HS2.3.1

Concurrent excesses of nitrogen (N) and phosphorous (P) compounds in the environment are causing the eutrophication of water bodies worldwide, including the North Sea and Baltic Sea that border Germany. The N:P ratio is a crucial measure of the nature of nutrient limitation and of the state of aquatic ecosystems. While many studies focus on the diffuse sources of N and P, point sources from urban and industrial wastewater can substantially contribute to in-stream N and P levels. Yet, systematic studies of the co-development of N and P point sources that span different river basins and a long time period are greatly lacking at a national scale like Germany.

To this end, we provide a comprehensive investigation of the long-term trajectories of N and P point sources in German catchments over the last seven decades (1950-2019). We construct a novel gridded dataset of N and P point sources for Germany, adapting the methodology proposed by Morée et al. (2013) and using country-specific datasets on population counts, protein supply, food wastes, and population connection to sewer and wastewater treatment plants. In addition, we estimate the consumption of P detergents combining datasets of household detergent phosphate and phosphonate sales, household ownership of automatic dishwashers, and professional detergent use. Our reconstruction approach accounts for the uncertainty in coefficients (e.g. efficiency of wastewater treatment, N content in proteins). We create an ensemble of plausible combinations of coefficient values that are constrained by the contemporary observed N and P loading from urban wastewater treatment plants (2012-2016 values; Büttner 2020).

From the newly constructed dataset, we analyze the trajectories of N and P loading, the N:P ratio and the relative importance of diffuse and point sources across major German river basins. In particular, N and P loadings show large differences between West and East Germany. In addition, P loading exhibits a stronger decrease in the 1980s and early 1990s than N loading because of the introduction of phosphate-free laundry detergents. Overall, N and P trajectories have large temporal and spatial variations, in particular due to differences in treatment efficiency, in population density, and in regulations that limit the maximum phosphate content in detergents.

Büttner, O.: DE-WWTP - data collection of wastewater treatment plants of Germany (status 2015, metadata), https://doi.org/10.4211/hs.712c1df62aca4ef29688242eeab7940c, 2020.

Morée, A. L., Beusen, A. H. W., Bouwman, A. F., and Willems, W. J.: Exploring global nitrogen and phosphorus flows in urban wastes during the twentieth century, Global Biogeochemical Cycles, 27, 836–846, https://doi.org/10.1002/gbc.20072, 2013.

How to cite: Sarrazin, F., Attinger, S., and Kumar, R.: Long-term trajectories of Nitrogen and Phosphorous point sources to German river systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5742, https://doi.org/10.5194/egusphere-egu22-5742, 2022.

Nitrate is one of the key parameters for the assessment of water quality, since an excess of NO₃ in drinking water can lead to health risks, especially for young children. The purpose of our study was not only to detect occasionally exceedances of the water quality standards, but also to monitor the temporal highly resolved behavior of NO₃ concentrations in the stream water over a one year period. To reach this goal we picked the small headwater catchment of the Nesselbach, located at Grebenstein in the North-Hessian low-mountain-ranges as our study area. We installed a UV-ViS-probe (s::can spectro::lyser), capable of detecting small quantities of nitrate with a 5 minutes resolution and added an automatic sampler to collect samples for lab calibration. Additionally, we installed discharge measurement in the stream and collected event-based samples of stable water isotopes with the installed automated samplers. The stable water isotopes are used to perform hydrograph separation for differentiation between event-water and baseflow, and therefore to gain deeper insights into the hydrology of the Nesselbach catchment.  

The sampling results show that the E.U. environmental quality standard of 50 mg/l NO₃ is almost always exceeded during baseflow in the Nesselbach. Rain-event driven discharge dilutes the baseflow strong enough to reduce the concentrations below the threshold for a short time span, but snowmelt shows the opposite behavior, increasing the NO₃ concentrations in the discharge over a longer period of time. While headwater catchments are often considered to be of good water quality in comparison to the much bigger catchments downstream, our findings suggest, that in catchments with agricultural landuse even the headwaters lag a good water quality and exceed the E.U. environmental quality standards for NO₃. This first evaluation of the data of our study points to the relevance of monitoring NO₃ concentrations in the baseflow. Because headwater catchments are often used for the extraction of drinking water and cattle watering, it could be necessary to expand the monitoring of NO₃ to a higher number of headwater catchments.

