Long-term water quality monitoring in agricultural catchments in Sweden: Impact of climatic drivers on diffuse nutrient loads

Water quality related to non-point source pollution continues to pose challenges in agricultural landscapes, despite two completed cycles of Water Framework Directive actions by farmers and landowners. Future climate projections will cause new challenges in landscape hydrology and subsequently, the potential responses in water quality. Investigating the nutrient trends in surface waters and studying the efficiency of mitigation measures revealed that loads and mea-sures are highly variable both spatially and temporally in catchments with different agro-climatic and environmental conditions. In Sweden, nitrogen and phosphorus loads in eight agricultural catchments (470-3300 ha) have been in-tensively monitored for >20 years. This study investigated the relationship between precipitation, air temperature, and discharge patterns in relation to nitrogen (N) and phosphorus (P) loads at catchment outlets. The time series data anal-ysis was carried out by integrating Mann-Kendall test, Pettitt break-points, and Generalized Additive Model. The re-sults showed that the nutrient loads highly depend on water discharge, which had large variation in annual average (158-441 mm yr-1). The annual average loads were also considerably different among the catchments with total N (TN) loads ranging from 6.76 to 35.73 kg ha-1, and total P (TP) loads ranging from 0.11 to 1.04 kg ha-1. The climatic drivers were highly significant indicators of nutrient loads but with varying degree of significance. Precipitation (28-962 mm yr-1) was a significant indicator of TN loads in five catchments (loamy sand/sandy loam) while annual average temperature (6.5-8.7 degrees C yr-1) was a significant driver of TN loads in six out of eight catchments. TP loads were associated with precipitation in two catchments and significantly correlated to water discharge in six catchments. Con-sidering the more frequent occurrence of extreme weather events, it is necessary to tailor N and P mitigation measures to future climate-change features of precipitation, temperature, and discharge

Far-future hydrology will differentially change the phosphorus transfer continuum

Climate change is likely to exacerbate land to water phosphorus (P) transfers, causing a degradation of water quality in freshwater bodies in Northwestern Europe. Planning for mitigation measures requires an understanding of P loss processes under such conditions. This study assesses how climate induced changes to hydrology will likely influence the P transfer continuum in six contrasting river catchments using Irish national observatories as exemplars. Changes or stability of total P (TP) and total reactive P (TRP) transfer processes were estimated using far-future scenarios (RCP4.5 and RCP8.5) of modelled river discharge under climate change and observed links between hydrological regimes (baseflow and flashiness indices) and transfer processes (mobilisation and delivery indices). While there were no differences in P mobilisation between RCP4.5 and RCP8.5, both mobilisation and delivery were higher for TP. Comparing data from 2080 (2070–2099) with 2020 (2010–2039), suggests that P mobilisation is expected to be relatively stable for the different catchments. While P delivery is highest in hydrologically flashy catchments, the largest increases were in groundwater-fed catchments in RCP8.5 (+ 22% for TRP and + 24% for TP). The inter-annual variability of P delivery in the groundwater-fed catchments is also expected to increase. Since the magnitude of a P source may not fully define its mobility, and hydrological connections of mobilisation areas are expected to increase, we recommend identifying critical mobilisation areas to target future mitigation strategies. These are hydrologically connected areas where controls such as soil/bedrock chemistry, biological activity and hydrological processes are favourable for P mobilisation

The Complex Pathway towards Farm-Level Sustainable Intensification: An Exploratory Network Analysis of Stakeholders’ Knowledge and Perception

peer-reviewedFarm-level sustainable intensification of agriculture (SIA) has become an important concept to ensuring food security while minimising negative externalities. However, progress towards its achievement is often constrained by the different perceptions and goals of various stakeholders that affect farm management decisions. This study examines farm-level SIA as a dynamic system with interactive components that are determined by the interests of the stakeholders involved. A systems thinking approach was used to identify and describe the pathways towards farm-level SIA across the three main pillars of sustainability. An explanatory network analysis of fuzzy cognitive maps (FCMs) that were collectively created by representative groups of farmers, farm advisors and policy makers was performed. The study shows that SIA is a complex dynamic system, affected by cognitive beliefs and particular knowledge within stakeholder groups. The study concludes that, although farm-level SIA is a complex process, common goals can be identified in collective decision making

