The need for comprehensive assessments of agrochemicals use and its potential risk of environmental contamination are imperative, but studies currently exist only at regional and watershed scales. By coupling the recently developed PEST-CHEMGRIDS data product to the BRTSim (BioReactive Transport Simulator) computational framework, we conducted the first mechanistic assessment of the environmental hazard of glyphosate (GLP) use at global scales. PEST-CHEMGRIDS provides the annual application rate of 95 active ingredients, including GLP, on various dominant and aggregated crops (Maggi et al., 2019), and is used to feed the biogeochemical reaction network of GLP biogeochemistry embedded in BRTSim (la Cecilia et al., 2018). Deployment of BRTSim over a georeferenced global-scale grid allowed us to assess four key quantities that determine the level of environmental hazard, namely: (i) soil residue, (ii) biodegradation recalcitrance, (iii) leaching rate below the root zone, and (iv) persistence in the root zone. Our assessment (Maggi et al., 2020) shows that the total average residue in the root zone and leaching below root zone is important only in minor areas globally, but also show that biodegradation recalcitrance and persistence can lead to an environmental hazard in vast agricultural areas worldwide. The latter were largely related to the GLP transformation product, aminomethylphosphonic acid (AMPA), because of slow reaction kinetics, further inhibited by the presence of aqueous inorganic phosphate. With the four key quantities, we have mapped the aggregated hazard geographically to identify hotspots where GLP contamination may have to be assessed with greater level of detail. High hazard hotspots cover less than 1% of the agriculture area (inclusive of pastures) and are identified in north Europe, USA, Brazil, and China.

Maggi F., Tang F.H.M., la Cecilia D., McBratney A., (2019), Scientific Data 6(1), 1-20.

la Cecilia D., Tang F.H.M., Coleman N., Conoley C., Veervort R.W., and Maggi F., (2018), Water Research, 146, 37-54.

Maggi F., la Cecilia D., Tang F.H., & McBratney A., (2020). Science of the Total Environment, 717, 137167.

How to cite: Maggi, F., Tang, F., and la Cecilia, D.: Global-scale assessment of agrochemicals contamination — the case study of glyphosate , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4930, https://doi.org/10.5194/egusphere-egu21-4930, 2021.

Karst aquifers are an important water resource for a large part of the world’s population. Because of their natural susceptibility towards contamination, they have to be managed carefully. Human activities such as agriculture, roads or settlements in karst aquifer catchments often lead to the contamination of karstic springs. Due to their special geology, they are at risk of both, long- and short-term contamination. Long-term contamination is due to adsorption of anthropogenic substances in the overlaying soil, the epikarst or rock matrix whereas short-term contamination can be due to spills or precipitation events. Such precipitation events can lead to the mobilization of substances. These are then readily transported to karstic springs where pollutant peaks might be observed. However, current monitoring strategies are not suitable (infrequent, regular sampling intervals) to reveal such peaks. The goal of this study was in a first step, to investigate the contamination level of ten karstic springs (part of NAQUA Swiss National Groundwater Monitoring) in the Swiss Jura, screening for plant protection products (PPP) and transformation products (TP). This was achieved by a monitoring campaign that was conducted from March 2020 until October 2020. Two-week composite samples were collected in addition to the continuous acquisition of electrical conductivity and water level, i.e. spring discharge. Samples were then analyzed by large volume direct injection into a HPLC-HRMS/MS setup using a target list of 130 compounds (105 PPP’s, 25 TP’s).

Analysis of a first batch of samples of three springs did not reveal many compounds with elevated concentrations (33 detections in 15 samples above 100 ng/L of 3 compounds: chloridazone desphenyl, chloridazone methyl desphenyl, chlorothalonil TP R471811). No PPP’s were observed to be continuously leaching from the catchment and the aquifer in concentrations above 100 ng/L. The detected compounds above 100 ng/L were TP’s which indicates that their parent compounds might be adsorbed to the aquifer matrix or the soil cover, therefore leaching TP’s continuously or pulse like during rain events. In total, 19 compounds were detected above their quantification limits. Of those, 10 PPP’s and 9 TP’s were found. We further evaluated spring responses during rain events based on electrical conductivity and determined response times between 3 and 5.5 hours. Since two-week composite samples cannot reveal short-term concentration dynamics given the fast response times and dilution (both leading to low concentrations in composite samples), we will conduct a sampling campaign with a different strategy in 2021. Therein, in a second step, the goal is to study the pollutant dynamics induced by precipitation events with temporally highly resolved measurements. To achieve this we will install a transportable, liquid chromatography, high resolution mass spectrometer at three selected springs and conduct an automatic sampling and analysis with a high temporal resolution.

