Bieroza, Magdalena

Dupas, Remi

Glendell, Miriam

McGrath, Gavan

Mellander, Per-Erik

English

Epsilon Open Archive

waterEditorialHydrological and Chemical Controls on Nutrient andContaminant Loss to Water inAgricultural LandscapesMagdalena Bieroza 1,* , Rémi Dupas 2 , Miriam Glendell 3 , Gavan McGrath 4 andPer-Erik Mellander 51 Department of Soil and Environment, Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden2 UMR SAS, INRAE, Institut Agro, 35000 Rennes, France; remi.dupas@inrae.fr3 The James Hutton Institute, Aberdeen AB15 8QH, Scotland, UK; miriam.glendell@hutton.ac.uk4 Department of Biodiversity, Conservation and Attractions Locked Bag 104, Bentley Delivery Centre, Bentley,WA 6983, Australia; gavan.mcgrath@dbca.wa.gov.au5 Agricultural Catchments Programme, Department of Environment, Soils and Land Use, Teagasc,Johnstown Castle, Y35 Y521 Wexford, Ireland; Per-Erik.Mellander@teagasc.ie* Correspondence: magdalena.bieroza@slu.seReceived: 16 November 2020; Accepted: 28 November 2020; Published: 2 December 2020 1. IntroductionNutrient and contaminant losses in agricultural landscapes are directly controlled by hydrological(flow pathways), chemical (sorption, speciation and transformations), biological processes (fixation,uptake) and indirectly by demographic (growing population), economic (food production) andsocietal drivers (individual attitudes, farming tradition) that control how agricultural landscapesare managed. Global change will likely increase nutrient and contaminant losses due to intensifiedhydro-meteorological drivers, higher nutrient inputs to meet growing food demand and continuouslosses of nutrients from legacy stores in soils and aquifers. To offset the impact of global changeand manage nutrients and contaminants in an efficient way, there is a growing need to mitigatetheir losses along the transfer continuum from agricultural land to aquatic ecosystems. To meetthis challenge, we need a comprehensive understanding of how hydrological and chemical controlsinfluence contaminants over a range of spatial and temporal scales, for different catchment typologies,and residence times, while also considering the role of changing climatic drivers, as well as economicand societal factors.Our current understanding of nutrient and contaminant losses is framed by the pollutant transfercontinuum [1]. This framework identifies critical pollutant loss pathways in space and time includingsources, mobilisation, delivery and impact. Existing research rarely covers the full continuum, due tolarge distances and time lags between sources and delivery points in the stream network where weobserve the impact. Current research mostly focuses on individual steps along the pollutant transfer,analysing their complexity and links with the immediate next steps in the continuum. At any step ofthe transfer continuum, an attenuation or transformation of pollutant delivery can occur, e.g., at theinterface of land and water in the soil, groundwater, hyporheic and riparian zones [2]. This nutrientattenuation capacity in agricultural catchments can be further enhanced by implementing mitigationmeasures by farmers and land owners. The effect of mitigation measures on water quality is controlledby a number of environmental and societal factors, e.g., how awareness of pollution problems affectsbehavioural change and uptake of measures by stakeholders.This special issue provides an overview of novel approaches to identify and understand thecomplexity of pollutant transport processes and suggest solutions how this evidence can informWater 2020, 12, 3379; doi:10.3390/w12123379 www.mdpi.com/journal/waterWater 2020, 12, 3379 2 of 5management decisions. We summarise these findings and provide a synthesis of future needs anddirections in monitoring and managing of nutrient and contaminant losses in agricultural landscapes.2. Overview of the ArticlesHigh spatial and temporal resolution hydrochemical data are now more available thanks toadvances in monitoring techniques [3], and used to elucidate controls on nutrient mobilisationand delivery in agricultural streams. Although hydrochemical data can show similar patterns,the underlying mechanisms can be different depending on catchment typology and specific land useand management. In their study, Vero et al. [4] showed that elevated stream phosphorus concentrations,typically observed in Irish streams during summer months, can result from a number of controls:transport through groundwater and lack of dilution in a well-drained grassland, in-stream mobilizationin a well-drained arable catchment, and a combination of point sources and cumulative loading ina poorly drained grassland catchment. The authors point out that although phosphorus fluxes aregenerally low during summer baseflows, high concentrations pose a great risk to stream ecology.These