MPC
Research Projects (2006-07)

Identifying Number

MPC-281

Project Title

The Assignment of Chloride Injury from De-Icing Salts in Trees Along State Highways in the Black Hills, Year 1

University

South Dakota State University

Project Investigator:

Dr. John Ball
South Dakota State University

External Project Contact

Dan Johnston
South Dakota Dept of Transportation
dan.johnston@state.sd.us

Project Objective

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

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 stand 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.

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.

Research is needed to clearly delineate the effects of de-icing in the Black Hills on pine trees adjacent to the roadside as well as the extent of any damages with respect to he surrounding forest and soils. Efforts have been successful in recent years at reducing the amount of de-icing chemicals applied to the roadways in the Black Hills. Determining the effects on roadside pines and soil properties due to de-icing practices will provide a critical baseline for evaluating the consequences of continuing current practices and offer insights into possible modifications of maintenance activities in the Black Hills.

Task Descriptions

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.
2. Meet with the technical panel to review project scope and the proposed work plan.
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.
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.
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.
6. Meet and conduct a field trip with technical review panel in October 2006 to illustrate initial findings.
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.
8. Conduct snowpack chloride measurements in February-March 2007.
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.
10. Analyze data.
11. Prepare a final report and executive summary of the literature review, research methodology, findings, conclusions and recommendations.
12. Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.

Milestones, Dates

Starting Date: July 1, 2006
Ending Date: May 16, 2008

Yearly and Total Budget

$69,104.00

Student Involvement

One graduate student and two undergraduate students.

Relationship to Other Research Projects

This project is not related to any current research project.

Technology Transfer Activities

A final report will be prepared by March 2008. 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 determining best practices to minimize detrimental effects on roadside vegetation while maintaining public safety. Since the project focuses on the affects of de-icing salts on soils and vegetation the investigators are soils, environmental and forestry scientists. A presentation of these findings will be made to the SDDOT Research Review Board.

Potential Benefits of the Project

The potential benefits of the research will include a clearer understanding of the role of de-icing salts in stressing ponderosa pines 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 Management's assessment of the roadside damage that can be attributed to de-icing salts. The results of the study will also be valuable in reducing the future impact of de-icing salts on roadside vegetation. Since the public's 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.

TRB Keywords

De-icing Salt, Chloride Injury, Roadside Vegetation