Understanding the effects of future climate, land cover and land management change on total phosphorus losses to lakes in Scotland

This study simulated the terrestrial losses of total phosphorus (TP) likely to be delivered to 6,836 standing waters in Scotland via surface and sub-surface pathways to explore the potential of measures to mitigate the impact of future climatic and land cover change on TP loads. TP losses from land were simulated in kg^-1 ha^-1 yr^-1 at 100 × 100 m raster resolution, using a spatial Bayesian Belief Network (BBN)¹. Diffuse sources through drains and by soil erosion; incidental losses from farmyards; sewage treatment works (STWs) and septic tanks (STs) were included.

To understand the effects of future climate change, two Representative Concentration Pathways  RCP2.6 (~1.5^oC warming by 2080) and RCP6 (~3 ^oC warming by 2080) were coupled with future land cover change until 2040, 2060 and 2080 from CRAFTY-GB² (based on stakeholder-elaborated Shared Socioeconomic Pathways SSP1 – Sustainability and SSP3 – Regional rivalry). In addition, land management mitigation measures were simulated to examine their potential to reduce TP losses from land during baseline period. Modelled scenarios included fertiliser application rates ‘at’ and ‘below’ agronomic optimum; increase in extent of buffer strips to 8m and a combination of measures.

Expansion of arable land and intensification of agriculture under the higher emissions scenario RCP6 linked to unfavourable land use changes in SSP3, could more than double TP inputs to standing waters, while sustainable land use reconfiguration in SSP1 associated with lower emissions scenarios RCP2.6 was found to reduce TP losses by up to 20% by 2080.

Land-based mitigation measures focused on maintaining soil nutrient status at, or below, the agronomic optimum reduced TP inputs to standing waters, in some cases by more than 40% during the baseline period. This shows that holistic management of soils to maximise soil organic matter content and nutrient use efficiency, supported by soil testing and optimisation of fertiliser applications, would reduce terrestrial TP losses. Conversely, smaller-scale interventions, such as buffer strips, did not affect TP losses to water significantly at a catchment scale.

• May, L., Glendell, M., Adams, K., Gagkas, Z., Gouldsbrough, L., Gunn, I., Hannah, M., Roberts, M., Spears, B., Taylor, P., Thackeray, S., Troldborg, M., Zaja, E. (2024) Mitigating Climate Change Impacts on the Water Quality of Scottish Standing Waters. Centre of Expertise for Waters https://www.crew.ac.uk/publication/mitigating-climate-change-phase-2
• Brown, C. et al. (2022) Agent-Based Modeling of Alternative Futures in the British Land Use System. Earth’s Futur. 10. 10.1029/2022EF002905