Monday, 28 August 2017

Mud, mud and more mud: salt marsh sampling in Essex... by Helen Brooks

Hi, I’m Helen and I’m a 1st year PhD student at the University of Cambridge, in partnership with BUFI, the BGS University Funding Initiative. My research looks at sediment properties of salt marshes and tidal flats and how these relate to the stability of salt marshes. This means I get to spend a lot of time sampling in the field, which is great fun (if the weather is good)!

Why are we interested in salt marsh stability?

Salt marshes help protect the land behind them from flooding and erosion, however marsh areas are declining globally. My research will improve models that simulate future marsh evolution, particularly in a changing climate. This will help us to understand whether marshes will continue to protect us from flooding in the future.
Sunset on Tillingham marsh in February
What exactly do I sample?

I’m interested in the sediment properties and how these relate to erosion resistance. During my PhD I hope to look mainly at the sediment shear strength, compressibility, shrink-swell behaviour and plasticity (i.e. how the sediment behaves at different moisture contents). Most of these tests will be done in the lab and will require undisturbed samples. That means a sample where we try to keep in the in situ condition. For anyone who hasn’t done undisturbed sampling before, you’ll probably think I’m crazy by the end of this paragraph. I’m going to try and explain the process of collecting the samples. Essentially, you dig the outside of a pit, leaving the central section untouched (see photo). Then you carefully remove the vegetation and the uppermost sediment (and by 'carefully' I mean 'using small kitchen knives to remove 2 cm2 chunks of sediment, bit by bit'!). The next step is to place the sampling equipment on the surface, push down gently by 1-2 mm, then scrape the excess 1-2 mm of sediment carefully from around the side of the equipment (see photo). Then we repeat pushing down and scraping the excess sediment until the sediment reaches the top of the sample! In total, digging the pit and taking the sample can frequently take three hours! Finally, the samples are wrapped in A LOT of bubble wrap, placed on trays and packed in boxes to reduce disturbance during transport! But after all this, do you know what the best part of the day was? Enjoying a glass of freshly squeezed orange juice! To explain: the rest of my research group were in the field flying a drone over the marsh and used halved oranges as ground control points (novel, I know!). However, so as not to waste the oranges, these were squeezed before we went out to the field!
Digging the outside of the pit, leaving the central section untouched.
Carefully pushing the sampler into the sediment, then scraping away the sediment around the outside. This particular sample is nearly done, as the sediment inside the sampler has now reached the top of the sampler.
 Where do I sample?

Most recently, I was sampling at Tillingham Marsh in Essex. We spent two days meticulously taking undisturbed samples in the glorious sunshine (though unfortunately it isn’t always like this!), before carefully transporting the samples back to Cambridge. The samples were taken from the lower marsh, close to, but not on, the tidal flat.

Tillingham Marsh in summer
What next?

I’m now about to start work on these samples at BGS Keyworth. This will involve three weeks of more sample preparation, plus lots of loading the samples into machines which allow me to assess properties such as consolidation, shear strength and shrink-swell behaviour.

If you’re interested in finding out more about my project, please follow me on Twitter at @hbrooks94 

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