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Water quality at the catchment scale: measuring and modelling of nutrients, sediment and eutrophication impacts

Land use and climate change as well as legal requirements (e.g. the EU Water Framework Directive) pose challenges for the assessment and sustainable management of surface water quality at the catchment scale. Sources and pathways of nutrients and other pollutants as well as nutrient interactions have to be characterized to understand and manage the impacts in river systems. Additionally, water quality assessment needs to cover the chemical and ecological status to link the hydrological view to aquatic ecology.
Models can help to optimize monitoring schemes and provide assessments of future change and management options. However, insufficient temporal and/or spatial resolution, a short duration of observations and the widespread use of different analytical methods restrict the data base for model application. Moreover, model-based water quality calculations are affected by errors in input data, model errors, inappropriate model complexity and insufficient process knowledge or implementation. Additionally, models should be capable of representing changing land use and climate conditions, which is a prerequisite to meet the increasing needs for decision making. The strong need for advances in water quality models remains.

This session aims to bring scientist together who work on experimental as well as on modelling studies to improve the prediction and management of water quality constituents (nutrients, organic matter, algae, or sediment) at the catchment scale. Contributions are welcome that cover the following issues:

- Experimental and modelling studies on the identification of sources, hot spots, pathways and interactions of nutrients and other, related pollutants at the catchment scale
- New approaches to develop efficient water quality monitoring schemes
- Innovative monitoring strategies that support both process investigation and model performance
- Advanced modelling tools integrating catchment as well as in-stream processes
- Observational and modelling studies at catchment scale that relate and quantify water quality changes to changes in land use and climate
- Measurements and modelling of abiotic and biotic interaction and feedback involved in the transport and fate of nutrients and other pollutants at the catchment scale
- Catchment management: pollution reduction measures, stakeholder involvement, scenario analysis for catchment management

Convener: Paul Wagner | Co-conveners: Sarah HallidayECSECS, Ype van der Velde, Nicola Fohrer
| Mon, 23 May, 13:20–14:37 (CEST), 15:10–16:27 (CEST)
Room B

Mon, 23 May, 13:20–14:50

Chairpersons: Paul Wagner, Alexander Buzacott

Fanny Sarrazin et al.

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.

Golnaz Ezzati et al.

The EU Water framework demands the Member States to set up water management plans with the aim that water bodies should reach good ecological status. However, the overall progress is slow and more efforts are needed to reach the goals. This study presents how long-term monitoring of water quality and agricultural management practices in four agriculturally dominated catchments in Sweden contribute to the knowledge to nutrient leaching and their behaviour in relation to catchment characteristics.

20 years of water quality data were analysed to understand nitrogen (N) and phosphorus (P) trends and variations in surface waters leaving the catchments. The catchments represent a wide range of soil types and climate and hence different farming practices. Followed to time series analysis and in order to investigate how water quality data relate to management practices, two modelling approaches were used: non-parametric Pettitt test to determine significant changes in mean values of time series data; and generalized additive model (GAM) to identify the impact of climate/ anthropogenic variables on nutrient loads as a flexible model which avoids overfitting for long time series data.

Despite the general progress in preventing deterioration of water quality, the time series analysis indicated drastic changes over years in loads leaving some of the catchments. At the same time, there were large variations in N and P loads among catchments while runoff was the only significant indicator of losses in all. Clay dominated catchment showed more fluctuations in daily TN (0-40 mg/l) and TP (0-3.2 mg/l) concentrations, and also very high values of P (>0.07 mg PO4P/l) compared to other catchments. On the other hand, sandy loam catchment was more consistent in losses despite the high values of N (>7 mg NO3N/l). Although nutrients were washed into water bodies after the first heavy rain following a prolonged drought period, Pettitt model, which is insensitive against spikes, proved that permanent change points in P or N loads was not always following immediately after a change point in runoff or rainfall. Finally, GAM modelling did not generate a direct relationship between a single management practice and trend of nutrient concentration, and demonstrated the complexity in analysing the commutative impact of temporal/spatial factors that influence nutrients loads.

