But here may be an important line of inquiry, one I have long suspected:
According to an article in Scientific American, it looks like the US Government is finally taking notice of the nitrogen cycle that has spun out of control! A quote from the report:
"In the U.S. there are neither comprehensive laws nor adequate monitoring devices for regulating atmospheric nitrogen emissions from livestock and farms. Europeans passed the Gothenburg Protocol to Abate Acidification, Eutrophication and Ground-Level Ozone in 1999, a pact signed by 49 countries, but the U.S. has dragged its feet. Schlesinger thinks that national arguments over climate change have allowed the U.S. to ignore the nitrogen problem, which he predicts will be the next big environmental issue. 'It's another example of humans upsetting global biogeochemical cycles with unintended consequences,' he says.""It's clear that humans are adding nitrogen to Earth's surface. Researchers do not know yet where it all goes, 'but we do know that increasing concentrations of nitrogen in unexpected places will cause significant environmental damage that we will all learn to regret,' Schlesinger wrote in a 2009 report in Proceedings of the National Academy of Sciences."
"In general, the Committee finds that:
In the United States, human activities across multiple sources currently introduce more than five times the reactive nitrogen into the environment than natural processes. The largest US sources of new reactive nitrogen entering the US environment include; the creation and use of inorganic fertilizers, reactive nitrogen created by legumes, and the combustion of fossil fuels.
Much of the reactive nitrogen used to ensure a plentiful supply of food, fiber and biofuel is lost to the environment as is the reactive nitrogen formed during fossil fuel combustion.
The introduction of human created reactive nitrogen into the environment causes degradation of air and water quality, harmful algae blooms, hypoxia, fish kills, loss of drinking water, loss of biodiversity, forest declines, and human health problems resulting in losses of billions of dollars per year."
"Impacts of Reactive Nitrogen on Terrestrial Ecosystems
4. Ozone-induced predisposition of forest trees to damage by fungal diseases and insect pests, most clearly established in the case of root disease and bark beetles in the pine forests of southern California.
5. Ozone-induced inhibition of photosynthesis in both softwood and hardwood tree species most clearly established in controlled exposure studies in both the United States and Europe at ambient concentrations of ozone above 60 ppb. Such concentrations occur frequently throughout the eastern United States and southeastern Canada.
6. Ozone induced direct injury to foliage, most clearly established in the case of “emergence tip burn” in eastern white pine.
7. Acidification induced decrease in frost hardiness of high-elevation conifer forests, most clearly established in the case of red spruce in the northeastern United States.
8. Acidification induced alteration of beneficial symbiotic relationships in forest soils, especially mycorrhizae, most clearly established in both northern and central Europe
Nr saturation and ecosystem function
There are limits to how much plant growth can be increased by N fertilization. At some point, when the natural N deficiencies in an ecosystem are fully relieved, plant growth becomes limited by availability of other resources such as phosphorus, calcium, or water and the vegetation can no longer respond to further additions of Nr. In theory, when an ecosystem is fully Nr-saturated and its soils, plants, and microbes cannot use or retain any more, all new Nr deposits will be dispersed to streams, groundwater, and the atmosphere.
Nr saturation has a number of damaging consequences for the health and functioning of ecosystems. These impacts first became apparent in Europe almost three decades ago when scientists observed significant increases in nitrate concentrations in some lakes and streams and also extensive yellowing and loss of needles in spruce and other conifer forests subjected to heavy Nr deposition. In soils, most notably forest soils because of their natural low pH, as NH4+ builds up it is converted to nitrate by bacterial action, a process that releases hydrogen ions and contributes to soil acidification.
The buildup of NO3 ̄ enhances emissions of nitrous oxides from the soil and also encourages leaching of highly water-soluble NO3 ̄ into streams or groundwater. As negatively charged NO3 ̄ seeps away, positively charged alkaline minerals such as calcium, magnesium, and potassium are carried along. Thus, soil fertility is decreased by greatly accelerating the loss of calcium and other nutrients that are vital for plant growth. As calcium is depleted and the soil acidified, aluminum ions are mobilized, eventually reaching toxic concentrations that can damage tree roots or kill fish if the aluminum washes into streams (Vitousek et al., 1997).
Forests, grasslands, and wetlands vary substantially in their capacity to retain added nitrogen. Interacting factors that are known to affect this capacity include soil texture, degree of chemical weathering of soil, fire history, rate at which plant material accumulates, and past human land use. However, we still lack a fundamental understanding of how and why N-retention processes vary among ecosystems much less how they have changed and will change with time and climate change (Clark and Tilman, 2008).
An over-arching impact of excess Nr on unmanaged terrestrial ecosystems is biodiversity loss. In North America, dramatic reductions in biodiversity have been created by fertilization of grasslands in Minnesota and California. In England, N fertilizers applied to experimental grasslands have led to similarly increased dominance by a few N-responsive grasses and loss of many other plant species.
In formerly species-rich heathlands across Western Europe, Nr deposition has been blamed for great losses of biodiversity in recent decades, with shallow soils containing few alkaline minerals to buffer acidification (Vitousek et al., 1997; Bobbink et al., 2009). Losses of biodiversity driven by Nr deposition can in turn affect other ecological processes. Experiments in Minnesota grasslands showed that in ecosystems made species-poor by fertilization, plant productivity was much less stable in the face of a major drought. Even in non-drought years, the normal vagaries of climate produced much more year-to-year variation in the productivity of species-poor grassland plots than in more diverse plots (Vitousek et al., 1997)."