John Livsey

Our efforts to reduce anthropogenic pressures on aquatic ecosystems and their catchments are still unsatisfactory as aquatic nutrient and pollutant exports remain constant or continue to increase. Geomorphologic modifications and diffuse pollution from agricultural land use are the two dominant pressures responsible for aquatic degradation and water pollution. In recent years the main focus has been on mitigating these pressures through various measures implemented at the catchment level, including rewetting/constructing wetlands and channel restoration and remediation. In this study we looked at the environmental effects of channel remediation for over 30 Swedish agricultural headwater streams and ditches. Our aim was two-fold: 1) to evaluate the effects of channel remediation on chemical and ecological conditions in streams and ditches; and 2) to evaluate the linkages between stream and ditch exports of N and C and catchment and in-stream properties. The aquatic sites analysed in our study all shared high levels of anthropogenic disturbance, with high levels of nutrients and suspended sediments. Despite these common pressures, we found large variations in N and C exports through the stream network (as nitrate nitrogen NO3-N and dissolved organic carbon DOC) and gaseous losses (as CO2, CH4 and N2O). Using our extensive dataset, we were able to link these differences to catchment and in-stream properties describing N and C transport (e.g., flow discharge, contributing area) and processing (e.g., channel area, channel substrate, macrophyte stands) and carbon quality measured as fluorescent dissolved organic matter. Together, our results indicate that both intrinsic and extrinsic factors control catchment N and C losses to water and air, leading to a large variation in observed fluxes and the effects of remediation.

Agricultural drainage systems are essential for managing water levels in farmland, yet they often prioritize conveyance efficiency over ecological function, contributing to biodiversity loss and water quality degradation. Remediation measures, such as two-stage ditches, re-meandering, and bank regrading, are typically aimed at reducing sediment and nutrient loads, but frequently neglect habitat complexity and biodiversity. This study investigates how these remediation practices influence macroinvertebrate communities in agricultural ditches across central and southern Sweden, highlighting novel insights on integrating ecological considerations into drainage system design. We evaluated ecological impacts across 18 paired sites, each consisting of an upstream conventional trapezoidal channel and a downstream remediated section. Water chemistry, sediments, and channel morphology were measured alongside macroinvertebrate sampling, while trait-based analyses were conducted to assess macroinvertebrates’ utility as bioindicators of water quality. Bayesian linear mixed-effects (BLM) models were used to determine the relative influence of climate, region, and remediation efforts on biodiversity outcomes. Results indicate that remediated sections generally supported slightly higher species richness than upstream controls, suggesting modest ecological benefits. However, Shannon and Simpson indices revealed no significant differences in community evenness, and macroinvertebrate composition varied substantially among sites, with no distinct patterns separating remediated and non-remediated sections. The BLM confirmed that remediation had a small but positive effect on species richness, though climatic and regional factors also emerged as key drivers of macroinvertebrate diversity. Our findings show that ditch remediation does not negatively affect aquatic biodiversity and may confer slight ecological gains. Future remediation efforts could further enhance biodiversity by emphasizing habitat complexity. Overall, this study underscores the value of integrating biodiversity considerations into agricultural water management and calls for additional research on structural complexity and natural geomorphological processes, thereby promoting multifunctionality in agricultural drainage systems.

Improving water quality at the catchment scale proves difficult as indicated by shifting deadlines of the Water Framework Directive for achieving good chemical and ecological status in European freshwaters. Low-hanging fruits of reducing point sources of pollution have already been targeted in most catchments, with more challenging and persistent diffuse pollution jeopardising widespread water quality improvements. Diffuse pollution originates from a range of anthropogenic activities such as agriculture, forestry and mining and leads to gradual accumulation of pollutants in impacted catchments. These abundant pools of pollution, also known as legacies, can control water quality and limit the effectiveness of mitigation measures in the long term. Yet, our understanding of hydrological and biogeochemical processes controlling mobilisation, transformation, transport and impact of pollution legacies in catchments is still limited. Here, we present results from multiple projects focusing on identifying processes controlling eutrophication and erosion in headwater agricultural catchments to support management and mitigation. We use a suite of experimental and modelling tools from high-frequency stream chemistry data, in situ measurements of dominant processes, laboratory assays, and process-based models to quantify hydrological and biogeochemical processes. Our results show that despite common pollution pressures, agricultural catchments differ in how they modulate pollution legacies. Their resilience/sensitivity to pollution depends on the interplay between hydrological and biogeochemical processes. Biogeochemical processes such as sorption, sedimentation and denitrification show potential for pollution retention and removal; however, their capacity is rapidly exhausted during hydrologic events mobilising large fluxes of legacy pollutants. As the importance of hydrological accumulation increases with catchment size, the cumulative impact of mitigation measures on water quality declines along the stream network. Finally, our modelling approach shows that only large-scale mitigation interventions are likely to bring the required water quality improvements, particularly under future climatic conditions with accelerated biogeochemical and hydrological processes. Understanding these processes is key to effective mitigation and reducing potential pollution swapping in heavily impacted catchments.

