Wildfires are a threat to water security worldwide, due to the negative effect of the post-fire mobilization of sediments and associated nutrients and contaminants on the waterbodies located downstream of burned areas. Such impacts have been assessed in field studies and, more recently, also through modelling approaches. Models are valuable tools for anticipating the potential negative impacts of wildfires, allowing to test different environmental scenarios. The state of the art in post-fire model adaptation has shown that most studies simulate the hydrological and erosion response in the first post-fire year in situ, without considering the cascading effects on downstream waterbodies. In addition, few studies have evaluated the long-term impacts of wildfires, likely due to the limited available data. Among the existing gaps in post-fire modelling, ash transport has recently been identified as a priority. The lack of ash modelling studies has been ascribed to the limited understanding of ash behavior and the difficulties of incorporating ash-related processes into the structure of existing models.

As a way to fulfill these research gaps and advance the state of the art in post-fire hydrological modeling, the authors provided several contributions in recent years.

For instance, a watershed model has been coupled with a reservoir model to simulate the effects of fires on drinking water supplies, using the outputs of the main streams as inputs to the reservoir branches. As most simulations commonly end at the watershed outlet, a simple methodology was proposed to assess how the impacts on watercourses propagate to the drinking water supply inlet. The results showed that integrated modeling frameworks are critical for anticipating the off-site impacts of fires.

Post-fire management can also influence the impacts of fires beyond the first post-fire rainfall events, when the soil is exposed and ash and sediment transport is greatest. Another modelling exercise evaluates the long-term impacts of different post-fire management options, more specifically terracing, mulching and natural recovery, on water availability and quality.

As post-fire ash and sediment mobilization is typically limited to the duration of the rainfall events, which typically lasts for a few hours, hydrological models that run at a daily time-step can underestimate the environmental impacts of fires. To improve the knowledge of post-fire hydrological processes at event-based scale, two hydrological models (LISEM and MOHID) were calibrated, accounting for burn severity and initial soil moisture conditions before each specific rainfall event.

The work done in the past years is expected to be of added value for the post-fire modeling community, providing future directions on post-fire hydrological modelling studies.

How to cite: Basso, M., Keizer, J., Serpa, D., Mateus, M., and Vieira, D.: Wildfire impacts on water: improving impact assessment though model adaptation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-276, https://doi.org/10.5194/egusphere-egu23-276, 2023.

Wildfires in the Mediterranean basin, especially in Portugal, have increased in extent and frequency over the last few years. One of the many impacts of wildfires on humans and ecosystems is on the water quality of surface waters. Ashes and increased erosion rates might elevate the influx of nutrients, sediments, or other water quality-related components, possibly affecting the water supply. This study has three main objectives. (1) Identifying post-fire water contamination events in over 60 Portuguese reservoirs, through changepoint analysis of historical time series for (2) Testing the relationship between post-fire water contamination events with fire-, watershed-, reservoir-, and climatic drivers through logistic regression using generalized additive models. (3) The modelling and evaluation of post-fire water supply contamination risks in Portugal, using a deterministic approach. Results showed increases in TSS in 13.6% of all wildfires. Most changes fell into the unusually large fire seasons of 2003-2005 and 2017, while the most significant impacts could be seen in southern reservoirs after 2005. Fire size was identified as the main driver of post-fire water contamination, while reservoir and climate-related characteristics like water levels also played a significant role in TSS. Increased levels of suspended sediments were identified as a potential threat to the water supply, especially when large wildfires coincide with drought-induced low reservoir water levels. The modelling of past water contamination episodes shows a similar spatial distribution as the structural fire risk in Portugal, identifying the centre (and southern) regions as the most affected areas. This study may support numerous case and modelling studies and inform water managers about possible future threats.

How to cite: Nitzsche, N., Schuurman, J., Dias, L., Nunes, J. P., and Parente, J.: Post-fire water contamination risk assessment in Portugal, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-572, https://doi.org/10.5194/egusphere-egu23-572, 2023.

The paper discusses the limits of data sources that are widely available, used and applicable for soil erosion and sediment transport modelling. It emphasizes the accuracy and spatial detail of land use and stream topology data. These two inputs are critical in terms of sediment transport dynamics. The aim of the paper is to point out the error propagation into results at the small catchment scale if the data is used inappropriately. In contrast, we show how the quality and accuracy can be significantly improved by checking, verifying and modifying the directly available data sources to make them applicable at the scale of smaller catchment (tens of km²). The accuracy that can be achieved by directly measuring and describing the real situation in the field (land use, streams, crops) is discussed.

WaTEM/SEDEM (based on RUSLE and sediment transport capacity assessment) was selected as a modelling approach. The results will be interpreted using a case-study of the Oostanaula watershed, Tennessee, USA, approximately 10km². Modelling utilized the most recent available DEM, land use and soil data in raster resolution 10x10 m.

Research has been supported by project TUDI (European Union's Horizon 2020 research and innovation programme under grant agreement No 101000224), LTA-USA 19019 (Ministry of Education of the Czech Rep.), TAČR SS02030027 and SS05010180 (Technology Agency of the Czech Republic)

How to cite: Bauer, M., Dostal, T., Krasa, J., Schwartz, J., and Bynum, K.: Can we trust our data sources? A case study presenting limits of spatial detail of sediment transport modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4890, https://doi.org/10.5194/egusphere-egu23-4890, 2023.

Controlling non-point source pollution is often difficult and costly. Therefore, focusing on areas that contribute the most, so-called critical source areas (CSAs), can have economic and ecological benefits. CSAs are often determined using a modelling approach, yet it has proved difficult to calibrate the models in regions with limited data availability. Since identifying CSAs is based on the relative contributions of sub-basins to the total load, it has been suggested that uncalibrated models could be used to identify CSAs to overcome data scarcity issues. Here, we use the SWAT model to study the extent to which an uncalibrated model can be applied to determine CSAs. We classify and rank sub-basins to identify CSAs for sediment, total nitrogen (TN), and total phosphorus (TP) in the Fengyu River Watershed (China) with and without model calibration. The results show high similarity (81%-93%) between the identified sediment and TP CSA number and locations before and after calibration both on the yearly and seasonal scale. For TN alone, the results show moderate similarity on the yearly scale (73%). This may be because, in our study area, TN is determined more by groundwater flow after calibration than by surface water flow. We conclude that CSA identification with the uncalibrated model for TP is always good because its CSA number and locations changed least, and for sediment, it is generally satisfactory. The use of the uncalibrated model for TN is acceptable, as its CSA locations did not change after calibration; however, the TN CSA number decreased by around 60% compared to the figures before calibration on both yearly and seasonal scales. Therefore, we advise using an uncalibrated model to identify CSAs for TN only if water yield composition changes are expected to be limited. This study shows that CSAs can be identified based on relative loading estimates with uncalibrated models in data-deficient regions.

