LMM, the Netherlands is divided in 4 main and 14 subregions based on soil type. The water sampling at participating farms, enables to analyse the effect of farming practices on water quality in the different LMM regions. 


Nutrients applied during the growing season can leach to shallow groundwater and surface water in the following autumn and winter. Summer drought inhibits the uptake of nutrients by crop, hampers the process of denitrification and leads to thickening of the soil moist and upper groundwater, leading to accumulation of excess nitrates in the soil. These excess nitrates can potentially increase nitrogen concentrations in leaching water in winter. Not every soil region responds similarly to a drought period. The aim of this study is to investigate why certain regions experience a stronger impact of drought on nitrogen leaching than others. 


We used monthly spatial Standardized Precipitation Evaporation Index data provided by the Royal Meteorological Institute (KNMI) over the period 1990-2022 to identify where (region) and when (year) summer droughts occurred. The LMM dataset was used to analyse the change in groundwater levels, nitrogen concentrations in leaching water and soil nitrogen surplus following a summer drought. Furthermore, we investigated the role of soil type and land use on the change in nitrogen concentrations in leaching water caused by drought.


Our findings reveal that the magnitude of the increase in nitrogen concentration in leaching water following a summer drought is determined by the duration and intensity of the drought. Furthermore, soil type and agricultural practices influenced the variation of the impact by droughts between regions. These results can be used to identify areas that are more sensitive to impacts of droughts on water quality based on their soil and land use characteristics and thus support the development of adaptation strategies by farmers, water authorities and national government. 

How to cite: Oosterwoud, M., Wismans, H., Vrijhoef, A., van Duijnen, R., and Wuijts, S.: Impact of drought on nitrogen concentrations in leaching water from agricultural areas in the Netherlands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17979, https://doi.org/10.5194/egusphere-egu24-17979, 2024.

12:20–12:30

Posters on site: Fri, 19 Apr, 16:15–18:00 | Hall A

Display time: Fri, 19 Apr, 14:00–Fri, 19 Apr, 18:00
A.1
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EGU24-20400
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ECS
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Highlight
Josie Ashe, Emilie Grand-Clement, and Richard. E Brazier

Patterns and variability in the concentration-discharge relationship may be used to describe the complex interactions and combined effects of catchment processes affecting sources, mobilisation and transport of contaminants. Many concentration-discharge relationships display temporal variability on diurnal, event, seasonal and annual scales. This has been widely demonstrated through both routine regular sampling and targeted storm sampling.

The set-up costs of high frequency in-situ river and reservoir sensors is high, and operation and maintenance of a wide network is both time and resource intensive and the conditions for operation (e.g. environmental conditions, signal, power) are rarely ideal. Yet with technological advances and the growth in availability of high-frequency is-situ water quality sensors, the complexity of the water quality response to changes in flow, across multiple timescales, has become increasingly evident. The observed dynamics during events, and range of hysteresis patterns displayed, shows that the sources of contaminates, mechanisms for mobilisation, and transport times are highly variable both spatially and temporally. Furthermore, seasonal and interannual controls on catchment functioning are seen to result in pronounced differences in the behaviour of parameters between sites, and between individual events at the same site.

This study shows how routine high-frequency data, collected with an operational focus for source protection and in raw water at drinking water treatment works, provide opportunities when trying to identify sources and pathways for contaminants. Despite challenges, these data support the development of a baseline understanding for water quality within a specific catchment or region, and provide insight into catchment specific event-driven dynamics. In catchments where routinely collected data is the only source of multiannual high-frequency water quality data, these data may be crucial in building understanding of long term (decadal) variability and trends; in particular, gaining understanding the changing interactions and effects due to extremes in seasonal patterns across different years. However, the key limitations in the use of these data include undefined uncertainties and missing data, monitoring design, and limited metadata. Therefore, building on initial analysis of routine data, efficient monitoring campaigns for targeted research can be designed to investigate any previously unexplored or unidentified processes and pathways.