Under persistent eutrophication of European water bodies and a changing climate, there is an increasing need to evaluate best‐management practices for reducing nutrient losses from agricultural catchments. In this study, we set up a daily discharge and water quality model in Hydrological Predictions of the Environment for two agricultural catchments representative for common cropping systems in Europe's humid continental regions to forecast the impacts of future climate trajectories on nutrient loads. The model predicted a slight increase in inorganic nitrogen (IN) and total phosphorus (TP) loads under RCP2.6, likely due to precipitation‐driven mobilization. Under RCP4.5 and RCP8.5, the IN loads were forecasted to decrease from 16% to 26% and 21%–50% respectively, most likely due to temperature‐driven increases in crop uptake and evapotranspiration. No distinct trends in TP loads were observed. A 50% decrease in nutrient loads, as targeted by the European Green Deal, was backcasted using a combination of management scenarios, including (a) a 20% reduction in mineral fertilizer application, (b) introducing cover crops (CC), and (c) stream mitigation (SM) by introducing floodplains. Target TP load reductions could only be achieved by SM, which likely results from secondary mobilization of sources within agricultural streams during high discharge events. Target IN load reductions were backcasted with a combination of SM, fertilizer reduction, and CC, wherein the required measures depended strongly on the climatic trajectory. Overall, this study successfully demonstrated a modeling approach for evaluating best‐management practices under diverging climate change trajectories, tailored to the catchment characteristics and specific nutrient reduction targets.

Agricultural headwaters are positioned at the interface between terrestrial and aquatic ecosystems and, therefore, at the margins of scientific disciplines. They are deemed devoid of biodiversity and too polluted by ecologists, overlooked by hydrologists, and are perceived as a nuisance by landowners and water authorities. While agricultural streams are widespread and represent a major habitat in terms of stream length, they remain understudied and thereby undervalued. Agricultural headwater streams are significantly modified and polluted but at the same time are the critical linkages among land, air, and water ecosystems. They exhibit the largest variation in streamflow, water quality, and greenhouse gas emission with cascading effects on the entire stream networks, yet they are underrepresented in monitoring, remediation, and restoration. Therefore, we call for more intense efforts to characterize and understand the inherent variability and sensitivity of these ecosystems to global change drivers through scientific and regulatory monitoring and to improve their ecosystem conditions and functions through purposeful and evidence-based remediation.

Drawing on collective experience from ten collaborative research projects focused on the Global South, we identify three major challenges that impede the translation of research on sustainability and resilience into better-informed choices by individuals and policy-makers that in turn can support transformation to a sustainable future. The three challenges comprise: (i) converting knowledge produced during research projects into successful knowledge application; (ii) scaling up knowledge in time when research projects are short-term and potential impacts are long-term; and (iii) scaling up knowledge across space, from local research sites to larger-scale or even global impact. Some potential pathways for funding agencies to overcome these challenges include providing targeted prolonged funding for dissemination and outreach, and facilitating collaboration and coordination across different sites, research teams, and partner organizations. By systematically documenting these challenges, we hope to pave the way for further innovations in the research cycle.