How to cite: Chen, M., Janssen, A. B. G., de Klein, J. J. M., Du, X., Lei, Q., Li, Y., Zhang, T., Pei, W., Kroeze, C., and Liu, H.: Comparing Critical Source Areas for the Sediment and Nutrients of Calibrated and Uncalibrated Models in a Plateau Watershed in Southwest China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1074, https://doi.org/10.5194/egusphere-egu23-1074, 2023.

Current state-of-art studies have been largely focusing on analysing how headwater catchment characteristics influence the sensitivity of the water yield in response to climate change. However, there has been little research combining both hydrological analysis with in situ water quality assessment and understanding how extreme climate events could influence the water quality of the headwater catchment, especially under anthropogenic stress. Therefore, this research aims at understanding the mechanisms of how different types of droughts modify the water quality of an anthropogenically impacted catchment.

The research is performed on the Lauter river, which takes its source from two headstreams, the Scheidbach and the Wartenbach in the Palatinate Forest, Rhineland-Palatinate and flows between the French-German border and ultimately flow into the Rhine River. The discharge time series of 59 years and water quality data of 48 years are being analysed. We will present the methodology of the research and current updates on the progress. The research is planned to proceed in three steps, 1) understanding the water partitioning mechanism and defining different drought types by using the SWAT (The Soil & Water Assessment Tool), 2) studying the water quality behavior under different hydrologic scenarios by conducting in situ water quality monitoring experiments, 3) predicting the water quality trend under future climate change and anthropogenically impacted scenarios. Current results include water quantity trend analysis based on the daily flow rate data at the Salmbacher Passage measuring station on the Lauter river and a primary catchment modeling result with the SWAT.

Keywords: Drought, Water quality, SWAT model, Headwater catchment

How to cite: Liu, X. and de Jong, C.: Analysis of the impacts of droughts on the water quality of the transboundary German-French Lauter catchment with SWAT, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5376, https://doi.org/10.5194/egusphere-egu23-5376, 2023.

Te-Chi Reservoir is an multipurpose reservoir, which supplies drinking water for a population of ~2,800,000 and generate hydroelectric power in the Taichung city, Taiwan. In the past 10 years, this reservoir experienced several events of algal blooms and extreme drought. According to the historical water quality data, the frenauency of the trophic state for the reservoir has increased in the recent years. The N/P ratios of the reservoir are generally greater than 15, indicating that the limited nutrient of eutrophication is phosphorous. In this study, we developed an integrated model to predict the water quality of the reservoir using an input of 10-year observational data. A hydrological stream flow model (i.e., SWAT) was integrated with the simple phosphorous (P) input-output models (i.e., the Vollenweider model) to simulate the change of the trophic state and the concentration of P in the reservoir. We first investigated the hydrological variability impact on the P load in past three year when the extreme weather (drought) happened.The results showed that the concentraion of total phosphorous (TP) was significantly influenced by the inflow of the river to the reservoir and the precipitation (rainfall). The simulated concentrations of TP in dry seasons were typically higher than that in the wet seasons. During the drought, the internal loading, such as resuspension, played a significant source of P for the reservoir. We also investigated the sources and loads of key water pollutants, especially nitrogen and phosphorous, from the spatial aspect in the watershed of the reservoir. The results indicated that the TP loads of each sub-catchment area ranged from 2.76 to 4.12 kg/h. Furthermore, in order to understant the feasibility of establishment of riparian buffer strip, the effect of the land use change on water quality was simulated. This study demonstrated the application of the integrated SWAT-Vollenweider model for a reservior to identify the drivers of pollutants for managing its watershed to mitigate the potential of eutrophication.

How to cite: Lin, Y.-I., Yu, M.-S., Chang, H.-S., and Pan, S.-Y.: Modeling the impact of land-use and climate change on water quality of a deep dam reservoir, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17358, https://doi.org/10.5194/egusphere-egu23-17358, 2023.

Forest status in natural catchment is substantially important for hydrology and water quality, but it has been increasingly altered by human activities and climatic factors. Due to recent rapid changes in forest cover, there is an urgent need for hydrological water quality models which can adapt to these changing environmental conditions. The objective of this study was to analyse the impact of rapid continuous forest decline on nitrogen losses in a temperate mountain range catchment using a dynamic setting of the HYPE (HYdrological Predictions for the Environment) model. The modified model was applied to the Große Ohe catchment, Germany, which has experienced severe forest dieback (caused by bark beetle infestations) and its recovery over the last three decades. The model was validated by using also additional 25 years data from an internal gauge station (Forellenbach) and two soil measurement sites. Three scenarios, namely, no forest change, deforestation with subsequent regeneration, and deforestation without regeneration, were compared to identify key factors influencing catchment discharge and nitrogen export due to deforestation and regeneration. Results showed that the model performed well at the Große Ohe catchment scale, with Nash-Sutcliffe Efficiency values of 0.77 and 0.57 for discharge and IN concentration, respectively, and percentage BIAS values of -11.6% and 0.5%, respectively, during the validation period. Similar good performances were also observed at other scales. The simulation results proved that the improved model was able to (1) well capture the timing of peak flows and the seasonal dynamics of inorganic nitrogen (IN) concentration, and more importantly, (2) reflect the first increasing and then decreasing trend of discharge and IN concentration, in accordance with the deforestation and forest regeneration, respectively. By comparing scenarios, after experienced forest dieback without regeneration, the discharge and IN concentration exports were 24.9% and 160%, respectively, greater than those of scenario without forest change. However, the discharge and IN concentration exports were only 3.63% and 39.6% greater, respectively, with the help of continuous regeneration, indicating that forest regeneration is important for restoring hydrological and water quality status in the catchment. Compared to non-change scenario, the deforestation scenario exhibited decreased annual plant uptake of 34.7%, and strong increase in annual denitrification and N mineralization suggesting that the increased nitrogen export was likely induced by the reduction in vegetation uptake and the increased availability of soil nitrogen from tree residues. Overall, the adapted mechanistic modelling under the changing catchment forest conditions can strongly support forest management in terms of water quality.

How to cite: Chen, M., Lausch, A., Jomaa, S., Ghaffar, S., Beudert, B., and Rode, M.: Impact of deforestation on catchment hydrology and nitrogen losses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12436, https://doi.org/10.5194/egusphere-egu23-12436, 2023.

