Okavango Delta Expedition

These tools are used by the AquaRAP limnology team to measure the physics, chemistry and biology of the river system.

Jane measuring plankton with a net.

Zoo-plankton (animal), Phyto-plankton (plant)

Scientists use nets with different sized mesh to capture the plankton in the water. The 20 micrometer net shown in this photo (right) is dipped repeatedly into the water. Water with zoo and phyto-plankton is then given to taxonomic experts for identification.

Dissolved oxygen meter

This tool is used to measure the content of dissolved oxygen at a certain depth. "Don't bloody do this to me," Rob moans as his meter drifts around. Like any meter, it can be sensitive and act up in the field.

Bottom tester

This high-tech tool is a four-meter long wooden stick used to probe the bottom and give scientists an idea of what the riverbed looks like. "If it feels hard yet squishes down when you push it, there is sand with rocky bottom," Innocent Tylol of the Department of Water Affairs tells me. The type of sand also reflects the kind of current. Finer silt and sand will be swept away by stronger currents.

Peter Ashton measures the current.

Current measurements

A meter measures the current force using hollow rod and a bubble sensor. Measurements are taken at half-meter intervals and then 10cm from the surface and 10 cm from the bottom.

pH meter

The pH is a measure of potential hydrogen running across a glass plate. The lower the pH, the higher the acidity and the higher the pH, the higher alkalinity. Pure water, with a pH of seven, is regarded as neutral. In the field, scientists must "be very careful that the glass bauble doesn't bang against anything and break."

Secchi

The secchi measures light penetration in water. If you forget yours in the field, a circular disk, like a white plate, weighted with a rock and held together by a rope works just fine. When it's lowered into the water, the level at which the disk disappears from view is recorded in centimeters: that is the secchi disk reading. This measurement reflects the depth of the euphotic zone, the depth at which active photosynthesis takes place.