How to cite: Ditzel, L., Spill, C., and Gaßmann, M.: Nitrate flux monitoring in small headwater catchments in the German low mountain range –  Threshold exceedance during baseflow and snowmelt., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9830, https://doi.org/10.5194/egusphere-egu22-9830, 2022.

Water quality monitoring is essential to understanding the complex dynamics of water ecosystems, the impact of human infrastructure on them and to ensure the safe use of water resources for drinking, recreation and transport. High frequency in-situ monitoring systems are being increasingly employed in water quality monitoring schemes due to their much finer temporal measurement scales possible and reduced cost associated with manual sampling, manpower and time needed to process results compared to traditional grab-sampling.

Modelling water quality data at higher frequency reduces uncertainty and allows for the capture of transient events, although due to potential constraints of data storage, inducement of noise, and power conservation it is worthwhile not using an excessively high sampling frequency.

This study explores the issue of frequency optimisation of water quality monitoring schemes by applying three different statistical approaches for determining the optimum sampling frequency.

The proposed approaches are tested utilising a high frequency dataset built from recording continuous physical and chemical water quality parameters (temperature, dissolved oxygen (DO), fluorescent dissolved organic matter (fDOM), turbidity and conductivity) with multiparameter sondes at 3 sites in Bristol’s Floating Harbour.

As a result, this analysis provides practical tools to understand how different sampling frequencies are representative of the water quality changes. Furthermore, it helps determine the minimum frequency required to communicate periodic fluctuations in water quality and investigate the additional benefit of recording data at a frequency higher than the minimum required.

How to cite: Coraggio, E., Han, D., Gronow, C., and Tryfonas, T.: Determination of the optimum sampling frequency for water quality monitoring schemes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11307, https://doi.org/10.5194/egusphere-egu22-11307, 2022.

Wildfires change vegetation cover and soil properties, and create a layer of highly mobile ash. Enhanced runoff generation induced by the wildfire can transfer can transfer the ash to streams and water bodies, potentially causing contamination problems and imposing limitations on human uses. This is the focus of project FRISCO: Managing fire-induced risks of water quality contamination, an ongoing applied research project funded by the Portuguese government (PCIF/MPG/0044/2018). The project brings together scientists and water managers to develop tools to better assess post-fire water contamination risks, and identify the best risk mitigation options for water managers working in fire-prone watersheds.

This presentation will focus on the work to identify the main impacts of fires on surface water quality in Portugal based on an analysis of existing water quality data, and to examine the drivers for water quality deterioration. The Portuguese water quality database was examined for sampling stations in watersheds without significant upstream modifications, with data for at least 4 years before and after wildfires of at least 100 ha burned area. In the period 2000-2020, 28 sampling points in rivers and 15 points in 10 reservoirs were found with these characteristics, with monthly data for 6 parameters which are direct and indirect indicators of fire impacts in water quality. The datasets were assessed using Change-Point Analysis to determine the occurrence of breakpoints in water quality following the fire occurrence.

The results show that most fires led to changes in indirect indicators of fire impacts, including significant decrease in dissolved oxygen and pH levels in water, and significant increase of water conductivity. Moreover, changes to direct indicators of fire impacts occurred mostly in reservoir sampling stations, with significant increase in suspended solids, chemical oxygen demand and nitrates concentrations. An in-depth analysis of some stations indicates that the monthly sampling frequency might not be sufficient to capture fast changes associated with large post-fire rainfall events, which nevertheless have impacts on downstream reservoirs. This highlights the importance of finding proxies for water quality impacts which can either be monitored continuously or which can highlight fire impacts despite a monthly sampling frequency.

The work to identify drivers for these changes is ongoing. Special effort is being put in mapping the characteristics of the fires which occurred in the watersheds of the sampling points, including: (i) fire severity, assessed from satellite imagery using the difference Normalized Burn Ratio dNBR index; and (ii) hydrological connectivity between burned areas and the stream network, assessed using the Index of Connectivity by Borselli and Cavalli.

There is also ongoing communication with a group of water managers which operate in fire-prone watersheds, to (i) assess the resilience of the water intake and treatment operations, as well as the capacity to respond to different water qualities, (i) identify the levels of water quality impacts that can be classified as being of concern, and (iii) discuss potential risk mitigation options, including interventions before fire occurrence, emergency post-fire interventions, and changes to water quality treatment.

How to cite: Nunes, J. P., Aparício, B., Carvalho, M., Brito, C., Jahanianfard, D., Benali, A., Parente, J., Nitzsche, N., Faria, B., Baartman, J., and Dias, L. F.: Assessing and predicting the impacts of wildfires on water quality in Portugal: Project FRISCO, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10710, https://doi.org/10.5194/egusphere-egu22-10710, 2022.