This study is part of a wider programme of research on the identification of sources and pathways for contaminants of concern in catchments supplying drinking water in the south west of the UK, and how water quality dynamics are impacted by meteorological and catchment conditions, including atypical events. It supports work on increasing resilience in drinking water source areas and reducing treatment demands and costs, through improving understanding of how water quality in rivers and reservoirs is affected by landscape and farm-based catchment interventions.

How to cite: Ashe, J., Grand-Clement, E., and Brazier, R. E.: Understanding hysteresis in high-frequency water quality data in rivers: adding value to targeted research using routinely collected operational data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20400, https://doi.org/10.5194/egusphere-egu24-20400, 2024.

A.2
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EGU24-5683
Rémi Dupas, Thibault Lambert, and Patrick Durand

Dissolved organic carbon (DOC) in surface waters originates mainly from riparian soils, where several processes affect the mobilisation/immobilisation of organic compounds. Among these processes, iron reduction is thought to be of primary importance for DOC mobilisation and export to surface waters. However, this process can be inhibited by the presence of nitrate due to its higher redox potential than Fe(III), making microbial nitrate reduction thermodynamically favourable compared to iron reduction. In agricultural catchments, the groundwater is typically enriched in nitrate. Thus, rising water tables in riparian areas during the (winter) wet season may inhibit iron reduction and the subsequent DOC mobilisation in soil and surface water. In this study, we tested this hypothesis in a well-monitored agricultural catchment belonging to the OZCAR network, the so-called Kervidy-Naizin catchment (5 km²). We installed 21 zero-tension lysimeters in the riparian zone of the catchment along three transects to sample soil solution in organic-rich top soil horizons (15 cm below the soil surface), at weekly to fortnightly intervals (oct 2022 – jun 2023). We analysed DOC, nitrate, Fe(II) concentrations as well as dissolved organic matter (DOM) composition through its optical properties (3D fluorescence coupled with PARAFAC modelling) to obtain information about DOM sources and dynamics across the hydrological cycle. We found that DOC concentrations were positively correlated with Fe(II) concentrations both spatially and temporally. In contrast nitrate concentrations were negatively related to Fe(II) in the soil solutions during the winter period. These observations support the hypothesis that nitrate is an inhibitor of iron reduction and subsequent DOC mobilisation. Data on the optical properties of DOM show that the DOC mobilised by this process contains large proportions of organic molecules of microbial origin, probably derived from the processing of soil organic matter. In addition, the mobilisation of high amounts of DOC unrelated to iron reduction in some zero-tension lysimeters suggests that other controls, such as wet-dry cycles, may be equally important for sustaining organic compounds in soil solutions and surface waters.

How to cite: Dupas, R., Lambert, T., and Durand, P.: The influence of nitrogen and iron biogeochemical cycles on the production and export of dissolved organic matter in headwater catchments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5683, https://doi.org/10.5194/egusphere-egu24-5683, 2024.

A.3
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EGU24-18955
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ECS
Pia Ebeling, Rémi Dupas, Benjamin Abbott, Rohini Kumar, Sophie Ehrhardt, Jan H. Fleckenstein, Nils Turner, and Andreas Musolff