The study results proved that having long term water quality record is of great importance to show the pattern of nutrient trends, signal any undesirable changes, and to observe the impact of environment including cumulative impact of management practices on nutrient mobilization/retention. Therefore, continuing monitoring is critical to support the EU WFD 3rd cycle actions. However, better information on peak load events is needed as climate and especially precipitation–runoff evenest are changing. In addition, application of technologies such as sensors or remote sensing will increase accuracy of the measurement by providing high temporal data regardless of any logistic complications.

How to cite: Ezzati, G., Kyllmar, K., and Barron, J.: Trend analysis of nutrient losses in agricultural catchments using Generalised Additive Model and Pettitt test, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4569, https://doi.org/10.5194/egusphere-egu22-4569, 2022.

Lukas Ditzel et al.

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.

Elisa Coraggio et al.

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.

Jingshui Huang et al.

Nutrient dynamics play an essential role in aquatic ecosystems. Despite advances in sensor technology, nutrient concentrations are difficult and expensive to monitor in-situ and in real-time. Emerging data-driven methods may provide surrogate measures for nutrient concentrations. In this work, 4-year high-frequency (15-min interval) regularly monitored variables and 2 data-driven algorithms are used to build surrogate measures for nitrate, orthophosphate, and ammonium at 2 stations in the German part of the Danube River. The variables used as input futures are dissolved oxygen (DO), temperature (Temp), conductivity (EC), pH, discharge rate (Q), and chlorophyll-a (Chl-a). Multiple linear regression (MLR) and Random Forest Regression (RF) are trained and cross-validated for the concentration predictions of nutrient constituents. Prior to training, pre-processing procedures were implemented, including removing outliers and filling missing values by linear interpolation. This work presented a thorough description of the workflow, including intermediate steps for feature engineering, feature selection, hyper-parameter optimization. The results of the 12 surrogate models (2 algorithms * 3 constituents * 2 stations) are compared. The results show that the RF algorithm can reproduce the environmental phenomena and contribute to water quality management. The RF algorithm already outperformed MLR when adding at least three predictors in this work. The five-fold CV has identified the reliable and stable prediction of the targets NO3--N (R2 = 0.9967 and 0.9992), NH4+-N (R2 = 0.9861 and 0.9927), PO43--P (R2 = 0.9638 and 0.9643).

How to cite: Huang, J., Tran, B. Y., and Arias-Rodriguez, L. F.: Predicting high-frequency nutrient dynamics in the Danube River from surrogates with sensors and machine-learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12914, https://doi.org/10.5194/egusphere-egu22-12914, 2022.

Joao Pedro Nunes et al.

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.

Caroline Spill et al.

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 (PO43- ) 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 PO43- 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.

Paola Di Fluri et al.

The deterioration of superficial water quality is a relevant issue as regards water management. Until today, most European rivers do not achieve qualitative standards defined by the Water Framework Directive (WFD). Given the goals of the WFD and taking into account current guidance for water quality management, this study has been carried out to evaluate pressures of anthropic activities - like industrial effluents, wastewater treatment plants, waste-to-energy plant, waste handling facilities, contaminates sites- on superficial waters.

In this study, we propose a simplified multidisciplinary methodology to perform a semi-quantitative analysis of water pressures on river segment starting from easily accessible data, thus attempting to overcome the endemic scarcity of monitoring data. In particular, the methodology proposes a procedure for: (1) identifying river segment exposed to pollution spills by the application of an expeditive raster-based numerical model; (2) determining a pressure index value for each identified river segment in relation to allocated spills. The developed pressure index offers the possibility of quantifying the significant pressures of several pollutant hotspots that impact simultaneously on a single river segment. The methodology has been tested over two rivers differently exposed to industrial and anthropogenic pressure and for which punctual environmental pollution hotspot were available at catchment scale.

The results allow to identify river segments most exposed to pollutant spills and, based on pressure index values, to do a comparative analysis between rivers segments with similar characteristics or to draw up a ranking magnitude of the river pressures. In this prospective, the developed methodology can represent a solid tool for decision-making processes and predictive studies in areas with no, or poor, monitoring data.

How to cite: Di Fluri, P., Di Talia, V., Leonardi, A., Antonioni, G., Domeneghetti, A., and Cozzani, V.: Study of environmental pressure of industrial effluent on rivers with a composed pressure index, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4601, https://doi.org/10.5194/egusphere-egu22-4601, 2022.

