Connecting Nitrogen Deposition and Ecosystem Services

There are tremendous human health and well-being consequences of nitrogen release into the atmosphere, land, and water. The effects on human health are related to the fundamental ecosystem services providing clean air and water for human consumption. Among the highest available damage cost estimates are those associated with respiratory and cardiac issues arising from breathing ozone and particulates formed through the release of NO_x and NH_x. Nitrate in drinking water continues to be a widespread issue in the US posing a number of human health risks. Nearly two million Americans live in homes with water supply nitrate concentrations at or above the human consumption maximum contaminant level, and the number of nitrate violations in community drinking water systems continues to increase, doubling between 1998 and 2008. The issue of nitrate in drinking water is largely driven by agricultural inputs and atmospheric deposition is a small component.Terrestrial ecosystems respond to increasing N deposition with increased productivity but decreased biodiversity, and the response is load-dependent. Nitrogen deposition, at levels up to 11 kg N ha^-1 yr^-1 increased productivity in forests ecosystems in the northeastern US and yielded a 40% increase in carbon sequestration. Many other terrestrial ecosystems are currently considered to be above their critical load for nitrogen, where adverse effects begin to be observed. However, the net impact on ecosystem services and human well-being has not been examined at this point. These include not only effects on biodiversity and productivity, but also the consequences for other services such as fire, temperature tolerances, and disease dynamics.In the US, the release of NO_x has decreased as a consequence of regulations on industry and transportation, and proposed regulations are expected to continue this decrease into the future. The smaller net release of NH_x, however, is not specifically regulated and has not seen the same declines, yet also forms particulates that are harmful to human health and deposits N to nearby ecosystems. Recovery appears to be rapid for the provision of clean air, but aquatic and particularly terrestrial ecosystem services may respond more slowly, depending on the mechanism of impact. If fundamental changes to ecosystem structure or processes drive the response, such as soil N content or acidification, then recovery may require longer time frames.Human alteration of the nitrogen cycle has more than doubled the release of N into the environment resulting in a cascade of effects on ecosystem structure and function. Many of these changes in structure and function in turn affect key ecosystem services that affect human health and well-being. Nitrogen release to the atmosphere affects human health, ecosystem production, biodiversity, and a host of related ecosystem services. Human respiratory health and recreation had the highest damage costs per unit nitrogen of the services examined here. Nitrogen deposition is declining but the recovery of some services may lag behind the decline in deposition depending on the mechanisms influencing these services.