How to cite: Schorr, J., Jud, F., Beck, B., Longree, P., Singer, H., and Hollender, J.: Long-term monitoring of plant protection products and their transformation products at karstic springs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8016, https://doi.org/10.5194/egusphere-egu21-8016, 2021.

Modelling environmental concentrations of plant protection products at landscape-level is of growing interest for pesticide registration and product stewardship, including higher-tier studies in risk assessment, mitigation measures, monitoring support and decision making. However, landscape-level modelling is challenging due to uncertainties by modelling concepts and scaling as well as the extensive (geo)data demand for model parametrization and validation. This includes also limited information about application timing of pesticide products having strong impact on the model performance predicting pesticide concentrations in water bodies. Our work explores the impact of pesticide application timing using the eco-hydrological model SWAT+ (revised version of Soil and Water Assessment Tool) to explore uncertainty effects of application timing and the underlying mechanisms for the surface water exposure pattern in a small-scale catchment. Specific focus thereby was on method development to mimic realistic application timing considering plant stage, hydrology and weather conditions.

On this account, we setup a SWAT+ model of the Funne catchment (54.6 km²) in the North-West of Germany. The simulated daily streamflow was calibrated using publicly available gauge data (Selm-Ondrup) showing a very good hydrological performance of the model (NSE: 0.746). The impact of application timing was subsequently explored by different synthetic application scenarios for three pesticides with varying physio-chemical properties, in combination with static and rule-based timing options. First results taking runoff and drainage into account indicated that a simple forward oriented ruleset (i.e. using weather forecast) could significantly decrease pesticide loads at the catchment outlet on average by 16 to 46%. For individual years and substances, channel loads decreased by up to 92%, which could be attributed to the interaction of rainfall and wash-off timing as the main driver of concentration variation during runoff events. We will further explore the impact of drift entry and other processes (e.g. channel dissipation) as well as different application schemes.

These findings underpin the importance of realistic application timing in landscape-level simulations of pesticide concentration in surface water bodies. It is hence expected that landscape-level tools will play an important role in the future, e.g., for the development and operation of smart decision tools in agriculture.

How to cite: Fuchs, M., Gebler, S., and Lorke, A.: Modelling landscape-level pesticide concentrations with SWAT+ - an uncertainty assessment of application timing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8322, https://doi.org/10.5194/egusphere-egu21-8322, 2021.

Modern agriculture routinely uses Plant Protection Products (PPPs) to guarantee food security. However, PPPs can reach surface waters where they pose a threat to susceptible non-target organisms. Understanding the contamination sources and flowpaths is of utmost importance to design optimal pollution mitigation strategies. While highest concentration peaks typically occur during rainfalls following PPPs applications, a monitoring campaign in a small Swiss agricultural stream in 2019 detected several compounds in concentrations exceeding the precautionary limit of 100 ng/l by up to 14 times during a dry period. The further exploration of the time series revealed for the first time diel fluctuations of some PPPs. Such peculiar patterns excluded the occurrence of known contamination pathways including spray drift, wind erosion and dry deposition. Despite the availability of an unprecedented high-temporal resolution dataset, we were not able to disentangle the source-flowpath combination driving the observed peculiar dynamics.

Here we present the results of the follow-up 1-day field campaign aiming to close this knowledge gap. The campaign was carried out on the dry day of August 12^th 2020 and we collected water samples every 6 hours from the stream at 6 different locations and from 4 outlets of active tile drains.

The results revealed widespread contamination by the fungicide fluopyram; its transformation product fluopyram-benzamide followed identical dynamics but its concentration was 10 times lower than the parent compound. This result is in line with the high DT50 of fluopyram and its broad use in the catchment. The data showed that diel fluctuations were a reoccurring phenomenon; concentrations were higher in the early morning and lower in the early evening at the most downstream location. However, the fluctuating PPPs showed a concentration peak in the upstream location at midday. We were able to narrow down the contamination sources of napropamide, clothianidin, and oxadixyl; the first is a current herbicide, the second is an insecticide not reapproved since 2020, while the third is an old fungicide banned in Switzerland in 2005, which we measured at approximately 200 ng/l. Finally, the investigated tile drains delivered PPPs at lower concentrations compared to the levels measured in the surface water, with the exception of the herbicide metamitron, which was measured at nearly 20 ng/l only at the outlet of 1 tile drain.

The presented research suggested that contamination sources can be localized by means of grab samples collected along the stream. However, it was not conclusive on the flowpath delivering PPPs to the stream. We hypothesize that 2 processes may explain the reported patterns: (i) irrigation at the upstream locations in the early morning; (ii) intra-daily exchanges at the interface between surface water and contaminated shallow groundwater. We will complement the study with expert knowledge by local stakeholders, satellite-derived soil moisture indices, high-resolution land use data and regulatory information to establish a methodology to optimally identify critical source areas in dry periods, where mitigation strategies should be put in place.