Nitrate pollution in streams, although attempts have been made to combat it, remains a persistent problem, especially in highly anthropogenically impacted landscapes such as Western Europe. Nitrate concentrations and discharge typically vary with the seasons, as does the vulnerability of water bodies to high nitrate inputs. However, the degree of variability and seasonal timing vary in space and time while nitrate inputs in catchments have undergone drastic long-term changes. The changing N sources and distribution in the catchments and their variable hydrological activation suggest that different nitrate seasonality has emerged across catchments over the decades. In this study, we hypothesize that nitrate concentrations respond faster to changes in input during the high-flow season than during the low-flow season, as shallow sources are typically activated during high flow and are the first to be affected by changes in management. To test this hypothesis, we propose a hysteresis approach of long-term nitrate seasonality during low- and high-flow seasons, which we applied in 290 catchments in Germany and France with nitrate and discharge time series of 20 or more years. Our results show that in the majority of catchments, nitrate and discharge vary synchronously with peaks in winter. Deviating average nitrate-discharge typologies could be linked to topography and hydroclimatic seasonality as well as to the regionally characteristic source heterogeneity and lithology in northwestern France. Contrary to our hypothesis, we found both types of trajectories with preceding high-flow and low-flow nitrate concentrations were equally present. We could exemplarily show high-flow concentrations responded first in an agricultural catchment and low-flow concentrations reacted first in a more point source intense catchment. However, across the large number of catchments, consistency was not observed suggesting higher complexity of interacting processes. In a further step, we plan to investigate the long-term trajectories of phosphorus to account for the ratios of the major nutrients affecting the resulting impact of land-stream transfer processes on eutrophication.

References: Ebeling, P., Dupas, R., Abbott, B., Kumar, R., Ehrhardt, S., Fleckenstein, J. H., & Musolff, A. (2021). Long-term nitrate trajectories vary by season in Western European catchments. Global Biogeochemical Cycles, 35, e2021GB007050. https://doi.org/10.1029/2021GB007050

How to cite: Ebeling, P., Dupas, R., Abbott, B., Kumar, R., Ehrhardt, S., Fleckenstein, J. H., Turner, N., and Musolff, A.: Shifting nitrate seasonality along decades of anthropogenic impact in western European catchments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18955, https://doi.org/10.5194/egusphere-egu24-18955, 2024.

A.4
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EGU24-1326
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ECS
Tassiane Junqueira and Bas Vriens

The North American Great Lakes constitute a distinctive hydrological system comprising five interconnected lakes (Superior, Michigan, Huron, Erie, and Ontario) that together represent one of the planet's most significant freshwater reserves. Extensive environmental surveillance by federal, state, and provincial governments targets major water quality parameters such as temperature, pH, total dissolved solids, electrical conductivity, and dissolved oxygen, as well as concentrations of nutrients and major ions. However, trace element concentrations are more scarcely measured, and the comparatively little available data on trace element concentrations in the Great Lakes is typically older, discontinuous, or focused on historically contaminated areas. Consequently, the myriad of processes and sources involved in the distribution patterns of trace elements is poorly studied, and there remains a lack of understanding the natural baselines for these elements, including for the Rare Earth Elements (REE). The REE play a crucial role in various technological applications, including electronics, renewable energy technologies, and other high-tech industries. Because of their increasingly applications, REE are currently a significant concern, particularly in mining and industrialized areas, due to their enduring toxicity, radioactive properties, and the potential for bioaccumulation.

To understand the REE distribution pattern in the North American Great Lakes, we assessed REE concentrations in >70 surface water samples from Lakes Huron, Erie, and Ontario. The concentrations of dissolved REE, filtered at <0.22 µm, exhibited significant spatial heterogeneity across the lakes, with higher ΣREE values in Lake Huron (0.065±0.082 μg/L, n=27, 2022) than in Lake Erie (0.041±0.033 μg/L, n=14, 2021 and 2022) and Lake Ontario (0.033±0.041 μg/L, n=27, 2021 and 2022). Interestingly, there was no consistent upstream-to-downstream increase in dissolved REE concentrations within the basin, but dissolved REE levels decreased nearshore-to-offshore across all lakes. Enrichment of light REE over heavy REE, particularly in samples closer to the shore, was suggestive of riverine inputs and aqueous speciation modeling indicated strong control of speciation (hydrochemistry) on REE dynamics. Finally, we employed normalization and pattern-filling to assess REE enrichments in lake surface waters. Anomalies for Gadolinium (Gd), exceeding 20%, on average, across the lakes, were notably higher than for other REE but exhibited significant spatial variability, with enrichment observed especially in proximity to urban centers and in Lake Ontario. This research contributes valuable baseline data, enhancing our understanding of the dynamics of Rare Earth Elements in the Great Lakes and providing a foundation for further studies worldwide.