Sustainable treatment technologies using mixed waste media to mitigate agricultural contaminants in land drainage

Intensification of agriculture in the European Union has resulted in nutrient losses from farms, which have contributed to a deterioration in water quality. As soil in drainage water ditch networks has limited capacity to attenuate nutrients leaving farms, efforts to reduce nutrient loads have been unsuccessful. Therefore, innovative solutions and experimental approaches are needed to intercept nutrients in ditches before final discharge to receiving waters. The existing ditch networks on farms may offer an opportunity for implementation of nutrient attenuation measures, by combining the natural attenuation capacity of the ditch with in-ditch engineered structures containing media capable of adsorbing nutrients. Although these structures have gained in popularity as a mitigation option, their configuration or optimal placement in the landscape has not yet been fully considered. The selection of appropriate media depends on the type of nutrient losses, the nutrient loads, media adsorption capacity and lifetime. In addition, the identification of an optimal location for the placement of in-ditch engineered structures is crucial for successful implementation as such structures are capable of only removing a proportion of nutrient loads exiting the farm, so the natural attenuation capacity of the ditch is important to further reduce the load. This thesis proposes two innovative mitigation techniques to remove both nitrogen (N) and phosphorus (P) in an agricultural drainage system: an in-ditch engineered system filled with reactive media and a natural solution which utilises soil chemistry of the ditch network for nutrient removal. In order to develop the first technique, a novel, internationally applicable decision support tool (DST) was developed to select locally sourced media for single or dual mitigation of N and P. The developed DST was validated in several case studies and it was then used to select an optimal combination of media for the removal of ammonium (NH4+) and P in water draining from an intensive dairy farm in south-east Ireland. Normally, large-scale column tests need to be conducted to develop design criteria for engineered structures, but as these are time consuming and expensive, rapid small-scale column tests (RSSCTs) were used, for the first time, to assess the media performance and longevity in simultaneous N and P removal in comparison with large-scale columns. The adsorption capacity and lifetime of the selected media in large- and small-scale column studies were consistent and the generated data using RSSCTs were successfully used to model P and N removals in the large-scale filters. This indicated that RSSCTs may be used to accurately and quickly develop design criteria for in-ditch engineered structures. In the second technique, the natural P remediation capacity of the ditch network of the study site was investigated with a view to identifying the optimum location for the placement of an engineered structure and to examine the capacity of a ditch in retaining or mobilising P. Experimental analyses indicated that the ideal location for installation of an in-ditch structure was at the point where a sharp increase in nutrient concentration was observed, which was due to discharges from the farm yard. The results also showed that P inputs into the drainage network accumulated in the sediments and bankside over time. This not only contributed to degradation of water quality leaving this farm, but the stored nutrients in the ditch network, as a result of decades of application, had also changed the chemistry of sediments to act as a secondary source of P, adding to the already polluted water. Arising from the findings of this thesis, in order to limit nutrient losses from intensive farms into drainage waters, implementation of an enhanced remediation technique is essential where natural attenuation is insufficient to eliminate pollution. An efficient mitigation measure starts with characterisation of the type of nutrient losses and then the development of appropriate in-ditch engineered structures filled with media to remove the identified nutrients. However, cognisance must also be taken of potential pollution swapping as a result of using the media, appropriate structure dimension and optimal location, and the nutrient remediation or immobilisation capacity of the ditches. This thesis provides a design framework that will contribute to sustainable, environmentally friendly farm management.2024-01-3

Sustainable treatment technologies using mixed waste media to mitigate agricultural contaminants in land drainage

