IAP-24-085

Invasions and extractions in Lough Neagh and their role in water quality deterioration

We are amid a freshwater biodiversity crisis. Freshwater bodies, such as lakes, are significant biodiversity hotspots providing key natural resources and ecosystem services to millions of people worldwide. These benefits may be disrupted because of changes in climate, water quality, ecosystem degradation and pressures on the extraction/withdrawal of natural resources. Sometimes these changes can take place over medium (decadal) timescales, whilst in some cases these changes may occur rapidly (annually). Economic pressures drive resource extraction which can lead to additional pressures on freshwater habitat that facilitate other stressors such as invasion by non-native species.

Lough Neagh is the largest freshwater lake in the UK and the largest eel fishery in Europe, contributing £3.2M to the Northern Irish economy. Lough Neagh has undergone rapid deterioration of water quality over the past few years, culminating in major algal blooms in 2023 and 2024 (https://www.bbc.co.uk/news/uk-northern-ireland-67717507). Nutrient loading, in particular phosphates, is on the rise across Lough Neagh (Reid et al., 2014) with steep declines in eel fisheries catch from a peak of 40 kg ha-1 in the 1970s to ~15 kg ha-1 (Aprahamian et al., 2021). Although previous studies have identified historical eutrophication events in the 1960s and 1970s (Battarbee, 1978), in recent times additional, previously unquantified pressures across the lake have increased. This includes the extraction of sand from the Lough bed (https://www.irishtimes.com/environment/2022/12/20/lough-neagh-scars-from-dredging-will-take-decades-if-not-centuries-to-recover/) which has been shown to disrupt bed morphologies and eel breeding grounds. This extraction process also creates additional disturbances which has favoured the recent spread of invasive species such as the Zebra Mussel (McLean et al., 2010).

The complex interactions between increased anthropogenic disturbance via nutrient loading, resource extraction, invasion by non-native species and economic pressure on the Lough Neagh is currently unquantified. This project will assess each of these pressures and their contribution as drivers of the environmental changes across Lough Neagh. The project will provide new knowledge of freshwater habitat responses to multiple pressures, by addressing the following research questions
1. What are the spatial and temporal rates of change in sediment accumulation and nutrient loading across Lough Neagh?
2. What is the role of sand extraction on nutrient loading or resuspension and does this influence the establishment and spread of invasive species?
3. Are there correlations between spatial distributions of nutrient loading and extractions with the spread of invasive species?

This project will comprise three key methodologies:
1. High resolution bathymetric surveys of the Lough bed using multibeam echo sounders (MBES) to quantify the morphological impacts of sand extraction. MBES data can be gridded at sub-meter resolution to provide digital elevation models of the Lough. MBES surveys can also be used to infer sediment calibre, so this data will also enable a mapping of sediment distributions (sand, mud, bare rock etc.) across the lough. Repeat surveys in targeted areas impacted by extraction will enable quantification of the impacts of extraction on lough bed levels and resulting changes in sediment availability.
2. Water quality surveys and sediment samples (surface grab samples and lake cores) will be taken across the Lough and analysed to quantify and map the spatio-temporal distribution of nutrient loads (nitrates and phosphates) and rates of recent sedimentation/deterioration of lough bed material using Pb210 dating. The samples will be taken over multiple seasons to capture seasonal changes in nutrient loading.
3. Mapping of invasive species will be undertaken around the Lough with a focus on zebra mussel presence and absence. These maps can be correlated with existing data in invasive species atlases to map spatial and temporal trends, using sediment lake cores to assess temporal trends in invasion rates.

Secondary data will look at previously collected sediment cores to compare recent findings with historical data to highlight changing patterns and rates of change within the Lough.

Year 1

Literature review and initial reading, fieldwork planning (months 0 – 6)
Training and upskilling (months 3 – 9)
Undertaking initial surveys and sampling campaign (months 9 – 12)

Year 2

Sediment sample analysis (months 12 – 15)
Water quality analysis (months 12 – 15)
Multibeam processing (months 14 – 18)
Planning and undertaking second surveys and sampling campaign (months 18 – 24)

Year 3

Writing thesis chapters, attendance at an international conference
(months 30-36)

Year 3.5

Writing publications and thesis submission (months 37-42)

The student will receive training from a multidisciplinary supervisory team, particularly in
some of the key NERC most wanted skills:
*Data management and modelling: the student will be supported by supervisors and
partners with strong modelling skills and as such will have the opportunity to learn an
array of modelling methods best suited to their data.
*Translating research into practice: As the output of this PhD will be integral to
management of Lough Neagh the student will work closely with Friends of the Earth and the Lough Neagh Partnership to translate the findings of the research into practice. The student will receive training in science communication to multiple audiences (e.g. policy makers, non-governmental organisations (NGOs) and the wider public).
The student will also participate in IAPETUS training and events. A training budget is
included for any external training required by the student.