Displays

Increased use of phosphorus (P) fertilizers and detergents, as well as the growth of animal feeding operations, have more than doubled P inputs to human-impacted watersheds over pre-industrial levels. While P fertilizer use and manure application help to maximize crop yields, excess P is lost to runoff, leading to eutrophication of downstream waters—a phenomenon of great concern in the North American Great Lakes region. Excess P also accumulates across the landscape, leading to legacies that serve as long-term sources of P to surface waters, even after inputs to the watershed are reduced. We developed, for the first time, a process-based model, ELEMeNT-P, designed to capture legacy P accumulation and depletion trajectories along the land-aquatic continuum. To drive the model, we reconstructed a more than 100-year trajectory of P inputs to the Grand River Watershed (GRW), Canada’s largest river basin draining directly to Lake Erie. Our results show that since 1900 the GRW has served as a net P sink, with an estimated accumulation of more than 480 ktons P, of which 89% resides in soils and 6% in reservoirs and riparian areas. Future simulations suggest that while a 40% reduction in P discharge to Lake Erie is possible under aggressive management scenarios, legacy P will continue to elevate P loads to Lake Erie for centuries.

How to cite: Basu, N., Van Meter, K., Van Cappellen, P., Liu, Y., McLeod, M., Hall, R., and Tenkuano, G.: Beyond the Mass Balance: Watershed phosphorus legacies and the evolution of the current water quality policy challenge, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20724, https://doi.org/10.5194/egusphere-egu2020-20724, 2020.

Long-term Soluble Reactive Phosphorus (SRP) monitoring in headwater streams in central Europe revealed a seasonal pattern of SRP concentrations during low flow periods, with highest concentrations in summer and lowest in winter. These seasonal concentration amplitudes often exceed the eutrophication threshold during the summer eutrophication-sensitive period. It is assumed that temperature dependent biogeochemical processes control the underlying P release mechanism, where redox processes may be responsible for this increase. Several studies have highlighted the crucial role of reactive zones such as riparian wetlands in controlling solute export regimes. Moreover especially in forest headwater streams, in-stream assimilatory uptake shows a distinct seasonal behaviour because of varying shading conditions. This can also lead to seasonal SRP amplitudes. Furthermore sorption and desorption processes are temperature dependent which may alter in-stream SRP release during the year.

Often SRP concentrations are higher in agricultural streams than in more pristine headwaters. It is not clear how land use (e.g. P status of soils) may impact the baseline SRP concentrations and which factors control the seasonal change in SRP stream concentration (riparian groundwater heads and redox processes, temperature, in-stream release and uptake processes). Therefore the objective of this study is to disentangle land use impacts from hydrological and biogeochemical controls of low flow SRP losses.  A comparative study on seasonal SRP concentration patterns will be presented comprising around 53 long term monitored headwater catchments in humid temperate climate of northern Europe and the United States. Based on hydrological and SRP headwater signals and catchment properties, P release processes are discussed. The results of the study will allow to target SRP mitigation strategies based on knowledge of the dominating control of SRP loss from headwater streams. 

How to cite: Rode, M. and Dupas, R.: Major controls of base flow soluble reactive phosphorus losses in humid temperate headwater streams , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4625, https://doi.org/10.5194/egusphere-egu2020-4625, 2020.

Soil colloids with high sorbing capacities can enhance transport of phosphorus (P) from soils to groundwater and the delivery of P to surface water via groundwater pathways. However, only particulate and dissolved P fractions are generally monitored at the catchment scale.

To add important insights into the particulate to dissolved P concentration spectrum in the soil-water environment, the role of colloidal P delivery processes to surface water was studied in two agricultural catchments. The catchments were dominated by belowground pathways but had contrasting land use (arable and grassland). Particulate, coarse colloidal (0.20 – 0.45 μm) and finer colloidal (< 0.20 μm) P fractions were monitored along hillslopes in the free soil solution, shallow groundwater and stream water on a weekly basis for background characterisation and at higher frequency during rainfall events. An automated sampler was deployed in the stream and an automated, low-flow and low-disturbance sampler was developed to sample groundwater. Multi-parameter probes were also deployed to monitor stream water and shallow groundwater physico-chemical parameters. Stream discharge was measured at high frequency using a flow velocimeter in order to quantify P loads, apportion hydrological pathways and study concentration-discharge hysteresis.

Preliminary findings showed higher background P and unreactive P concentrations in the stream and groundwater in the grassland catchment. In the arable catchment (rainfall event in June 2019) P was mainly lost through deeper baseflow (92% of the total event flow) as reactive P in the finer colloidal fraction (0.070 mg P/ha) and only a small fraction lost as particulate unreactive P (0.008 mg P/ha). In the grassland catchment (rainfall event in October 2019), P was mainly lost through quickflow (37% of the total flow) even tough deeper baseflow was also important (33%). Losses were mainly reactive P in the finer colloidal fraction (13.6 mg P/ha) but also as unreactive P (4.5 mg P/ha). Concentration-discharge hysteresis suggested a smaller and easily mobilised P source in the arable catchment and a larger P source, followed by the mobilisation of a second but smaller source via a second hydrological surface pathway in the grassland catchment.

Further monitoring campaigns during more rainfall events in the grassland catchment are required to better understand colloidal P delivery and the spatial/temporal dynamics between rainfall events in relation to soil conditions and rainfall patterns. This will help to better target mitigations measures according to P species and fractions, hydrological flowpaths, and rainfall patterns – important in the context of a changing climate.

How to cite: Fresne, M., Jordan, P., Daly, K., Fenton, O., and Mellander, P.-E.: Assessing the role of colloidal phosphorus delivery processes in groundwater-fed agricultural catchments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7081, https://doi.org/10.5194/egusphere-egu2020-7081, 2020.

Water pollution is an important reason for the failure of 17 % of Scottish waterbodies to reach Good Ecological Status under the Water Framework Directive (WFD). Among the multiple pressures affecting water quality, phosphorus (P) pollution is a major cause of surface water quality failures. Reducing the P pollution in agricultural catchments requires evidence-based decision-making about the effectiveness of land management mitigation measures and their spatial targeting, under current conditions and future scenarios.

Here we introduce a decision-support tool, PhosphoRisk, that uses a Bayesian Belief Network to integrate information on the potential effects of water quality mitigation measures, including data and expert opinion, and parameterizations of the uncertainties in these quantities, in a single model. Specifically, the model integrates spatially distributed geographic information system data about land use and crops, soil erosion risk, topographic connectivity, presence of soil drains, soil hydrological leaching and P binding properties, farm yard locations for incidental P losses, sewage treatment works and septic tank location, with catchment rainfall and runoff data, fertiliser application rates and likely buffer effectiveness. Critical source areas of diffuse and point source pollution risk are mapped on 100x100 m raster grids for two pilot catchments in north-east Scotland – Lunan Water (124 km²) and Tarland (72 km²). The model simulates the probability of P concentration falling into the WFD high-good-moderate-poor classification categories at the catchment outlet and models P source apportionment alongside the effectiveness of mitigation measures such as buffer strips and fertiliser application rates.

Sensitivity analysis of the model reveals the importance of hydrology for the seasonal dilution of P concentrations at the catchment outlet. Diffuse point sources, such as incidental losses from farmyards, are also important for this model of P pollution risk, along with sewage treatment works. The presence/absence of soil drains and septic tanks have a smaller influence on the outputs from the model.

The PhosphoRisk decision support tool facilitates system-level thinking about phosphorus pollution and brings together academic and stakeholder communities to co-construct a model structure appropriate to the region it is modelling. The model reveals the causal relationships between the modelled factors driving an understanding of the effects of land use on P pollution risk in Scottish catchments. The modelled scenarios will help to inform and target water quality mitigation measures in high risk areas, while the quantified model uncertainties will inform further research and motivate targeted data collection.

How to cite: Glendell, M., Vinten, A., Richards, S., Gagkas, Z., Lilly, A., Baggaley, N., Coull, M., Schurch, N., Gimona, A., Pohle, I., Troldborg, M., and Stutter, M.: A systems approach to modelling phosphorus pollution risk in Scottish rivers using Bayesian Belief Networks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8229, https://doi.org/10.5194/egusphere-egu2020-8229, 2020.

Catchments store and release water of different ages. The time of a water parcel remaining in contact with the catchment subsurface affects the solute dynamics in the catchment and ultimately in the stream. Catchment storage can be conceptualized as a collection of different water parcels with different ages, the so-called residence time distribution (RTD). Similarly, the distribution of water ages in streamflow at the catchment outlet, which is sampled from the RTD, is called the travel time distribution (TTD). The selection preferences for discharge can be characterized by StorAge selection (SAS) functions. In recent years, numerical experiments have shown that SAS functions are time-variant and can be approximated, for example, by the beta distribution function. SAS functions have been emerging as a promising tool for modeling catchment-scale solute export.

In this study, we aim to integrate the SAS-based description of nitrate transport with the mHM-Nitrate model (Yang et al., 2018) to simulate solute transport and turnover above and below the soil zone including legacy effects. The mHM-Nitrate is a grid based distributed model with the hydrological concept taken from the mesoscale Hydrologic Model (mHM) and the water quality concept taken from the HYdrological Predictions for the Environment (HYPE) model. Here, we replaced the description of nitrate transport in groundwater from the original mHM-Nitrate with time-variant SAS-based modeling, while we kept the detailed description of turnover of organic and inorganic nitrogen in the near-surface (root zone) from mHM-Nitrate. First-order decay was used to represent biogeochemical (denitrification) processes below the root zone and in the stream. The proposed model was tested in a mixed agricultural-forested headwater catchment in the Harz Mountains, Germany. Results show that the proposed SAS augmented nitrate model (with the time-variant beta function) is able to represent streamflow and catchment nitrate export with satisfactory results (NSE for streamflow = 0.83 and for nitrate = 0.5 at the daily time step). Overall, our combined model provides a new approach for a spatially distributed simulation of nitrogen reaction processes in the soil zone and a spatially implicit simulation of transport pathways of nitrate and denitrification in the entire catchment.

Yang, X., Jomaa, S., Zink, M., Fleckenstein, J. H., Borchardt, D., & Rode, M. ( 2018). A new fully distributed model of nitrate transport and removal at catchment scale. Water Resources Research, 54, 5856– 5877.

How to cite: Nguyen, T., Kumar, R., Lutz, S. R., Musolff, A., and Fleckenstein, J. H.: Modeling Nitrate Export at the Catchment Scale using StorAge Selection Functions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7967, https://doi.org/10.5194/egusphere-egu2020-7967, 2020.

