on Lawrenz, Head of the Science Division at the Science Museum, studies freshwater organisms to learn about past and present environmental changes. Learn more in our Global Climate Change exhibit.
Lawrenz took samples of sediments from the lakes he studied. The samples preserved the most recent sediment at the top and the oldest--sometimes more than 10,000 years old--at the bottom. He found pollen and the remains of insect called Chironomids, or midges, in different layers of the samples. He had some layers of the samples carbon dated so he could associate kinds of pollen and insects with particular time periods.
The mix of different species--pollen and insects--at different time periods told him that long-term changes in water temperature and lake water levels had taken place over time. The midges responded to small changes in lake temperatures and depth, making them a very good tool to measure climate change. Lawrenz was able to recreate a picture of environmental change since the last glaciers left the Upper Midwest.
Lawrenz studied the impact of acid rain on lake ecosystems. In one experiment, his team added 10,000 pounds of powdered limestone to a small Minnesota lake to test how much was needed to neutralize the acidity of the water, how long any neutralizing effect would last, and what changes would occur in the lake's biology. The scientists wanted to know if this technique could be used to save the ecosystem.
They monitored the lake, tracking changes in the biology and water chemistry over time. The good news? Almost immediately, they saw a 100-fold reduction in the acidity of the water, and an increase in biodiversity and population sizes. The effect lasted about five years. The bad news? It's an expensive way to treat acidic water and the effect doesn't last very long. Still, adding powdered limestone may buy time for lakes that are just starting to acidify while society works to reduce the emissions that cause acid rain.