pressures are likely to increase under future climate resulting in a worse ecological status insummer and a worse chemical status in winter.High spatial and temporal monitoring is also needed to evaluate the effectiveness of mitigationmeasures. Johnes et al. [5] showed large complexity of multiple pathways and water sources feedinginto a riparian wetland, generating large spatial and temporal variations in nutrient cycling andretention. They suggest a multiproxy approach based on the identification of the spatial distributionof functional units, using vegetation mapping, geophysical surveys, and isotopic ratios in soil water,sediments and vegetation, to estimate potential effectiveness of mitigation measures before they areimplemented. This type of comprehensive monitoring can provide evidence for building and testingconceptual models of biogeochemical functioning of riparian wetlands and an important diagnostictool for catchment managers.Although critically needed to inform management decisions in undrained agricultural catchments,the identification of key delivery pathways for nutrients and other contaminants can be extremelycomplex. Adams et al. [6] demonstrated an approach in which high-frequency water quality data wereused to calibrate an event-scale model of flow and P transport, the Catchment Runoff Attenuation FluxTool (CRAFT). This approach, referred to by the authors as event forensics, provides detailed analysisof multiple flow and water quality parameters, along with their key pathways.Artificial subsurface drainage in agricultural landscapes provides fast delivery pathways that cancontribute large amounts of nutrients and sediments to streams. However, as shown by Klaiber et al. [7],despite higher total runoff, an artificially drained field contributed lower soluble reactive phosphorusand suspended sediment exports in a two-year study that compared two arable plots. Both drainedand undrained plots contributed similar exports of total phosphorus and further studies from differentsoil, climatic and land use conditions are needed to corroborate these results. However, the study didnot consider the effect of drainage on other pollutants, e.g., nitrate, which can be particularly importantfor achieving overall improvements in ecological status and avoiding pollution swapping effects [8].Transport of contaminants, especially nutrients, along flow pathways is typically not conservativedue to biogeochemical transformations that can change nutrient concentrations and fluxes. This makesestablishing the causal links between flow pathways, source and delivery points and impact difficultand requires application of modelling studies or smart tracers. Severini et al. [9] tested a conservativetracer that helps to monitor vertical transport of nitrate from agricultural soils to groundwaters.The authors found that silica SiO2 and nitrate NO3- showed a similar spatial distribution in thesubsurface suggesting their common origin from manure spreading. They also pointed out largespatial heterogeneity in redox conditions and distribution of microbial communities that can havecritical impact on nitrate behaviour and concentrations. As many aquifers exceed nitrate concentrationlimits, we need better tracing techniques to resolve discrete flow pathways and the significance ofbiogeochemical heterogeneity at multiple scales.Water 2020, 12, 3379 3 of 5Hydrological controls in agricultural catchments are also changing as shown by Uusheimo et al. [10].The authors showed a significant increase in winter nutrient and sediment loads driven by increasedflashiness. Small agricultural catchments are particularly sensitive to changes in hydrological forcing,with large consequences for water quality impairment. To offset these changes in hydrology, moreintensive management efforts are needed, including implementation of mitigation measures thatincrease water residence time in the catchment e.g., retention ponds and constructed wetlands.Although the efficiency of these mitigation measures changes on a seasonal basis, their overall effect onwater quality is positive and the authors encourage harnessing of all available retention potential inagricultural catchments.Hydrological pathways and climatic variability are intrinsically linked. Uusheimo et al. [10],as well as Vero et al. [4], point to the sensitivity of nutrient outcomes to weather variability at thescale of individual rainfall events, up to seasonal variation in flow. These contributions add to ourunderstanding of the role that climate variability has on the multitude of processes controlling nutrientexport from agricultural catchments. Such knowledge lets us appreciate variability in outcomes despitemitigation efforts [8], as well as identify apparent trends that may be the result of longer-term weathervariations (e.g., Mellander et al. [11]).An