How to cite: la Cecilia, D., Dax, A., Odermatt, D., Singer, H., and Stamm, C.: High-concentrations diel-fluctuations of Plants Protection Products in dry periods, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14188, https://doi.org/10.5194/egusphere-egu21-14188, 2021.

Biocides used as film protection products to prevent algae and fungi growth on facades wash off during rain events and represent a potential risk to the environment. So far, urban monitoring studies focused mainly on large heterogeneous urban areas. Thus, little information about individual sources and entry pathways were obtained. However, this is important to understand the potential risk of biocide entry to groundwater.

This study investigates biocide emissions from a 2 ha residential area, 13 years after construction has ended. Investigated substances represent commonly used biocides for film protection, i.e. Terbutryn, Diuron and Octylisothiazolinone (OIT) and some of their known transformation products (TPs, Diuron-Desmethyl, Terbumeton, 2-Hydroxy-Terbutylazin and Terbutryn-Desethyl). We used existing urban infrastructure for efficient monitoring and applied a three-step approach to (a) determine the overall relevance of biocides, (b) identify source areas and long-term emission and (c) characterize entry pathways into surface- and groundwater.

Initial sampling in the swale system gave an integrated signal from the entire district and confirmed the relevance of biocide leaching, more than a decade after construction. Concentrations peaked at 174 ng/L for Diuron and 40 ng/L for Terbutryn during a high magnitude event and were above PNEC values. During later events, transformation products were detected, though at lower concentrations. For all substances, source areas were identified in a second step. Artificial elution experiments confirmed expected sources, i.e. façades, but we also found additional sources through sampling of rainfall downpipes from flat roofs. A small part of the roof façade was repainted two years before sampling and thereby showed a magnitude higher leaching rates than the remaining façades. Since all biocide wash-off arrived on a flat roof and was drained by rainfall down pipes, we could estimate net biocide emission and arrived at 155 mg Diuron, 17 mg Terbutryn, 12 mg OIT and 17 mg Diuron-Desmethyl from a 10 m² painted façade area over a time period of two years. In a third step, we characterized entry pathways comparing samples from a drainage pipe that collected road runoff (surface pathway) with two others that collected infiltrated water on top of an underground garage (soil pathway). All drainage pipes showed Terbutryn, two of them also Diuron but none OIT. The drainage pipe representing the surface pathway showed a smaller number of individual transformation products but similar concentrations of parent compounds. One pipe representing the soil pathway had highest concentrations of Terbutryn and its TPs which suggests a high leaching potential of this biocide also away from concentrated infiltration in urban stormwater management infrastructure.

How to cite: Linke, F., Olsson, O., Preusser, F., Kümmerer, K., Schnarr, L., and Lange, J.: Sources and pathways of biocides and their transformation products in 2ha urban district, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5485, https://doi.org/10.5194/egusphere-egu21-5485, 2021.

Biocides are added in building materials like renders or paints on façades as protection against algae and fungi growth. With wind driven rainfall, biocides can leach from buildings and eventually contaminate urban groundwater. Studies on transfer, degradation kinetics, degradation mechanisms and persistence in the environment of urban biocides are rare. Traditional methods based on concentrations often reflect both dilution, due to non-destructive processes, and degradation involving bond-breaking of biocide molecules. Established since two decades for legacy point-source industrial contaminants, Compound-Specific Isotope Analysis (CSIA) is an emerging approach to evaluate magnitudes and mechanisms of non-point source micropollutant degradation in the environment, although it has not been applied yet to urban biocides. To use CSIA in field-based approaches, reference laboratory degradation experiments have to be conducted.

Here we carried out reference abiotic hydrolysis, photodegradation and biodegradation experiments for the urban biocide terbutryn to compare kinetics and evaluate the spectrum of stable isotope fractionation to interpret transformation pathways. Experimental setups for hydrolysis include pH = 1, pH = 13 and pH = 7. Photodegradation experiments were conducted under direct UV irradiation (λ = 254 nm) and under simulated sunlight. Simulated sunlight assays involved both direct and indirect photodegradation experiments. Biodegradation experiments were conducted in activated sewage sludge, soil and for the sediment-water interface of artificial wetland systems to evaluate various environmental compartments. We estimated degradation rates, followed-up the isotopic signatures based on carbon, nitrogen and sulphur stable isotopes and quantified the formation of transformation product using LC-MS. Reference degradation experiments for terbutryn showed that CSIA can be used as concentration-independent tool to identify the dominant degradation processes in the environment by combining (i) the isotopic enrichment of stable isotopes by dual isotope plots and (ii) the pattern of formed transformation products. For carbon, isotope fractionation values range from ɛ_C= -3.4 ± 0.3 ‰ for abiotic hydrolysis at pH=1 to an inverse isotope effect of ɛ_C= 0.8 ± 0.4 ‰ in direct photodegradation experiment under UV irradiation, which underscore the potential of terbutryn CSIA to differentiate degradation mechanisms. Biodegradation rates in soil and the sediment-water interface are rather low (t_1/2 > 200 days), indicating that terbutryn may not be easily biodegraded. Altogether, our study underscores that lab scale experiments are necessary to retrieve reference kinetics and mechanistic values to follow micropollutant degradation based on CSIA in the environment. It also emphasizes the applicability of CSIA for the urban biocide terbutryn. Reference isotope fractionation values can be used in the future to monitor transport and transformation of terbutryn at urban sites while supporting predictive model development for urban biocide export.