Intensification of agriculture in the European Union has resulted in nutrient losses from farms, which have contributed to a deterioration in water quality. As soil in drainage water ditch networks has limited capacity to attenuate nutrients leaving farms, efforts to reduce nutrient loads have been unsuccessful. Therefore, innovative solutions and experimental approaches are needed to intercept nutrients in ditches before final discharge to receiving waters. The existing ditch networks on farms may offer an opportunity for implementation of nutrient attenuation measures, by combining the natural attenuation capacity of the ditch with in-ditch engineered structures containing media capable of adsorbing nutrients. Although these structures have gained in popularity as a mitigation option, their configuration or optimal placement in the landscape has not yet been fully considered. The selection of appropriate media depends on the type of nutrient losses, the nutrient loads, media adsorption capacity and lifetime. In addition, the identification of an optimal location for the placement of in-ditch engineered structures is crucial for successful implementation as such structures are capable of only removing a proportion of nutrient loads exiting the farm, so the natural attenuation capacity of the ditch is important to further reduce the load. This thesis proposes two innovative mitigation techniques to remove both nitrogen (N) and phosphorus (P) in an agricultural drainage system: an in-ditch engineered system filled with reactive media and a natural solution which utilises soil chemistry of the ditch network for nutrient removal. In order to develop the first technique, a novel, internationally applicable decision support tool (DST) was developed to select locally sourced media for single or dual mitigation of N and P. The developed DST was validated in several case studies and it was then used to select an optimal combination of media for the removal of ammonium (NH4+) and P in water draining from an intensive dairy farm in south-east Ireland. Normally, large-scale column tests need to be conducted to develop design criteria for engineered structures, but as these are time consuming and expensive, rapid small-scale column tests (RSSCTs) were used, for the first time, to assess the media performance and longevity in simultaneous N and P removal in comparison with large-scale columns. The adsorption capacity and lifetime of the selected media in large- and small-scale column studies were consistent and the generated data using RSSCTs were successfully used to model P and N removals in the large-scale filters. This indicated that RSSCTs may be used to accurately and quickly develop design criteria for in-ditch engineered structures. In the second technique, the natural P remediation capacity of the ditch network of the study site was investigated with a view to identifying the optimum location for the placement of an engineered structure and to examine the capacity of a ditch in retaining or mobilising P. Experimental analyses indicated that the ideal location for installation of an in-ditch structure was at the point where a sharp increase in nutrient concentration was observed, which was due to discharges from the farm yard. The results also showed that P inputs into the drainage network accumulated in the sediments and bankside over time. This not only contributed to degradation of water quality leaving this farm, but the stored nutrients in the ditch network, as a result of decades of application, had also changed the chemistry of sediments to act as a secondary source of P, adding to the already polluted water. Arising from the findings of this thesis, in order to limit nutrient losses from intensive farms into drainage waters, implementation of an enhanced remediation technique is essential where natural attenuation is insufficient to eliminate pollution. An efficient mitigation measure starts with characterisation of the type of nutrient losses and then the development of appropriate in-ditch engineered structures filled with media to remove the identified nutrients. However, cognisance must also be taken of potential pollution swapping as a result of using the media, appropriate structure dimension and optimal location, and the nutrient remediation or immobilisation capacity of the ditches. This thesis provides a design framework that will contribute to sustainable, environmentally friendly farm management.2024-01-3

A common agricultural soil test can identify legacy P hotspots in a drainage ditch network

Agricultural soils have accumulated considerable phosphorus (P) reserves along the transport pathways within land-water continuum. Where P concentrations are excessive compared to the soil P sorption capacity, dissolved soluble P can leach to waterbodies. A phosphorus saturation ratio (PSR = P/(Fe + Al)) can be used to classify high and low risk soils based on a commonly applied Mehlich-3 soil test. PSR has been used for acid mineral soils, but in this study it was applied to sediments and drainage ditch bankside samples. Previous published data was converted to PSR and compared to P availability measurements. The results confirmed earlier findings, that a PSR threshold of 0.1 can delineate high and low P risk sites. By quantifying the amount of P in excess to the threshold, legacy P hotspots could be located in the network which would act as an additional source of P inputs to waters. In the study site, two soils contained over 80% of the excess legacy P, presenting a localized long-term risk to water quality. The findings support using the cost effective Mehlich-3 extraction to identify hotspots with most susceptible soil-P to losses and quantify the amount of potentially leachable legacy P. Highlights • Agricultural ditches accumulate legacy P and present a risk for water quality. • Mehlich-3 soil test can identify P saturation and total legacy P amount. • Use of a common soil test allows broad scale mapping of high P risk hotspots