Water quantity and quality of headwater catchments can react very sensitive to human impacts. While many studies focus on the influence of bigger cities on urban streams, the influence of rural villages and their associated infrastructure onto stream discharge and water quality dynamics is not often part of research.

We installed discharge measurements, UV-Vis probes Nitrate (NO₃^-) monitoring and conductivity probes on two neighboured headwater catchments, the Kelze (2.64 km²) and the Nesselbach (3.23 km²) catchment. All probes sample with a high temporal resolution of five minutes. We additionally equipped the sites with automatic samplers for also monitoring Nitrite (NO₂^-), Ammonium (NH₄⁺), ortho-Phosphate (PO₄^3- ) and total Phosphate (_totP). All over the catchments are characterized by agriculture and forests, while the Kelze catchment is also influenced by a village. A part of the village is drained by a stormwater sewer while most of the area is drained by mixed sewer. A small wastewater treatment plant (WWTP), which is very common in rural areas, treats solely the wastewater of this village. The WWTP consists of four ponds in a series. Water flows solely driven by gravity and it is not possible to manually control the discharge of the WWTP.

First measurements show that during low flow conditions Nitrate concentrations are generally higher in the Nesselbach, which is more influenced by agricultural areas. While the outflow of the WWTP dilutes the NO₃^- concentration in the Kelze, it causes increased levels of NO₂^-, NH₄⁺ and PO₄^3- concentrations. Even though the village is comparatively small, the sealed area, which is connected to the sewer system, as well as private drainages lead to a fast runoff during rainfall events. The rainwater is directly transported to the WWTP. Due to the limited storage capacity of such WWTP high discharge peaks can be observed shortly after the event. Depending on the water storage in the WWTP, even small events can produce a discharge wave, leading to short time rise of water levels in the Kelze stream, while the Nesselbach catchment shows smaller peak flows and thus bigger storage effects for the same events.

Overall, the first measurements show, that understanding the interplay between agricultural and urban areas is crucial to understand the coupling of different hydrologic and biogeochemical processes and could lead to a better understanding of catchment processes.

How to cite: Spill, C., Ditzel, L., and Gassmann, M.: Influence of urban infrastructure on headwater streams – first insights into water quantity and quality measurements in two rural areas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4087, https://doi.org/10.5194/egusphere-egu22-4087, 2022.

Managing river water quality at critical checkpoints that have significant impacts on water use is important for sustainable catchment development. This requires managing the whole multi-catchment systems upstream of a critical checkpoint. Concepts of systems headroom (deficit below permit) and excess (extra above permit) have been used to distinguish sub-catchments’ roles in pollution contribution. Based on the concepts, we propose a three-phase management approach. In the first phase, we frame the headroom and excess at temporal, spatial, and source domains and evaluate them to investigate the systems mechanisms. The evaluation is by simulating physical processes a semi-distributed integrated model (CatchWat-SD). We apply the model to 12 sub-catchments that make up the Upper Thames river basin and validate it using monitoring data. In the second phase, we incorporate the evaluated headroom and excess in loads allocation to develop a strategy that coordinates systems headroom for more efficient and realistic interventions. In the last phase, we validate the strategies by simulating the scenarios that coordinate headroom at different domains and evaluating them in water quality improvement, efficiency, temporal steadiness, spatial homogeneity, and practical feasibility. Results show that dry seasons, downstream catchments and urban sources generally have more excess. Thus, more target loads reduction is allocated to dry season, downstream catchments and urban sources in the fully coordinated scenario. The higher degree of headroom coordination a strategy achieves, the better performance this strategy generally obtains in all five metrics. This study emphasises the need to incorporate headroom in loads reduction allocation, which helps to more efficiently improve systems water quality performance with a more realistic degree of intervention. The whole procedure can be further expanded to water quality management at multiple checkpoints for sustainable management in large catchments.

How to cite: Liu, L., Dobson, B., and Mijic, A.: Coordinating systems headroom for more efficient multi-catchment water quality management at a critical checkpoint, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6221, https://doi.org/10.5194/egusphere-egu22-6221, 2022.

