The importance of organic phosphorus sources, transfers and impacts across the agricultural continuum

This thesis investigates the risks posed by organic phosphorus (P) from agriculture to river and stream chemical water quality and the ecology. Organic P compounds have received limited attention in past research, due to the agronomic focus on inorganic P and the analytical challenges of quantifying organic P in environmental matrices. Through laboratory and field experiments, this thesis aimed to: (i) characterise organic P within fresh and stored livestock slurry; (ii) quantify organic P export within overland flow and leachate from grasslands, including following livestock slurry application; and (iii) determine the benthic microbial responses to organic P compounds in rivers and streams. Finally, a coupled terrestrial-aquatic modelling approach was developed to quantify the impact of diffuse agricultural P mitigation measures on river water quality. The organic P pool in fresh livestock slurry was substantial and dominated by monoesters, including glycerophosphates, other labile monoesters (e.g. ATP) and inositol-6-phosphates. Storage drove significant changes in the chemical and physical fractionation of P within slurry. Organic P was observed in overland flow and leachate from grassland soil. Significant increases in organic P concentrations within leachate followed slurry application, predominantly in the form of glycerophosphates and inositol-6-phosphates. Within streams, heterotrophic responses to glycerophosphates and inositol-6-phosphate were observed, although these varied depending on background stream P concentrations. However, under certain stream conditions, inhibitory effects of organic P on the autotrophic community were observed. Modelling the efficacy of agricultural P mitigation suggested a best-case scenario in which annual river total P loads decreased by 7.5%, yet this increased to 19.4-25.1% when wastewater effluent was addressed alongside agricultural sources of P. The outcomes of this thesis present an opportunity to develop an organic P focus to the P transfer continuum, alongside highlighting a range of future research priorities related to organic P in the environment

Physical and biological controls on fine sediment transport and storage in rivers

Excess fine sediment, comprising particles <2 mm in diameter, is a major cause of ecological degradation in rivers. The erosion of fine sediment from terrestrial or aquatic sources, its delivery to the river, and its storage and transport in the fluvial environment are controlled by a complex interplay of physical, biological and anthropogenic factors. Whilst the physical controls exerted on fine sediment dynamics are relatively well-documented, the role of biological processes and their interactions with hydraulic and physico-chemical phenomena has been largely overlooked. The activities of biota, from primary producers to predators, exert strong controls on fine sediment deposition, infiltration and resuspension. For example, extracellular polymeric substances (EPS) associated with biofilms increase deposition and decrease resuspension. In lower energy rivers, aquatic macrophyte growth and senescence are intimately linked to sediment retention and loss, whereas riparian trees are dominant ecosystem engineers in high energy systems. Fish and invertebrates also have profound effects on fine sediment dynamics through activities that drive both particle deposition and erosion depending on species composition and abiotic conditions. The functional traits of species present will determine not only these biotic effects but also the responses of river ecosystems to excess fine sediment. We discuss which traits are involved and put them into context with spatial processes that occur throughout the river network. Whilst strides towards better understanding of the impacts of excess fine sediment have been made, further progress to identify the most effective management approaches is urgently required through close communication between authorities and scientists

The ecological outcomes of collaborative governance in large river basins:Who is in the room and does it matter?

Although collaborative governance has been presented as central in environmental management, it does not guarantee sustainable natural resources management. Due to methodological challenges and a lack of robust interdisciplinary data, few studies have linked collaborative processes to ecological outcomes. This paper contributes to that research effort by investigating whether the relative involvement of different interest groups in deliberations matters from an ecological perspective. To that end, this interdisciplinary paper links social and ecological indicators across two large French river basins in a dataset spanning 25 years. We find that the presence of different interest groups - agricultural, industrial and NGOs - during deliberations, is linked to different ecological outcomes. Most notably, the composition of present members does not play the same role depending on the type of pollution source studied (e.g. point and/or diffuse sources)

How a water-resources crisis highlights social-ecological disconnects

The sustainable management of water resources is required to avoid water scarcity becoming widespread. This article explores the potential application of a social-ecological framework, used predominantly in the fields of ecology and conservation, as a tool to improve the sustainability and resilience of water resources. The “red-loop green-loop” (RL-GL) model has previously been used to map both sustainable and unsustainable social-ecological feedbacks between ecosystems and their communities in countries such as Sweden and Jamaica. In this article, we demonstrate the novel application of the RL-GL framework to water resources management using the 2017/18 Cape Town water crisis. We used the framework to analyse the social-ecological dynamics of pre-crisis and planned contingency scenarios. We found that the water resources management system was almost solely reliant on a single, non-ecosystem form of infrastructure, the provincial dam system. As prolonged drought impacted this key water resource, resilience to resource collapse was shown to be low and a missing feedback between the water resource and the Cape Town community was highlighted. The collapse of water resources (“Day Zero”) was averted through a combination of government and community group led measures, incorporating both local ecosystem (green-loop) and non-local ecosystem (red-loop) forms of water resource management, and increased rainfall returning to the area. Additional disaster management plans proposed by the municipality included the tighter integration of red and green-loop water management approaches, which acted to foster a stronger connection between the Cape Town community and their water resources. We advocate the wider development and application of the RL-GL model, theoretically and empirically, to investigate missing feedbacks between water resources and their communities

Structure determination by cryoEM at 100 keV.

Peer reviewed: TruePublication status: PublishedElectron cryomicroscopy can, in principle, determine the structures of most biological molecules but is currently limited by access, specimen preparation difficulties, and cost. We describe a purpose-built instrument operating at 100 keV-including advances in electron optics, detection, and processing-that makes structure determination fast and simple at a fraction of current costs. The instrument attains its theoretical performance limits, allowing atomic resolution imaging of gold test specimens and biological molecular structure determination in hours. We demonstrate its capabilities by determining the structures of eleven different specimens, ranging in size from 140 kDa to 2 MDa, using a fraction of the data normally required. CryoEM with a microscope designed specifically for high-efficiency, on-the-spot imaging of biological molecules will expand structural biology to a wide range of previously intractable problems