Developing and validating a decision support tool for media selection to mitigate drainage waters

The nitrate nitrogen (NO3-N) and ammonium (NH4-N) and/or dissolved reactive phosphorus (DRP) load in drainage water from farms can be managed by reactive or biological media filters. The nutrient content of the drainage water can be obtained directly from water analysis, which immediately focuses attention on filter media selection. There are many factors that may be important before choosing a medium or media e.g. nutrient removal capacity, lifetime, hydraulic conductivity, the potential for pollution swapping , attenuation of non-target contaminants (e.g. pesticides, organic carbon, etc.), and local availability and transportation cost of media to site. In this study, a novel decision support tool (DST) was developed, which brought all these factors together in one place for five nutrient scenarios. A systematic literature review was conducted to create a database containing 75 media with an associated static scoring system across seven criteria (% of nutrient concentration reduction, removal of other pollutants, lifetime, hydraulic conductivity, negative externalities) and a dynamic scoring system across two criteria (delivery cost and availability). The DST was tested using case studies from Ireland, Belgium and USA with different agricultural practices and nutrient scenarios. It was then validated by SWOT (strength, weakness, opportunities and threats) analysis. The DST provided a rapid, easily modifiable screening of many media-based treatments for specific dual or single nutrient-based water drainage problems. This provides stakeholders (farmers/regulators/advisors) with a versatile, flexible and robust yet easy-to-understand framework to make informed choices on appropriate media-based mitigation measures according to users relevant technical, economic and logistical factors.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 675120.2021-07-2

An integrated assessment of nitrogen source, transformation and fate within an intensive dairy system to inform management change.

From an environmental perspective optimised dairy systems, which follow current regulations, still have low nitrogen (N) use efficiency, high N surplus (kg N ha-1) and enable ad-hoc delivery of direct and indirect reactive N losses to water and the atmosphere. The objective of the present study was to divide an intensive dairy farm into N attenuation capacity areas based on this ad-hoc delivery. Historical and current spatial and temporal multi-level data- sets (stable isotope and dissolved gas) were combined and interpreted. Results showed that the farm had four distinct attenuation areas: high N attenuation: characterised by ammonium-N (NH4+-N) below 0.23 mg NH4+-N l-1 and nitrate (NO3--N) below 5.65 mg NO3-- N l-1 in surface, drainage and groundwater, located on imperfectly to moderately-well drained soils with high denitrification potential and low nitrous oxide (N2O) emissions (av. 0.0032 mg N2O-N l-1); moderate N attenuation: characterised by low NO3--N concentration in drainage water but high N2O production (0.0317 mg N2O-N l-1) and denitrification potential lower than group 1 (av. δ15N-NO3-: 16.4 , av. δ18O-NO3-: 9.2 ), on well to moderately drained soils; low N attenuation area 1: characterised by high NO3--N (av. 6.90 mg NO3--N l-1) in drainage water from well to moderately-well drained soils, with low denitrification potential (av. δ15N-NO3-: 9.5 , av. δ18O-NO3-: 5.9 ) and high N2O emissions (0.0319 mg N2O l-1); and low N attenuation area 2: characterised by high NH4+-N (av. 3.93 mg NH4+-N l-1 and high N2O emissions (av. 0.0521 mg N2O l-1) from well to imperfectly drained soil. N loads on site should be moved away from low attenuation areas and emissions to air and water should be assessed.The authors thank S. Leach, C. Somers, D. Brennan, M.M.R. Jahangir and D. Peyton for assistance during the project. J. Patton provided data on the N balance and R. Fox and A. Lawless facilitated access to the research farm and helped with the management scenario section.peer-reviewe