Our Nitrogen: A Threat to Local Biodiversity
Although the Bay Area has the widely beloved BART system to provide public transportation at low emission rates, many people still depend on commuting with their own vehicle. Getting caught in a gridlock is nothing out of the ordinary for a local resident.
The alternative for many residents, though convenient, is at the expense of the environment. Car emissions are composed of carbon monoxide, nitrogen oxides, particulate matter, volatile organic compounds and carbon dioxide. Nitrous Oxide (NOx) emissions are high in urban areas with heavy vehicle traffic. The surplus of atmospheric nitrogen in particular might do more harm than even modern scientists know of.
We already know that car exhaust worsens air quality and causes health problems over time. Irritated eyes, aggravated asthma, and cardiovascular weakness are all physiological reactions people experience in a region with a heavy load of air pollutants. But what about the other forms of life around us? What about the water and soil that we rely on? Reduced drinking water quality, eutrophication of estuaries, nitrate-induced toxic effects on freshwater biota are all examples of environmental problems we face as an increasingly urbanized society. Transportation and industrial greenhouse gas emissions are threatening the plant community’s well being and stability of the nitrogen cycle. The “nitrogen deposition” dilemma has gained more attention over the years as invasive plants threaten native species.
The nitrogen cycle is a very intricate process. As the most abundant gas in the air , nitrogen circulates through the atmosphere and soil. The atom occurs in various forms (N2, NH3,NH4+, NO3-); chemical reactions rearrange organic nitrogen compounds in order to nourish the many components in our environment. So what is “nitrogen deposition” and why is it of concern? As more nitrogen is emitted, more of it is included in the local nitrogen cycle. The natural process that all of life depends on is therefore unbalanced. Either through precipitation or nitrogen fixation, levels of nitrogen in the soil increase and cause an imbalance of nutrients.
A disruption of an ecosystem of any kind poses a threat to its health. Native plants are adapted to a certain composition of the soil, and when that changes, the entire ecosystem is thrown off balance. For example, inflated levels of NO3 cause an increase in soil acidity. Nitrogen deposition can harm species that are specifically immune to soils with low pH and nitrogen amounts. Outcrops of serpentinite rock accommodate plants and animals that are well-equipped to inhibit areas with these said conditions.
In the San Francisco area, the bay checkerspot butterfly is dependent on their host plant, Plantago erecta. Since invasive plants are able to occupy soils that are no longer low in nitrogen, native grasses are currently losing a battle with invasive plants, and species like the bay checkerspot are paying the price. In these scenarios, the disturbance in the nitrogen cycle and the growth of invasive species jeopardize the local biological diversity.
One might think that the enhancement of nitrogen might act as a fertilizer that would benefit surrounding gardens and landscapes. While that trait may get forest managers and plantation owners excited for further growth productivity, the negative impacts of vehicle emissions easily negate the favorable qualities nitrogen has on biomass as an elemental wedge of life.
Nutrients are recycled and reused by all types of organisms. Decomposition rates, microbial community dynamics, allocation patterns within plants, and species composition are all examples of factors that could be distorted as a result of increased nitrogen levels.
The solution is clear, but not so simple. I’m sure you have heard that taking the bus, walking, or riding a bike is more environmentally friendly than driving independently. While that option saves money and shrinks your carbon footprint, it also contributes less to the nitrogen deposition in your local area.
The key to keeping a relative chemical balance in nature is to monitor and manage protected lands so we can assess what treatments to utilize. Additionally, policy on transportation should be held to a higher standard in order to keep city exhaust under control. Not only would it make the preservation of native species more feasible, restrictions on exhaust would aid the health of urban residents in the Bay Area.
Unless we change the way we commute and perceive the metropolitan-environmental relationship, native species will continue to be outcompeted by more fit invasive species, soil acidity will rise, and the overall stability of the ecosystems we neighbor will crumble.
Environmental health and public health have countless areas of overlap, and nitrogen deposition is just one of the many. So if given the choice between a diverse set of transportation forms, in addition to considering the carbon footprint you are making, take potential nitrogen output into account.
The environmental realm is incredibly delicate and complex. It is impossible to determine how the imbalance of nitrogen will distress local ecosystems. Minimizing your personal exhaust pollution would help protect our native plants and animals. It’s a small step but a step nonetheless.