High nitrate concentrations in groundwater and surface water threaten drinking water quality and the integrity of aquatic ecosystems. Discharge events can play a disproportionate role in nitrate mobilization and transport from source to stream, while observed inter-event variability in export patterns is often high. One approach for analyzing the variability of nitrate export is the relationship between nitrate concentrations and discharge. Such C-Q relationships applied across different time scales can inform about source availability (or limitation) of the specific solute and hydrological connectivity to the stream network. Recent studies revealed striking differences between long-term and event-scale C-Q relationships for nitrate, and further that inter-event variability in C-Q relationships decreases with event magnitude (Knapp et al., 2020; Musolff et al., 2021; Winter et al., 2022). This suggests that an integrated measure for nitrate export from long-term data may be insufficient to understand these mechanisms. Here, we hypothesize that event-specific nitrate export patterns systematically diverge from long-term patterns and converge towards chemostatic or dilution patterns at high-magnitude events, depending on the availability and hydrological connectivity of nitrate sources within the catchment. To verify this hypothesis, we analyzed C-Q relationships across 41 catchments in the U.S., using daily discharge and nitrate concentration data. We compared long-term and event-specific C-Q relationships for 5067 discharge events and described inter-event variability in relation to event magnitude. We found that the long-term C-Q relationship was more dynamic than the one averaged for individual events and that the variability of event-specific C-Q slopes significantly decreased with event magnitude, indicating that different mechanisms of source mobilization and transport operate at different time scales and event magnitudes. Notably, high-magnitude events converged towards chemostatic patterns and rarely showed evidence of dilution and thus source limitation, which might hint at substantial nitrogen legacies. The divergence between long-term and event-specific C-Q slopes increased with the share of agricultural area and fertilizer application in the catchment. The consistent patterns in long-term and event-scale nitrate export patterns across a large number of catchments allow us to relate these patterns with the availability, spatial distribution and hydrological connectivity of nitrate sources within the catchments. As such, our study is an important step towards understanding the relevant mechanisms for nitrate mobilization and transport during runoff events.

References

Knapp, J. L., Freyberg, J. von, Studer, B., Kiewiet, L., and Kirchner, J. W.: Concentration-discharge relationships vary among hydrological events, reflecting differences in event characteristics, Hydrol. Earth Syst. Sci. Discuss., 1–27, https://doi.org/10.5194/hess-24-2561-2020, 2020.

Musolff, A., Zhan, Q., Dupas, R., Minaudo, C., Fleckenstein, J. H., Rode, M., Dehaspe, J., and Rinke, K.: Spatial and Temporal Variability in Concentration-Discharge Relationships at the Event Scale, Water Resour. Res., n/a, e2020WR029442, https://doi.org/10.1029/2020WR029442, 2021.

Winter, C., Tarasova, L., Lutz, S. R., Musolff, A., Kumar, R., and Fleckenstein, J. H.: Explaining the Variability in High-Frequency Nitrate Export Patterns Using Long-Term Hydrological Event Classification, Water Resour. Res., 58, e2021WR030938, https://doi.org/10.1029/2021WR030938, 2022.

How to cite: Winter, C., Jawitz, J. W., Cohen, M. J., Ebeling, P., and Musolff, A.: Surprising consistency in event-scale nitrate export patterns across catchments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5599, https://doi.org/10.5194/egusphere-egu23-5599, 2023.

Keywords

Freshwater pollution, climate change, water quality monitoring, emerging contaminants, diffuse agricultural pollution, catchment monitoring.

Abstract

Despite the implementation of river basin management plans across EU, river water quality is in decline with agriculture, forestry and hydromorphological pressures now the dominant pressure for river waters in Ireland.  The number of high quality river sites reflecting natural, undisturbed conditions declined from 31.6% of river sites monitored in 1990 to just 1.1% of monitored sites in 2021¹. 

Climate change increases in heavy rainfall events in conjunction with flooding will lead to increased suspended solid and nutrient loadings in rivers² with a substantial upsurge in the intensity of winter rainfall together with increasing frequency in heavy rainfall events³ in Ireland⁴ leading to increased pollution of freshwater systems and a surge in transient pollution events.

‘Reliable high quality information on the environmental quality of surface waters’ is critical for  agencies to make evidence based decisions on appropriate management measures to restore water quality at European scale⁵.  However current water quality monitoring programmes in Ireland rely heavily on grab water samples which is inadequate at detecting transient pollution⁶. 

Are transient pollution events contributing to increased solids, nutrients loads and emerging contaminants affecting aquatic species in these declining Q5 sites?  This research aims to investigate by applying field assessments, sensor technology and automatic sampling to two river stations in the North West of Ireland; on the River Unshin a high ecological status water body and on the River Owenmore, a moderate ecological status water body.  As the pathway from land to waters for multiple diffuse agricultural pollutants, including phosphorus, sediment and pesticide are similar⁷ and turbidity can be used as an indicator for suspended sediment⁸, a baseline turbidity survey is being carried out to identify a ‘trigger level’ above which the collection of water samples is initiated. 

Other research has shown no simple relationship between discharge, turbidity and precipitation⁹ but initial baseline data obtained shows some correlation with turbidity and increased flows.

References

(1)          Trodd, W.; O’Boyle, S.; Gurrie, M. 2022.

(2)          Whitehead, P.; Butterfield, D.; Wade, A., SC070043/SR1; Environment Agency: Bristol, 2008; p 115.

(3)          Murphy, C.; Broderick, C.; Matthews, T. K. R.; Noone, S.; Ryan, C. EPA Research Report 277; Maynooth University, 2019; p 76. https://www.epa.ie/publications/research/climate-change/research-277-irish-climate-futures-data-for-decision-making.php (accessed 2023-01-09).

(4)          O’Connor, P.; Meresa, H.; Murphy, C., Weather 2022. https://doi.org/10.1002/wea.4288.

(5)          Kristensen, P.; Bogestrand, J. Surface Water Quality Monitoring — European Environment Agency January 1996; European Topic Centre on Inland Waters; Publication; National Environmental Research Institute: Denmark, 1996; p 82. https://www.eea.europa.eu/publications/92-9167-001-4 (accessed 2023-01-09).

(6)          Regan, F.; Jones, L.; Ronan, J.; Crowley, D.; Mcgovern, E.; Mchugh, B.; 2018.

(7)          Thomas, I.; Bruen, M.; Mockler, E.; Werner, C.; Mellander, P.-E.; Reaney, S. M.; Rymsezewicz, A.; McGrath, G.; Eder, E.; Wade, A.; Collins, A.; Arheimer, B.; EPA RESEARCH PROGRAMME 2021–2030; EPA Research Report 396; University College Dublin: Dublin, 2021; p 64. https://www.epa.ie/publications/research/water/Research_Report_396.pdf.

(8)          Uhrich, M. A.; Bragg, H. M.; Water-Resources Investigations Report, 2003; p 2. https://doi.org/10.3133/wri034098.

(9)          Wang, K.; Steinschneider, S. Water Resources Research 2022, 58 (10), e2021WR031863. https://doi.org/10.1029/2021WR031863.

How to cite: Cronin, L., Regan, F., and Lucy, F. E.: Detection of transient pollution events in an Irish river catchment in the context of increasing frequency and intensity of rainfall events due to climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15993, https://doi.org/10.5194/egusphere-egu23-15993, 2023.

