Research Highlight

Air pollution that is in rain, snow, and dry particles can affect the biology and quality of stream ecosystems. iUTAH Postdoctoral researcher, Dr. Steven Hall’s work confirms that both urban and mountain snow in Northern Utah contains the same components that are in PM2.5, the fine particulate matter that is of the greatest health concern about air pollution. This demonstrates that local air pollution has a widespread environmental impact. Despite differences in air pollution in the Salt Lake, Cache, and Heber valleys, similar amounts of nitrogen were deposited in those areas during the winter of 2013-14.

Dr. Hall has found there is ample nitrogen in Utah’s urban streams, but air pollution isn’t the main culprit. Hall’s data shows that only a small amount of the nitrogen in precipitation actually ends up in streams. Most of the nitrogen is taken up or removed by plants and microorganisms. Rather, other urban sources appear to be the dominant contributors of nitrogen in streams. In Salt Lake City's Red Butte Creek, stream nitrogen peaked following inputs of urban groundwater. Measurements of nitrogen isotopes in streamside plants showed differences in nitrogen composition between plants in the mountains and those in urban areas. This suggests a shift in nitrogen sources and cycling as streams enter urban areas. The amount of nitrogen being measured is not directly hazardous, but can contribute to numerous changes in our aquatic ecosystems. These include shifts in biological communities (the identity and abundance of species) and the increased growth of algae.

What does this mean for those living in these urban areas? To decrease the nitrogen in our streams, use less fertilizer on your lawn or convert your yard to drought-tolerant vegetation. In many cases fertilizer is over-applied, and frequent applications are unnecessary given high background nitrogen inputs from atmospheric deposition, especially if clippings are retained on the lawn.