Exponential human population growth and the rapid co-development of agricultural and industrial sectors have caused a sharp increase of nitrogen loading to rivers and groundwaters worldwide since the 1950s. Reactive nitrogen species (e.g., nitrate, ammonium) are widely distributed compounds in rivers and groundwaters primarily as a result of diverse agricultural activities utilizing N-containing fertilizers and anthropogenic non-point sources, such as the disposal of sewage by centralized and individual systems, animal feeding operations, and elevated atmospheric N deposition. Systematic efforts to identify global patterns in nitrogen loss processes using nitrogen isotopes have mostly targeted soil and plant systems but remain rather limited for surface and/or groundwater systems. Here, synthesized published (4,492) and new data (425) for nitrogen and oxygen isotopes of nitrate in rivers and groundwater generated under an IAEA Coordinated Research Project, which aimed to utilize the application of nitrogen isotope techniques to assess nitrogen pollution in rivers and groundwaters, are presented. Among the two water types, we found that groundwater had higher average nitrate concentrations (~5.0 mg L^-1 NO₃-N) versus rivers (~2.0 mg L^-1 NO₃-N), slightly higher δ¹⁵N and much higher δ¹⁸O (+7.6 ‰ and +4.3 ‰, respectively) compared to rivers (+7.0 ‰ and +1.8 ‰, respectively). Seasonal variations in the concentrations and the isotopic compositions of N-species were found to be temperature related, given that biological activity increases with water temperature. Across a range of Köppen climate types, we found the δ¹⁵N and δ¹⁸O of NO₃ in rivers systematically increased when moving from temperate to tropical climates, following the increase of the average air temperature.

How to cite: Matiatos, I. and the IAEA Coordinated Research Project on Isotopes to study nitrogen pollution and eutrophication of rivers and lakes: A global synthesis of dual nitrate isotope values in rivers and groundwaters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22154, https://doi.org/10.5194/egusphere-egu2020-22154, 2020.

This study includes water quality monitoring data obtained since June, 2014 at the farm located in the middle part of Latvia. The water treatment system with two separate constructed wetlands was established to improve water quality in agricultural area. A surface flow constructed wetland received drainage runoff from the agricultural catchment basin. A subsurface flow constructed wetland was implemented to retain nutrients from the surface runoff collected in the area of impermeable pavements of the farmyard. As there are no other specific calculations recommended for the designing of constructed wetlands in Latvia, both wetlands were calculated basing on the surface area of the constructed wetland/catchment area ratio. The surface area of the subsurface flow constructed wetland was deigned by 1.2% of the catchment area and the ratio was 0.5 % for the surface flow constructed wetland.

Water samples were collected manually by grab sampling method once or twice per month basing on a flowrate. Water quality parameters such as total suspended solids (TSS), nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N), total nitrogen (TN), orthophosphate-phosphorus (PO4-P), and total phosphorus (TP), biochemical oxygen demand (BOD) and chemical oxygen demand (COD) were analysed to monitor the performance of both wetlands. The concentrations at the inlet and outlet were compared to evaluate the efficiency of the water treatment.

The concentrations of NO3-N, NH4-N and TN were reduced on average by 21 %, 35 % and 20 %, respectively for the surface flow constructed wetland. PO4-P and TP concentrations were reduced on average by 31 % and 45 %, respectively for the surface flow constructed wetland. Total suspended solids were reduced by 17% at the outlet of the surface flow constructed wetland. However, in some cases, an increase in nutrient concentrations in water leaving the wetland was observed. The study showed the constant reduction of the PO4-P and TP concentrations 82 % and 83 %, respectively in the subsurface flow constructed wetland. The concentrations of NO3-N, NH4-N and TN were reduced on average by 14 %, 66 % and 53 %, respectively for the subsurface flow constructed wetland. BOD and COD reduction on average by 93 % and 83 %, respectively in for the subsurface flow constructed wetland indicated the ability of the treatment system to be adapted for wastewater treatment with high content of organic matter under the given climate conditions. This study outlined that the farmyards should receive a special attention regarding surface runoff management.

How to cite: Grinberga, L. and Lagzdins, A.: The improvement of water quality indicators in constructed wetland treatment systems in Latvia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12678, https://doi.org/10.5194/egusphere-egu2020-12678, 2020.

Wildfires are an increasing threat in the Mediterranean area causing the loss of goods and frequently on the loss of human lives. Not only forest fires are worrisome for their first and visible impacts on vegetation and soil, but also for the secondary impacts on the quality of surface water bodies. Approximately one third of the world’s largest cities obtain their drinking water from forest catchments. The removal of vegetation and consequent increase in runoff with high concentration in sediments often leads to increased nutrients and sediment loads to water reservoirs damaging the aquatic ecosystem and human health.

In Portugal, the catastrophic events of Portuguese territory in 2017 occurred in strategic catchments from the water supply point of view. The Castelo de Bode reservoir, located in that area, with a total capacity of 1095 hm³, supplies the city of Lisbon and surrounding areas (2,000,000 inhabitants). During 2017, more than one hundred thousand hectares of land in the upstream watershed were burned, making it one of the most affected areas in Portugal.

This study focuses on the impacts of the fires on the water quality of Castelo de Bode reservoir. The Soil Water Assessment Tool (SWAT) was first calibrated and validated for simulating streamflow, sediments and nutrients transport. The post-fire impacts were implemented by adjusting land use characteristics (curve number, crop vegetation management factor), and soil properties (soil erodibility), taking into account the different impacts from fire (low, medium, and high severity). The output from this model was then used as input to CE-QUAL-W2 reservoir model. During the calibration phase, it was possible to observe that CE-QUAL-W2 presented some limitations in reproducing water quality parameters, according to the available field measurements in such large reservoir . Therefore, the parameters with the best fit to the measurements at the dam wall were chosen as water quality indicators in the post-fire.

Preliminary results indicated an increase in nutrients and algae concentrations in the year following the 2017 fire events, characterized also by a decrease in the water level due to the base flow reduction at the watershed scale. Although high concentrations of nutrients characterized the reservoir inlet, only phosphate concentration slightly overcame the thresholds limits foreseen in legislation for drinking water close to the dam wall, likely due to the large volume of the reservoir which diluted the inflow concentrations.

How to cite: Basso, M., Mateus, M., Ramos, T., and Vieira, D.: Post-fire impact on the water quality of a reservoir: an integrated watershed-reservoir modeling approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-225, https://doi.org/10.5194/egusphere-egu2020-225, 2020.

Inland surface waters like rivers, streams, lakes and reservoirs are subject to anthropogenic pollutant emissions from various sources. These emissions can have severe negative impacts on surface water ecology, as well as human health when surface waters are used for recreational activities, irrigation of cropland or drinking water production. In order to protect aquatic ecosystems and freshwater resources, the European Water Framework Directive (WFD) sets specific quality requirements which the EU member states must meet until 2027 for every water body.

Implementing effective measures and emission control strategies requires knowledge about the important emission pathways in a given river basin. However, due to the abundance of pollution sources and the heterogeneity of emission pathways in time and space, it is not feasible to gain this knowledge via water quality monitoring alone. In our study, we aim to combine SWAT ecohydrological modelling and long term water quality monitoring data to establish a spatially differentiated nitrogen emission inventory on the sub-catchment scale. SWAT (short for Soil and Water Assessment Tool) is a semi-distributed, dynamic and process-driven watershed model capable of simulating long term hydrology as well as nutrient fluxes on a daily time step.

The study area is the Swist river basin in North Rhine-Westphalia (Germany). Belonging to the Rhine river system, the Swist is the largest tributary of the Erft River and drains a basin area of approximately 290 km². As part of its legal obligations and research activities, the Erftverband local waterboard collects a large variety of long term monitoring data in the Swist river catchment, which is available for this study. This includes operational data from the wastewater treatment plants in the watershed, discharge data from four stream gauging stations, river water quality data from continuous and discontinuous monitoring, groundwater quality data as well as quality data from surface, sub-surface and tile drainage runoff from various land uses.

Our contribution will be made up of two equal parts: First, we will present our water quality monitoring activities in the catchment and the related data pool outlined above, with special emphasis on recent monitoring results from agricultural tile drainages. Apart from nutrients and other pollutants, the data suggests considerable inputs of herbicide transformation products like Chloridazon-Desphenyl (maximum concentration measured: 15 µg/l) via this pathway. Second, we will explain how we integrate the monitoring data into the SWAT simulations and how we tackle related challenges like parameter equifinality (meaning that multiple parameter sets can yield similar or identical model outputs). The overall goal is to take all possible emission pathways into consideration, including those often neglected in past SWAT studies, like tile drainages and combined sewer overflows (CSO). As the Swist catchment is affected by groundwater extraction due to lignite mining in the Lower Rhine Bay area, we will discuss how this is considered during SWAT model setup and calibration, and will present first simulation results concerning catchment hydrology.

How to cite: Ahring, A., Kothe, M., Gattke, C., Christoffels, E., and Diekkrüger, B.: Combining Ecohydrological Catchment Modelling and Water Quality Monitoring to Assess Surface Water Pollution in the Swist River Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19842, https://doi.org/10.5194/egusphere-egu2020-19842, 2020.

Explicit knowledge of the dynamics and spatial distribution of surface runoff, leaching and preferential flow paths in landscapes and their connections with surface water is critical for protecting the aquatic environment for inputs of sediment, nutrients, pesticides and other harmful substances. Therefore, there is a need for quantifying off-site surface runoff and the resulting transport of sediment, nutrients and pesticides to surface waters at the field scale combined with simultaneous measurements in receiving watercourses to increase our knowledge about the linkages between source areas, transport pathways and the resulting impacts on water quality in receiving water bodies. The importance of surface runoff for transport of sediment, nutrients and pesticides to surface waters have only been limited studied in Denmark even though forecasts of climate change predicts that extreme weather conditions with more intense precipitation events will increase in the future with a risk of having more frequent incidents with surface runoff from agricultural land.

