http://hdl.handle.net/1893/29 Electronic theses of Biological and Environmental Sciences students Fri, 25 Sep 2026 14:01:33 GMT 2026-09-25T14:01:33Z http://hdl.handle.net/1893/38180 Title: A changing climate for lake monitoring - harnessing satellite imagery and machine learning for tracking and forecasting algal blooms Author(s): Atton Beckmann, Daniel Abstract: Bloom-forming algae, particularly toxin-producing cyanobacteria, pose significant risks to inland water quality. Consequently, developing algae monitoring and forecasting capabilities is critical for understanding drivers, tracking long-term trends, and delivering early warnings. Satellite remote sensing and machine learning (ML) show considerable promise for addressing these challenges, but at present, operational algal bloom monitoring and forecasting programs are rare, and have only been implemented for large, economically-significant lakes. Therefore, extending these capabilities to smaller, less well-studied lakes is critical. Consequently, it is important to understand data requirements for ML forecasting and explore ways to monitor lakes which have, historically, been too small to study using satellites. Furthermore, climate change may exacerbate algal blooms and diminish the predictability of freshwater ecosystems, and so it is critical to understand and prepare for this. This thesis addresses these challenges through three novel studies: Chapter two explores data requirements for short-term ML algae forecasts. Subsequently, Chapter three evaluates the impact of several climate change scenarios on ML water temperature forecast performance. Finally, Chapter four evaluates the capabilities of new, high-resolution satellite imagery for monitoring small lakes. It is found that ML forecasts require approximately five or more years of fortnightly training data to be effective, but that performance improvements show diminishing returns as more training data are used. Furthermore, more extreme climate change scenarios are likely to diminish forecast performance. However, high-resolution satellite imagery may help to address these challenges with increased sampling frequency that can potentially offset climate-induced performance losses; and potential for widespread lake monitoring, which may lead to a step-change in the size of training datasets readily available for forecasting. Collectively, this work highlights potential future directions for algal monitoring and forecasting practices, and ultimately underlines the importance of harnessing synergies across diverse data sources for addressing present and future water quality challenges. Mon, 01 Dec 2025 00:00:00 GMT http://hdl.handle.net/1893/38180 2025-12-01T00:00:00Z http://hdl.handle.net/1893/38126 Title: The role of light and endocrine factors in the development of bimodality of growth in the juvenile Atlantic salmon (Salmo salar L.) Author(s): Villareal G, Cesar A Abstract: The timing of the development of bimodality in the frequency distribution of length and weight within sibling populations of juvenile Atlantic salmon was independent of change in day-length or photoperiod. However, photoperiod affected the proportion of fishes in the upper modal group, from none under short photoperiod to higher proportions under constant light. The photoperiod exerted its effects on the development of bimodality in two ways, through its proportional effects (length of daylight per se) and by its differential effects (rate of change in day-length). It is postulated that the rate of change in day-length exerted its effect during a period of sensitiveness to light, called the "critical photosensitive period" (CPP). Temperature had an unimportant role in development of bimodality relative to light since fish grew well in constant light when the temperature was declining, but poorly under short constant photoperiod at a time when the water temperature was increasing. The biochemical and morphometric assessment of cellular growth (nucleic acid content and muscle fibre diameter measurements) showed that fish growth was due to both cell enlargement (hypertrophy) and proliferation (hyperplasia). The preponderance of one process over the other depended on developmental stage and season. The lowest muscular DNA content and highest RNA-DNA ratio was reached at the end of July, independent of the photoperiod or family, indicating therefore that cellular processes of growth (e.g. cell enlargement and protein precursor accumulation) were photoperiod independent and under endogenous seasonal regulation. The lowest water content and highest dry weight values were reached by late summer for all photoperiodic treatments indicating their endogenous character. Specific growth rate was correlated significantly with RNA-DNA ratio before midsummer and with the natural logarithm of RNA concentration after that. RNA concentration then, as an index of growth, was more affected by cell size during spring than during summer. It is concluded that RNA concentration alone was an appropriate index of growth when it was not affected by cell size. Fishes of the upper modal group synthesised more protein and lipids than those of the lower group, since the former showed consistent and significantly higher dry and wet weights, total RNA and RNA concentrations, total DNA, DW-DNA ratios and RNA-DNA ratios. The female salmon allocated more resources to gonadal growth than the males did as assessed by histological measurements. Among males upper modal group fishes showed more advanced testicular development than did the lower modal ones. These results were at variance with the hypothesis that the development of bimodality was due to differential allocation of resources to somatic and gonadal growth. Gonadal growth was highly independent of the gonadotropes, since they did not show any parallel cytological changes with the gonads. The Somatotropes (GH cells) and thyrotropes (TSH cells) were involved