How to cite: Junginger, T., Payraudeau, S., Masbou, J., and Imfeld, G.: Transformation of the urban triazine type biocide terbutryn: insights from Compound-Specific Isotope Analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7865, https://doi.org/10.5194/egusphere-egu21-7865, 2021.

The Bienne river (Jura Mountain, France) drains a basin of medium altitude mountains characterized by extensive cattle breeding (mostly dairy cows). A monitoring of the contamination by veterinary pharmaceuticals was performed using passive sampling devices - POCIS (Polar Organic Chemical Integrative Samplers), between September 2019 and January 2020. Four hydrological conditions were analysed: a sever low-flow periods, two flood events and a winter situation close to the mean interannual flow. Each time, POCIS were exposed over 2 weeks at 2 stations located in the upper and downstream reaches of the river. 19 pharmaceuticals were selected from information given by local veterinarians and analysed by LC MS-MS: endo and ectoparasites treatments; antibiotics and non-steroidal anti-inflammatory drugs. The monitoring shows that most of these chemicals (12 substances) are quantified in all POCIS samples and the others show relatively high occurrences, between 25 and 88%. Average concentrations in water (calculated with the sampling rate i.e. considering the time of exposition of POCIS samplers in the river) are remarkably close between the 2 monitoring stations. Concentrations are high all over the studied period and reach a maximum during flood events. Thus, hazardous effects are expected on freshwater organisms, especially for macrocyclic lactones and pyrethroids and organophosphates pesticides. The antibiotics concentrations ranges can also disturb microbial communities existing in the river. Such results highlight an important impregnation by these pharmaceuticals at the catchment scale, involving diffuse sources as grasslands receiving contaminated cow dungs and manures. Veterinary compounds are strongly remobilized during rain episodes by run off and infiltration in soils. In the hydrogeological context of the Bienne basin, karstic flows emphasize the connectivity between grasslands and the river. Therefore, an important part of the contaminated leaching waters can rapidly reach the river via the soil drains and surface / subsurface flows. Rather than another part goes through less porosity pathways and delivers pollutants over a longer period. Wastewater discharges and sludges from rural and urban treatment plants can also contribute to this pollution for pharmaceuticals also used in human medications.

How to cite: Dhivert, E., Devillers, B., Al Badany, M., Mondamert, L., and Labanowski, J.: Monitoring of veterinary pharmaceuticals in the Bienne river (Jura Mountain, France), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-199, https://doi.org/10.5194/egusphere-egu21-199, 2020.

Arsenic (As) is a toxic element present in different natural systems. The aqueous As species and their concentrations in natural waters depend on a variety of parameters, including the presence of natural source and the local geochemical conditions. The primary source of As in natural waters is the oxidation of mineral sulphides like arsenopyrite (FeAsS) and As-rich pyrite (FeS₂) [1]. The trivalent iron (Fe³⁺) can act as oxidant for pyrite oxidative dissolution together with dissolved oxygen.In this work the attention is focused in As- contaminated area of the Calabria Region (Southern Italy). The high arsenic concentration is a peculiar characteristic of the shallow groundwaters circulating in a limited area of the Calabria region, which represents an unexplored mineralized area. Indeed, although pyrite is widely present in the crystalline rocks, its spatial distribution is highly variable and not predicable [2]. Generally, the As content of the studied granite rocks is within the normal global range but the presence of not-surfacing, hydrothermally-altered granites, could be the cause of As contamination in limited areas.  In order to explain the As-rich groundwaters occurring into crystalline aquifer, a reaction path modelling of granite dissolution was performed by using EQ3/6 software package version 8a.  The dissolving granite was considered to be constituted by quartz, two types of plagioclase (representing the rim and the core of the mineral), K-feldspar, biotite, muscovite, chlorite, epidote, fluorapatite and pyrite.  The considered value of pyrite content and its As concentration fall within the global estimations [3]. Two simulations were performed allowing the precipitation of moganite, gibbsite, kaolinite, illite-py and the calcite-rich solid solution of trigonal carbonate. Moreover, two oxy-hydroxide solid solutions composed of amorphous Fe(OH)₃ - amorphous ferric arsenate and 2 lines-ferrihydrite - scorodite were precipitated in two separate runs to evaluate their effects on dissolved As. Nine water samples were used to fix the boundary conditions as well as to validate the outcomes of geochemical modeling. The arsenic concentration detected ranging from 25 to 435 µg/L. The theoretical trend involving the precipitation of amorphous Fe(OH)₃ is in agreement with the groundwaters richest in As, because a higher amount of pyrite is dissolved due to a greater availability of trivalent Fe in the aqueous solution, which is caused by the higher solubility of amorphous Fe(OH)₃ compared to 2-line ferrihydrite. The analytical data of the As-rich groundwaters, as a whole, are well explained by the performed simulations, suggesting that these processes control the release and fate of arsenic during the water-rock interaction.

