Pesticide Water-Quality Data Associated with Arundo donax (Arundo Cane) Treatment on a Section of the Rio Grande in Webb County, Texas, 2020

Arundo donax (Arundo Cane) is an invasive perennial reed that can grow more than 30 feet tall and has become established in riparian zones along rivers throughout the southwestern United States. It grows in thick stands, readily displaces native riparian habitat, and provides no habitat or food for native species in the ecosystems it disrupts (McWilliams, 2004). The Texas State Soil and Water Conservation Board (TSSWCB) has been directed to develop and implement a program to eradicate Arundo Cane along the entire 1,255 mile length of the Rio Grande in Texas (Texas Senate Bill 1734). The TSSWCB has been using an ecosystem-based approach that integrates the use of biological, chemical, mechanical, and cultural controls to manage Arundo cane along the Rio Grande. As part of this approach, the TSSWCB plans to use various herbicides. To develop a better understanding of water quality associated with the use of herbicides applied to Arundo Cane, the USGS, in cooperation with the TSSWCB, conducted two synoptic water-quality sampling events. Water-quality samples for each synoptic sampling event were collected at four sites along the Rio Grande in Webb County, Texas upstream from Laredo: 1. Upstream from the treatment area, 2. Along the reach near the center of the treatment area, 3. Near the downstream limit of the treatment area, and 4. Downstream from the drainage area of the treatment reach. One sample from each site was collected on July 7, 2020 prior to herbicide application (synoptic sampling event 1) to establish a baseline concentration of constituents. A second set of samples (synoptic sampling event 2) were collected on August 4, 2020 to determine constituent concentrations immediately following herbicide application.