Water quality in European rivers is degraded by nutrient loss to waters, and such problems can be exacerbated by climate change. Climate smart mitigation measures are needed and these require insight into the underlying processes of nutrient loss under future weather conditions. To address this, the aim of this study was to assess how a changing climate may alter phosphorus (P) mobilisation, delivery and impact in two hydrologically contrasting agricultural river catchments (ca 11 km²) in Ireland. As part of the WaterFutures project and the Agricultural Catchments Programme, The Simply P model was calibrated with 10 years of high frequency data of hydro-chemo-metrics for the two catchments. Five downscaled Global Climate Models (CNRM-CM5, EC-EARTH, HadGEM2-ES, MIROC5 and MPI-ESM-LR) were used to simulate two far-future climate scenarios, one intermediate emission pathway (RCP4.5) and one intensive emission pathway (RCP8.5). The scenarios were used to estimate P concentrations and loads for the coming century. A newly developed P Mobilisation index (ratios of concentration percentiles) and P Delivery index (ratios of mass load percentiles) was used to assess changes in P transfer for the modelled P concentrations and P loads.

In a hydrological flashy catchment, it was estimated that climate change alone may increase mean annual total P (TP) concentration from 0.120 mg/L monitored between 2010-2019 to 0.184 mg/L by 2070-2100. A corresponding increase in Delivery index by around 25% and 40% (for RCP4.5 and RCP8.5, respectively) but no change in Mobilisation index suggests that the impact is mostly due to enhanced hydrological connection and/or reduced P retention. The mean annual total reactive P (TRP) concentration was estimated to show minor decreases from 0.079 mg/L to 0.075 mg/L. A corresponding decrease in the Mobilisation index by around 5% and 10% (for RCP4.5 and RCP8.5, respectively) but an increase in Delivery index by 25% and 40% suggests a possible decrease in soil P detachment and/or solubilisation, limiting the increased delivery potential. The same analysis on data from a groundwater-fed catchment suggests that climate induced changes in TP and TRP concentrations were mostly related to delivery processes for TP.

The underlying processes for P losses associated with climate change are likely to be different for TP and TRP and for catchments with different hydrological controls. Such information helps to target more resilient land use mitigation methods and further design these for scenarios of future weather conditions and land use.

How to cite: Mellander, P.-E., Hawtree, D., Ezzati, G., Murphy, C., Galloway, J., Jackson-Blake, L., Norling, M., Jordan, P., Pulley, S., and Collins, A.: Land to water phosphorus transfer processes under climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6014, https://doi.org/10.5194/egusphere-egu23-6014, 2023.

Data on the diffuse source annual flow weighted total phosphorus (TP) concentrations from 349 Danish streams draining smaller catchments (< 50 km²) for the period 1990-2019 were used for developing a model in machine learning software (DataRobot version 6.2; DataRobot Inc. Boston MA, USA). The developed diffuse source TP-concentration model will substitute an older model that have been in place to calculate P-loadings to Danish estuaries from ungauged areas. A total of 207 streams with 3,144 annual observations of flow-weighted TP concentrations together with information on 19 explanatory variables was entered into the DataRobot software. DataRobot divides the input data into three layers: Training dataset (64%), validation dataset (16%) and hold out dataset (20%). Thereafter, DataRobot conducts a five-layer cross-validation and tests among 72 different model types before suggesting final best solutions.

In this case, the TP-concentration model was developed as an ‘eXtreme Gradient Boosted Trees Regressor with early stopping’ as suggested by the DataRobot software to be superior for modelling the annual flow-weighted TP concentration based on 13 explanatory variables. The most influencing explanatory variables in the final model are: 1) tile drainage in the catchments; 2) ; 3) period (two periods with different sampling regimes; 4) proportion of agricultural land; 5) importance of bank erosion; 6) deviation of annual runoff from long-term mean. The final TP-concentration model has a R²=0.69 for the training dataset, R² = 0.71 for the validation dataset and R² = 0.67 for the hold out dataset.

A validation of the new machine learning TP-concentration model on 142 independent streams with 1,261 annual observations was conducted to investigate the uncertainty of the model simulations. The validation showed the TP-concentration model to have a high explanatory power (R²=0.60) and with a very good simulation performance in the nine Danish georegions, as well as for the 30 year long time series of data. 

An application of the model for calculating flow-weighted TP-concentrations within nearly 3,200 catchment polygons (ID15’s) covering the Danish land area showed that the new developed machine learning TP-model is a valuable tool both for calculation of TP-loadings from ungauged areas to lakes and coastal waters as well as for linking catchment pressures to stream ecological status.   

How to cite: Kronvang, B., Windolf, J., Tornberg, H., Rolighed, J., and Larsen, S.: A novel machine learning national model for diffuse source total phosphorus concentrations in streams, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2206, https://doi.org/10.5194/egusphere-egu23-2206, 2023.

The Agricultural Catchment Program (ACP) has collected over a decade’s worth of high frequency data for a number of hydrologic and chemical indicators at agricultural catchments around the Republic of Ireland. This dataset provides an excellent foundation for conducting robust modelling studies assessing long term hydrochemical dynamics in agricultural sites, within the context of EU regulations around the protection of water quality.

To examine the risks of phosphorus (P) export from agricultural catchment in this context, the parsimonious phosphorus model SimplyP was applied to two ACP study sites. These sites are in close proximity and are of similar size to each other but have contrasting physical characteristics and hydrochemical dynamics. Site “A” is dominated by grasslands with heavy soils and is P export risky, while site “B” is primarily arable land-use on lighter soils and has a lower risk of P export.

In these catchments, SimplyP was used to simulate streamflow, sediment, and phosphorus (PP, TRP, TP) over the period of 2010 – 2019. The model is calibrated and validated independently three times to different objective functions (NSE, KGE, NSE log) to provide models focused on peak flows, balanced, and low flows, respectively. Model performance is evaluated over the entire calibration and validation period, as well as year-by-year assessments, which highlights the influence of meteorological and antecedent moisture conditions on model behaviour.

How to cite: Hawtree, D., Galloway, J., Zurovec, O., Jackson-Blake, L., Norling, M., and Mellander, P.-E.: Performance of a Parsimonious Phosphorus Model (SimplyP) in Two Contrasting Agricultural Catchments in Ireland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7759, https://doi.org/10.5194/egusphere-egu23-7759, 2023.

The discharge of phosphorus associated with wastewater has decreased significantly in Europe over the past 25 years¹, however the problem of diffuse pollution persists².  Studies have shown that regulatory monitoring can miss elevated spikes in phosphorus concentrations³ and high frequency monitoring is required⁴. Such programmes are resource intensive, requiring effective tools which enable appropriate water quality data collection and quality assurance⁵.

A low cost, portable, and rapid phosphate detection system is needed to enable the quick detection of phosphate in areas affected by high phosphate levels⁶. A new system is being developed by evolving a colorimetric detection system using microfluidic lab-on-a-disc technology which has previously been demonstrated⁷. It utilizes a micro-spectrometer and the molybdenum blue method, and has been built with the intent of requiring limited training.

