International Rhodolith Workshop, Roscoff, France

Rhodolith-2018_Group

At the end of last month, the International Rhodolith Workshop took place in Roscoff, Brittany, France and around 50-60 international scientists came from the far reaches to present their work on maerl or rhodoliths. In the geology session, had the brilliant opportunity to present some of our work on the habitat dynamics and the impact of storminess on maerl:

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We went on a boat trip in the Bay of Brest and sampled some of the maerl from an unfished and a fished site. Here are some photos of our trip to collect some specimens from the Bay of Brest.

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Acknowledgements

This trip was funded by the Marine Insitute Travel and Networking Award, Ireland and we would like to thank the organisers of the conference and the Marine Institute for making this trip possible!

Geoscience and Sustainable Development

JoelGill Guest Post by Dr. Joel C. Gill

Executive Director, Geology for Global Development

Joel is an interdisciplinary geoscientist, integrating natural and social science methods to address issues relating to sustainable development and disaster risk reduction (DRR). Joel has a keen interest in improving the application of geology to international development, founding the charity “Geology for Global Development” in 2011. He has organised conferences, events and workshops on geoscience and sustainable development in the UK, Guatemala, India, Tanzania, Kenya, Zambia, and South Africa.

The agreement of the UN Sustainable Development Goals (SDGs) in 2015 reflects ‘a global consensus that business as usual is no option any longer, that changing the development trajectory is necessary’ (Spangenberg, 2016, p.1). The 17 SDGs and their 169 targets will be at the forefront of national and international policy discourse for the next 15 years. Collectively they aim to eradicate global poverty, end unsustainable consumption patterns, and facilitate sustained and inclusive economic growth, social development, and environmental protection.

The SDGs, together with various thematic frameworks (e.g., Sendai Framework for Disaster Risk Reduction, Paris Agreement, New Urban Agenda), all relate to the interaction of human activities with the natural environment. The ‘planet’ is a central pillar of sustainable development, alongside people and prosperity. Advances in science and technology, including geoscience (the study of the Earth), are therefore central to each framework. For example, managing natural resources, characterising natural hazards, or modelling future climate all require multiscale (spatial and temporal) understanding of Earth materials and/or processes. This requirement for geoscience input presents an opportunity for the geoscience community. Scientific business as usual, however, will not be sufficient, with changes to geoscience practice required for successful engagement (Lubchenco et al., 2015).

Geoscience and the SDGs

The environmental focus of the SDGs means geoscience is essential to their success. The matrix below (from Gill, 2017) illustrates the role of geoscience in the 17 SDGs. The matrix was populated by analysing the SDG sub-goals and targets, identifying links between SDG requirements and geoscience. Interconnections between many SDGs results in this approach giving a conservative estimate of the true impact of geoscience interventions. For example, goals on education (SDG 4) and gender equality (SDG 5) do not specifically refer to access to water/sanitation (SDG 6), but increased access to water/sanitation can support both. This matrix shows a role for geoscience within all 17 of the SDGs.

Matrix_SDGGeosciences

Contributions will be required from all sectors and sub-disciplines of geoscience, including those working in research, industry, the public sector and civil society. Examples of geoscience activities helping to deliver the SDGs include research projects, industry engagement, and civil society activities. Gill and Bullough (2017) listed examples of diverse activities geoscientists are undertaking that support the delivery of the SDGs.

Improving Geoscience Engagement in Sustainable Development

Engagement by geoscientists must be effective, culturally appropriate, and sustainable. Poor quality engagement (e.g., weak understanding of the social context of a project, or limited dialogue with stakeholders) can hinder development progress, may detrimentally affect a project, and does not serve society well. Effective engagement is rooted in understanding the science-policy-practice interface. This includes, for example, determining the information needs of stakeholders (e.g., policy makers, community groups, development NGOs), how they will use this information, and how best to present it to support policymakers. This requires the ability to build positive partnerships between geoscientists and diverse stakeholders, with engagement prioritised early in the research process. Increased dialogue, critical to our contributions being relevant, may also require the geoscience community to invest in additional and complementary skills. The geoscience community readily embraces advances in technology, informatics, and other physical sciences to advance their science. In contrast, whereas cultural and ethical understanding, cross-disciplinary communication, and social science research approaches can also support effective engagement and enhance our science, they are rarely included in a geoscientist’s education.

