Effects of De-Icing Salts on Roadside Vegetation in the Lake Tahoe Basin
Robert Nowak, Dept. Natural Resources & Environmental Science, University of Nevada, Reno
PROBLEM STATEMENT: The Lake Tahoe Basin is world renowned for its natural beauty, water clarity, and winter sports activities. The Tahoe Basin is also an environmentally sensitive area, but the increasing resident population and increasing visitor use require clear roadways during the winter and hence the application of anti-icing and de-icing salts. During 1990, Resource Concepts, Inc. studied salt effects on vegetation adjacent to highways in the Tahoe Basin. They observed that 15% of trees were apparently salt-affected, but about one third of these trees had evidence for other damage. However, 30% of trees exhibited damage from non-salt related causes, and slightly more than half the trees (55%) did not exhibit any symptoms of salt, drought, disease, insect, or other damage. These results indicate that salts may negatively impact roadside vegetation, but the drought conditions that existed prior to and during the study may have stressed vegetation and hence made plants more susceptible to salt injury. Furthermore, chemical analyses of soils did not indicate abnormal salt content. Thus, although salts appear to play some role in roadside vegetation damage, existing data from the Tahoe Basin also suggest that the role may be a minor, but un-quantified, source of vegetation damage. Clearly, long-term assessment of anti-icing and de-icing salts on soils and vegetation are needed to address these concerns.
RESEARCH PROGRAM: The study is designed primarily to answer two questions: (1) What is the degree of salt injury to roadside vegetation? and (2) What are the long-term impacts of de-icing salts on roadside vegetation? Specific tasks are:
1. Re-construct the tree inventories and study plots established from the previous research project.
2. Establish new control plots that are similar to the previous plots but outside the zone of influence of road salts.
3. Quantitatively assess the salt damage to trees adjacent to the highways using previously- developed methods.
4. Conduct chemical analyses of soil samples for pH, EC, Na, Cl, Ca, and other soluble elements.
5. Conduct chemical analyses of plant samples for Na and Cl in both symptomatic plants and healthy plants.
6. Provide recommendations for continued data collection to monitor salt effects on plants. If soil salt does not appear to be the source of salt that causes harm to plants, provide recommendations for design of an aerosol collection system to help assess if aerosols are the source of salt for vegetation damage.
7. Synthesize the results of the studies above plus those in the literature that takes into account: (a) improvements of salt application technology since 1990; (b) improved erosion and drainage projects since 1990; and (c) information on the amount, frequency, and timing of salt applications.
ANTICIPATED BENEFITS: Comparisons of the proposed results with those obtained from the previous research will be used to evaluate the potential long-term impact of salts on roadside soil salinity, the health trends of vegetation along highways, and the maximum potential impact of salts on vegetation in the Tahoe Basin. Although the previous study provides an excellent start towards quantifying the effects of salts on vegetation, improvements in sampling protocols (e.g. addition of new control plots, additional sampling of targeted soils and species) will strengthen the research and improve our ability to discern the damage due to salts. The proposed research program is not without limitations, but our methodology is designed to minimize potentially confounding effects where possible and to provide information that suggests likely explanations for the observed results.