In a recent project soil erosion and surface runoff risks have been modelled for the entire of Denmark on a 10 m x10 m grid scale (Onnen et al., 2019). The influence of surface runoff for transport of sediment, nutrients and pesticides to streams is measured in three carefully selected agricultural mini-catchments showing high risks for having surface runoff in the national model. Within each catchment, an edge of field monitoring site and a stream monitoring station has been established. The edge of field monitoring site consists of a flow chamber collecting surface runoff from the neighbouring field and an automatic sampler initiated at the onset of surface runoff. The edge of field station is established with communication to the stream station for starting an automatic sampler at the time of surface runoff. Selected water samples collected at the edge of field and stream station is analysed for sediment, nutrients and pesticides. A first pilot study from one of the small catchments during the winter of 2015-2016 showed that surface runoff from the field amounted to 48 mm. the loss of suspended sediment, total nitrogen and total phosphorus, respectively, 56 kg sediment ha^-1, 0.29 kg N ha^-1 and 0.30 kg P ha^-1 (Zak et al., 2019). The new edge of field and stream monitoring setup in three agricultural catchments was established during autumn and winter of 2019-2020. The first pilot results from the winter of 2019-2020 with the full monitoring programme in the three catchments have shown frequent surface runoff events and relatively high concentrations of a number of pesticides both in edge of field and stream samples.

References

Onnen, N., Heckrath, G., Stevens, A., Olsen, P., Greve, M.B., Pullens, J.W.M., Kronvang, B. and Van Oost, K. 2019. Distributed water erosion modelling at fine spatial resolution across Denmark. Geomorphology 342: 150-162.

Zak, D., Stutter, M., Jensen, H.S., egemose, S., Carstensen, M.V., Audet, J., Strand, J.A., Feuerbach, P., Hoffmann, C.C., Christen, B., Hille, S., Knudsen, M., Stockan, J., Watson, H., Heckrath, G. and Kronvang, B. 2019. An assessment of the multifuntionality of integrated buffer zones in northwestern Europe, JEQ 48: 362-375.

How to cite: Kronvang, B., Windolf, J., Tornbjerg, H., van't Veen, S., Zak, D., Ovesen, N., and Heckrath, G.: Advancing understanding of the importance of surface runoff for delivery of water, sediment, nutrients and pesticides to streams within agricultural catchments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7854, https://doi.org/10.5194/egusphere-egu2020-7854, 2020.

River phytoplankton provide food for primary consumers, and are a major source of oxygen in many rivers. However, high phytoplankton concentrations can hamper river water quality and ecosystem functioning, making it crucial to predict and prevent harmful phytoplankton growth in rivers. In this study, we modify an existing mechanistic water quality model to simulate sub-daily changes in water quality, and present its application in the River Thames catchment. So far, the modelling studies in the River Thames have focused on daily to weekly time-steps, and have shown limited predictive ability in modelling phytoplankton concentrations. With the availability of high-frequency water quality data, modelling tools can be improved to better understand process interactions for phytoplankton growth in dynamic rivers. The modified model in this study uses high-frequency water quality data along a 62 km stretch in the lower Thames to simulate river flows, water temperature, nutrients, and phytoplankton concentrations at sub-daily time-steps for 2013-14. Model performance is judged by percentage error in mean and Nash-Sutcliffe Efficiency (NSE) statistics. The model satisfactorily simulates the observed diurnal variability and transport of phytoplankton concentrations within the river stretch, with NSE values greater than 0.7 at all calibration sites. Phytoplankton blooms develop within an optimum range of flows (16-81 m³/s) and temperature (11-18° C), and are largely influenced by phytoplankton growth and death rate parameters. We find that phytoplankton growth in the lower Thames is mainly limited by physical controls such as residence time, light, and water temperature, and show some nutrient limitation arising from phosphorus depletion in summer. The model is tested under different future scenarios to evaluate the impact of changes in climate and management conditions on primary production and its controls. Our findings provide support for the argument that the sub-daily modelling of phytoplankton is a step forward in better prediction and management of phytoplankton dynamics in river systems.

How to cite: Pathak, D., Hutchins, M., and Edwards, F.: Modelling sub-daily phytoplankton dynamics and analysing primary production controls in the lower Thames catchment, UK, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8010, https://doi.org/10.5194/egusphere-egu2020-8010, 2020.

Freshwater ecosystems are threatened by multiple anthropic pressures. Understanding the effect of pressures on the ecological status is essential for the design of effective policy measures but can be challenging from a methodological point of view. In this study we propose to capture these complex relations by means of a machine learning model that predicts the ecological response of surface water bodies to several anthropic stressors. The model was applied to the Spanish stretch of the Tagus River Basin. The performance of two machine learning algorithms -Random Forest (RF) and Boosted Regression Trees (BRT) - was compared. The response variables in the model were the biotic quality indices of macroinvertebrates (Iberian Biomonitoring Working Party) and diatoms (Indice de Polluosensibilité Spécifique). The stressors used as explanatory variables belong to the following categories: physicochemical water quality, land use, alteration of the hydrological regime and hydromorphological degradation. Variables describing the natural environmental variability were also included. According to the coefficient of determination, the root mean square error and the mean absolute error, the RF algorithm has the best explanatory power for both biotic indices. The categories of land cover in the upstream catchment area, the nutrient concentrations and the elevation of the water body are ranked as the main features at play in determining the quality of biological communities. Among the hydromorphological elements, the alteration of the riparian forest (expressed by the Riparian Forest Quality Index) is the most relevant feature, while the hydrological alteration does not seem to influence significantly the value of the biotic indices. Our model was used to identify potential policy measures aimed at improving the biological quality of surface water bodies in the most critical areas of the basin. Specifically, the biotic quality indices were modelled imposing the maximum concentration of nutrients that the Spanish legislation prescribes to ensure a good ecological status. According to our model, the nutrient thresholds set by the Spanish legislation are insufficient to ensure values of biological indicators consistent with the good ecological status in the entire basin. We tested several scenarios of more restrictive nutrient concentrations and values of hydromorphological quality to explore the conditions required to achieve the good ecological status. The predicted percentage of water bodies in good status increases when a high  Riparian Forest Quality Index is set, confirming the importance of combining physico-chemical and hydromorphological improvements in order to ameliorate the status of freshwater ecosystems. 

How to cite: Valerio, C., Garrido, A., Martinez-Muñoz, G., and De Stefano, L.: A machine learning model to link ecological response and anthropogenic stressors: a tool for water management in the Tagus River Basin (Spain) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9567, https://doi.org/10.5194/egusphere-egu2020-9567, 2020.

Freshwater ecosystems can be negatively affected by climate change and human interventions through the alteration of water supply and demand. There is an urgent need to protect the ecosystems, and the services they provide, to maintain their essential contribution to human wellbeing and economic prosperity, especially in a rapid and unpredictable global change context. In this work, we developed an integrated approach, coupling the outputs of ecosystem services (InVEST), climate (COSMO-CLM) and land use (LUISA) change models utilizing Bayesian Networks (BNs), to map freshwater-related Ecosystem Services (ESs), namely, water yield, nitrogen and phosphorus retention, and to assess their changes until 2050 under different management scenarios. First, InVEST was calibrated and validated with climate and land-use data to map and quantify ESs. Second, outputs of the ES model were integrated into the BN and the changes induced by different learning techniques and input settings were investigated. Finally, thousands of different scenarios were simulated testing multiple input variables configurations, thus allowing to describe the uncertainty of climate conditions, land-use change and water demand. Two types of inferences were conducted, namely, diagnostic and prognostic inference. The former permitted to find the best combination of the key drivers (i.e.  precipitation, land-use, and water demand) so that ESs are maximized while the latter concentrated on the quantification of ESs under different scenarios. This approach was applied and validated in the Taro River basin in Italy. The results show that the values of all the three types of ESs would decline in the medium-term period under most scenarios. Moreover, there would be a limit of space to improve those values, especially for nutrient retention services. The obtained results provide valuable support to identify and prioritize the best management practices for sustainable water use, balancing the tradeoffs among services. This analysis allows decision-makers to pick up one scenario with a specific configuration of land-use and water demand to optimize relevant ESs within their basin. Finally, these decisions are transformed into a “decision space” where the values of selected services are plotted in the space of ES to represent the gain/loss of each decision.

How to cite: Critto, A., Pham, H. V., Sperotto, A., Torresan, S., Furlan, E., and Marcomini, A.: An ecosystem-based approach to support water quality assessment and management under climate and land-use condition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17117, https://doi.org/10.5194/egusphere-egu2020-17117, 2020.

Reducing eutrophication requires large financial investments that can be for example used to support catchment stakeholders in building agri-environment mitigation measures. These measures aim at reducing nutrient and sediment losses from agricultural land to recipient waters. In recent years, a large number of studies has looked into their effectiveness and generally show that some measures are successful and others fail to deliver expected improvements in water quality, which is increasingly difficult to communicate to stakeholders expecting immediate results. Particularly, transport mitigation measures that aim at intercepting stream or drainage flow, can have a varying effectiveness. Two measures of the same type and built in a seemingly similar way can have completely opposite impact on water quality, depending on the local catchment properties. In this paper we examine factors controlling effectiveness of mitigation measures looking at their hydrochemical positioning in the catchment in relation to pollution sources including nutrient legacy sources, their hydrochemical behaviour, design, management and stakeholders’ engagement, using examples for transport mitigation measures: constructed wetlands, sedimentation ponds, two-stage ditches and drainage filters. We discuss also typical trade-offs in attainment of different ecosystem services which catchment stakeholders should consider prior to selecting and building the measures, including pollution swapping mechanisms e.g. reducing P-controlled eutrophication but increasing N-controlled eutrophication or reducing eutrophication vs. increasing greenhouse gas emissions. We show also how increasing weather variability and nutrient saturation can lead to further deterioration in water quality despite implementation of measures, making mitigation efforts ineffective under changing climate and in catchments with nutrient legacy sources.

How to cite: Bieroza, M., Ulen, B., Geranmayeh, P., Djodjic, F., and Heeb, A.: Combating eutrophication in agricultural catchments: factors controlling effectiveness and challenges of changing climate and nutrient legacies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21472, https://doi.org/10.5194/egusphere-egu2020-21472, 2020.

This study reports data from field sampling of catchment and reservoir bed sediments undertaken in October 2013 in the Wala catchment, Jordan, and findings of geochemical analysis of the sediments. The primary aim of this study is to investigate the relationship between sediments from different locations within the catchment and those deposited within the reservoir. This is set within the overall context of an attempt to rationalise the use of modelling in a data-poor environment. Can targeted, limited acquisition of geochemical information within a logistically challenging environment add value to existing datasets in respect of ground truth for model predictions of sediment provenance within the catchment? Channel bed sediments were collected from sub-catchment outlets throughout the Wala catchment and shallow cores (c. 500 mm) extracted from three locations around the Wala reservoir. XRF and particle size analysis were performed on all samples and the data analysed in respect of mineralogical and pollutant geochemical signatures. Contrary to evidence from temperate lake studies, there was no strong record of discrete event-driven deposition at the Wala, likely due to reworking of sediments during high-flow recharge events following complete draw-down of the reservoir in the highly intermittent hydrological setting. Pollutant geochemistry shows variations consistent with patterns of land-use in the catchment, with levels of Pb, Co, Cu and Cr associated with urbanised regions in the north and west of the region. Sampled concentrations, particularly those of the reservoir sediments, are typically below thresholds for environmental health concern. However, combined with the modelled bias in flow and sediment inputs from this region (driven by asymmetric rainfall distribution), this emphasises a potential concern for future management of water quality and protection of groundwater during aquifer recharge.