Continue reading “Geoscience and Sustainable Development”

Modelling maerl habitat dynamics in response to increased storminess

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Figure 1. A. Biogenic gravel composed entirely of dead maёrl (debris) at Trá an Doilin (Carraroe) beach, County Galway. B. Individual clasts of maёrl debris on beach (photo length: 0.05m). C. Living maёrl beds in approximately 5m bathymetry (photo length: c.0.60m). D & E. Concentric patterns at Trá an Doilin suggests  maёrl has a higher mobility than quartz sediments.

An exciting new project involving field work has begun at NUI Galway School of Geography, which focuses on quantifying the impacts of storminess on maerl beach morphodynamics. Rhodolith (maerl) beds are unique, relatively rare, free-living, non-geniculate coralline red algae forming biodiverse habitats and dense biogenic debris beaches. These beds provide hard habitat for other marine algae on their surface and for invertebrates living on and in the rhodoliths. This one year field research project investigates the response of offshore maerl beds and maerl debris beaches to storminess. Specifically, the morpho-sedimentary evolution of maerl beaches over timescales of seconds (swash dynamics) to months (seasonal weather) will be measured using a suite of integrated, multi-disciplinary field and laboratory methods based on hydrodynamic modelling, bathymetric and topographic mapping, and groundwater fluxes. The experiments will utilise results from previous research. The impact of the Intergovernmental Panel on Climate Change (IPCC) scenarios on the regional hydrodynamic model will be made to quantify possible impacts of climate change on maerl. Using XBeach, an open-source numerical model with a domain size of kilometres, on the time scales of storms, outputs will be compared with nearshore-beach DEMs derived from UAV surveys (water and land), and supplemented with baseline INFOMAR LiDAR data from Greatman’s Bay. This project will integrate oceanographic observations (waves, currents, tide) to compliment habitat mapping. A poster of this work was presented at the Irish Geomorphology Group Meeting at the Geological Survey Ireland in Dublin. A0 Poster - Siddhi Joshi Poster FinalThe poster is available for download here: Siddhi Joshi Eugene Farrell Poster Final

Acknowledgements

This project is funded by the Geological Survey Ireland Short call 2017-SC-043.

Fête du Maërl

Fête du maërl

Historically, when fishermen in Brittany would land maërl, not only would they land more fish, they would also be able to use the maërl to condition their soils as fertiliser. This meant not only would they get fish, but also a fertile harvest. Hence, this was such a prized commodity; there is a cultural festival of maerl which happens every four years in Brittany- Fête du Maërl. Commercial extraction no longer occurs in Brittany, where it is banned. A friend in Brittany sent me this lovely poster of this year’s fête, which happened in August. Thank you so much Andre!

Critical bed shear stress of maerl experiment

Maerl Beach
Concentric patterns at Maerl Beach, Trá an Doilín in Carraroe, County Galway

Just by going to the beach, I had been fascinated by how maerl was freely moving, carried, mobilised and transported by almost every wave. The beach, composed almost entirely of “coral” is actually made of branched free-living coralline algal gravels (maerl). I was intrigued to see these concentric patterns, almost like “beach cusps,” observed at Trá an Doilín maerl beach in Carraroe, County Galway.  Furthermore, large maerl megaripples (or sub-aqueous dunes) had been observed subtidally, such as those in Northern Ireland (video). The flow strength required for initiation of motion is a classical problem in fluid dynamics and we found very little work had been done on maerl and the conditions under which it is mobilised and transported.

 

 

Our new study entitled “Critical bed shear stress and threshold of motion of maerl biogenic gravel” has just been published in Estuarine, Coastal and Shelf Science (in press). The critical bed shear stress is a fundamental sediment dynamics quantity – a measure of the threshold of motion of sediment. When we began our study on modelling the sediment mobility of maerl in Galway Bay, we found that this quantity for maerl coralline alga was an unknown which had largely been overlooked in classical sediment transport experiments. Its knowledge was a prerequisite for quantifying maerl mobility, rate of erosion and deposition in conservation management. Through as series of lab (flume) experiments on biogenic free-living maerl beds, our study determines the critical Shields parameter for maerl in three contrasting environments (open marine, intertidal and beach) in Galway Bay, west of Ireland.