[1]. Sracek, O., Bhattacharya, P., Jacks, G., Gustafsson, J. P., & Von Brömssen, M. ,2004. Behavior of arsenic and geochemical modeling of arsenic enrichment in aqueous environments. Applied Geochemistry, 19(2), 169-180.

[2]. Bonardi G., De Vivo B., Giunta G., Lima A., Perrone V., Zuppetta A., 1982. Mineralizzazioni dell’Arco Calabro Peloritano.Ipotesi genetiche e quadro evolutivo. Boll.Soc.Geol.It. 101

[3]. Smedley, P. L., & Kinniburgh, D. G.,2002. A review of the source, behaviour and distribution of arsenic in natural waters. Applied geochemistry, 17(5), 517-568.

How to cite: Fuoco, I., De Rosa, R., and Apollaro, C.: Geochemical modelling of arsenic release into the crystalline aquifers: preliminary study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-712, https://doi.org/10.5194/egusphere-egu21-712, 2021.

Copper is an ubiquitous essential element but also toxic to aquatic organisms, Environmental Quality Standards being 1 µg.L^-1 for surface water (annual mean concentration). Rivers and estuaries are mainly concerned by copper accumulation in sediments and in organisms. Copper can originate from various manufactured products (antifouling painting, vineyards fungicides, brake linings….) and anthropic activities (industrial, landfills…). As a result, copper French median concentration in oysters is about 200 mg.kg^-1 DM (Ifremer, 2017).

Transportation, especially road transport, is the main French source of copper air emissions (92% of total emissions) (CITEPA, 2019). Then, urban areas, mainly impervious, constitute a major non-point source of copper from abrasion of brake pads and tires, and fuels. This contaminant is released from the road surfaces through stormwater runoff directly to water bodies or after collection in sustainable urban drainage systems (SUDS). As the epuration performance of SUDS for copper was shown to be low, this study is carried out to evaluate if copper mobility can be explained by its physical speciation. The distribution of copper among dissolved, colloidal and particulate fractions is studied by size fractionation, assuming that the mobility of copper is related to a high dissolved and colloidal occurrence.

The study site is a retention-infiltration basin collecting the runoff waters of the main bridge of Nantes (France; about 90 000 vehicles/day), and overflowing to the Loire river . Size fractionation by in series filtration and ultrafiltration was performed on stormwater runoff and surface waters sampled within the basin. Five fractions were analyzed for major and trace elements: ] ; 8µm ], ] 8µm ; 1,2µm ], ] 1,2µm ; 0,45µm ], ] 0,45µm ; 5kDa ] and ] 5kDa. Among these fractions ] ; 8µm ] correspond to particulate copper, ] 8µm ; 1,2µm ], ] 1,2µm ; 0,45µm ], ] 0,45µm ; 5kDa ] to colloidal copper and ] 5kDa ; [ to dissolved copper. Size fractionations were implemented for 8 samples with 2 replicates for each sample and over 1 year. 0.45 µm filtrations were also conducted as a reference.

The total copper concentration in runoff was around 100µg.L^-1, which is in the upper part of the concentrations observed in the area of Nantes in SUDS. The results of the size fractionation are as follows : 1) for the stormwater runoffs, particulate copper is about 70% of the total amount, colloidal copper is present for 20% and 10% of dissolved copper is measured. Thus 30 % of copper are mobile; 2) for the surface waters in the basin, the distribution of copper among the dissolved, colloidal and particulate fractions, is respectively 20 %, 70 % and 10 %.

We concluded that 1) the concentration of copper is 100 times higher the regulation value for natural environment, and 2) particulate fractions of copper are trapped at the entrance of the basin, and an high content of mobile copper (dissolved and colloidal fractions) is observed in the basin that could either be overflowed or infiltrated in the sub-soil of the basin.

