Water Quality Monitoring of Arundo Cane Removal Treatment

Science Center Objects

The USGS Texas Water Science Center is evaluating the water-quality effects of certain herbicides used in Arundo cane eradication along the Rio Grande from Del Rio downstream to the confluence with Sycamore Creek (approximately 10 miles), along which the Texas State Soil and Water Conservation Board (TSSWCB) will be conducting cane eradication using herbicides.

The invasive bamboo-like perennial Arundo donax (Arundo cane) is an invasive species and one of the greatest threats to the health of riparian ecosystems in the southwestern United States. Arundo cane is linked to many problems including

  • Channel restriction
  • Biodiversity limitations
  • Water resource decreases
  • Non-food for native species
  • Habitat for cattle ticks
  • Reduces visibility
  • Border security problems

TSSWCB has been directed to eradicate Arundo cane along the Rio Grande in Texas (Texas Senate Bill 1734). The TSSWCB plans to use an ecosystem-based approach that will integrate the use of biological, chemical, mechanical, and cultural controls to manage Arundo cane along the Rio Grande (TSSWCB, 2016). As part of this approach, the TSSWCB plans to use various herbicides (including imazapyr and/or glyphosate) on the Arundo cane.

The potential water-quality effects of the herbicides utilized in the treatment of Arundo cane on nearby water bodies are not well understood. The results of this initial characterization study will help water managers better understand the effects of chemical application to the water column and water supply resources.

  • Do the herbicides make their way into the water?
  • If so, at what concentrations?
  • How long do they stay in the water?

Study Design

To develop a better understanding of water quality associated with the use of herbicides applied to Arundo cane, the USGS Texas Water Science Center conducted three synoptic water-quality sampling events (“snap shot” samplings). Water-quality samples for each synoptic sampling event were collected at 3 sites along the Rio Grande and included the following sites, in downstream order:

  1. downstream from Del Rio - to assess the effects of urbanization on the water quality,
  2. along the reach near the center of the treatment area - to assess the effects of standard herbicide application on water supply bodies, and
  3. upstream from the confluence with Sycamore Creek which is below the drainage area of the treatment reach - to assess the cumulative effects coming from the treatment area.

One sample from each site was collected

  • prior to herbicide application to establish a baseline concentration of constituents,  
  • immediately following herbicide application to assess effect of treatment, and 
  • a few months after application to determine the degree to which the selected constituents might have persisted in the environment.

The samples were analyzed by the National Water Quality Laboratory and Kansas Water Science Center Laboratory for more than 60 pesticides including the herbicides imazapyr, glyphosate, and selected degradates.

Study Results

Glyphosate and imazapyr were detected in samples from upstream and downstream locations, but at very low concentrations - near laboratory minimum reporting levels.