Large industrial pollution, agricultural runoff, and disposal of untreated sewage into the river have made Kanpur the most critical water pollution hotspot of Ganga River. This study assesses the risk of nutrient pollution and resulting eutrophication in this industrialized stretch passing through Kanpur for the mid-21st century under climate change and land use land cover projections. For this assessment, climate projections from an ensemble of 20 GCMs for the RCP 4.5 and RCP 8.5 scenarios, and future land use land cover (LULC) projections from a multi-layer perceptron neural network are used to drive a hydrological model HEC-HMS which is coupled to the water quality model QUAL2K. The nutrients assessed are ammonia, nitrate, total nitrogen, organic-, inorganic- and total phosphorous. An increase in nutrient pollution is simulated for future climate change due to a reduction in dilution volume caused by reduced low flows. An increase in nutrient pollution is also simulated for future land use land cover because of an increase in pollution from agricultural runoff. Both nitrogen and phosphorous components are highly sensitive to climate change, while only phosphorous components are highly susceptible to land use land cover. This is because, the major contribution of phosphorous pollution in this stretch is from agricultural runoff and only a negligible contribution is from point sources. The risk of nitrate pollution decreases and ammonia pollution increases with future climate change due to higher denitrification rate with warming, but the risk of total phosphorous pollution slightly decreases due to an overall reduction in phosphorous with warming following an overall increase in mean streamflow. A shift in the hotspot of eutrophication from Kanpur to Jajmau is also simulated due to limiting phosphorous eutrophication for future climate at Kanpur. The risk of eutrophication would increase with future climate change due to increased total nitrogen and total phosphorous with warming, and the risk is likely to become higher for the combined climate change and land use land cover projections. The results of this ongoing study will be presented in the meeting. Our study would be highly beneficial for the policymakers to save the Ganga River from further pollution in the future.

How to cite: Santy, S., Mujumdar, P., and Bala, G.: Projection of the risk of nutrient pollution and eutrophication for mid-21st century under changing climate and land use land cover, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-75, https://doi.org/10.5194/egusphere-egu22-75, 2022.

Modelling and predicting nitrate (NO₃-N) concentrations at the catchment scale remain challenging as they are controlled by available sources, hydrological connectivity and biogeochemical transformations along the dominant flow paths, which are often spatially heterogenous and highly interacted. To unravel the controlling factors of catchment NO₃-N cycling, a grid-based model, mHM-Nitrate, was applied to a 68 km² mixed land use catchment (Demnitzer Millcreek) near Berlin. Results showed that landscape characteristics dictated the spatial distribution of NO₃-N while hydroclimatic variability dominated its temporal dynamics. Restoration of riparian wetlands also mediated the NO₃-N concentrations, leading to a modest reduction on NO₃-N export (~10% reduction during 2001-2019). Further, the influence of three factors was validated in a spatially distributed sensitivity analysis (SSA) applied on key hydrological and nitrate parameters with a one-year moving window. The SSA results showed that the spatial pattern of parameter sensitivity was determined by NO₃-N inputs and hydrological transport capacity, while its temporal dynamics were regulated by annual wetness conditions. Restoration management also contributed to the increase in sensitivity of denitrification parameters. Moreover, SSA identified the influential zones and time periods affecting simulation of NO₃-N mobilisation and transport, which provides an evidence base for future model development and optimising of monitoring schemes.

How to cite: Wu, S., Tetzlaff, D., Yang, X., and Soulsby, C.: Landscape characteristics, hydroclimate and management control spatiotemporal NO3-N patterns in a lowland catchment: implication from 30-year modelling and sensitivity analyses, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-46, https://doi.org/10.5194/egusphere-egu22-46, 2022.

Human activities, especially agricultural practices, have significantly altered the Earth’s landscape and the global cycle of nitrogen. In Europe, diffuse nitrogen (N) input from agriculture has been identified as a major driver of marine eutrophication. Despite a long history of measures, little improvement in groundwater and surface water quality has been observed. Recent studies have attempted to provide insights into nitrogen dynamics at the catchment scale, helping to explain the causes and effects of persistent water quality problems. However, there is a lack of large-scale, long-term studies that provide insights into both biogeochemical and hydrological N legacies under different landscape settings. Here using data of more than 100 German catchments of the last seven decades, we synthesis the nitrogen transport and retention dynamics, as well as their dominant (landscape and climate) controls in a large-sample setting. To this end, we adapted the mHM-SAS model (Nguyen et al., 2021) to reflect regional-scale biogeochemical and hydrological N legacies, taking into account the historical development of both diffuse and point sources. The underlying parameterizations were constrained using instream N concentrations. We found high heterogeneity in catchment responses to N inputs. The fractions of N surplus that were stored in the soil, removed by denitrification, stored in the subsurface, and finally exported to the stream vary over a wide range. Our analysis of the long-term (1950-2014) average N balances from all catchments suggests that a majority (mean = 57%) of N surplus was removed by denitrification, followed by stream N export (27%) and the rest was stored in the catchment (16%). Despite the reduction in N surplus after 1990s, biogeochemical legacy reflected in the soil N build-up showed an increasing trend over the analyzed period (1950-2014) across a majority of the study catchments. As for the hydrologic legacy, we found a varying range of mean transit times of discharge between 3.5 years and 13.1 years (95% confidence interval) among the analyzed catchments. Overall, our large-sample analysis provides a detailed overview of biogeochemical and hydrological N legacies across Germany; and thus provides useful insights for an improvement of agricultural practices and water quality management in Central European landscapes.

