The Oregon Department of Transportation (ODOT) uses an integrated vegetation management (IVM) plan to control road side vegetation and to provide safe driving conditions for the operation of motor vehicles. The plan utilizes a number of methods, including the application of herbicides and roadside mowing. Herbicides can be transported from treated roadsides to the aquatic environment through spray drift, volatilization, overland runoff, or by infiltration to subsurface ground water. Herbicides may volatilize before or after they contact foliage. The most direct route to adjacent waters, however, is through surface runoff. Because many of these herbicides are water-soluble, they reside a short period of time at the point of application before being transported from highway ditches to local waterways. The extent to which these herbicides are transported from the point of application on the road shoulders to nearby streams is unknown.
The effect of herbicides in highway runoff on biological communities--including anadromous fish, like salmon--also is unknown. If large amounts of these herbicides end up in streams, stream biota could be adversely affected and the stream ecosystem disrupted. The small streams that often parallel or cross roadways are particularly susceptible because their dilution capacity is small.
OBJECTIVEPhase I
The objective of Phase I is to determine from previous studies herbicide concentrations typically reaching small streams adjacent to roads as a result of IVM programs, the mechanisms and length of time for herbicide degradation, factors contributing to or retarding the transport of herbicides to streams, biological effects resulting from herbicide exposure, and approaches used to assess biological affects. Of special interest will be types and quantaties of herbicides used, application rates, timing and method of application, types of vegetation targeted, and concentrations of herbicides reaching waterways under varying streamflow and rainfall conditions. The final product of Phase I will be a plan for Phase II--a field study characterizing the effect of IVM practices on the transport of herbicides to streams and the effect of herbicides used in IVM programs on aquatic biota.
Phase II
The objectives of the Phase II study are as follows:
Determine how much of the targeted compounds is removed from the application area by a known volume of runoff, as a function of time after application.
Determine the correspondence between the concentration of a compound in the runoff from the application area and the concentration in the receiving stream.
Collect runoff and stream samples that will be used by other investigators to conduct bioassays to determine the toxicity of runoff collected from the application area and receiving stream water to a colonized species of benthic algae and to rainbow trout.
Phase I
A search strategy will be devised using DIALOG, an Internet resource. Once the strategy is refined, numerous searchable data bases will be queried for herbicide-effects data relating to IVM. Herbicides targeted will coincide with the herbicide-use listing provided by ODOT. Pertinent journal articles will be obtained, reviewed, and summarized. Particular effort will be given to determining herbicide concentrations associated with runoff from IVM programs and the associated biological effects. Additionally, study designs for other highway IVM programs will be reviewed for applicability in the development of a Phase II study plan.
Phase II
The Phase II data collection effort will involve collecting runoff from experimental plots located on a road shoulder where herbicides have been applied. Simulated rainfall will be used on the experimental plots so that both the amount of incident rainfall and its timing after application of the compound can be controlled. It is particularly important to be able to simulate a heavy rain within a day of the application of the compound and again 1 week later.
REPORT
WRIR 01-4065. Herbicide Use in the Management of Roadside Vegetation, Western Oregon, 19992000: Effects on the Water Quality of Nearby Streams, by Tamara M. Wood Abstract | Available online
Contact: info-or@usgs.gov