The bed shear stress was determined using two methods, Law of the Wall and Turbulent Kinetic Energy, in a rotating annular flume and in a linear flume. The velocity profile of flowing water above a bed of natural maerl grains was measured in four runs of progressively increasing flow velocity until the flow exceeded the critical shear stress of grains on the bed (from Abstract, Joshi et.al 2017b).

The critical Shields parameter and the mobility number are estimated and compared with the equivalent curves for natural quartz sand. The critical Shields parameters for the maerl particles from all three environments fall below the Shields curve. Along with a previously reported correlation between maerl grain shape and settling velocity, these results suggest that the highly irregular shapes also allow maerl grains to be mobilised more easily than quartz grains with the same sieve diameter (from Abstract, Joshi et.al 2017b).

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Live maerl thalli (Lithothamnion glaciale, Image credit to Jason Hall-Spencer, University of Plymouth)

The intertidal beds with the roughest particles exhibit the greatest critical shear stress because the particle thalli interlock and resist entrainment. In samples with a high percentage of maerl and low percentage of siliciclastic sand, the lower density, lower settling velocity and lower critical bed shear stress of maerl results in its preferential transport over the siliciclastic sediment. At velocities ∼10 cm s−1 higher than the threshold velocity of grain motion, rarely-documented subaqueous maerl dunes formed in the annular flume (from Abstract, Joshi et.al 2017b).

The full research paper can be found here, as well as the related papers in the full study below.

References

Joshi, S., Duffy, G., & Brown, C. (2014). Settling Velocity and Grain Shape of Maerl Biogenic Gravel Journal of Sedimentary Research, 84 (8), 718-727 DOI: https://doi.org/10.2110/jsr.2014.51   (Paper 1)

Joshi, S., Duffy, G., & Brown, C. (2017a). Mobility of maerl-siliciclastic mixtures: Impact of waves, currents and storm events Estuarine, Coastal and Shelf Science DOI: https://doi.org/10.1016/j.ecss.2017.03.018    (Paper 3)

Joshi, S., Duffy, G., & Brown, C. (2017b), Critical bed shear stress and threshold of motion of maerl biogenic gravel, Estuarine, Coastal and Shelf Science, https://doi.org/10.1016/j.ecss.2017.06.010   (Paper 2)

Sediment Mobility of Maerl Modelling Study

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Maerl biogenic gravel beach at Carraroe, County Galway

ResearchBlogging.orgOur new study on “Mobility of maerl-siliciclastic mixtures: impact of waves, currents and storm events,” has just been published (in press) in Estuarine, Coastal and Shelf Science. This is the final part of my PhD in maerl sediment dynamics. Sediment mobility in its simplest form is the percentage of time grains of a particular size are mobile during  a tidal cycle (Idier et.al., 2010). This study focuses on the sediment mobility of maerl in particular, utilising coupled hydrodynamic-wave-sediment transport models to model the oceanography during calm and storm conditions and the resulting sediment transport. Sediment mobility models are another way of quantifying the disturbance of the seafloor as a result of currents, waves and combined wave-currents. This study calculates two sediment mobility indices, the Mobilization Frequency Index (MFI) and the Sediment Mobility Index (SMI), related to the magnitude and frequency of disturbance events (Li et.al, 2015). The residual currents, which are the part of the current remaining after removing the oscillatory tidal component, show that maerl prefers intermediate mobility environments and is often found at the periphery of the residual current gyres. Sediment mobility maps can be used to inform marine spatial planning for the management of both live and dead (fossil) maerl beds, as a result of climate change or anthropogenic activity.

The full research paper, Joshi et.al. 2017, can be found here.

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References

Idier, D., Romieu, E., Pedreros, R., & Oliveros, C. (2010). A simple method to analyse non-cohesive sediment mobility in coastal environment Continental Shelf Research, 30(3-4), 365-377 DOI: 10.1016/j.csr.2009.12.006

Joshi, S., Duffy, G., & Brown, C. (2017). Mobility of maerl-siliciclastic mixtures: Impact of waves, currents and storm events Estuarine, Coastal and Shelf Science DOI: 10.1016/j.ecss.2017.03.018

Li, M., Hannah, C., Perrie, W., Tang, C., Prescott, R., Greenberg, D., & Rygel, M. (2015). Modelling seabed shear stress, sediment mobility, and sediment transport in the Bay of Fundy Canadian Journal of Earth Sciences, 52 (9), 757-775 DOI:10.1139/cjes-2014-0211