Elizabeth Flint et al.

The release of phosphorus into aquatic environments as a result of anthropogenic activity has led to eutrophication of many fresh and coastal waters around the globe and across the United States (US). Dosing of public water supplies (PWS) with phosphate (PO4) compounds is undertaken around the globe, including many parts of the US, in order to inhibit corrosion and release of lead and copper within water distribution network pipes. However, 17% of this treated water is released into the environment due to leakage, resulting in previously unquantified fluxes of phosphorus into the environment. We have calculated this PWS leakage PO4 flux (as phosphorus; PO4-P) for the US to be between 2.2-6.7 kt PO4-P yr-1. County PWS leakage fluxes range from 0-2,865 kg PO4-P km-2 yr-1, and the relative magnitude of the fluxes in many urban counties across the northeastern US highlights the need for these previously unquantified fluxes to be incorporated into catchment nutrient balances. Not only do PWS leakage fluxes of PO4-P make a potentially significant contribution to eutrophication in urban catchments, but they also represent a loss of phosphorus that subsequently cannot be easily recovered at wastewater treatment plants, driving increased extraction of non-renewable and dwindling global phosphorus rock reserves.


How to cite: Flint, E., Ascott, M. J., Gooddy, D. C., Surridge, B. W. J., and Stahl, M. O.: Leakage of water from public supply distribution networks is responsible for significant phosphorus fluxes within many urban catchments across the United States, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6063, https://doi.org/10.5194/egusphere-egu22-6063, 2022.

Leyang Liu et al.

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.

Erica Matta et al.

Water quality and availability are nowadays essential requirements for all those activities that need an exploitation of the water resource: e.g. potable use, hydroelectricity production, agriculture, recreation. Inland water originates from atmospheric events and is stored in solid state as glaciers or snow (e.g. on the mountains) or in natural and artificial lakes at any altitude. The well documented climate warming has, among its multiple effects, the modification of the equilibrium between liquid and solid phase of water, its storage and availability, as well as changes in the precipitation regime, such as the reduction and intensification of rainfall events alternated to long dry periods. All these changes alter water quality and water availability at the catchment level.

We are experimenting the use of earth observation data (Sentinel-2) to track temporal variations of snow cover, water bodies (in terms of size and numbers) and water colour over the last five years in a small high-altitude, glacierized catchment in Italy (Lake Ceresole watershed, Orco Valley, Western Alps). In particular, water colour is chosen here as a proxy of water quality and is considered as mainly driven by the presence of suspended particles, because of the conditions that feature a mountainous environment (e.g.  minimized anthropic pressure and prevailing natural processes). Water colour is then supposed to change following the release of suspended particles from snow/glaciermelting during thaw periods at seasonal timescale, as well as be modified due to the transport of solid particles as river flow or runoff, which can be generated as a consequence of heavy rainfall events.

Satellite derived products on snow cover, lake size/number and water colour are then coupled with meteorological measurements (e.g. precipitation), and information on geo-hydrological events (e.g. floods) in order to find possible linkages between lake water dynamics and both snow/glaciermelting and significant meteorological and geo-hydrological events. Field measurements allow a validation of the satellite data on lake water colour to be performed.


With this study, we aim to understand if the high spatial resolution of Sentinel-2 acquisitions, except for the drawbacks of all optical satellite sensors (e.g. cloud cover), can provide useful information on water and sediment dynamics in an alpine glacierized basin, that can allow to follow the on-going modifications that the mountainous environment is facing due to the global warming. The use of Sentinel-2 data for this purpose would be a valuable tool in helping both monitoring and understanding of climate change consequences, and in managing the water resource in places not easily accessible for periodic in-situ measures. In fact, mountains respond promptly to climatic pressures, but are also the water sink of fresh water for downstream valleys.

How to cite: Matta, E., Giardino, C., Bresciani, M., Chiarle, M., and Nigrelli, G.: Potentialities of Sentinel-2 images for the study of the fresh water resource in a glacierized mountainous catchment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5733, https://doi.org/10.5194/egusphere-egu22-5733, 2022.

Mon, 23 May, 15:10–16:40

Chairpersons: Paul Wagner, Alexander Buzacott

Sneha Santy et al.

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.

Ingo Heidbüchel et al.

