Determining the controls on faecal stanol concentrations and ratios in
tropical lake sediments
Abstract
Faecal stanols offer an exciting opportunity to determine population
change in the past but the controls of their concentrations and ratios
within lake sediments are not well understood. We present the
variability in stanol concentrations and ratios from lakes across
environmental gradients, both between and in lakes across climatic and
land-use gradients in Mexico, Guatemala, and Belize in order to
determine the factors controlling preservation and degradation in
lacustrine sediments. We also measured physical properties of lakes such
as dissolved oxygen, pH, and water column temperature and estimated the
approximate human population in each catchment, with the goal of
producing a semi-quantitative calibration of human population to
coprostanol+epi-coprostanol as a ratio to cholestanol, a more widely
produced bacterial stanol. In particular we explore the hypothesis that
a dominant control on concentrations and ratios is proximity to a human
settlement. We evaluate this hypothesis in two lakes (L. Peten-Itza and
L. Izabal) where we collected samples at varying distances from major
population centres. This will have implications for the targeting of
lake cores in studies where determining population change is the goal.
In addition to this work we will share three intriguing preliminary
palaeo-records of stanol concentrations from Guatemala (Laguna Itzan,
Laguna Peten-Itza, and Lago Izabal). These records imply highly dynamic
millennial scale changes in human populations, and we apply the modern
sediment data to better constrain the interpretation of these data. Our
work shows that faecal stanols have a strong potential as proxies for
changes in human population and land-use change through time, and can be
used to complement archaeological datasets to link human populations
with palaeoenvironmental change.