How to cite: Tarawneh, E., Bridge, J., and Macdonald, N.: Sediments of the Wala catchment and reservoir, Jordan: Geochemical analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-629, https://doi.org/10.5194/egusphere-egu2020-629, 2020.

Delhi, India’s capital is the second largest urban agglomeration in the world. It is expected to surpass Tokyo to become world’s largest city by 2028 with ~37 million inhabitants (UNDESA, 2018). This rapid growth is characterized by unsystematic urbanization, rapid shifts in its landuse patterns and tremendous pressure on the city’s natural resources. Among other forms of resource degradation, rapidly shrinking and stinking wetlands are of primary concern. Thus evidence-based policy making for their sustainable development and conservation require regular reporting and monitoring of their status.
Present study compares the hydrochemistry of two urban wetlands of Delhi (Sanjay lake and Bhalswa lake) having some crucial differences in their nature and catchment area activities. Surface water quality of these wetlands was studied for winter and summer with respect to their physico-chemical properties (temperature, pH, dissolved oxygen, electrical conductivity, total dissolved solids, alkalinity and hardness) including major ions and trace metals employing standard analytical methods (APHA, 2005). Waters from both the wetlands are alkaline in nature. While pH of Sanjay lake shows a greater variation (7.9 to 10.8), that of Bhalswa lake is fairly constant (8.4 to 8.7), across the seasons. The wetland waters also vary seasonally in their chemistry. Differences in the nature and associated landuse of the wetlands is reflected in their water quality. Hydrogeochemistry of these wetlands were determined by Piper plot and Gibb’s diagram. While water from both the wetlands are Na⁺- SO₄^2- type during summer, water from Bhalswa lake is Na⁺- SO₄^2- type and that from Sanjay lake is Ca²⁺-Mg²⁺- SO₄^2- type during winter. While water from Bhalswa lake shows an evaporation dominance regime, that from Sanjay lake show dominance of rock-water interaction. Water from both the wetlands are generally unsuitable for drinking purpose. While water from Bhalswa lake is unsuitable for irrigation as well, water from Sanjay lake is generally suitable as determined using various indices (% Na, Residual Sodium Carbonate, Sodium Absorption Ratio, etc.). Both the drinking and irrigational water quality of these wetlands deteriorate during summer. Factor analysis was also used to determine sources of pollution for the two wetlands during both winter and summer. Domestic sewage is observed to be a major source of pollution for both the wetlands. Thus, this study indicates that urban wetlands of Delhi are fast depleting in their health. In light of their importance as a significant urban water resource, a crucial ecological niche and an essential recreational spot for urban areas, there is an urgent need for positive interventions.

How to cite: Joshi, P. and Siddaiah, N. S.: Hydrogeochemistry of Urban Wetlands of Delhi, India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-945, https://doi.org/10.5194/egusphere-egu2020-945, 2020.

In the small, forested Kuzlovec stream catchment near Ljubljana, Slovenia, nitrate flushing data were monitored in years 2018 and 2019. The amount of exported nitrates, determined based on the nitrate concentration in the stream, depends on hydrometeorological and biogeochemical conditions in the catchment. Therefore, various measuring equipment was installed in the catchment: tipping buckets for measuring precipitation amount and rainfall rates, pressure sensors in the stream for evaluation of water level and consequently of stream discharge, soil moisture sensors in three depths, a multiparameter probe for measuring the physical and chemical properties of water, including concentration of nitrates, etc. Moreover, occasionally, some discrete measurements were performed: discharge measurements using a dilution method, leaf area index measurements for determination of vegetation conditions using a plant canopy analyser, determination of soil properties including nitrate content in different soil horizons, etc.

Data, which were obtained using in-situ equipment for continuous measurements, were collected or recalculated to a 20-min time step. Due to geological properties and steep slope of the terrain, the catchment is very responsive to rainfall events. This is reflected in a short time of concentration, meaning that both flood peak and nitrate concentration peak occur shortly after the rainfall event. However, concentration of nitrates in stream and consequently the amount of flushed nitrates vary on event basis. This paper presents results of analysis of different events which occurred during the monitoring in order to identify hydrometeorological and seasonal conditions on nitrate flushing.

Acknowledgment: We acknowledge the financial support of the Slovenian Research Agency (research core funding No. P2-0180, and the PhD grant of the first author).

How to cite: Sapac, K., Vidmar, A., and Rusjan, S.: Event-based analysis of nitrate flushing from forested catchment using high-frequency in-stream monitoring data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1872, https://doi.org/10.5194/egusphere-egu2020-1872, 2020.

Due to the intensified influence of human activities, Yongding river presents a sharp decrease in water quantity and a trend of continuous deterioration of water environment, and the ecological environment is seriously damaged. Under this background, Yongding river ecological reconstruction project needs to be carried out urgently, and ecological water replenishment mode needs to be determined urgently. In order to explore the influence of multi-water source ecological replenishment mode on the evolution of river water quality and riverbank percolation water quality, this study conducted a simulation experiment to explore the influence of flow rate, temperature and soil percolation on reclaimed water replenishment water quality. The results show that the increase of flow velocity is beneficial to the degradation of pollutants. Compared with high temperature, the degradation capacity of pollutants at low temperature is significantly better than that at high temperature, indicating that low temperature is beneficial to the improvement of reclaimed water quality to some extent. Some water quality indexes of riverbank leachate improved to some extent, but the water passing through the soil was slightly eutrophication due to the aggregation and adsorption of river bottom sediments. The final results show that the velocity of flow has the greatest influence on the quality index of regenerated water.

How to cite: guo, Z. and pan, C.: Experimental Study on the Evolution of River Water Quality and Riverbank Percolation Water Quality under Reclaimed Water Replenishment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3201, https://doi.org/10.5194/egusphere-egu2020-3201, 2020.

Influence of lands use patterns on water quality is complex and scale dependent. The relationship among land use patterns/configurations, topography, and surface roughness of riparian zones and river water quality in the middle and down streams Han River, China, was analyzed using geographically weighted (GWR) multiple regression models. The land use types within 50 m and 100 m of riparian zones that exhibit the strongest association with riverine water quality were investigated. Water quality samplings were collected from 94 sites during November in 2015 (dry season) and May in 2016 (wet season) under the rainy days. GWR models have better predictions of PO₄^3- and TP in the Wet season and those of NO₃-N, TN, and Chl-a in the Dry season. High prediction differences of PO₄^3- and TP between Dry and Wet seasons. Most water quality variables in 50 m riparian zone have higher local parameter estimate (LPE) values than those in 100 m riparian zone, indicating 50 m riparian zone significantly influences riverine water quality. In the middle section, grass lands represent the source area of pollutants, which may discharge pollutants with runoff into Han River. However, forest land with high vegetation height can retard the rainfall becoming surface runoff and its relevant high surface roughness can increase infiltration and reduce the nutrient transport ability. Therefore, forest land exhibited a stronger contribution to water quality improvements. These findings provide important information for sustainable landscape management of riparian zones to improve riverine water quality.

How to cite: Kuo, Y.-M. and Zhao, E.: Effects of hydrology, riparian topography, and land uses on the water quality in the middle and down streams Han River, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3858, https://doi.org/10.5194/egusphere-egu2020-3858, 2020.

Studies on hydrogeochemical characteristics and an assessment of the groundwater quality for drinking purposes were conducted in and around the riverside source field of Wuchang, Northeast China. Twenty-seven and twenty-three shallow groundwater samples were collected for measuring on-site parameters and major components in the years 2000 and 2014, respectively. In 2014, the average concentrations of major ions of shallow groundwater were found to be in the following order: Ca²⁺> Na⁺> Mg²⁺> K⁺ for cations and HCO₃^-> SO₄^2-> Cl^-> NO₃^- for anions. The spatial distribution patterns of K⁺ and NO₃^- had no obvious regularity, whereas Cl^- and Na⁺ showed similar spatial distribution patterns. Ca-HCO₃ and mixed type water were the dominant hydrochemical types. The analysis of the SI values for minerals and the Gibbs plot illustrated that the concentrations of major components were mainly controlled by rock weathering, such as the dissolution of calcite, dolomite, halite, gypsum and aragonite, followed by ion exchange. Indicators, such as Total hardness (TH), Total Dissolved Solids (TDS), Cl^-, SO₄^2- and NO₃^-, were selected to assess the groundwater quality using a comprehensive evaluation method of dividing the groundwater quality into five classes: excellent, good, fair, poor and very poor water. The results showed that 7.4% and 34.8% of the total groundwater sample in 2000 and 2014, respectively, were unsuitable for drinking use, indicating that the shallow groundwater quality has gradually worsened in the past few decades. The concentration of NO₃^- was a major factor that influenced the observed groundwater quality changes.

Acknowledgments

This study was supported by the NSFC (No.41877355), Beijing Advanced Innovation Program for Land Surface Science, and the 111 Project of China (B18006).

How to cite: Teng, Y., Zhai, Y., Chen, H., and Chen, R.: Characteristics of Hydrogeochemistry and Groundwater Quality in a Riverbank Filtration Site, Northeastern China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4690, https://doi.org/10.5194/egusphere-egu2020-4690, 2020.