How to cite: Dang, D. P. T., Béchet, B., and Jean-Soro, L.: Size fractionation highlights the mobility of copper from urban stormwater to river, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12165, https://doi.org/10.5194/egusphere-egu21-12165, 2021.

Extensive industrialization and urbanization have adversely affected the quality of consumable water on the earth. The industrial effluents are the major source of micropollutants such as heavy metals, which deteriorates the environment making it toxic to the flora and fauna sustaining in the water. Heavy metals such as lead, cobalt, arsenic, chromium, and mercury are toxic even in trace amounts, whereas presence of higher concentration of iron, cobalt and zinc could be detrimental. Bioaccumulation and hypertoxicity of these heavy metals mark them one of important micropollutants to be monitored. Most of these heavy metals are soft Lewis acid metals such as Ag⁺, Au⁺, Cd²⁺, Hg²⁺, Pb²⁺ are considered as thiophilic. In nature, proteins responsible for metabolizing and binding to heavy metals are rich in sulphur functionalized groups such as cysteine and glutathione. This work will address the various sulphur functionalized nanomaterials which are inspired by nature will enhance the monitoring and trapping of heavy metals in water environment.

How to cite: Dodla, A., Shukla, S., Adyel, T., and Saxena, S.: Sulphur functionalized nanomaterials for monitoring and trapping heavy metals in water environment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-116, https://doi.org/10.5194/egusphere-egu21-116, 2020.

Agroecological schemes are implemented worldwide in order to reduce water quality impairment from agricultural pesticide use. However, evaluating the success or failure of these schemes is challenging because other influencing factors can confound their effects. For instance, aquatic pesticide pollution has been found to vary greatly due to the interannual variability in weather conditions (e.g., the timing, intensity, and duration of precipitation events) and changes in pesticide application practices (e.g., changing pest pressure, phasing-out and replacement of specific products, development of pesticide resistance).

Our research investigates the necessary conditions to detect significant trends in pesticide concentrations in the context of the Swiss National Action Plan (NAP), which aims to halve aquatic pesticide pollution risk from agricultural pesticide use within Swiss river networks by 2027.

We base our analyses for temporal trends on a calibrated model for pesticide transport at the catchment scale, which we use to separate the long-term effects of the NAP from interannual variability due to weather conditions. Our results indicate that the interannual variability due to weather conditions can override the effects of even a 50% reduction in pesticide application for rain-driven input. This implies that the concentration levels themselves may be insufficient to demonstrate the effectiveness of the NAP within a reasonable time horizon of a decade. This is because the lowering of in-stream pesticide concentrations can be due to the timing and intensity of precipitation relative to the application of pesticides and not from the effectiveness of pesticide mitigation measures. Therefore, we have further explored potential methods to account for the weather effects on the pesticide concentration levels. Accounting for the weather conditions by considering the dependence of concentration levels on discharge conditions during the application period improves the statistical power to detect trends.

Furthermore, we assess the potential to extrapolate the trends observed at 23 monitoring sites from different catchments (varying in size 1 km² to > 20,000 km²) across Switzerland to the entire Swiss river network. As a first step, we analyzed substances applied to corn because this crop is widespread in the country, is easy to follow as herbicides are applied only once a year, and only a few pesticides are applied. The analysis revealed that for some of these corn herbicides, the seasonal patterns were consistent across many catchments and in agreement with the crop specific expectations. However, for other herbicides we identified regional patterns with unexpected concentration peaks in the fall. This observation requires more detailed inquiries in regional use patterns and highlights the need to account for regionalized pesticide use when extrapolating monitoring data to larger scales.

How to cite: Fabre, C., Chow, R., Scheidegger, R., Doppler, T., Dietzel, A., Fenicia, F., and Stamm, C.: Can mitigation schemes produce detectable long-term temporal trends and spatial patterns in aquatic pesticide pollution?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15263, https://doi.org/10.5194/egusphere-egu21-15263, 2021.

Surface runoff from agricultural fields is a major input pathway of pesticides into surface waters. The aim of this project was to i) analyze the effectiveness of various mitigation measures to reduce pesticide runoff and erosion inputs into surface waters, ii) assess the suitability of the measures found effective for use in the quantitative environmental exposure assessment for authorization of plant protection products (PPP), and iii) make recommendations how the potentially suitable measures could be applied in risk assessment of PPP in Germany.