important aspect in addressing diffuse pollution challenges in agricultural landscapes is ourability to understand and influence the attitudes of land owners and farmers, who may have thebest understanding of pollution pressures in agricultural catchments. These stakeholders are key forthe implementation of best management practices and mitigation measures to reduce nutrient andcontaminant losses from land to water. Okumah et al. [12] systematically reviewed the evidence baseof awareness–behavioural change–water quality improvement pathway, with a focus on Europe andNorth America. They found that although there is a generally a positive effect between awareness andbehavioural change, meaning that well-informed farmers are more likely to introduce land managementchanges for water quality improvement, the link between awareness and water quality is typicallymore complex and less understood. This contrasting evidence for a relationship between uptake ofmitigation measures and improvements in water quality results from a number of confounding factors,e.g., time lags, variation in climatic drivers and the level of uptake by farmers, making the effectivenessof mitigation efforts both pollutant, and measure dependent. This inherent complexity within thepollutant transfer continuum and the uptake of mitigation measures challenge our ability to designuniversally effective mitigation measures. A growing body of evidence shows that, while managementpractices help to decrease nutrient loading in agricultural catchments, their positive effects can becounterbalanced by increasing runoff attributed to changes in climatic drivers [8,11,13].3. Novel Science Drives New Solutions to Future Catchment Monitoring and ManagementMeeting future environmental, economic and societal needs required from agricultural landscapes,calls for new approaches in catchment monitoring and management as well as better communicationamong researchers, stakeholders and policy makers. The scientific papers in this special issue provideinnovative solutions towards such new approaches.To improve future monitoring, high spatial and temporal resolution measurements of streamwater and sediments should be targeted to different catchment typologies, as similar hydrochemicalpatterns do not necessarily indicate the same underlying controls on nutrient and sediment losses [4].Understanding of these controls is critical in designing appropriate mitigation measures andmanagement practices that are likely to reduce sources and intercept pollution pathways. Johnes et al. [5]provided a tool for evaluation of potential impact of riparian wetlands that can be validated for othertypes of mitigation measures and catchment typologies. Minimum information requirement models,as in the study of Adams et al. [6], can be used to interpret water quality data and provide evidenceneeded for smart management of flow pathways. Decision makers can use this information to designappropriate mitigation measures along critical pollution pathways. However, as Severini et al. [9] pointout, contaminant transport along flow pathways is rarely conservative. The challenge here is to be ableWater 2020, 12, 3379 4 of 5to identify critical sinks along the flow pathways and further enhance their function through mitigationoptions. For this, a combination of modelling studies and smart tracers is needed. This intensifiedmanagement effort is critically needed with a changing climate, according to Uusheimo et al. [10].Okumah et al. [12] stress that land owners and farmers are more likely to adopt mitigation practices ifthey receive a well-placed, consistent, and well-framed message on pollutant pressures, mitigationoptions and their expected outcome. This provides a challenge for researchers and policy makers tomake this information transparent and evidence-based.A common theme of this collection of papers is that of complexity, and how we unravel theimportant processes, mediating and moderating factors in both the social and biophysical spheres ofcomplex catchment systems. While, over the past decade, high-resolution observational data haveallowed us better insights into the ‘black boxes’ that may appear to represent complex catchment systems,such data is expensive to obtain at large scale [5] and may not even ‘readily indicate the type or locationof sources or quantification of the pathways’ [4]. Hence, several papers in this special issue are proposinglower-cost solutions that could be used to answer outstanding knowledge gaps at larger geographicalscales. Application of conservative tracers [6,9], and stable isotopes [5], to understand pollutant sourcesand transformations is proving particularly promising in this respect. In combination with additionaltechniques, including geophysical and vegetation surveys [5] and synoptic geochemical sampling atlower