In this paper, a comprehensive early-warning method of sudden water pollution is used to systematically evaluate the hazards of sensitive receptors after accidents. A coupling model of the river network hydrodynamic and water quality for conventional pollutants and conservative substance is developed to track and predict the behavior and fate of the accidental pollution mass, the expert questionnaires and other means are used to construct a quantitative and qualitative early warning index system to describe the accidental hazard, the AHP and fuzzy comprehensive evaluation method are used to quantitatively evaluate the consequences of accidental hazards and a sudden water pollution risk early warning method based on the process of "accident occurrence-pollution prediction-consequence evaluation" is finally formed. The method is applied to the Yincungang River in the Yixing River Network, and the response of sensitive receptors to the discharge status of risk sources under different water regime is analyzed. The results show that: (a) the duration of the impact from the accident, the maximum standard-exceeding multiple of water quality and the degradation degree of water quality in the sensitive receptors are positively related to the discharge intensity or discharge time of the accident source, but the response time from the accidental impact is negatively related to them. (b) during the non-flood season, the warning situation in the Yincungang River shows a gradual decrease from upstream to downstream; during the main flood season, the warning situation in the upper and middle reaches of Yincungang River shows a decreasing trend, but in the middle and lower reaches that increases.(c) the transport distance and speed of accidental pollutants in the river and the concentration of accidental pollutants in the background at the sensitive receptors determine the quantitative early warning indexes dynamically, which is the fundamental reason for the spatial change of warning situation in different water regime.

How to cite: Li, D.: Analysis on the warning situation of sudden water pollution for typical river under different water regime in the river network area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6417, https://doi.org/10.5194/egusphere-egu2020-6417, 2020.

Base cation such as calcium and potassium is important nutrient for tree growth in forest ecosystems.  Major sources of basic cation to forest soil are precipitation, weathering of parent material and litter fall.  Weathering rate of basic cation is estimated from the input from precipitation, runoff from stream and uptake by vegetation.  Nutrient cycling of many Japanese forest ecosystems has been studied but information about the contribution of these sources is limited.  This study compared three nutrient sources in four forest watersheds in Japan.  These are Oyasan (Gunma Pref.), Kamikamo (Kyoto Pref.), Kiryu (Shiga pref.) and Takatori (Kochi Pref.).  We calculated nutrient budget of potassium, calcium and magnesium.  The rate of rock weathering of base cation ranged from 0.22 to 4.37 kmolc ha^-1 yr^-1 and increased in the order of Kamigamo < Kiryu < Oyasan < Takatori.  In potassium cycling, the contribution of litter fall was greater than that of weathering or precipitation.  The runoff of calcium and magnesium from soil was greater in Takatori, where the rate of weathering was high.  Although the rate of weathering varied substantially among forest watersheds, the annual flux of litter fall was relatively constant.  Similar calculation was applied for nitrogen cycling and the　source from soil was treated as that from nitrogen accumulated during the past pedogenesis.  Nitrogen input from the accumulated soil source was 36 % in Oyasan whereas that in other three watersheds was 0%. Oyasan was considered as a nitrogen-saturated forest and the result of the study suggest the ecosystem relies on different nitrogen source.

How to cite: Inagaki, Y. and Fujii, K.: Nutrient sources in four forest watersheds in Japan: the contribution of precipitation, weathering and litter fall, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6460, https://doi.org/10.5194/egusphere-egu2020-6460, 2020.

Radium-224 /Thorium-228 (²²⁴Ra/²²⁸Th) disequilibrium in sediments is an advanced proxy of benthic processes and has been gradually used to quantify the fluxes and solute transfer across the sediment–water interface (SWI). This study makes the first attempt to explore the nitrogen fluxes across the SWI of Lake Taihu, the third largest and highly eutrophic freshwater lake in eastern China, based on the plumbing of ²²⁴Ra/²²⁸Th disequilibrium in the lake sediments. The microscopic sediment cores (0-20 cm) were collected in different parts of the lake, and exchangeable ²²⁴Ra and ²²⁸Th in bulk sediments were measured. Dissolved inorganic nitrogen (DIN) in pore water and overlying lake water were also analyzed. Deficits of ²²⁴Ra compared to its parent isotopes ²²⁸Th were observed in the lake sediments, suggesting the influences of mixing processes. The deficits were relatively significant in the western and northern parts, which are consistent with the relative high-eutrophicated areas of the lake. One-dimensional (1D) radium-thorium diagenetic model in the sediment was used to estimate the benthic fluxes based on the ²²⁴Ra deficits. Results show that the benthic fluxes of ²²⁴Ra varied from -0.428 to 1.170 dpm cm^-2 d^-1, and the bio-irrigation and molecular diffusion are considered to be the major factors. Specifically, in the severely eutrophicated area of the lake, the bio-irrigation predominates in benthic fluxes, reaching up to 97.1% of the deficit of ²²⁴Ra. The DIN benthic fluxes were also quantified, leading to a flux estimation of 3.41 mol m^-2 d^-1, which exceeds riverine input (2.63 mol m^-2 d^-1) and the loading derived from lacustrine groundwater discharge (0.02~0.03 mol m^-2 d^-1). This study reveals that sediment processes could be the vital factors for the lake nutrient loadings, and highly contribute to the lake eutrophication. This study is constructive for the water remediation and ecosystem restoration in Lake Taihu and other large eutrophic lakes elsewhere.

How to cite: shi, X., luo, X., jiao, J. J., huang, J., lu, M., and liang, W.: 224Ra/228Th disequilibrium in sediments of Lake Taihu: Implications of nitrogen fluxes across the sediment–water interface, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8207, https://doi.org/10.5194/egusphere-egu2020-8207, 2020.

There is mounting evidence that the extreme weather conditions, either droughts or floods, could likely be more frequent than what was thought before, resulting in increased impacts on our ecosystems. This study aims to investigate the effect of the extreme drought events that occurred in the period 2015-2019 on the nitrate-N concentrations and loads in the Bode catchment (3300 km²) located in the transition areas of central uplands and northern lowlands of Germany. To this, a combination of high-frequency (15 min data in the period 2011-2019) and long-term (1993-2010) of continuous discharge and biweekly nitrate-N records in five typical gauging stations, representing different landscape features and dominant-runoff components of the catchment, were utilized. In the period 2015-2019, mean annual precipitation decreased by about 10%, and mean temperature increased by 1.46 °C compared to the period 1969-2014. Results suggested no evident changes in nitrate-N concentrations and loads in the upper mountainous areas of the Bode catchment (mainly forest) and groundwater-dominated gauging station, reflecting no impact of the droughts on these two archetypical sub-catchments. However, results showed that the nitrate-N concentrations and loads declined significantly in the lowland, agriculture dominated areas of the Bode catchment. This can be explained by the reduction of nitrate-N contribution from the lower part of the catchment during the spring and summer periods. It seems that the drought-induced increased evapotranspiration and decreased precipitation resulted in the reduced runoff from lowland areas of the catchment, affecting the nitrate-N mixing of different N source areas within the catchment. These findings suggest that recent changes of temperature and precipitation unlikely change considerably nitrate-N dynamics in terms of yearly load, but significantly reduce nitrate-N concentrations during low-flow periods in summer.  

How to cite: Jomaa, S., Wachholz, A., Yang, X., Borchardt, D., and Rode, M.: Recent nitrate transport response to extreme weather conditions in the Bode lower-mountain range catchment, central Germany , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8400, https://doi.org/10.5194/egusphere-egu2020-8400, 2020.

Climate change is likely to threaten the consistent provision of clean drinking water in the UK, in terms of both water quantity and quality. Water quality could be especially problematic due to projected increases in extreme weather events such as droughts and flooding, both of which have a deleterious impact on water quality.

This study uses the Soil and Water Assessment Tool (SWAT) with UK Climate Projections (UKCP) 2018 data to model the impacts of a worst-case global emissions scenario (RCP8.5), on water quality for five catchments in Wales, UK. Our five study catchments (Clwyd, Conwy, Dyfi, Teifi, and Tywi) cover approximately 21% of the total area of Wales and are an important source of water supply for the North, West, and South-West Wales regions. We use an ensemble of 12 regionally downscaled Global Climate Models as inputs to account for uncertainty in the projections and temporal snapshots are taken for the 2020-39, 2040-59 and 2060-78 periods. We focus on the concentrations of four specific water quality variables: nitrogen (N), phosphorous (P), suspended sediment (SS), and dissolved oxygen (DO).

At all five catchments, SWAT is calibrated using river flow data only, due to the lack of water quality measurements. SWAT parameters related to water quality are kept at their default values. While this approach increases the uncertainty related to the specific values of water quality variables, it does provide the relative changes in specific water quality variables under future climate conditions. Results show that changing river flow patterns, both long term averages and extreme events, have a large impact on water quality. Concentrations of all four water quality variables show clear correlations with river flow. The largest changes in seasonal water quality are generally observed in spring and autumn, especially for P and N concentrations. Sediment concentrations and DO levels have an inverse relationship, with SS levels increasing with increased river flow and DO levels decreasing.

Results of this study are useful for water resource management and planning, especially in terms of the potential adaptation measures required to cope with the additional treatment required at water treatment works. By taking twenty-year snapshots our study also allows for short, medium and long term solutions to be planned.

How to cite: Dallison, R. and Patil, S.: Model based climate change impact assessment of river water quality in Wales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9335, https://doi.org/10.5194/egusphere-egu2020-9335, 2020.

For the quantitative assessment of the circulation of fluxes, the differentiation between point, quasi-stationary sources and diffuse, non-stationary sources play a significant role. The firsts include municipal and industrial wastewater discharges. The flow of substances from diffuse sources depends substantially on the landscape characteristics of the basin, water runoff, etc. In contrast to point sources, which always have an anthropogenic origin, the diffuse flow is associated with both natural processes and the influence of human activity.

The aim of this work was to estimate the diffuse flow within the Ukrainian part of the Severskyi Donets and Dniester basins. The focus was on evaluating the nutrients emission, among which nitrogen and phosphorus compounds were considered.

To quantify nutrient emissions from point and diffuse sources the special conceptual approach was proposed. It was a simple method for the first assessment which didn’t require detailed initial information and was based on the catchment characteristics, export coefficients and statistical data.

The Dniester basin is located in Eastern Europe and flows through Ukraine and Moldova into the Black Sea. According to the natural conditions it’s divided into 3 separate parts: Upper Carpathian, Middle Podil and Lower Dniester.

The main nitrogen pollution in the Dniester basin is caused by diffuse sources of agricultural origin. Their share in Podil Upland (about 80%) and Low part (about 90%) significantly exceeds the corresponding values in the Upper Dniester of 60%. This is due to the fact of occupying by forests about 30% of the slopes of this mountain part.

About 30% of the total phosphorus emission is formed within the Upper Carpathian part.  Municipal discharged and agricultural territories approximately equally determined this load. On the contrary within the plain territory the role of agriculture was dominant and increased from the middle to the lower part of the Dniester river - from 55 to 75%.