Predicting dynamic nitrate fluxes at the catchment scale is relevant to understand solute transport processes, assess eutrophication risks and improve water quality management. In order to simplify the complex biogeochemical processes without disregarding the spatial heterogeneity and changing flow paths, we combine physical modeling and a conceptual transit time approach. First, we use the physically-based, 3D, spatially distributed hydrologic model HydroGeoSphere (HGS) to extract transit time distributions (TTDs) of a conservative tracer for different parts of a catchment (partitioned by land use). We systematically combine different initial and boundary conditions analyzing apparent changes in shape and scale of the TTDs. Then we modify the resulting land use-specific TTDs according to the typical decay and retardation processes that are associated with nitrate. This includes retention of organic nitrogen, as well as attenuation by plant uptake and denitrification of inorganic nitrate. Finally, we superimpose and convolve the time series of nitrate-specific TTDs to compute the total nitrate outflux from the catchment.

How to cite: Heidbüchel, I., Schütz, S., Yang, J., Van Nguyen, T., Ebeling, P., and Fleckenstein, J.: Spatially distributed modeling of nitrate fluxes at the catchment scale using a transit time distribution approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10051, https://doi.org/10.5194/egusphere-egu22-10051, 2022.

Songjun Wu et al.

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.

Tam Nguyen et al.

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.

Anna Maria De Girolamo and Antonio Lo Porto

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.

Giovanni Francesco Ricci et al.

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.

Brian Omondi Oduor et al.

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.

Zheng Duan et al.

Stream temperature is an important parameter to evaluate the water quality and biodiversity in aquatic ecosystems. Climate change and human activities (e.g. land use change) are affecting stream temperature, potentially leading to negative impacts on the habitats of native species and sustainability of aquatic ecosystems. Therefore, it is important to monitor and understand stream temperature under different conditions to better protect the aquatic ecosystems. The conventional in-situ measurements from gauge stations provide the most accurate stream temperature data, but they are often sparse and limited in terms of data length (temporal) and spatial coverages (many regions have no measurements). Stream temperature modelling is an effective way to extrapolate from limited measurements in both space and time, and it is the only way to predict the future to assess the climate change impacts. The stream temperature is influenced by meteorological and hydrological factors, and the relationship between the stream temperature and physical conditions is complex and can vary spatially and temporally. Different statistical and process/physically-based stream temperature models have been developed with the latter generally performing better. The Soil and Water Assessment Tool (SWAT) is a semi-distributed process-based hydrological model built with a simple statistical model to simulate stream temperature using only air temperature. Two hydroclimatological stream temperature models were recently developed to improve the capability of the SWAT model for simulation of stream temperature by considering influences of hydrological conditions and more detailed water-air heat transfer processes. The two recently developed models were tested mainly in a few river basins in U.S. and Canada. This study aims to compare and evaluate -for the first time- the performance of three models in simulating stream temperature in the Vils Basin located in Bavaria, Germany. The SWAT model is first calibrated and validated against the measured streamflow at the basin outlet on a daily timescale to ensure satisfactory streamflow simulation. Then the three different stream temperature models are run and evaluated with measured stream temperature at both daily and monthly time scales. The parameters and simulation results from the three different stream temperature models are analyzed. This study complements existing studies to improve our understanding of the performance of different stream temperature models in different river basins.

How to cite: Duan, Z., Duggan, E., Tuo, Y., Li, Y., Dong, J., Liu, J., and Gao, H.: Modelling stream temperature with multiple hydroclimatological temperature models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13198, https://doi.org/10.5194/egusphere-egu22-13198, 2022.

Jens Kiesel et al.

Stream ecosystems are impacted by multiple stressors in complex spatio-temporal interactions. The lack of understanding of these interactions and impacts hampers the successful restoration of streams and rivers. The German Research Foundation-funded collaborative research centre RESIST (https://sfb-resist.de/index.html) aims to disentangle these complex dependencies applying a novel theoretical framework: the ‘Asymmetric Response Concept’. The concept hypothesizes that degradation and recovery processes depend on different, non-linear biotic and abiotic interactions between stressors, environmental variables, and organisms. Therefore, unprecedented data and information are required which are collected through lab and field experiments, species sampling, observations of environmental variables and modelling.