The range of the system is 5-400 µg/L, which encompasses the threshold value of 35 µg/L P for Irish rivers and groundwaters⁸. The system is extremely portable due to its compact size and weighing less than 2 kg. With a run time of 15 minutes per ten samples, it enables the in-situ detection of phosphate for rapid on-site monitoring.

To test the system, rivers in the northwest of Ireland were identified. Three of these rivers have historical orthophosphate readings in the range of 5 - 47 µg/L and two others were reported considerably higher at 84 µg/L.  

With this microfluidic phosphate detection system, rapid in-situ detection and reliable, real-time monitoring of phosphorus in freshwater systems can be achieved. 

References:

1)European waters -- Assessment of status and pressures 2018 — European Environment Agency. https://www.eea.europa.eu/publications/state-of-water (accessed 2022-06-13).

2)Biddulph, M.; Collins, A. l.; Foster, I. d. l.; Holmes, N. The Scale Problem in Tackling Diffuse Water Pollution from Agriculture: Insights from the Avon Demonstration Test Catchment Programme in England. River Research and Applications 2017, 33 (10), 1527–1538. https://doi.org/10.1002/rra.3222.

3)Fones, G. R.; Bakir, A.; Gray, J.; Mattingley, L.; Measham, N.; Knight, P.; Bowes, M. J.; Greenwood, R.; Mills, G. A. Using High-Frequency Phosphorus Monitoring for Water Quality Management: A Case Study of the Upper River Itchen, UK. Environ Monit Assess 2020, 192 (3), 184. https://doi.org/10.1007/s10661-020-8138-0.

4)Bowes, M. J.; Palmer-Felgate, E. J.; Jarvie, H. P.; Loewenthal, M.; Wickham, H. D.; Harman, S. A.; Carr, E. High-Frequency Phosphorus Monitoring of the River Kennet, UK: Are Ecological Problems Due to Intermittent Sewage Treatment Works Failures? Environ. Monit. 2012, 14 (12), 3137–3145. https://doi.org/10.1039/C2EM30705G.

5)Quinn, N. W. T.; Dinar, A.; Sridharan, V. Decision Support Tools for Water Quality Management. Water 2022, 14 (22), 3644. https://doi.org/10.3390/w14223644.

6)Park J.; Kim, K. T.; Lee; W. H. Recent advances in information and communications technology (ICT) and sensor technology for monitoring water quality. 2020, Water, 12 (2)

7)O’Grady, J., Kent N., Regan, F. (2021). Design, build and demonstration of a fast, reliable  portable phosphate field analyser. Case Stud. Chem. Environ. Eng., 2020, 4, 100168

8)Tierney, D.; O’Boyle, S. Water Quality in 2016: An Indicators Report; Environmental Protection Agency, Ireland: Wexford, 2018; p 48.

How to cite: Bracker, R., Cronin, L., Grubliauskas, A., Free, L., O’Grady, J., Power, S., Daly, K., Kent, N., Regan, F., and White, B.: Rapid Phosphate Monitoring in Irish Freshwater Systems Using a Novel Microfluidic Colorimetric System, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16201, https://doi.org/10.5194/egusphere-egu23-16201, 2023.

Intensive livestock production has raised enormous water quality concerns in Europe and elsewhere around the world. There is a need to examine long-term water quality trends and understand the drivers for the trends based on detailed catchment monitoring. Given orthophosphate-phosphorus (P) is highly relevant to eutrophication in freshwater lakes and rivers, we monitored its concentration and load trends in streamwater of a livestock-intensive catchment in western Norway for a 20-year period, using the approaches of continuous flow measurements and flow-proportional composite water sampling. Precipitation and catchment-level soil P balance, as well as field-level measurements of soil P status, were monitored to examine the drivers. Trend analyses showed that both annual mean P concentration (range: 0.05–0.14 mg L^-1; mean: 0.08 mg L^-1; p = 0.001) and annual P load (range: 0.35–1.46 kg ha^-1; mean: 0.65 kg ha^-1; p = 0.0003) increased significantly over the 20-year monitoring period. The mean concentrations were positively correlated with cumulative soil P surplus (R² = 0.55, p = 0.0002). Although discharge of the streamflow significantly affected annual P load, the P surplus appeared to be an even more important factors. The study highlights that long-term P surplus plays a critical role in influencing orthophosphate-P concentration and loads in livestock-intensive regions. There is a big challenge to reduce the P surplus, which however may be achieved through integrated strategies such as reducing livestock density, manure refinement and transport to crop-intensive regions, improving livestock feeding management, and increasing crop P removal.

How to cite: Liu, J., Bechmann, M., and Øgaard, A. F.: Water quality trends and the drivers in livestock-intensive regions: Results from 20 years of catchment monitoring in Norway, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3176, https://doi.org/10.5194/egusphere-egu23-3176, 2023.

Landscape disturbance pressures in forested headwater regions can modify both the supply and transport of sediment from hillslopes to river networks. The effects of these pressures on phosphorus (P) mobility in rivers vary regionally depending upon the type and severity of the disturbance as well as interactions amongst other watershed scale controls such as climate, geology, hydrology and vegetation. The present study examines P dynamics in a gravel-bed river across multiple disturbances during environmentally sensitive periods of summer low-flow. Six study sites were selected to represent a gradient of sediment pressures from landscape disturbances (e.g., roads, harvesting, wildfire, sewage) in the Crowsnest River, Alberta. Interactions between fine bed sediments and soluble reactive phosphorus (SRP) were examined using equilibrium phosphorus concentrations (EPC0) and diffusive fluxes of SRP from the riverbed sediments. Diffusive fluxes at each site were estimated using gradients of SRP between pore-water in the bed and water column, determined from vertical distributions of SRP in the gravel matrix measured with pore-water peepers. SRP concentrations in pore-water were variable among depths and sites but were elevated downstream of the stream reach receiving primary sewage effluent outflow. Larger SRP concentration gradients were observed at sites that had either smaller substrate or increased biofilm activity. The EPC0 and diffusive pore-water flux data suggest that fine sediment in the riverbed acted as a source of SRP to the water column under low-flow conditions when the risk for eutrophication is higher and such conditions favor the growth of biofilms. EPC0 concentrations showed large inter- and intra-site variability indicating heterogeneous responses to disturbance. Furthermore, overlapping, and varying proportions of historic and contemporary harvesting, roads, road-stream or culvert crossings, and OHV use confounds the apportionment of landscape impacts. This study provides insight into the potential for the regulation of P by sediments in gravel-bed rivers following a range of landscape disturbance effects.

How to cite: Stone, M. and Watt, C.: Cumulative disturbance effects on phosphorus mobility in a gravel-bed river at the catchment scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10511, https://doi.org/10.5194/egusphere-egu23-10511, 2023.