The Siversky Donets basin is located on the southwestern slope of the Central Russian Upland within forest-steppe and steppe zones. One of the features of this basin is the extremely high level of cultivation resulting significantly water pollution. More than 78% of the territory is covered by agricultural lands, what is much large compare to many European countries, where it does not exceed 35%. This is due to the dominance within the Siverskyi Donets basin of the most fertile chernozem soils. Disruption of the soil cover due to plowing led to significant nutrient losses due to deflation and water runoff.

More than 80% nitrogen emission are strongly affected by arable lands. The rest of the factors have a negligible impact. Compare to nitrogen the dominant part of phosphorus load comes to rivers as solid particles due to erosion processes - 56% and 36% - due to agriculture.

How to cite: Ukhan, O., Luzovitska, Y., Osadcha, N., and Osadchyi, V.: Nutrient Losses to the Siverskyi Donets and Dniestr River Basins (Ukraine), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10587, https://doi.org/10.5194/egusphere-egu2020-10587, 2020.

Reducing nitrogen (N) levels in European water bodies is a pressing issue, as evidenced by the recent fines imposed by the European Count Justice on countries such as France, Germany and Greece for exceeding the regulatory limits for nitrate (World Bank report on “Quality Unknown: The Invisible Water Crisis” by Damania et al., 2019). N levels can depend not only on current N inputs to the landscape, but also on the past N inputs that have accumulated through time in the soil root zone and the groundwater in so-called ‘legacy stores’. Effective N management strategies should therefore account for these N legacies.

This study aims to gain a better understanding of the impact of N legacies on in-stream nitrate concentration and loading at annual time scale in European catchments. To this end, we apply a parsimonious nitrate model, called ELEMENT (Van Meter et al., 2017, Global Biogeochem Cycles), given the limited amount of information available to constrain and test the model simulations. We construct a nitrogen input dataset (N-surplus) to force the model from the early 19^th Century, thus ensuring the build-up of the model soil and groundwater legacy stores. We estimate the model parameters based on the application of ‘soft rules’, to account for the uncertainty in the model inputs and the output measurements, and we examine the model controlling processes using sensitivity analysis.

We present here the results for the case of the Weser catchment, a large catchment in northern Germany that discharges into the North Sea. In particular, our results show that the model reproduces well nitrate stream loading. Despite the parsimonious structure of the ELEMENT model, we identify the presence of parameter equifinality, when the model is constrained using in-stream concentration and loading only. We discuss the possibility of using additional information (such as soil organic N content) to improve parameter identifiability and the overall simulation results.

How to cite: Sarrazin, F., Kumar, R., Van Meter, K., Weber, M., Musolff, A., Basu, N., and Attinger, S.: Towards understanding nitrogen legacies in European catchments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11202, https://doi.org/10.5194/egusphere-egu2020-11202, 2020.

Chemical elements transported to the streams may originate from anthropogenic activities including agriculture through the supply of fertilizers and agrochemicals or from natural sources, as the result of weathering and leaching in the soil profile. The amount of nutrients that is transported from the soil to the rivers varies according to the characteristics of the rainfall events in the different seasons of the year. The aim of this study was to evaluate the characteristics of the rainfall event that may explain the transport of N-P-K nutrients. The study site is located in Arvorezinha catchment (1.23 km²) in southern Brazil. The land use comprises forests (36.5%), tobacco (19.6%), soybean (18.7%), pasture (12.8%), yerba mate (4.9%), corn (4.7%) and others (7.9%). The soil management of cropfields is characterized by conservationist tillage (no-till system) (59%) and or conventional tillage (41%) system. The rainfall is measured by rain gauges and discharge by pressure sensor installed in a Parshall flume. Samples were taken during seven rainfall-runoff events occurred along 2018 (winter, spring and summer 2018/2019) and the elements analysed were total N and dissolved P and K. Water + sediment samples were collected during rising, peak and falling limb of the hydrograph. In the laboratory, they were filtered through a 0.45 µm filter to separate the dissolved fraction. The concentrations of N, P and K were determined by the methods proposed by Kjeldahl (1883), Murphy and Riley (1962) and Tedesco et al. (1995), respectively. A simple regression analysis between the maximum N-P-K concentrations with the maximum discharge (Q_peak), precipitation depth (PPT) and maximum intensity in 30 min (I₃₀) was performed. In addition, total nutrients (kg) was calculated. The PPT varies from 21 to 103 mm triggered discharges between 55 to 3,366 L s^-1. The total losses of N, P and K varied from 1.7 to 195; 0.02 to 2.34; and 7.2 to 399 kg, respectively. The losses were more significant in the event of 11/23/2018, which presented Q_peak= 905 L s^-1 with an average rainfall intensity of 5.3 mm h^-1 and PPT of 91 mm. The regression analysis showed that PPT does not explain the variations of N, P and K concentration, where the highest R² was 0.05 for P. Although, I₃₀ was able to explain 75% of the total N variation between the events. Q_peak was the hydrological variable which best explained the variations of N, P and K concentrations, i.e., R² = 0.43, 0.50 and 0.71 for P, K and N, respectively. In 2018 there was a significant change in land use in the catchment. Many areas with Eucalyptus plantation were replaced by soybean and tobacco cultivated using inverting tillage system. These changes may have affected the large losses of these elements, mainly N (594 kg) and K (1220 kg), since P (7.1 kg) is preferably transported in particulate form. Thus, even evaluating a small number of events it is possible to verify the impact of these losses on agricultural production, in addition to the environmental impact they may cause in aquatic environments.

How to cite: Barros, C. A. P., Minella, J. P. G., Ramon, R., Schlesner, A. A., Levandoski, A. P., Koefender, D. E., and Tiecher, T.: Dissolved N-P-K losses and their relation to the magnitude of rainfall event in a rural catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11892, https://doi.org/10.5194/egusphere-egu2020-11892, 2020.

Recognizing intra- and inter-daily dynamics of Chlorophyll a (Chl-a) and its related environmental variables in consecutive days play an important role in assessing and managing water quality and eutrophication. In this study, the water temperature, nutrients, Chl-a concentration  and meteorological factors were collected at six sampling times in Guanting reservoir during summer. Chl-a concentration generally decreased from last May to primary September. At both test times, thermal stratification and mixing in the water column controlled the variation of maximum Chl-a concentration layer at both temporal and vertical scale. The position of the maximum Chl-a concentration layer between days generally followed the same dynamics as thermocline. Daily stratifications were temporary and maximum Chl-a concentration layer varies downwelling by wind driven; hence, the vertical distribution of Chl-a concentration was homogenized at night. Surface Chl-a concentration decreased during the day and increased at night, except on rainy days. The results of Person correlations and principal component analysis indicated that raw surface and daily average Chl-a concentration generally changed as a negative function of solar radiation, wind speed, water temperature and air temperature. However, when a five hour time lag is considered, the relationship between surface Chl-a concentration, water temperature and all meteorological factors became significantly positive.

How to cite: Weiwei, J. and Jingshan, Y.: Within-day and between-day chlorophyll a dynamics during summer in Guanting Reservoir, Beijing, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12473, https://doi.org/10.5194/egusphere-egu2020-12473, 2020.

Baiyangdian Lake is the largest freshwater lake in the North China Plain. In order to examine the driving mechanisms of changes on the lake’s water quality, an improved Water Quality Index (WQI) method and multivariate statistical techniques were applied to analyze water quality in this study. Water quality data from six monitoring stations for the period of 2006 to 2016 were used. The calculation of the annual WQI indicated an improvement in lake’s water quality over the past decade. Cluster analysis classified 12 months and the six monitoring stations into two clusters (dry-wet period and western-eastern part), respectively. Discriminant analysis provided fewer effective variable with only two parameters and six parameters to afford 96.0% and 93.8% correct assignations in the temporal and spatial clusters. Principal component analysis and factor analysis detected similar varifactors in the two temporal clusters, interpreting more variance related human activities in the water quality variation than the ones representing natural factors. The different varifactors related to pollution source were evaluated in the two spatial clusters. The result indicated water quality in the two regions are influenced by different types of anthropogenic activities. Our findings provide valuable information for decision-making related to pollution control, ecosystem restoration, and water resource management in Baiyangdian Lake, as well as other large, shallow lakes in high-intensity hu+man activities regions.

How to cite: Quan, H., Wenchao, S., and Zhanjie, L.: Spatial-temporal variation assessment of the water quality in the Baiyangdian Lake of North China for the period of 2006 to 2016, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12499, https://doi.org/10.5194/egusphere-egu2020-12499, 2020.

Lake Ecosystem is a key component of biosphere that supports aquatic life and provide sink to the untreated effluent (domestic, industrial, and agricultural). Due to rapid industrialisation and changing climate, 30-40% of the lakes in the world are now eutrophic. The basic cause of eutrophication is the addition of nutrients (nitrogen and phosphate) into the lake system. Phosphate has been observed to be the limiting nutrient in 80% of the lakes and reservoirs in the world. Unlike other elements, phosphate does not escape from the system but changes from one form to the other depending upon the prevailing physico-chemical conditions. Chemical parameters like pH and redox potential are the major governing factors for phosphate fluxes. Sediments in the benthic zone serves as a sink as well as the source of phosphate for the photic zone. In the present study, a relationship between the physico-chemical properties of water and the fractions of phosphate in the sediments were studied. The study was conducted during three different seasons i.e. post-monsoon, winter, and summer to observe the seasonal variation. The pH, DO, ORP, and available phosphate in the water varied from 8.5, 14.7 mg/l, 39 mV, and 5.8 mg/l, 8.4, 3.5 mg/l, -64 mV, and 8.7 mg/l, and 7.8, 7.3 mg/l, 119 mV, and 10.5 mg/l during post-monsoon, winter, and summer, respectively. Phosphate in sediments was fractionated using SMT protocol. It was categorised under inorganic and organic phosphate classes, and the inorganic phosphate was further categorised as Non apatite inorganic phosphate (NAIP: Fe/Al bound) and Apatite inorganic phosphate (AIP: Ca bound).  The inorganic phosphate in the sediments was observed to be more than organic phosphate during post monsoon and summer, and at the same time the available phosphate in the overlying water was found low in concentration. The growth of phytoplankton is constrained by decreasing bio available phosphate in water. Concentration of NAIP was observed to vary with redox potential and concentration of AIP with pH. The study justified the hypothesis of direct relationship of sediment chemistry with bio availability of phosphate in water. Winter was found to be the extreme weather for phosphate fluxes. The findings point towards need of proper management such as chemical precipitation, sediment dredging etc. during this extreme weather conditions.

How to cite: Singh, P., Haritash, A. K., and Joshi, H.: Phosphate dynamics in a sub-tropical lake ecosystem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12727, https://doi.org/10.5194/egusphere-egu2020-12727, 2020.

