Monday, 16 February 2015

Faecal lipids and fungal spores as proxies for ancient pastoralism

I was recently alerted to this interesting new paper (open access!) through Google Scholar citation alerts, which is a very useful service for finding out when your papers are cited by other authors (in this case my 2011 paper on faecal lipid residues at Catalhoyuk). The authors studied a sequence of lake sediments from Lake Igaliku in SW Greenland, looking at changes in the quantity of DOC and fungal spores. DOC is a bile acid (deoxycholic acid), and is found in both human and ruminant faeces, but at a higher concentration in ruminants. Humans have higher amounts of LC (another bile acid, lithocholic acid). Interestingly no LC was found, suggesting that the DOC comes entirely from herbivores (and that the runoff 'polluting' the lake is largely agricultural, rather than coming from settlement sewage waste).

The fungal spores that were found are from coprophilous fungi - i.e. fungi that grow on faeces! The amount of DOC present correlated with the number of fungal spores, with both being at their highest during periods of intensive human occupation, firstly in the Norse period, then later in the 1920s.
Also of interest is that the 'background' levels of DOC and spores that were present prior to Norse occupation, and interpreted as coming from wild herbivores, dropped significantly after Norse abandonment, suggesting that the wild herbivore population had disappeared, or at least dropped significantly.

Sporomiella photo by Alain Brissard
The only downside to the paper is that it doesn't include a representative GC trace showing the DOC, which I find quite useful for visualising the quantities that were recovered. There is also a peak in fungal spores around AD 500 that does not have a corresponding DOC increase, which suggests there may be something a little more complicated going on than a straight correlation between the two. There is no discussion of depositional pathways for the DOC or fungal spores, perhaps this is related to changing hydrological conditions within the lake? The quantification is also different to what I am used to, and it is not entirely clear how the flux rates were calculated  - I would have preferred to see the absolute quantities recovered. But still, it is a great little case study in how you can integrate different analytical methods to provide multi-proxy evidence for human activity, and proposes some interesting hypotheses that can be investigated further through archaeology.

I've never looked at spores much myself, but maybe I need to start, I found a lovely photo of one of the major dung loving fungal spores, Sporomiella, which amusingly looks rather like a mini coprolite. For more reading on the fascinating world of dung fungal spores and photos of other types, check out this website, Mykoweb!

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