How did the pollen get to the bottom of a lake or into a peat deposit?

The swirls above represent pollen grains circulating in the air. Some of this pollen will land in the lake. Inflowing streams, rainwater, and snow melt also transport pollen to the lake.

Insect Pollination
Most plants are pollinated by either insects or the wind. In the first method, insects, especially bees, transport pollen from one flower to another. Because pollination by insect is very efficient, most of the plants pollinated by insects produce less pollen, and only a little of this pollen is released into the air. 

Wind Pollination
On the other hand, wind-pollinated plants produce large amounts of pollen because it is less likely that an individual pollen grain will actually land on another flower of the same species. Many of our forest trees are wind pollinated, as are important prairie plants such as grasses, ragweed, and sage. 

Some pollen eventually falls into lakes or peatlands where it collects with other sediments, layer after layer, year after year. A cubic centimeter of lake sediment (about the size of a big pea) will typically contain tens or hundreds of thousands of pollen grains.