Hillslope, groundwater, near- and in-stream interactions are key processes to understand in order to reduce the impact of agriculture on natural ecosystem. Indeed, hydrologic connectivity controls the fate of the nutrients within a catchment. The dynamics of nutrients (Nitrates NO₃ and Phosphates PO₄) and dissolved organic carbon (DOC) at the outlet are the product of past agricultural practices and local climate conditions. DOC, NO₃ and PO₄ are usually studied and modelled separately and originate from wetlands, groundwater and surface flows respectively. The simultaneous modelling of these elements is an opportunity to better understand the hydrologic connectivity because of their specific spatial origin, reactivity and mobilization processes. We developed a parsimonious rainfall-runoff model coupled with solutes reactivity and transport module in an agricultural research catchment (Kervidy-Naizin, 5km²). We used a three boxes lumped model (soil, groundwater and wetland) and StorAge-Selection function (SAS-function), agricultural surplus and daily climatic variables (precipitations, temperature, evapotranspiration) in order to simulate the daily discharge and stream concentrations at the outlet. Model tests confirmed that adding constraints such as solutes concentrations to a hydrological model helped to avoid unlikely sets of parameters. Simulations also showed that air temperature and agricultural practices are the major drivers of the supply of elements available within the catchment by controlling their biogeochemical reactivity; and that water table levels and precipitations are the major drivers of the variability of the concentrations in the stream by controlling the hydrological connectivity and the mixing between sources areas.

How to cite: Strohmenger, L., Hrachowitz, M., Fovet, O., and Gascuel-Odoux, C.: Coupled modelling of daily stream concentrations of carbon, nitrogen and phosphorus in a small agricultural watershed, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15233, https://doi.org/10.5194/egusphere-egu2020-15233, 2020.

Dissolved organic carbon (DOC) serves as one of the major energy sources in aquatic ecosystems, which is an important pathway connecting terrestrial and marine carbon reservoirs. DOC transport at catchment scale is recognized as being regulated by runoff, slope, soil organic carbon (SOC), biome, and wetland proportion; however, the controls in subtropical small mountainous rivers (SMRs) is rarely discovered before. This study investigated DOC export in 19 catchments in northern Taiwan supplemented with landscape and land use dataset to characterize the controlling factors of DOC transport. Meanwhile, the principle component analysis (PCA) and redundancy analysis (RDA) are applied to untangle the dependence of the controlling factors. Results showed that DOC concentration in Taiwan is very low at approx. 0.8 mg L^-1, yet the annual DOC yields of the 19 catchments is around 25.23 kg ha^-1 yr^-1, which is much higher than the global mean (14.4–19.3 kg-C ha^-1 yr^-1). PCA and RDA shows that the human activities and landscape can explain 87% and 77% of the explained variance, yet runoff play an independent role in DOC transport.  Excluding the overlap, human activities and landscape only accounts for 15 % and 5% of the explained variance, respectively. The overlap between the two components are as high as 72%, indicating the two components could not be separated subjectively. Conclusively, DOC export is mostly dominated by human activities and landscape together, which suggests that they should be considered simultaneously. Besides, DOC yield is positively correlated with streamflow and SOC, but negatively correlated with slope gradient. Our study suggests that interpretation of spatial variation in DOC export should address the overlap between human activities and landscape, which can help predicting the ungauged catchments in catchment management.

How to cite: Liu, E.-R., Shih, Y.-T., and Lee, L.-C.: Clarify the dependency of controlling factors in DOC transport in small mountainous rivers by redundancy analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19530, https://doi.org/10.5194/egusphere-egu2020-19530, 2020.

The Danube is Europe`s second longest river, stretching from Germany to the Black Sea. Water quality in the Danube River Basin is regularly monitored by the national authorities of all riparian countries and in addition for specific water quality data during the Joint Danube Surveys (JSD), which is organised by the International Commission for the Protection of the Danube River every 6 years.

This study presents the results of water stable isotopes and stable isotopes (¹⁵N and ¹⁸O) of nitrate as well as major ion analysis from 3 JDS (2001, 2007, 2019). Results indicate that water stable isotopes allow to trace differences in the amount of snowmelt contribution to the Danube and hence the dilution effects of pollutants e.g. nitrate. The oxygen and nitrogen isotope compositions of nitrate are clearly indicating that nitrate in the Danube main stream mainly derives from waste water effluents, which input is increasing along the stream. This can furthermore be confirmed by results of micropollutant studies that demonstrate an increase of widely consumed pharmaceuticals (carbamazepine, diclofenac and caffeine) at different sections of the Danube River affected by tributary inflows and discharge from urban settlements.

In summary, this study is an example of combining isotope techniques, hydrological methods but also emerging compounds in order to approach the fate of anthropogenically derived nitrate within the Danube Basin. The results of this study aim to support the 2021 update of the Danube River Basin Management Plan as well as water monitoring practices across the Danube countries.

How to cite: Halder, J., Vystavna, Y., Douence, C., Resch, C., Gruber, R., Heiling, M., and Wassenaar, L. I.: Identification of nitrate sources, hot spots, and dilution in the Danube River Basin using a multitracer approach , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20266, https://doi.org/10.5194/egusphere-egu2020-20266, 2020.

Little is known about the chemical and biological effects of tidal flooding on adjacent aquatic environments. Terrestrial systems accumulate various types of organic and inorganic matter that can be dissolved or carried into adjacent water bodies as floodwaters recede. In the northeast coast of the United States, the incidence and duration of coastal flooding has increased due to the high relative rates of sea level rise in the region.  Much of this flooding is tidal, occurring in the absence of rainfall during spring tides and/or when wind-induced Ekman transport is onshore.  While there are estimates of stormwater inputs into coastal systems, material (e.g., sediment, nutrients and contaminating bacteria) transported into the water bodies as tidal floodwaters recede have not been measured. Here, we will report estimates of nutrient loads transported in receding floodwaters during tidal flooding associated with perigean spring tides in 2017, 2018, and 2019. During each of the three years, at the highest point of the tide trained, citizen scientists were deployed to areas known to routinely flood in the Lafayette River watershed, a sub-tributary of the lower Chesapeake Bay, located in Norfolk, Virginia (USA). More than 100 samples were collected during each year as the flood waters retreated. Particulate carbon and nitrogen, total dissolved nitrogen, ammonium, nitrite, nitrate, urea, and phosphate were analyzed using standard colorimetric methods. Additionally, samples were analyzed for Enterococcus abundance each year. Results suggest that dissolved inorganic nitrogen loading during a single tidal flooding event exceeds the total annual load allocated for runoff in this sub-estuary.  Because tidal flooding is projected to increase in the future as sea level continues to rise, further research should proceed to better constraint the amounts and characteristics of loadings associated to tidal flooding events. Furthermore, these results suggest that managers should consider nutrient inputs via coastal flooding when setting restoration goals and targets.

How to cite: Macias-Tapia, A., Mulholland, M., Loftis, D., Selden, C., and Bernhardt, P.: Water quality impacts from tidal flooding in the northeast coast of the U.S., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-71, https://doi.org/10.5194/egusphere-egu2020-71, 2020.

Coastal waters around Hong Kong are affected by persistent and increasing eutrophication which to a certain extent is caused by the ecosystem’s responses to the nutrient discharge from the Pear River basin in South China. Large agricultural lands and high density of population contribute to both non-point source and point source pollution over the whole basin. It is important to identify dominant factors of water pollution in different watersheds and the major nutrient outputs to the estuary. In this study, SWAT (Soil and Water Assessment Tool) is selected to simulate the terrestrial processes in the Pearl River basin. Both point source (PS) and non-point source (NPS) pollution are considered and various forms of nitrogen (N) and phosphorus (P) are selected as pollution loads. The study would help to assess the primary source and type of water pollution in different watersheds and contribute to provide suggestions for local land use management and trends of eutrophication in the Pearl River estuary.

How to cite: Feng, X.: Influences of point source and non-point source pollution of the Pearl River Basin on the Pearl River Estuary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4430, https://doi.org/10.5194/egusphere-egu2020-4430, 2020.

Nutrient excess in rivers leads to ecosystem harm and can induce detrimental algae growths in coastal areas. In Germany and Europe, the management of riverine systems is complicated by the lack of understanding of nutrient pathways and effectiveness of retention processes from application to export. In this work, we hypothesize that in-stream nitrate uptake effects are linked to the shape or ‘bending’ of the concentration discharge (C-Q) relationship. Therefore, the analysis of observational C-Q data may give insight into the dominant controls of the magnitude of in-stream nitrate uptake across different catchment. To explore the concentration discharge (C-Q) behavior in a range of hydrological and biogeochemical conditions, we developed a catchment wide parsimonious (7 parameter) network model framework (spatially explicit at 1x1km²). Here, land-to-stream nutrient transfer was modelled as a power law (C=aQ^b), resulting in different nutrient loading according to the contributing area of each grid cell in the network and in-stream load uptake follows Li = Lin*e^-v_f*w*L/Q, with v_f the uptake rate, w and L the width and length of the river section. This approach acknowledges both, spatial variability between river sections (e.g. residence time distributions) as well as at-a-station temporal variability depending on Q. Ten existing stream networks in Germany were evaluated with this model framework in a ‘Monte Carlo approach’ for about 1000 predefined parameter combinations and 10 years of discharge data. First results show total nitrate uptakes ranging from almost 0 to 15% and high bending of C-Q curves correlated to high uptake rates. Furthermore, it was found that mean in-stream residence times, more than land-to-stream loading concentrations influence exported nutrient concentrations. The final result of our analysis will allow us to argue if the observed C-Q bending can be indeed related to instream uptake and not to other processes (e.g. denitrification along the subsurface flow path) and to derive the dominant processes shaping the uptake (such as light availability, instream travel time, nutrient stoichiometry, and impact of fine sediments).

How to cite: Dehaspe, J. and Musolff, A.: Modelling of in-stream nutrient uptake beyond the river reach scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13440, https://doi.org/10.5194/egusphere-egu2020-13440, 2020.

