MPC
Research Projects (2007-08)

Identifying Number

MPC-281

Project Title

The Assessment of Chloride Injury from De-Icing Salts in Trees along State Highways in the Black Hills, Year 2

University

South Dakota State University

Project Investigator

Dr. John Ball

Description of Project Abstract

During the past several years there has been an increasing concern from the general public regarding the poor appearance and mortality of tree stands along the highways and roads in the Black Hills. The trees, almost exclusively ponderosa pines (Pinus ponderosa), were exhibiting stunted growth, needle chlorosis and burn, and shoot dieback. These stands generally have between 5 to 30 or more symptomatic trees along with several dead trees. Due to the proximity of these symptomatic trees to the road, many occur within 60 feet of the edge of the pavement, the primary suspect for the decline and mortality been road de-icing salt. A limited random sampling of symptomatic ponderosa pines was made during the summer of 2004. At that time foliage samples taken from trees along state highways 79 and 87 and analyze for foliage chloride content and the presence of picloram, a herbicide that can produce similar symptoms.

Chloride levels in normal, healthy foliage and twigs are generally less than 0.1% (dry weight basis). Symptoms and injury of trees may occur when the internal chloride concentration rises above 0.3%. The foliage samples collected from symptomatic pines along the highways showed chloride levels of 0.47 to 0.63%. Picloram, a common herbicide used to clear weeds from roadsides, produces similar symptoms. The samples were also analyzed for this herbicide and only a few samples taken along highway 87 within Custer State Park had any detectable levels of this chemical. Herbicide applications do not appear to be responsible for the injury of roadside pines outside of the park but there is a high likelihood that de-icing salts, specifically chloride, is responsible for tree decline and mortality along state highways.

Project Objectives

1. Define the extent, distribution, sources and contributing factors involved in roadside tree damage and injury adjacent to highways in the Black Hills
2. Develop recommendations and guidelines for modifying current de-icing and roadside maintenance practices to minimize impact to roadside trees

Project Approach/Methods

• Task 1 – Interview appropriate SDDOT staff to acquire knowledge of current SDDOT de-icing procedures and usage and collect information on the highway network in the Black Hills such as ADT (average daily traffic), maintenance priority and geometry.
• Task 2 – Meet with the technical panel to review project scope and the proposed work plan.
• Task 3 – Review current literature with respect to de-icer impacts to roadside vegetation, including effects of de-icer form and composition will be conducted and completed by May 2006.
• Task 4 – Identify sampling locations. Four sites with symptomatic trees will be identified from the survey and these will be paired with other forested sites that have similar site characteristics but with vegetation that is not expressing symptoms commonly associated with de-icing salts exposure.
• Task 5 – Conduct first and second sampling. Sampling will take place at these four-paired sites, a total of eight sites, and include a sampling of soils and trees at two-time periods, May/June and August/September of 2006. At each sampling site, soil and pine foliage samples will be collected at approximately 3 feet (1m) from the edge of the pavement and a second sample taken 20 feet (6m) further out from the first sample. Soil sampling will involve sampling to a depth of 60 cm, or to the depth it can be excavated if rock is present, with samples collected from 0-15 cm, 15-30 cm and 30-60 cm. The soil samples will be analyzed for soil extractable chloride and cations, pH, EC of a saturated paste extract, standard elemental levels (e.g. N, P and K), organic carbon, aggregate stability and texture.
• Task 6 – Meet and conduct a field trip with technical review panel in October 2006 to illustrate initial findings.
• Task 7 – Prepare interim report outlining the finding from the sampling and presented to the panel to discuss the status of the project, and the plans for further sampling and testing during the second year.
• Task 8 – Conduct snowpack chloride measurements in February-March 2007.
• Task 9 – Conduct third and fourth sampling in May/June and August/September of 2007. The purpose of a second year of sampling at these sites is that conditions change from year to year and it will be beneficial to examine the influence that the accumulation of de-icing salts has on specific sites.
• Task 10 – Analyze data.
• Task 11 – Prepare a final report and executive summary of the literature review, research methodology, findings, conclusions and recommendations.
• Task 12 – Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.

Contributions/Potential Applications of Research

The potential applications of the research will include a clearer understanding of the role of de-icing salts in stressing ponderosa pines and degrading soils in the Black Hills and the extent of damage that can be associated with de-icing salts. This will be helpful in the SDDOT and Risk Managements assessment of the roadside damage that can attribute to de-icing salts. The results of the study will also be valuable in reducing the future impact that de-icing salts on roadside vegetation and soil degradation. Since the publics heighten awareness of the affects of de-icing salts and the potential injury of trees there has been discussion of lawsuits resulting from suspected damage. Minimizing the impact of de-icing salts on roadside vegetation may reduce the threat of lawsuits.

Technology Transfer Activities

A final report will be prepared by February 2008 and will provide an assessment of the impact of de-icing salts on the vegetation and soils along side state highways in the Black Hills. The report will include recommendations and guidelines based upon the results of this study as well as others conducted on this issue, as identified in the literature review, and will include a decision matrix for assisting SDDOT personnel in determining best practices to minimize detrimental effects on roadside vegetation while maintaining public safety.

Time Duration

July 1, 2007 - June 30, 2008

Yearly and Total Project Costs

$69,104 Total: $158,571

TRB Keywords

Deicing salt, chloride injury, roadside vegetation