Following a literature analysis, 16 risk mitigation measures were presented to five experts in the field. Measures finally selected for quantitative analysis belong to 3 groups: vegetative filter strips (VFS), soil conservation measures (including no-till) and microdams in row crops. VFS effectiveness was analysed with CART (Classification and Regression Trees) using the dataset compiled by Reichenberger et al. (2019). CART was performed for three target variables: i) relative reduction of total inflow by the VFS (ΔQ), ii) relative reduction of sediment load (ΔE), and relative reduction of pesticide load (ΔP). The main data sources for soil conservation measures were a plot database with annual runoff volumes and soil losses (Maetens et al., 2012), a literature review (Fawcett et al., 1994) and a field study with event-based data (Erlach, 2005), while for microdams the principal source were the data compiled by Sittig et al. (2020).

The following conclusions were drawn from the analysis:

VFS can be recommended for application in quantitative risk assessment.  However, infiltration and sedimentation should be simulated with a mechanistic model such as VFSMOD.

Due to the high variability of results and limited availability of high-quality data, effectiveness of mulch-till could not be quantified sufficiently well. It can therefore not be recommended for now as a regulatory mitigation measure.

Before recommending no-till as a regulatory mitigation measure for surface runoff and erosion, the question of potentially increased pesticide loss via leaching and drainage should be clarified.

Microdams in row crops can also be recommended as a regulatory mitigation measure, since they have shown to be effective and their effect can be modelled as a reduction of the runoff Curve Number. However, elaborating a CN table for e.g. the FOCUS scenarios would require an in-depth analysis of the available data.

How to cite: Klein, M., Reichenberger, S., Spycher, S., O'Connor, I., Thomas, K., Multsch, S., Sittig, S., Großmann, D., and Flade, J.: How can risk mitigation measures for surface runoff and erosion be included in the regulatory environmental risk assessment for pesticides in Germany?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2567, https://doi.org/10.5194/egusphere-egu21-2567, 2021.

Inclusion of quantitative mitigation of pesticides in regulatory environmental risk assessment (ERA) using common agricultural field conservation practices is a critical need recently identified by experts in North America and EU [1]. Currently, mitigation by vegetative filter strips (VFS) is available by coupling the event-based model VFSMOD in continuous simulations within current long-term higher-tier surface water ERA frameworks (EU FOCUS SWAN, US EPA PWC, PRMA Canada, California CDPR PREM, etc.). In this case, the field management and pesticide-laden surface runoff at the edge of the field is calculated by the model PRZM and VFSMOD routes it from the edge of field through a VFS of desired characteristics to estimate potential load reductions before entering the aquatic environment, simulated by the receiving water body model (FOCUS TOXSWA, EPA VVWM). While under proper settings VFS could effectively reduce pesticide concentrations in surface water below thresholds of concern- what happens to the residues trapped in the VFS? The current ERA VFS framework uses a highly risk-conservative assumption, whereby the pesticide trapped in the VFS undergoes degradation between storm events and the surface residue (soil mixing layer and adsorbed to trapped sediment) is remobilized in full and added to the incoming pesticide load in the next event in the series. While risk conservative, this initial approach is not consistent with the nonuniform pesticide redistribution and extraction with depth used in the model PRZM within current ERA, and it has also been found too conservative for highly sorbed compounds with high specific toxicity like pyrethroids and others. The objective of this study is to develop a complete VFSMOD component to quantify the fate of VFS pesticide residues between runoff events for use in long-term ERA simulations. This includes realistic assumptions of the fate of the residues, including non-linear pesticide redistribution in the soil, mass balance of the VFS soil mixing layer and sediment trapped, degradation between runoff events, and partial remobilization and carryover of the remaining residue to the next event. Initial sensitivity and limited testing with existing field data are discussed.

How to cite: Muñoz-Carpena, R., Reichenberger, S., Sur, R., and Hammel, K.: Fate of pesticide residues in vegetative filter strips in long-term exposure assessments: VFSMOD development and analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1735, https://doi.org/10.5194/egusphere-egu21-1735, 2021.

The most widely implemented mitigation measure to reduce transfer of pesticides to surface water bodies via surface runoff are vegetative filter strips (VFS). To reliably model the reduction of surface runoff, eroded sediment and pesticide load by VFS an event-based model is needed. The most commonly used model for this purpose is VFSMOD. VFSMOD simulates reduction of total inflow (∆Q) and reduction of incoming eroded sediment load (∆E) mechanistically. These variables are subsequently used to calculate the reduction of pesticide load (∆P). While ∆P can be relatively well predicted from ∆Q, ∆E and some other variables, errors in ∆Q and ∆E will propagate to ∆P. Hence, for strongly sorbing compounds, an accurate prediction of ∆E is crucial. The most important parameter characterizing the incoming sediment in VFSMOD is the median particle diameter d50. The objective of this study was to derive a generic d50 parameterization methodology for sediment trapping in VFSMOD that can be readily used for regulatory VFS scenarios.