How to cite: Junqueira, T. and Vriens, B.: Rare Earth Elements Concentration Patterns in Surface Waters of Lakes Ontario, Erie, and Huron (North America), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1326, https://doi.org/10.5194/egusphere-egu24-1326, 2024.

A.5
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EGU24-11237
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ECS
Hongzheng Zhu, Kieran Khamis, David M. Hannah, and Stefan Krause

Emerging sensor technology offers new opportunities to monitor different fractions of Dissolved Organic Matter (DOM) in high resolution. Concentration-discharge (C-Q) relationships (e.g. hysteresis or c-q slopes), derived from high frequency observation can offer insight into source mobilization and reactive transport processes of DOM. However, few studies have explored patterns in urban catchments, where understanding of storm event DOM responses under different hydrometeorological conditions remains elusive. To bridge this gap, we collected 2-years (15 min resolution) fluorescence data (humic-like fluorescence [HLF: Ex. 325 nm/ Em 470 nm] and tryptophan-like fluorescence [TLF: Ex 275 nm/ Em 350 nm]) in an urban headwater stream (Birmingham, UK). We used c-q slopes and two indices, the hysteresis index (HI) and flushing index (FI), to explore the inter-event variability in DOM dynamics. In addition, we assessed the hydrometeorological factors (e.g., antecedent conditions, temperature, discharge and rainfall characteristics) that govern DOM mobilisation and transport using statistical multiple linear regression. Our findings reveal pronounced seasonal variation in the behaviour of TLF and HLF. In warmer periods, the chemodynamic characteristics of both fluorescence peaks become evident. We observed a consistent counter-clockwise hysteresis pattern accompanied by flushing behaviour. The magnitude of discharge, antecedent temperature, and rainfall intensity were identified as key drivers of HLF and TLF flushing and hysteresis dynamics. Conversely, during colder months, a shift in DOM mobilisation was observed. For TLF, source limitation was apparent, characterized by clockwise hysteresis and a notable dilution. In contrast, HLF exhibited a more variability during this period, with complex hysteresis patterns and a combination of solute flushing and dilution. The magnitude of discharge and antecedent wetness were identified as the key factors influencing the solute behaviour in this cooler period. Our research indicates that the responses of DOM in urban rivers exhibit distinct responses to hydrometeorological conditions which were relatively predictable (i.e. low stochasticity within particular event types). However, variability in DOM composition and magnitude was pronounced between event types which has implications for managing urban rivers, specifically ensuring ecological health and resilience are maintained in the face of increasing climatic extremes.

How to cite: Zhu, H., Khamis, K., Hannah, D. M., and Krause, S.: Using field deployable sensors to identify the inter-event predictability of Dissolved Organic Matter mobilisation in an urban river, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11237, https://doi.org/10.5194/egusphere-egu24-11237, 2024.

A.6
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EGU24-7589
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ECS
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Highlight
Andrea Schmid, Andreas Scheidl, and Alexander Eder

Cover crops (CC) have shown promise in reducing nitrogen (N) leaching, but in semi-arid regions, they might compete with subsequent field culture for water availability. In Austria's Marchfeld region, which is intensively used for agriculture, nitrate levels in groundwater exceed threshold values due to N surplus and limited dilution of seepage water caused by low annual precipitation. Early sown CC with sufficient emergence and N uptake might reduce such groundwater contamination. Further, later tillage dates keep the N stored in the organic pool and reduce mineralisation during autumn and winter. However, CC induced changes in soil water availability could impact the follow-up crop.
This study investigates the impact of cover crop (CC) varieties with different i) seed compositions, ii) tillage dates and iii) on-demand irrigation on N leaching and soil water availability for subsequent field culture.

