Wild salmonids, including Atlantic salmon, brown trout, and sea trout, are vital components of Scotland’s natural capital. They provide key ecosystem services, including marine-to-freshwater nutrient cycling and food-web regulation, and contribute an estimated £80m/year to the Scottish economy. Their populations are declining due to the pressures of habitat degradation, disease, climate change, pollution, and overfishing. They are also expected to come under increased threat from the invasive Pink Salmon.

Phosphorus (P) pollution remains a major cause of surface water quality failures. Future climate and land use change are likely to impact P losses to running waters, however the relative balance between these drivers and the scale of future change is uncertain as is the effectiveness of proposed mitigation measures. Bayesian Belief Networks (BBNs) are graphical models that enable representation of these uncertainties through probabilistic modelling.

Regenerative and agroecological management practices have a major role to play in the transformation of future food production systems to net zero. However, agroecological approaches will only be widely adopted by farmers when there is guidance available on how management interacts with local conditions allowing evidence-based decisions to be made on what practices are effective where and when. The aim of this PhD is to improve the delivery of ecosystem services through interventions such as cover cropping and herbal leys by analysing data from different environments and farming systems.

The seemingly intractable societal challenges of the first half of the 21st Century, including climate change, the biodiversity crisis and managing infectious disease, are systems challenges. Many proposed mitigations can induce unintended behavioural changes that dampen or even reverse any gains. To solve many of these societal challenges, then, requires understanding and quantification of how large scale systems behave and respond to external drivers e.g. global change, and interventions.

Gastro-intestinal nematode (GIN) infections have serious negative consequences on the health and welfare of livestock worldwide and threaten the economic viability of livestock production. Infection also increases peak methane yield in parasitised lambs, making crucial greenhouse gas emissions targets even harder to reach. The ongoing impacts of climate change are only expected to exacerbate these challenges. Anthelmintics are widely used to control GIN populations in livestock; however, parasite populations are increasingly developing resistance to treatments.