High amounts of nutrients favor the growth of algae that consume oxygen from the aquatic environment causing eutrophication. In the case of phosphorus, it comes mainly from two sources: fertilizers washed from agricultural areas by runoff water and urban and industrial development. In the first case, the phosphorus loads do not have a clear point of entry into the water channels, whereas in the second one, the phosphorus loads can be generated from point sources, such as discharges from the wastewater treatment plants (WWTP) but also from non-point sources, such as urban areas runoff in episodes of intense rainfall. 
The main purpose of this work is to analyze the content of phosphorus in water for more than 40 years and inquiry into the origin of the sources that may have produced the phosphorus loads. For this purpose, the Guadaira river basin (South of Spain), where agricultural land uses converge with numerous human activities resulting in high pressures on water quality, was selected. 
The results highlight that the phosphates threshold value established for good/moderate state (0.32 mg PO4/l) is exceeded by 96% of the measurements during the period 1981-2022 in a water quality control point located downstream of the main WWTP, which threat the wastewater of Seville, and that in addition collects the contributions from the other WWTPs and agricultural lands located in the basin. The episodes of sediment contribution that occurred during the period 1981-2022 were analyzed at this control point, and from the 184 episodes found, 30 episodes may have been due to runoff (which also may have originated from agricultural areas or from the overflow of water collectors) (type 1 episodes) and 79 may have been due to urban spills (type 2). 80% of both types of episodes were found to be higher than 1.5 mg/l being able to reach concentration values of up to 14 mg/l. Most of the episodes of dry months were categorized as type 2, reaching the highest concentration values (8-17 mg/l), while type 1 episodes were mostly present in rainy months.

Finally, despite the increase of the stable population (+0.52% ∼ +1.42% per year between 2000 and 2012) and tourism (average ≈ +3.23% per year), the WWTP improvement has achieved a decrease in the mean phosphorus concentrations of -0,2% per year. Despite the investment in the WWTP of the basin is necessary to improve its operation and efficiency as well as its adaptation to the increase in population and tourism to ensure better water quality of the water resources.

Acknowledgements: This work has been funded by the project TransDMA – Adaptation of the Water Framework Directive to the Andalusian reality: The Guadalquivir estuary as an integrated management model, promoted by the Ministry of Economy, Knowledge, Business and University and co-financed by the operational program FEDER 2014-2020 in Andalusia.

How to cite: Jurado-Ezqueta, M. J., Contreras, E., Hidalgo, C., Serrano, L., and Polo, M. J.: Main drivers of the seasonal and annual changes in phosphorus content in the Guadaira river (South of Spain), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16398, https://doi.org/10.5194/egusphere-egu23-16398, 2023.

Irrigation in arid and semi-arid regions is key to maintain the productivities and the well-being of farmers. However, irrigation is an important source of pollution to rivers due to the impact of agricultural drainage [1], which may contain high levels of salts, nutrients and other pollutants. In the present study we quantified the impact of implementing irrigation in a 10,000 ha semi-arid basin of the Noguera Ribagorçana river (Ebro Basin, NE Spain). Water quality data obtained during 20 years (2002-2022) in four different sampling points in the river (three before, and one after the main agricultural drainage returns of the basin, which drains 4,366 ha) were analyzed, focusing on nitrate concentration (NO₃^-, ppm), phosphate concentration (PO₄^3-, ppm), and electrical conductivity of the water (EC, dS/m). In 2002, less than 4,000 ha were under irrigation and during the studied period, a total of 5,571 hectares were brought under irrigation progressively over time, with the implementation of a new irrigation district in the area. Results showed a significative difference in the concentration of NO₃^- in the river water before and after the main agricultural drainage return of the new irrigation district. However, phosphorous concentration and electrical conductivity showed no significative differences between the sampling points before and after the main agricultural drainage returns. On the other hand, NO₃^- values at the sampling point after the main agricultural drainage return have increased over time as it did the irrigated area. Thus, along the 18 km of the Noguera Ribagorçana river observed in this study, NO₃^- levels have increased on average from 1.7 ppm at the first sampling point to 10.9 ppm at the last sampling point, after the returns of agricultural drainage in the basin. Therefore, we could state that implementing irrigation in 5,571 ha represents an increase of 9.2 ppm of NO₃^- in the water of the Noguera Ribagorçana river in the studied area.

[1] Blann, K. L.; Anderson, J. L.; Sands, G. R.; Vondracek, B. Effects of Agricultural Drainage on Aquatic Ecosystems: A Review. Crit. Rev. Environ. Sci. Technol. 2009, 39 (11), 909–1001. https://doi.org/10.1080/10643380801977966.

How to cite: Altés, V., Pascual, M., Escorihuela, M. J., and Villar, J. M.: Quantifying the Downstream Impact of Implementing Irrigation in a Semi-Arid Mediterranean Basin in NE of Spain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11746, https://doi.org/10.5194/egusphere-egu23-11746, 2023.

Nitrate excess in rivers is caused by anthropogenic nitrogen sources, such as agriculture and wastewater. Diffuse sources stemming from agricultural fertilization can remain in the soil for long periods of time as a legacy and are mobilized through hydrological pathways that connect sources with rivers. Previous studies show that drought periods can increase nitrogen stored in the soil due to lower nitrate transport to streams and less nitrate uptake by plants due to dry conditions. This accumulation of nitrogen during drought and its subsequent transport under wet conditions during the post-drought period can result in high nitrate concentrations in rivers.

In our study, we analyze the nitrate response of 190 German rivers during hydrological post-drought conditions from 1978 to 2019. We define droughts as periods with more than 30 consecutive days of discharge deficit using a variable threshold method and post-droughts as 100-day periods following the termination of a drought. We particularly focus on post-drought periods in the winter season that display the most pronounced concentration anomalies. Our results show that during the winter post-drought period, 66% of the catchments export higher nitrate concentrations compared to non-drought conditions, with 19% of the catchments exporting significantly higher nitrate concentrations (Kruskal-Wallis test, p-value<0.05). Catchments that exhibit a significant increase in nitrate concentrations during winter post-drought periods tend to be characterized by higher annual precipitation and shallower aquifers, indicating that fast hydrological transport could be a key factor in the winter post-drought delivery of nitrate excess. A projected increase in the frequency of severe droughts due to climate change could lead to more frequent post-drought episodes with high nitrate concentrations in the future. Understanding the main drivers of post-drought transport of nitrate across catchments is crucial for focusing management efforts efficiently.

How to cite: Saavedra, F., Musolff, A., Von Freiberg, J., Merz, R., Knoll, K., Müller, C., Brunner, M., and Tarasova, L.: Post-drought nitrate mobilization in German catchments    , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7069, https://doi.org/10.5194/egusphere-egu23-7069, 2023.