With the implementation of relevant policies on pollution control, the water environment of the Yellow River basin has been improved during recent years. However, for the river basin management agency, there remains an urgent need for gaining better knowledge of the changing patterns of water quality throughout the basin in order to get early warnings of water quality deterioration and make decisions on water allocation schemes. In this study, we collected water quality data including 24 routine monitoring parameters during 2014-2019 from over 100 monitoring stations located along the Yellow River. After assessing the water quality grade for each section according to the Environmental Quality Standards for Surface Water in China, we identified the key parameters that affect the water quality condition of the basin. The spatial and temporal variations of the key water quality parameters, in particular the relationships with driving factors which include natural factors (i.e., precipitation, temperature and evaporation) as well as anthropogenic factors (i.e., land cover and land use, pollution emission, population and social economy), were presented by conducting correlation analysis. Furthermore, based on the characteristics of the water quality time series and the significances of the driving factors to water quality, we built several data-driven models to predict the water quality condition at a monthly scale for the Yellow River basin, such as seasonal autoregressive model (SAR), multivariate linear regression (MLR) and artificial neural network (ANN), while the performances of those models were evaluated. This study provides critical information for understanding the response relationship between water quality and its related factors for a typical river basin, thus facilitating the dynamic assessment of water resources.

How to cite: Si, Y., Peng, W., Dong, F., and Du, X.: Spatial-temporal variation analysis and prediction of water quality in the Yellow River basin, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21393, https://doi.org/10.5194/egusphere-egu2020-21393, 2020.

Semi-distributed hydrological models are broadly used for estimating nonpoint source pollutant inputs to receiving waterbodies and their source areas and predicting the effects of climate and land-use change on water quality. However, satisfactory assessment of such models is required to test their ability to represent different physiographical characteristics of subjected catchments for future predictions. This spatially-distributed internal model validation is rare. To cover this aspect, the semi-distributed model HYPE (Hydrological Predictions for the Environment) was used to simulate nitrate-N (NO₃-N) and total phosphorus (TP) concentrations for spatially distributed non-calibrated internal gauging stations. First, HYPE model was applied at a mesoscale nested catchment Selke (463 km²) in central Germany to simulate discharge, NO₃-N and TP concentrations at three gauging stations in main river, which represent the whole geographical features of the catchment from upstream forest-dominant to downstream agricultural-dominant land use. An automatic calibration procedure and uncertainty analysis using the DiffeRential Evolution Adaptive Metropolis (DREAM) tool and a multi-site and multi-objective calibration approach was conducted. Second, the model performance was evaluated using additional internal stations not used for model calibration.

Results showed that HYPE could represent reasonably well discharge for both calibration (1994-1998) and validation (1999-2014) periods with lowest Nash-Sutcliffe Efficiency (NSE) of 0.75 and percentage bias (PBIAS) of less than 18% with lower predictive uncertainty. There is a decreasing behavior in model performance during the validation period compared to the calibration period, which can be explained by the reduction of precipitation stations. Model performance declined substantially when only the outlet gauging station, representing the mixed land use of the study catchment, was used instead of multisite calibration. Well representation of NO₃-N and TP load dynamics were resulted by the model showing a highest PBIAS of -16% and -20% for NO₃-N and TP loads simulations, respectively. Results confirmed that changing seasonal pattern of NO₃-N concentrations were controlled by combined effects of both hydrological and biogeochemical processes. TP concentration simulations were strongly impacted by the availability of accurate point source data. Results, also, showed the capability of HYPE to simulate spatio-temporal dynamics of NO₃-N and TP concentrations at eight internal[MRr1] [SGg2]  validation stations with PBIAS values varies in the range of -9% to 14% and -25% to 34% for NO₃-N and TP concentrations, respectively. Overall results suggested that combination of multi-site and multi-objective calibration using key archetypes gauging stations can strongly support spatio-temporal performance of the semi-distributed HYPE model.

Keywords: HYPE model, Nitrate-N, Phosphorus, Internal validation, Uncertainty analysis, multi-site and multi-objective calibration and archetype gauging stations.

How to cite: Ghaffar, S., Jomaa, S., and Rode, M.: Spatial capability of the catchment model HYPE to simulate nitrate and phosphorus concentration in the mixed land use Selke catchment, Germany , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7968, https://doi.org/10.5194/egusphere-egu2020-7968, 2020.

The Impacts of Water Quality Changes on Aquatic Ecosystems: A Case Study of Clariano River, Spain

Hamed Vagheei¹, Paolo Vezza², Guillermo Palau-Salvador³, Fulvio Boano⁴

1. PhD Student, the Polytechnic University of Turin, hamed.vagheei@polito.it
2. Assistant professor, the Polytechnic University of Turin, paolo.vezza@polito.it
3. Associate Professor, the Polytechnic University of Valencia, guipasal@agf.upv.es
4. Associate Professor, the Polytechnic University of Turin, fulvio.boano@polito.it

Abstract

Water quality degradation resulting from different anthropogenic activities such as agriculture, deforestation and urbanization is a serious worldwide challenge which have negative impacts on aquatic ecology. Unfortunately, it is still difficult to quantitatively determine the impacts of water quality changes on aquatic communities. The objective of the present research activity is to investigate aquatic ecosystem responses to water quality deterioration using a case study of Clariano River, Spain. The Clariano River faces low water quality and the loss of biodiversity in some parts as a result of agricultural, industrial and livestock activities as well as wastewater treatment plants (WWTP) effluents entering the river. The Soil and Water Assessment Tool (SWAT), an eco-hydrological model, is used in the present study for the modelling of discharge, sediment and nutrients. SWAT-CUP is also used to calibrate and validate the SWAT model. We are currently employing the results from the calibrated model to obtain a better understanding of possible relations between water quality and biodiversity. In fact, the present study will focus on macroinvertebrates as biological indicators of stream health, and the model predictions will be coupled with empirical correlations between stream water quality and macroinvertebrates presence in order to assess the impacts of water quality changes on aquatic ecosystem. In addition, different model scenarios will be compared to explore the potential impacts of changes in land use, climate and WWTPs operation on the aquatic ecosystem.

Keywords: aquatic ecosystem, Clariano River, eco-hydrological modelling, water quality, water resources management

How to cite: Vagheei, H., Vezza, P., Palau-Salvador, G., and Boano, F.: The Impacts of Water Quality Changes on Aquatic Ecosystems: A Case Study of Clariano River, Spain , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8585, https://doi.org/10.5194/egusphere-egu2020-8585, 2020.

Groundwater connects the agricultural fields in a catchment with the drainage network and it therefore plays an important role in the pollution of surface waters. To study this transport mechanism, we derived dynamic groundwater travel time distributions from a distributed, transient 3D groundwater flow model using forward particle tracking. We then calculated in-stream concentrations by coupling the travel time distributions with input time-series of tritium and the agricultural tracers chloride and nitrate, representing the water quality of the groundwater recharge throughout the catchment. We tested this approach for a lowland stream in the Netherlands and found that the variable contribution of different groundwater flow paths to stream water quality reasonably explained most of the long-term and seasonal variation in the measured stream nitrate concentrations. To study the observed lag in the breakthrough of agricultural solutes we performed a sensitivity analysis and found that the main contributors to such a time lag are the unsaturated zone, increased mean travel times and longer distances between agricultural fields and the drainage network. We found that the time between the application and effect of measures aimed to reduce in-stream concentrations depends on the combination of the input reduction rate and the mean travel time of the catchment. Furthermore, the location of agricultural fields in relation to the catchments’ drainage network was found to be an important factor that largely governs the travel times of the agricultural pollutants.

How to cite: Kaandorp, V., Broers, H. P., and de Louw, P.: Aged streams: Time lags of nitrate, chloride and tritium assessed by Dynamic Groundwater Flow Tracking, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8944, https://doi.org/10.5194/egusphere-egu2020-8944, 2020.

Microbial communities occur in almost every habitat. To evaluate the homeostasis disruption of in situ microbiomes, dredged sediments from Guanabara Bay-Brazil (GB) were mixed with sediments outside the bay (D) in three different proportions (25%, 50% and 75%) which we called GBD25, GBD50 and GBD75. Grain size, TOC and metals -as indicators of complex contamination-; dehydrogenase (DHA) and esterases enzymes (EST) – as indicators of microbial community availability, were determined. Microbial community composition was addressed by amplifying the 16S rRNA gene for DGGE analysis and sequencing using MiSeq platform (Illumina). We applied the Quality Ratio index (QR) to the GB, D and every GBD mixture to integrate geochemical parameters with our microbiome data. QR indicated high environmental risk for GB and every GBD mixture; and low risk for D. The community shifted from aerobic to anaerobic profile, consistent with the characteristics of GB. Sample D was dominated by JTB255 marine benthic group, related to low impacted areas. Milano-WF1B-44 was the most representative of GB, often found in anaerobic and sulfur enriched environments. In GBD, the denitrifying sulfur-oxidizing bacteria, Sulfurovum, was the most representative, typically found in suboxic or anoxic niches. The canonical correspondence analysis was able to explain 60% of the community composition variation and exhibit the decrease of environmental quality as the contamination increases. Physiological and taxonomic shifts of the microbial assemblage in sediments was inferred by QR, which was suitable to determinate sediment risk. The study produced sufficient information to improve dredging plan and management.

How to cite: Nascimento, J., Easson, C., Jurelevicius, D., Lopes, J., Bidone, E., and Sabadini-Santos, E.: Microbial community shift under exposure of dredged sediments from a tropical eutrophic bay, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11893, https://doi.org/10.5194/egusphere-egu2020-11893, 2020.

Pollutants from the agricultural field are the main cause of water pollution in reach. Especially, in heavy rainfall seasons, non-point source pollutants from agricultural land contaminate stream with nitrogen, phosphorus, and other pollutants. To reduce the components of the contaminations that outflow from the agricultural areas, Best Management Practices (BMPs) have been installed. Integrated factors including weather, geographic characteristics and kind of crops should be considered for choosing proper BMPs in each field. In the fields which have long slope-length, the vegetated ridge is one of the best methods and wildly used method to reduce soil loss. In this study, the Soil & Water Assessment Tool (SWAT) was used to assess the effects of the vegetated ridge on streamflow and sediment within non-point source pollutant management areas. The LS factor in the modified Universal Soil Loss Equation (MUSLE) in SWAT was modified in order to simulate sediment loss reduction by the vegetated ridge in the target fields. This study aims to assess sediment loss reduction by implication of the vegetated ridge using SWAT and to propose the importance of vegetated ridge for reducing non-point source pollutants in agricultural fields. For further research, the development of a vegitated ridge application tool for SWAT will be conducted.

How to cite: Hong, J., Lee, D., Kim, S., Kim, J., and Lim, K. J.: Assessment of Sediment Loss Reduction by Vegetated Ridge Using SWAT, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12878, https://doi.org/10.5194/egusphere-egu2020-12878, 2020.