Nguyen, V.T., Kumar, R., Musolff, A., Lutz, S. R., Sarrazin, F., Attinger, S., & Fleckenstein, J. (2021 WRR - in revision). Disparate Seasonal Nitrate Export from Nested Heterogeneous Subcatchments Revealed with StorAge Selection Functions. https://doi.org/10.1002/essoar.10507516.1

How to cite: Nguyen, T., Fleckenstein, J., Sarrazin, F., Ebeling, P., Lutz, S., Musolff, A., and Kumar, R.: Nitrogen transport and retention dynamics across central European catchments using large-sample data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2591, https://doi.org/10.5194/egusphere-egu22-2591, 2022.

To achieve and maintain the good ecological status of surface waters, each EU Member State is expected to invest economic resources in a programme of measures. To do this, a preliminary analysis to quantify the anthropogenic pressures and their impacts on surface waters is necessary to prioritise the measures to be undertaken.

The objectives of this work were to: (i) quantify the nutrient loads from point and diffuse pollution to the Rio Mannu stream identifying the critical time in terms of water quality, and (ii) simulate some mitigation measures for reducing the nutrient loads being delivered to the wetland. Two “measures” were tested to mitigate nutrient pollution in high flow and low flow conditions: (1) the use of treated wastewater from urban wastewater treatment plants (WWTPs) for the irrigation of cultivated olive trees and a (2) reduction in fertiliser usage rates (20%).

Results showed that under high flow conditions, NO₃-N and TP loads accounted for 89% and 99% of the total load, respectively. The low flow contribution to the total load was very low, with NO₃-N and TP accounting for 2.8% and 0.7%, respectively. However, the natural hydrological regime in the study area is intermittent, and low flow represents a critical condition for the water quality due to the high concentrations of TP and NO₃-N from WWTP discharge. Results indicated that agriculture is the main source of NO₃-N in the surface waters. The point sources made a minor contribution, in terms of nutrient load to the surface waters, but they constitute a relevant hydrological pressure for the Rio Mannu, producing a shift from an intermittent hydrological regime (natural conditions) towards a perennial regime. The measures are effective to reduce nutrient loads in surface waters at the outlet for all hydrological conditions. Under high flow conditions, the reduction was 9% and 12% for NO₃-N and TP loads, respectively. The reduction increased under normal and low flow conditions (75% and 83% for NO₃-N and TP loads, respectively).

Based on this study, it is evident that a “programme of measures” for improving the current status of surface waters must be oriented towards reducing nutrient loads, both under high and low flow conditions. The results show that a 20% reduction in fertiliser usage on the main crops in this area, and the reuse of wastewater from selected WWTPs, would result in a significant reduction in the nutrient loads delivered to the wetland, although this reduction is not large enough, and supplementary measures would be required.

How to cite: De Girolamo, A. M. and Lo Porto, A.: Testing potential mitigation measures to reduce nutrient loads to a temporary river, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11352, https://doi.org/10.5194/egusphere-egu22-11352, 2022.