There is growing awareness of the potential value of agricultural land for climate change mitigation. In Sweden, cropland areas have decreased by approximately 30% over recent decades, creating opportunities for these former croplands to be managed for climate change mitigation by increasing soil organic carbon (SOC) stocks. One potential land‐use change is conversion of cropland to grazed grasslands, but the long‐term effect of such change in management is not well understood and likely varies with soil type and site‐specific conditions. Through sampling of mineral and peatland soils within a 75‐year chronosequence of land converted from crop production to grazed grassland, we assessed how time since conversion, catenary position, and soil depth affected SOC storage. The SOC stocks calculated at an equivalent soil or ash mass increased through time since conversion in mineral soils at all topographic positions, at a rate of ~0.65% year ⁻¹ . Soils at low topographic positions gained the most carbon. Peat SOC stock gains after conversion were large, but only marginally significant and only when calculated at an equivalent ash mass. We conclude that the conversion of mineral soil to grazed grassland promotes SOC accumulation at our sites, but climate change mitigation potential would need to be evaluated through a full greenhouse gas balance.

Agricultural drainage ditches are critical for the removal of excess water from fields. Their traditional trapezoidal shape is effective for this purpose, while also minimizing their footprint and being easy to maintain. However, these drainage ditches also act as transport pathways for phosphorus and nitrogen. Moreover, their steep banks are susceptible to erosion during high flows, which can be a source of additional sediment and phosphorous mobilisation in river systems. Within Sweden, 60% of water bodies are classified as having poor chemical and ecological status, with diffuse agricultural pollution and hydromorphological pressures being key drivers. Further, the European Green Deal has the ambition to reduce nutrient losses from agricultural catchments by 50%. Therefore, mitigation strategies in agricultural catchments are urgently needed. Ditch remediation, through the construction of two-stage or shallow slope ditches, has been proposed as a solution to reduce nutrient exports and hydromorphological pressures, while maintaining good drainage. Numerous ditch remediation actions have taken place within Sweden, with encouragement and funding from agricultural agencies. However, we currently lack an understanding of the factors controlling the effectiveness of ditch remediation strategies. Further, as aquatic ecosystems provide services beyond simple water conveyance, we are also limited in our understanding of benefits/trade-offs that may occur to these ecosystems as a result of remediation. Therefore, through the synoptic sampling of traditional and remediated ditches, we will analyse and compare channel properties, stream chemistry and macroinvertebrate communities to assess the effect of ditch remediation on both pollution reduction and ecosystems. The obtained data will then be used to model the effectiveness of various remediation strategies. This unique integration of hydrological and ecological methods will increase our understanding of ditch remediation and ultimately support farmers, landowners, and authorities in the design of cost-effective mitigation measures.

Climate change and agricultural intensification are placing enormous pressure on soil to provide essential services, from water storage and nutrient provision to carbon sequestration. Indeed, storing carbon in agricultural systems is proposed as an effective climate mitigation approach. Yet, storing carbon comes often at a cost in terms of water consumed—water used either to increase productivity and carbon inputs to soil, or to create conditions in the soil that promote carbon storage. These linkages are perhaps most evident in rice paddy systems.Rice – a staple food for 3 billion people – consumes more water than any other crop, leading to unsustainable water withdrawals. However, this large water consumption allows paddy soils to store more carbon than under other land uses, because flooding of the fields keeps soils saturated and inhibits organic matter decomposition. Therefore, changing water saving approaches such as alternate wetting and drying has the potential to reduce carbon storage and alter the provision of other ecosystem services. But how much can soil organic carbon change across land uses and when water management is altered?In this contribution, we discuss the mechanisms of carbon storage in paddy fields, using data from a meta-analysis of soil carbon budgets in tropical rice paddies and from a detailed investigation of carbon storage along a gradient of a land use and soil age in a temperate rice system. The meta-analysis shows that, as expected, reducing the time of flooding decreases soil organic carbon, but also results in a net decrease of greenhouse gas emissions. The more detailed study shows that in temperate conditions with relative short flooding time, rice paddies can store as much organic carbon as forest sites, despite the higher carbon inputs of forests compared to rice systems. This higher carbon storage is achieved thanks to decreased soil respiration in anaerobic conditions and increased mineral associations of organic carbon. These results show that water management strongly affects soil carbon storage, and that trade-offs emerge between sustainable water use and long-term provision of soil-related ecosystem services.