High-resolution ecohydrological modelling is a core component in this process to provide historic information on water quality in two mesoscale catchments (Boye with 124km² and Kinzig with 1065km²) in Germany. Due to history, storage- and hysteresis effects in the hydrologic system, the spatio-temporal dynamics of in-stream environmental variables follow an asymmetric function to degradation and recovery. The model SWAT+ (Soil and Water Assessment Tool) is therefore applied to simulate streamflow as well as the water quality components temperature, oxygen, nitrogen components and salinity (TONS) at more than 20 sites in each catchment.

We present the conceptual framework of the approach, including data sources and data collection, model parameterization, required code adaptations, calibration techniques and expected results. 

How to cite: Kiesel, J., Peters, K., Wagner, P., and Fohrer, N.: High-resolution water quality simulation to disentangle multiple stressor effects on aquatic species , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12369, https://doi.org/10.5194/egusphere-egu22-12369, 2022.

José Rodolfo Scarati Martins et al.

Modelling water quality of polluted heavy loaded water courses as those crossing highly urbanized catchment areas are a complex task that involves several processes based on coefficients like unit loads, decay rates and self-depuration effects among others. The fate of pollutants as organic matter and nutrients are usually done through transport equations added by sourcing and sinking terms that implies the use of decay factors. The so-called k’s coefficients are present in the literature and were derived from typical water samples that don’t represent the local conditions founded in the urban rivers, usually affected by the catchment scale. This article presents an approach method used for local determination of the k’s coefficient for Biological Oxygen Demand (BOD-k1), Atmospheric Reaeration (AR-k2) and Sediment Oxygen Demand (SOD-k4) and compares results to typical adopted values bye modelists. The approach is based on local waters and sediment laboratory tests adjusted to consider specific driving forces as water temperature, constituent concentration and flow turbulence. Considering the catchment area (286 km²) and the river reach (25 km long) 4 sampling stations were defined to collect depth integrated water samples and the bed material. The k1 coefficient is the most sensible one due to the influence of the biological components and the relation between labile and refractory fractions, that varies along the reach with the contribution from the sub catchments’ land use and sanitary infrastructure. Considering Fujimoto’s and Thomas’ equations, different values of local dependent k1 were found. For k2, the concept of river shear stress velocity was applied to correlate the oxygen mass transferred to the water in the JAR test run for the observed range of velocity gradients in the natural flow. Results lead to a more realistic air entrainment rate due to hydraulic, superficial tension and presence of oils and greases. The SOD-k4 were determined after bottom sediment samples collected in the same defined stations for 3 different concentrations in clean water. The continuous oxygen demand for each sample was taken hourly in the first day and daily in the next 5, and then converted to the Toro’s active sediment layer demand considering local porosity and specific weight. Results showed considerably lower than the typical values referenced in the literature for all k’s, denoting the influence of the above-mentioned characteristics and the level of uncertainties that could affect modelling results when non-local parameters are employed.

How to cite: Scarati Martins, J. R., Amorim, L., Nogueira, F., Magalhães, A., and Duarte, B.: Local determination of constituent's decay coefficients for river water quality modelling considering the catchment scale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13347, https://doi.org/10.5194/egusphere-egu22-13347, 2022.

Katri Rankinen et al.

The catchment is the appropriate scale to observe and quantify processes related to the water cycle and water quality. In the Karjaanjoki river basin (located in southern Finland) we aim to sustainable agricultural production that does not harm water ecosystems. Indicator species are trout and river pearl mussels. This is one of the few rivers that still has a natural pearl mussel population. Their living conditions have deteriorated, and the population is aging. We used mathematical models to assess the threats of human activity in the catchment area that can influence water quality and thus living conditions of these species. We estimated the change in living conditions from long water quality time series. We created an integrated, process-based model chain (Persist and INCA) to assess different loading scenarios from agricultural practices. Our results show that the agri-environmental measures are sufficient to maintain the current water quality, but more effective measures are needed to improve it. Climate change in particular is putting additional pressure on ecosystems.

How to cite: Rankinen, K., Cano-Bernal, J., and Vähä, J.-P.: An integrated catchment modelling for assessment of water quality and its effect on aquatic ecology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7661, https://doi.org/10.5194/egusphere-egu22-7661, 2022.