Droughts are significant hydrological and environmental hazards that threaten the ecological functioning of water bodies. Low flow with increased water temperature leads to a cascade of hydrochemical processes. This is a particular cause of concern for regions like eastern Austria, where agricultural land use and the projected risk of low flows and increased water temperatures due to climate change are particularly high. Under these scenarios, nutrient release from river sediments may become the dominant factor for the water quality of Iotic ecosystems. The role of this remobilization-potential for water quality is assessed in the project DIRT based on a combination of laboratory experiments with at-site water quality monitoring and regionalized streamflow observations.

Here we focus on space-time models of low flow and stream temperature, which are crucial for upscaling the remobilization potential along the river network. We present a study that compares different models for spatio-temporal low flow regionalization at the monthly scale in eastern Austria.

We evaluate three different statistical models: (i) a tree-based boosting model, (ii) a simple linear regression model with 3-way interactions, and (iii) a combination of a non-linear boosting approach and Top-kriging. Our results show a very high performance for all models, with an overall R² of 0.88 and a median R² of 0.70. The best performance is reached by the combination of Top-kriging with a non-linear boosting approach. However, accuracy of the model is somewhat lower in headwater gauges, whereas non-headwater catchments are even better modeled by a simple spatio-temporal Top-kriging approach. In a next step, the model shall be integrated with laboratory experiments and water-quality monitoring to develop space-time models that can predict the remobilization of pollutants from river sediments.

How to cite: Laimighofer, J., Pressl, A., Langergraber, G., Weigelhofer, G., and Laaha, G.: Comparison of spatio-temporal low-flow models for predicting remobilization of water pollutants, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5516, https://doi.org/10.5194/egusphere-egu23-5516, 2023.

The river Thames catchment  passes through rural and urban centres covering many different environments and land uses. Therefore, it is exposed to a range of stresses from sewage pollution to run off from agriculture. As such, UKCEH has been conducting water quality monitoring of the Thames since 1997, which later expanded into the Thames Initiative. The Thames Initiative collects a wide range of chemical and biological data, at 19 sites across the Upper Thames Catchment and its tributaries. For 18 months, in 2012-13, fluorescence spectroscopy and PARAFAC analysis was used to identify 4 components of fluorescent organic matter (FOM). This research focusses on the role of the fourth component, C4, which represents a tryptophan like FOM(TLF). The study is looking at the peak’s temporal variability at all 19 sites within the Thames catchment, alongside nutrient and biological data. This will enable greater understanding TLF’s sources and pathways by analysing TLF’s interaction with other nutrients and pollutants.  There is robust research linking TLF to sewerage pollution and more widely anthropogenic activity. However, the understanding of TLF as a product of insitu production from microorganisms is still in relative infancy, particularly when looking for evidence in the field at a catchment level. In this study multiple variate linear modelling using forward stepwise regression techniques have been applied to the data at each site to investigate the sources of C4 across the catchment to understand both catchment and instream processes. The possible predictors available to each model were dissolved potassium (DK), total dissolved nitrogen (TDN), dissolved calcium (DCa), total bacterial counts(TBC) and chlorophyll a. The models used between 2-3 predictors (σ=2.53, μ =0.678). DK was the most common (18 models),  followed by TBC (11 models), then DCa and TDN (both 8 models) and finally chlorophyll a (2 Models). These results suggest a dominant source of C4 across the catchment is from the wastewater as dissolved potassium is a sewerage indicator.  Secondly the occurrence of TDN or dissolved  calcium suggest a more dominate baseflow path of the fluorescence at these sites, as found in previous analysis of these sites.  However, most novelty is the regular occurrence of TBC in the models. This suggests  the C4 component has a bacteriological element as well, which means it is likely there is an important contribution of TLF by insitu-production from microorganisms.

How to cite: Harris, N., Old, G., Bowes, M., Scarlet, P., Nicholls, D., Armstrong, L., Read, D., Marchant, B., and Sorensen, J.: Shedding light on the organic matter black box: Using fluorescence spectroscopy to understanding microbial sources and pathways TLF, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3184, https://doi.org/10.5194/egusphere-egu23-3184, 2023.

The water quality in Republic of Ireland is regulated under the water framework directive (WFD), which requires all EU countries achieve good ecological and chemical status before 2027. However, the Irish Environmental Protection Agency (EPA) reports in 2021 that just half of the rivers, lakes, estuaries, and coastal waters achieved satisfactory or higher status.

Water quality in Ireland is monitored by traditional methods, which cannot provide timely spatiotemporal information. While remote sensing (RS)-based water quality monitoring work have been carried out in many EU countries in accordance with WFD directive, the use of RS for water quality estimation in Ireland has not been fully explored.

To explore the feasibility of RS for Irish waters, Sentinel-2 surface reflectance has been used to assess several water quality parameters (chlorophyll-a, transparency, turbidity, suspended solids (SS), total nitrogen, total phosphorus, biological oxygen demand (BOD), dissolved oxygen, and chemical oxygen demand (COD)) from March 2017 to July 2022. These were compared with the Sentinel-2 surface reflectance data resulting in a total of 6509 corresponding data points.

Initially, empirical algorithms were used to derive water quality concentrations in rivers, lakes, estuaries, and coastal waters separately. Initial results indicate that the combination of green and blue bands was correlated to coastal waters’ chlorophyll-a (R² = 0.27). For chlorophyll-a in transitional waters, the combination of red and red edge was highly correlated. However, no single band or combination were suitable for deriving chlorophyll-a in lakes. For SS, red and near infrared band are useful in detecting changes in coastal and transitional waters. Whereas, for lakes and rivers, blue and shortwave infrared band were best to derive SS. In addition to empirical algorithms, multiple machine learning methods have been used to derive water quality parameters from Sentinel-2 reflectance, with the aim of exploring if machine learning approaches can improve estimates compared with the empirical approaches.

How to cite: Zhao, M. and O'Loughlin, F.: The Derivation of Irish Water Quality via Sentinel-2 Imagery, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6952, https://doi.org/10.5194/egusphere-egu23-6952, 2023.

Agricultural production and sewer systems have been the main contributors to nutrient losses to surface waters. A high load of nutrients by rivers causes coastal eutrophication and leads to harmful algal blooms. Several negative environmental impacts of eutrophication include the production of toxins by cyanobacteria, fish kills, increased production of algae, and reduction in coral reef communities and aquatic vegetation. Despite the environmental policies and targets in Europe, rivers transport large amounts of nutrients to coastal waters and thus, coastal eutrophication is still an issue. Half of the nitrogen (N) exports by the European rivers to coastal waters is from agricultural production. The losses can increase if effective actions are not taken to improve agricultural management. As a result, the risks of coastal eutrophication will likely increase in the future coupled with global change including socio-economic development and climate change.