Four studies with 16 hydrological events were selected for modelling. A first set of VFSMOD simulations, following the SWAN-VFSMOD sediment parameterization with d50 = 20 µm yielded a general overestimation of ∆E. Consequently, a maximum-likelihood-based calibration and uncertainty analysis with the DREAM-ZS algorithm was performed for the 16 events. The resulting d50 values were all in the low range (1.3-5.4 µm) and did not allow to establish a robust relationship to predict a wider range of d50 from the available explanatory variables. To increase the sample size and the range of d50 values, the comprehensive Kinston dataset for a loamy sand in North Carolina was calibrated with DREAM-ZS. Calibration was performed separately for each hydrological event. Further data points with measured particle size distributions in run-on were assimilated from the literature. The extended test data set of d50 values and explanatory variables was analysed using an extended multiple linear regression (MLR) approach and Classification and Regression Trees (CART).

A good calibration of event totals and outflow hydrographs could be achieved for most events and VFS treatments of the Kinston site. The calibrated d50 values yielded a wider range (2-16 µm) than the initial 16 events.

The improved d50 parameterization method derived with MLR/CART will be adopted in the next version of SWAN-VFSMOD to provide more realistic quantitative mitigation within FOCUS STEP4.

How to cite: Reichenberger, S., Sur, R., Sittig, S., Multsch, S., and Muñoz-Carpena, R.: An improved method for the parameterization of sediment trapping in VFSMOD, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-117, https://doi.org/10.5194/egusphere-egu21-117, 2020.

Quantitative mitigation of pesticides entering surface water using vegetative filter strips (VFS) is currently available within the regulatory SWAN tool for EU FOCUS STEP 4 simulations. For the VFSMOD model option, field estimates of surface runoff, sediment and pesticide loads simulated with the model PRZM are routed through the VFS where VFSMOD estimates the reductions of total inflow (dQ), eroded sediment (dE) and pesticide (dP) loads before the remaining runoff enters the waterbody. The reduced runoff is handed over to the TOXSWA aquatic model to calculate predicted environmental concentrations in surface water (PECsw). Brown et al. (2012) proposed VFSMOD parametrization rules including the selection of VFS soils and other characteristics for use in the FOCUS R1 to R4 (Rx) SWAN scenarios. The rules apply to free-draining soils, described in VFSMOD by the Green-Ampt model extended for unsteady rainfall. However, in some EU regions, the presence of a seasonal shallow water table (sWT) is common. In these cases, the VFS efficiency can be limited, depending on water table depth (WTD) and soil type. VFSMOD incorporates a sWT mechanistic infiltration component that has proven successful to predict sWT effects in VFS experiments. This component requires soil hydraulic characteristics, described by e.g. the Mualem-van Genuchten (MvG) equations.

The main objective of this study is to identify Rx representative VFS soils to study the effects of sWT on pesticide mitigation for a combination of illustrative storms and pesticides, as well as on PECsw from long-term SWAN simulations.

The selection and testing of the Rx VFS soils seeks to reflect a 90^th-percentile worst case in space of dP. The multicriteria adopted in the soil selection evaluate not only dP, but also the percentile of important soil parameters for noWT (K_s, S_av) and sWT infiltration conditions (fillable pore volume f_pv). The framework consisted of 4 steps: (a) soil spatial soil database analysis for VFS Rx mitigation scenarios; (b) selection of VFS candidate soils; (c) analysis of effects of sWT and sorption on dP for individual storm events; (d) Effect of sWT on long-term STEP 4 SWAN VFS mitigation simulations. For (a), representative soil profiles and area coverage for each of the EU Rx were obtained by combining the latest EU JRC soil profile databases SPADE2 and SPADE14. Each multilayer soil was aggregated into single-layer depth-weighted profiles, and MvG parameters were estimated using HYPRES pedotransfer functions (PTF). Water table depths (WTD) were set at equilibrium with TOXSWA median surface water level, and S_av and f_pv were calculated by numerical integration from MvG characteristics. For (b), 10644 VFSMOD simulations were run for all combinations of soils, T=1 and 10 yr storms, high/low Koc pesticides, and sWT/noWT conditions. Candidate Rx VFS soils were selected for the most conservative case (low Koc=100 Kg/L pesticide, T=10 yr storm) and noWT to achieve the target spatial 90^th percentile worst case of pesticide load reduction by the VFS. 

The implementation of the new sWT VFS mitigation component provides a more realistic description of pesticide reduction in accordance with STEP 4 EU FOCUS objectives.

How to cite: Sur, R., Muñoz-Carpena, R., Reichenberger, S., Hammel, K., Meyer, H., and Kehrein, N.: Implementation of shallow water table effects on pesticide runoff mitigation efficiency by vegetative filter strips within SWAN-VFSMOD, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7829, https://doi.org/10.5194/egusphere-egu21-7829, 2021.