Inappropriate tillages and the intensive use of mineral fertilizers are fundamental driver of soil erosion and land diffuse pollution. The new European environmental policies, such as the European Green Deal (EUGD) and the Farm to fork strategy aims to restore the natural functions of ground and surface soil by 2030. Best Management Practices (BMPs) are mitigation measures which will be included in EU Member States management programs to achieve the policies goals. Most of BMPs have as their first function to reduce soil erosion, however these can have effect also on the nutrient loads. This work assessed the power of soil erosion oriented BMPs in achieving nutrient load reduction by means of the Soil and Water Assessment Tool (SWAT) in the Carapelle basin (Apulia, Italy). Moreover, their economic convenience was evaluated for both the public and the private sector. Five alternative scenarios were implemented: Contour farming (CF), no tillage (NT), reforestation (RF), and two additional scenarios, including the 20% reduction of fertilizers in CF and NT, (CFR) and (NTR), following the EUGD strategy. With the current management of the areas total nitrogen (TN) was ~49 kg ha^-1y^-1, while total phosphorous (TP) was ~0.044 kg ha^-1y^-1. N-NO₃ load increased for NT and CT in terms of surface runoff and leaching. Contrariwise RF, as well as CFR and NTR scenarios showed a reduction of N-NO₃ losses. In particular CFR and NTR abated of ~20% surface runoff and leached N-NO₃ load. Economically, RF was profitable in sloped areas while CFR and NTR were the best alternative in those hilly and flat. This suggested that RF may be implemented in combination with other practices to have a greater impact at the basin scale. BMP implementation requires significant investments (public and private). The results of this study provide the scientific basis for decision-making for agriculture and watershed management.

How to cite: Ricci, G. F., D'Ambrosio, E., De Girolamo, A. M., and Gentile, F.: Efficiency of BMPs for the reduction of sediment loads in the control of nutrients., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8467, https://doi.org/10.5194/egusphere-egu22-8467, 2022.

Agriculture intensification, such as irrigation, creates a lot of pressure on the available water resources and the environment. This paper explored the water quality dynamics, specifically nitrates, before and after transformation from rainfed to irrigation agriculture within the Cidacos River Watershed in Navarra, Spain. The watershed occupies 477 km², of which approximately 260 km² have been traditionally rainfed cultivated, whereas 77 km² were transformed from rainfed to pressurized irrigation between 2009 and 2011. The newly irrigated area is located in the watershed's lower region, close to the river's mouth. Water quality data sampling has been taken at several points along the watershed from 2000 to date, up to the outlet of the Cidacos River in Traibuenas, where it joins with the Aragón River. Streamflow and nitrate concentration data have been measured at the watershed's outlet in Traibuenas since 2017. A previous baseline study by Merchán et al. (2020) showed an increase in the electrical conductivity and nitrate concentration in the river's lower reaches affected by irrigation. However, no information about the effect on streamflow, nitrate loads, and yields resulting from the irrigation was explored. The aim of this study was therefore to fill this research gap by using hydrological models such as the Soil Water Assessment Tool (SWAT) model, to recreate, simulate and understand the behaviour of the Cidacos River in the irrigated area from 2017 to the present, if the transformation from rainfed to irrigation had not occurred; and then compare those simulated variables with the measured ones since 2017. Simulation of streamflow and nitrate loads were done using the SWAT model until Olite from 2000 to 2020 under rainfed conditions. This was later extended for the entire watershed up to the mouth of the Cidacos River from 2017 to the present when the transformation to irrigation was fully completed and the Traibuenas outlet gauging station started operating. The results were then compared to the measured data for the irrigated region before and after the transformation to irrigation. For the simulations, the model was calibrated from 2000 to 2010 and validated from 2011 to 2020, and its sensitivity and uncertainties were analyzed for streamflow and nitrates at the Olite gauging station. The model evaluation results were satisfactory for both streamflow and nitrate loads, with streamflow having values of NSE = 0.82/0.83 and R² = 0.83/0.84 during calibration and validation periods, respectively. Similarly, the statistical evaluation values for nitrate loads were NSE = 0.71/0.68 and R² = 0.72/0.79 during calibration and validation periods, respectively. Subsequently, the calibrated parameters were used to simulate the entire watershed, considering all the territorial variables specific to each zone. Comparative analysis between the periods before and after the implementation of irrigation indicated a 6.6% and 43.2% increase in streamflow and nitrate loads, respectively, which subsequently increased the nitrate concentrations. The results from this study could provide useful information and guidance on nitrate pollution control, thus contributing to the management of the effects of agriculture on water quality and enhancing sustainable agricultural practices.

How to cite: Oduor, B. O., Campo-Bescós, M. Á., Lana-Renault, N. S., and Sarasibar, J. C.: Evaluating the Impacts of Agricultural Transformation from Rainfed to Irrigation on Streamflow and Nitrates in a Mediterranean Agricultural Watershed in Spain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6032, https://doi.org/10.5194/egusphere-egu22-6032, 2022.