This study aims to assess the future river export of N and phosphorous (P) and explore options to reduce associated coastal eutrophication in Europe under global change with a focus on sustainable agriculture and urbanization. We use the MARINA-Nutrients (Model to Assess River Inputs of Nutrients to seAs) model for 601 European basins to quantify river exports of N and P in the 21^st century, and calculate an indicator for coastal eutrophication potential (ICEP) to evaluate their impacts on coastal waters. We develop scenarios based on existing storylines (e.g., Shared Socio-economic Pathways, Representative Concentration Pathways) to quantify the impacts of socio-economic and climate changes on future coastal pollution in Europe. In our scenarios, we reflect on environmental policies (e.g., Green Deal, reduced waste, and improved wastewater treatment) from optimistic views.

Model results show that under the current practice approximately one-third of the European basin area, including 59% of the total population, is responsible for over half of nutrient losses to European rivers. Over one-fourth of river exports of N and P ended up in the Atlantic Ocean and the Mediterranean Sea around 2017-2020, respectively. On the other hand, intensive agriculture and technological development will increase nutrient pollution in coastal waters. For example, river exports of N and P to coastal waters are projected to increase by approximately 20-30% by 2050 under a scenario with high global warming and high urbanization rates. The Atlantic Ocean is projected to receive the largest portion of nutrient losses in the future compared to other European seas in 2050. In our scenarios, we analyze optimistic options to reduce future coastal eutrophication in European coastal waters. during the presentation, we will show the effects of several optimistic options (e.g., recycling of organic waste) on reducing coastal eutrophication. We will discuss the possible implications of the Green Deal and European environmental policies for coastal water quality in Europe.

How to cite: Ural-Janssen, A., Kroeze, C., and Strokal, M.: Reducing future coastal eutrophication under global change in Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6212, https://doi.org/10.5194/egusphere-egu23-6212, 2023.

Browning of surface waters due to increased terrestrial loading of dissolved organic carbon is observed across the Northern Hemisphere. Brownification is often explained by changes in large scale anthropogenic pressures (acidification, climate and land use). We quantified the effect of environmental changes on observed brownification of an important bird lake Kukkia in Central Finland. Water bird densities have decreased there during last decades, probably due to brownification of the lake. We studied past trends of organic carbon loading from catchments based on observations since 1990’s. We created scenarios for atmospheric deposition, climate and land use change to simulate their quantitative effect on brownification of the lake by process-based models (PERSiST for hydrology, INCA-C for carbon loading and MyLake for carbon processes in the lake). Increase in forest cut area appeared to be the primary reason for brownification of the lake. Decrease in acidic deposition has resulted in a lower leaching of dissolved organic carbon, but the effect is small. Runoff and total organic carbon leaching from terrestrial areas to the lake is smaller than it would have been without observed increasing trend in temperature by two degrees. 

How to cite: Rankinen, K., Junttila, V., Futter, M., Cano Bernal, J. E., Butterfield, D., and Holmberg, M.: Quantification of the reasons for the bird lake brownification in Finland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5744, https://doi.org/10.5194/egusphere-egu23-5744, 2023.

The requirements under the present River Basin Management Plans (RBMP) for the EU Water Framework Directive (WFD) are to reduce the total nitrogen (TN) loadings to the Hjarbæk Estuary in Denmark from the present (2015-2019) annual loading of 1900 tonnes N to 662 tonnes N in 2027. The catchment area to the estuary represents a total of 1177 km² and the catchment is drained by four major streams. The Danish national monitoring programme has established gauging stations covering 969 km² of the catchment area the remaining 208 km² being ungauged areas. Modelled data on N-leaching from the root zone on agricultural fields and surface water monitoring data on N-export losses are available from the 1980’ies and onward.

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 large differences in N-retention in groundwater within the ID15 sub-catchment (<20 % to >80 %) and the same large variation is seen for N-retention in surface waters (<20 % to >80 %). An analysis of delays in the transport for N from fields to surface waters have shown that especially one of the four monitored catchments (Simested stream) experiences a long delay in N repsonses (> 10 years).  

A new portfolio of N mitigation measures to be adopted at source (e.g. catch crops, early seeding, set a side, afforestation) or during transport from field to surface water (several types of constructed wetlands, riparian buffers and restored wetlands) has been scientifically approved and made available for farmers by the Danish EPA and Agricultural Agency.

The huge N-reduction needed in the Hjarbæk coastal catchment (65%) will require management efforts where farmers and authorities utilize both source oriented and transport oriented mitigation measures. These solutions should be implemented in a targeted manner guided by the local N-retention maps, as well as using all available monitoring data to pinpoint high-risk areas for N-leaching from fields and N-exports from the four sub-catchments as well as the ungauged areas. In this presentation we will showcase examples on how both targeted and collective mitigation measures can optimally be dosed in the Hjarbæk coastal catchment to reach the targets set in the RBMP 3.   

How to cite: Windolf, J., Tornbjerg, H., Larsen, S., and Kronvang, B.: Use of high spatial resolution nitrogen attenuation mapping in groundwater and surface waters for planning how to reach nitrogen reduction goals in 3rd River Basin Management Plans: Hjarbæk coastal catchment, Denmark, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5800, https://doi.org/10.5194/egusphere-egu23-5800, 2023.

Denitrification in groundwater is an important process that helps to maintain environmental standards, yet there are very few studies that determine the spatial variation of denitrification conditions in aquifers on a regional scale. We introduce a procedure to derive spatially continuous estimates of denitrification conditions in groundwater based on the interpolation of measurements of the redox-sensitive parameters oxygen, nitrate, iron, manganese and DOC, combined with the quantification of denitrification using a 2D-hydrodynamic model based on first-order reaction kinetics. We applied this procedure to Germany, using measured values from more than 24,000 groundwater monitoring sites from 2007 to 2016. Annual concentrations of the five parameters at the monitoring sites were regionalized using an optimized, iterative inverse distance weighting procedure within 15 aquifer typologies for spatial delineation. The annual grids (2007–2016) of each parameter were then overlaid and a median over time was calculated. Discrete ranks were then assigned to the concentrations of each parameter based on their redox class, and ultimately, after overlaying the five parameters, a mean value was calculated describing the nitrate degradation conditions in groundwater. After assigning half-life times and reaction constants to those denitrification conditions, we quantified denitrification in groundwater using the hydrodynamic model WEKU.

To assess the plausibility of the derived denitrification in groundwater, we compared our results with the proportion of denitrified nitrate determined with the N2/Ar method at 820 groundwater monitoring wells in three German Federal States, which showed an overall good agreement. Accordingly, the method presented here is suitable to be used for the regionally differentiated derivation of denitrification conditions in groundwater. For regions with denitrifying groundwater conditions, the results provide an explanation for frequently observed discrepancies between high nitrate emissions from the soil and low nitrate concentrations in the groundwater of intensively used agricultural areas.

How to cite: Wolters, T., Bach, T., Eisele, M., Eschenbach, W., Kunkel, R., McNamara, I., Well, R., and Wendland, F.: The derivation of denitrification conditions in groundwater: Combined method approach and application for Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5299, https://doi.org/10.5194/egusphere-egu23-5299, 2023.