in fish growth regulation, because they showed consistent and in some cases significant increases in cell and nucleus diameters and cell numbers during the somatic growth season. The prolactin cells (LTH cells) were larger in female and in small fish. No interaction was found between the two factors (sex and size). This result suggested that the t wo fish groups were under osmotic stress. It was concluded that photoperiod exerted its effects on fish body growth through the hypothalamo-hypophysial axis, since good correlations were found between morphometric estimates of pituitary cell activity and somatic growth and development. Sat, 01 Jan 1983 00:00:00 GMT http://hdl.handle.net/1893/38126 1983-01-01T00:00:00Z http://hdl.handle.net/1893/38034 Title: Nature based solutions in agricultural landscapes: an ecosystem service perspective Author(s): Bryan, David R Abstract: Nature-based solutions (NbS) are interventions that work with, manage, or restore natural processes to address societal challenges such as climate change, biodiversity loss, and sustainable resource management. They are promoted for their potential to deliver multiple ecological, social, and economic benefits, yet their effectiveness in agricultural landscapes remains uncertain. This thesis examines the ecological performance and social dimensions of NbS, focusing on rural sustainable drainage systems (RSuDS) and beaver-influenced habitats, to assess contributions to natural capital, ecosystem service delivery, disservices, and barriers to uptake. Beavers were shown to make a substantial contribution to Scotland’s woodland natural capital. Through expert elicitation and integration into the Natural Capital Asset Index, results highlighted how beaver activity enhances regulating services at a national scale, with benefits expected to increase as populations expand. Complementary analysis of RSuDS using the Rapid Assessment of Wetland Ecosystem Services (RAWES) framework and spatial methods revealed that these interventions primarily deliver regulating services, especially water quality improvement and flow regulation, while also exposing trade-offs, limited provisioning benefits, and methodological gaps in cultural service valuation. Further investigation into greenhouse gas disservices from agricultural ponds, using direct measurement and structural equation modelling, showed that all ponds acted as net emitters of methane and carbon dioxide, with methane exerting the greatest climate forcing. Emission drivers were linked to depth, nutrient status, and oxygen availability, offering pathways for mitigation. In parallel, a national survey of farmers and advisers shed light on the social and governance dimensions of NbS. Financial risk, inflexible design, and limited advisory support were identified as key barriers to uptake, with recommendations for simplified applications, outcome-based payments, and farmer-led collaboration. Together, these studies provide an integrated ecological and social assessment of NbS in UK agricultural landscapes. By linking natural capital accounting, ecosystem service evaluation, and stakeholder perspectives, the thesis advances understanding of multifunctionality, disservices, and governance challenges, offering evidence to inform the design and scaling of more effective, inclusive NbS. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/1893/38034 2025-01-01T00:00:00Z http://hdl.handle.net/1893/38033 Title: Ecological connectivity between Gabon's protected areas Author(s): Orbell, Christopher M Abstract: This thesis investigates wildlife connectivity in Gabon using large‑scale camera‑trap data to inform national conservation policy and guide the creation of ecological corridors. Building on the country’s commitment to expand protected and conserved areas under the 30×30 framework, the thesis integrates multi‑species occupancy modelling, landscape permeability analysis, and policy evaluation to produce an evidence‑based corridor‑design strategy. Chapter 2 examines how camera‑trap placement strategies influence biodiversity assessments. Using a 36 km² grid, three deployment protocols, random, semi‑random, and optimized, are compared for five key large mammals. Optimised placement along forest and skidder trails substantially increased capture rates, naïve occupancy, and detection probabilities for forest elephants, leopards, African golden cats, and chimpanzees, highlighting the need for transparent, standardised survey design to ensure comparability across sites and over time. Chapter 3 integrates detection histories from eleven nationwide surveys (2015–2021; 941 stations; 49,303 trap‑days) to develop multi‑scale occupancy models for four focal species. Forest cover, productivity, rugged terrain, and distance to villages consistently structured occupancy patterns. These species‑level models were combined into a national conductance surface, and CircuitScape omnidirectional current‑flow analyses were used to map wildlife permeability. High‑permeability linkages were identified between major protected areas, notably Loango–Moukalaba‑Doudou, Waka–Lopé, and Lopé–Ivindo. Chapter 4 applies these models to delineate ecological corridors in two priority regions (southwest and northeast). Corridor routing incorporated planned protected areas, HCV forests, land‑use constraints, and community considerations. Leopard occupancy, showing the strongest correlation with national connectivity, was identified as the most suitable proxy for monitoring long‑term corridor functionality. Chapter 5 highlights the policy relevance of camera‑trap by‑catch data for updating IUCN categories, informing national land‑use planning, and confirming corridor choices for ape taxa. Chapter 6 synthesises findings and outlines future directions for integrating connectivity science into Gabon’s conservation strategy. Tue, 01 Apr 2025 00:00:00 GMT http://hdl.handle.net/1893/38033 2025-04-01T00:00:00Z