Mapping the Roots of Sneezing and Wheezing

Big, watery sneezes. Red, itchy eyes. Wheezing. Runny noses. That irritating tickle in the back of the throat.

We’ve all suffered those symptoms and others. We know that these symptoms often are the result of an allergic reaction to something in the air. That something is usually tiny bits of plant pollen.

Billions and trillions of bits of pollen fill the air in central Arizona every spring and fall. Different types of pollen affect people in different ways. Scientists know that the pollen is found in different amounts in different parts of the Phoenix metropolitan area.

It might be helpful to have a large pollen map. The map would show which parts of the city have the highest amounts of pollen. People with bad allergy problems could use the map to choose the healthiest area to live. It might also be nice to find a way to predict which areas of a city are likely to change in terms of pollen count.

Three ASU scientists are working on both of those ideas. Work by Glenn Stuart, Diane Hope, and Corinna Gries is done as part of ASU’s Central Arizona-Phoenix Long-Term Ecological Research (CAP LTER) project. Hope and Gries are scientists at ASU’s Center for Environmental Studies.

Stuart is a doctoral student in anthropology. He often uses pollen to help find answers to anthropological questions. For example, he studied old pollen to learn how people farmed an area of western Mexico a long time ago. By looking at pollen found at different levels in the ground, Stuart can reconstruct past environments. He looks at ecological change over time.

The CAP LTER project is different. The scientists are using pollen to provide a look at Phoenix as it is today and to predict how the whole area might look in the future.

Palynology is the study of pollen deposits. Work by Stuart, Hope, and Gries is a new use for an old technique. In fact, their study is one is one of the most extensive pollen mapping projects ever attempted.

“Nothing like this has ever been done. Not on this scale,” says Stuart. The ASU scientists have collected lots of data and looked at lots and lots of plants.

They have compiled some early findings. The pollen count of any particular neighborhood in Phoenix is largely affected by how the land immediately around it is being used.

For example, say a person is extremely allergic to ragweed. That person might have a problem if he or she happens to live in a relatively expensive home near one of the Phoenix mountain preserves. Levels of ragweed pollen are very high in those areas. But in central Phoenix, the levels are low. It might be reason enough to consider moving.

However, just living away from the mountain preserve might not protect the person. Ragweed is a rapid colonizer. The plant likes to grow in areas where the ground is churned and broken. People living anywhere near a developing area, or a vacant lot, are more likely to suffer from the allergy. At least until the development is complete.

No place is truly safe. Ragweed is a prolific pollen producer. The plant’s pollen is found everywhere in the city. Some areas with well-maintained landscapes simply have lower concentrations of the sneeze-producing grains.

Look at other parts of Phoenix and you’ll see other plants and other kinds of pollen. Olive trees produce pollen that triggers allergic reactions in many people. The olive pollen count is high in older areas where these plants have been used as landscaping.

The same is true of pine trees. There are few natural pine trees in desert areas. But developers planted lots of pines in Phoenix neighborhoods built in the 1970s and 1980s. Fortunately, pine pollen is less likely to cause an allergic reaction. But landscaping patterns can tell a person much about how he or she will suffer during allergy season.

These findings come from the CAP LTER 200 point survey. The scientists looked at top layer soil samples from 200 locations in and around Phoenix. These samples were less than 1 centimeter deep. The pollen in these samples was deposited within the last few years.

Stuart analyzed the 200 soil samples for pollen content. Then he and Hope and Gries mapped how pollen types and levels of pollen vary across different parts of the city.

They are now studying how the pollen count reflects the actual number of plants and the changing uses of the land.

The information they collect might be used to help residents and future home buyers. The data can be used to predict how types and concentration of pollen might change in the future, depending on plans for neighborhood land use. It will also help to refine the use of palynology in anthropology and ecology.—Matthew Shindell