The randomized block trial included a) frosting CC – autumn conversion, b) frosting CC – spring conversion, c) a mixture of winter hardy and frosting CC – spring conversion and d) fallow plots. On-demand irrigation was performed at plots with same varieties to enhance CC emergence and simulate conditions of both wet and dry years. Within each plot soil moisture sensors and suction cups were installed. Some plots were equipped with matrix potential sensors. Monthly soil samples were analysed for plant available N and plant samples were taken twice. Evaporation was evaluated using four mini-lysimeters, one for each CC composition. STOTRASIM, which is a soil water and mass transport model was used to model the amount of seepage water of each plot and was calibrated on matrix potential measurements.

In general, the results show that all tested varieties of CC significantly reduce plant available nitrogen during winter compared to fallow. Despite the relatively low levels of leached N, in semi-arid regions even minor amounts pose a risk of groundwater contamination. Soil water content analysis revealed no significant differences between the CC varieties. The yield of the subsequent crop remained unaffected by the different CC.
While CC reduced N leaching and did not compete with the subsequent field culture, integrating practical considerations like phyto-sanitation, seedbed preparation, tillage methods, crop rotation and succeeding crop selection into CC practices is crucial to prevent adverse effects on subsequent field culture.

How to cite: Schmid, A., Scheidl, A., and Eder, A.: Cover crop varieties, tillage dates and irrigation on-demand: their impact on nitrogen and soil water dynamics in Austria’s semi-arid Marchfeld region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7589, https://doi.org/10.5194/egusphere-egu24-7589, 2024.

A.7
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EGU24-8959
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ECS
Águeda M. Sánchez-Martín, Sara Pérez Dalí, Tomás Undabeytia López, Jorge Marquez Moreno, Alba Dieguez-Alonso, Frank Behrendt, Germán Almuiña-Villar, and José María De la Rosa

Finding a sustainable solution to the increasing amount of organic waste generated, and reducing air, soil and water pollution are two most pressing environmental issues today. In both problems, agriculture plays a crucial role. Within this context, this study aims to valorize abundant agricultural waste via its transformation into activated carbon (AC), useful for the removal of emerging organic contaminants (EOCs) in water.
Thus, rice husk (RH) and almond shell (AS) were characterized, pyrolyzed and tested as feedstock for ACs to be used as water filters. In addition, chemical (with KOH) and physical activation (with water vapor) of the pyrolyzed materials were performed.
The elemental composition and physical properties were suitable in both cases (alkaline pH, high water retention capacity, Carbon content and Iodine index). The specific surface area (SSA-BET) increased significantly to values 600 m2 gr-1 on the ACs produced from physically activated and pyrolyzed RH.
Furthermore, adsorption tests of anti-inflammatory and antibiotic compounds in water showed that ACs produced from RH were able to adsorb up to 100 % of the these persistent EOPs, performing similarly to commercial AC.

 

Acknowledgements:
This study received financial support in the framework of the Project RICERES4CHANGE (grant TED2021-130964B-I00), by the Spanish Agency of Research (MCIN/AEI/10.13039/501100011033) and the European Union (Next Generation EU/PRTR funding).
A.M. Sánchez-Martín thanks The Spanish Ministry of Science and Innovation (MICIN) for her contract as Technical Support Personnel (PTA2021-020000-I). M. Arenas is thanked for this technical and analytical support.

How to cite: Sánchez-Martín, Á. M., Pérez Dalí, S., Undabeytia López, T., Marquez Moreno, J., Dieguez-Alonso, A., Behrendt, F., Almuiña-Villar, G., and De la Rosa, J. M.: Valorization of agricultural residues through its transformation into sustainable filters for water treatment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8959, https://doi.org/10.5194/egusphere-egu24-8959, 2024.

