In the first field season, a range of potential field sites were initially considered. We were looking for sites which contained lagoons of different sizes. We also wanted a range of sites lying on different geology.
Lagoons can be classified into two - open and closed systems. Small lakes with no out flow are classified as closed systems and provide very sensitive indications of localised climate change. Larger water bodies, which are drained by rivers are classed as open systems. These are often less sensitive indicators of change. They are still useful in palaeo-ecological studies such as this one, however, as their large size makes it likely that they will never have dried up during the time period studied.
With the exception of the granitic intrusion that forms the Maya Mountains, the geology of Belize is dominated by limestone. Sites were chosen in both limestone and non-limestone areas to provide a contrast in geochemistry.
The selected fieldsites
Four locations were finally selected for detailed investigation. Their positions are marked on the map of Belize shown to the right.
A series of sediment cores were taken at each site, some at sites at the edge of the lagoon, some in the water. To provide information about the current condition of the lagoon, its water chemistry was measured and collections made of modern algae.
|This image shows the top section of a percussion core taken at the edge of Honey Camp Lagoon. It's dark colour and coarse texture reflects the high organic content of t he material (over 12% by dry weight).|
|Further down the core, the sediment becomes much finer - dominated by silt and clay-sized particles. A large snail shell can be seen in the left of the core. The fact that this shell is still complete suggests that the sediment was deposited in a low energy environment.|
|This final image is from the base of the core. The sediment here is mostly clay. The distinct red and green mottling is indicative of conditions of very limited (or no) oxygen. The se bright colours are caused by the reduction of metal ions such as iron and manganese.|