Tuesday, 22 January 2013

Tiny bits of rock and very small living things...

Taking great care to not leave any trace of
where we've sampled on the marsh!
Our next stop has been Rio Lingue, a site about 60 km north of Valdivia. Locals have been telling us of the devastation and land subsidence caused by the 1960 earthquake, and also told us how the 2010 tsunami reached this far south.

We found an excellent marsh to work on, which allowed us to take lots of samples to help us properly understand the present day environment. In our work we need a sound understanding of what is happening today to be able to interpret what happened in the past. We take small samples along a transect across the marsh from the mudflat exposed at low tide, across the low marsh, high marsh, and up to where freshwater vegetation grows. We look at how diatom communities (small microscopic single-celled algae) change across these different zones as the amount of tidal inundation decreases the further you get from the sea. We mainly find marine diatom species in mudflat samples and freshwater diatoms in the high marsh samples. Then when we look at our sediment cores from the past, if we find lots of marine diatoms we interpret the environment at this time was most like the present day mudflat. From this we are able to reconstruct how the land level has changed through time.

Taking a modern sample from the low marsh

Freshwater diatom of the Pinnularia genus (about half the width of a
human hair - thanks to Melanie Leng for giving this comparison!)

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