A.8
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EGU24-11516
Daniel Graeber, Anika Große, Katja Westphal, Alexander Wachholz, Marc Stutter, Gabriele Weigelhofer, Thomas Alexander Davidson, Tom Shatwell, Andreas Musolff, Rohini Kumar, and Dietrich Borchardt

Agricultural nutrient management tends to treat nitrogen (N) and phosphorus (P) in surface waters as separate entities, potentially overlooking their strong interactions in biogeochemical cycles. This study proposes a unifying approach by integrating these nutrients through a stoichiometric nutrient management framework. This framework suggests two paradigm shifts in inland-water nutrient management: 1. It improves catchment and ecosystem-level understanding of N and P sources and effects via N : P ratio assessments of sources, transport and ecological effects, such as eutrophication. 2. It proposes that provision of organic carbon (OC) can increase the retention of N and P in agriculturally impacted inland waters, which can be assessed using C : N : P ratios. Provision of OC to modify C : N : P ratios may be reached through restoring natural OC sources. This can be done by focusing on areas such as wetlands, riparian forests, and bogs at catchment scale. Here, stoichiometric rules are utilized to assess the responses of key microbial processes, which includes examining how nutrients are assimilated by microbial primary producers and heterotrophs, as well as the process of denitrification. Understanding the secondary effects of wetted area development through the stoichiometric nutrient management framework will also support decision making for flood and drought protection based on such wetted areas. With these aspects, the stoichiometric nutrient management framework provides comprehensive understanding of nutrient dynamics, retention, and their ecological impacts in inland water catchments and ecosystems. In the presentation, we will present evidence supporting the comprehensiveness of the stoichiometric nutrient management framework. This evidence is based on a series of studies we conducted, including conceptual modeling, statistical modeling, ratio-based monitoring, and targeted proof-of-concept microcosm experiments. We conclude that the stoichiometric nutrient management framework could provide crucial strategies to mitigate current nutrient pollution issues in agriculturally-impacted inland waters, thereby aligning with the Water Framework Directive’s objectives for improving water quality.

How to cite: Graeber, D., Große, A., Westphal, K., Wachholz, A., Stutter, M., Weigelhofer, G., Davidson, T. A., Shatwell, T., Musolff, A., Kumar, R., and Borchardt, D.: Integrating and managing nitrogen and phosphorus dynamics in agriculturally impacted inland waters via a stoichiometric nutrient management framework, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11516, https://doi.org/10.5194/egusphere-egu24-11516, 2024.

A.9
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EGU24-15361
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ECS
Sabi Kidirou Gbedourorou, Pierre G. Tovihoudji, Marnik Vanclooster, and Irénikatché P. B. Akponikpe

Water pollution by nitrogen residues from agricultural intensification has become a recurring problem, particularly in wetlands used for rice production. As a solution to remediate this issue, sustainable water and nutrient management are being explored. These practices involve matching water and nutrient availability with plant needs in space and time while ensuring production objectives are met. In this study, we performed a meta-analysis to synthesize the current knowledge on the effect of water and nutrient management practices on nitrogen losses and uptake by plants in rice cropping systems. Using a random effects model, we summarized the effect sizes of 103 observations from 27 peer-reviewed studies. Tree water management practices were evaluated: “Continuous Flooding” (used as control), “Alternate Wet and Dry (AWD)” and “Controlled Irrigation (CI)”. The response ratio (RR) of nitrate leaching and total nitrogen loss was negative for CI (-0.53 and -0.34, respectively) and AWD (-0.13 and -0.36, respectively). Regardless of water management practices (AWD or CI), desaturating the soil before re-irrigation reduced nitrate and total nitrogen losses. When considering the source of nitrogen input, water management practices involving desaturation of the soil before re-irrigating were effective in reducing nitrogen losses in urea-only applications. However, in the case of controlled release urea (CRF) applications, water management treatments (AWD or CI) were not necessary to reduce nitrogen losses, especially those due to ammonia volatilization. This result also indicates the effectiveness of CRF treatment in retaining the essential nitrogen component required for plant growth and development. Nevertheless, when nitrogen rates exceed 200 kg N/ha, adopting water management practices such as CI and AWD becomes necessary to decrease nitrate leaching and total nitrogen loss in rice fields. Regarding the rice grain yield, water management practices that involve reducing the amount of water (AWD and CI) have shown no significant effect on yield (RR 0.017 and -0.0001). In conclusion, AWD and CI water management practices have been shown to reduce nitrogen losses without compromising rice grain yield. Additionally, the application of CRF reduces nitrogen losses that may occur in a continuous flooding system.

