IAP-24-013

Uncovering the impacts of volcanic ash deposition on plant and soil communities

This project will investigate how communities of plants and soil organisms recover from catastrophic disturbance events. Volcanic eruptions provide a natural laboratory to study this process, because they disturb ecosystems in different ways, often over large areas. For example, continental-scale ash deposits produced during explosive volcanic eruptions can have profound ecological impacts, both above- and belowground. Aboveground, the ash smothers vegetation, reducing photosynthesis and killing vulnerable (usually low growing) plant species. Belowground, decaying organic matter releases a pulse of nutrients; the supply of organic matter from plants diminishes and physical properties (e.g., soil temperature and moisture) are altered. These processes are likely to result in complex changes to plant and soil microbial communities (SMCs), a loss of carbon and nutrient capital and the interruption of critical ecosystem functions, e.g., nutrient cycling. However, despite the obvious impacts of thick ash deposits proximal to eruption centres, the ecological impact of much more extensive distal deposits on biological communities – particularly in terms of the SMCs – remain largely unknown. The project addresses this knowledge gap by studying the resilience of plant and soil microbial communities in timescales relevant to human societies (years – decades).

The project will use the 1980 eruption of Mount St Helens in Washington State, USA, as a model system. During the eruption, forests around Mount St Helens were devastated by blast waves and lahars (mudflows); the impacts of these events are still visible, over 40 years after the event. Further away, thousands of square kilometres – including valuable forestry and agricultural land – were buried in fine ash. The eruption was studied in detail as it progressed, and since 1980 Washington State has become a global centre for studying volcanic hazards and the process of ecological succession. The project will draw on this expertise through collaboration with researchers in the USA. It will also make use of existing databases and research facilities, notably a 40+ year record of ecological succession taken from a network of experimental plots established shortly after the eruption.

The project will involve fieldwork in Washington State, laboratory work and data handling, both of contemporary and archive data. The PhD student on the project will receive training in all these techniques, thereby acquiring a suite of complementary transferable skills.

The project will utilise a variety of research techniques, encompassing both the field and laboratory.

Field work. Fieldwork will be conducted in the Gifford Pinchot National Forest (GPNF) in western Washington State. The GPNF is the location of a unique, long-term ecological experiment that is central to the project. The experiment comprises six sites arranged along a gradient of ash depth (23 – 150 mm). Permanent vegetation plots – 150 on each site – were established in 1980 and have been monitored ever since. On each site, 50 of the plots had the ash cover removed immediately after the eruption: they are, in effect, undisturbed controls against which to assess the process of ecological recovery on sites affected by ash deposition. The PhD student on the project will survey vegetation cover and collect samples of topsoil from a subset of the plots to assess different trajectories of post-disturbance recovery. The student will also design and implement a new field experiment involving the experimental application of ash (or, alternatively, sand) to assess the short-term (one-year) impacts of ash deposition on SMCs and soil physical conditions (assessed with automated soil moisture and temperature probes).

Laboratory work. The soil samples collected in Washington State will be returned to the UK for molecular (DNA) analysis. The PhD student will extract DNA from the soil samples and profile the fungal and bacterial communities present using the technique of DNA metabarcoding. Undisturbed soil microbial communities will be compared to SMCs disturbed recently (the ash application experiment) and decades ago (the permanent plots) to assess the rate and direct of change in the soil.

Data analysis. The project will require the analysis of complex ecological and environmental data sets, gathered during the study and from archive sources. Training will be provided in relevant statistical and multivariate analytical techniques.

Year 1

Preparatory research into disturbance ecology, soil microbiology; liaison with US collaborators and planning of fieldwork; experimental design; field trip 1 (experimental set-up and collection of soil samples).

Year 2

Molecular and chemical analysis of soil samples; analysis of ecological data from permanent plots

Year 3

Analysis of soil samples from experiment plots; conference presentation of preliminary results; draft manuscript preparation

Year 3.5

Manuscript preparation

Survey skills in plant community ecology (botanical identification and quantification)
Use of molecular (DNA) methods, specifically DNA metabarcoding, to characterise soil microbial communities (fungi and bacteria).
Lab-based analysis of physical and chemical properties of soil.
Statistical techniques, specifically statistical modelling of biological communities.