temporal resolution [4,5], these approaches may offer practical tools to inform the spatial targetingand understand the likely effectiveness of mitigation measures. However, major knowledge gaps stillremain both in the physical domain along the source–mobilisation–delivery–impact continuum, and inthe social domain along the awareness–behavioural change–water quality improvement continuum.Anticipating catchment responses to common drivers remains difficult, as, whilst the symptoms mayappear similar, the underlying causes often differ and are context specific [4,6]. Whilst this complexitymay appear frustrating to both scientists and catchment managers, it also presents opportunities forthe development of novel research tools and transdisciplinary frameworks to gain fresh insights intocatchment controls of nutrient and contaminant losses.Author Contributions: All authors jointly wrote this paper. All authors have read and agreed to the publishedversion of the manuscript.Funding: This research received no external funding.Conflicts of Interest: The authors declare no conflict of interest.References1. Haygarth, P.M.; Condron, L.M.; Heathwaite, A.L.; Turner, B.L.; Harris, G.P. The phosphorus transfercontinuum: Linking source to impact with an interdisciplinary and multi-scaled approach. Sci. Total Environ.2005, 344, 5–14. [CrossRef]2. Wollheim, W.M.; Bernal, S.; Burns, D.A.; Czuba, J.A.; Driscoll, C.T.; Hansen, A.T.; Hensley, R.T.; Hosen, J.D.;Inamdar, S.; Kaushal, S.S.; et al. River network saturation concept: Factors influencing the balance ofbiogeochemical supply and demand of river networks. Biogeochemistry 2018, 141, 503–521. [CrossRef]3. Rode, M.; Wade, A.J.; Cohen, M.J.; Hensley, R.T.; Bowes, M.J.; Kirchner, J.W.; Arhonditsis, G.B.; Jordan, P.;Kronvang, B.; Halliday, S.J.; et al. Sensors in the Stream: The High-Frequency Wave of the Present. Environ.Sci. Technol. 2016, 50, 10297–10307. [CrossRef]4. Vero, S.E.; Daly, K.; McDonald, N.T.; Leach, S.; Sherriff, S.C.; Mellander, P.-E. Sources and Mechanismsof Low-Flow River Phosphorus Elevations: A Repeated Synoptic Survey Approach. Water 2019, 11, 1497.[CrossRef]5. Johnes, P.; Gooddy, D.; Heaton, T.; Binley, A.; Kennedy, M.; Shand, P.; Prior, H. Determining the Impact ofRiparian Wetlands on Nutrient Cycling, Storage and Export in Permeable Agricultural Catchments. Water2020, 12, 167. [CrossRef]6. Adams, R.; Quinn, P.; Barber, N.; Burke, S. Identifying Flow Pathways for Phosphorus Transport UsingObserved Event Forensics and the CRAFT (Catchment Runoff Attenuation Flux Tool). Water 2020, 12, 1081.[CrossRef]Water 2020, 12, 3379 5 of 57. Klaiber, L.B.; Kramer, S.R.; Young, E.O. Impacts of Tile Drainage on Phosphorus Losses from Edge-of-FieldPlots in the Lake Champlain Basin of New York. Water 2020, 12, 328. [CrossRef]8. Bieroza, M.; Bergström, L.; Ulén, B.; Djodjic, F.; Tonderski, K.; Heeb, A.; Svensson, J.; Malgeryd, J. HydrologicExtremes and Legacy Sources Can Override Efforts to Mitigate Nutrient and Sediment Losses at theCatchment Scale. J. Environ. Qual. 2019, 48, 1314. [CrossRef]9. Severini, E.; Bartoli, M.; Pinardi, M.; Celico, F. Reactive Silica Traces Manure Spreading in Alluvial AquifersAffected by Nitrate Contamination: A Case Study in a High Plain of Northern Italy. Water 2020, 12, 2511.[CrossRef]10. Uusheimo, S.; Tulonen, T.; Huotari, J.; Arvola, L. Long-Term (2001–2020) Nutrient Transport from a SmallBoreal Agricultural Watershed: Hydrological Control and Potential of Retention Ponds. Water 2020, 12, 2731.[CrossRef]11. Mellander, P.E.; Jordan, P.; Bechmann, M.; Fovet, O.; Shore, M.M.; McDonald, N.T.; Gascuel-Odoux, C.Integrated climate-chemical indicators of diffuse pollution from land to water. Sci. Rep. 2018, 8, 944.[CrossRef]12. Okumah, M.; Chapman, P.; Martin-Ortega, J.; Novo, P. Mitigating Agricultural Diffuse Pollution: Uncoveringthe Evidence Base of the Awareness–Behaviour–Water Quality Pathway. Water 2018, 11, 29. [CrossRef]13. Ockenden, M.C.; Hollaway, M.J.; Beven, K.J.; Collins, A.L.; Evans, R.; Falloon, P.D.; Forber, K.J.; Hiscock, K.M.;Kahana, R.; Macleod, C.J.A.; et al. Major agricultural changes required to mitigate phosphorus losses underclimate change. Nat. Commun. 2017, 8, 161. [CrossRef]Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutionalaffiliations.© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open accessarticle distributed under the terms and conditions of the Creative Commons Attribution(CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Hydrological and Chemical Controls on Nutrient and Contaminant Loss to Water in Agricultural Landscapes

https://pub.epsilon.slu.se/21764/1/bieroza_m_et_al_210127.pdf

Hydrological and Chemical Controls on Nutrient and Contaminant Loss to Water in Agricultural Landscapes

Abstract

Similar works

Full text

Available Versions

Epsilon Open Archive