Nitrogen emissions from car exhaust and industrial sources might be increasing forest fires across the California desert by fueling the spread of invasive grasses, according to a new report by the Ecological Society of America. Agricultural nitrogen is also causing groundwater contamination in the state, the report concluded.Most nitrogen in the atmosphere is trapped in an inert form that is unusable by most plants and animals. In nature, bacteria in the nodules of nitrogen-fixing plants, such as soybeans, must convert this bound nitrogen into a form that plants and animals use to grow.But cars and power plants emit a form of nitrogen and oxygen called NOx, which falls to the ground when it rains or snows, said Eric Davidson, a soil ecologist and executive director at the Woods Hole Research Center in Falmouth, Mass., who led the study [PDF]. Unlike atmospheric nitrogen, NOx emissions deposit nitrates, which are readily taken up by plants.In California, weedy, non-native grasses are edging out native plants in desert areas such as Joshua Tree National Park, and NOx is likely to blame."The native plants in the desert were not adapted to have that extra nitrogen, so they don't really grow all that much better, whereas these exotic grasses have evolved to make use of that nitrogen," he said.The grasses are highly flammable, unlike the bare rock, soil and islands of shrubs that used to predominate, Davidson said. As a result, "an ecosystem that once hardly ever had a fire in it now has fire more routinely."
More at the link. A significant and increasing portion of it comes from fertilizers however. Obviously transportation isn't an answer to that, but it would be an interesting move if the high speed rail authority or other rail agencies dealt with farmer complaints on eminent domain by building hydro or aeroponic systems to make up for the lost farmland and increase overall production. If that's done instead of a straight cash payment for the land, it may very well be cost-neutral or even beneficial, as well as killing two birds with one stone.