Key-words: Water management; Nitrogen; Rice; Controlled release urea; Water pollution

How to cite: Gbedourorou, S. K., Tovihoudji, P. G., Vanclooster, M., and Akponikpe, I. P. B.: Mitigation of nitrogen loss in rice fields through soil desaturation prior to re-irrigation and the application of controlled-release nitrogen fertilizer: a meta-analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15361, https://doi.org/10.5194/egusphere-egu24-15361, 2024.

A.10
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EGU24-18419
Timo Brussée and Marieke Oosterwoud

The Nitrates Directive (91/676/EEC) obliges all EU Member States to protect groundwater and surface water against pollution caused by nitrates from agricultural sources. To meet this objective, the Netherlands has developed standards for the use of manure and inorganic fertilisers. Empirical models are used to evaluate these standards to ensure that they are consistent with the objectives of the Nitrates Directive. This study has evaluated field data over a period of 30 years to assess leaching fractions of nitrogen surplus for different soil types and land use (arable vs grassland).   The results serve as input for the empirical models.

The aim of this study was to calculate the part of the nitrogen surplus on arable land and grassland that leaches into ground and surface water (nitrogen leaching fraction). This is done for four regions characterised by different soil types (sand, loess, clay and peat). The sand region is herein divided in different groundwater depth regime classes (GRC’s) which are an indicator for the soil drainage condition. 

The type of soil and its usage impact specific soil microorganisms. These microorganisms are able to break down nitrate. The more denitrification takes place, the less of the nitrogen surplus, in the form of nitrate, reaches ground and surface water, resulting in a reduced leaching fraction. 

This study utilised monitoring data from the Minerals Policy Monitoring Programme (LMM). This long term monitoring programme monitors the agricultural practice and water quality on agricultural farms in the Netherlands since 1991 onwards. All farms in this study were randomly sampled and selected (about 750 farms over the whole period).

Nitrogen surplus was derived by subtracting nitrogen outputs from input at the farm level. Precipitation surpluses were used to calculate nitrogen loads from nitrate concentrations per soil region and land use (arable or grassland). This was done using year specific long-term median precipitation surplus based on fractions of crop types, soil types and GRC’s. 

The nitrogen leaching fraction is highest in dry sandy soils, followed by loess, clay and peat. Leaching fractions were found to be significantly higher on arable land than on grassland. The findings of this study closely align with prior research on leaching fractions from 1991 to 2014   even though input data was completely renewed.

The most remarkable change in input data from the former version was visible on Dutch soil and GRC maps: soil types and GRC’s have shifted over the monitoring period. Shallow peat soils located on sands have shifted, due to oxidation, to a more sandy soil, whereas groundwater tables have fallen. 

This method is, as far as known, unique because of the use of a large sample of random, shallow water quality measurements, aggregating to a long term leaching fraction, without the use of complex model instruments. This measurement-based method can be a helpful tool to derive environmentally sound N use standards to meet with the objectives of the Nitrate Directive.

How to cite: Brussée, T. and Oosterwoud, M.: Estimating nitrogen leaching fractions to ground and surface water on agricultural farms from long-term monitoring data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18419, https://doi.org/10.5194/egusphere-egu24-18419, 2024.

A.11
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EGU24-22015
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ECS
Seasonal and temporal drivers of carbon and nutrient export from Finnmark rivers: Results of a 23-year time series of water chemistry and satellite imagery from Northern Norway
(withdrawn)
Maeve McGovern, Stein Karlsen, Kjell Høgda, and Benoît Demars